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Molecular-Scale Imaging Enables Direct Visualization of Molecular Defects and Chain Structure of Conjugated Polymers
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  • Stefania Moro
    Stefania Moro
    School of Chemistry, University of Birmingham, Birmingham B15 2TT, U.K.
    Department of Chemistry, University of Warwick, Coventry CV4 7AL, U.K.
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  • Simon E.F. Spencer
    Simon E.F. Spencer
    Department of Statistics, University of Warwick, Coventry CV4 7AL, U.K.
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  • Daniel W. Lester
    Daniel W. Lester
    Polymer Characterisation Research Technology Platform, University of Warwick, Coventry CV4 7AL, U.K.
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  • Fritz Nübling
    Fritz Nübling
    Institute for Macromolecular Chemistry, University of Freiburg, Freiburg 79104, Germany
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  • Michael Sommer
    Michael Sommer
    Institute for Chemistry, Chemnitz University of Technology, Chemnitz 09111, Germany
    Center for Materials, Architectures and Integration of Nanomembranes (MAIN), Chemnitz University of Technology, Chemnitz 09126, Germany
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    Orcidhttps://orcid.org/0000-0002-2377-5998
  • Giovanni Costantini*
    Giovanni Costantini
    School of Chemistry, University of Birmingham, Birmingham B15 2TT, U.K.
    Department of Chemistry, University of Warwick, Coventry CV4 7AL, U.K.
    *Email: [email protected]
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    Orcidhttps://orcid.org/0000-0001-7916-3440
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ACS Nano

Cite this: ACS Nano 2024, 18, 18, 11655–11664
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https://doi.org/10.1021/acsnano.3c10842
Published April 23, 2024

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Abstract

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Conjugated polymers have become materials of choice for applications ranging from flexible optoelectronics to neuromorphic computing, but their polydispersity and tendency to aggregate pose severe challenges to their precise characterization. Here, the combination of vacuum electrospray deposition (ESD) with scanning tunneling microscopy (STM) is used to acquire, within the same experiment, assembly patterns, full mass distributions, exact sequencing, and quantification of polymerization defects. In a first step, the ESD-STM results are successfully benchmarked against NMR for low molecular mass polymers, where this technique is still applicable. Then, it is shown that ESD-STM is capable of reaching beyond its limits by characterizing, with the same accuracy, samples that are inaccessible to NMR. Finally, a recalibration procedure is proposed for size exclusion chromatography (SEC) mass distributions, using ESD-STM results as a reference. The distinctiveness of the molecular-scale information obtained by ESD-STM highlights its role as a crucial technique for the characterization of conjugated polymers.

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Introduction

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Semiconducting conjugated polymers are attracting increasing attention in the broad field of organic electronics, as they offer tunable chemical structures, low-cost production, robust mechanical properties, and high charge mobility in applications. Their use ranges from organic photovoltaics (OPV) (1−3) to organic field effect transistors (OFETs) (4,5) and from organic thermoelectrics (OTEs) (6) to (bio)sensors based on organic electrochemical transistors (OECTs). (7,8) One of the major strengths of conjugated polymers when compared to inorganic semiconductors is the extreme variety of design pathways that can be followed to achieve, improve, or fine-tune their performance for specific applications. Typically, parameters that can be engineered to alter the performance of conjugated polymers in devices are (i) electronic structure of the materials, for example, by tuning the energy levels of the frontier orbitals and (ii) microstructural characteristics, such as backbone planarity, chain length, and chain–chain interactions resulting in ordered supramolecular architectures and eventually semicrystalline morphologies. Often, these properties are mutually dependent and thus a deep understanding of both electronic and structural characteristics and of their interdependence is necessary, not only to explain different behaviors and performances in devices, but also to improve the design of new materials. (9−11)
Precise determination of chain length and chain length distribution is central to understanding structure–function relationships of these polymers in devices and thus constitutes a fundamental milestone in the pathway to producing high-performance materials. (12−16) However, the analytical tools that are currently available and routinely used for investigations of the structural and chemical properties of these materials still struggle to consistently provide exact information. Size exclusion chromatography (SEC) is typically used for average mass (Mn, Mw, Mz) determination but is known to suffer from systematic overestimation due to the calibration being done with polystyrene, a material with drastically different hydrodynamic properties from conjugated polymers. The issue of relative calibration and overestimation can be addressed with more elaborate detection such as viscosimetry, static light scattering, or field flow fractionation that enable universal calibration, as has been shown for individual examples. (17−20) Moreover, aggregation is often present, enhancing the problem of overestimated molar masses. At higher temperature, aggregates can be dissolved depending on the system and, thus, high-temperature SEC is a viable option. (21,22) By combining SEC with other techniques such as nuclear magnetic resonance (NMR) and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-ToF MS), characterization of molecular weight of conjugated polymers with better accuracy has been achieved. (23−25) However, all of these combinations and techniques suffer from drawbacks, being limited information, tedious handling, extensive costs, or a combination of those. For example, while MALDI-ToF MS delivers distributions, absolute average masses and information on end groups, (23) this method tends to underestimate molecular weight and dispersity. (26,27) This is especially problematic for conjugated polymer samples made by polycondensation and having broad mass distributions. (28) Finally, NMR can be reliably used for average mass determination and for sequencing of conjugated polymers, but this method is limited to lower molar masses. (24,27,29)
A further essential aspect for establishing reliable structure–function relationships in conjugated polymers is the identification and quantification of defects in the polymer sequence caused by errors in the polymerization process. This is true for cross-coupling techniques such as direct arylation polycondensation (DArP), (30−33) that use shorter reaction sequences and less toxic reagents, aiming at greener reaction pathways. However, it is interesting to note that defects such as homocoupling reactions have been reported for copolymers made also by other cross-coupling techniques, including Suzuki and Stille polycondensation, (34−39) suggesting that a large fraction of materials investigated so far are defective. A number of possibilities exists for defect formation in cross-coupling techniques, including unselective C–H activation, homocoupling (hc) reactions of equal monomers, or reactions with solvent, ligand or other components of the catalytic system. (40−42) Among these possibilities for deviations from the ideal catalytic cycle, hc reactions are the most prevalent and have the potential to significantly influence optoelectronic properties. The extent to which this happens is, however, strongly system-dependent. For example, for carbazole-based PCDTBT and diketopyrrolopyrrole (DPP) copolymers used as hole transporters in polymer/fullerene solar cells, carbazole, and DPP hc are detrimental to device performance. (35,43,44) Similarly, hc defects have shown to negatively affect fullerene intercalation and charge-transfer absorption in pBTTT/fullerene blends for photovoltaic applications. (37) However, there are also indications that electron mobility of DPP copolymers used in n-channel transistors is not strongly influenced by hc. (45) Identification and quantification of such defects have been attempted with MALDI-MS and NMR but this approach is severely limited. In this case, the main issue with MALDI-MS is the fact that this technique is not inherently quantitative while, despite major recent progress, the intrinsically rather low sensitivity of NMR and the need for reference models render defect identification and quantification in the few percent range extremely cumbersome. (34,43,46,47)
Here, we demonstrate that the combination of electrospray deposition (ESD) of conjugated macromolecules with ultrahigh vacuum (UHV) high-resolution scanning tunnelling microscopy (STM) imaging is a solution to the lack of reliable and multifunctional analytical tools to investigate conjugated polymers. (37,48−54) In particular, we demonstrate how high-resolution STM imaging of conjugated polymers, combined with advanced statistical approaches, can be used to simultaneously gather precise information on: (i) intermolecular interaction patterns; (ii) mass distribution; and (iii) direct sequencing with in-depth information on their chemical structure and molecular defects. In particular, we first benchmark the validity of the ESD-STM analytical approach against results from 1H NMR spectroscopy for low number-average molecular mass (Mn) polymers that have been specifically synthesized as model systems exhibiting sufficient NMR baseline resolution. For these materials, the ESD-STM data show excellent quantitative agreement with the NMR results of the Mn values and the type and average frequency of homocoupling defects. In a second step, we show that ESD-STM allows for this information to be obtained, with the same level of accuracy, also for polymers for which a quantitative analysis of the 1H NMR spectra is hampered by polymer aggregation. Furthermore, we propose a recalibration procedure for SEC mass distributions, using ESD-STM results as a reference. Our work thus demonstrates that, when applied to conjugated polymers, the ESD-STM technique is capable of reaching beyond the limits of traditional analytical techniques in terms of materials that can be measured, level of molecular-scale details that can be achieved and, sometimes, even the type of information that can be obtained.

Results and Discussion

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The materials studied in this work are based on widely employed DPP motifs that are rigid and strong absorbers with high mobility, and are of great relevance for photovoltaic and charge transport applications. (1,2,55,56) Specifically, the investigated PThDPPThF4 copolymers comprise alternating dithienyldiketopyrrolopyrrole (ThDPPTh) and tetrafluorobenzene (F4) units prepared by DArP. The first polymer, P1, (Figure 1a, x = 0) was chosen for benchmarking the experiment since, despite its strong aggregation in solution, it shows sufficient solubility to be well-characterized by 1H NMR. (34,45,57) Moreover, PThDPPThF4 has been extensively studied by density functional theory (DFT) calculations and grazing incidence wide-angle X-ray scattering (GIWAXS) and shows high mobility. (57) P2 has the same structure as P1 but was synthesized under different conditions with the aim of having a different hc defect content. P3, instead, shares the same backbone structure as P1 and P2 but its side chain branching point is further away from the backbone (Figure 1a, x = 4). While this improves the polymer assembly capability and thus produces more ordered thin films for device applications, (58−60) the stronger aggregation of P3 makes 1H NMR spectra with a baseline resolution elusive even at elevated temperature. Details of synthetic procedures are given in the Supporting Information (SI). In the following, the linear aliphatic side chain between the aromatic backbone and the branching point will be referred to as a linker (red in Figure 1a), while the two branches will be called arms (blue in Figure 1a).

Figure 1

Figure 1. (a) Chemical structure of PThDPPThF4. The colored parts of the side chain indicate the linear linker of different length (red) and two asymmetric branched arms (blue). High-resolution STM images are shown in (b) and (c) for P1 and P3, respectively. The inset in (b) displays an example of the ordered parts of the assembly (top-right corner, in red) and a case where side chains are not arranged into a regular pattern (bottom-left corner, in green). The inset in (c) shows an ordered area of P3. The scale bar in (b) and (c) is 4 nm, and the lateral size of the insets is 5 nm. STM images were acquired in constant current mode with tunneling parameters: (b) 1.4 V, 70 pA; (c) 1.3 V, 90 pA.

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As mentioned, among the factors influencing the efficiency of conjugated polymers in devices, a major role is played by their chain length (often indicated also as molecular weight). (13,15,16) With the aim of determining this, all three polymers have been preliminarily characterized by standard analytical methodologies. P1 and P2 yield 1H NMR spectra with sufficient resolution such that assignments of end groups and determination of the number-average molar masses (Mn) is feasible (see Figures S7 and S8 and Table 1). In contrast to P1 and P2, the extended side chains of P3 and the subsequent increased aggregation of the backbones cause significant broadening of the peaks in the 1H NMR spectra (see Figure S9). In this case, it is therefore not possible to assign and quantify end group intensities for Mn determination (see Table 1).
Table 1. Comparison of Average Mass Values (DPn, Mn, Mw) for P1, P2, and P3, Obtained by Different Experimental or Statistical Approachesa
  P1P2P3
DPnSTM8.7 ± 0.17.7 ± 0.17.6 ± 0.1
KM10.2 ± 0.29.5 ± 0.29.2 ± 0.2
parametric fit9.9 ± 0.29.3 ± 0.39.0 ± 0.2
1H NMR9.3 ± 1.07.5 ± 3.0--
SEC42.332.267.7
Mn/kDaSTM8.5 ± 0.17.5 ± 0.18.3 ± 0.1
KM10.0 ± 0.29.3 ± 0.210.0 ± 0.2
parametric fit9.7 ± 0.29.1 ± 0.29.8 ± 0.2
1H NMR9.4 ± 1.07.5 ± 3.0--
SEC41.531.674.0
Mw/kDaSTM9.6 ± 0.38.9 ± 0.39.4 ± 0.3
KM11.4 ± 0.511.1 ± 0.511.9 ± 0.7
parametric fit11.4 ± 0.511.5 ± 0.612.0 ± 0.5
SEC88.5103.4358.9
a

1H NMR spectra were measured in C2D2Cl4 at 120 °C, SEC was measured in chloroform at 30 °C.

All three polymers were also measured by ESD-STM with the aim of determining their molecular weights. The samples were prepared by electrospray deposition of the polymers under identical conditions onto an atomically clean Au(111) substrate kept at room temperature in a vacuum (see the SI for further details). The deposition parameters were chosen so as to form a monolayer of polymer chains. The self-assembled polymers were then imaged by UHV-STM at 77K. In the STM images, all three polymers are seen to adsorb face on onto the surface and show a tendency to form compact islands characterized by interacting polymers (Figure S4). In closely packed regions (see Figure 1b,c for P1 and P3 and Figure S5a for P2), individual polymer chains can be identified in the images through extended, straight and continuous features, corresponding to their backbones.
The interbackbone distance (i.e., the 2D equivalent of the lamellar spacing in 3D films) is (2.0 ± 0.1) nm for P1 and P2 and (2.5 ± 0.2) nm for P3. For P1 and P2, this is in excellent agreement with the value of 2.04 nm (2.11 after annealing) obtained for the lamellar spacing of thin films of the same polymers by GIWAXS. (57) For all three polymers, these values are consistent with the interdigitation of their side chains.
The branched side chains are seen in the STM images as shorter, bright, and, in the case of P1 and P2, mostly angled features that flank the backbones. As shown in Figure 1b,c, different assembly patterns and degree of regularity can be found for x = 0 (P1, P2) and x = 4 (P3). For P1 and P2, in the more regular areas of the assembly, the branched side chains appear as bright L-shaped objects with arms of different lengths (red part of the inset in Figure 1b). In disordered or defective areas of the assembly (the green part of the inset in Figure 1b), the only part of the side chains that appears bright in the STM images corresponds to the carbon located nearest to the lactam-N of ThDPPTh, while the two arms appear darker and form rather irregular patterns. This is due to the presence of sp3 carbon atoms and the associated tetrahedral angles. (51) The side chains of P3 instead appear as bright segments protruding from the backbone at a typical angle of 60 ± 1° followed by a darker pair of segments that form an overall uniform assembly (inset in Figure 1c).
In order to exactly identify the regular patterns formed by P1 and P3, geometry-optimized molecular models were built in the Avogadro molecular editor (using the MMFF94 force field) and fitted to the STM images. For the x = 0 polymers (P1 and P2), the areas of regular side chain packing are well represented by models in which the arms form a 120° angle with the linker and among themselves, as shown in Figure 2a and Figure S5a for P1 and P2, respectively. The shorter arms (C8H17) tend to orient almost parallel to the backbones, possibly interacting with the F atoms of the F4 units. The longer arms (C10H21) interdigitate with other longer arms from adjacent polymers, most probably through van der Waals (vdW) forces. For P3, instead, the best fitting model shows the two arms orienting along a single line, with the shorter and longer arms forming angles of 60° and 120° with the linker, respectively (Figure 2b). This conformation allows very favorable vdW interactions and thus dense packing of side chains from neighboring polymers. Overall, the proposed fits represent all of the features visible in the STM images. Details of the fitting procedure can be found in Section 3 of the SI.

Figure 2

Figure 2. In (a) and (b), geometry-optimized molecular models superposed onto high-resolution STM images are shown for P1 and P3, respectively. This modeling allows one to identify the details of the backbone sequence and of the polymer assembly, including complex side chain interdigitation patterns. All scale bars correspond to 1 nm. The STM images were acquired in constant current mode, with tunnelling parameters (a) 1.4 V, 70 pA; (b) 1.3 V, 140 pA.

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The optimal fit of the molecular models to the STM images grants access to the full conformations of the backbones, and the prevalent configuration adopted by the polymer backbones can be inferred. For all three polymers, the DPP units show a N,S-syn orientation with respect to the neighboring thiophene rings, with an anti configuration of the thiophenes flanking a single F4 unit. This is in excellent agreement with solid state NMR results and DFT simulations on PThDPPThF4 (x = 0) polymers, that identified this as a minimum energy configuration stabilized by an intramolecular conformational lock between the hydrogen atom in the thiophene units and the carbonyl oxygen of the DPP core. (57,61) By ESD-STM, however, it is also possible to establish the presence of other, minority configurations that are not detectable by standard averaging characterization techniques. In fact, occasional instances where the DPP units are in N,S-anti orientation with respect to one of the flanking Th rings were also observed (see Figure S6a for an example).
Even though the presence of the gold substrate might have an influence on the intermolecular interactions, we expect that several features of the assembly observed in the 2D monolayers will characterize also the packing of these polymers in 3D thin films, as already reported in other cases. (53) A first confirmation of this is given by the excellent agreement between the lamellar spacings measured by GIWAXS and those determined through STM, and by the analogies of the backbone conformation as determined by STM and solid state NMR. However, we expect that this similarity also extends to other structural details of the molecular assembly, such as the interaction motifs between the side chains. Thus, we expect the patterns observed in the STM images (Figure 2) to be a good representation of those characterizing the side chain interaction in 3D thin films, which are typically challenging to determine by X-ray diffraction or solid state NMR.
Based on this detailed interpretation of the ESD-STM data, it becomes now possible to determine the polymer molecular weight through direct analysis of STM images by measuring the length of individual polymer chains. Even more directly, in high-resolution images, one can count just the number of repeat units. Unlike more traditional techniques such as viscosimetry, SEC, and NMR, polymer aggregation is not expected to represent a limitation for ESD-STM. Aggregation within the microdroplets produced during the ESD process is a known phenomenon that does not prevent the formation of the monolayers required for STM analysis. Single polymer strands are clearly distinguished in STM images of these assembled monolayers and are individually accounted for in the analysis. Moreover, since ESD is not a mass-selective deposition technique, (62) the polymers measured by STM are expected to represent an unbiased sample of the original material. As a consequence, when this analysis is performed on a large enough set of data, the results can be taken as a representative description of the polymer mass distribution. This is in contrast to MALDI-MS, where shorter chains are detected with higher probability leading to underestimated molecular weight distributions. (26,63) A further significant strength of ESD-STM over traditional techniques is that not only does it provide a description of the polymers’ mass through average quantities (such as the number-average molar mass, Mn, the weight-average molar mass, Mw, and the degree of polymerization, DPn) but it also gives the complete mass distribution of the material, thus allowing for a much more accurate description of the polymer population. In the following, we will first benchmark the ESD-STM results on the mass of the PThDPPThF4 polymers against the NMR-derived data for P1 and P2 and then present the mass distribution for P3, which cannot be obtained from NMR (vide supra).
For the ESD-STM analysis, a large number of polymer lengths have been collected for all three molecules, and the experimental distributions are shown as bar histograms in Figure 3. The corresponding average values are reported in Table 1 and the details on the line-profile acquisition can be found in Section 5 of the SI. This approach has a limitation in the fact that only polymers that are fully distinguishable from the beginning to the end can be directly included in these distributions (see green lines in Figure S10b). Polymers that cross through the borders of the STM images and polymers whose line-profiles cannot be unambiguously distinguished in their entirety–for example because they cross another polymer or traverse a poorly resolved part of an image–are excluded from the initial length distributions (see blue lines in Figure S10b). Both of these cases tend to affect longer polymers more than shorter ones. Since almost half of the polymers present in an STM image pertain to such excluded categories, not accounting for their presence can produce a significant skewing of the final histograms toward smaller masses. We therefore tackled this issue by means of a statistical analysis based on the survival analysis approach. (64)

Figure 3

Figure 3. Length and mass distributions obtained from measuring a large number of polymer line-profiles from the STM images. Only polymers fully visible and entirely contained within the STM images were used for the bar histogram distributions (see Figure S11). (a) Distribution for P1, (b) for P2, and (c) for P3. Two statistical approaches from survival analysis have been implemented to correct the length underestimation caused by polymers either not fully visible or not entirely contained within the STM images: the Kaplan–Meier nonparametric distribution (red circles) and the parametric distribution (black diamonds). See the text for further details.

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In essence, this method consists of combining the distribution of the fully visible polymers (green in Figure S10b) with the distribution of polymers that have been classified as “longer than” (blue in Figure S10b), based on their maximal unambiguously determined length. In particular, the latter distribution is used to “correct” the former by taking into account that the observed incomplete polymers must be a section of longer molecules. Among the different possibilities offered by survival analysis, we chose two complementary approaches for performing this correction: a nonparametric approach (with a Kaplan–Meier estimator) that makes no a priori assumption on the final mass distribution, and a parametric approach where a Flory–Schulz (geometric) mass distribution was assumed, according to what is expected from an ideal step-growth polymerization process. Moreover, in order to take into account the effects of the purification processes that cause the preferential removal of shorter polymers (e.g., Soxhlet extraction purification), the geometric Flory–Schulz distribution was multiplied by a logistic curve (see Section 6 of the SI).
The results of these two approaches are overlaid as red dots and black diamonds, respectively, on the histogram distributions directly derived from the STM images in Figure 3. It is clear that both corrections move the distributions toward higher masses, as expected. The same effect is visible in the evaluation of the average quantities Mn, Mw, and DPn, where the values obtained from the Kaplan–Meier and the parametric corrections are all larger than those obtained from the direct STM analysis (Table 1). The Mn values estimated with the two different statistical correction approaches only differ by about 2%, showing that as long as the intrinsic limitations of finite size STM images are taken into account, the specific approach used does not significantly influence the result. These corrected distributions, therefore, represent the best evaluation that can be obtained by ESD-STM of the masses of these polymers. The measures of uncertainty for the STM, KM, and parametric approaches given in Table 1 were calculated using bootstrapping. The uncertainty given is the sample standard deviation of the corresponding quantities calculated from 200 nonparametric bootstrap data sets.
The STM-derived Mn, Mw, and DPn values can be directly compared to the results obtained from NMR (Table 1). For nominally identical polymers P1 and P2, the NMR values agree very well with the STM ones. This excellent comparison allows us to benchmark the ESD-STM approach also for the characterization of mean mass values, while showing that this technique is not affected by the same limitations of NMR. This is directly demonstrated by the results obtained by ESD-STM for P3, that have the same accuracy as those for P1 and P2, but for which high quality NMR spectra were not available (Figure S9). Finally, we notice that having access to the full mass distributions allows one to use the STM data to further characterize these polymers in ways that are inaccessible by NMR. In fact, from the fitting procedure by means of a Flory-Schultz distribution and a logistic curve, different parameters can be derived (such as an effective fractional monomer conversion, see Section 7 of the SI) that provide an accurate and specific description of the mass distribution.
Full mass distributions can theoretically be obtained also by SEC, although in the specific case of conjugated polymers the aforementioned intrinsic limitations and inaccuracies of SEC caused by polystyrene calibration and aggregation severely limit its reliable use. Nevertheless, SEC is still often used in the literature as an “effective characterization tool”, and we thus decided to compare its outcomes with the ESD-STM results, for completeness. SEC was employed for all three samples to obtain the Mn values that are reported in Table 1 (see Section 10 of the SI for details). The Mn values determined by SEC for P1 and P2 are in the same relationship as the values determined by ESD-STM, i.e., Mn,P1 > Mn,P2, but this is not true for P3, for which SEC gives significantly larger Mn values than for P1 and P2, while the ESD-STM data show that Mn,P3 is comparable to the Mn of P1 and P2. Moreover, for all three polymers, the absolute Mn values obtained by SEC are significantly larger than the corresponding ESD-STM ones.
This becomes even more evident when directly comparing the full mass distributions derived from the STM analysis with those obtained by SEC: the well-known issue of the overestimation of the SEC masses (20,21,23,27) is clearly observable, as can be seen in Figure S13b–d for P1, P2, and P3, respectively. However, a careful look at the SEC curves (Figure 4a) reveals that oligomer peaks, which were probably not completely removed during Soxhlet extraction, are visible in the low-mass regions of P2 and P3. Using these peaks as a reference, it is possible to evaluate the functional relationship between the SEC measured masses (determined though universal calibration using the viscometer detector) and their actual values (see Figure S14). The inverse of this functional relationship can then be used to rescale the full SEC mass distribution. Figure 4b,c shows the results of applying this procedure to the original SEC data for P2 and P3, respectively, and the direct comparison with the STM data now demonstrates a much better agreement between the two techniques. Note that the STM data are reported as histograms and not as continuous distributions since they are based on counts of integer multiples of the polymer repeat unit and thus their x-axis scale is discrete. The aggregation shoulder is clearly still present also in the rescaled SEC data, as it represents an intrinsic feature of the SEC measurement. However, this shoulder is not present in the STM histograms, since even longer polymer strands can be clearly identified and do not suffer issues of aggregation after the ESD process. The fact that, for both polymers, a quadratic functional dependence relates the SEC masses and the theoretical values (see Figure S14), could represent a general trend in the calibration of SEC data of conjugated polymers, and will be investigated in more detail in the future. At the same time, these results indicate that the ESD-STM technique is potentially an ideal way to recalibrate SEC data for conjugated polymers.

Figure 4

Figure 4. (a) SEC mass distributions for the three polymers. P1 and P2 have similar average masses and aggregation shoulders in similar positions; on the contrary, P3 displays a much wider aggregation shoulder caused by its longer and more flexible side chains promoting aggregation. After the recalibration of the SEC horizontal mass scales, the comparison with the STM data (corrected through the parametric survival approach) demonstrates an excellent agreement, as shown in (b) and (c) for P2 and P3, respectively. The STM results are shown as histograms, the rescaled SEC data as continuous lines and the original SEC data as dotted black lines.

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Another essential characteristic of conjugated polymers that can influence the properties of devices is the type and frequency of chemical defects that alter the ideal sequence and that are caused by side reactions during polycondensation. (35,37,43,44) In the case of PThDPPThF4, CH/CH hc reactions of the ThDPPTh monomer have already been verified by 1H NMR spectroscopy. (34) Specifically for the polymers investigated here, end group and defect integration of 1H NMR peaks assigned to ThDPPTh hc defects provides a relative frequency of (6.2 ± 0.5)% and (2 ± 1)% for P1 and P2, respectively (see Figures S7 and S8 and Table 2). This proves that the different synthetic conditions used for these two polymers (see theSI) indeed produce different hc defect content. Similar to what already discussed for the NMR evaluation of the Mn values, it is not possible to identify or quantify hc defects for P3, since its much stronger aggregation tendency causes a significant broadening of the peaks in the 1H NMR spectra (see Table 2 and Figure S9).
Table 2. Homocoupling Defect Content for P1, P2, and P3 as Measured by STM and NMR
polymerSTM (%) (total # counts)NMR (%)
P1 (x = 0)5.9 ± 1.0 (547)6.0 ± 1.0
P2 (x = 0)3.0 ± 0.8 (434)2 ± 1
P3 (x = 4)6.7 ± 1.0 (551)--
The presence of ThDPPTh hc defects can also be determined from the ESD-STM data, as the side chains are well visible and their separation along the backbone is significantly shorter in the case of an hc defect than for a normal heterocoupling (see Figure 5 and Figure S5). A careful analysis of high-resolution STM images indeed confirms the presence of ThDPPTh hc in all studied polymers, as shown in Figures 5c,d for P1 and P3, respectively, and in Figure S5b for P2. To verify this quantitatively, the polymer backbones were fitted for a large number of STM images (see Section 3 of the SI for details), resulting in an average value of (1.21 ± 0.09) nm for the shorter distances between successive side chains and (1.62 ± 0.07) nm for the longer ones. The comparison between these values and the corresponding theoretical ones obtained from optimized molecular models is highly satisfactory (Table S1), unambiguously proving the nature of the hc defects. By analyzing a large number of STM images, the hc content was quantified through this approach for all three polymers and reported in Table 2. In the case of P1 and P2, for which the corresponding NMR-based values are available, the agreement is excellent, representing a reliable benchmarking of the ESD-STM technique. Since for P3 the 1H NMR signals are broad and ill-resolved, its hc content can only be determined based on STM imaging, demonstrating how this method reaches beyond the limits of current analytical techniques. We also observe that the overall trend of hc defects obtained from the STM analysis is confirmed by UV–vis measurements, where the intensity of the hc shoulder at about 750 nm, is similar for P1 and P3, but lower for P2 (Figure S15). (34) It should be further noticed that the uncertainties associated with the STM measurements are purely statistical in nature, as they are estimated as the standard deviation of a binomial distribution with n trials (i.e., total number of bonds counted) and success probability p (that is the probability of having a correct, nondefective bond between successive monomers). These errors could, therefore, be further reduced by increasing the number of analyzed polymers. On the contrary, errors associated with the NMR measurements are inherently linked to the resolution of the spectra, and therefore cannot be further minimized. Finally, it is important to note that while the signal obtained from spectroscopic techniques only depends on the average frequencies of the polymerization defects, ESD-STM grants access to the entire distribution of backbone sequences. This allows one to investigate specific characteristics of the defects such as preferential locations within the backbones (e.g., in correspondence to end groups) or possible spatial correlations between defects. This kind of information is mostly inaccessible to traditional analytical techniques but represents a fundamental knowledge in order to determine how defects affect the catalytic cycle, e.g., if they increase the probability of side reactions or enhance the chances of terminating the polymerization process. Future research will explore this specific insight offered by the ESD-STM technique.

