Enhanced Organic Electrochemical Transistor Performance of Donor–Acceptor Conjugated Polymers Modified with Hybrid Glycol/Ionic Side Chains by Postpolymerization Modification

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This article references 49 other publications.

1. 1

   Paudel, P. R.; Tropp, J.; Kaphle, V.; Azoulay, J. D.; Lüssem, B. Organic electrochemical transistors – from device models to a targeted design of materials. J. Mater. Chem. C 2021, 9, 9761,  DOI: 10.1039/D1TC01601F

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   Organic electrochemical transistors - from device models to a targeted design of materials

   Paudel, Pushpa Raj; Tropp, Joshua; Kaphle, Vikash; Azoulay, Jason David; Lussem, Bjorn

   Journal of Materials Chemistry C: Materials for Optical and Electronic Devices (2021), 9 (31), 9761-9790CODEN: JMCCCX; ISSN:2050-7534. (Royal Society of Chemistry)

   A review. Org. electrochem. transistors (OECTs) are highly versatile in terms of their form factor, fabrication approach that can be applied, and freedom in the choice of substrate material. Their ability to transduce ionic into elec. signals and the use of bio-compatible org. materials makes them ideally suited for a wide range of applications, in particular in areas where electronic circuits are interfaced with biol. matter. OECT technol. has attracted widespread interest in recent years, which has been accompanied by a steady increase in its performance. However, this progress was mainly driven by device optimization and less by targeting the design of new device geometries and OECT materials. To narrow this gap, this provides an overview on the different device models that are used to explain the underlying physics governing the steady and transient behavior of OECTs. We show how the models can be used to identify synthetic targets to produce higher performing OECT materials and summarize recently reported materials classes. Overall, a road-map of future research in new device models and material design is presented summarizing the most pressing open questions in the understanding of OECTs.
2. 2

   Shi, J.; Li, P.; Deng, X.-Y.; Xu, J.; Huang, Z.; Lei, Y.; Wang, Y.; Wang, J.-Y.; Gu, X.; Lei, T. Revealing the Role of Polaron Distribution on the Performance of n-Type Organic Electrochemical Transistors. Chem. Mater. 2022, 34, 864,  DOI: 10.1021/acs.chemmater.1c04037

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   Revealing the Role of Polaron Distribution on the Performance of n-Type Organic Electrochemical Transistors

   Shi, Junwei; Li, Peiyun; Deng, Xin-Yu; Xu, Jingcao; Huang, Zhen; Lei, Yuqiu; Wang, Yunfei; Wang, Jie-Yu; Gu, Xiaodan; Lei, Ting

   Chemistry of Materials (2022), 34 (2), 864-872CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)

   Org. electrochem. transistors (OECTs) have shown great potential in bioelectronics and neuromorphic computing. However, the low performance of n-type OECTs impedes the construction of complementary-type circuits for low-power-consumption logic circuits and high-performance sensing. Compared with their p-type counterparts, the low electron mobility of n-type OECT materials is the primary challenge, leading to low μC* and slow response speed. Nevertheless, no successful method has been reported to address the issue. Here, we find that the charge carrier mobility of n-type OECTs can be significantly enhanced by redistributing the polarons on the polymer backbone. As a result, 1 order of magnitude higher electron mobility is achieved in a new polymer, P(gPzDPP-CT2), with a simultaneously enhanced μC* value and faster response speed. This work reveals the important role of polaron distribution in enhancing the performance of n-type OECTs.
3. 3

   Cong, S.; Chen, J.; Wang, L.; Lan, L.; Wang, Y.; Dai, H.; Liao, H.; Zhou, Y.; Yu, Y.; Duan, J.; Li, Z.; McCulloch, I.; Yue, W. Donor Functionalization Tuning the N-Type Performance of Donor–Acceptor Copolymers for Aqueous-Based Electrochemical Devices. Adv. Funct. Mater. 2022, 32, 2201821,  DOI: 10.1002/adfm.202201821

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   Donor Functionalization Tuning the N-Type Performance of Donor-Acceptor Copolymers for Aqueous-Based Electrochemical Devices

   Cong, Shengyu; Chen, Junxin; Wang, Lewen; Lan, Liuyuan; Wang, Yazhou; Dai, Haojie; Liao, Hailiang; Zhou, Yecheng; Yu, Yaping; Duan, Jiayao; Li, Zhengke; McCulloch, Iain; Yue, Wan

   Advanced Functional Materials (2022), 32 (29), 2201821CODEN: AFMDC6; ISSN:1616-301X. (Wiley-VCH Verlag GmbH & Co. KGaA)

   In this work, three n-type donor-acceptor copolymers consisting of glycolated naphthalene tetracarboxylicdiimide (gNDI) coupled with variable donating companion moieties are reported. Using 2,2'-bis(3,4-ethylenedioxy)bithiophene, 2, 2'- bithiophene, 3,3'-difluoro-2,2'-bithiophene (FBT), the donating strength of the donor units is systematically functionalized. These copolymers are used as a platform for aq.-based electrochem. devices, including energy-storage devices, electrochromic devices (ECDs), and org. electrochem. transistors (OECTs). It is found that the electrochem. redox stability and electron mobility of copolymers are significantly improved via weakening the electron-donating strength of donor units. The gNDI coupling with FBT (gNDI-FBT) exhibits a charge-storage capacity exceeding 190 Fg-1, which is the highest value reported to date for NDI-based polymer electrodes in aq. media. For ECDs, gNDI-FBT remains 100% of initial electrochromism contrast (Δ%T = 20%) up to 1200 s. In addn., gNDI-FBT outperforms its two analogs in OECTs, including lower threshold voltage (0.19 V), faster response time (45.5 ms), and higher volumetric capacitance (197 F cm-3). Moreover, gNDI-FBT with fluorine atoms leads to the bipolarons delocalization along the polymer backbone and favorable mol. packing for ion-electron transport. Through such weak donor functionalization strategy, this work provides ways for n-type copolymers tuning to access desirable performance metrics in optical, electrochem., and bioelectronic applications.
4. 4

   Nawaz, A.; Liu, Q.; Leong, W. L.; Fairfull-Smith, K. E.; Sonar, P. Organic Electrochemical Transistors for In Vivo Bioelectronics. Adv. Mater. 2021, 33, 2101874,  DOI: 10.1002/adma.202101874

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   Organic Electrochemical Transistors for In Vivo Bioelectronics

   Nawaz, Ali; Liu, Qian; Leong, Wei Lin; Fairfull-Smith, Kathryn E.; Sonar, Prashant

   Advanced Materials (Weinheim, Germany) (2021), 33 (49), 2101874CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)

   A review. Org. electrochem. transistors (OECTs) are presently a focus of intense research and hold great potential in expanding the horizons of the bioelectronics industry. The notable characteristics of OECTs, including their electrolyte-gating, which offers intimate interfacing with biol. environments, and aq. stability, make them particularly suitable to be operated within a living organism (in vivo). Unlike the existing in vivo bioelectronic devices, mostly based on rigid metal electrodes, OECTs form a soft mech. contact with the biol. milieu and ensure a high signal-to-noise ratio because of their powerful amplification capability. Such features make OECTs particularly desirable for a wide range of in vivo applications, including electrophysiol. recordings, neuron stimulation, and neurotransmitter detection, and regulation of plant processes in vivo. In this review, a systematic compilation of the in vivo applications is presented that are addressed by the OECT technol. First, the operating mechanisms, and the device design and materials design principles of OECTs are examd., and then multiple examples are provided from the literature while identifying the unique device properties that enable the application progress. Finally, one critically looks at the future of the OECT technol. for in vivo bioelectronic applications.
5. 5

   Lee, H.; Won, Y.; Oh, J. H. Neuromorphic bioelectronics based on semiconducting polymers. J. Polym. Sci. 2022, 60, 348,  DOI: 10.1002/pol.20210502

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   Neuromorphic bioelectronics based on semiconducting polymers

   Lee, HaeRang; Won, Yousang; Oh, Joon Hak

   Journal of Polymer Science (Hoboken, NJ, United States) (2022), 60 (3), 348-376CODEN: JPSHBC; ISSN:2642-4169. (John Wiley & Sons, Inc.)

   A review. The recent development of neuromorphic devices with low power consumption and rapid response has been driven primarily by the growing demand for brain-inspired computing in human-like machines and human-machine interfaces. Remarkable progress has been made in developing neuromorphic bioelectronics that combine neuromorphic devices with electronic sensors. In this review, we provide an overview of semiconducting polymer-based neuromorphic devices and their applications in neuromorphic bioelectronics. We focus on recent advances in semiconducting polymer-based three-terminal artificial synapses that mimic neural communication behaviors. Various types of semiconducting polymers and synaptic platforms have been investigated, allowing significant improvement in their performance and expansion of their functionality. Proper selection of materials and device structures can help artificial sensory synapses to react to various external stimuli and to further modulate elec. signals. Advances in semiconducting polymer-based neuromorphic bioelectronics will accelerate the commercialization of human-machine interfacial systems, including intelligent prosthetics and implantable diagnostic devices.
6. 6

   Janzakova, K.; Ghazal, M.; Kumar, A.; Coffinier, Y.; Pecqueur, S.; Alibart, F. Dendritic Organic Electrochemical Transistors Grown by Electropolymerization for 3D Neuromorphic Engineering. Adv. Sci. 2021, 8, 2102973,  DOI: 10.1002/advs.202102973

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   Dendritic Organic Electrochemical Transistors Grown by Electropolymerization for 3D Neuromorphic Engineering

   Janzakova, Kamila; Ghazal, Mahdi; Kumar, Ankush; Coffinier, Yannick; Pecqueur, Sebastien; Alibart, Fabien

   Advanced Science (Weinheim, Germany) (2021), 8 (24), 2102973CODEN: ASDCCF; ISSN:2198-3844. (Wiley-VCH Verlag GmbH & Co. KGaA)