Figure 5

Figure 5. Sequencing the backbones of the polymers allows for the precise identification of homocoupling defects. (a) and (b) show the same STM images of Figure 1, with white dashed circles indicating the positions of ThDPPTh homocoupling defects. (c, d) Higher-resolution STM images with examples of homocoupling defects highlighted by white circles. The red and black double arrows indicate the distance along the backbones between two successive side chain exit points, showing that in the case of a homocoupling (red double arrows), this quantity is significantly reduced with respect to the regular heterocouplings (black double arrows). Scale bars correspond to 4 nm for parts (a) and (b) and to 1 nm for parts (c) and (d). The STM images were acquired in constant current mode, with tunneling parameters (a) 1.4 V, 70 pA; (b) 1.3 V, 90 pA; (c) 1.4 V, 70 pA; (d) 1.3 V, 90 pA.

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Conclusions

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In this work, we demonstrate that ESD-STM is a reliable analytical methodology for characterizing conjugated polymers by showing that it can accurately and quantitatively reproduce the results of traditional analytical techniques where they are applicable, while providing equivalent precision in cases where these methods are inadequate. Furthermore, we establish its ability to deliver microstructural information that cannot be obtained by any other current analytical technique, such as molecularly resolved assembly patterns, backbone conformations, exact sequencing, nature and frequency of polymerization defects, and full mass distributions of the macromolecules. The ESD-STM benchmarking was performed by measuring three low-molecular-weight DPP conjugated polymers synthesized by DArP (two with the same structure but different homocoupling content, the third one with the side chain branching point farther away from the backbone) and comparing the results with the outcomes of GIWAXS, solid-state NMR, NMR, and SEC.
The average separation between backbones determined by analyzing a large number of STM images showed excellent agreement with the lamellar separation derived from GIWAXS measurement. Furthermore, otherwise inaccessible details of the molecular assembly were obtained by fitting geometry-optimized molecular models onto high-resolution STM images. These revealed the submolecular characteristics of the interdigitation patterns between polymer side chains, which are driven by the maximization of van der Waal interactions. Moreover, the same analysis allowed us to establish that the conformation of the backbones is characterized by N,S-anti configurations between DPP and neighboring thiophene units, in excellent agreement with the results of solid-state NMR spectroscopy and DFT calculations. (57,61)
By measuring the length of a large number of individual polymer molecules in wide-scan STM images and renormalizing the ensuing distribution via a survival analysis approach, we determined the polymer length (mass) distributions. The corresponding Mn values agree extremely well with those obtained by integrating the NMR spectra for the two polymers where the baseline resolution is high enough for this to be possible. However, ESD-STM can also determine, with the same degree of accuracy, the mass distribution for the third polymer whose higher aggregation tendency causes broadening of the NMR spectra and prevents a reliable integration of the end-group signals. A further advantage of ESD-STM is that it establishes the full mass distribution as opposed to only average mass values as obtained from NMR. This gives access to much richer data about the polymers and allows us to derive direct information on the synthetic pathway by which they were made. The decision to focus this study on low Mn conjugated polymers stemmed from the objective of benchmarking the ESD-STM technique against traditional analytical methods like NMR. This necessitated working with low Mn polymers, as NMR can only achieve adequate baseline resolution if chains can be solubilized sufficiently well. This requires either high solubility or a short chain length. On the other hand, many high-performance polymers of practical relevance show strong aggregation and thus broad signals in 1H NMR spectra even for short lengths. It is therefore crucial to recognize that a limited molecular weight analysis pertains to NMR and not ESD-STM. Indeed, our previous studies have demonstrated ESD-STM’s capability to measure and analyze much longer conjugated polymers (for example IDT-BT-C16 polymers with Mn exceeding 50 kDa). (52)
An internal calibration procedure was proposed for rescaling the SEC mass distributions of the analyzed polymers, based on the signals of short oligomers. The agreement of the resulting, corrected distributions with those determined by ESD-STM was excellent in the low and medium mass range, further proving the reliability of ESD-STM. In the higher mass range, SEC distributions showed the well-known aggregation shoulders, which could be directly evaluated by comparison with the ESD-STM distribution, since this latter technique is not affected by polymer aggregation.
Finally, the modeling of high-resolution STM images also allowed us to determine the nature and to quantify the occurrence of homocoupling defects. When compared with the NMR analysis of the two polymers with shorter side chains, the agreement was again excellent, both in terms of the type of homocoupling (only ThDPPTh hc were observed by both techniques) and of their average frequencies. Similar to the case of the average molecular mass, while the NMR analysis cannot be performed on the third, more aggregating polymer, ESD-STM is not affected by polymer aggregation and thus also provides results on the homocoupling defects of the polymer with the longer side chains. It is to be noted that, while the degree of uncertainty associated with the NMR estimation of the average mass values and the defect frequencies depends on the specific polymer and on the quality of the spectrum, ESD-STM affords the same accuracy in different measurements, provided that a similarly sized statistical sample is analyzed.
Overall, this work showcases the power of ESD-STM as an analytical tool for the characterization of conjugated polymers, capable of providing a wealth of high-resolution quantitative information that is inaccessible to traditional analytical techniques. Particularly attractive are its sensitivity to the presence of minimal quantities of chemical defects or specific molecular conformations and the fact that, being a microscopy technique, it allows access to information about individual members of a sample population. Thus, at variance with more traditional, population-integrating spectroscopy techniques, the information that can be extracted from ESD-STM also includes correlations within populations (e.g., spatial correlations of polymerization defects), which give a previously unattainable insight into the synthetic pathways through which these macromolecules are made and a way to test hypotheses on reaction mechanisms. Thus, we expect that ESD-STM will deliver a fundamental contribution toward the rational optimization of the synthesis of conjugated polymer materials with tailored and improved functional properties.

Methods

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Nuclear Magnetic Resonance (NMR)

Polymers were measured on a Bruker AVANCE III 500 spectrometer (1H: 500.1 MHz, 13C: 125.8 MHz). C2D2Cl4 (at 120 °C) was used as a solvent. The spectra were referenced to the residual solvent peak (C2D2Cl4: δ(1H) = 5.98 ppm). Monomers and other compounds were measured on a Bruker Avance 300 instrument (1H NMR at 300 MHz and 13C NMR spectra at 75 MHz at room temperature in CDCl3 (δ(1H) 7.26 ppm; δ(13C) 77.0 ppm).

UV–vis Spectroscopy

UV–vis spectra were recorded at 25 °C on a UV-1800 Series (Shimadzu) instrument equipped with a heated sample holder in 2-chloronaphthalene solutions (c = 0.02 mg/mL) at 150 °C.

Size Exclusion Chromatography (SEC)

The polymers were measured with an Agilent Infinity II MDS instrument with differential refractive index (DRI), viscometry (VS), dual angle light scatter (LS), and multiple wavelength UV detectors. The system was equipped with 2 x PLgel Mixed C columns (300 mm × 7.5 mm) and a PLgel 5 μm guard column, with CHCl3 as the eluent. Samples were run at 1 mL/min at 30 °C. Poly(methyl methacrylate) and polystyrene standards (Agilent EasiVials) were used for calibration. Ethanol was added as a flow rate marker. Analyte samples were filtered through a nylon membrane with a 0.22 μm pore size before injection. Experimental molar mass (Mn) and dispersity (Đ) values of the synthesized polymers were determined by conventional calibration using Agilent GPC/SEC software.

Scanning Tunnelling Microscopy (STM)

STM measurements have been performed on a low temperature (LT) ultrahigh vacuum (UHV) scanning tunnelling microscope equipped with an electrospray deposition (ESD) setup. The three polymer samples (P1, P2, and P3, see main text for definition) were dissolved in chlorobenzene at concentrations ∼ 0.025 g/L, and methanol was added to a 4:1 volume ratio. The molecules were deposited from solution by ESD with a 4-stage Molecular Spray system on a room temperature Au(111)/mica sample. The deposition current was monitored on the target substrate and typical total deposition charges were 4 pAh. Gold on mica thin films (Georg Albert PVD, 300 nm thickness) were used as substrates and prepared in UHV by cycles of argon ion sputtering (1 kV) and subsequent annealing to 500 °C. The LT-STM (CreaTec Fischer & Co. GmbH) was kept at −196 °C by a liquid nitrogen bath cryostat during measurements. All images were acquired in constant current feedback mode with an electrochemically etched tungsten tip that was treated by argon ion sputtering after insertion in UHV. The bias voltage indicated in the figure captions was applied to the sample. The STM images were processed with WSxM (65) and Gwyddion, (66) the molecular models were made and optimized in Avogadro (67) and their fitting to the STM images was performed with the LMAPper software. (68)

Data Availability

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The datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request.

Supporting Information

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The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsnano.3c10842.

  • Further details on the experimental and synthetic methods, STM images displaying different molecular coverages and the assembly and modeling of P2 polymers, molecular models and procedure used for fitting the STM images, details of the quantitative analysis of the NMR spectra, procedure for determining polymer length profiles from STM images, survival analysis method used to correct the polymer length distributions, discussion of effective extents of reaction, SEC analysis details, UV–vis spectroscopy data, method for calculating average values from distributions (PDF)

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Author Information

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  • Corresponding Author
  • Authors
    • Stefania Moro - School of Chemistry, University of Birmingham, Birmingham B15 2TT, U.K.;  Department of Chemistry, University of Warwick, Coventry CV4 7AL, U.K.
    • Simon E.F. Spencer - Department of Statistics, University of Warwick, Coventry CV4 7AL, U.K.
    • Daniel W. Lester - Polymer Characterisation Research Technology Platform, University of Warwick, Coventry CV4 7AL, U.K.
    • Fritz Nübling - Institute for Macromolecular Chemistry, University of Freiburg, Freiburg 79104, Germany
    • Michael Sommer - Institute for Chemistry, Chemnitz University of Technology, Chemnitz 09111, Germany;  Center for Materials, Architectures and Integration of Nanomembranes (MAIN), Chemnitz University of Technology, Chemnitz 09126, Germany;  Orcidhttps://orcid.org/0000-0002-2377-5998
  • Notes
    The authors declare no competing financial interest.

Acknowledgments

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S.M. acknowledges funding though an EU Chancellor’s Scholarship by the University of Warwick. G.C. and S.M. acknowledge support from a UK – Saudi Challenge Fund grant from the British Council’s Going Global Partnerships Programme. M.S. and F.N. thank S. Broll for providing P1 and D. Tran for synthesizing the ThDPPTh monomer with x = 4.

References

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This article references 68 other publications.

  1. 1
    Zhao, C.; Wang, J.; Jiao, J.; Huang, L.; Tang, J. Recent advances of polymer acceptors for high-performance organic solar cells. J. Mater. Chem. C 2020, 8, 28– 43,  DOI: 10.1039/C9TC05567C
    Google Scholar
    1
    Recent advances of polymer acceptors for high-performance organic solar cells
    Zhao, Congcong; Wang, Jiuxing; Jiao, Jiqing; Huang, Linjun; Tang, Jianguo
    Journal of Materials Chemistry C: Materials for Optical and Electronic Devices (2020), 8 (1), 28-43CODEN: JMCCCX; ISSN:2050-7534. (Royal Society of Chemistry)
    A review. In the past few decades, polymer solar cells (PSCs) have been intensively investigated in academic fields. The study of non-fullerene polymer acceptors has become a hot research focus due to their excellent opto-electronic properties such as wide light-absorbing ability, appropriate mol. energy levels, and easy chem. modifications. The much higher power conversion efficiencies (PCEs) of non-fullerene PSCs relative to fullerene PSCs revealed the significant potential of non-fullerene acceptors in PSCs. This review systematically summarizes the recent advancements of efficient polymer acceptors, including perylene diimide-based, naphthalene diimide-based, diketopyrrolopyrrole-based, double B ← N bridged bipyridyl-based, and other polymer acceptors. Their structure-property relationships were thoroughly analyzed and summarized, which may provide new guidance for the rational structural design of high-performance photovoltaic materials.
  2. 2
    Li, W.; Hendriks, K. H.; Wienk, M. M.; Janssen, R. A. J. Diketopyrrolopyrrole Polymers for Organic Solar Cells. Acc. Chem. Res. 2016, 49, 78– 85,  DOI: 10.1021/acs.accounts.5b00334
    Google Scholar
    2
    Diketopyrrolopyrrole Polymers for Organic Solar Cells
    Li, Weiwei; Hendriks, Koen H.; Wienk, Martijn M.; Janssen, Rene A. J.
    Accounts of Chemical Research (2016), 49 (1), 78-85CODEN: ACHRE4; ISSN:0001-4842. (American Chemical Society)
    Conjugated polymers have been extensively studied for application in org. solar cells. In designing new polymers, particular attention has been given to tuning the absorption spectrum, mol. energy levels, crystallinity, and charge carrier mobility to enhance performance. As a result, the power conversion efficiencies (PCEs) of solar cells based on conjugated polymers as electron donor and fullerene derivs. as electron acceptor have exceeded 10% in single-junction and 11% in multijunction devices. Despite these efforts, it is notoriously difficult to establish thorough structure-property relationships that will be required to further optimize existing high-performance polymers to their intrinsic limits.In this Account, we highlight progress on the development and our understanding of diketopyrrolopyrrole (DPP) based conjugated polymers for polymer solar cells. The DPP moiety is strongly electron withdrawing and its polar nature enhances the tendency of DPP-based polymers to crystallize. As a result, DPP-based conjugated polymers often exhibit an advantageously broad and tunable optical absorption, up to 1000 nm, and high mobilities for holes and electrons, which can result in high photocurrents and good fill factors in solar cells. Here we focus on the structural modifications applied to DPP polymers and rationalize and explain the relationships between chem. structure and org. photovoltaic performance. The DPP polymers can be tuned via their arom. substituents, their alkyl side chains, and the nature of the π-conjugated segment linking the units along the polymer chain. We show that these building blocks work together in detg. the mol. conformation, the optical properties, the charge carrier mobility, and the soly. of the polymer. We identify the latter as a decisive parameter for DPP-based org. solar cells because it regulates the diam. of the semicryst. DPP polymer fibers that form in the photovoltaic blends with fullerenes via soln. processing. The width of these fibers and the photon energy loss, defined as the energy difference between optical band gap and open-circuit voltage, together govern to a large extent the quantum efficiency for charge generation in these blends and thereby the power conversion efficiency of the photovoltaic devices. Lowering the photon energy loss and maintaining a high quantum yield for charge generation is identified as a major pathway to enhance the performance of org. solar cells. This can be achieved by controlling the structural purity of the materials and further control over morphol. formation. We hope that this Account contributes to improved design strategies of DPP polymers that are required to realize new breakthroughs in org. solar cell performance in the future.
  3. 3
    Wadsworth, A. Critical review of the molecular design progress in non-fullerene electron acceptors towards commercially viable organic solar cells. Chem. Soc. Rev. 2019, 48, 1596– 1625,  DOI: 10.1039/C7CS00892A
    Google Scholar
    3
    Critical review of the molecular design progress in non-fullerene electron acceptors towards commercially viable organic solar cells
    Wadsworth, Andrew; Moser, Maximilian; Marks, Adam; Little, Mark S.; Gasparini, Nicola; Brabec, Christoph J.; Baran, Derya; McCulloch, Iain
    Chemical Society Reviews (2019), 48 (6), 1596-1625CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
    A review. Fullerenes have formed an integral part of high performance org. solar cells over the last 20 years, however their inherent limitations in terms of synthetic flexibility, cost and stability have acted as a motivation to develop replacements; the so-called non-fullerene electron acceptors. A rapid evolution of such materials has taken place over the last few years, yielding a no. of promising candidates that can exceed the device performance of fullerenes and provide opportunities to improve upon the stability and processability of org. solar cells. In this review we explore the structure-property relationships of a library of non-fullerene acceptors, highlighting the important chem. modifications that have led to progress in the field and provide an outlook for future innovations in electron acceptors for use in org. photovoltaics.
  4. 4
    Lamport, Z. A.; Haneef, H. F.; Anand, S.; Waldrip, M.; Jurchescu, O. D. Tutorial: Organic field-effect transistors: Materials, structure and operation. J. Appl. Phys. 2018, 124, 071101  DOI: 10.1063/1.5042255
    Google Scholar
    4
    Tutorial: Organic field-effect transistors: Materials, structure and operation
    Lamport, Zachary A.; Haneef, Hamna F.; Anand, Sajant; Waldrip, Matthew; Jurchescu, Oana D.
    Journal of Applied Physics (Melville, NY, United States) (2018), 124 (7), 071101/1-071101/25CODEN: JAPIAU; ISSN:0021-8979. (American Institute of Physics)
    A review. Chem. versatility and compatibility with a vast array of processing techniques has led to the incorporation of org. semiconductors in various electronic and opto-electronic devices. One such device is the org. field-effect transistor (OFET). In this tutorial, we describe the structure, operation, and characterization of OFETs. Following a short historical perspective, we introduce the architectures possible for OFETs and then describe the device physics and the methods for extg. relevant device parameters. We then provide a brief overview of the myriad org. semiconductors and deposition methods that were adopted for OFETs in the past decades. Non-ideal device characteristics, including contact resistance, are then discussed along with their effects on elec. performance and on the accuracy of extg. device parameters. Finally, we highlight several measurements involving OFETs that allow access to fundamental properties of org. semiconductors and the mechanism of charge transport in these materials. (c) 2018 American Institute of Physics.
  5. 5
    Wang, C.; Dong, H.; Hu, W.; Liu, Y.; Zhu, D. Semiconducting π-conjugated systems in field-effect transistors: A material odyssey of organic electronics. Chem. Rev. 2012, 112, 2208– 2267,  DOI: 10.1021/cr100380z
    Google Scholar
    5
    Semiconducting π-Conjugated Systems in Field-Effect Transistors: A Material Odyssey of Organic Electronics
    Wang, Chengliang; Dong, Huanli; Hu, Wenping; Liu, Yunqi; Zhu, Daoben
    Chemical Reviews (Washington, DC, United States) (2012), 112 (4), 2208-2267CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
    A review.
  6. 6
    Russ, B.; Glaudell, A.; Urban, J. J.; Chabinyc, M. L.; Segalman, R. A. Organic thermoelectric materials for energy harvesting and temperature control. Nat. Rev. Mater. 2016, 1, 16050,  DOI: 10.1038/natrevmats.2016.50
    Google Scholar
    6
    Organic thermoelectric materials for energy harvesting and temperature control
    Russ, Boris; Glaudell, Anne; Urban, Jeffrey J.; Chabinyc, Michael L.; Segalman, Rachel A.
    Nature Reviews Materials (2016), 1 (10), 16050CODEN: NRMADL; ISSN:2058-8437. (Nature Publishing Group)
    Conjugated polymers and related processing techniques have been developed for org. electronic devices ranging from lightwt. photovoltaics to flexible displays. These breakthroughs have recently been used to create org. thermoelec. materials, which have potential for wearable heating and cooling devices, and near-room-temp. energy generation. So far, the best thermoelec. materials have been inorg. compds. (such as Bi2Te3) that have relatively low Earth abundance and are fabricated through highly complex vacuum processing routes. Mol. materials and hybrid org.-inorg. materials now demonstrate figures of merit approaching those of these inorg. materials, while also exhibiting unique transport behaviors that are suggestive of optimization pathways and device geometries that were not previously possible. In this Review, we discuss recent breakthroughs for org. materials with high thermoelec. figures of merit and indicate how these materials may be incorporated into new module designs that take advantage of their mech. and thermoelec. properties.
  7. 7
    Rivnay, J. Organic electrochemical transistors. Nat. Rev. Mater. 2018, 3, 17086,  DOI: 10.1038/natrevmats.2017.86
    Google Scholar
    7
    Organic electrochemical transistors
    Rivnay, Jonathan; Inal, Sahika; Salleo, Alberto; Owens, Roisin M.; Berggren, Magnus; Malliaras, George G.
    Nature Reviews Materials (2018), 3 (2), 17086CODEN: NRMADL; ISSN:2058-8437. (Nature Research)
    A review. Org. electrochem. transistors (OECTs) make effective use of ion injection from an electrolyte to modulate the bulk cond. of an org. semiconductor channel. The coupling between ionic and electronic charges within the entire vol. of the channel endows OECTs with high transconductance compared with that of field-effect transistors, but also limits their response time. The synthetic tunability, facile deposition and biocompatibility of org. materials make OECTs particularly suitable for applications in biol. interfacing, printed logic circuitry and neuromorphic devices. In this Review, we discuss the physics and the mechanism of operation of OECTs, focusing on their identifying characteristics. We highlight org. materials that are currently being used in OECTs and survey the history of OECT technol. In addn., form factors, fabrication technologies and applications such as bioelectronics, circuits and memory devices are examd. Finally, we take a crit. look at the future of OECT research and development.
  8. 8
    Kukhta, N. A.; Marks, A.; Luscombe, C. K. Molecular Design Strategies toward Improvement of Charge Injection and Ionic Conduction in Organic Mixed Ionic-Electronic Conductors for Organic Electrochemical Transistors. Chem. Rev. 2022, 122, 4325– 4355,  DOI: 10.1021/acs.chemrev.1c00266
    Google Scholar
    8
    Molecular Design Strategies toward Improvement of Charge Injection and Ionic Conduction in Organic Mixed Ionic-Electronic Conductors for Organic Electrochemical Transistors
    Kukhta, Nadzeya A.; Marks, Adam; Luscombe, Christine K.
    Chemical Reviews (Washington, DC, United States) (2022), 122 (4), 4325-4355CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
    A review. Expanding the toolbox of the biol. and electronics mutual conjunction is a primary aim of bioelectronics. The org. electrochem. transistor (OECT) has undeniably become a predominant device for mixed conduction materials, offering impressive transconduction properties alongside a relatively simple device architecture. In this review, we focus on the discussion of recent material developments in the area of mixed conductors for bioelectronic applications by means of thorough structure-property investigation and anal. of current challenges. Fundamental operation principles of the OECT are revisited, and characterization methods are highlighted. Current bioelectronic applications of org. mixed ionic-electronic conductors (OMIECs) are underlined. Challenges in the performance and operational stability of OECT channel materials as well as potential strategies for mitigating them, are discussed. This is further expanded to sketch a synopsis of the history of mixed conduction materials for both p- and n-type channel operation, detailing the synthetic challenges and milestones which have been overcome to frequently produce higher performing OECT devices. The cumulative work of multiple research groups is summarized, and synthetic design strategies are extd. to present a series of design principles that can be utilized to drive figure-of-merit performance values even further for future OMIEC materials.
  9. 9
    Guo, X.; Baumgarten, M.; Müllen, K. Designing π-conjugated polymers for organic electronics. Prog. Polym. Sci. 2013, 38, 1832– 1908,  DOI: 10.1016/j.progpolymsci.2013.09.005
    Google Scholar
    9
    Designing π-conjugated polymers for organic electronics
    Guo, Xin; Baumgarten, Martin; Muellen, Klaus
    Progress in Polymer Science (2013), 38 (12), 1832-1908CODEN: PRPSB8; ISSN:0079-6700. (Elsevier Ltd.)
    A review. Conjugated polymers have attracted an increasing amt. of attention in recent years for various org. electronic devices because of their potential advantages over inorg. and small-mol. org. semiconductors. Chemists can design and synthesize a variety of conjugated polymers with different architectures and functional moieties to meet the requirements of these org. devices. This review concs. on five conjugated polymer systems with 1D and 2D topol. structures, and on one polymer designing approach. This includes (i) conjugated polyphenylenes (polyfluorenes, polycarbazoles, and various stepladder polymers), (ii) other polycyclic arom. hydrocarbons (PAHs) as substructures of conjugated polymers, (iii) thiophene and fused thiophene contg. conjugated polymers, (iv) conjugated macrocycles, (v) graphene nanoribbons, and finally (vi) a design approach, the alternating donor-acceptor (D-A) copolymers. By summarizing the performances of the different classes of conjugated polymers in devices such as org. light-emitting diodes (OLEDs), org. field-effect transistors (OFETs), and polymer solar cells (PSCs), the correlation of polymer structure and device property, as well as the remaining challenges, will be highlighted for each class sep. Finally, we summarize the current progress for conjugated polymers and propose future research opportunities to improve their performance in this exciting research field.
  10. 10
    Himmelberger, S.; Salleo, A. Engineering semiconducting polymers for efficient charge transport. MRS Commun. 2015, 5, 383– 395,  DOI: 10.1557/mrc.2015.44
    Google Scholar
    10
    Engineering semiconducting polymers for efficient charge transport
    Himmelberger, Scott; Salleo, Alberto
    MRS Communications (2015), 5 (3), 383-395CODEN: MCROF8; ISSN:2159-6867. (Cambridge University Press)
    Electronic performance in semiconducting polymers has improved dramatically in recent years owing to a host of novel materials and processing techniques. Our understanding of the factors governing charge transport in these materials has also been enhanced through advancements in both exptl. and computational techniques, with disorder appearing to play a central role. In this prospective, we propose that disorder is an inextricable aspect of polymer morphol. which need not be highly detrimental to charge transport if it is embraced and planned for. We discuss emerging guidelines for the synthesis of polymers which are resilient to disorder and present our vision for how future advances in processing and mol. design will provide a path toward further increases in charge-carrier mobility.
  11. 11
    He, Y.; Kukhta, N. A.; Marks, A.; Luscombe, C. K. The effect of side chain engineering on conjugated polymers in organic electrochemical transistors for bioelectronic applications. J. Mater. Chem. C 2022, 10, 2314– 2332,  DOI: 10.1039/D1TC05229B
    Google Scholar
    11
    The effect of side chain engineering on conjugated polymers in organic electrochemical transistors for bioelectronic applications
    He, Yifei; Kukhta, Nadzeya A.; Marks, Adam; Luscombe, Christine K.
    Journal of Materials Chemistry C: Materials for Optical and Electronic Devices (2022), 10 (7), 2314-2332CODEN: JMCCCX; ISSN:2050-7534. (Royal Society of Chemistry)
    A review. Bioelectronics focuses on the establishment of the connection between the ion-driven biosystems and readable electronic signals. Org. electrochem. transistors (OECTs) offer a viable soln. for this task. Org. mixed ionic/electronic conductors (OMIECs) rest at the heart of OECTs. The balance between the ionic and electronic conductivities of OMIECs is closely connected to the OECT device performance. While modification of the OMIECs electronic properties is largely related to the development of conjugated scaffolds, properties such as ion permeability, soly., flexibility, morphol., and sensitivity can be altered by side chain moieties. In this review, we uncover the influence of side chain mol. design on the properties and performance of OECTs. We summarise current understanding of OECT performance and focus specifically on the knowledge of ionic-electronic coupling, shedding light on the significance of side chain development of OMIECs. We show how the versatile synthetic toolbox of side chains can be successfully employed to tune OECT parameters via controlling the material properties. As the field continues to mature, more detailed investigations into the crucial role side chain engineering plays on the resultant OMIEC properties will allow for side chain alternatives to be developed and will ultimately lead to further enhancements within the field of OECT channel materials.
  12. 12
    Katsouras, A. Systematic Analysis of Polymer Molecular Weight Influence on the Organic Photovoltaic Performance. Macromol. Rapid Commun. 2015, 36, 1778– 1797,  DOI: 10.1002/marc.201500398
    Google Scholar
    12
    Systematic Analysis of Polymer Molecular Weight Influence on the Organic Photovoltaic Performance
    Katsouras, Athanasios; Gasparini, Nicola; Koulogiannis, Chrysanthos; Spanos, Michael; Ameri, Tayebeh; Brabec, Christoph J.; Chochos, Christos L.; Avgeropoulos, Apostolos
    Macromolecular Rapid Communications (2015), 36 (20), 1778-1797CODEN: MRCOE3; ISSN:1022-1336. (Wiley-VCH Verlag GmbH & Co. KGaA)
    A review is presented. The mol. wt. of an electron donor-conjugated polymer is as essential as other well-known parameters in the chem. structure of the polymer, such as length and the nature of any side groups (alkyl chains) positioned on the polymeric backbone, as well as their placement, relative strength, the ratio of the donor and acceptor moieties in the backbone of donor-acceptor (D-A)-conjugated polymers, and the arrangement of their energy levels for org. photovoltaic performance. Finding the "optimal" mol. wt. for a specific conjugated polymer is an important aspect for the development of novel photovoltaic polymers. Therefore, it is evident that the chem. of functional conjugated polymers faces major challenges and materials have to adopt a broad range of specifications in order to be established for high photovoltaic performance. In this review, the approaches followed for enhancing the mol. wt. of electron-donor polymers are presented in detail, as well as how this influences the optoelectronic properties, charge transport properties, structural conformation, morphol., and the photovoltaic performance of the active layer.
  13. 13
    Nahid, M. M. Unconventional Molecular Weight Dependence of Charge Transport in the High Mobility n-type Semiconducting Polymer P(NDI2OD-T2). Adv. Funct. Mater. 2017, 27, 1604744  DOI: 10.1002/adfm.201604744
    Google Scholar
    There is no corresponding record for this reference.
  14. 14
    Kline, R. J. Dependence of regioregular poly(3-hexylthiophene) film morphology and field-effect mobility on molecular weight. Macromolecules 2005, 38, 3312– 3319,  DOI: 10.1021/ma047415f
    Google Scholar
    14
    Dependence of Regioregular Poly(3-hexylthiophene) Film Morphology and Field-Effect Mobility on Molecular Weight
    Kline, R. Joseph; McGehee, Michael D.; Kadnikova, Ekaterina N.; Liu, Jinsong; Frechet, Jean M. J.; Toney, Michael F.
    Macromolecules (2005), 38 (8), 3312-3319CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
    Morphol. characterization has been used to explain the previously obsd. strong correlation between charge carrier mobility measured with thin-film transistors and the no.-av. mol. wt. (MW) of the conjugated polymer regioregular poly(3-hexylthiophene). At. force microscopy and x-ray diffraction show that the low-mobility, low-MW films have a highly ordered structure composed of nanorods and the high-mobility, high-MW films have a less ordered, isotropic nodule structure. Modifying the morphol. for a const. MW by changing the casting conditions or annealing the samples strongly affects the charge transport and morphol. in the low-mobility, low-MW films, but has little effect on the high-MW films. In-plane grazing incidence x-ray scattering shows the in-plane π-stacking peak increases when the mobility increases for a const. MW. When the MW is changed, this correlation breaks down, confirming that in-plane π-stacking does not cause the mobility-MW relationship. We believe a combination of disordered domain boundaries and inherent effects of chain length on the electronic structure cause the mobility-MW relationship.
  15. 15
    Deshmukh, K. D. Tuning the Molecular Weight of the Electron Accepting Polymer in All-Polymer Solar Cells: Impact on Morphology and Charge Generation. Adv. Funct. Mater. 2018, 28, 1707185  DOI: 10.1002/adfm.201707185
    Google Scholar
    There is no corresponding record for this reference.
  16. 16
    Tran, D. K. Elucidating the impact of molecular weight on morphology, charge transport, photophysics and performance of all-polymer solar cells. J. Mater. Chem. A 2020, 8, 21070– 21083,  DOI: 10.1039/D0TA08195G
    Google Scholar
    16
    Elucidating the impact of molecular weight on morphology, charge transport, photophysics and performance of all-polymer solar cells
    Tran, Duyen K.; Robitaille, Amelie; Hai, I. Jo; Ding, Xiaomei; Kuzuhara, Daiki; Koganezawa, Tomoyuki; Chiu, Yu-Cheng; Leclerc, Mario; Jenekhe, Samson A.
    Journal of Materials Chemistry A: Materials for Energy and Sustainability (2020), 8 (40), 21070-21083CODEN: JMCAET; ISSN:2050-7496. (Royal Society of Chemistry)
    Understanding the influence of polymer mol. wt. on the morphol., photophysics, and photovoltaic properties of polymer solar cells is central to further advances in the design, processing, performance and optimization of the materials and devices for large scale applications. We have synthesized six no.-av. mol. wt. (Mn) values (21-127 kDa) of biselenophene-naphthalenediimide copolymer (PNDIBS) via direct heteroarylation polymn. and used them to investigate the effects of the acceptor polymer mol. wt. on the charge transport, blend photophysics, blend morphol., and photovoltaic properties of all-polymer solar cells (all-PSCs) based on PNDIBS and the donor polymer PBDB-T. The short-circuit current and power conversion efficiency (PCE) of the PBDB-T:PNDIBS blend devices were found to increase with increasing Mn until reaching peaks at an optimal mol. wt. of 55 kDa and then decreased with further increases in Mn. The max. PCE of 10.2% obsd. at the optimal Mn value of 55 kDa coincided with optimal blend charge transport properties, blend photophysics, and blend morphol. at this crit. mol. wt. Compared to the bi-continuous network of ~ 5.5-6.5 nm cryst. domains with predominantly face-on mol. orientations obsd. at 55 kDa, a relatively disordered microstructure with larger scale phase sepn. was evident at higher Mn while more finely packed cryst. domains were seen at 21 kDa. The sensitivity of the device efficiency to the active layer thickness was found to also depend on the PNDIBSMn value. These results highlight the importance of tuning the mol. wt. of the polymer components to optimize the morphol., charge transport, photophysics and efficiency of all-polymer solar cells. The results also provide new insights on structure-property relationships for a promising n-type semiconducting copolymer.
  17. 17
    Vanhee, S. Synthesis and characterization of rigid rod poly(p-phenylenes). Macromolecules 1996, 29, 5136– 5142,  DOI: 10.1021/ma960124p
    Google Scholar
    17
    Synthesis and Characterization of Rigid Rod Poly(p-phenylenes)
    Vanhee, S.; Rulkens, R.; Lehmann, U.; Rosenauer, C.; Schulze, M.; Koehler, W.; Wegner, G.
    Macromolecules (1996), 29 (15), 5136-5142CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
    The polymer PP, which consists of a poly(p-phenylene) backbone with sulfonate ester and dodecyl side groups, is synthesized by a Pd-catalyzed coupling of the 1,3-propanediol diester of 2-dodecyl-5-methyl-1,4-benzenediboronic acid with 2,2'-bis(3,5-di-tert-butylbenzenesulfonato)-4,4'-dibromobiphenyl. Polymers with various molar masses are obtained, which are sol. without aggregation in conventional org. solvents. The good soly. of this rodlike polymer allows the accurate detn. of the molar mass by light scattering, osmometry, and SEC with universal calibration. The dependence of the intrinsic viscosity [η] on the molar mass is detd. from both the Mark-Houwink-Sakurada equation and the wormlike chain model. The low value of the persistence length (13 nm) indicates that these polymers are relatively flexible. It is shown that an approx. value of the persistence length, together with the parameters of the Mark-Houwink-Sakurada equation and the wormlike chain model, can be detd. using only a single polydisperse sample.
  18. 18
    Fair, R. A.; Xie, R.; Lee, Y.; Colby, R. H.; Gomez, E. D. Molecular Weight Characterization of Conjugated Polymers through Gel Permeation Chromatography and Static Light Scattering. ACS Appl. Polym. Mater. 2021, 3, 4572– 4578,  DOI: 10.1021/acsapm.1c00647
    Google Scholar
    18
    Molecular Weight Characterization of Conjugated Polymers Through Gel Permeation Chromatography and Static Light Scattering
    Fair, Ryan A.; Xie, Renxuan; Lee, Youngmin; Colby, Ralph H.; Gomez, Enrique D.
    ACS Applied Polymer Materials (2021), 3 (9), 4572-4578CODEN: AAPMCD; ISSN:2637-6105. (American Chemical Society)
    Mol. wt. is a key parameter of any polymer. Characterizing the mol. wt. of conjugated polymers is often nontrivial due to their semiflexible backbones and poor solubilities. Perhaps the most used technique for measuring the mol. wt. is gel permeation chromatog. (GPC), and results are often calibrated relative to flexible polymer stds. This mismatch between chain flexibilities of samples and stds., combined with poor sample soly. in the mobile phase, leads to inaccuracies in many GPC measurements of conjugated polymers. In this work, we use a universal calibration combined with in-line concn. measurements to yield reliably accurate results for polymers of various stiffnesses. Accuracy of results is verified with abs. mol. wts. obtained from static light scattering. We show that measuring the refractive index increment is key to confirm full recovery of the polymer and ensure accurate values of the abs. mol. wt. from GPC.
  19. 19
    Grubisic, Z.; Rempp, P.; Benoit, H. A Universal Calibration for Gel Permeation Chromatography. Polym. Lett. 1967, 5, 753– 759,  DOI: 10.1002/pol.1967.110050903
    Google Scholar
    There is no corresponding record for this reference.
  20. 20
    Holdcroft, S. Determination of molecular weights and Mark–Houwink constants for soluble electronically conducting polymers. J. Polym. Sci., Part B: Polym. Phys. 1991, 29, 1585– 1588,  DOI: 10.1002/polb.1991.090291303
    Google Scholar
    20
    Determination of molecular weights and Mark-Houwink constants for soluble electronically conducting polymers
    Holdcroft, Steven
    Journal of Polymer Science, Part B: Polymer Physics (1991), 29 (13), 1585-8CODEN: JPBPEM; ISSN:0887-6266.
    Intrinsic viscosities and gel-permeation chromatog. (GPC) data are used to evaluate the Mark-Houwink consts. (K and a) of the sol. elec. conducting polymer, poly(3-hexylthiophene) (I): K and a are 2.28 × 10-3 cm3/g and 0.96, resp., in THF at 25°. The Mark-Houwink consts. are used to calibrate GPC columns for I. The no.-av. mol. wt. of I detd. with modified calibration curves agreed well with those detd. by an abs. method, embulliometry. The mol. wt. estd. using unmodified polystyrene calibration procedures was significantly larger than the true value.
  21. 21
    Lou, X. Superheated high-temperature size-exclusion chromatography with chloroform as the mobile phase for π-conjugated polymers. Polym. Chem. 2014, 5, 558– 561,  DOI: 10.1039/C3PY00933E
    Google Scholar
    21
    Superheated high-temperature size-exclusion chromatography with chloroform as the mobile phase for π-conjugated polymers
    Lou, Xianwen; van Dongen, Joost L. J.; Braeken, Yasmine; Brebels, Jeroen; van Pruissen, Gijs W. P.; Li, Weiwei; Wienk, Martijn M.; Janssen, Rene A. J.
    Polymer Chemistry (2014), 5 (2), 558-561CODEN: PCOHC2; ISSN:1759-9962. (Royal Society of Chemistry)
    π-Conjugated polymers for org. electronic applications are often designed to aggregate or crystallize to enhance their charge carrier mobility. Their electronic properties often improve with increasing mol. wt. Detg. the mol. wt. of these polymers via size-exclusion chromatog. (SEC), however, is complicated due to their significant aggregation in soln. We demonstrate that superheated high-temp. SEC with chloroform as the mobile phase, operated at temps. well above the normal b.p. of the solvent, can effectively be used to det. the mol. wt. for these polymers by dissolving the aggregates.
  22. 22
    Matthews, J. R. Scalable synthesis of fused thiophene-diketopyrrolopyrrole semiconducting polymers processed from nonchlorinated solvents into high performance thin film transistors. Chem. Mater. 2013, 25, 782– 789,  DOI: 10.1021/cm303953e
    Google Scholar
    22
    Scalable Synthesis of Fused Thiophene-Diketopyrrolopyrrole Semiconducting Polymers Processed from Nonchlorinated Solvents into High Performance Thin Film Transistors
    Matthews, James R.; Niu, Weijun; Tandia, Adama; Wallace, Arthur L.; Hu, Jieyu; Lee, Wen-Ya; Giri, Gaurav; Mannsfeld, Stefan C. B.; Xie, Yingtao; Cai, Shucheng; Fong, Hon Hang; Bao, Zhenan; He, Mingqian
    Chemistry of Materials (2013), 25 (5), 782-789CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