   One of the major limitations of std. top-down technologies used in today's neuromorphic engineering is their inability to map the 3D nature of biol. brains. Here, it is shown how bipolar electropolymn. can be used to engineer 3D networks of PEDOT:PSS dendritic fibers. By controlling the growth conditions of the electropolymd. material, it is investigated how dendritic fibers can reproduce structural plasticity by creating structures of controllable shape. Gradual topologies evolution is demonstrated in a multielectrode configuration. A detailed elec. characterization of the PEDOT:PSS dendrites is conducted through DC and impedance spectroscopy measurements and it is shown how org. electrochem. transistors (OECT) can be realized with these structures. These measurements reveal that quasi-static and transient response of OECTs can be adjusted by controlling dendrites' morphologies. The unique properties of org. dendrites are used to demonstrate short-term, long-term, and structural plasticity, which are essential features required for future neuromorphic hardware development.
7. 7

   Cucchi, M.; Kleemann, H.; Tseng, H.; Ciccone, G.; Lee, A.; Pohl, D.; Leo, K. Directed Growth of Dendritic Polymer Networks for Organic Electrochemical Transistors and Artificial Synapses. Adv. Electron. Mater. 2021, 7, 2100586,  DOI: 10.1002/aelm.202100586

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   Directed Growth of Dendritic Polymer Networks for Organic Electrochemical Transistors and Artificial Synapses

   Cucchi, Matteo; Kleemann, Hans; Tseng, Hsin; Ciccone, Giuseppe; Lee, Alexander; Pohl, Darius; Leo, Karl

   Advanced Electronic Materials (2021), 7 (10), 2100586CODEN: AEMDBW; ISSN:2199-160X. (Wiley-VCH Verlag GmbH & Co. KGaA)

   Org. electrochem. transistors (OECTs) are an emerging class of devices which operate in electrolytic soln. and show controllable memory effects. For these reasons, OECT hold great potential for applications in bioelectronics and neuromorphic computing. Among the methods proposed to fabricate OECT channels, electropolymn. stands out because it allows to produce elec. connections on the substrates on-demand and further modify them to adjust their elec. properties to meet circuit requirements. However, the practical application of this method is hampered by the difficulty in controlling the growth direction as well as the morphol. of the film, resulting in a large device-to-device variability and limiting the down-scaling of the devices. In this study, AC-electropolymn. is proposed to produce directionally controlled channels. The method allows to adjust phys. properties such as resistance and capacitance by varying the polymn. parameters, such as voltage, frequency, and salt concn. The growth mechanism, material morphol., and network topol. is investigated, and the advantages of this approach by showing tunable neuromorphic features and the possibility to scale down the channels to the micrometer scale is demonstrated.
8. 8

   Kim, Y.; Kim, G.; Ding, B.; Jeong, D.; Lee, I.; Park, S.; Kim, B. J.; McCulloch, I.; Heeney, M.; Yoon, M.-H. High-Current-Density Organic Electrochemical Diodes Enabled by Asymmetric Active Layer Design. Adv. Mater. 2022, 34, 2107355,  DOI: 10.1002/adma.202107355

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   High-Current-Density Organic Electrochemical Diodes Enabled by Asymmetric Active Layer Design

   Kim, Youngseok; Kim, Gunwoo; Ding, Bowen; Jeong, Dahyun; Lee, Inho; Park, Sungjun; Kim, Bumjoon J.; McCulloch, Iain; Heeney, Martin; Yoon, Myung-Han

   Advanced Materials (Weinheim, Germany) (2022), 34 (7), 2107355CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)

   Owing to their outstanding elec./electrochem. performance, operational stability, mech. flexibility, and decent biocompatibility, org. mixed ionic-electronic conductors have shown great potential as implantable electrodes for neural recording/stimulation and as active channels for signal switching/amplifying transistors. Nonetheless, no studies exist on a general design rule for high-performance electrochem. diodes, which are essential for highly functional circuit architectures. In this work, generalizable electrochem. diodes with a very high c.d. over 30 kA cm-2 are designed by introducing an asym. active layer based on org. mixed ionic-electronic conductors. The underlying mechanism on polarity-sensitive balanced ionic doping/dedoping is elucidated by numerical device anal. and in operando spectroelectrochem. potential mapping, while the general material requirements for electrochem. diode operation are deduced using various types of conjugated polymers. In parallel, analog signal rectification and digital logic processing circuits are successfully demonstrated to show the broad impact of circuits incorporating org. electrochem. diodes. It is expected that org. electrochem. diodes will play vital roles in realizing multifunctional soft bioelectronic circuitry in combination with org. electrochem. transistors.
9. 9

   Rivnay, J.; Inal, S.; Salleo, A.; Owens, R. M.; Berggren, M.; Malliaras, G. G. Organic electrochemical transistors. Nat. Rev. Mater. 2018, 3, 17086,  DOI: 10.1038/natrevmats.2017.86

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   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.
10. 10

    Kim, J. H.; Kim, S.-M.; Kim, G.; Yoon, M.-H. Designing Polymeric Mixed Conductors and Their Application to Electrochemical-Transistor-Based Biosensors. Macromol. Biosci. 2020, 20, 2000211,  DOI: 10.1002/mabi.202000211

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    Designing Polymeric Mixed Conductors and Their Application to Electrochemical-Transistor-Based Biosensors

    Kim, Ji Hwan; Kim, Seong-Min; Kim, Gunwoo; Yoon, Myung-Han

    Macromolecular Bioscience (2020), 20 (11), 2000211CODEN: MBAIBU; ISSN:1616-5187. (Wiley-VCH Verlag GmbH & Co. KGaA)

    A review. Org. electrochem. transistors that employ polymeric mixed conductors as their active channels are one of the most prominent biosensor platforms because of their signal amplification capability, low fabrication cost, mech. flexibility, and various properties tunable through mol. design. For application to biomedical devices, polymeric mixed conductors should fulfill several requirements, such as excellent conductivities of both holes/electrons and ions, long-term operation stability, and decent biocompatibility. However, trade-offs may exist, for instance, one between ionic conduction and overall device stability. In this report, the fundamental understanding of polymeric mixed conductors, the recent advance in enhancing their ionic and elec. cond., and their practical applications as biosensors based on org. electrochem. transistors are reviewed. Finally, key strategies are suggested for developing novel polymeric mixed conductors that may exceed the trade-off between device performance and stability.
11. 11

    Paulsen, B. D.; Tybrandt, K.; Stavrinidou, E.; Rivnay, J. Organic mixed ionic–electronic conductors. Nat. Mater. 2020, 19, 13,  DOI: 10.1038/s41563-019-0435-z

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    Organic mixed ionic-electronic conductors

    Paulsen, Bryan D.; Tybrandt, Klas; Stavrinidou, Eleni; Rivnay, Jonathan

    Nature Materials (2020), 19 (1), 13-26CODEN: NMAACR; ISSN:1476-1122. (Nature Research)

    A review. Materials that efficiently transport and couple ionic and electronic charge are key to advancing a host of technol. developments for next-generation bioelectronic, optoelectronic and energy storage devices. Here we highlight key progress in the design and study of org. mixed ionic-electronic conductors (OMIECs), a diverse family of soft synthetically tunable mixed conductors. Across applications, the same interrelated fundamental phys. processes dictate OMIEC properties and det. device performance. Owing to ionic and electronic interactions and coupled transport properties, OMIECs demand special understanding beyond knowledge derived from the study of org. thin films and membranes meant to support either electronic or ionic processes only. We address seemingly conflicting views and terminol. regarding charging processes in these materials, and highlight recent approaches that extend fundamental understanding and contribute to the advancement of materials. Further progress is predicated on multimodal and multi-scale approaches to overcome lingering barriers to OMIEC design and implementation.
12. 12

    Berggren, M.; Crispin, X.; Fabiano, S.; Jonsson, M. P.; Simon, D. T.; Stavrinidou, E.; Tybrandt, K.; Zozoulenko, I. Ion Electron–Coupled Functionality in Materials and Devices Based on Conjugated Polymers. Adv. Mater. 2019, 31, 1805813,  DOI: 10.1002/adma.201805813

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    Zeglio, E.; Inganäs, O. Active Materials for Organic Electrochemical Transistors. Adv. Mater. 2018, 30, 1800941,  DOI: 10.1002/adma.201800941

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    Bernards, D. A.; Malliaras, G. G. Steady-State and Transient Behavior of Organic Electrochemical Transistors. Adv. Funct. Mater. 2007, 17, 3538,  DOI: 10.1002/adfm.200601239

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    Steady-state and transient behavior of organic electrochemical transistors

    Bernards, Daniel A.; Malliaras, George G.

    Advanced Functional Materials (2007), 17 (17), 3538-3544CODEN: AFMDC6; ISSN:1616-301X. (Wiley-VCH Verlag GmbH & Co. KGaA)

    In recent years, org. electrochem. transistors (OECTs) have emerged as attractive devices for a variety of applications, particularly in the area of sensing. While the elec. characteristics of OECTs are analogous to those of conventional org. field effect transistors, appropriate models for OECTs have not yet been developed. In particular, little is known about the transient characteristics of OECTs, which are detd. by a complex interplay between ionic and electronic motion. In this paper a simple model is presented that reproduces the steady-state and transient response of OECTs by considering these devices in terms of an ionic and an electronic circuit. A simple anal. expression is derived that can be used to fit steady-state OECT characteristics. For the transient regime, comparison with exptl. data allowed an estn. of the hole mobility in poly(3,4-ethylenedioxythiophene) doped with poly(styrene sulfonate). This work paves the way for rational optimization of OECTs.
15. 15

    Goel, M.; Heinrich, C. D.; Krauss, G.; Thelakkat, M. Principles of Structural Design of Conjugated Polymers Showing Excellent Charge Transport toward Thermoelectrics and Bioelectronics Applications. Macromol. Rapid Commun. 2019, 40, 1800915,  DOI: 10.1002/marc.201800915

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    Bischak, C. G.; Flagg, L. Q.; Yan, K.; Rehman, T.; Davies, D. W.; Quezada, R. J.; Onorato, J. W.; Luscombe, C. K.; Diao, Y.; Li, C.-Z.; Ginger, D. S. A Reversible Structural Phase Transition by Electrochemically-Driven Ion Injection into a Conjugated Polymer. J. Am. Chem. Soc. 2020, 142, 7434,  DOI: 10.1021/jacs.9b12769

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    16

    A Reversible Structural Phase Transition by Electrochemically-Driven Ion Injection into a Conjugated Polymer

    Bischak, Connor G.; Flagg, Lucas Q.; Yan, Kangrong; Rehman, Tahir; Davies, Daniel W.; Quezada, Ramsess J.; Onorato, Jonathan W.; Luscombe, Christine K.; Diao, Ying; Li, Chang-Zhi; Ginger, David S.