    The synthesis and characterization of a fused thiophene-diketopyrrolopyrrole based semiconducting polymer PTDPPTFT4 is presented. A no. of synthetic challenges were overcome in the development of a practical scalable synthesis. Characterization by Gel Permeation Chromatog. (GPC) over a range of temps. revealed the tendency of this polymer to aggregate even at elevated temps. and confirmed that the mol. wt. values obtained are for nonaggregated material. This polymer meets a no. of important requirements for potential industrial applications, such as scalable synthesis, soly. in industrially suitable solvents, and material stability and processability into stable high performance thin film transistor devices. Computational modeling was used to help explain the structure property relations contributing to the high performance. Grazing incidence x-ray of the thin films showed out of plane lamellar packing and in plane π-π stacking, both good indicators of a preferentially oriented thin film, desirable for high charge carrier mobility. Hole mobilities >2 cm2/V·s, on/off ratio of >106, and threshold voltage <2 V were achieved.
  23. 23
    Liu, J.; Loewe, R. S.; McCullough, R. D. Employing MALDI-MS on poly(alkylthiophenes): Analysis of molecular weights, molecular weight distributions, end-group structures, and end-group modifications. Macromolecules 1999, 32, 5777– 5785,  DOI: 10.1021/ma9905324
    Google Scholar
    23
    Employing MALDI-MS on Poly(alkylthiophenes): Analysis of Molecular Weights, Molecular Weight Distributions, End-Group Structures, and End-Group Modifications
    Liu, Jinsong; Loewe, Robert S.; McCullough, Richard D.
    Macromolecules (1999), 32 (18), 5777-5785CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
    Regioregular, head-to-tail coupled, poly(3-alkylthiophenes), synthesized by three different methods, were subjected to MALDI-TOF MS anal. Polymer samples of both high and low polydispersities were examd. Polymer samples of narrow polydispersity were obtained by fractionation of the polymer by Soxhlet extn. with various solvents. Comparisons between the mol. wts. calcd. by MALDI and GPC of all fractionated polymer samples showed that GPC calcd. mol. wts. are a factor of 1.2-2.3 times higher than MALDI. The polydispersities calcd. by MALDI were identical or slightly lower than those calcd. by GPC. Polymer end-group compns. were also analyzed. We found that more than one type of end-group structure could be detected, and these structures are dependent on the synthetic method employed. Chem. modification of the end-group structure was also performed and monitored by MALDI with successful results. We obsd. that smaller polymer chains were subject to end-group fragmentation when the MALDI laser power was high. Larger polymer chains, however, showed no such fragmentation.
  24. 24
    Wong, M. An apparent size-exclusion quantification limit reveals a molecular weight limit in the synthesis of externally initiated polythiophenes. ACS Macro Lett. 2012, 1, 1266– 1269,  DOI: 10.1021/mz300333f
    Google Scholar
    24
    An Apparent Size-Exclusion Quantification Limit Reveals a Molecular Weight Limit in the Synthesis of Externally Initiated Polythiophenes
    Wong, Michael; Hollinger, Jon; Kozycz, Lisa M.; McCormick, Theresa M.; Lu, Yijie; Burns, Darcy C.; Seferos, Dwight S.
    ACS Macro Letters (2012), 1 (11), 1266-1269CODEN: AMLCCD; ISSN:2161-1653. (American Chemical Society)
    We report the linear and nonlinear regions of the relationship between no. av. mol. wt. detd. by gel permeation chromatog. (GPC) and 1H NMR end-group anal. for a series of o-tolyl-initiated poly(3-hexylthiophene)s (P3HTs). For conjugated polymers with chains that are 39-138 repeat units in length (6.5-23 kDa), GPC systematically overestimates the no. av. mol. wt. (Mn) by a factor of 1.3 ± 0.1 (std. error), and GPC and 1H NMR end-group anal. correlate in a linear manner. For chains 138-1130 (23-188 kDa) repeat units in length, we observe a nonlinear relationship between GPC and end-group anal. Static light-scattering expts. confirm that at high mol. wt. (>70 kDa) decreasing the catalyst loading does not appreciably increase the polymer chain length. Thus, we conclude that there is a mol. wt. limit in the synthesis of externally initiated polythiophenes and a propensity for the growth of nonexternally initiated chains which increases as a function of Mn. This is significant as external initiation has been reported to result in nearly 100% externally initiated chains as well as reduce the possibility of chain-chain coupling in a typical synthesis. Our data show that 100% external initiation only holds true for polymers that are less than 40 kDa and encourages caution when detg. Mn by NMR using this synthetic methodol. at high mol. wts.
  25. 25
    Gu, K.; Onorato, J.; Xiao, S. S.; Luscombe, C. K.; Loo, Y. L. Determination of the Molecular Weight of Conjugated Polymers with Diffusion-Ordered NMR Spectroscopy. Chem. Mater. 2018, 30, 570– 576,  DOI: 10.1021/acs.chemmater.7b05063
    Google Scholar
    25
    Determination of the Molecular Weight of Conjugated Polymers with Diffusion-Ordered NMR Spectroscopy
    Gu, Kaichen; Onorato, Jonathan; Xiao, Steven Shuyong; Luscombe, Christine K.; Loo, Yueh-Lin
    Chemistry of Materials (2018), 30 (3), 570-576CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
    Size exclusion chromatog. (SEC) is not well suited for characterizing the mol. wt. (MW) and MW distribution of conjugated polymers, esp. those that absorb strongly at the detection wavelengths, or those that interact with and adsorb on the walls of SEC columns. We demonstrate diffusion-ordered NMR spectroscopy (DOSY) as a complementary method for characterizing the size and size distribution of conjugated polymers. Starting with four batches of poly(3-hexylthiophene), whose distinct and narrow MW distributions had been fully characterized, as a model system, we establish a power-law relationship between the wt.-av. MW and the diffusion coeff. measured through DOSY. We extend this approach to characterizing poly[4-(4,4-dihexadecyl-4H-cyclopenta[1,2-b:5,4-b']dithiophen-2-yl)-alt-[1,2,5]thiadiazolo-[3,4-c]pyridine], whose absorption properties preclude its characterization with light scattering based techniques, including SEC. By applying the same power law on the diffusion coeffs. obtained by DOSY measurements, we extd. P3HT-equiv. MWs and MW distributions for six different batches of PCDTPT. By circumventing the practical issues in SEC measurements, DOSY shows promise as a versatile complement for detg. polymer size.
  26. 26
    De Winter, J. MALDI-ToF analysis of polythiophene: use of trans-2-[3-(4-t-butyl-phenyl)-2-methyl- 2-propenylidene]malononitrile─DCTB─as matrix. J. Mass Spectrom. 2011, 46, 237– 246,  DOI: 10.1002/jms.1886
    Google Scholar
    There is no corresponding record for this reference.
  27. 27
    Kohn, P. On the role of single regiodefects and polydispersity in regioregular poly(3-hexylthiophene): Defect distribution, synthesis of defect-free chains, and a simple model for the determination of crystallinity. J. Am. Chem. Soc. 2012, 134, 4790– 4805,  DOI: 10.1021/ja210871j
    Google Scholar
    27
    On the Role of Single Regiodefects and Polydispersity in Regioregular Poly(3-hexylthiophene): Defect Distribution, Synthesis of Defect-Free Chains, and a Simple Model for the Determination of Crystallinity
    Kohn, Peter; Huettner, Sven; Komber, Hartmut; Senkovskyy, Volodymyr; Tkachov, Roman; Kiriy, Anton; Friend, Richard H.; Steiner, Ullrich; Huck, Wilhelm T. S.; Sommer, Jens-Uwe; Sommer, Michael
    Journal of the American Chemical Society (2012), 134 (10), 4790-4805CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    Identifying structure formation in semicryst. conjugated polymers is the fundamental basis to understand electronic processes in these materials. Although correlations between phys. properties, structure formation, and device parameters of regioregular, semicryst. poly(3-hexylthiophene) (P3HT) have been established, it has remained difficult to disentangle the influence of regioregularity, polydispersity, and mol. wt. Here we show that the most commonly used synthetic protocol for the synthesis of P3HT, the living Kumada catalyst transfer polycondensation (KCTP) with Ni(dppp)Cl2 as the catalyst, leads to regioregular chains with one single tail-to-tail (TT) defect distributed over the whole chain, in contrast to the hitherto assumed exclusive location at the chain end. NMR end-group anal. and simulations are used to quantify this effect. A series of entirely defect-free P3HT materials with different mol. wts. is synthesized via new, sol. nickel initiators. Data on structure formation in defect-free P3HT, as elucidated by various calorimetric and scattering expts., allow the development of a simple model for estg. the degree of crystallinity. We find very good agreement for predicted and exptl. detd. degrees of crystallinities as high as ∼70%. For Ni(dppp)Cl2-initiated chains comprising one distributed TT unit, the comparison of simulated crystallinities with calorimetric and optical measurements strongly suggests incorporation of the TT unit into the crystal lattice, which is accompanied by an increase in backbone torsion. Polydispersity is identified as a major parameter detg. crystallinity within the mol. wt. range investigated. We believe that the presented approach and results not only contribute to understanding structure formation in P3HT but are generally applicable to other semicryst. conjugated polymers as well.
  28. 28
    Byrd, H. C. M.; McEwen, C. N. The limitations of MALDI-TOF mass spectrometry in the analysis of wide polydisperse polymers. Anal. Chem. 2000, 72, 4568– 4576,  DOI: 10.1021/ac0002745
    Google Scholar
    28
    The Limitations of MALDI-TOF Mass Spectrometry in the Analysis of Wide Polydisperse Polymers
    Byrd, H. C. Michelle; McEwen, Charles N.
    Analytical Chemistry (2000), 72 (19), 4568-4576CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)
    Av. mol. wt. detn. of polymers with polydispersity >1.2 is an ongoing challenge in the field of MALDI mass spectrometry (MALDI-MS). Mass discrimination effects obsd. in the anal. of these polymers are attributed to sample prepn., desorption/ionization, and instrumental factors. In an effort to sep. these factors, we studied PMMA stds. using two different ion detection systems installed on the same time-of-flight mass analyzer. Equimass blends of narrow PMMA stds. were used to simulate a polymer with a wide polydispersity. MALDI-MS anal. also was performed on a PMMA std. with polydispersity 1.7. All samples were analyzed by SEC for comparison. Although sample prepn. and ionization/desorption factors influence the spectral appearance of the MMA distributions, we demonstrate that under similar sample prepn. and instrument conditions, different ion detection systems produce different results for synthetic polymer blends. The differences in the detector responses for the blends and wide polydisperse std. arise from several factors related to the ion detection system: detection mechanisms, satn. effects and signal-to-noise limitations.
  29. 29
    Matsidik, R.; Komber, H.; Sommer, M. Rational Use of Aromatic Solvents for Direct Arylation Polycondensation: C-H Reactivity versus Solvent Quality. ACS Macro Lett. 2015, 4, 1346– 1350,  DOI: 10.1021/acsmacrolett.5b00783
    Google Scholar
    29
    Rational Use of Aromatic Solvents for Direct Arylation Polycondensation: C-H Reactivity versus Solvent Quality
    Matsidik, Rukiya; Komber, Hartmut; Sommer, Michael
    ACS Macro Letters (2015), 4 (12), 1346-1350CODEN: AMLCCD; ISSN:2161-1653. (American Chemical Society)
    The solvent for direct arylation polycondensation (DAP) is of crucial importance. For conjugated polymers exhibiting reduced soly., the choice of solvent decides on the max. mol. wt. that can be achieved, hence, good arom. solvents are generally desirable. However, unintentional activation of C-H bonds present in arom. solvents under DAP conditions leads to in situ solvent termination which competes with step growth. Here we evaluate relative C-H reactivity and solvent quality of seven arom. solvents for the DAP of defect-free naphthalene diimide (NDI)-based copolymers of different soly. C-H reactivity is strongly reduced with increasing degree of substitution for both chlorine and Me substituents. Mesitylene is largely C-H unreactive and, thus, albeit being a moderate solvent, enables very high mol. wts. at elevated temp. for NDI copolymers with limited soly.
  30. 30
    Okamoto, K.; Zhang, J.; Housekeeper, J. B.; Marder, S. R.; Luscombe, C. K. C-H arylation reaction: Atom efficient and greener syntheses of π-conjugated small molecules and macromolecules for organic electronic materials. Macromolecules 2013, 46, 8059– 8078,  DOI: 10.1021/ma401190r
    Google Scholar
    30
    C-H Arylation Reaction: Atom Efficient and Greener Syntheses of π-Conjugated Small Molecules and Macromolecules for Organic Electronic Materials
    Okamoto, Ken; Zhang, Junxiang; Housekeeper, Jeremy B.; Marder, Seth R.; Luscombe, Christine K.
    Macromolecules (Washington, DC, United States) (2013), 46 (20), 8059-8078CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
    A review. π-Conjugated small mols., oligomers, and macromols. are being used in the fabrication of a wide variety of org. electronic devices such as org. field-effect transistors (OFETs), org. photovoltaic (OPV) devices, and org. light-emitting diodes (OLEDs). Efficient syntheses involving fewer steps, fewer toxic reagents, and highly reactive compds. are needed to lower the cost of materials in a manner that is fundamentally more eco-friendly. Addnl., synthetic approaches for π-conjugated materials with more functional group tolerance are desirable to expand the range of properties that can be realized in such materials. Developing new synthetic routes to materials can both broaden the scope of science that can be explored and increase the probability that interesting materials can be developed in an economically viable manner for inclusion in consumer products. One such synthetic strategy that can impact all of these issues is carbon-hydrogen bond activation and subsequent carbon-carbon bond formation (C-H functionalization). While the C-H functionalizations represented by direct arylation-based methods are not as developed as the widely used Stille and Suzuki methods at this stage, they allow for the use of readily accessible halogenated arom. substances and can negate the need for toxic organotin reagents. They also hold promise of allowing for the synthesis of previously inaccessible materials. In this Perspective, our goal is to provide an overview of the current status in this challenging field by highlighting (1) the history of prepg. π-conjugated small mols. and macromols. via cross-coupling reactions, (2) advances in prepn. of versatile π-conjugated small mols. and macromols. via transition-metal-catalyzed direct arylation, and (3) the scope, limitations, and challenges for materials science.
  31. 31
    Wakioka, M.; Ozawa, F. Highly Efficient Catalysts for Direct Arylation Polymerization (DArP). Asian J. Org. Chem. 2018, 7, 1206– 1216,  DOI: 10.1002/ajoc.201800227
    Google Scholar
    31
    Highly Efficient Catalysts for Direct Arylation Polymerization (DArP)
    Wakioka, Masayuki; Ozawa, Fumiyuki
    Asian Journal of Organic Chemistry (2018), 7 (7), 1206-1216CODEN: AJOCC7; ISSN:2193-5807. (Wiley-VCH Verlag GmbH & Co. KGaA)
    A review. Recently, the palladium-catalyzed direct arylation polymn. (DArP) has emerged as a viable alternative to conventional synthetic means of making π-conjugated polymers based on catalytic cross-coupling reactions. The DArP, which proceeds through C-H bond activation, has a distinct advantage over cross-coupling polymn. in terms of fewer reaction steps and higher functional group tolerance. We have developed novel catalysts for DArP by using P(2-MeOC6H4)3 (L1) and P(2-Me2NC6H4)3 (L2) as ligands. Although common direct arylation catalysts require the use of strongly coordinating solvents such as DMA and DMF, our catalysts exhibit high activity in THF and toluene, which are good solvents for π-conjugated polymers. Thus, we could realize the precise synthesis of highly head-to-tail regioregular poly(3-hexylthiophene) (HT-P3HT) and donor-acceptor type alternating copolymers (DA polymers) with well-controlled structures through DArP.
  32. 32
    Bura, T.; Blaskovits, J. T.; Leclerc, M. Direct (Hetero)arylation Polymerization: Trends and Perspectives. J. Am. Chem. Soc. 2016, 138, 10056– 10071,  DOI: 10.1021/jacs.6b06237
    Google Scholar
    32
    Direct (Hetero)arylation Polymerization: Trends and Perspectives
    Bura, Thomas; Blaskovits, J. Terence; Leclerc, Mario
    Journal of the American Chemical Society (2016), 138 (32), 10056-10071CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    A review. Conjugated polymers have attracted much attention in recent years, as they can combine the best features of metals or inorg. semiconducting materials (excellent elec. and optical properties) with those of synthetic polymers (mech. flexibility, simple processing, and low-cost prodn.), thereby creating altogether new scientific synergies and technol. opportunities. In the search for more efficient synthetic methods for the prepn. of conjugated polymers, this Perspective reports advances in the field of direct (hetero)arylation polymn. This recently developed polymn. method encompasses the formation of carbon-carbon bonds between simple (hetero)arenes and (hetero)aryl halides, reducing both the no. of synthetic steps and the prodn. of organometallic byproducts. Along these lines, we describe the most general and adaptable reaction conditions for the prepn. of high-mol.-wt., defect-free conjugated polymers. We also discuss the bottleneck presented by the utilization of certain brominated thiophene units and propose some potential solns. It is, however, firmly believed that this polymn. method will become a versatile tool in the field of conjugated polymers by providing a desirable atom-economical alternative to std. cross-coupling polymn. reactions.
  33. 33
    Gobalasingham, N. S.; Thompson, B. C. Direct arylation polymerization: A guide to optimal conditions for effective conjugated polymers. Prog. Polym. Sci. 2018, 83, 135– 201,  DOI: 10.1016/j.progpolymsci.2018.06.002
    Google Scholar
    33
    Direct arylation polymerization: A guide to optimal conditions for effective conjugated polymers
    Gobalasingham, Nemal S.; Thompson, Barry C.
    Progress in Polymer Science (2018), 83 (), 135-201CODEN: PRPSB8; ISSN:0079-6700. (Elsevier Ltd.)
    The rapid increase in the breadth and scope of transformations that involve metal-promoted activation of C-H bonds is fundamentally changing the field of synthetic chem. Direct arylation polymn. is a newly established synthetic protocol for atom economical, effective, and affordable prepn. of conjugated polymers, which continue to be incredibly advantageous as operative materials for a diverse and continually evolving array of applications. This route toward conjugated polymers for high performance materials is particularly appealing because it circumvents the prepn. of organometallic derivs. and the assocd. cryogenic air- and water-free reactions. Although a broad range of monomers are now readily polymerizable, direct arylation polymn. is known to produce defects in the chem. structure, which have a strong impact on the optical, electronic, and thermal properties of conjugated polymers. Fundamental understanding of the underlying considerations when employing different reaction protocols is required to truly enable a broad reaching platform.
  34. 34
    Broll, S. Defect Analysis of High Electron Mobility Diketopyrrolopyrrole Copolymers Made by Direct Arylation Polycondensation. Macromolecules 2015, 48, 7481– 7488,  DOI: 10.1021/acs.macromol.5b01843
    Google Scholar
    34
    Defect Analysis of High Electron Mobility Diketopyrrolopyrrole Copolymers Made by Direct Arylation Polycondensation
    Broll, Sebastian; Nuebling, Fritz; Luzio, Alessandro; Lentzas, Dimitros; Komber, Hartmut; Caironi, Mario; Sommer, Michael
    Macromolecules (Washington, DC, United States) (2015), 48 (20), 7481-7488CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
    Defect structures in high-performance conjugated polymers are generally known but still challenging to characterize on a quant. basis. Here, we present a detailed anal. of backbone topol. of a series of copolymers PDPPTh2F4 having alternating dithienyldiketopyrrolopyrrole (DPPTh2) and tetrafluorobenzene (F4) units made by direct arylation polycondensation (DAP). In contrast to early expectations of unselective C-H activation during the DAP of monomers with multiple C-H bonds, detailed structure anal. by high-temp. 1H NMR spectroscopy reveals well-defined and alternating backbones with a quantifiable amt. of 0-12% DPPTh2 homocouplings as the only defect structure in the main chain. Homocoupled -DPPTh2-DPPTh2- structural units are addnl. characterized by UV-vis spectroscopy. While -DPPTh2-H end groups are inert to other side reactions, -F4-Br end groups are weakly susceptible to both dehalogenation and reaction with toluene. However, despite the presence of DPPTh2 homocouplings, high field-effect transistor electron mobilities up to ∼0.6 cm2/(V s) are achieved. This study highlights both that DPPTh2 homocouplings pose a prevalent structural defect in DPPTh2-based conjugated polymers made by DAP and that a simple four-step DAP protocol can yield materials with varying molar mass and excellent n-type transistor performance.
  35. 35
    Hendriks, K. H. Homocoupling defects in diketopyrrolopyrrole-based copolymers and their effect on photovoltaic performance. J. Am. Chem. Soc. 2014, 136, 11128– 11133,  DOI: 10.1021/ja505574a
    Google Scholar
    35
    Homocoupling defects in diketopyrrolopyrrole-based copolymers and their effect on photovoltaic performance
    Hendriks, Koen H.; Li, Weiwei; Heintges, Gael H. L.; van Pruissen, Gijs W. P.; Wienk, Martijn M.; Janssen, Rene A. J.
    Journal of the American Chemical Society (2014), 136 (31), 11128-11133CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    We study the occurrence and effect of intrachain homocoupling defects in alternating push-pull semiconducting PDPPTPT polymers based on dithienyl-diketopyrrolopyrrole (TDPPT) and phenylene (P) synthesized via a palladium-catalyzed cross-coupling polymn. Homocoupled TDPPT-TDPPT segments are readily identified by the presence of a low-energy shoulder in the UV/vis/NIR absorption spectrum. Remarkably, the signatures of these defects are found in many diketopyrrolopyrrole (DPP)-based copolymers reported in the literature. The defects cause a redn. of the band gap, a higher HOMO (HOMO) level, a lower LUMO (LUMO) level, and a localization of these MOs. By synthesizing copolymers with a predefined defect concn., we demonstrate that their presence reduces the short-circuit current and open-circuit voltage of solar cells based on blends of PDPPTPT with [70]PCBM. In virtually defect-free PDPPTPT, the power conversion efficiency is as high as 7.5%, compared to 4.5-5.6% for polymers contg. 20% to 5% defects.
  36. 36
    Hong, W. Is a polymer semiconductor having a ‘perfect’ regular structure desirable for organic thin film transistors?. Chem. Sci. 2015, 6, 3225– 3235,  DOI: 10.1039/C5SC00843C
    Google Scholar
    There is no corresponding record for this reference.
  37. 37
    Vanderspikken, J. On the Importance of Chemical Precision in Organic Electronics: Fullerene Intercalation in Perfectly Alternating Conjugated Polymers. Adv. Funct. Mater. 2023, 33, 2309403  DOI: 10.1002/adfm.202309403
    Google Scholar
    There is no corresponding record for this reference.
  38. 38
    Pirotte, G.; Verstappen, P.; Vanderzande, D.; Maes, W. On the “True” Structure of Push–Pull-Type Low-Bandgap Polymers for Organic Electronics. Adv. Electron. Mater. 2018, 4, 1700481  DOI: 10.1002/aelm.201700481
    Google Scholar
    There is no corresponding record for this reference.
  39. 39
    Vangerven, T. Molar mass versus polymer solar cell performance: Highlighting the role of homocouplings. Chem. Mater. 2015, 27, 3726– 3732,  DOI: 10.1021/acs.chemmater.5b00939
    Google Scholar
    39
    Molar Mass versus Polymer Solar Cell Performance: Highlighting the Role of Homocouplings
    Vangerven, Tim; Verstappen, Pieter; Drijkoningen, Jeroen; Dierckx, Wouter; Himmelberger, Scott; Salleo, Alberto; Vanderzande, Dirk; Maes, Wouter; Manca, Jean V.
    Chemistry of Materials (2015), 27 (10), 3726-3732CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
    Although a strong link between the molar mass of conjugated polymers and the performance of the resulting polymer:fullerene bulk heterojunction org. solar cells has been established on numerous occasions, a clear understanding of the origin of this connection is still lacking. Moreover, the usual description of molar mass and polydispersity does not include the shape of the polymer distribution, although this can have a significant effect on the device properties. In this work, the effect of molar mass distribution on photovoltaic performance is investigated using a combination of structural and electro-optical techniques for the state-of-the-art low bandgap copolymer PTB7. Some of the studied com. PTB7 batches exhibit a bimodal distribution, of which the low molar mass fraction contains multiple homocoupled oligomer species, as identified by MALDI-TOF anal. This combination of low molar mass and homocoupling drastically reduces device performance, from 7.0-2.7%. High molar mass batches show improved charge carrier transport and extn. with much lower apparent recombination orders, as well as a more homogeneous surface morphol. These results emphasize the important effect of molar mass distributions and homocoupling defects on the operation of conjugated polymers in photovoltaic devices.
  40. 40
    Leclerc, M.; Brassard, S.; Beaupré, S. Direct (hetero)arylation polymerization: toward defect-free conjugated polymers. Polym. J. 2020, 52, 13– 20,  DOI: 10.1038/s41428-019-0245-9
    Google Scholar
    40
    Direct (hetero)arylation polymerization: toward defect-free conjugated polymers
    Leclerc, Mario; Brassard, Samuel; Beaupre, Serge
    Polymer Journal (Tokyo, Japan) (2020), 52 (1), 13-20CODEN: POLJB8; ISSN:0032-3896. (Nature Research)
    In a very short time, direct (hetero)arylation polymn. (DHAP) has established itself as a valuable and atom-economical alternative to traditional cross-coupling methods such as the Migita-Stille and Suzuki-Miyaura polymns. for the synthesis of low cost and efficient conjugated polymers for org. electronics. Because of sustained research efforts combining in-depth theor. calcns., the development of new ligands and the careful fine-tuning of polymn. conditions, selectivity and reactivity issues should be soon a thing of the past. This focus review highlights the recent advances that lead to defect-free polymeric semiconductors and conductors and the current limitations and challenges of DHAP as it moves toward simultaneously becoming an industrially feasible, environmentally friendly, and synthetically powerful polymn. technique.
  41. 41
    Rudenko, A. E.; Thompson, B. C. Optimization of direct arylation polymerization (DArP) through the identification and control of defects in polymer structure. J. Polym. Sci. Part A. Polym. Chem. 2015, 53, 135– 147,  DOI: 10.1002/pola.27279
    Google Scholar
    41
    Optimization of direct arylation polymerization (DArP) through the identification and control of defects in polymer structure
    Rudenko, Andrey E.; Thompson, Barry C.
    Journal of Polymer Science, Part A: Polymer Chemistry (2015), 53 (2), 135-147CODEN: JPACEC; ISSN:0887-624X. (John Wiley & Sons, Inc.)
    A review. As a newly emerged protocol for the synthesis of conjugated polymers, direct arylation polymn. (DArP) is an environmentally friendly and cost-effective alternative to traditional methods of polymn. DArP efficiently yields conjugated polymers with high yield and high mol. wt. However, DArP is also known to produce defects in polymer chem. structure. Together with mol. wt. and polydispersity, these defects are considered to be important parameters of polymer structure and they have a strong impact on optical, electronic and thermal properties of conjugated polymers. The four major classes of conjugated polymer defects inherent for DArP have been identified: homocoupling regiodefects, branching defects, end group defects, and residual metal defects. To have a precise control over the polymer properties, it is important to understand what causes the defects to form during the polymn. process and be able to control their content. Here within the scope of current literature, we discuss in detail the definition and origin of all these defects, their influence on polymer properties and effective means to control the defects through fine tuning of the DArP reaction parameters. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014.
  42. 42
    Sommer, M. 2 - Development of conjugated polymers for organic flexible electronics. In Organic Flexible Electronics, Woodhead Publishing, (pp 27- 70) 2021.
    Google Scholar
    There is no corresponding record for this reference.
  43. 43
    Lombeck, F. On the Effect of Prevalent Carbazole Homocoupling Defects on the Photovoltaic Performance of PCDTBT:PC71BM Solar Cells. Adv. Energy Mater. 2016, 6, 1601232  DOI: 10.1002/aenm.201601232
    Google Scholar
    There is no corresponding record for this reference.
  44. 44
    Streiter, M. Homocoupling Defects in a Conjugated Polymer Limit Exciton Diffusion. Adv. Funct. Mater. 2019, 29, 1903936  DOI: 10.1002/adfm.201903936
    Google Scholar
    44
    Homocoupling Defects in a Conjugated Polymer Limit Exciton Diffusion
    Streiter, Martin; Beer, Daniel; Meier, Fabian; Goehler, Clemens; Lienert, Caroline; Lombeck, Florian; Sommer, Michael; Deibel, Carsten
    Advanced Functional Materials (2019), 29 (46), 1903936CODEN: AFMDC6; ISSN:1616-301X. (Wiley-VCH Verlag GmbH & Co. KGaA)
    Copolymers such as PCDTBT (poly(N-9'-heptadecanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole))) are commonly employed as donor material in bulk heterojunction solar cells. Recently, chem. defects such as homocouplings have been shown to form at the material synthesis stage, strongly reducing the short circuit current in org. photovoltaics. Here it is shown that both low mol. wt. and homocoupling defects reduce the short circuit current of solar cells because of limited exciton diffusion. A model that unites and explains the influence of both chem. parameters with the distribution of conjugation lengths is proposed. The connection between limited exciton diffusion and short circuit current is revealed via kinetic Monte Carlo simulation of bulk heterojunctions. The findings are likely applicable for copolymers in general.
  45. 45
    Wang, Q. Electron Mobility of Diketopyrrolopyrrole Copolymers Is Robust against Homocoupling Defects. Chem. Mater. 2021, 33, 668– 677,  DOI: 10.1021/acs.chemmater.0c03998
    Google Scholar
    45
    Electron Mobility of Diketopyrrolopyrrole Copolymers Is Robust against Homocoupling Defects
    Wang, Qian; Lenjani, Shayan Vazirieh; Dolynchuk, Oleksandr; Scaccabarozzi, Alberto D.; Komber, Hartmut; Guo, Yuejie; Guenther, Florian; Gemming, Sibylle; Magerle, Robert; Caironi, Mario; Sommer, Michael
    Chemistry of Materials (2021), 33 (2), 668-677CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
    Structural defects in semiconducting conjugated polymers are usually suspected to deteriorate their properties and device performance and therefore complicate batch-to-batch reproducibility. This study investigates homocoupling (hc) defects in copolymers made from dithiazolyldiketopyrrolopyrrole (TzDPPTz) and tetrafluorobenzene (F4) by direct arylation polycondensation (DAP). Hc defects are quantified by 1H NMR spectroscopy with good accuracy, and the effect of several reaction parameters on the TzDPPTz hc content in the resulting copolymers PTzDPPTzF4 is investigated in detail. A range of polymers with hc contents between 0.6 and 12.4% is used for a detailed structure-function relationship study. Exptl., it is obsd. that TzDPPTz hc defects cause bathochromically shifted absorption spectra, decrease photoluminescence, and lower the LUMO energy level. Thin film morphol., nanostructure, and electron mobility probed by field-effect devices is marginally or not affected. The latter result is explained by theor. calcns. that suggest a localization of the HOMO on the hc defect, but not that of the LUMO, the latter being relevant for electron transport. Thus, under these conditions, the hc content is not limiting device performance, which makes PTzDPPTzF4 a robust electron-transporting copolymer. These results are promising in the context of batch-to-batch reproducibility and further guide efforts toward a more detailed understanding of hc-function relationships.
  46. 46
    Lombeck, F.; Komber, H.; Gorelsky, S. I.; Sommer, M. Identifying homocouplings as critical side reactions in direct arylation polycondensation. ACS Macro Lett. 2014, 3, 819– 823,  DOI: 10.1021/mz5004147
    Google Scholar
    46
    Identifying Homocouplings as Critical Side Reactions in Direct Arylation Polycondensation
    Lombeck, Florian; Komber, Hartmut; Gorelsky, Serge I.; Sommer, Michael
    ACS Macro Letters (2014), 3 (8), 819-823CODEN: AMLCCD; ISSN:2161-1653. (American Chemical Society)
    Homocouplings are identified as major side reactions in direct arylation polycondensation (DAP) of 4,7-bis(4-hexyl-2-thienyl)-2,1,3-benzothiadiazole (TBT) and 2,7-dibromo-9-(1-octylnonyl)-9H-carbazole (CbzBr2). Using size exclusion chromatog. (SEC) and NMR spectroscopy, we demonstrate that both TBT and Cbz homocouplings occur at a considerable extent. TBT homocoupling preferentially occurs under phosphine-free conditions but can be suppressed in the presence of a phosphine ligand. Cbz homocoupling is temp.-dependent and more prevalent at higher temps. By contrast, evidence for chain branching as a result of unselective C-H arylation is not found for this monomer combination. These results emphasize that particular attention has to be paid to homocouplings in direct arylation polycondensations as a major source of main-chain defects, esp. under phosphine-free conditions.
  47. 47
    Matsidik, R.; Komber, H.; Luzio, A.; Caironi, M.; Sommer, M. Defect-free Naphthalene Diimide Bithiophene Copolymers with Controlled Molar Mass and High Performance via Direct Arylation Polycondensation. J. Am. Chem. Soc. 2015, 137, 6705– 6711,  DOI: 10.1021/jacs.5b03355
    Google Scholar
    47
    Defect-free Naphthalene Diimide Bithiophene Copolymers with Controlled Molar Mass and High Performance via Direct Arylation Polycondensation
    Matsidik, Rukiya; Komber, Hartmut; Luzio, Alessandro; Caironi, Mario; Sommer, Michael
    Journal of the American Chemical Society (2015), 137 (20), 6705-6711CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    A highly efficient, simple, and environmentally friendly protocol for the synthesis of an alternating naphthalene diimide bithiophene copolymer (PNDIT2) via direct arylation polycondensation (DAP) is presented. High mol. wt. (MW) PNDIT2 can be obtained in quant. yield using arom. solvents. Most crit. is the suppression of two major termination reactions of NDIBr end groups: nucleophilic substitution and solvent end-capping by arom. solvents via C-H activation. In situ solvent end-capping can be used to control MW by varying monomer concn., whereby end-capping is efficient and MW is low for low concn. and vice versa. Reducing C-H reactivity of the solvent at optimized conditions further increases MW. Chain perfection of PNDIT2 is demonstrated in detail by NMR spectroscopy, which reveals PNDIT2 chains to be fully linear and alternating. This is further confirmed by investigating the optical and thermal properties as a function of MW, which sat. at Mn ≈ 20 kDa, in agreement with controls made by Stille coupling. Field-effect transistor (FET) electron mobilities μsat up to 3 cm2/(V·s) are measured using off-center spin-coating, with FET devices made from DAP PNDIT2 exhibiting better reproducibility compared to Stille controls.
  48. 48
    Lawton, S. S. Determining the sequence and backbone structure of ‘semi-statistical’ copolymers as donor-acceptor polymers in organic solar cells. Sustain. Energy Fuels 2020, 4, 2026– 2034,  DOI: 10.1039/C9SE01261C
    Google Scholar
    There is no corresponding record for this reference.
  49. 49
    Xiao, M. Anisotropy of Charge Transport in a Uniaxially Aligned Fused Electron-Deficient Polymer Processed by Solution Shear Coating. Adv. Mater. 2020, 32, 2000063– 2000071,  DOI: 10.1002/adma.202000063
    Google Scholar
    49
    Anisotropy of Charge Transport in a Uniaxially Aligned Fused Electron-Deficient Polymer Processed by Solution Shear Coating
    Xiao, Mingfei; Kang, Boseok; Lee, Seon Baek; Perdigao, Luis M. A.; Luci, Alex; Warr, Daniel A.; Senanayak, Satyaprasad P.; Nikolka, Mark; Statz, Martin; Wu, Yutian; Sadhanala, Aditya; Schott, Sam; Carey, Remington; Wang, Qijing; Lee, Mijung; Kim, Chaewon; Onwubiko, Ada; Jellett, Cameron; Liao, Hailiang; Yue, Wan; Cho, Kilwon; Costantini, Giovanni; McCulloch, Iain; Sirringhaus, Henning
    Advanced Materials (Weinheim, Germany) (2020), 32 (23), 2000063CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
    Precise control of the microstructure in org. semiconductors (OSCs) is essential for developing high-performance org. electronic devices. Here, a comprehensive charge transport characterization of two recently reported rigid-rod conjugated polymers that do not contain single bonds in the main chain is reported. It is demonstrated that the mol. design of the polymer makes it possible to achieve an extended linear backbone structure, which can be directly visualized by high-resoln. scanning tunneling microscopy (STM). The rigid structure of the polymers allows the formation of thin films with uniaxially aligned polymer chains by using a simple one-step soln.-shear/bar coating technique. These aligned films show a high optical anisotropy with a dichroic ratio of up to a factor of 6. Transport measurements performed using top-gate bottom-contact field-effect transistors exhibit a high satn. electron mobility of 0.2 cm2 V-1 s-1 along the alignment direction, which is more than six times higher than the value reported in the previous work. This work demonstrates that this new class of polymers is able to achieve mobility values comparable to state-of-the-art n-type polymers and identifies an effective processing strategy for this class of rigid-rod polymer system to optimize their charge transport properties.
  50. 50
    Chen, H. The Effect of Ring Expansion in Thienobenzo[ b]indacenodithiophene Polymers for Organic Field-Effect Transistors. J. Am. Chem. Soc. 2019, 141, 18806– 18813,  DOI: 10.1021/jacs.9b09367
    Google Scholar
    50
    The Effect of Ring Expansion in Thienobenzo[b]indacenodithiophene Polymers for Organic Field-Effect Transistors
    Chen, Hu; Wadsworth, Andrew; Ma, Chun; Nanni, Alice; Zhang, Weimin; Nikolka, Mark; Luci, Alexander M. T.; Perdigao, Luis M. A.; Thorley, Karl J.; Cendra, Camila; Larson, Bryon; Rumbles, Garry; Anthopoulos, Thomas D.; Salleo, Alberto; Costantini, Giovanni; Sirringhaus, Henning; McCulloch, Iain
    Journal of the American Chemical Society (2019), 141 (47), 18806-18813CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    A fused donor, thienobenzo[b]indacenodithiophene (TBIDT), was designed and synthesized using a novel acid-promoted cascade ring closure strategy, and copolymd. with a benzothiadiazole (BT) monomer. The backbone of TBIDT is an expansion of the well-known indacenodithiophene (IDT) unit and was expected to enhance the charge carrier mobility, by improving backbone planarity and facilitating short-contacts between polymer chains. However, the optimized field-effect transistors demonstrated an av. satn. hole mobility of 0.9 cm2 V-1s-1, lower than the performance of IDT-BT (∼1.5 cm2 V-1s-1). Mobilities extd. from time-resolved microwave cond. (TRMC) measurements were consistent with the trend in hole mobilities in OFET devices. Scanning Tunneling Microscopy (STM) measurements and computational modeling illustrated that TBIDT-BT exhibits a less ordered microstructure in comparison to IDT-BT. This reveals that a regular side chain packing d., independent of conformational isomers, is crit. to avoid local free vol. due to irregular packing, which can host trapping impurities. DFT calcns. indicated that TBIDT-BT, despite contg. a larger, planar unit, showed less stabilization of planar backbone geometries, in comparison to IDT-BT. This is due to the reduced electrostatic stabilizing inter-actions between the peripheral thiophene of the fused core with the BT unit, resulting in a redn. of the barrier to rotation around the single bond. These insights provide a greater understanding of the general structure-property relationships required for semiconducting polymer repeat units to ensure optimal backbone planarization, as illustrated with IDT-type units, guiding the design of novel semiconducting polymers with extended fused backbones for high-performance field-effect transistors.
  51. 51
    Warr, D. A. Sequencing conjugated polymers by eye. Sci. Adv. 2018, 4, eaas9543  DOI: 10.1126/sciadv.aas9543
    Google Scholar
    There is no corresponding record for this reference.
  52. 52
    Ponder, J. F. Low-Defect, High Molecular Weight Indacenodithiophene (IDT) Polymers Via a C-H Activation: Evaluation of a Simpler and Greener Approach to Organic Electronic Materials. ACS Mater. Lett. 2021, 3, 1503– 1512,  DOI: 10.1021/acsmaterialslett.1c00478
    Google Scholar
    52
    Low-Defect, High Molecular Weight Indacenodithiophene (IDT) Polymers Via a C-H Activation: Evaluation of a Simpler and Greener Approach to Organic Electronic Materials
    Ponder Jr, James F.; Chen, Hu; Luci, Alexander M. T.; Moro, Stefania; Turano, Marco; Hobson, Archie L.; Collier, Graham S.; Perdigao, Luis M. A.; Moser, Maximilian; Zhang, Weimin; Costantini, Giovanni; Reynolds, John R.; McCulloch, Iain
    ACS Materials Letters (2021), 3 (10), 1503-1512CODEN: AMLCEF; ISSN:2639-4979. (American Chemical Society)
    The development, optimization, and assessment of new methods for the prepn. of conjugated materials is key to the continued progress of org. electronics. Direct C-H activation methods have emerged and developed over the last 10 years to become an invaluable synthetic tool for the prepn. of conjugated polymers for both redox-active and solid-state applications. Here, we evaluate direct (hetero)arylation polymn. (DHAP) methods for the synthesis of indaceno[1,2-b:5,6-b']dithiophene-based polymers. We demonstrate, using a range of techniques, including direct visualization of individual polymer chains via high-resoln. scanning tunneling microscopy, that DHAP can produce polymers with a high degree of regularity and purity that subsequently perform in org. thin-film transistors comparably to those made by other cross-coupling polymns. that require increased synthetic complexity. Ultimately, this work results in an improved atom economy by reducing the no. of synthetic steps to access high-performance mol. and polymeric materials.
  53. 53
    Hallani, R. K. Regiochemistry-Driven Organic Electrochemical Transistor Performance Enhancement in Ethylene Glycol-Functionalized Polythiophenes. J. Am. Chem. Soc. 2021, 143, 11007– 11018,  DOI: 10.1021/jacs.1c03516
    Google Scholar
    53
    Regiochemistry-Driven Organic Electrochemical Transistor Performance Enhancement in Ethylene Glycol-Functionalized Polythiophenes
    Hallani, Rawad K.; Paulsen, Bryan D.; Petty, Anthony J.; Sheelamanthula, Rajendar; Moser, Maximilian; Thorley, Karl J.; Sohn, Wonil; Rashid, Reem B.; Savva, Achilleas; Moro, Stefania; Parker, Joseph P.; Drury, Oscar; Alsufyani, Maryam; Neophytou, Marios; Kosco, Jan; Inal, Sahika; Costantini, Giovanni; Rivnay, Jonathan; McCulloch, Iain
    Journal of the American Chemical Society (2021), 143 (29), 11007-11018CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    Novel p-type semiconducting polymers that can facilitate ion penetration, and operate in accumulation mode are much desired in bioelectronics. Glycol side chains have proven to be an efficient method to increase bulk electrochem. doping and optimize aq. swelling. One early polymer which exemplifies these design approaches was p(g2T-TT), employing a bithiophene-co-thienothiophene backbone with glycol side chains in the 3,3' positions of the bithiophene repeat unit. In this paper, the analogous regioisomeric polymer, namely pgBTTT, was synthesized by relocating the glycol side chains position on the bithiophene unit of p(g2T-TT) from the 3,3' to the 4,4' positions and compared with the original p(g2T-TT). By changing the regio-positioning of the side chains, the planarizing effects of the S--O interactions were redistributed along the backbone, and the influence on the polymer's microstructure organization was investigated using grazing-incidence wide-angle X-ray scattering (GIWAXS) measurements. The newly designed pgBTTT exhibited lower backbone disorder, closer π-stacking, and higher scattering intensity in both the in-plane and out-of-plane (GIWAXS) measurements. The effect of the improved planarity of pgBTTT manifested as higher hole mobility (μ) of 3.44 ± 0.13 cm2 V-1 s-1. Scanning tunneling microscopy (STM) was in agreement with the GIWAXS measurements and demonstrated, for the first time, that glycol side chains can also facilitate intermol. interdigitation analogous to that of pBTTT. Electrochem. quartz crystal microbalance with dissipation of energy (eQCM-D) measurements revealed that pgBTTT maintains a more rigid structure than p(g2T-TT) during doping, minimizing mol. packing disruption and maintaining higher hole mobility in operation mode.
  54. 54
    Moro, S. The Effect of Glycol Side Chains on the Assembly and Microstructure of Conjugated Polymers. ACS Nano 2022, 16, 21303– 21314,  DOI: 10.1021/acsnano.2c09464
    Google Scholar
    54
    The Effect of Glycol Side Chains on the Assembly and Microstructure of Conjugated Polymers
    Moro, Stefania; Siemons, Nicholas; Drury, Oscar; Warr, Daniel A.; Moriarty, Thomas A.; Perdigao, Luis M. A.; Pearce, Drew; Moser, Maximilian; Hallani, Rawad K.; Parker, Joseph; McCulloch, Iain; Frost, Jarvist M.; Nelson, Jenny; Costantini, Giovanni
    ACS Nano (2022), 16 (12), 21303-21314CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
    Conjugated polymers with polar side chains, such as ethylene glycol chains, are emerging as a material class with promising applications as org. mixed ionic-electronic conductors, particularly in bioelectronics and thermoelecs. However, very little is still known about their microstructure and the role of the side chains in detg. intermol. interactions and polymer packing. Here, we use the combination of electrospray deposition and scanning tunnelling microscopy to det. the microstructure of prototypical glycolated conjugated polymers (pgBTTT and p(g2T-TT)) with submonomer resoln. Mol. dynamics simulations of the same surface-adsorbed polymers exhibit an excellent agreement with the exptl. images, allowing us to extend the characterization of the polymers to the at. scale. Our results prove that, similarly to their alkylated counterparts, glycolated polymers assemble through interdigitation of their side chains although significant differences are found in their conformation and interaction patterns. A model is proposed that identifies the driving force for the polymer assembly in the tendency of the side chains to adopt the conformation of their free analogs, i.e. polyethylene and polyethylene glycol, for alkyl or ethylene glycol side chains, resp. For both classes of polymers, it is also demonstrated that the backbone conformation is detd. to a higher degree by the interaction between the side chains rather than by the backbone torsional potential energy. The generalization of these findings from 2D monolayers to 3D thin films is discussed, together with the opportunity to use this type of 2D study to gain so far inaccessible, subnm scale information on the microstructure of conjugated polymers.
  55. 55
    Nielsen, C. B.; Turbiez, M.; McCulloch, I. Recent advances in the development of semiconducting DPP-containing polymers for transistor applications. Adv. Mater. 2013, 25, 1859– 1880,  DOI: 10.1002/adma.201201795
    Google Scholar
    55
    Recent Advances in the Development of Semiconducting DPP-Containing Polymers for Transistor Applications
    Nielsen, Christian B.; Turbiez, Mathieu; McCulloch, Iain
    Advanced Materials (Weinheim, Germany) (2013), 25 (13), 1859-1880CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
    A review. This progress report summarizes the numerous DPP-contg. polymers recently developed for field-effect transistor applications including diphenyl-DPP and dithienyl-DPP-based polymers as the most commonly reported materials, but also difuranyl-DPP, diselenophenyl-DPP and dithienothienyl-DPP-contg. polymers. The hole and electron mobilities that are reported in relation to structural properties such as alkyl substitution patterns, polymer mol. wts. and solid state packing, as well as electronic properties including HOMO and LUMO energy levels are discussed. The authors also consider important aspects of ambipolar charge transport and highlight fundamental structure-property relations such as the relations between the thin film morphologies and the charge carrier mobilities obsd. for DPP-contg. polymers.
  56. 56
    Genene, Z.; Mammo, W.; Wang, E.; Andersson, M. R. Recent Advances in n-Type Polymers for All-Polymer Solar Cells. Adv. Mater. 2019, 31, 1807275  DOI: 10.1002/adma.201807275
    Google Scholar
    There is no corresponding record for this reference.
  57. 57
    Luzio, A. Microstructural control suppresses thermal activation of electron transport at room temperature in polymer transistors. Nat. Commun. 2019, 10, 3365,  DOI: 10.1038/s41467-019-11125-9
    Google Scholar
    57
    Microstructural control suppresses thermal activation of electron transport at room temperature in polymer transistors
    Luzio Alessandro; Caironi Mario; Nubling Fritz; Sommer Michael; Martin Jaime; Martin Jaime; Fazzi Daniele; Selter Philipp; Hansen Michael Ryan; Gann Eliot; McNeill Christopher R; Gann Eliot; Gann Eliot; Brinkmann Martin; Stingelin Natalie
    Nature communications (2019), 10 (1), 3365 ISSN:.
    Recent demonstrations of inverted thermal activation of charge mobility in polymer field-effect transistors have excited the interest in transport regimes not limited by thermal barriers. However, rationalization of the limiting factors to access such regimes is still lacking. An improved understanding in this area is critical for development of new materials, establishing processing guidelines, and broadening of the range of applications. Here we show that precise processing of a diketopyrrolopyrrole-tetrafluorobenzene-based electron transporting copolymer results in single crystal-like and voltage-independent mobility with vanishing activation energy above 280 K. Key factors are uniaxial chain alignment and thermal annealing at temperatures within the melting endotherm of films. Experimental and computational evidences converge toward a picture of electrons being delocalized within crystalline domains of increased size. Residual energy barriers introduced by disordered regions are bypassed in the direction of molecular alignment by a more efficient interconnection of the ordered domains following the annealing process.
  58. 58
    Shivhare, R. Alkyl Branching Position in Diketopyrrolopyrrole Polymers: Interplay between Fibrillar Morphology and Crystallinity and Their Effect on Photogeneration and Recombination in Bulk-Heterojunction Solar Cells. Chem. Mater. 2018, 30, 6801– 6809,  DOI: 10.1021/acs.chemmater.8b02739
    Google Scholar
    58
    Alkyl Branching Position in Diketopyrrolopyrrole Polymers: Interplay between Fibrillar Morphology and Crystallinity and Their Effect on Photogeneration and Recombination in Bulk-Heterojunction Solar Cells
    Shivhare, Rishi; Erdmann, Tim; Hoermann, Ulrich; Collado-Fregoso, Elisa; Zeiske, Stefan; Benduhn, Johannes; Ullbrich, Sascha; Huebner, Rene; Hambsch, Mike; Kiriy, Anton; Voit, Brigitte; Neher, Dieter; Vandewal, Koen; Mannsfeld, Stefan C. B.
    Chemistry of Materials (2018), 30 (19), 6801-6809CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
    Diketopyrrolopyrrole (DPP)-based donor-acceptor copolymers have gained a significant amt. of research interest in the org. electronics community because of their high charge carrier mobilities in org. field-effect transistors (OFETs) and their ability to harvest near-IR (NIR) photons in solar cells. Here, we have synthesized 4 DPP-based donor-acceptor copolymers with variations in the donor unit and the branching point of the solubilizing alkyl chains (at the 2nd or 6th C position). Grazing incidence wide-angle x-ray scattering (GIWAXS) results suggest that moving the branching point further away from the polymer backbone increases the tendency for aggregation and yields polymer phases with a higher degree of crystallinity (DoC). The polymers were blended with PC70BM and used as active layers in solar cells. A careful anal. of the energetics of the neat polymer and blend films reveals that the charge-transfer state energy (ECT) of the blend films lies exceptionally close to the singlet energy of the donor (ED*), indicating near zero electron transfer losses. The difference between the optical gap and open-circuit voltage (VOC) is therefore detd. to be due to rather high nonradiative (∼418±13 mV) and unavoidable radiative voltage losses (∼255±8 mV). Even though the 4 materials have similar optical gaps, the short-circuit c.d. (JSC) covers a vast span from 7 to 18 mA/cm2 for the best performing system. Using photoluminescence (PL) quenching and transient charge extn. techniques, we quantify geminate and nongeminate losses and find that fewer excitons reach the donor-acceptor interface in polymers with further away branching points due to larger aggregate sizes. In these material systems, the photogeneration is therefore mainly limited by exciton harvesting efficiency.
  59. 59
    Back, J. Y. Investigation of structure-property relationships in diketopyrrolopyrrole-based polymer semiconductors via side-chain engineering. Chem. Mater. 2015, 27, 1732– 1739,  DOI: 10.1021/cm504545e
    Google Scholar
    59
    Investigation of Structure-Property Relationships in Diketopyrrolopyrrole-Based Polymer Semiconductors via Side-Chain Engineering
    Back, Jang Yeol; Yu, Hojeong; Song, Inho; Kang, Il; Ahn, Hyungju; Shin, Tae Joo; Kwon, Soon-Ki; Oh, Joon Hak; Kim, Yun-Hi
    Chemistry of Materials (2015), 27 (5), 1732-1739CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
    Systematic side-chain engineering has been performed for diketopyrrolopyrrole-selenophene vinylene selenophene (DPP-SVS) polymers to det. the optimal side-chain geometries for the most efficient charge transport, and the structure-property relationship has been thoroughly investigated using a range of analyses. A series of DPP-SVS polymers, ranging from 25-DPP-SVS to 32-DPP-SVS, with branched alkyl groups contg. linear spacer groups from C2 to C9 has been synthesized, and the elec. performance of these polymers is significantly dependent on both the length of the spacer group and its odd-even characteristics. Spacer groups with even nos. of carbon atoms exhibit charge-carrier mobilities that are 1 order of magnitude higher than those with odd nos. of carbon atoms. The optimized charge transport has been obtained from 29-DPP-SVS with a C6 spacer, showing the max. mobility of 13.9 cm2 V-1 s-1 (VGS, VDS = -100 V) and 17.8 cm2 V-1 s-1 (VGS, VDS = -150 V). Longer spacer groups deviate from the odd-even trend. In addn. to the exceptionally high charge-carrier mobilities of the DPP-SVS polymers, the results obtained herein provide new insight into the mol. design of high-performance polymer semiconductors.
  60. 60
    Meager, I. Photocurrent enhancement from diketopyrrolopyrrole polymer solar cells through alkyl-chain branching point manipulation. J. Am. Chem. Soc. 2013, 135, 11537– 11540,  DOI: 10.1021/ja406934j
    Google Scholar
    60
    Photocurrent Enhancement from Diketopyrrolopyrrole Polymer Solar Cells through Alkyl-Chain Branching Point Manipulation
    Meager, Iain; Ashraf, Raja Shahid; Mollinger, Sonya; Schroeder, Bob C.; Bronstein, Hugo; Beatrup, Daniel; Vezie, Michelle S.; Kirchartz, Thomas; Salleo, Alberto; Nelson, Jenny; McCulloch, Iain
    Journal of the American Chemical Society (2013), 135 (31), 11537-11540CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    Systematically moving the alkyl-chain branching position away from the polymer backbone afforded 2 new thieno[3,2-b]thiophene-diketopyrrolopyrrole (DPPTT-T) polymers. When used as donor materials in polymer:fullerene solar cells, efficiencies exceeding 7% were achieved without the use of processing additives. The effect of the position of the alkyl-chain branching point on the thin-film morphol. was studied using x-ray scattering techniques and the effects on the photovoltaic and charge-transport properties were also studied. For both solar cell and transistor devices, moving the branching point further from the backbone was beneficial. This is the 1st time that this effect was shown to improve solar cell performance. Strong evidence is presented for changes in microstructure across the series, which is most likely the cause for the photocurrent enhancement.
  61. 61
    Wang, Q. Hydrogen Bonds Control Single-Chain Conformation, Crystallinity, and Electron Transport in Isoelectronic Diketopyrrolopyrrole Copolymers. Chem. Mater. 2021, 33, 2635– 2645,  DOI: 10.1021/acs.chemmater.1c00478
    Google Scholar
    61
    Hydrogen Bonds Control Single-Chain Conformation, Crystallinity, and Electron Transport in Isoelectronic Diketopyrrolopyrrole Copolymers
    Wang, Qian; Boeckmann, Steffen; Guenther, Florian; Streiter, Martin; Zerson, Mario; Scaccabarozzi, Alberto D.; Tan, Wen Liang; Komber, Hartmut; Deibel, Carsten; Magerle, Robert; Gemming, Sibylle; McNeill, Christopher R.; Caironi, Mario; Hansen, Michael Ryan; Sommer, Michael
    Chemistry of Materials (2021), 33 (7), 2635-2645CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
    The combination of computational methods and advanced characterization techniques is used to highlight the role of the intramol. hydrogen bond in thienyldiketopyrrolopyrrole (ThDPPTh) copolymd. with tetrafluorobenzene (F4) to PThDPPThF4. We investigate how the torsion potentials of ThDPPTh and isoelectronic dithiazolyldiketopyrrolopyrrole (TzDPPTz) are influenced by hydrogen bonding and translate into different conformation, mol., structural, and opto-electronic characteristics. ThDPPTh exhibits N,S-syn orientation in the most stable conformer locked by an intramol. hydrogen bond. In TzDPPTz, such a hydrogen bond is not possible, which leads to a "ring flip" and makes the N,S-anti conformer most stable. Copolymers with F4, PThDPPThF4 and PTzDPPTzF4, exhibit straight and curved backbones, resp., but similar chain rigidity. These conformations are exptl. confirmed by local packing motifs from solid-state NMR spectroscopy. The differences in conformation strongly influence the opto-electronic and structural properties. X-ray scattering and at. force microscopy reveal lamellar morphologies of both PThDPPThF4 and PTzDPPTzF4, but increased long range order, reduced paracrystallinity, and larger domains of the former. In-depth anal. of solid-state NMR spectra allows for obtaining information on abs. degrees of crystallinity, which are substantially higher for PThDPPThF4. These differences in structural properties cause field-effect electron mobilities of PThDPPThF4 to be larger by a factor of 20.
  62. 62
    O’Shea, J. N. Electrospray deposition of carbon nanotubes in vacuum. Nanotechnology 2007, 18, 035707  DOI: 10.1088/0957-4484/18/3/035707
    Google Scholar
    There is no corresponding record for this reference.
  63. 63
    Räder, H. J.; Nguyen, T. T. T.; Müllen, K. MALDI-TOF mass spectrometry of polyphenylene dendrimers up to the megadalton range. elucidating structural integrity of macromolecules at unrivaled high molecular weights. Macromolecules 2014, 47, 1240– 1248,  DOI: 10.1021/ma402347y
    Google Scholar
    There is no corresponding record for this reference.
  64. 64
    Cox, D. R.; Oakes, D. Analysis of survival data. Monographs on Statistics and Applied Probability 21; CHAPMAN & HALL/CRC: New York, 2018.
    Google Scholar
    There is no corresponding record for this reference.
  65. 65
    Horcas, I. WSXM: A software for scanning probe microscopy and a tool for nanotechnology. Rev. Sci. Instrum. 2007, 78, 013705– 013713,  DOI: 10.1063/1.2432410
    Google Scholar
    65
    WSXM: a software for scanning probe microscopy and a tool for nanotechnology
    Horcas, I.; Fernandez, R.; Gomez-Rodriguez, J. M.; Colchero, J.; Gomez-Herrero, J.; Baro, A. M.
    Review of Scientific Instruments (2007), 78 (1), 013705/1-013705/8CODEN: RSINAK; ISSN:0034-6748. (American Institute of Physics)
    In this work we briefly describe the most relevant features of WSXM, a freeware scanning probe microscopy software based on MS-Windows. The article is structured in three different sections: The introduction is a perspective on the importance of software on scanning probe microscopy. The second section is devoted to describe the general structure of the application; in this section the capabilities of WSXM to read third party files are stressed. Finally, a detailed discussion of some relevant procedures of the software is carried out.
  66. 66
    Nečas, D.; Klapetek, P. Gwyddion: An open-source software for SPM data analysis. Cent. Eur. J. Phys. 2012, 10, 181– 188,  DOI: 10.2478/s11534-011-0096-2
    Google Scholar
    There is no corresponding record for this reference.
  67. 67
    Hanwell, M. D. Avogadro: An advanced semantic chemical editor, visualization, and analysis platform. J. Cheminform. 2021, 4, 1– 17,  DOI: 10.1186/1758-2946-4-17
    Google Scholar
    There is no corresponding record for this reference.
  68. 68
    LMAPper - The SPM and Mol Viewer | https://sourceforge.net/projects/spm-and-mol-viewer/. Accessed on 22.03.2024.
    Google Scholar
    There is no corresponding record for this reference.