    Journal of the American Chemical Society (2020), 142 (16), 7434-7442CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)

    We find that conjugated polymers can undergo reversible structural phase transitions during electrochem. oxidn. and ion injection. We study poly[2,5-bis(thiophenyl)-1,4-bis(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)benzene] (PB2T-TEG), a conjugated polymer with glycolated side chains. Using grazing incidence wide-angle X-ray scattering (GIWAXS), we show that, in contrast to previously known polymers, this polymer switches between two structurally distinct cryst. phases assocd. with electrochem. oxidn./redn. in an aq. electrolyte. Importantly, we show that this unique phase change behavior has important phys. consequences for ion-polaron pair transport. Notably, using moving front expts. visualized by both optical microscopy and super-resoln. photoinduced force microscopy (PiFM), we show that a laterally propagating ion-polaron pair front in PB2T-TEG exhibits non-Fickian transport, retaining a sharp step-edge profile, in stark contrast to the Fickian diffusion more commonly obsd. in polymers like P3MEEMT. This structural phase transition is reminiscent of those accompanying ion uptake in inorg. materials like LiFePO4. We propose that the engineering of similar properties in future conjugated polymers may enable the realization of new materials with superior performance in electrochem. energy storage or neuromorphic memory applications.
17. 17

    Savva, A.; Hallani, R.; Cendra, C.; Surgailis, J.; Hidalgo, T. C.; Wustoni, S.; Sheelamanthula, R.; Chen, X.; Kirkus, M.; Giovannitti, A.; Salleo, A.; McCulloch, I.; Inal, S. Balancing Ionic and Electronic Conduction for High-Performance Organic Electrochemical Transistors. Adv. Funct. Mater. 2020, 30, 1907657,  DOI: 10.1002/adfm.201907657

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    17

    Balancing Ionic and Electronic Conduction for High-Performance Organic Electrochemical Transistors

    Savva, Achilleas; Hallani, Rawad; Cendra, Camila; Surgailis, Jokubas; Hidalgo, Tania C.; Wustoni, Shofarul; Sheelamanthula, Rajendar; Chen, Xingxing; Kirkus, Mindaugas; Giovannitti, Alexander; Salleo, Alberto; McCulloch, Iain; Inal, Sahika

    Advanced Functional Materials (2020), 30 (11), 1907657CODEN: AFMDC6; ISSN:1616-301X. (Wiley-VCH Verlag GmbH & Co. KGaA)

    Conjugated polymers that support mixed (electronic and ionic) conduction are in demand for applications spanning from bioelectronics to energy harvesting and storage. To design polymer mixed conductors for high-performance electrochem. devices, relationships between the chem. structure, charge transport, and morphol. must be established. A polymer series bearing the same p-type conjugated backbone with increasing percentage of hydrophilic, ethylene glycol side chains is synthesized, and their performance in aq. electrolyte gated org. electrochem. transistors (OECTs) is studied. By using device physics principles and electrochem. analyses, a direct relationship is found between the OECT performance and the balanced mixed conduction. While hydrophilic side chains are required to facilitate ion transport-thus enabling OECT operation-swelling of the polymer is not de facto beneficial for balancing mixed conduction. It is shown that heterogeneous water uptake disrupts the electronic cond. of the film, leading to OECTs with lower transconductance and slower response times. The combination of in situ electrochem. and structural techniques shown here contributes to the establishment of the structure-property relations necessary to improve the performance of polymer mixed conductors and subsequently of OECTs.
18. 18

    Flagg, L. Q.; Bischak, C. G.; Onorato, J. W.; Rashid, R. B.; Luscombe, C. K.; Ginger, D. S. Polymer Crystallinity Controls Water Uptake in Glycol Side-Chain Polymer Organic Electrochemical Transistors. J. Am. Chem. Soc. 2019, 141, 4345,  DOI: 10.1021/jacs.8b12640

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    18

    Polymer Crystallinity Controls Water Uptake in Glycol Side-Chain Polymer Organic Electrochemical Transistors

    Flagg, Lucas Q.; Bischak, Connor G.; Onorato, Jonathan W.; Rashid, Reem B.; Luscombe, Christine K.; Ginger, David S.

    Journal of the American Chemical Society (2019), 141 (10), 4345-4354CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)

    We study poly(3-{[2-(2-methoxyethoxy)ethoxy]methyl}thiophene-2,5-diyl) (P3MEEMT), a new polythiophene deriv. with ethylene glycol-based side chains, as a promising semiconducting polymer for accumulation-mode org. electrochem. transistors (OECTs) with figures of merit comparable to those of state-of-the-art materials. By characterizing the OECT performance of P3MEEMT transistors as a function of the anion, we find that large hydrophobic anions lower the threshold voltage. We find that, compared to poly(3-hexylthiophene-2,5-diyl) (P3HT), P3MEEMT has faster anion injection rates, which we attribute to the hydration of the P3MEEMT crystal lattice. We study P3MEEMT-based OECT and org. field-effect transistor (OFET) performance as a function of film crystallinity and show that changing the crystallinity of the polymer by thermal annealing increases the OFET mobility yet decreases the OECT mobility. We attribute this difference to the fact that, unlike OFETs, OECTs operate in aq. environments. To probe how hydration affects the operation of OECTs, we investigate the role of water in electrochem. doping using electrochem. quartz microbalance (EQCM) gravimetry. We find that steady-state hydration and hydration dynamics under electrochem. bias differ dramatically between the cryst. and amorphous P3MEEMT films. These results suggest that the presence of water reduces the electronic connectivity between the cryst. regions of P3MEEMT, thus lowering the mobility in soln. Overall, our study highlights the importance of the role of polymer hydration and nanoscale morphol. in elucidating design principles for OECT operation.
19. 19

    Paterson, A. F.; Faber, H.; Savva, A.; Nikiforidis, G.; Gedda, M.; Hidalgo, T. C.; Chen, X.; McCulloch, I.; Anthopoulos, T. D.; Inal, S. On the Role of Contact Resistance and Electrode Modification in Organic Electrochemical Transistors. Adv. Mater. 2019, 31, 1902291,  DOI: 10.1002/adma.201902291

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    Parr, Z. S.; Halaksa, R.; Finn, P. A.; Rashid, R. B.; Kovalenko, A.; Weiter, M.; Rivnay, J.; Krajčovič, J.; Nielsen, C. B. Glycolated Thiophene-Tetrafluorophenylene Copolymers for Bioelectronic Applications: Synthesis by Direct Heteroarylation Polymerisation. ChemPlusChem. 2019, 84, 1384,  DOI: 10.1002/cplu.201900254

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    Glycolated Thiophene-Tetrafluorophenylene Copolymers for Bioelectronic Applications: Synthesis by Direct Heteroarylation Polymerisation

    Parr, Zachary S.; Halaksa, Roman; Finn, Peter A.; Rashid, Reem B.; Kovalenko, Alexander; Weiter, Martin; Rivnay, Jonathan; Krajcovic, Jozef; Nielsen, Christian B.

    ChemPlusChem (2019), 84 (9), 1384-1390CODEN: CHEMM5; ISSN:2192-6506. (Wiley-VCH Verlag GmbH & Co. KGaA)

    A series of copolymers contg. a glycolated 1,4-dithienyl-2,3,5,6-tetrafluorophenylene unit copolymd. with thiophene, bithiophene, thienothiophene and 1,2,4,5-tetrafluorobenzene comonomer units were designed and synthesized by direct heteroarylation polymn. The optical, electrochem., electrochromic and solid-state structural properties of the copolymers were investigated. The copolymers exhibit stable redox properties in org. solvents and promising redox properties in thin film configuration with an aq. electrolyte. Finally, the potential of the copolymers as active materials in org. electrochem. transistors (OECTs) was assessed, and promising performance was shown as an accumulation-mode OECT material with a peak transconductance of 0.17 mS and a good on/off ratio of 105 for the thiophene copolymer.
21. 21

    Nielsen, C. B.; Giovannitti, A.; Sbircea, D.-T.; Bandiello, E.; Niazi, M. R.; Hanifi, D. A.; Sessolo, M.; Amassian, A.; Malliaras, G. G.; Rivnay, J.; McCulloch, I. Molecular Design of Semiconducting Polymers for High-Performance Organic Electrochemical Transistors. J. Am. Chem. Soc. 2016, 138, 10252,  DOI: 10.1021/jacs.6b05280

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    Molecular design of semiconducting polymers for high-performance organic electrochemical transistors

    Nielsen, Christian B.; Giovannitti, Alexander; Sbircea, Dan-Tiberiu; Bandiello, Enrico; Niazi, Muhammad R.; Hanifi, David A.; Sessolo, Michele; Amassian, Aram; Malliaras, George G.; Rivnay, Jonathan; McCulloch, Iain

    Journal of the American Chemical Society (2016), 138 (32), 10252-10259CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)

    The org. electrochem. transistor (OECT), capable of transducing small ionic fluxes into electronic signals in an aq. environment, is an ideal device to utilize in bioelectronic applications. Currently, most OECTs are fabricated with com. available conducting poly(3,4-ethylenedioxythiophene) (PEDOT)-based suspensions and are therefore operated in depletion mode. Here, the authors present a series of semiconducting polymers designed to elucidate important structure-property guidelines required for accumulation mode OECT operation. They discuss key aspects relating to OECT performance such as ion and hole transport, electrochromic properties, operational voltage, and stability. The demonstration of their mol. design strategy is the fabrication of accumulation mode OECTs that clearly outperform state-of-the-art PEDOT-based devices, and show stability under aq. operation without the need for formulation additives and cross-linkers.
22. 22

    Savva, A.; Cendra, C.; Giugni, A.; Torre, B.; Surgailis, J.; Ohayon, D.; Giovannitti, A.; McCulloch, I.; Di Fabrizio, E.; Salleo, A.; Rivnay, J.; Inal, S. Influence of Water on the Performance of Organic Electrochemical Transistors. Chem. Mater. 2019, 31, 927,  DOI: 10.1021/acs.chemmater.8b04335

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    22

    Influence of Water on the Performance of Organic Electrochemical Transistors

    Savva, Achilleas; Cendra, Camila; Giugni, Andrea; Torre, Bruno; Surgailis, Jokubas; Ohayon, David; Giovannitti, Alexander; McCulloch, Iain; Di Fabrizio, Enzo; Salleo, Alberto; Rivnay, Jonathan; Inal, Sahika

    Chemistry of Materials (2019), 31 (3), 927-937CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)

    Org. electrochem. transistors (OECTs) composed of org. mixed conductors can operate in aq., biol. media and translate low-magnitude ionic fluctuations of biol. origin into measurable elec. signals. The growing technol. interest in these biotransducers makes the fundamental understanding of ion-to-electron coupling extremely important for the design of new materials and devices. One crucial aspect in this process that has been so far disregarded is the water taken up by the film during device operation and its effects on device performance. Here, using a series of the same electrolyte with varying ion concns., we quantify the amt. of water that is incorporated into a hydrophilic p-type org. semiconductor film alongside the dopant anions and investigate structural and morphol. changes occurring in the film upon electrochem. doping. We show that infiltration of the hydrated dopant ions into the film irreversibly changes the polymer structure and neg. impacts the efficiency, reversibility, and speed of charge generation. When less water is injected into the channel, OECTs exhibit higher transconductance and faster switching speeds. Although swelling is commonly suggested to be a necessity for efficient ion-to-electron transduction, this work uncovers the neg. impact of a swollen channel material on the performance of accumulation mode OECTs and lays the foundation for future materials design.
23. 23

    Moser, M.; Wang, Y.; Hidalgo, T. C.; Liao, H.; Yu, Y.; Chen, J.; Duan, J.; Moruzzi, F.; Griggs, S.; Marks, A.; Gasparini, N.; Wadsworth, A.; Inal, S.; McCulloch, I.; Yue, W. Propylene and butylene glycol: new alternatives to ethylene glycol in conjugated polymers for bioelectronic applications. Mater. Horiz. 2022, 9, 973,  DOI: 10.1039/D1MH01889B

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    Propylene and butylene glycol: new alternatives to ethylene glycol in conjugated polymers for bioelectronic applications

    Moser, Maximilian; Wang, Yazhou; Hidalgo, Tania Cecilia; Liao, Hailiang; Yu, Yaping; Chen, Junxin; Duan, Jiayao; Moruzzi, Floriana; Griggs, Sophie; Marks, Adam; Gasparini, Nicola; Wadsworth, Andrew; Inal, Sahika; McCulloch, Iain; Yue, Wan

    Materials Horizons (2022), 9 (3), 973-980CODEN: MHAOBM; ISSN:2051-6355. (Royal Society of Chemistry)

    To date, many of the high-performance conjugated polymers employed as OECT channel materials make use of ethylene glycol (EG) chains to confer the materials with mixed ionic-electronic conduction properties, with limited emphasis placed on alternative hydrophilic moieties. While a degree of hydrophilicity is required to facilitate some ionic conduction in hydrated channels, an excess results in excessive swelling, with potentially detrimental effects on charge transport. This is therefore a subtle balance that must be optimized to maximise elec. performance. Herein a series of polymers based on a bithiophene-thienothiophene conjugated backbone was synthesized and the conventional EG chains substituted by their propylene and butylene counterparts. Specifically, the use of propylene and butylene chains was found to afford polymers with a more hydrophobic character, thereby reducing excessive water uptake during OECT operation and in turn significantly boosting the polymers' electronic charge carrier mobility. Despite the polymers' lower water uptake, the newly developed oligoether chains retained sufficiently high degrees of hydrophilicity to enable bulk volumetric doping, ultimately resulting in the development of polymers with superior OECT performance.
24. 24

    Moser, M.; Gladisch, J.; Ghosh, S.; Hidalgo, T. C.; Ponder, J. F., Jr; Sheelamanthula, R.; Thiburce, Q.; Gasparini, N.; Wadsworth, A.; Salleo, A.; Inal, S.; Berggren, M.; Zozoulenko, I.; Stavrinidou, E.; McCulloch, I. Controlling Electrochemically Induced Volume Changes in Conjugated Polymers by Chemical Design: from Theory to Devices. Adv. Funct. Mater. 2021, 31, 2100723,  DOI: 10.1002/adfm.202100723

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    24

    Controlling Electrochemically Induced Volume Changes in Conjugated Polymers by Chemical Design: from Theory to Devices

    Moser, Maximilian; Gladisch, Johannes; Ghosh, Sarbani; Hidalgo, Tania Cecilia; Ponder, James F. Jr.; Sheelamanthula, Rajendar; Thiburce, Quentin; Gasparini, Nicola; Wadsworth, Andrew; Salleo, Alberto; Inal, Sahika; Berggren, Magnus; Zozoulenko, Igor; Stavrinidou, Eleni; McCulloch, Iain

    Advanced Functional Materials (2021), 31 (26), 2100723CODEN: AFMDC6; ISSN:1616-301X. (Wiley-VCH Verlag GmbH & Co. KGaA)

    Electrochem. induced vol. changes in org. mixed ionic-electronic conductors (OMIECs) are particularly important for their use in dynamic microfiltration systems, biomedical machinery, and electronic devices. Although significant advances have been made to maximize the dimensional changes that can be accomplished by OMIECs, there is currently limited understanding of how changes in their mol. structures impact their underpinning fundamental processes and their performance in electronic devices. Herein, a series of ethylene glycol functionalized conjugated polymers is synthesized, and their electromech. properties are evaluated through a combined approach of exptl. measurements and mol. dynamics simulations. As demonstrated, alterations in the mol. structure of OMIECs impact numerous processes occurring during their electrochem. swelling, with sidechain length shortening decreasing the no. of incorporated water mols., reducing the generated void vols. and promoting the OMIECs to undergo different phase transitions. Ultimately, the impact of these combined mol. processes is assessed in org. electrochem. transistors, revealing that careful balancing of these phenomena is required to maximize device performance.
25. 25

    Moser, M.; Hidalgo, T. C.; Surgailis, J.; Gladisch, J.; Ghosh, S.; Sheelamanthula, R.; Thiburce, Q.; Giovannitti, A.; Salleo, A.; Gasparini, N.; Wadsworth, A.; Zozoulenko, I.; Berggren, M.; Stavrinidou, E.; Inal, S.; McCulloch, I. Side Chain Redistribution as a Strategy to Boost Organic Electrochemical Transistor Performance and Stability. Adv. Mater. 2020, 32, 2002748,  DOI: 10.1002/adma.202002748

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    Side Chain Redistribution as a Strategy to Boost Organic Electrochemical Transistor Performance and Stability

    Moser, Maximilian; Hidalgo, Tania Cecilia; Surgailis, Jokubas; Gladisch, Johannes; Ghosh, Sarbani; Sheelamanthula, Rajendar; Thiburce, Quentin; Giovannitti, Alexander; Salleo, Alberto; Gasparini, Nicola; Wadsworth, Andrew; Zozoulenko, Igor; Berggren, Magnus; Stavrinidou, Eleni; Inal, Sahika; McCulloch, Iain

    Advanced Materials (Weinheim, Germany) (2020), 32 (37), 2002748CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)

    A series of glycolated polythiophenes for use in org. electrochem. transistors (OECTs) is designed and synthesized, differing in the distribution of their ethylene glycol chains that are tethered to the conjugated backbone. While side chain redistribution does not have a significant impact on the optoelectronic properties of the polymers, this mol. engineering strategy strongly impacts the water uptake achieved in the polymers. By careful optimization of the water uptake in the polymer films, OECTs with unprecedented steady-state performances in terms of [μC*] and current retentions up to 98% over 700 electrochem. switching cycles are developed.
26. 26

    Moser, M.; Savagian, L. R.; Savva, A.; Matta, M.; Ponder, J. F.; Hidalgo, T. C.; Ohayon, D.; Hallani, R.; Reisjalali, M.; Troisi, A.; Wadsworth, A.; Reynolds, J. R.; Inal, S.; McCulloch, I. Ethylene Glycol-Based Side Chain Length Engineering in Polythiophenes and its Impact on Organic Electrochemical Transistor Performance. Chem. Mater. 2020, 32, 6618,  DOI: 10.1021/acs.chemmater.0c02041

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    Ethylene Glycol-Based Side Chain Length Engineering in Polythiophenes and its Impact on Organic Electrochemical Transistor Performance

    Moser, Maximilian; Savagian, Lisa R.; Savva, Achilleas; Matta, Micaela; Ponder, James F.; Hidalgo, Tania Cecilia; Ohayon, David; Hallani, Rawad; Reisjalali, Maryam; Troisi, Alessandro; Wadsworth, Andrew; Reynolds, John R.; Inal, Sahika; McCulloch, Iain

    Chemistry of Materials (2020), 32 (15), 6618-6628CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)

    Replacing the alkyl side chains on conventional semiconducting polymers with ethylene glycol (EG)-based chains is a successful strategy in the mol. design of mixed conduction materials for bioelectronic devices, including org. electrochem. transistors (OECTs). Such polymers have demonstrated the capability to conduct both ionic and electronic charges and can offer superior performance compared to the most commonly used active material, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate). While many research efforts have been dedicated to optimizing OECT performance through the engineering of the semiconducting polymers' conjugated backbones, variation of the EG chain length has been investigated considerably less. In this work, a series of glycolated polythiophenes with pendant EG chains spanning two to six EG repeat units was synthesized and the electrochem. and structural characteristics of the resulting films were characterized by exptl. means and mol. dynamics simulations. OECTs were fabricated and tested, and their performance showed a strong correlation to the EG side chain length, thereby elucidating important structure-property guidelines for the mol. design of future channel materials. Specifically, a careful balance in the EG length must be struck during the design of EG-functionalized conjugated polymers for OECTs. While minimizing the EG side chain length appears to boost both the capacitive and charge carrier transport properties of the polymers, the chosen EG side chain length must be kept sufficiently long to induce soly. for processing, and allow for the necessary ion interactions with the conjugated polymer backbone.
27. 27