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  • Abstract

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    Figure 1

    Figure 1. (a) Chemical structure of PThDPPThF4. The colored parts of the side chain indicate the linear linker of different length (red) and two asymmetric branched arms (blue). High-resolution STM images are shown in (b) and (c) for P1 and P3, respectively. The inset in (b) displays an example of the ordered parts of the assembly (top-right corner, in red) and a case where side chains are not arranged into a regular pattern (bottom-left corner, in green). The inset in (c) shows an ordered area of P3. The scale bar in (b) and (c) is 4 nm, and the lateral size of the insets is 5 nm. STM images were acquired in constant current mode with tunneling parameters: (b) 1.4 V, 70 pA; (c) 1.3 V, 90 pA.

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    Figure 2

    Figure 2. In (a) and (b), geometry-optimized molecular models superposed onto high-resolution STM images are shown for P1 and P3, respectively. This modeling allows one to identify the details of the backbone sequence and of the polymer assembly, including complex side chain interdigitation patterns. All scale bars correspond to 1 nm. The STM images were acquired in constant current mode, with tunnelling parameters (a) 1.4 V, 70 pA; (b) 1.3 V, 140 pA.

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    Figure 3

    Figure 3. Length and mass distributions obtained from measuring a large number of polymer line-profiles from the STM images. Only polymers fully visible and entirely contained within the STM images were used for the bar histogram distributions (see Figure S11). (a) Distribution for P1, (b) for P2, and (c) for P3. Two statistical approaches from survival analysis have been implemented to correct the length underestimation caused by polymers either not fully visible or not entirely contained within the STM images: the Kaplan–Meier nonparametric distribution (red circles) and the parametric distribution (black diamonds). See the text for further details.

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    Figure 4

    Figure 4. (a) SEC mass distributions for the three polymers. P1 and P2 have similar average masses and aggregation shoulders in similar positions; on the contrary, P3 displays a much wider aggregation shoulder caused by its longer and more flexible side chains promoting aggregation. After the recalibration of the SEC horizontal mass scales, the comparison with the STM data (corrected through the parametric survival approach) demonstrates an excellent agreement, as shown in (b) and (c) for P2 and P3, respectively. The STM results are shown as histograms, the rescaled SEC data as continuous lines and the original SEC data as dotted black lines.

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    Figure 5

    Figure 5. Sequencing the backbones of the polymers allows for the precise identification of homocoupling defects. (a) and (b) show the same STM images of Figure 1, with white dashed circles indicating the positions of ThDPPTh homocoupling defects. (c, d) Higher-resolution STM images with examples of homocoupling defects highlighted by white circles. The red and black double arrows indicate the distance along the backbones between two successive side chain exit points, showing that in the case of a homocoupling (red double arrows), this quantity is significantly reduced with respect to the regular heterocouplings (black double arrows). Scale bars correspond to 4 nm for parts (a) and (b) and to 1 nm for parts (c) and (d). The STM images were acquired in constant current mode, with tunneling parameters (a) 1.4 V, 70 pA; (b) 1.3 V, 90 pA; (c) 1.4 V, 70 pA; (d) 1.3 V, 90 pA.

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  • References

    This article references 68 other publications.