    Lan, L.; Chen, J.; Wang, Y.; Li, P.; Yu, Y.; Zhu, G.; Li, Z.; Lei, T.; Yue, W.; McCulloch, I. Facilely Accessible Porous Conjugated Polymers toward High-Performance and Flexible Organic Electrochemical Transistors. Chem. Mater. 2022, 34, 1666,  DOI: 10.1021/acs.chemmater.1c03797

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    Facilely Accessible Porous Conjugated Polymers toward High-Performance and Flexible Organic Electrochemical Transistors

    Lan, Liuyuan; Chen, Junxin; Wang, Yazhou; Li, Peiyun; Yu, Yaping; Zhu, Genming; Li, Zhengke; Lei, Ting; Yue, Wan; McCulloch, Iain

    Chemistry of Materials (2022), 34 (4), 1666-1676CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)

    Porous morphologies have shown great potential in optimizing the capacitance and charge carrier transport for semiconducting polymers in org. electrochem. transistors (OECTs). Nevertheless, it remains arduous and time-consuming to obtain such desired microstructures due to the requirement of rigorous humidity control and templates/additives. Herein, three new glycolated conjugated polymers based on a fused-ring cyclopentadithiophene (CPDT) skeleton are developed, which feature readily obtained large-area porous thin films via spin-casting from binary solvent mixts. under ambient conditions. These polymers afford fascinating capacitances reaching a max. of 353 F cm-3, which is the highest value reported to date for p-type OECT materials. The optimal combination of volumetric capacitance and hole mobility in a representative polymer enables the fabrication of OECTs with a high μC* value up to 476 F cm-1 V-1 s-1 and a current retention of 98% upon 600 switching cycles. Moreover, the corresponding flexible OECTs exhibit exceptional mech. stability at various bending radii down to 5 mm and under repetitive bending cycles. This work provides a simple yet effective binary solvent strategy to fabricate porous conjugated polymers for high-performance OECTs and flexible devices, which will further advance the development of org. mixed ionic-electronic conductors in OECT research fields and beyond.
28. 28

    Wang, Y.; Zeglio, E.; Liao, H.; Xu, J.; Liu, F.; Li, Z.; Maria, I. P.; Mawad, D.; Herland, A.; McCulloch, I.; Yue, W. Hybrid Alkyl–Ethylene Glycol Side Chains Enhance Substrate Adhesion and Operational Stability in Accumulation Mode Organic Electrochemical Transistors. Chem. Mater. 2019, 31, 9797,  DOI: 10.1021/acs.chemmater.9b03798

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    Hybrid Alkyl-Ethylene Glycol Side Chains Enhance Substrate Adhesion and Operational Stability in Accumulation Mode Organic Electrochemical Transistors

    Wang, Yazhou; Zeglio, Erica; Liao, Hailiang; Xu, Jinqiu; Liu, Feng; Li, Zhengke; Maria, Iuliana Petruta; Mawad, Damia; Herland, Anna; McCulloch, Iain; Yue, Wan

    Chemistry of Materials (2019), 31 (23), 9797-9806CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)

    Donor-acceptor copolymers featuring electron-deficient isoindigo units and electron-rich 3,4-ethylenedioxy (EDOT) groups are presented as new materials for accumulation mode org. electrochem. transistors (OECTs). Grafting hybrid alkyl-ethylene glycol side chains on the isoindigo units of the copolymer leads to OECTs with outstanding substrate adhesion and operational stability in contact with an aq. electrolyte, as demonstrated by their preserved performance after extensive ultrasonication (1.5 h) or after continuous on-off switching for over 6 h. Hybrid side chains outperform copolymers with alkyl only or ethylene glycol only side chains, which retain only 27% and 10% of the on currents after 40 min of on-off switching, resp., under the same biasing conditions. These devices are promising candidates for in vitro and in vivo bioelectronics, applications where stability as well as robust adhesion of the conjugated polymer to the substrate are essential.
29. 29

    Ohayon, D.; Savva, A.; Du, W.; Paulsen, B. D.; Uguz, I.; Ashraf, R. S.; Rivnay, J.; McCulloch, I.; Inal, S. Influence of Side Chains on the n-Type Organic Electrochemical Transistor Performance. ACS Appl. Mater. Interfaces 2021, 13, 4253,  DOI: 10.1021/acsami.0c18599

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    Influence of Side Chains on the n-Type Organic Electrochemical Transistor Performance

    Ohayon, David; Savva, Achilleas; Du, Weiyuan; Paulsen, Bryan D.; Uguz, Ilke; Ashraf, Raja S.; Rivnay, Jonathan; McCulloch, Iain; Inal, Sahika

    ACS Applied Materials & Interfaces (2021), 13 (3), 4253-4266CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)

    N-Type (electron transporting) polymers can make suitable interfaces to transduce biol. events that involve the generation of electrons. However, n-type polymers that are stable when electrochem. doped in aq. media are relatively scarce, and the performance of the existing ones lags behind their p-type (hole conducting) counterparts. Here, the authors report a new family of donor-acceptor-type polymers based on a naphthalene-1,4,5,8-tetracarboxylic-diimide-bi-thiophene (NDI-T2) backbone where the NDI unit always bears an ethylene glycol (EG) side chain. The authors study how small variations in the side chains tethered to the acceptor as well as the donor unit affect the performance of the polymer films in the state-of-the-art bioelectronic device, the org. electrochem. transistor (OECT). First, substitution of the T2 core with an electron-withdrawing group (i.e., methoxy) or an EG side chain leads to ambipolar charge transport properties and causes significant changes in film microstructure, which overall impairs the n-type OECT performance. Thus the best n-type OECT performer is the polymer that has no substitution on the T2 unit. Next, the authors evaluate the distance of the oxygen from the NDI unit as a design parameter by varying the length of the C spacer placed between the EG unit and the backbone. The distance of the EG from the backbone affects the film order and crystallinity, and thus, the electron mobility. Consequently, work reports the best-performing NDI-T2-based n-type OECT material to date, i.e., the polymer without the T2 substitution and bearing a 6-C spacer between the EG and the NDI units. Work provides new guidelines for the side-chain engineering of n-type polymers for OECTs and insights on the structure-performance relations for mixed ionic-electronic conductors, crucial for devices where the film operates at the aq. electrolyte interface.
30. 30

    Brendel, J. C.; Schmidt, M. M.; Hagen, G.; Moos, R.; Thelakkat, M. Controlled Synthesis of Water-Soluble Conjugated Polyelectrolytes Leading to Excellent Hole Transport Mobility. Chem. Mater. 2014, 26, 1992,  DOI: 10.1021/cm500500t

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    Controlled Synthesis of Water-Soluble Conjugated Polyelectrolytes Leading to Excellent Hole Transport Mobility

    Brendel, Johannes C.; Schmidt, Martina M.; Hagen, Gunter; Moos, Ralf; Thelakkat, Mukundan

    Chemistry of Materials (2014), 26 (6), 1992-1998CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)

    Conjugated polyelectrolytes (CPE) find widespread applications due to their soly. in aq. systems or highly polar solvents. However, ion reorganization under applied fields and low charge carrier mobility limit their use as active layers in electronic devices. Here, we present a novel controlled synthetic route for CPEs based on polythiophene carrying sulfonate side groups. We prepd. three different polymers with varying mol. wts. and narrow polydispersity. For the CPE with the highest mol. wt., we obsd. the formation of small aggregates in aq. soln. which was confirmed by UV-vis absorption and fluorescence spectroscopy. In the UV-vis spectrum, vibrational bands are obsd., which are maintained in the thin film. These absorption bands are similar to those of cryst. poly(3-hexylthiophene). The fluorescence signal is almost completely quenched for these aggregates. Adding other polar solvents such as DMSO results in the dissoln. of the aggregates indicated by the decrease of the vibrational bands in UV-vis and the increase of the fluorescence signal. This polymer further exhibits a remarkably high hole transport mobility of (1.2 ± 0.5) × 10-2 cm2/(V s) as detd. by the space charge limited current method. The underlying transport mechanism was studied by current (J)-voltage (V) measurements and impedance spectroscopy. The former shows a quadratic dependence of J vs V and a fast response within microseconds characteristic for a classical semiconductor, while the latter shows no sign of any ion motion. In contrast to other reported CPEs, the regioregular chain conformation and the narrow mol. wt. distribution here promote the formation of aggregates which improve the electronic charge transport throughout the bulk. Addnl., the presence of sterically demanding counterions suppress the ion motion and reorganization, resulting in a water-sol. semiconducting material with high hole transport mobility.
31. 31

    Lill, A. T.; Cao, D. X.; Schrock, M.; Vollbrecht, J.; Huang, J.; Nguyen-Dang, T.; Brus, V. V.; Yurash, B.; Leifert, D.; Bazan, G. C.; Nguyen, T.-Q. Organic Electrochemical Transistors Based on the Conjugated Polyelectrolyte PCPDTBT-SO3K (CPE-K). Adv. Mater. 2020, 32, 1908120,  DOI: 10.1002/adma.201908120

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    Organic electrochemical transistors based on the conjugated polyelectrolyte PCPDTBT-SO3K (CPE-K)

    Lill, Alexander T.; Cao, David X.; Schrock, Max; Vollbrecht, Joachim; Huang, Jianfei; Nguyen-Dang, Tung; Brus, Viktor V.; Yurash, Brett; Leifert, Dirk; Bazan, Guillermo C.; Nguyen, Thuc-Quyen

    Advanced Materials (Weinheim, Germany) (2020), 32 (33), 1908120CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)

    PCPDTBT-SO3K (CPE-K), a conjugated polyelectrolyte, is presented as a mixed conductor material that can be used to fabricate high transconductance accumulation mode org. electrochem. transistors (OECTs). OECTs are utilized in a wide range of applications such as analyte detection, neural interfacing, impedance sensing, and neuromorphic computing. The use of interdigitated contacts to enable high transconductance in a relatively small device area in comparison to std. contacts is demonstrated. Such characteristics are highly desired in applications such as neural-activity sensing, where the device area must be minimized to reduce invasiveness. The phys. and elec. properties of CPE-K are fully characterized to allow a direct comparison to other top performing OECT materials. CPE-K demonstrates an elec. performance that is among the best reported in the literature for OECT materials. In addn., CPE-K OECTs operate in the accumulation mode, which allows for much lower energy consumption in comparison to commonly used depletion mode devices.
32. 32