    1. 1
      Zhao, C.; Wang, J.; Jiao, J.; Huang, L.; Tang, J. Recent advances of polymer acceptors for high-performance organic solar cells. J. Mater. Chem. C 2020, 8, 28– 43,  DOI: 10.1039/C9TC05567C
      1
      Recent advances of polymer acceptors for high-performance organic solar cells
      Zhao, Congcong; Wang, Jiuxing; Jiao, Jiqing; Huang, Linjun; Tang, Jianguo
      Journal of Materials Chemistry C: Materials for Optical and Electronic Devices (2020), 8 (1), 28-43CODEN: JMCCCX; ISSN:2050-7534. (Royal Society of Chemistry)
      A review. In the past few decades, polymer solar cells (PSCs) have been intensively investigated in academic fields. The study of non-fullerene polymer acceptors has become a hot research focus due to their excellent opto-electronic properties such as wide light-absorbing ability, appropriate mol. energy levels, and easy chem. modifications. The much higher power conversion efficiencies (PCEs) of non-fullerene PSCs relative to fullerene PSCs revealed the significant potential of non-fullerene acceptors in PSCs. This review systematically summarizes the recent advancements of efficient polymer acceptors, including perylene diimide-based, naphthalene diimide-based, diketopyrrolopyrrole-based, double B ← N bridged bipyridyl-based, and other polymer acceptors. Their structure-property relationships were thoroughly analyzed and summarized, which may provide new guidance for the rational structural design of high-performance photovoltaic materials.
    2. 2
      Li, W.; Hendriks, K. H.; Wienk, M. M.; Janssen, R. A. J. Diketopyrrolopyrrole Polymers for Organic Solar Cells. Acc. Chem. Res. 2016, 49, 78– 85,  DOI: 10.1021/acs.accounts.5b00334
      2
      Diketopyrrolopyrrole Polymers for Organic Solar Cells
      Li, Weiwei; Hendriks, Koen H.; Wienk, Martijn M.; Janssen, Rene A. J.
      Accounts of Chemical Research (2016), 49 (1), 78-85CODEN: ACHRE4; ISSN:0001-4842. (American Chemical Society)
      Conjugated polymers have been extensively studied for application in org. solar cells. In designing new polymers, particular attention has been given to tuning the absorption spectrum, mol. energy levels, crystallinity, and charge carrier mobility to enhance performance. As a result, the power conversion efficiencies (PCEs) of solar cells based on conjugated polymers as electron donor and fullerene derivs. as electron acceptor have exceeded 10% in single-junction and 11% in multijunction devices. Despite these efforts, it is notoriously difficult to establish thorough structure-property relationships that will be required to further optimize existing high-performance polymers to their intrinsic limits.In this Account, we highlight progress on the development and our understanding of diketopyrrolopyrrole (DPP) based conjugated polymers for polymer solar cells. The DPP moiety is strongly electron withdrawing and its polar nature enhances the tendency of DPP-based polymers to crystallize. As a result, DPP-based conjugated polymers often exhibit an advantageously broad and tunable optical absorption, up to 1000 nm, and high mobilities for holes and electrons, which can result in high photocurrents and good fill factors in solar cells. Here we focus on the structural modifications applied to DPP polymers and rationalize and explain the relationships between chem. structure and org. photovoltaic performance. The DPP polymers can be tuned via their arom. substituents, their alkyl side chains, and the nature of the π-conjugated segment linking the units along the polymer chain. We show that these building blocks work together in detg. the mol. conformation, the optical properties, the charge carrier mobility, and the soly. of the polymer. We identify the latter as a decisive parameter for DPP-based org. solar cells because it regulates the diam. of the semicryst. DPP polymer fibers that form in the photovoltaic blends with fullerenes via soln. processing. The width of these fibers and the photon energy loss, defined as the energy difference between optical band gap and open-circuit voltage, together govern to a large extent the quantum efficiency for charge generation in these blends and thereby the power conversion efficiency of the photovoltaic devices. Lowering the photon energy loss and maintaining a high quantum yield for charge generation is identified as a major pathway to enhance the performance of org. solar cells. This can be achieved by controlling the structural purity of the materials and further control over morphol. formation. We hope that this Account contributes to improved design strategies of DPP polymers that are required to realize new breakthroughs in org. solar cell performance in the future.
    3. 3
      Wadsworth, A. Critical review of the molecular design progress in non-fullerene electron acceptors towards commercially viable organic solar cells. Chem. Soc. Rev. 2019, 48, 1596– 1625,  DOI: 10.1039/C7CS00892A
      3
      Critical review of the molecular design progress in non-fullerene electron acceptors towards commercially viable organic solar cells
      Wadsworth, Andrew; Moser, Maximilian; Marks, Adam; Little, Mark S.; Gasparini, Nicola; Brabec, Christoph J.; Baran, Derya; McCulloch, Iain
      Chemical Society Reviews (2019), 48 (6), 1596-1625CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
      A review. Fullerenes have formed an integral part of high performance org. solar cells over the last 20 years, however their inherent limitations in terms of synthetic flexibility, cost and stability have acted as a motivation to develop replacements; the so-called non-fullerene electron acceptors. A rapid evolution of such materials has taken place over the last few years, yielding a no. of promising candidates that can exceed the device performance of fullerenes and provide opportunities to improve upon the stability and processability of org. solar cells. In this review we explore the structure-property relationships of a library of non-fullerene acceptors, highlighting the important chem. modifications that have led to progress in the field and provide an outlook for future innovations in electron acceptors for use in org. photovoltaics.
    4. 4
      Lamport, Z. A.; Haneef, H. F.; Anand, S.; Waldrip, M.; Jurchescu, O. D. Tutorial: Organic field-effect transistors: Materials, structure and operation. J. Appl. Phys. 2018, 124, 071101  DOI: 10.1063/1.5042255
      4
      Tutorial: Organic field-effect transistors: Materials, structure and operation
      Lamport, Zachary A.; Haneef, Hamna F.; Anand, Sajant; Waldrip, Matthew; Jurchescu, Oana D.
      Journal of Applied Physics (Melville, NY, United States) (2018), 124 (7), 071101/1-071101/25CODEN: JAPIAU; ISSN:0021-8979. (American Institute of Physics)
      A review. Chem. versatility and compatibility with a vast array of processing techniques has led to the incorporation of org. semiconductors in various electronic and opto-electronic devices. One such device is the org. field-effect transistor (OFET). In this tutorial, we describe the structure, operation, and characterization of OFETs. Following a short historical perspective, we introduce the architectures possible for OFETs and then describe the device physics and the methods for extg. relevant device parameters. We then provide a brief overview of the myriad org. semiconductors and deposition methods that were adopted for OFETs in the past decades. Non-ideal device characteristics, including contact resistance, are then discussed along with their effects on elec. performance and on the accuracy of extg. device parameters. Finally, we highlight several measurements involving OFETs that allow access to fundamental properties of org. semiconductors and the mechanism of charge transport in these materials. (c) 2018 American Institute of Physics.
    5. 5
      Wang, C.; Dong, H.; Hu, W.; Liu, Y.; Zhu, D. Semiconducting π-conjugated systems in field-effect transistors: A material odyssey of organic electronics. Chem. Rev. 2012, 112, 2208– 2267,  DOI: 10.1021/cr100380z
      5
      Semiconducting π-Conjugated Systems in Field-Effect Transistors: A Material Odyssey of Organic Electronics
      Wang, Chengliang; Dong, Huanli; Hu, Wenping; Liu, Yunqi; Zhu, Daoben
      Chemical Reviews (Washington, DC, United States) (2012), 112 (4), 2208-2267CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
      A review.
    6. 6
      Russ, B.; Glaudell, A.; Urban, J. J.; Chabinyc, M. L.; Segalman, R. A. Organic thermoelectric materials for energy harvesting and temperature control. Nat. Rev. Mater. 2016, 1, 16050,  DOI: 10.1038/natrevmats.2016.50
      6
      Organic thermoelectric materials for energy harvesting and temperature control
      Russ, Boris; Glaudell, Anne; Urban, Jeffrey J.; Chabinyc, Michael L.; Segalman, Rachel A.
      Nature Reviews Materials (2016), 1 (10), 16050CODEN: NRMADL; ISSN:2058-8437. (Nature Publishing Group)
      Conjugated polymers and related processing techniques have been developed for org. electronic devices ranging from lightwt. photovoltaics to flexible displays. These breakthroughs have recently been used to create org. thermoelec. materials, which have potential for wearable heating and cooling devices, and near-room-temp. energy generation. So far, the best thermoelec. materials have been inorg. compds. (such as Bi2Te3) that have relatively low Earth abundance and are fabricated through highly complex vacuum processing routes. Mol. materials and hybrid org.-inorg. materials now demonstrate figures of merit approaching those of these inorg. materials, while also exhibiting unique transport behaviors that are suggestive of optimization pathways and device geometries that were not previously possible. In this Review, we discuss recent breakthroughs for org. materials with high thermoelec. figures of merit and indicate how these materials may be incorporated into new module designs that take advantage of their mech. and thermoelec. properties.
    7. 7
      Rivnay, J. Organic electrochemical transistors. Nat. Rev. Mater. 2018, 3, 17086,  DOI: 10.1038/natrevmats.2017.86
      7
      Organic electrochemical transistors
      Rivnay, Jonathan; Inal, Sahika; Salleo, Alberto; Owens, Roisin M.; Berggren, Magnus; Malliaras, George G.
      Nature Reviews Materials (2018), 3 (2), 17086CODEN: NRMADL; ISSN:2058-8437. (Nature Research)
      A review. Org. electrochem. transistors (OECTs) make effective use of ion injection from an electrolyte to modulate the bulk cond. of an org. semiconductor channel. The coupling between ionic and electronic charges within the entire vol. of the channel endows OECTs with high transconductance compared with that of field-effect transistors, but also limits their response time. The synthetic tunability, facile deposition and biocompatibility of org. materials make OECTs particularly suitable for applications in biol. interfacing, printed logic circuitry and neuromorphic devices. In this Review, we discuss the physics and the mechanism of operation of OECTs, focusing on their identifying characteristics. We highlight org. materials that are currently being used in OECTs and survey the history of OECT technol. In addn., form factors, fabrication technologies and applications such as bioelectronics, circuits and memory devices are examd. Finally, we take a crit. look at the future of OECT research and development.
    8. 8
      Kukhta, N. A.; Marks, A.; Luscombe, C. K. Molecular Design Strategies toward Improvement of Charge Injection and Ionic Conduction in Organic Mixed Ionic-Electronic Conductors for Organic Electrochemical Transistors. Chem. Rev. 2022, 122, 4325– 4355,  DOI: 10.1021/acs.chemrev.1c00266
      8
      Molecular Design Strategies toward Improvement of Charge Injection and Ionic Conduction in Organic Mixed Ionic-Electronic Conductors for Organic Electrochemical Transistors
      Kukhta, Nadzeya A.; Marks, Adam; Luscombe, Christine K.
      Chemical Reviews (Washington, DC, United States) (2022), 122 (4), 4325-4355CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
      A review. Expanding the toolbox of the biol. and electronics mutual conjunction is a primary aim of bioelectronics. The org. electrochem. transistor (OECT) has undeniably become a predominant device for mixed conduction materials, offering impressive transconduction properties alongside a relatively simple device architecture. In this review, we focus on the discussion of recent material developments in the area of mixed conductors for bioelectronic applications by means of thorough structure-property investigation and anal. of current challenges. Fundamental operation principles of the OECT are revisited, and characterization methods are highlighted. Current bioelectronic applications of org. mixed ionic-electronic conductors (OMIECs) are underlined. Challenges in the performance and operational stability of OECT channel materials as well as potential strategies for mitigating them, are discussed. This is further expanded to sketch a synopsis of the history of mixed conduction materials for both p- and n-type channel operation, detailing the synthetic challenges and milestones which have been overcome to frequently produce higher performing OECT devices. The cumulative work of multiple research groups is summarized, and synthetic design strategies are extd. to present a series of design principles that can be utilized to drive figure-of-merit performance values even further for future OMIEC materials.
    9. 9
      Guo, X.; Baumgarten, M.; Müllen, K. Designing π-conjugated polymers for organic electronics. Prog. Polym. Sci. 2013, 38, 1832– 1908,  DOI: 10.1016/j.progpolymsci.2013.09.005
      9
      Designing π-conjugated polymers for organic electronics
      Guo, Xin; Baumgarten, Martin; Muellen, Klaus
      Progress in Polymer Science (2013), 38 (12), 1832-1908CODEN: PRPSB8; ISSN:0079-6700. (Elsevier Ltd.)
      A review. Conjugated polymers have attracted an increasing amt. of attention in recent years for various org. electronic devices because of their potential advantages over inorg. and small-mol. org. semiconductors. Chemists can design and synthesize a variety of conjugated polymers with different architectures and functional moieties to meet the requirements of these org. devices. This review concs. on five conjugated polymer systems with 1D and 2D topol. structures, and on one polymer designing approach. This includes (i) conjugated polyphenylenes (polyfluorenes, polycarbazoles, and various stepladder polymers), (ii) other polycyclic arom. hydrocarbons (PAHs) as substructures of conjugated polymers, (iii) thiophene and fused thiophene contg. conjugated polymers, (iv) conjugated macrocycles, (v) graphene nanoribbons, and finally (vi) a design approach, the alternating donor-acceptor (D-A) copolymers. By summarizing the performances of the different classes of conjugated polymers in devices such as org. light-emitting diodes (OLEDs), org. field-effect transistors (OFETs), and polymer solar cells (PSCs), the correlation of polymer structure and device property, as well as the remaining challenges, will be highlighted for each class sep. Finally, we summarize the current progress for conjugated polymers and propose future research opportunities to improve their performance in this exciting research field.
    10. 10
      Himmelberger, S.; Salleo, A. Engineering semiconducting polymers for efficient charge transport. MRS Commun. 2015, 5, 383– 395,  DOI: 10.1557/mrc.2015.44
      10
      Engineering semiconducting polymers for efficient charge transport
      Himmelberger, Scott; Salleo, Alberto
      MRS Communications (2015), 5 (3), 383-395CODEN: MCROF8; ISSN:2159-6867. (Cambridge University Press)
      Electronic performance in semiconducting polymers has improved dramatically in recent years owing to a host of novel materials and processing techniques. Our understanding of the factors governing charge transport in these materials has also been enhanced through advancements in both exptl. and computational techniques, with disorder appearing to play a central role. In this prospective, we propose that disorder is an inextricable aspect of polymer morphol. which need not be highly detrimental to charge transport if it is embraced and planned for. We discuss emerging guidelines for the synthesis of polymers which are resilient to disorder and present our vision for how future advances in processing and mol. design will provide a path toward further increases in charge-carrier mobility.
    11. 11
      He, Y.; Kukhta, N. A.; Marks, A.; Luscombe, C. K. The effect of side chain engineering on conjugated polymers in organic electrochemical transistors for bioelectronic applications. J. Mater. Chem. C 2022, 10, 2314– 2332,  DOI: 10.1039/D1TC05229B
      11
      The effect of side chain engineering on conjugated polymers in organic electrochemical transistors for bioelectronic applications
      He, Yifei; Kukhta, Nadzeya A.; Marks, Adam; Luscombe, Christine K.
      Journal of Materials Chemistry C: Materials for Optical and Electronic Devices (2022), 10 (7), 2314-2332CODEN: JMCCCX; ISSN:2050-7534. (Royal Society of Chemistry)
      A review. Bioelectronics focuses on the establishment of the connection between the ion-driven biosystems and readable electronic signals. Org. electrochem. transistors (OECTs) offer a viable soln. for this task. Org. mixed ionic/electronic conductors (OMIECs) rest at the heart of OECTs. The balance between the ionic and electronic conductivities of OMIECs is closely connected to the OECT device performance. While modification of the OMIECs electronic properties is largely related to the development of conjugated scaffolds, properties such as ion permeability, soly., flexibility, morphol., and sensitivity can be altered by side chain moieties. In this review, we uncover the influence of side chain mol. design on the properties and performance of OECTs. We summarise current understanding of OECT performance and focus specifically on the knowledge of ionic-electronic coupling, shedding light on the significance of side chain development of OMIECs. We show how the versatile synthetic toolbox of side chains can be successfully employed to tune OECT parameters via controlling the material properties. As the field continues to mature, more detailed investigations into the crucial role side chain engineering plays on the resultant OMIEC properties will allow for side chain alternatives to be developed and will ultimately lead to further enhancements within the field of OECT channel materials.
    12. 12
      Katsouras, A. Systematic Analysis of Polymer Molecular Weight Influence on the Organic Photovoltaic Performance. Macromol. Rapid Commun. 2015, 36, 1778– 1797,  DOI: 10.1002/marc.201500398
      12
      Systematic Analysis of Polymer Molecular Weight Influence on the Organic Photovoltaic Performance
      Katsouras, Athanasios; Gasparini, Nicola; Koulogiannis, Chrysanthos; Spanos, Michael; Ameri, Tayebeh; Brabec, Christoph J.; Chochos, Christos L.; Avgeropoulos, Apostolos
      Macromolecular Rapid Communications (2015), 36 (20), 1778-1797CODEN: MRCOE3; ISSN:1022-1336. (Wiley-VCH Verlag GmbH & Co. KGaA)
      A review is presented. The mol. wt. of an electron donor-conjugated polymer is as essential as other well-known parameters in the chem. structure of the polymer, such as length and the nature of any side groups (alkyl chains) positioned on the polymeric backbone, as well as their placement, relative strength, the ratio of the donor and acceptor moieties in the backbone of donor-acceptor (D-A)-conjugated polymers, and the arrangement of their energy levels for org. photovoltaic performance. Finding the "optimal" mol. wt. for a specific conjugated polymer is an important aspect for the development of novel photovoltaic polymers. Therefore, it is evident that the chem. of functional conjugated polymers faces major challenges and materials have to adopt a broad range of specifications in order to be established for high photovoltaic performance. In this review, the approaches followed for enhancing the mol. wt. of electron-donor polymers are presented in detail, as well as how this influences the optoelectronic properties, charge transport properties, structural conformation, morphol., and the photovoltaic performance of the active layer.
    13. 13
      Nahid, M. M. Unconventional Molecular Weight Dependence of Charge Transport in the High Mobility n-type Semiconducting Polymer P(NDI2OD-T2). Adv. Funct. Mater. 2017, 27, 1604744  DOI: 10.1002/adfm.201604744
      There is no corresponding record for this reference.
    14. 14
      Kline, R. J. Dependence of regioregular poly(3-hexylthiophene) film morphology and field-effect mobility on molecular weight. Macromolecules 2005, 38, 3312– 3319,  DOI: 10.1021/ma047415f
      14
      Dependence of Regioregular Poly(3-hexylthiophene) Film Morphology and Field-Effect Mobility on Molecular Weight
      Kline, R. Joseph; McGehee, Michael D.; Kadnikova, Ekaterina N.; Liu, Jinsong; Frechet, Jean M. J.; Toney, Michael F.
      Macromolecules (2005), 38 (8), 3312-3319CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      Morphol. characterization has been used to explain the previously obsd. strong correlation between charge carrier mobility measured with thin-film transistors and the no.-av. mol. wt. (MW) of the conjugated polymer regioregular poly(3-hexylthiophene). At. force microscopy and x-ray diffraction show that the low-mobility, low-MW films have a highly ordered structure composed of nanorods and the high-mobility, high-MW films have a less ordered, isotropic nodule structure. Modifying the morphol. for a const. MW by changing the casting conditions or annealing the samples strongly affects the charge transport and morphol. in the low-mobility, low-MW films, but has little effect on the high-MW films. In-plane grazing incidence x-ray scattering shows the in-plane π-stacking peak increases when the mobility increases for a const. MW. When the MW is changed, this correlation breaks down, confirming that in-plane π-stacking does not cause the mobility-MW relationship. We believe a combination of disordered domain boundaries and inherent effects of chain length on the electronic structure cause the mobility-MW relationship.
    15. 15
      Deshmukh, K. D. Tuning the Molecular Weight of the Electron Accepting Polymer in All-Polymer Solar Cells: Impact on Morphology and Charge Generation. Adv. Funct. Mater. 2018, 28, 1707185  DOI: 10.1002/adfm.201707185
      There is no corresponding record for this reference.
    16. 16
      Tran, D. K. Elucidating the impact of molecular weight on morphology, charge transport, photophysics and performance of all-polymer solar cells. J. Mater. Chem. A 2020, 8, 21070– 21083,  DOI: 10.1039/D0TA08195G
      16
      Elucidating the impact of molecular weight on morphology, charge transport, photophysics and performance of all-polymer solar cells
      Tran, Duyen K.; Robitaille, Amelie; Hai, I. Jo; Ding, Xiaomei; Kuzuhara, Daiki; Koganezawa, Tomoyuki; Chiu, Yu-Cheng; Leclerc, Mario; Jenekhe, Samson A.
      Journal of Materials Chemistry A: Materials for Energy and Sustainability (2020), 8 (40), 21070-21083CODEN: JMCAET; ISSN:2050-7496. (Royal Society of Chemistry)
      Understanding the influence of polymer mol. wt. on the morphol., photophysics, and photovoltaic properties of polymer solar cells is central to further advances in the design, processing, performance and optimization of the materials and devices for large scale applications. We have synthesized six no.-av. mol. wt. (Mn) values (21-127 kDa) of biselenophene-naphthalenediimide copolymer (PNDIBS) via direct heteroarylation polymn. and used them to investigate the effects of the acceptor polymer mol. wt. on the charge transport, blend photophysics, blend morphol., and photovoltaic properties of all-polymer solar cells (all-PSCs) based on PNDIBS and the donor polymer PBDB-T. The short-circuit current and power conversion efficiency (PCE) of the PBDB-T:PNDIBS blend devices were found to increase with increasing Mn until reaching peaks at an optimal mol. wt. of 55 kDa and then decreased with further increases in Mn. The max. PCE of 10.2% obsd. at the optimal Mn value of 55 kDa coincided with optimal blend charge transport properties, blend photophysics, and blend morphol. at this crit. mol. wt. Compared to the bi-continuous network of ~ 5.5-6.5 nm cryst. domains with predominantly face-on mol. orientations obsd. at 55 kDa, a relatively disordered microstructure with larger scale phase sepn. was evident at higher Mn while more finely packed cryst. domains were seen at 21 kDa. The sensitivity of the device efficiency to the active layer thickness was found to also depend on the PNDIBSMn value. These results highlight the importance of tuning the mol. wt. of the polymer components to optimize the morphol., charge transport, photophysics and efficiency of all-polymer solar cells. The results also provide new insights on structure-property relationships for a promising n-type semiconducting copolymer.
    17. 17
      Vanhee, S. Synthesis and characterization of rigid rod poly(p-phenylenes). Macromolecules 1996, 29, 5136– 5142,  DOI: 10.1021/ma960124p
      17
      Synthesis and Characterization of Rigid Rod Poly(p-phenylenes)
      Vanhee, S.; Rulkens, R.; Lehmann, U.; Rosenauer, C.; Schulze, M.; Koehler, W.; Wegner, G.
      Macromolecules (1996), 29 (15), 5136-5142CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      The polymer PP, which consists of a poly(p-phenylene) backbone with sulfonate ester and dodecyl side groups, is synthesized by a Pd-catalyzed coupling of the 1,3-propanediol diester of 2-dodecyl-5-methyl-1,4-benzenediboronic acid with 2,2'-bis(3,5-di-tert-butylbenzenesulfonato)-4,4'-dibromobiphenyl. Polymers with various molar masses are obtained, which are sol. without aggregation in conventional org. solvents. The good soly. of this rodlike polymer allows the accurate detn. of the molar mass by light scattering, osmometry, and SEC with universal calibration. The dependence of the intrinsic viscosity [η] on the molar mass is detd. from both the Mark-Houwink-Sakurada equation and the wormlike chain model. The low value of the persistence length (13 nm) indicates that these polymers are relatively flexible. It is shown that an approx. value of the persistence length, together with the parameters of the Mark-Houwink-Sakurada equation and the wormlike chain model, can be detd. using only a single polydisperse sample.
    18. 18
      Fair, R. A.; Xie, R.; Lee, Y.; Colby, R. H.; Gomez, E. D. Molecular Weight Characterization of Conjugated Polymers through Gel Permeation Chromatography and Static Light Scattering. ACS Appl. Polym. Mater. 2021, 3, 4572– 4578,  DOI: 10.1021/acsapm.1c00647
      18
      Molecular Weight Characterization of Conjugated Polymers Through Gel Permeation Chromatography and Static Light Scattering
      Fair, Ryan A.; Xie, Renxuan; Lee, Youngmin; Colby, Ralph H.; Gomez, Enrique D.
      ACS Applied Polymer Materials (2021), 3 (9), 4572-4578CODEN: AAPMCD; ISSN:2637-6105. (American Chemical Society)
      Mol. wt. is a key parameter of any polymer. Characterizing the mol. wt. of conjugated polymers is often nontrivial due to their semiflexible backbones and poor solubilities. Perhaps the most used technique for measuring the mol. wt. is gel permeation chromatog. (GPC), and results are often calibrated relative to flexible polymer stds. This mismatch between chain flexibilities of samples and stds., combined with poor sample soly. in the mobile phase, leads to inaccuracies in many GPC measurements of conjugated polymers. In this work, we use a universal calibration combined with in-line concn. measurements to yield reliably accurate results for polymers of various stiffnesses. Accuracy of results is verified with abs. mol. wts. obtained from static light scattering. We show that measuring the refractive index increment is key to confirm full recovery of the polymer and ensure accurate values of the abs. mol. wt. from GPC.
    19. 19
      Grubisic, Z.; Rempp, P.; Benoit, H. A Universal Calibration for Gel Permeation Chromatography. Polym. Lett. 1967, 5, 753– 759,  DOI: 10.1002/pol.1967.110050903
      There is no corresponding record for this reference.
    20. 20
      Holdcroft, S. Determination of molecular weights and Mark–Houwink constants for soluble electronically conducting polymers. J. Polym. Sci., Part B: Polym. Phys. 1991, 29, 1585– 1588,  DOI: 10.1002/polb.1991.090291303
      20
      Determination of molecular weights and Mark-Houwink constants for soluble electronically conducting polymers
      Holdcroft, Steven
      Journal of Polymer Science, Part B: Polymer Physics (1991), 29 (13), 1585-8CODEN: JPBPEM; ISSN:0887-6266.
      Intrinsic viscosities and gel-permeation chromatog. (GPC) data are used to evaluate the Mark-Houwink consts. (K and a) of the sol. elec. conducting polymer, poly(3-hexylthiophene) (I): K and a are 2.28 × 10-3 cm3/g and 0.96, resp., in THF at 25°. The Mark-Houwink consts. are used to calibrate GPC columns for I. The no.-av. mol. wt. of I detd. with modified calibration curves agreed well with those detd. by an abs. method, embulliometry. The mol. wt. estd. using unmodified polystyrene calibration procedures was significantly larger than the true value.
    21. 21
      Lou, X. Superheated high-temperature size-exclusion chromatography with chloroform as the mobile phase for π-conjugated polymers. Polym. Chem. 2014, 5, 558– 561,  DOI: 10.1039/C3PY00933E
      21
      Superheated high-temperature size-exclusion chromatography with chloroform as the mobile phase for π-conjugated polymers
      Lou, Xianwen; van Dongen, Joost L. J.; Braeken, Yasmine; Brebels, Jeroen; van Pruissen, Gijs W. P.; Li, Weiwei; Wienk, Martijn M.; Janssen, Rene A. J.
      Polymer Chemistry (2014), 5 (2), 558-561CODEN: PCOHC2; ISSN:1759-9962. (Royal Society of Chemistry)
      π-Conjugated polymers for org. electronic applications are often designed to aggregate or crystallize to enhance their charge carrier mobility. Their electronic properties often improve with increasing mol. wt. Detg. the mol. wt. of these polymers via size-exclusion chromatog. (SEC), however, is complicated due to their significant aggregation in soln. We demonstrate that superheated high-temp. SEC with chloroform as the mobile phase, operated at temps. well above the normal b.p. of the solvent, can effectively be used to det. the mol. wt. for these polymers by dissolving the aggregates.
    22. 22
      Matthews, J. R. Scalable synthesis of fused thiophene-diketopyrrolopyrrole semiconducting polymers processed from nonchlorinated solvents into high performance thin film transistors. Chem. Mater. 2013, 25, 782– 789,  DOI: 10.1021/cm303953e
      22
      Scalable Synthesis of Fused Thiophene-Diketopyrrolopyrrole Semiconducting Polymers Processed from Nonchlorinated Solvents into High Performance Thin Film Transistors
      Matthews, James R.; Niu, Weijun; Tandia, Adama; Wallace, Arthur L.; Hu, Jieyu; Lee, Wen-Ya; Giri, Gaurav; Mannsfeld, Stefan C. B.; Xie, Yingtao; Cai, Shucheng; Fong, Hon Hang; Bao, Zhenan; He, Mingqian
      Chemistry of Materials (2013), 25 (5), 782-789CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
      The synthesis and characterization of a fused thiophene-diketopyrrolopyrrole based semiconducting polymer PTDPPTFT4 is presented. A no. of synthetic challenges were overcome in the development of a practical scalable synthesis. Characterization by Gel Permeation Chromatog. (GPC) over a range of temps. revealed the tendency of this polymer to aggregate even at elevated temps. and confirmed that the mol. wt. values obtained are for nonaggregated material. This polymer meets a no. of important requirements for potential industrial applications, such as scalable synthesis, soly. in industrially suitable solvents, and material stability and processability into stable high performance thin film transistor devices. Computational modeling was used to help explain the structure property relations contributing to the high performance. Grazing incidence x-ray of the thin films showed out of plane lamellar packing and in plane π-π stacking, both good indicators of a preferentially oriented thin film, desirable for high charge carrier mobility. Hole mobilities >2 cm2/V·s, on/off ratio of >106, and threshold voltage <2 V were achieved.
    23. 23
      Liu, J.; Loewe, R. S.; McCullough, R. D. Employing MALDI-MS on poly(alkylthiophenes): Analysis of molecular weights, molecular weight distributions, end-group structures, and end-group modifications. Macromolecules 1999, 32, 5777– 5785,  DOI: 10.1021/ma9905324
      23
      Employing MALDI-MS on Poly(alkylthiophenes): Analysis of Molecular Weights, Molecular Weight Distributions, End-Group Structures, and End-Group Modifications
      Liu, Jinsong; Loewe, Robert S.; McCullough, Richard D.
      Macromolecules (1999), 32 (18), 5777-5785CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      Regioregular, head-to-tail coupled, poly(3-alkylthiophenes), synthesized by three different methods, were subjected to MALDI-TOF MS anal. Polymer samples of both high and low polydispersities were examd. Polymer samples of narrow polydispersity were obtained by fractionation of the polymer by Soxhlet extn. with various solvents. Comparisons between the mol. wts. calcd. by MALDI and GPC of all fractionated polymer samples showed that GPC calcd. mol. wts. are a factor of 1.2-2.3 times higher than MALDI. The polydispersities calcd. by MALDI were identical or slightly lower than those calcd. by GPC. Polymer end-group compns. were also analyzed. We found that more than one type of end-group structure could be detected, and these structures are dependent on the synthetic method employed. Chem. modification of the end-group structure was also performed and monitored by MALDI with successful results. We obsd. that smaller polymer chains were subject to end-group fragmentation when the MALDI laser power was high. Larger polymer chains, however, showed no such fragmentation.
    24. 24
      Wong, M. An apparent size-exclusion quantification limit reveals a molecular weight limit in the synthesis of externally initiated polythiophenes. ACS Macro Lett. 2012, 1, 1266– 1269,  DOI: 10.1021/mz300333f
      24
      An Apparent Size-Exclusion Quantification Limit Reveals a Molecular Weight Limit in the Synthesis of Externally Initiated Polythiophenes
      Wong, Michael; Hollinger, Jon; Kozycz, Lisa M.; McCormick, Theresa M.; Lu, Yijie; Burns, Darcy C.; Seferos, Dwight S.
      ACS Macro Letters (2012), 1 (11), 1266-1269CODEN: AMLCCD; ISSN:2161-1653. (American Chemical Society)
      We report the linear and nonlinear regions of the relationship between no. av. mol. wt. detd. by gel permeation chromatog. (GPC) and 1H NMR end-group anal. for a series of o-tolyl-initiated poly(3-hexylthiophene)s (P3HTs). For conjugated polymers with chains that are 39-138 repeat units in length (6.5-23 kDa), GPC systematically overestimates the no. av. mol. wt. (Mn) by a factor of 1.3 ± 0.1 (std. error), and GPC and 1H NMR end-group anal. correlate in a linear manner. For chains 138-1130 (23-188 kDa) repeat units in length, we observe a nonlinear relationship between GPC and end-group anal. Static light-scattering expts. confirm that at high mol. wt. (>70 kDa) decreasing the catalyst loading does not appreciably increase the polymer chain length. Thus, we conclude that there is a mol. wt. limit in the synthesis of externally initiated polythiophenes and a propensity for the growth of nonexternally initiated chains which increases as a function of Mn. This is significant as external initiation has been reported to result in nearly 100% externally initiated chains as well as reduce the possibility of chain-chain coupling in a typical synthesis. Our data show that 100% external initiation only holds true for polymers that are less than 40 kDa and encourages caution when detg. Mn by NMR using this synthetic methodol. at high mol. wts.
    25. 25
      Gu, K.; Onorato, J.; Xiao, S. S.; Luscombe, C. K.; Loo, Y. L. Determination of the Molecular Weight of Conjugated Polymers with Diffusion-Ordered NMR Spectroscopy. Chem. Mater. 2018, 30, 570– 576,  DOI: 10.1021/acs.chemmater.7b05063
      25
      Determination of the Molecular Weight of Conjugated Polymers with Diffusion-Ordered NMR Spectroscopy
      Gu, Kaichen; Onorato, Jonathan; Xiao, Steven Shuyong; Luscombe, Christine K.; Loo, Yueh-Lin
      Chemistry of Materials (2018), 30 (3), 570-576CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
      Size exclusion chromatog. (SEC) is not well suited for characterizing the mol. wt. (MW) and MW distribution of conjugated polymers, esp. those that absorb strongly at the detection wavelengths, or those that interact with and adsorb on the walls of SEC columns. We demonstrate diffusion-ordered NMR spectroscopy (DOSY) as a complementary method for characterizing the size and size distribution of conjugated polymers. Starting with four batches of poly(3-hexylthiophene), whose distinct and narrow MW distributions had been fully characterized, as a model system, we establish a power-law relationship between the wt.-av. MW and the diffusion coeff. measured through DOSY. We extend this approach to characterizing poly[4-(4,4-dihexadecyl-4H-cyclopenta[1,2-b:5,4-b']dithiophen-2-yl)-alt-[1,2,5]thiadiazolo-[3,4-c]pyridine], whose absorption properties preclude its characterization with light scattering based techniques, including SEC. By applying the same power law on the diffusion coeffs. obtained by DOSY measurements, we extd. P3HT-equiv. MWs and MW distributions for six different batches of PCDTPT. By circumventing the practical issues in SEC measurements, DOSY shows promise as a versatile complement for detg. polymer size.
    26. 26
      De Winter, J. MALDI-ToF analysis of polythiophene: use of trans-2-[3-(4-t-butyl-phenyl)-2-methyl- 2-propenylidene]malononitrile─DCTB─as matrix. J. Mass Spectrom. 2011, 46, 237– 246,  DOI: 10.1002/jms.1886
      There is no corresponding record for this reference.
    27. 27
      Kohn, P. On the role of single regiodefects and polydispersity in regioregular poly(3-hexylthiophene): Defect distribution, synthesis of defect-free chains, and a simple model for the determination of crystallinity. J. Am. Chem. Soc. 2012, 134, 4790– 4805,  DOI: 10.1021/ja210871j
      27
      On the Role of Single Regiodefects and Polydispersity in Regioregular Poly(3-hexylthiophene): Defect Distribution, Synthesis of Defect-Free Chains, and a Simple Model for the Determination of Crystallinity
      Kohn, Peter; Huettner, Sven; Komber, Hartmut; Senkovskyy, Volodymyr; Tkachov, Roman; Kiriy, Anton; Friend, Richard H.; Steiner, Ullrich; Huck, Wilhelm T. S.; Sommer, Jens-Uwe; Sommer, Michael
      Journal of the American Chemical Society (2012), 134 (10), 4790-4805CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      Identifying structure formation in semicryst. conjugated polymers is the fundamental basis to understand electronic processes in these materials. Although correlations between phys. properties, structure formation, and device parameters of regioregular, semicryst. poly(3-hexylthiophene) (P3HT) have been established, it has remained difficult to disentangle the influence of regioregularity, polydispersity, and mol. wt. Here we show that the most commonly used synthetic protocol for the synthesis of P3HT, the living Kumada catalyst transfer polycondensation (KCTP) with Ni(dppp)Cl2 as the catalyst, leads to regioregular chains with one single tail-to-tail (TT) defect distributed over the whole chain, in contrast to the hitherto assumed exclusive location at the chain end. NMR end-group anal. and simulations are used to quantify this effect. A series of entirely defect-free P3HT materials with different mol. wts. is synthesized via new, sol. nickel initiators. Data on structure formation in defect-free P3HT, as elucidated by various calorimetric and scattering expts., allow the development of a simple model for estg. the degree of crystallinity. We find very good agreement for predicted and exptl. detd. degrees of crystallinities as high as ∼70%. For Ni(dppp)Cl2-initiated chains comprising one distributed TT unit, the comparison of simulated crystallinities with calorimetric and optical measurements strongly suggests incorporation of the TT unit into the crystal lattice, which is accompanied by an increase in backbone torsion. Polydispersity is identified as a major parameter detg. crystallinity within the mol. wt. range investigated. We believe that the presented approach and results not only contribute to understanding structure formation in P3HT but are generally applicable to other semicryst. conjugated polymers as well.
    28. 28
      Byrd, H. C. M.; McEwen, C. N. The limitations of MALDI-TOF mass spectrometry in the analysis of wide polydisperse polymers. Anal. Chem. 2000, 72, 4568– 4576,  DOI: 10.1021/ac0002745
      28
      The Limitations of MALDI-TOF Mass Spectrometry in the Analysis of Wide Polydisperse Polymers
      Byrd, H. C. Michelle; McEwen, Charles N.
      Analytical Chemistry (2000), 72 (19), 4568-4576CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)
      Av. mol. wt. detn. of polymers with polydispersity >1.2 is an ongoing challenge in the field of MALDI mass spectrometry (MALDI-MS). Mass discrimination effects obsd. in the anal. of these polymers are attributed to sample prepn., desorption/ionization, and instrumental factors. In an effort to sep. these factors, we studied PMMA stds. using two different ion detection systems installed on the same time-of-flight mass analyzer. Equimass blends of narrow PMMA stds. were used to simulate a polymer with a wide polydispersity. MALDI-MS anal. also was performed on a PMMA std. with polydispersity 1.7. All samples were analyzed by SEC for comparison. Although sample prepn. and ionization/desorption factors influence the spectral appearance of the MMA distributions, we demonstrate that under similar sample prepn. and instrument conditions, different ion detection systems produce different results for synthetic polymer blends. The differences in the detector responses for the blends and wide polydisperse std. arise from several factors related to the ion detection system: detection mechanisms, satn. effects and signal-to-noise limitations.
    29. 29
      Matsidik, R.; Komber, H.; Sommer, M. Rational Use of Aromatic Solvents for Direct Arylation Polycondensation: C-H Reactivity versus Solvent Quality. ACS Macro Lett. 2015, 4, 1346– 1350,  DOI: 10.1021/acsmacrolett.5b00783
      29
      Rational Use of Aromatic Solvents for Direct Arylation Polycondensation: C-H Reactivity versus Solvent Quality
      Matsidik, Rukiya; Komber, Hartmut; Sommer, Michael
      ACS Macro Letters (2015), 4 (12), 1346-1350CODEN: AMLCCD; ISSN:2161-1653. (American Chemical Society)
      The solvent for direct arylation polycondensation (DAP) is of crucial importance. For conjugated polymers exhibiting reduced soly., the choice of solvent decides on the max. mol. wt. that can be achieved, hence, good arom. solvents are generally desirable. However, unintentional activation of C-H bonds present in arom. solvents under DAP conditions leads to in situ solvent termination which competes with step growth. Here we evaluate relative C-H reactivity and solvent quality of seven arom. solvents for the DAP of defect-free naphthalene diimide (NDI)-based copolymers of different soly. C-H reactivity is strongly reduced with increasing degree of substitution for both chlorine and Me substituents. Mesitylene is largely C-H unreactive and, thus, albeit being a moderate solvent, enables very high mol. wts. at elevated temp. for NDI copolymers with limited soly.
    30. 30
      Okamoto, K.; Zhang, J.; Housekeeper, J. B.; Marder, S. R.; Luscombe, C. K. C-H arylation reaction: Atom efficient and greener syntheses of π-conjugated small molecules and macromolecules for organic electronic materials. Macromolecules 2013, 46, 8059– 8078,  DOI: 10.1021/ma401190r
      30
      C-H Arylation Reaction: Atom Efficient and Greener Syntheses of π-Conjugated Small Molecules and Macromolecules for Organic Electronic Materials
      Okamoto, Ken; Zhang, Junxiang; Housekeeper, Jeremy B.; Marder, Seth R.; Luscombe, Christine K.
      Macromolecules (Washington, DC, United States) (2013), 46 (20), 8059-8078CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      A review. π-Conjugated small mols., oligomers, and macromols. are being used in the fabrication of a wide variety of org. electronic devices such as org. field-effect transistors (OFETs), org. photovoltaic (OPV) devices, and org. light-emitting diodes (OLEDs). Efficient syntheses involving fewer steps, fewer toxic reagents, and highly reactive compds. are needed to lower the cost of materials in a manner that is fundamentally more eco-friendly. Addnl., synthetic approaches for π-conjugated materials with more functional group tolerance are desirable to expand the range of properties that can be realized in such materials. Developing new synthetic routes to materials can both broaden the scope of science that can be explored and increase the probability that interesting materials can be developed in an economically viable manner for inclusion in consumer products. One such synthetic strategy that can impact all of these issues is carbon-hydrogen bond activation and subsequent carbon-carbon bond formation (C-H functionalization). While the C-H functionalizations represented by direct arylation-based methods are not as developed as the widely used Stille and Suzuki methods at this stage, they allow for the use of readily accessible halogenated arom. substances and can negate the need for toxic organotin reagents. They also hold promise of allowing for the synthesis of previously inaccessible materials. In this Perspective, our goal is to provide an overview of the current status in this challenging field by highlighting (1) the history of prepg. π-conjugated small mols. and macromols. via cross-coupling reactions, (2) advances in prepn. of versatile π-conjugated small mols. and macromols. via transition-metal-catalyzed direct arylation, and (3) the scope, limitations, and challenges for materials science.
    31. 31
      Wakioka, M.; Ozawa, F. Highly Efficient Catalysts for Direct Arylation Polymerization (DArP). Asian J. Org. Chem. 2018, 7, 1206– 1216,  DOI: 10.1002/ajoc.201800227
      31
      Highly Efficient Catalysts for Direct Arylation Polymerization (DArP)
      Wakioka, Masayuki; Ozawa, Fumiyuki
      Asian Journal of Organic Chemistry (2018), 7 (7), 1206-1216CODEN: AJOCC7; ISSN:2193-5807. (Wiley-VCH Verlag GmbH & Co. KGaA)
      A review. Recently, the palladium-catalyzed direct arylation polymn. (DArP) has emerged as a viable alternative to conventional synthetic means of making π-conjugated polymers based on catalytic cross-coupling reactions. The DArP, which proceeds through C-H bond activation, has a distinct advantage over cross-coupling polymn. in terms of fewer reaction steps and higher functional group tolerance. We have developed novel catalysts for DArP by using P(2-MeOC6H4)3 (L1) and P(2-Me2NC6H4)3 (L2) as ligands. Although common direct arylation catalysts require the use of strongly coordinating solvents such as DMA and DMF, our catalysts exhibit high activity in THF and toluene, which are good solvents for π-conjugated polymers. Thus, we could realize the precise synthesis of highly head-to-tail regioregular poly(3-hexylthiophene) (HT-P3HT) and donor-acceptor type alternating copolymers (DA polymers) with well-controlled structures through DArP.
    32. 32
      Bura, T.; Blaskovits, J. T.; Leclerc, M. Direct (Hetero)arylation Polymerization: Trends and Perspectives. J. Am. Chem. Soc. 2016, 138, 10056– 10071,  DOI: 10.1021/jacs.6b06237
      32
      Direct (Hetero)arylation Polymerization: Trends and Perspectives
      Bura, Thomas; Blaskovits, J. Terence; Leclerc, Mario
      Journal of the American Chemical Society (2016), 138 (32), 10056-10071CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      A review. Conjugated polymers have attracted much attention in recent years, as they can combine the best features of metals or inorg. semiconducting materials (excellent elec. and optical properties) with those of synthetic polymers (mech. flexibility, simple processing, and low-cost prodn.), thereby creating altogether new scientific synergies and technol. opportunities. In the search for more efficient synthetic methods for the prepn. of conjugated polymers, this Perspective reports advances in the field of direct (hetero)arylation polymn. This recently developed polymn. method encompasses the formation of carbon-carbon bonds between simple (hetero)arenes and (hetero)aryl halides, reducing both the no. of synthetic steps and the prodn. of organometallic byproducts. Along these lines, we describe the most general and adaptable reaction conditions for the prepn. of high-mol.-wt., defect-free conjugated polymers. We also discuss the bottleneck presented by the utilization of certain brominated thiophene units and propose some potential solns. It is, however, firmly believed that this polymn. method will become a versatile tool in the field of conjugated polymers by providing a desirable atom-economical alternative to std. cross-coupling polymn. reactions.
    33. 33
      Gobalasingham, N. S.; Thompson, B. C. Direct arylation polymerization: A guide to optimal conditions for effective conjugated polymers. Prog. Polym. Sci. 2018, 83, 135– 201,  DOI: 10.1016/j.progpolymsci.2018.06.002
      33
      Direct arylation polymerization: A guide to optimal conditions for effective conjugated polymers
      Gobalasingham, Nemal S.; Thompson, Barry C.
      Progress in Polymer Science (2018), 83 (), 135-201CODEN: PRPSB8; ISSN:0079-6700. (Elsevier Ltd.)
      The rapid increase in the breadth and scope of transformations that involve metal-promoted activation of C-H bonds is fundamentally changing the field of synthetic chem. Direct arylation polymn. is a newly established synthetic protocol for atom economical, effective, and affordable prepn. of conjugated polymers, which continue to be incredibly advantageous as operative materials for a diverse and continually evolving array of applications. This route toward conjugated polymers for high performance materials is particularly appealing because it circumvents the prepn. of organometallic derivs. and the assocd. cryogenic air- and water-free reactions. Although a broad range of monomers are now readily polymerizable, direct arylation polymn. is known to produce defects in the chem. structure, which have a strong impact on the optical, electronic, and thermal properties of conjugated polymers. Fundamental understanding of the underlying considerations when employing different reaction protocols is required to truly enable a broad reaching platform.
    34. 34
      Broll, S. Defect Analysis of High Electron Mobility Diketopyrrolopyrrole Copolymers Made by Direct Arylation Polycondensation. Macromolecules 2015, 48, 7481– 7488,  DOI: 10.1021/acs.macromol.5b01843
      34
      Defect Analysis of High Electron Mobility Diketopyrrolopyrrole Copolymers Made by Direct Arylation Polycondensation
      Broll, Sebastian; Nuebling, Fritz; Luzio, Alessandro; Lentzas, Dimitros; Komber, Hartmut; Caironi, Mario; Sommer, Michael
      Macromolecules (Washington, DC, United States) (2015), 48 (20), 7481-7488CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      Defect structures in high-performance conjugated polymers are generally known but still challenging to characterize on a quant. basis. Here, we present a detailed anal. of backbone topol. of a series of copolymers PDPPTh2F4 having alternating dithienyldiketopyrrolopyrrole (DPPTh2) and tetrafluorobenzene (F4) units made by direct arylation polycondensation (DAP). In contrast to early expectations of unselective C-H activation during the DAP of monomers with multiple C-H bonds, detailed structure anal. by high-temp. 1H NMR spectroscopy reveals well-defined and alternating backbones with a quantifiable amt. of 0-12% DPPTh2 homocouplings as the only defect structure in the main chain. Homocoupled -DPPTh2-DPPTh2- structural units are addnl. characterized by UV-vis spectroscopy. While -DPPTh2-H end groups are inert to other side reactions, -F4-Br end groups are weakly susceptible to both dehalogenation and reaction with toluene. However, despite the presence of DPPTh2 homocouplings, high field-effect transistor electron mobilities up to ∼0.6 cm2/(V s) are achieved. This study highlights both that DPPTh2 homocouplings pose a prevalent structural defect in DPPTh2-based conjugated polymers made by DAP and that a simple four-step DAP protocol can yield materials with varying molar mass and excellent n-type transistor performance.
    35. 35
      Hendriks, K. H. Homocoupling defects in diketopyrrolopyrrole-based copolymers and their effect on photovoltaic performance. J. Am. Chem. Soc. 2014, 136, 11128– 11133,  DOI: 10.1021/ja505574a
      35
      Homocoupling defects in diketopyrrolopyrrole-based copolymers and their effect on photovoltaic performance
      Hendriks, Koen H.; Li, Weiwei; Heintges, Gael H. L.; van Pruissen, Gijs W. P.; Wienk, Martijn M.; Janssen, Rene A. J.
      Journal of the American Chemical Society (2014), 136 (31), 11128-11133CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      We study the occurrence and effect of intrachain homocoupling defects in alternating push-pull semiconducting PDPPTPT polymers based on dithienyl-diketopyrrolopyrrole (TDPPT) and phenylene (P) synthesized via a palladium-catalyzed cross-coupling polymn. Homocoupled TDPPT-TDPPT segments are readily identified by the presence of a low-energy shoulder in the UV/vis/NIR absorption spectrum. Remarkably, the signatures of these defects are found in many diketopyrrolopyrrole (DPP)-based copolymers reported in the literature. The defects cause a redn. of the band gap, a higher HOMO (HOMO) level, a lower LUMO (LUMO) level, and a localization of these MOs. By synthesizing copolymers with a predefined defect concn., we demonstrate that their presence reduces the short-circuit current and open-circuit voltage of solar cells based on blends of PDPPTPT with [70]PCBM. In virtually defect-free PDPPTPT, the power conversion efficiency is as high as 7.5%, compared to 4.5-5.6% for polymers contg. 20% to 5% defects.
    36. 36
      Hong, W. Is a polymer semiconductor having a ‘perfect’ regular structure desirable for organic thin film transistors?. Chem. Sci. 2015, 6, 3225– 3235,  DOI: 10.1039/C5SC00843C
      There is no corresponding record for this reference.
    37. 37
      Vanderspikken, J. On the Importance of Chemical Precision in Organic Electronics: Fullerene Intercalation in Perfectly Alternating Conjugated Polymers. Adv. Funct. Mater. 2023, 33, 2309403  DOI: 10.1002/adfm.202309403
      There is no corresponding record for this reference.
    38. 38
      Pirotte, G.; Verstappen, P.; Vanderzande, D.; Maes, W. On the “True” Structure of Push–Pull-Type Low-Bandgap Polymers for Organic Electronics. Adv. Electron. Mater. 2018, 4, 1700481  DOI: 10.1002/aelm.201700481
      There is no corresponding record for this reference.
    39. 39
      Vangerven, T. Molar mass versus polymer solar cell performance: Highlighting the role of homocouplings. Chem. Mater. 2015, 27, 3726– 3732,  DOI: 10.1021/acs.chemmater.5b00939
      39
      Molar Mass versus Polymer Solar Cell Performance: Highlighting the Role of Homocouplings
      Vangerven, Tim; Verstappen, Pieter; Drijkoningen, Jeroen; Dierckx, Wouter; Himmelberger, Scott; Salleo, Alberto; Vanderzande, Dirk; Maes, Wouter; Manca, Jean V.
      Chemistry of Materials (2015), 27 (10), 3726-3732CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
      Although a strong link between the molar mass of conjugated polymers and the performance of the resulting polymer:fullerene bulk heterojunction org. solar cells has been established on numerous occasions, a clear understanding of the origin of this connection is still lacking. Moreover, the usual description of molar mass and polydispersity does not include the shape of the polymer distribution, although this can have a significant effect on the device properties. In this work, the effect of molar mass distribution on photovoltaic performance is investigated using a combination of structural and electro-optical techniques for the state-of-the-art low bandgap copolymer PTB7. Some of the studied com. PTB7 batches exhibit a bimodal distribution, of which the low molar mass fraction contains multiple homocoupled oligomer species, as identified by MALDI-TOF anal. This combination of low molar mass and homocoupling drastically reduces device performance, from 7.0-2.7%. High molar mass batches show improved charge carrier transport and extn. with much lower apparent recombination orders, as well as a more homogeneous surface morphol. These results emphasize the important effect of molar mass distributions and homocoupling defects on the operation of conjugated polymers in photovoltaic devices.
    40. 40
      Leclerc, M.; Brassard, S.; Beaupré, S. Direct (hetero)arylation polymerization: toward defect-free conjugated polymers. Polym. J. 2020, 52, 13– 20,  DOI: 10.1038/s41428-019-0245-9
      40
      Direct (hetero)arylation polymerization: toward defect-free conjugated polymers
      Leclerc, Mario; Brassard, Samuel; Beaupre, Serge
      Polymer Journal (Tokyo, Japan) (2020), 52 (1), 13-20CODEN: POLJB8; ISSN:0032-3896. (Nature Research)
      In a very short time, direct (hetero)arylation polymn. (DHAP) has established itself as a valuable and atom-economical alternative to traditional cross-coupling methods such as the Migita-Stille and Suzuki-Miyaura polymns. for the synthesis of low cost and efficient conjugated polymers for org. electronics. Because of sustained research efforts combining in-depth theor. calcns., the development of new ligands and the careful fine-tuning of polymn. conditions, selectivity and reactivity issues should be soon a thing of the past. This focus review highlights the recent advances that lead to defect-free polymeric semiconductors and conductors and the current limitations and challenges of DHAP as it moves toward simultaneously becoming an industrially feasible, environmentally friendly, and synthetically powerful polymn. technique.
    41. 41
      Rudenko, A. E.; Thompson, B. C. Optimization of direct arylation polymerization (DArP) through the identification and control of defects in polymer structure. J. Polym. Sci. Part A. Polym. Chem. 2015, 53, 135– 147,  DOI: 10.1002/pola.27279
      41
      Optimization of direct arylation polymerization (DArP) through the identification and control of defects in polymer structure
      Rudenko, Andrey E.; Thompson, Barry C.
      Journal of Polymer Science, Part A: Polymer Chemistry (2015), 53 (2), 135-147CODEN: JPACEC; ISSN:0887-624X. (John Wiley & Sons, Inc.)
      A review. As a newly emerged protocol for the synthesis of conjugated polymers, direct arylation polymn. (DArP) is an environmentally friendly and cost-effective alternative to traditional methods of polymn. DArP efficiently yields conjugated polymers with high yield and high mol. wt. However, DArP is also known to produce defects in polymer chem. structure. Together with mol. wt. and polydispersity, these defects are considered to be important parameters of polymer structure and they have a strong impact on optical, electronic and thermal properties of conjugated polymers. The four major classes of conjugated polymer defects inherent for DArP have been identified: homocoupling regiodefects, branching defects, end group defects, and residual metal defects. To have a precise control over the polymer properties, it is important to understand what causes the defects to form during the polymn. process and be able to control their content. Here within the scope of current literature, we discuss in detail the definition and origin of all these defects, their influence on polymer properties and effective means to control the defects through fine tuning of the DArP reaction parameters. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014.
    42. 42
      Sommer, M. 2 - Development of conjugated polymers for organic flexible electronics. In Organic Flexible Electronics, Woodhead Publishing, (pp 27- 70) 2021.
      There is no corresponding record for this reference.
    43. 43
      Lombeck, F. On the Effect of Prevalent Carbazole Homocoupling Defects on the Photovoltaic Performance of PCDTBT:PC71BM Solar Cells. Adv. Energy Mater. 2016, 6, 1601232  DOI: 10.1002/aenm.201601232
      There is no corresponding record for this reference.
    44. 44
      Streiter, M. Homocoupling Defects in a Conjugated Polymer Limit Exciton Diffusion. Adv. Funct. Mater. 2019, 29, 1903936  DOI: 10.1002/adfm.201903936
      44
      Homocoupling Defects in a Conjugated Polymer Limit Exciton Diffusion
      Streiter, Martin; Beer, Daniel; Meier, Fabian; Goehler, Clemens; Lienert, Caroline; Lombeck, Florian; Sommer, Michael; Deibel, Carsten
      Advanced Functional Materials (2019), 29 (46), 1903936CODEN: AFMDC6; ISSN:1616-301X. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Copolymers such as PCDTBT (poly(N-9'-heptadecanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole))) are commonly employed as donor material in bulk heterojunction solar cells. Recently, chem. defects such as homocouplings have been shown to form at the material synthesis stage, strongly reducing the short circuit current in org. photovoltaics. Here it is shown that both low mol. wt. and homocoupling defects reduce the short circuit current of solar cells because of limited exciton diffusion. A model that unites and explains the influence of both chem. parameters with the distribution of conjugation lengths is proposed. The connection between limited exciton diffusion and short circuit current is revealed via kinetic Monte Carlo simulation of bulk heterojunctions. The findings are likely applicable for copolymers in general.
    45. 45
      Wang, Q. Electron Mobility of Diketopyrrolopyrrole Copolymers Is Robust against Homocoupling Defects. Chem. Mater. 2021, 33, 668– 677,  DOI: 10.1021/acs.chemmater.0c03998
      45
      Electron Mobility of Diketopyrrolopyrrole Copolymers Is Robust against Homocoupling Defects
      Wang, Qian; Lenjani, Shayan Vazirieh; Dolynchuk, Oleksandr; Scaccabarozzi, Alberto D.; Komber, Hartmut; Guo, Yuejie; Guenther, Florian; Gemming, Sibylle; Magerle, Robert; Caironi, Mario; Sommer, Michael
      Chemistry of Materials (2021), 33 (2), 668-677CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
      Structural defects in semiconducting conjugated polymers are usually suspected to deteriorate their properties and device performance and therefore complicate batch-to-batch reproducibility. This study investigates homocoupling (hc) defects in copolymers made from dithiazolyldiketopyrrolopyrrole (TzDPPTz) and tetrafluorobenzene (F4) by direct arylation polycondensation (DAP). Hc defects are quantified by 1H NMR spectroscopy with good accuracy, and the effect of several reaction parameters on the TzDPPTz hc content in the resulting copolymers PTzDPPTzF4 is investigated in detail. A range of polymers with hc contents between 0.6 and 12.4% is used for a detailed structure-function relationship study. Exptl., it is obsd. that TzDPPTz hc defects cause bathochromically shifted absorption spectra, decrease photoluminescence, and lower the LUMO energy level. Thin film morphol., nanostructure, and electron mobility probed by field-effect devices is marginally or not affected. The latter result is explained by theor. calcns. that suggest a localization of the HOMO on the hc defect, but not that of the LUMO, the latter being relevant for electron transport. Thus, under these conditions, the hc content is not limiting device performance, which makes PTzDPPTzF4 a robust electron-transporting copolymer. These results are promising in the context of batch-to-batch reproducibility and further guide efforts toward a more detailed understanding of hc-function relationships.
    46. 46
      Lombeck, F.; Komber, H.; Gorelsky, S. I.; Sommer, M. Identifying homocouplings as critical side reactions in direct arylation polycondensation. ACS Macro Lett. 2014, 3, 819– 823,  DOI: 10.1021/mz5004147
      46
      Identifying Homocouplings as Critical Side Reactions in Direct Arylation Polycondensation
      Lombeck, Florian; Komber, Hartmut; Gorelsky, Serge I.; Sommer, Michael
      ACS Macro Letters (2014), 3 (8), 819-823CODEN: AMLCCD; ISSN:2161-1653. (American Chemical Society)
      Homocouplings are identified as major side reactions in direct arylation polycondensation (DAP) of 4,7-bis(4-hexyl-2-thienyl)-2,1,3-benzothiadiazole (TBT) and 2,7-dibromo-9-(1-octylnonyl)-9H-carbazole (CbzBr2). Using size exclusion chromatog. (SEC) and NMR spectroscopy, we demonstrate that both TBT and Cbz homocouplings occur at a considerable extent. TBT homocoupling preferentially occurs under phosphine-free conditions but can be suppressed in the presence of a phosphine ligand. Cbz homocoupling is temp.-dependent and more prevalent at higher temps. By contrast, evidence for chain branching as a result of unselective C-H arylation is not found for this monomer combination. These results emphasize that particular attention has to be paid to homocouplings in direct arylation polycondensations as a major source of main-chain defects, esp. under phosphine-free conditions.
    47. 47
      Matsidik, R.; Komber, H.; Luzio, A.; Caironi, M.; Sommer, M. Defect-free Naphthalene Diimide Bithiophene Copolymers with Controlled Molar Mass and High Performance via Direct Arylation Polycondensation. J. Am. Chem. Soc. 2015, 137, 6705– 6711,  DOI: 10.1021/jacs.5b03355
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      Defect-free Naphthalene Diimide Bithiophene Copolymers with Controlled Molar Mass and High Performance via Direct Arylation Polycondensation
      Matsidik, Rukiya; Komber, Hartmut; Luzio, Alessandro; Caironi, Mario; Sommer, Michael
      Journal of the American Chemical Society (2015), 137 (20), 6705-6711CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      A highly efficient, simple, and environmentally friendly protocol for the synthesis of an alternating naphthalene diimide bithiophene copolymer (PNDIT2) via direct arylation polycondensation (DAP) is presented. High mol. wt. (MW) PNDIT2 can be obtained in quant. yield using arom. solvents. Most crit. is the suppression of two major termination reactions of NDIBr end groups: nucleophilic substitution and solvent end-capping by arom. solvents via C-H activation. In situ solvent end-capping can be used to control MW by varying monomer concn., whereby end-capping is efficient and MW is low for low concn. and vice versa. Reducing C-H reactivity of the solvent at optimized conditions further increases MW. Chain perfection of PNDIT2 is demonstrated in detail by NMR spectroscopy, which reveals PNDIT2 chains to be fully linear and alternating. This is further confirmed by investigating the optical and thermal properties as a function of MW, which sat. at Mn ≈ 20 kDa, in agreement with controls made by Stille coupling. Field-effect transistor (FET) electron mobilities μsat up to 3 cm2/(V·s) are measured using off-center spin-coating, with FET devices made from DAP PNDIT2 exhibiting better reproducibility compared to Stille controls.
    48. 48
      Lawton, S. S. Determining the sequence and backbone structure of ‘semi-statistical’ copolymers as donor-acceptor polymers in organic solar cells. Sustain. Energy Fuels 2020, 4, 2026– 2034,  DOI: 10.1039/C9SE01261C
      There is no corresponding record for this reference.
    49. 49
      Xiao, M. Anisotropy of Charge Transport in a Uniaxially Aligned Fused Electron-Deficient Polymer Processed by Solution Shear Coating. Adv. Mater. 2020, 32, 2000063– 2000071,  DOI: 10.1002/adma.202000063
      49
      Anisotropy of Charge Transport in a Uniaxially Aligned Fused Electron-Deficient Polymer Processed by Solution Shear Coating
      Xiao, Mingfei; Kang, Boseok; Lee, Seon Baek; Perdigao, Luis M. A.; Luci, Alex; Warr, Daniel A.; Senanayak, Satyaprasad P.; Nikolka, Mark; Statz, Martin; Wu, Yutian; Sadhanala, Aditya; Schott, Sam; Carey, Remington; Wang, Qijing; Lee, Mijung; Kim, Chaewon; Onwubiko, Ada; Jellett, Cameron; Liao, Hailiang; Yue, Wan; Cho, Kilwon; Costantini, Giovanni; McCulloch, Iain; Sirringhaus, Henning
      Advanced Materials (Weinheim, Germany) (2020), 32 (23), 2000063CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Precise control of the microstructure in org. semiconductors (OSCs) is essential for developing high-performance org. electronic devices. Here, a comprehensive charge transport characterization of two recently reported rigid-rod conjugated polymers that do not contain single bonds in the main chain is reported. It is demonstrated that the mol. design of the polymer makes it possible to achieve an extended linear backbone structure, which can be directly visualized by high-resoln. scanning tunneling microscopy (STM). The rigid structure of the polymers allows the formation of thin films with uniaxially aligned polymer chains by using a simple one-step soln.-shear/bar coating technique. These aligned films show a high optical anisotropy with a dichroic ratio of up to a factor of 6. Transport measurements performed using top-gate bottom-contact field-effect transistors exhibit a high satn. electron mobility of 0.2 cm2 V-1 s-1 along the alignment direction, which is more than six times higher than the value reported in the previous work. This work demonstrates that this new class of polymers is able to achieve mobility values comparable to state-of-the-art n-type polymers and identifies an effective processing strategy for this class of rigid-rod polymer system to optimize their charge transport properties.
    50. 50
      Chen, H. The Effect of Ring Expansion in Thienobenzo[ b]indacenodithiophene Polymers for Organic Field-Effect Transistors. J. Am. Chem. Soc. 2019, 141, 18806– 18813,  DOI: 10.1021/jacs.9b09367
      50
      The Effect of Ring Expansion in Thienobenzo[b]indacenodithiophene Polymers for Organic Field-Effect Transistors
      Chen, Hu; Wadsworth, Andrew; Ma, Chun; Nanni, Alice; Zhang, Weimin; Nikolka, Mark; Luci, Alexander M. T.; Perdigao, Luis M. A.; Thorley, Karl J.; Cendra, Camila; Larson, Bryon; Rumbles, Garry; Anthopoulos, Thomas D.; Salleo, Alberto; Costantini, Giovanni; Sirringhaus, Henning; McCulloch, Iain
      Journal of the American Chemical Society (2019), 141 (47), 18806-18813CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      A fused donor, thienobenzo[b]indacenodithiophene (TBIDT), was designed and synthesized using a novel acid-promoted cascade ring closure strategy, and copolymd. with a benzothiadiazole (BT) monomer. The backbone of TBIDT is an expansion of the well-known indacenodithiophene (IDT) unit and was expected to enhance the charge carrier mobility, by improving backbone planarity and facilitating short-contacts between polymer chains. However, the optimized field-effect transistors demonstrated an av. satn. hole mobility of 0.9 cm2 V-1s-1, lower than the performance of IDT-BT (∼1.5 cm2 V-1s-1). Mobilities extd. from time-resolved microwave cond. (TRMC) measurements were consistent with the trend in hole mobilities in OFET devices. Scanning Tunneling Microscopy (STM) measurements and computational modeling illustrated that TBIDT-BT exhibits a less ordered microstructure in comparison to IDT-BT. This reveals that a regular side chain packing d., independent of conformational isomers, is crit. to avoid local free vol. due to irregular packing, which can host trapping impurities. DFT calcns. indicated that TBIDT-BT, despite contg. a larger, planar unit, showed less stabilization of planar backbone geometries, in comparison to IDT-BT. This is due to the reduced electrostatic stabilizing inter-actions between the peripheral thiophene of the fused core with the BT unit, resulting in a redn. of the barrier to rotation around the single bond. These insights provide a greater understanding of the general structure-property relationships required for semiconducting polymer repeat units to ensure optimal backbone planarization, as illustrated with IDT-type units, guiding the design of novel semiconducting polymers with extended fused backbones for high-performance field-effect transistors.
    51. 51
      Warr, D. A. Sequencing conjugated polymers by eye. Sci. Adv. 2018, 4, eaas9543  DOI: 10.1126/sciadv.aas9543
      There is no corresponding record for this reference.
    52. 52
      Ponder, J. F. Low-Defect, High Molecular Weight Indacenodithiophene (IDT) Polymers Via a C-H Activation: Evaluation of a Simpler and Greener Approach to Organic Electronic Materials. ACS Mater. Lett. 2021, 3, 1503– 1512,  DOI: 10.1021/acsmaterialslett.1c00478
      52
      Low-Defect, High Molecular Weight Indacenodithiophene (IDT) Polymers Via a C-H Activation: Evaluation of a Simpler and Greener Approach to Organic Electronic Materials
      Ponder Jr, James F.; Chen, Hu; Luci, Alexander M. T.; Moro, Stefania; Turano, Marco; Hobson, Archie L.; Collier, Graham S.; Perdigao, Luis M. A.; Moser, Maximilian; Zhang, Weimin; Costantini, Giovanni; Reynolds, John R.; McCulloch, Iain
      ACS Materials Letters (2021), 3 (10), 1503-1512CODEN: AMLCEF; ISSN:2639-4979. (American Chemical Society)
      The development, optimization, and assessment of new methods for the prepn. of conjugated materials is key to the continued progress of org. electronics. Direct C-H activation methods have emerged and developed over the last 10 years to become an invaluable synthetic tool for the prepn. of conjugated polymers for both redox-active and solid-state applications. Here, we evaluate direct (hetero)arylation polymn. (DHAP) methods for the synthesis of indaceno[1,2-b:5,6-b']dithiophene-based polymers. We demonstrate, using a range of techniques, including direct visualization of individual polymer chains via high-resoln. scanning tunneling microscopy, that DHAP can produce polymers with a high degree of regularity and purity that subsequently perform in org. thin-film transistors comparably to those made by other cross-coupling polymns. that require increased synthetic complexity. Ultimately, this work results in an improved atom economy by reducing the no. of synthetic steps to access high-performance mol. and polymeric materials.
    53. 53
      Hallani, R. K. Regiochemistry-Driven Organic Electrochemical Transistor Performance Enhancement in Ethylene Glycol-Functionalized Polythiophenes. J. Am. Chem. Soc. 2021, 143, 11007– 11018,  DOI: 10.1021/jacs.1c03516
      53
      Regiochemistry-Driven Organic Electrochemical Transistor Performance Enhancement in Ethylene Glycol-Functionalized Polythiophenes
      Hallani, Rawad K.; Paulsen, Bryan D.; Petty, Anthony J.; Sheelamanthula, Rajendar; Moser, Maximilian; Thorley, Karl J.; Sohn, Wonil; Rashid, Reem B.; Savva, Achilleas; Moro, Stefania; Parker, Joseph P.; Drury, Oscar; Alsufyani, Maryam; Neophytou, Marios; Kosco, Jan; Inal, Sahika; Costantini, Giovanni; Rivnay, Jonathan; McCulloch, Iain
      Journal of the American Chemical Society (2021), 143 (29), 11007-11018CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      Novel p-type semiconducting polymers that can facilitate ion penetration, and operate in accumulation mode are much desired in bioelectronics. Glycol side chains have proven to be an efficient method to increase bulk electrochem. doping and optimize aq. swelling. One early polymer which exemplifies these design approaches was p(g2T-TT), employing a bithiophene-co-thienothiophene backbone with glycol side chains in the 3,3' positions of the bithiophene repeat unit. In this paper, the analogous regioisomeric polymer, namely pgBTTT, was synthesized by relocating the glycol side chains position on the bithiophene unit of p(g2T-TT) from the 3,3' to the 4,4' positions and compared with the original p(g2T-TT). By changing the regio-positioning of the side chains, the planarizing effects of the S--O interactions were redistributed along the backbone, and the influence on the polymer's microstructure organization was investigated using grazing-incidence wide-angle X-ray scattering (GIWAXS) measurements. The newly designed pgBTTT exhibited lower backbone disorder, closer π-stacking, and higher scattering intensity in both the in-plane and out-of-plane (GIWAXS) measurements. The effect of the improved planarity of pgBTTT manifested as higher hole mobility (μ) of 3.44 ± 0.13 cm2 V-1 s-1. Scanning tunneling microscopy (STM) was in agreement with the GIWAXS measurements and demonstrated, for the first time, that glycol side chains can also facilitate intermol. interdigitation analogous to that of pBTTT. Electrochem. quartz crystal microbalance with dissipation of energy (eQCM-D) measurements revealed that pgBTTT maintains a more rigid structure than p(g2T-TT) during doping, minimizing mol. packing disruption and maintaining higher hole mobility in operation mode.
    54. 54
      Moro, S. The Effect of Glycol Side Chains on the Assembly and Microstructure of Conjugated Polymers. ACS Nano 2022, 16, 21303– 21314,  DOI: 10.1021/acsnano.2c09464
      54
      The Effect of Glycol Side Chains on the Assembly and Microstructure of Conjugated Polymers
      Moro, Stefania; Siemons, Nicholas; Drury, Oscar; Warr, Daniel A.; Moriarty, Thomas A.; Perdigao, Luis M. A.; Pearce, Drew; Moser, Maximilian; Hallani, Rawad K.; Parker, Joseph; McCulloch, Iain; Frost, Jarvist M.; Nelson, Jenny; Costantini, Giovanni
      ACS Nano (2022), 16 (12), 21303-21314CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
      Conjugated polymers with polar side chains, such as ethylene glycol chains, are emerging as a material class with promising applications as org. mixed ionic-electronic conductors, particularly in bioelectronics and thermoelecs. However, very little is still known about their microstructure and the role of the side chains in detg. intermol. interactions and polymer packing. Here, we use the combination of electrospray deposition and scanning tunnelling microscopy to det. the microstructure of prototypical glycolated conjugated polymers (pgBTTT and p(g2T-TT)) with submonomer resoln. Mol. dynamics simulations of the same surface-adsorbed polymers exhibit an excellent agreement with the exptl. images, allowing us to extend the characterization of the polymers to the at. scale. Our results prove that, similarly to their alkylated counterparts, glycolated polymers assemble through interdigitation of their side chains although significant differences are found in their conformation and interaction patterns. A model is proposed that identifies the driving force for the polymer assembly in the tendency of the side chains to adopt the conformation of their free analogs, i.e. polyethylene and polyethylene glycol, for alkyl or ethylene glycol side chains, resp. For both classes of polymers, it is also demonstrated that the backbone conformation is detd. to a higher degree by the interaction between the side chains rather than by the backbone torsional potential energy. The generalization of these findings from 2D monolayers to 3D thin films is discussed, together with the opportunity to use this type of 2D study to gain so far inaccessible, subnm scale information on the microstructure of conjugated polymers.
    55. 55
      Nielsen, C. B.; Turbiez, M.; McCulloch, I. Recent advances in the development of semiconducting DPP-containing polymers for transistor applications. Adv. Mater. 2013, 25, 1859– 1880,  DOI: 10.1002/adma.201201795
      55
      Recent Advances in the Development of Semiconducting DPP-Containing Polymers for Transistor Applications
      Nielsen, Christian B.; Turbiez, Mathieu; McCulloch, Iain
      Advanced Materials (Weinheim, Germany) (2013), 25 (13), 1859-1880CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
      A review. This progress report summarizes the numerous DPP-contg. polymers recently developed for field-effect transistor applications including diphenyl-DPP and dithienyl-DPP-based polymers as the most commonly reported materials, but also difuranyl-DPP, diselenophenyl-DPP and dithienothienyl-DPP-contg. polymers. The hole and electron mobilities that are reported in relation to structural properties such as alkyl substitution patterns, polymer mol. wts. and solid state packing, as well as electronic properties including HOMO and LUMO energy levels are discussed. The authors also consider important aspects of ambipolar charge transport and highlight fundamental structure-property relations such as the relations between the thin film morphologies and the charge carrier mobilities obsd. for DPP-contg. polymers.
    56. 56
      Genene, Z.; Mammo, W.; Wang, E.; Andersson, M. R. Recent Advances in n-Type Polymers for All-Polymer Solar Cells. Adv. Mater. 2019, 31, 1807275  DOI: 10.1002/adma.201807275
      There is no corresponding record for this reference.
    57. 57
      Luzio, A. Microstructural control suppresses thermal activation of electron transport at room temperature in polymer transistors. Nat. Commun. 2019, 10, 3365,  DOI: 10.1038/s41467-019-11125-9
      57
      Microstructural control suppresses thermal activation of electron transport at room temperature in polymer transistors
      Luzio Alessandro; Caironi Mario; Nubling Fritz; Sommer Michael; Martin Jaime; Martin Jaime; Fazzi Daniele; Selter Philipp; Hansen Michael Ryan; Gann Eliot; McNeill Christopher R; Gann Eliot; Gann Eliot; Brinkmann Martin; Stingelin Natalie
      Nature communications (2019), 10 (1), 3365 ISSN:.
      Recent demonstrations of inverted thermal activation of charge mobility in polymer field-effect transistors have excited the interest in transport regimes not limited by thermal barriers. However, rationalization of the limiting factors to access such regimes is still lacking. An improved understanding in this area is critical for development of new materials, establishing processing guidelines, and broadening of the range of applications. Here we show that precise processing of a diketopyrrolopyrrole-tetrafluorobenzene-based electron transporting copolymer results in single crystal-like and voltage-independent mobility with vanishing activation energy above 280 K. Key factors are uniaxial chain alignment and thermal annealing at temperatures within the melting endotherm of films. Experimental and computational evidences converge toward a picture of electrons being delocalized within crystalline domains of increased size. Residual energy barriers introduced by disordered regions are bypassed in the direction of molecular alignment by a more efficient interconnection of the ordered domains following the annealing process.
    58. 58
      Shivhare, R. Alkyl Branching Position in Diketopyrrolopyrrole Polymers: Interplay between Fibrillar Morphology and Crystallinity and Their Effect on Photogeneration and Recombination in Bulk-Heterojunction Solar Cells. Chem. Mater. 2018, 30, 6801– 6809,  DOI: 10.1021/acs.chemmater.8b02739
      58
      Alkyl Branching Position in Diketopyrrolopyrrole Polymers: Interplay between Fibrillar Morphology and Crystallinity and Their Effect on Photogeneration and Recombination in Bulk-Heterojunction Solar Cells
      Shivhare, Rishi; Erdmann, Tim; Hoermann, Ulrich; Collado-Fregoso, Elisa; Zeiske, Stefan; Benduhn, Johannes; Ullbrich, Sascha; Huebner, Rene; Hambsch, Mike; Kiriy, Anton; Voit, Brigitte; Neher, Dieter; Vandewal, Koen; Mannsfeld, Stefan C. B.
      Chemistry of Materials (2018), 30 (19), 6801-6809CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
      Diketopyrrolopyrrole (DPP)-based donor-acceptor copolymers have gained a significant amt. of research interest in the org. electronics community because of their high charge carrier mobilities in org. field-effect transistors (OFETs) and their ability to harvest near-IR (NIR) photons in solar cells. Here, we have synthesized 4 DPP-based donor-acceptor copolymers with variations in the donor unit and the branching point of the solubilizing alkyl chains (at the 2nd or 6th C position). Grazing incidence wide-angle x-ray scattering (GIWAXS) results suggest that moving the branching point further away from the polymer backbone increases the tendency for aggregation and yields polymer phases with a higher degree of crystallinity (DoC). The polymers were blended with PC70BM and used as active layers in solar cells. A careful anal. of the energetics of the neat polymer and blend films reveals that the charge-transfer state energy (ECT) of the blend films lies exceptionally close to the singlet energy of the donor (ED*), indicating near zero electron transfer losses. The difference between the optical gap and open-circuit voltage (VOC) is therefore detd. to be due to rather high nonradiative (∼418±13 mV) and unavoidable radiative voltage losses (∼255±8 mV). Even though the 4 materials have similar optical gaps, the short-circuit c.d. (JSC) covers a vast span from 7 to 18 mA/cm2 for the best performing system. Using photoluminescence (PL) quenching and transient charge extn. techniques, we quantify geminate and nongeminate losses and find that fewer excitons reach the donor-acceptor interface in polymers with further away branching points due to larger aggregate sizes. In these material systems, the photogeneration is therefore mainly limited by exciton harvesting efficiency.
    59. 59
      Back, J. Y. Investigation of structure-property relationships in diketopyrrolopyrrole-based polymer semiconductors via side-chain engineering. Chem. Mater. 2015, 27, 1732– 1739,  DOI: 10.1021/cm504545e
      59
      Investigation of Structure-Property Relationships in Diketopyrrolopyrrole-Based Polymer Semiconductors via Side-Chain Engineering
      Back, Jang Yeol; Yu, Hojeong; Song, Inho; Kang, Il; Ahn, Hyungju; Shin, Tae Joo; Kwon, Soon-Ki; Oh, Joon Hak; Kim, Yun-Hi
      Chemistry of Materials (2015), 27 (5), 1732-1739CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
      Systematic side-chain engineering has been performed for diketopyrrolopyrrole-selenophene vinylene selenophene (DPP-SVS) polymers to det. the optimal side-chain geometries for the most efficient charge transport, and the structure-property relationship has been thoroughly investigated using a range of analyses. A series of DPP-SVS polymers, ranging from 25-DPP-SVS to 32-DPP-SVS, with branched alkyl groups contg. linear spacer groups from C2 to C9 has been synthesized, and the elec. performance of these polymers is significantly dependent on both the length of the spacer group and its odd-even characteristics. Spacer groups with even nos. of carbon atoms exhibit charge-carrier mobilities that are 1 order of magnitude higher than those with odd nos. of carbon atoms. The optimized charge transport has been obtained from 29-DPP-SVS with a C6 spacer, showing the max. mobility of 13.9 cm2 V-1 s-1 (VGS, VDS = -100 V) and 17.8 cm2 V-1 s-1 (VGS, VDS = -150 V). Longer spacer groups deviate from the odd-even trend. In addn. to the exceptionally high charge-carrier mobilities of the DPP-SVS polymers, the results obtained herein provide new insight into the mol. design of high-performance polymer semiconductors.
    60. 60
      Meager, I. Photocurrent enhancement from diketopyrrolopyrrole polymer solar cells through alkyl-chain branching point manipulation. J. Am. Chem. Soc. 2013, 135, 11537– 11540,  DOI: 10.1021/ja406934j
      60
      Photocurrent Enhancement from Diketopyrrolopyrrole Polymer Solar Cells through Alkyl-Chain Branching Point Manipulation
      Meager, Iain; Ashraf, Raja Shahid; Mollinger, Sonya; Schroeder, Bob C.; Bronstein, Hugo; Beatrup, Daniel; Vezie, Michelle S.; Kirchartz, Thomas; Salleo, Alberto; Nelson, Jenny; McCulloch, Iain
      Journal of the American Chemical Society (2013), 135 (31), 11537-11540CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      Systematically moving the alkyl-chain branching position away from the polymer backbone afforded 2 new thieno[3,2-b]thiophene-diketopyrrolopyrrole (DPPTT-T) polymers. When used as donor materials in polymer:fullerene solar cells, efficiencies exceeding 7% were achieved without the use of processing additives. The effect of the position of the alkyl-chain branching point on the thin-film morphol. was studied using x-ray scattering techniques and the effects on the photovoltaic and charge-transport properties were also studied. For both solar cell and transistor devices, moving the branching point further from the backbone was beneficial. This is the 1st time that this effect was shown to improve solar cell performance. Strong evidence is presented for changes in microstructure across the series, which is most likely the cause for the photocurrent enhancement.
    61. 61
      Wang, Q. Hydrogen Bonds Control Single-Chain Conformation, Crystallinity, and Electron Transport in Isoelectronic Diketopyrrolopyrrole Copolymers. Chem. Mater. 2021, 33, 2635– 2645,  DOI: 10.1021/acs.chemmater.1c00478
      61
      Hydrogen Bonds Control Single-Chain Conformation, Crystallinity, and Electron Transport in Isoelectronic Diketopyrrolopyrrole Copolymers
      Wang, Qian; Boeckmann, Steffen; Guenther, Florian; Streiter, Martin; Zerson, Mario; Scaccabarozzi, Alberto D.; Tan, Wen Liang; Komber, Hartmut; Deibel, Carsten; Magerle, Robert; Gemming, Sibylle; McNeill, Christopher R.; Caironi, Mario; Hansen, Michael Ryan; Sommer, Michael
      Chemistry of Materials (2021), 33 (7), 2635-2645CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
      The combination of computational methods and advanced characterization techniques is used to highlight the role of the intramol. hydrogen bond in thienyldiketopyrrolopyrrole (ThDPPTh) copolymd. with tetrafluorobenzene (F4) to PThDPPThF4. We investigate how the torsion potentials of ThDPPTh and isoelectronic dithiazolyldiketopyrrolopyrrole (TzDPPTz) are influenced by hydrogen bonding and translate into different conformation, mol., structural, and opto-electronic characteristics. ThDPPTh exhibits N,S-syn orientation in the most stable conformer locked by an intramol. hydrogen bond. In TzDPPTz, such a hydrogen bond is not possible, which leads to a "ring flip" and makes the N,S-anti conformer most stable. Copolymers with F4, PThDPPThF4 and PTzDPPTzF4, exhibit straight and curved backbones, resp., but similar chain rigidity. These conformations are exptl. confirmed by local packing motifs from solid-state NMR spectroscopy. The differences in conformation strongly influence the opto-electronic and structural properties. X-ray scattering and at. force microscopy reveal lamellar morphologies of both PThDPPThF4 and PTzDPPTzF4, but increased long range order, reduced paracrystallinity, and larger domains of the former. In-depth anal. of solid-state NMR spectra allows for obtaining information on abs. degrees of crystallinity, which are substantially higher for PThDPPThF4. These differences in structural properties cause field-effect electron mobilities of PThDPPThF4 to be larger by a factor of 20.
    62. 62
      O’Shea, J. N. Electrospray deposition of carbon nanotubes in vacuum. Nanotechnology 2007, 18, 035707  DOI: 10.1088/0957-4484/18/3/035707
      There is no corresponding record for this reference.
    63. 63
      Räder, H. J.; Nguyen, T. T. T.; Müllen, K. MALDI-TOF mass spectrometry of polyphenylene dendrimers up to the megadalton range. elucidating structural integrity of macromolecules at unrivaled high molecular weights. Macromolecules 2014, 47, 1240– 1248,  DOI: 10.1021/ma402347y
      There is no corresponding record for this reference.
    64. 64
      Cox, D. R.; Oakes, D. Analysis of survival data. Monographs on Statistics and Applied Probability 21; CHAPMAN & HALL/CRC: New York, 2018.
      There is no corresponding record for this reference.
    65. 65
      Horcas, I. WSXM: A software for scanning probe microscopy and a tool for nanotechnology. Rev. Sci. Instrum. 2007, 78, 013705– 013713,  DOI: 10.1063/1.2432410
      65
      WSXM: a software for scanning probe microscopy and a tool for nanotechnology
      Horcas, I.; Fernandez, R.; Gomez-Rodriguez, J. M.; Colchero, J.; Gomez-Herrero, J.; Baro, A. M.
      Review of Scientific Instruments (2007), 78 (1), 013705/1-013705/8CODEN: RSINAK; ISSN:0034-6748. (American Institute of Physics)
      In this work we briefly describe the most relevant features of WSXM, a freeware scanning probe microscopy software based on MS-Windows. The article is structured in three different sections: The introduction is a perspective on the importance of software on scanning probe microscopy. The second section is devoted to describe the general structure of the application; in this section the capabilities of WSXM to read third party files are stressed. Finally, a detailed discussion of some relevant procedures of the software is carried out.
    66. 66
      Nečas, D.; Klapetek, P. Gwyddion: An open-source software for SPM data analysis. Cent. Eur. J. Phys. 2012, 10, 181– 188,  DOI: 10.2478/s11534-011-0096-2
      There is no corresponding record for this reference.
    67. 67
      Hanwell, M. D. Avogadro: An advanced semantic chemical editor, visualization, and analysis platform. J. Cheminform. 2021, 4, 1– 17,  DOI: 10.1186/1758-2946-4-17
      There is no corresponding record for this reference.
    68. 68
      LMAPper - The SPM and Mol Viewer | https://sourceforge.net/projects/spm-and-mol-viewer/. Accessed on 22.03.2024.
      There is no corresponding record for this reference.

  • Supporting Information

    Supporting Information

    The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsnano.3c10842.

    • Further details on the experimental and synthetic methods, STM images displaying different molecular coverages and the assembly and modeling of P2 polymers, molecular models and procedure used for fitting the STM images, details of the quantitative analysis of the NMR spectra, procedure for determining polymer length profiles from STM images, survival analysis method used to correct the polymer length distributions, discussion of effective extents of reaction, SEC analysis details, UV–vis spectroscopy data, method for calculating average values from distributions (PDF)


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