    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,  DOI: 10.1021/acs.chemrev.1c00266

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    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.
33. 33

    Schmode, P.; Ohayon, D.; Reichstein, P. M.; Savva, A.; Inal, S.; Thelakkat, M. High-Performance Organic Electrochemical Transistors Based on Conjugated Polyelectrolyte Copolymers. Chem. Mater. 2019, 31, 5286,  DOI: 10.1021/acs.chemmater.9b01722

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    High-Performance Organic Electrochemical Transistors Based on Conjugated Polyelectrolyte Copolymers

    Schmode, Philip; Ohayon, David; Reichstein, Paul M.; Savva, Achilleas; Inal, Sahika; Thelakkat, Mukundan

    Chemistry of Materials (2019), 31 (14), 5286-5295CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)

    A new generation of polythiophene-based polyelectrolytes is reported to address fundamental issues in org. electrochem. transistors (OECTs). In such devices, the semiconductor must be able to transport and store ions and possess simultaneously a very high electronic mobility. For this, the ion-conducting 6-(thiophen-3-yl) hexane-1-sulfonate tetramethylammonium monomer (THS-TMA+) is copolymd. with the hole-conducting 3-hexylthiophene (3HT) to obtain copolymers, PTHS-TMA+-co-P3HT 1-3 with a gradient architecture. The copolymers having ≤ 50 mol. % 3HT content are easily oxidizable and are cryst. Consequently, for the copolymers, a higher stability in water is achieved, thus reducing the amt. of cross-linker needed to stabilize the film. Furthermore, OECTs using copolymers with 75 and 50 mol. % of PTHS-TMA+ content exhibit 2-3 orders of magnitude higher ON/OFF ratio and an extremely lower threshold voltage (-0.15 V) compared to PTHS-TMA+. Addnl., high volumetric capacitance (C* > 100 F/cm3) is achieved, indicating that the ion transport is not hampered by the hydrophobic 3HT ≤ 50 mol. %, for which a very high OECT hole mobility of 0.017 cm2/(V s) is also achieved. Thus, the concept of copolymn. to combine both ionic and electronic charge transport in an org. mixed conductor offers an elegant approach to obtain high-performance OECT materials.
34. 34

    Maria, I. P.; Paulsen, B. D.; Savva, A.; Ohayon, D.; Wu, R.; Hallani, R.; Basu, A.; Du, W.; Anthopoulos, T. D.; Inal, S.; Rivnay, J.; McCulloch, I.; Giovannitti, A. The Effect of Alkyl Spacers on the Mixed Ionic-Electronic Conduction Properties of N-Type Polymers. Adv. Funct. Mater. 2021, 31, 2008718,  DOI: 10.1002/adfm.202008718

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    The Effect of Alkyl Spacers on the Mixed Ionic-Electronic Conduction Properties of N-Type Polymers

    Maria, Iuliana P.; Paulsen, Bryan D.; Savva, Achilleas; Ohayon, David; Wu, Ruiheng; Hallani, Rawad; Basu, Aniruddha; Du, Weiyuan; Anthopoulos, Thomas D.; Inal, Sahika; Rivnay, Jonathan; McCulloch, Iain; Giovannitti, Alexander

    Advanced Functional Materials (2021), 31 (14), 2008718CODEN: AFMDC6; ISSN:1616-301X. (Wiley-VCH Verlag GmbH & Co. KGaA)

    Conjugated polymers with mixed ionic and electronic transport are essential for developing the complexity and function of electrochem. devices. Current n-type materials have a narrow scope and low performance compared with their p-type counterparts, requiring new mol. design strategies. This work presents two naphthalene diimide-bithiophene (NDI-T2) copolymers functionalized with hybrid alkyl-glycol side chains, where the naphthalene diimide unit is segregated from the ethylene glycol (EG) units within the side chain by an alkyl spacer. Introduction of hydrophobic Pr and hexyl spacers is investigated as a strategy to minimize detrimental swelling close to the conjugated backbone and balance the mixed conduction properties of n-type materials in aq. electrolytes. It is found that both polymers functionalized with alkyl spacers outperform their analog bearing EG-only side chains in org. electrochem. transistors (OECTs). The presence of the alkyl spacers also leads to remarkable stability in OECTs, with no decrease in the ON current after 2 h of operation. Through this versatile side chain modification, this work provides a greater understanding of the structure-property relationships required for n-type OECT materials operating in aq. media.
35. 35

    Giovannitti, A.; Maria, I. P.; Hanifi, D.; Donahue, M. J.; Bryant, D.; Barth, K. J.; Makdah, B. E.; Savva, A.; Moia, D.; Zetek, M.; Barnes, P. R. F.; Reid, O. G.; Inal, S.; Rumbles, G.; Malliaras, G. G.; Nelson, J.; Rivnay, J.; McCulloch, I. The Role of the Side Chain on the Performance of N-type Conjugated Polymers in Aqueous Electrolytes. Chem. Mater. 2018, 30, 2945,  DOI: 10.1021/acs.chemmater.8b00321

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    The Role of the Side Chain on the Performance of N-type Conjugated Polymers in Aqueous Electrolytes

    Giovannitti, Alexander; Maria, Iuliana P.; Hanifi, David; Donahue, Mary J.; Bryant, Daniel; Barth, Katrina J.; Makdah, Beatrice E.; Savva, Achilleas; Moia, Davide; Zetek, Matyas; Barnes, Piers R. F.; Reid, Obadiah G.; Inal, Sahika; Rumbles, Garry; Malliaras, George G.; Nelson, Jenny; Rivnay, Jonathan; McCulloch, Iain

    Chemistry of Materials (2018), 30 (9), 2945-2953CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)

    We report a design strategy that allows the prepn. of soln. processable n-type materials from low b.p. solvents for org. electrochem. transistors (OECTs). The polymer backbone is based on NDI-T2 copolymers where a branched alkyl side chain is gradually exchanged for a linear ethylene glycol-based side chain. A series of random copolymers was prepd. with glycol side chain percentages of 0, 10, 25, 50, 75, 90, and 100 with respect to the alkyl side chains. These were characterized to study the influence of the polar side chains on interaction with aq. electrolytes, their electrochem. redox reactions, and performance in OECTs when operated in aq. electrolytes. We obsd. that glycol side chain percentages of >50% are required to achieve volumetric charging, while lower glycol chain percentages show a mixed operation with high required voltages to allow for bulk charging of the org. semiconductor. A strong dependence of the electron mobility on the fraction of glycol chains was found for copolymers based on NDI-T2, with a significant drop as alkyl side chains are replaced by glycol side chains.
36. 36

    Ding, B.; Kim, G.; Kim, Y.; Eisner, F. D.; Gutiérrez-Fernández, E.; Martín, J.; Yoon, M.-H.; Heeney, M. Influence of Backbone Curvature on the Organic Electrochemical Transistor Performance of Glycolated Donor–Acceptor Conjugated Polymers. Angew. Chem., Int. Ed. 2021, 60, 19679,  DOI: 10.1002/anie.202106084

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    Influence of Backbone Curvature on the Organic Electrochemical Transistor Performance of Glycolated Donor-Acceptor Conjugated Polymers

    Ding, Bowen; Kim, Gunwoo; Kim, Youngseok; Eisner, Flurin D.; Gutierrez-Fernandez, Edgar; Martin, Jaime; Yoon, Myung-Han; Heeney, Martin

    Angewandte Chemie, International Edition (2021), 60 (36), 19679-19684CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)

    Two new glycolated semiconducting polymers PgBT(F)2gT and PgBT(F)2gTT of differing backbone curvatures were designed and synthesized for application as p-type accumulation mode org. electrochem. transistor (OECT) materials. Both polymers demonstrated stable and reversible oxidn., accessible within the aq. electrochem. window, to generate polaronic charge carriers. OECTs fabricated from PgBT(F)2gT featuring a curved backbone geometry attained a higher volumetric capacitance of 170 F cm-3. However, PgBT(F)2gTT with a linear backbone displayed overall superior OECT performance with a normalized peak transconductance of 3.00 × 104 mS cm-1, owing to its enhanced order, expediting the charge mobility to 0.931 cm2 V-1 s-1.
37. 37

    Flagg, L. Q.; Bischak, C. G.; Quezada, R. J.; Onorato, J. W.; Luscombe, C. K.; Ginger, D. S. P-Type Electrochemical Doping Can Occur by Cation Expulsion in a High-Performing Polymer for Organic Electrochemical Transistors. ACS. Mater. Lett. 2020, 2, 254,  DOI: 10.1021/acsmaterialslett.9b00501

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    P-Type Electrochemical Doping Can Occur by Cation Expulsion in a High-Performing Polymer for Organic Electrochemical Transistors

    Flagg, Lucas Q.; Bischak, Connor G.; Quezada, Ramsess J.; Onorato, Jonathan W.; Luscombe, Christine. K.; Ginger, David S.

    ACS Materials Letters (2020), 2 (3), 254-260CODEN: AMLCEF; ISSN:2639-4979. (American Chemical Society)

    We investigate the mechanism of ion-dependent charge compensation during electrochem. oxidn. (doping) of the model mixed ionic/electronic transporting polythiophene deriv. poly(3-{[2-(2-methoxyethoxy)ethoxy]methyl}thiophene-2,5-diyl) (P3MEEMT). Using a combination of electrochem. quartz microbalance gravimetry and glow discharge optical emission spectroscopy, we show that charge compensation during polymer redox processes proceeds via a cation-dependent mechanism. For p-type polymer oxidn. in certain electrolytes, charge compensation is achieved by both eventual injection of anions into the film, as well as initial expulsion of cations from the film. We compare doping mechanisms for a variety of electrolyte salts including potassium chloride, tetrabutylammonium chloride, potassium hexafluorophosphate (KPF6), and tetrabutylammonium hexafluorophosphate. For the electrolyte KPF6, both the cations and anions coexist in the water-swelled polymer even prior to application of elec. bias. Our data indicate that electrochem. doping (hole injection into the polymer and ionic charge compensation) proceeds via the following mechanism: (1) hydration of the neutral film by electrolyte (water, cations, anions), (2) cation (K+) expulsion from the film upon initial application of an oxidative bias, and (3) anion injection into the film at higher oxidn./doping levels (>∼2 × 1020/cm3). Understanding the mechanism of charge compensation during the doping process should allow for the design of improved mixed ionic/electronic conductors for use in applications ranging from org. supercapacitors and redox flow batteries to bioelectronic sensors, thermoelecs., and devices for neuromorphic computing.
38. 38

    Creamer, A.; Wood, C. S.; Howes, P. D.; Casey, A.; Cong, S.; Marsh, A. V.; Godin, R.; Panidi, J.; Anthopoulos, T. D.; Burgess, C. H.; Wu, T.; Fei, Z.; Hamilton, I.; McLachlan, M. A.; Stevens, M. M.; Heeney, M. Post-polymerisation functionalisation of conjugated polymer backbones and its application in multi-functional emissive nanoparticles. Nat. Commun. 2018, 9, 3237,  DOI: 10.1038/s41467-018-05381-4

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    Post-polymerisation functionalisation of conjugated polymer backbones and its application in multi-functional emissive nanoparticles

    Creamer Adam; Casey Abby; Cong Shengyu; Marsh Adam V; Godin Robert; Wu Tingman; Fei Zhuping; Heeney Martin; Creamer Adam; Casey Abby; Cong Shengyu; Marsh Adam V; Godin Robert; Panidi Julianna; Wu Tingman; Fei Zhuping; Hamilton Iain; Heeney Martin; Wood Christopher S; Howes Philip D; Burgess Claire H; McLachlan Martyn A; Stevens Molly M; Wood Christopher S; Howes Philip D; Stevens Molly M; Wood Christopher S; Howes Philip D; Stevens Molly M; Howes Philip D; Panidi Julianna; Anthopoulos Thomas D; Hamilton Iain; Anthopoulos Thomas D

    Nature communications (2018), 9 (1), 3237 ISSN:.

    Backbone functionalisation of conjugated polymers is crucial to their performance in many applications, from electronic displays to nanoparticle biosensors, yet there are limited approaches to introduce functionality. To address this challenge we have developed a method for the direct modification of the aromatic backbone of a conjugated polymer, post-polymerisation. This is achieved via a quantitative nucleophilic aromatic substitution (SNAr) reaction on a range of fluorinated electron-deficient comonomers. The method allows for facile tuning of the physical and optoelectronic properties within a batch of consistent molecular weight and dispersity. It also enables the introduction of multiple different functional groups onto the polymer backbone in a controlled manner. To demonstrate the versatility of this reaction, we designed and synthesised a range of emissive poly(9,9-dioctylfluorene-alt-benzothiadiazole) (F8BT)-based polymers for the creation of mono and multifunctional semiconducting polymer nanoparticles (SPNs) capable of two orthogonal bioconjugation reactions on the same surface.
39. 39

    Cong, S.; Creamer, A.; Fei, Z.; Hillman, S. A. J.; Rapley, C.; Nelson, J.; Heeney, M. Tunable Control of the Hydrophilicity and Wettability of Conjugated Polymers by a Postpolymerization Modification Approach. Macromol. Biosci. 2020, 20, 2000087,  DOI: 10.1002/mabi.202000087

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    Tunable Control of the Hydrophilicity and Wettability of Conjugated Polymers by a Postpolymerization Modification Approach

    Cong, Shengyu; Creamer, Adam; Fei, Zhuping; Hillman, Sam A. J.; Rapley, Charlotte; Nelson, Jenny; Heeney, Martin

    Macromolecular Bioscience (2020), 20 (11), 2000087CODEN: MBAIBU; ISSN:1616-5187. (Wiley-VCH Verlag GmbH & Co. KGaA)

    A facile method to prep. hydrophilic polymers by a postpolymn. nucleophilic arom. substitution reaction of fluoride on an emissive conjugated polymer (CP) backbone is reported. Quant. functionalization by a series of monofunctionalized ethylene glycol oligomers, from dimer to hexamer, as well as with high mol. wt. polyethylene glycol is demonstrated. The length of the ethylene glycol sidechains is shown to have a direct impact on the surface wettability of the polymer, as well as its soly. in polar solvents. However, the energetics and band gap of the CPs remain essentially const. This method therefore allows an easy way to modulate the wettability and soly. of CP materials for a diverse series of applications.
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    Reichsöllner, E.; Creamer, A.; Cong, S.; Casey, A.; Eder, S.; Heeney, M.; Glöcklhofer, F. Fast and Selective Post-polymerization Modification of Conjugated Polymers Using Dimethyldioxirane. Front. Chem. 2019,  DOI: 10.3389/fchem.2019.00123

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    There is no corresponding record for this reference.
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    Conboy, G.; Spencer, H. J.; Angioni, E.; Kanibolotsky, A. L.; Findlay, N. J.; Coles, S. J.; Wilson, C.; Pitak, M. B.; Risko, C.; Coropceanu, V.; Brédas, J.-L.; Skabara, P. J. To bend or not to bend – are heteroatom interactions within conjugated molecules effective in dictating conformation and planarity?. Mater. Horiz. 2016, 3, 333,  DOI: 10.1039/C6MH00051G

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    To bend or not to bend - are heteroatom interactions within conjugated molecules effective in dictating conformation and planarity

    Conboy, Gary; Spencer, Howard J.; Angioni, Enrico; Kanibolotsky, Alexander L.; Findlay, Neil J.; Coles, Simon J.; Wilson, Claire; Pitak, Mateusz B.; Risko, Chad; Coropceanu, Veaceslav; Bredas, Jean-Luc; Skabara, Peter J.

    Materials Horizons (2016), 3 (4), 333-339CODEN: MHAOBM; ISSN:2051-6355. (Royal Society of Chemistry)

    We consider the roles of heteroatoms (mainly nitrogen, the halogens and the chalcogens) in dictating the conformation of linear conjugated mols. and polymers through non-covalent intramol. interactions. While hydrogen bonding is a competitive and sometimes more influential interaction, we provide unambiguous evidence that heteroatoms are able to det. the conformation of such materials with reasonable predictability.
42. 42

    Guo, X.; Liao, Q.; Manley, E. F.; Wu, Z.; Wang, Y.; Wang, W.; Yang, T.; Shin, Y.-E.; Cheng, X.; Liang, Y.; Chen, L. X.; Baeg, K.-J.; Marks, T. J.; Guo, X. Materials Design via Optimized Intramolecular Noncovalent Interactions for High-Performance Organic Semiconductors. Chem. Mater. 2016, 28, 2449,  DOI: 10.1021/acs.chemmater.6b00850

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    42

    Materials Design via Optimized Intramolecular Noncovalent Interactions for High-Performance Organic Semiconductors

    Guo, Xiaojie; Liao, Qiaogan; Manley, Eric F.; Wu, Zishan; Wang, Yulun; Wang, Weida; Yang, Tingbin; Shin, Young-Eun; Cheng, Xing; Liang, Yongye; Chen, Lin X.; Baeg, Kang-Jun; Marks, Tobin J.; Guo, Xugang

    Chemistry of Materials (2016), 28 (7), 2449-2460CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)

    We report the design, synthesis, and implemention in semiconducting polymers of a novel head-to-head linkage contg. the TRTOR (3-alkyl-3'-alkoxy-2,2'-bithiophene) donor subunit having a single strategically optimized, planarizing noncovalent S···O interaction. Diverse complementary thermal, optical, electrochem., X-ray scattering, elec., photovoltaic, and electron microscopic characterization techniques are applied to establish structure-property correlations in a TRTOR-based polymer series. In comparison to monomers having double S···O interactions, replacing one alkoxy substituent with a less electron-donating alkyl one yields TRTOR-based polymers with significantly depressed (0.2-0.3 eV) HOMOs. Furthermore, the weaker single S···O interaction and greater TRTOR steric encumberance enhances materials processability without sacrificing backbone planarity. From another perspective, TRTOR has comparable electronic properties to ring-fused 5H-dithieno[3,2-b:2',3'-d]pyran (DTP) subunits, but a centrosym. geometry which promotes a more compact and ordered structure than bulkier, axisym. DTP. Compared to monosubstituted TTOR (3-alkoxy-2,2'-bithiophene), alkylation at the TRTOR bithiophene 3-position enhances conjugation and polymer crystallinity with contracted π-π stacking. Grazing incidence wide-angle X-ray scattering (GIWAXS) data reveal that the greater steric hindrance and the weaker single S···O interaction are not detrimental to close packing and high crystallinity. As a proof of materials design, copolymg. TRTOR with phthalimides yields copolymers with promising thin-film transistor mobility as high as 0.42 cm2/(V·s) and 6.3% power conversion efficiency in polymer solar cells, the highest of any phthalimide copolymers reported to date. The depressed TRTOR HOMOs imbue these polymers with substantially increased Ion/Ioff ratios and Voc's vs. analogous subunits with multiple electron donating, planarizing alkoxy substituents. Implementing a head-to-head linkage with an alkyl/alkoxy substitution pattern and a single S···O interaction is a promising strategy for org. electronics materials design.
43. 43

    Thorley, K. J.; McCulloch, I. Why are S–F and S–O non-covalent interactions stabilising?. J. Mater. Chem. C 2018, 6, 12413,  DOI: 10.1039/C8TC04252G

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    43

    Why are S-F and S-O non-covalent interactions stabilising?

    Thorley, Karl J.; McCulloch, Iain

    Journal of Materials Chemistry C: Materials for Optical and Electronic Devices (2018), 6 (45), 12413-12421CODEN: JMCCCX; ISSN:2050-7534. (Royal Society of Chemistry)

    Soft non-covalent interactions are important to bulk property materials, but can also affect mol. or single polymer chain properties in optoelectronic materials. S-F and S-O interactions are often used in material design to planarize π-systems and increase conjugation length, but how these interactions might actually be stabilizing is still not fully understood. Here, computational anal. using symmetry adapted perturbation theory and natural bond orbital methods uncovers the key electrostatic interactions between sulfur and neighboring heteroatoms within the same mol. or polymer chain. A future design rule for materials hoping to affect torsional conformation using these types of interactions is to consider the direction of dipoles of functional groups.
44. 44

    Ding, B.; Chan, B.; Proschogo, N.; Solomon, M. B.; Kepert, C. J.; D’Alessandro, D. M. A cofacial metal–organic framework based photocathode for carbon dioxide reduction. Chem. Sci. 2021, 12, 3608,  DOI: 10.1039/D0SC04691D

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    44

    A cofacial metal-organic framework based photocathode for carbon dioxide reduction

    Ding, Bowen; Chan, Bun; Proschogo, Nicholas; Solomon, Marcello B.; Kepert, Cameron J.; D'Alessandro, Deanna M.

    Chemical Science (2021), 12 (10), 3608-3614CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)

    Innovative and robust photosensitization materials play a cardinal role in advancing the combined effort towards efficient solar energy harvesting. Here, we demonstrate the photocathode functionality of a Metal-Org. Framework (MOF) featuring cofacial pairs of photo- and electro-active 1,4,5,8-naphthalenediimide (NDI) ligands, which was successfully applied to markedly reduce the overpotential required for CO2 redn. to CO by a well-known rhenium mol. electrocatalyst. Redn. of [Cd(DPNDI)(TDC)]n (DPNDI = N,N'-di(4-pyridyl)-1,4,5,8-naphthalenediimide, H2TDC = thiophene-2,5-dicarboxylic acid) to its mixed-valence state induces through-space Intervalence Charge Transfer (IVCT) within cofacial DPNDI units. Irradn. of the mixed-valence MOF in the visible region generates a DPNDI photoexcited radical monoanion state, which is stabilized as a persistent species by the inherent IVCT interactions and has been rationalised using D. Functional Theory (DFT). This photoexcited radical monoanion state was able to undergo charge transfer (CT) redn. of the rhenium mol. electrocatalyst to effect CO generation at a lower overpotential than that required by the discrete electrocatalyst itself. The exploitation of cofacial MOFs opens new directions for the design philosophy behind light harvesting materials.
45. 45

    Khodagholy, D.; Gurfinkel, M.; Stavrinidou, E.; Leleux, P.; Herve, T.; Sanaur, S.; Malliaras, G. G. High speed and high density organic electrochemical transistor arrays. Appl. Phys. Lett. 2011, 99, 163304,  DOI: 10.1063/1.3652912

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    High speed and high density organic electrochemical transistor arrays

    Khodagholy, Dion; Gurfinkel, Moshe; Stavrinidou, Eleni; Leleux, Pierre; Herve, Thierry; Sanaur, Sebastien; Malliaras, George G.

    Applied Physics Letters (2011), 99 (16), 163304/1-163304/3CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)

    A generic lithog. process is presented that allows the fabrication of high d. org. electrochem. transistor arrays meant to interface with aq. electrolytes. The channels of the transistors, which were 6 μm long, were made of the conducting polymer poly(3,4-ethylenedioxythiophene) doped with poly(styrene sulfonate) and were in direct contact with phosphate buffered saline. Source and drain electrodes and interconnects were insulated by parylene C, a biocompatible material. The transistors operated at low voltages and showed a response time of the order of 100 μs. (c) 2011 American Institute of Physics.
46. 46

    Friedlein, J. T.; McLeod, R. R.; Rivnay, J. Device physics of organic electrochemical transitors. Org. Electron. 2018, 63, 398,  DOI: 10.1016/j.orgel.2018.09.010

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    Device physics of organic electrochemical transistors

    Friedlein, Jacob T.; McLeod, Robert R.; Rivnay, Jonathan

    Organic Electronics (2018), 63 (), 398-414CODEN: OERLAU; ISSN:1566-1199. (Elsevier B.V.)

    Org. electrochem. transistors (OECTs) are thin-film transistors that have shown great promise in a range of applications including biosensing, logic circuits, and neuromorphic engineering. The device physics of OECTs are detd. by the interaction between ionic and electronic charge carriers. This interaction sets OECTs apart from conventional transistor technologies and has necessitated the development of device models for the unique behavior of OECTs. In this Review, we discuss existing models for OECTs and provide a framework for understanding these models. Moreover, we show how the insight from these models inform device optimization. Finally, we discuss details of OECT operation that are not well-understood and that provide exciting opportunities for future research.
47. 47

    Kaake, L. G.; Zou, Y.; Panzer, M. J.; Frisbie, C. D.; Zhu, X.-Y. Vibrational Spectroscopy Reveals Electrostatic and Electrochemical Doping in Organic Thin Film Transistors Gated with a Polymer Electrolyte Dielectric. J. Am. Chem. Soc. 2007, 129, 7824,  DOI: 10.1021/ja070615x

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    47

    Vibrational Spectroscopy Reveals Electrostatic and Electrochemical Doping in Organic Thin Film Transistors Gated with a Polymer Electrolyte Dielectric

    Kaake, L. G.; Zou, Y.; Panzer, M. J.; Frisbie, C. D.; Zhu, X.-Y.

    Journal of the American Chemical Society (2007), 129 (25), 7824-7830CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)

    We apply attenuated total internal reflection Fourier transform IR (ATR-FTIR) spectroscopy to directly probe active layers in org. thin film transistors (OTFTs). The OTFT studied uses the n-type org. semiconductor N-N'-dioctyl-3,4,9,10-perylene tetracarboxylic diimide (PTCDI-C8) and a polymer electrolyte gate dielec. made from poly(ethylene oxide) and LiClO4. FTIR spectroscopy of the device shows signatures of anionic PTCDI-C8 species and broad polaron bands when the org. semiconductor layer is doped under pos. gate bias (VG). There are two distinctive doping regions: a reversible and electrostatic doping region for VG ≤ 2 V and an irreversible and electrochem. doping regime for VG > 2 V. On the basis of intensity loss of vibrational peaks attributed to neutral PTCDI-C8, we obtain a charge carrier d. of 2.9 × 1014/cm2 at VG = 2 V; this charge injection d. corresponds to the conversion of slightly more than one monolayer of PTCDI-C8 mols. into anions. At higher gate bias voltage, electrochem. doping involving the intercalation of Li+ into the org. semiconductor film can convert all PTCDI-C8 mols. in a 30-nm film into anionic species. For comparison, when a conventional gate dielec. (polystyrene) is used, the max. charge carrier d. achievable at VG = 200 V is ∼4.5 × 1013/cm2, which corresponds to the conversion of 18% of a monolayer of PTCDI-C8 mols. into anions.
48. 48

    Natelson, D.; Di Ventra, M. Ion motion and electrochemistry in nanostructures. MRS Bull. 2011, 36, 914,  DOI: 10.1557/mrs.2011.266

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    Ion motion and electrochemistry in nanostructures

    Natelson, Douglas; Di Ventra, Massimiliano

    MRS Bulletin (2011), 36 (11), 914-920CODEN: MRSBEA; ISSN:0883-7694. (Materials Research Society)

    A review. Ionic motion and electrochem. in bulk materials and at their surfaces have long been studied for their relevance in several areas of science and technol., ranging from ionic conductors to batteries to fuel cells. The ability to engineer materials at the nanometer scale, however, has made these concepts even more relevant. This is due to the large surface-to-vol. ratios typical of nanostructures. This implies, for instance, that chem. reactivity and defect motion at surfaces or interfaces are enhanced or may be fundamentally different compared to their bulk counterparts. In addn., nominally modest voltages or differences in chem. potential when applied across nanoscale distances can produce large elec. fields and diffusive forces. While all of this may complicate the interpretation of exptl. results, it also presents us with new opportunities for materials engineering. In this article, the current research status of several systems where ionic motion and electrochem. effects are of particular importance is briefly reviewed. These include resistive switching systems, oxide heterostructures, ferroelec. materials, and ionic liqs. It is reported on exptl. results and also open questions regarding their interpretation are emphasized. It is concluded by discussing future research directions in the field.
49. 49

    Siemons, N.; Pearce, D.; Cendra, C.; Yu, H.; Tuladhar, S. M.; Hallani, R. K.; Sheelamanthula, R.; LeCroy, G. S.; Siemons, L.; White, A. J. P.; McCulloch, I.; Salleo, A.; Frost, J. M.; Giovannitti, A.; Nelson, J. Impact of Side-Chain Hydrophilicity on Packing, Swelling, and Ion Interactions in Oxy-Bithiophene Semiconductors. Adv. Mater. 2022, 34, 2204258,  DOI: 10.1002/adma.202204258

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    49

    Impact of Side-Chain Hydrophilicity on Packing, Swelling, and Ion Interactions in Oxy-Bithiophene Semiconductors

    Siemons, Nicholas; Pearce, Drew; Cendra, Camila; Yu, Hang; Tuladhar, Sachetan M.; Hallani, Rawad K.; Sheelamanthula, Rajendar; LeCroy, Garrett S.; Siemons, Lucas; White, Andrew J. P.; McCulloch, Iain; Salleo, Alberto; Frost, Jarvist M.; Giovannitti, Alexander; Nelson, Jenny

    Advanced Materials (Weinheim, Germany) (2022), 34 (39), 2204258CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)

    Exchanging hydrophobic alkyl-based side chains to hydrophilic glycol-based side chains is a widely adopted method for improving mixed-transport device performance, despite the impact on solid-state packing and polymer-electrolyte interactions being poorly understood. Presented here is a mol. dynamics (MD) force field for modeling alkoxylated and glycolated polythiophenes. The force field is validated against known packing motifs for their monomer crystals. MD simulations, coupled with XRD, show that alkoxylated polythiophenes will pack with a tilted stack and straight interdigitating side chains, while their glycolated counterpart will pack with a deflected stack and an s-bend side-chain configuration. MD simulations reveal H2O penetration pathways into the alkoxylated and glycolated crystals-through the π-stack and through the lamellar stack, resp. Finally, the 2 distinct ways triethylene glycol polymers can bind to cations are revealed, showing the formation of a metastable single bound state, or an energetically deep double bound state, both with a strong side-chain length dependence. The min. energy pathways for the formation of the chelates are identified, showing the phys. process through which cations can bind to 1 or 2 side chains of a glycolated polythiophene, with consequences for ion transport in bithiophene semiconductors.