Charge Transfer from Photoexcited Semiconducting Single-Walled Carbon Nanotubes to Wide-Bandgap Wrapping Polymer

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1. 1

   Nish, A.; Hwang, J.-Y.; Doig, J.; Nicholas, R. J. Highly selective dispersion of single-walled carbon nanotubes using aromatic polymers. Nat. Nanotechnol. 2007, 2 (10), 640– 646,  DOI: 10.1038/nnano.2007.290

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   1

   Highly selective dispersion of single-walled carbon nanotubes using aromatic polymers

   Nish, Adrian; Hwang, Jeong-Yuan; Doig, James; Nicholas, Robin J.

   Nature Nanotechnology (2007), 2 (10), 640-646CODEN: NNAABX; ISSN:1748-3387. (Nature Publishing Group)

   Solubilizing and purifying carbon nanotubes remains one of the foremost technol. hurdles in their investigation and application. We report a dramatic improvement in the prepn. of single-walled carbon nanotube solns. based on the ability of specific arom. polymers to efficiently disperse certain nanotube species with a high degree of selectivity. Evidence of this is provided by optical absorbance and photoluminescence excitation spectra, which show suspensions corresponding to up to ∼60% relative concn. of a single species of isolated nanotubes with fluorescence quantum yields of up to 1.5%. Different polymers show the ability to discriminate between nanotube species in terms of either diam. or chiral angle. Modeling suggests that rigid-backbone polymers form ordered mol. structures surrounding the nanotubes with n-fold symmetry detd. by the tube diam.
2. 2

   Graf, A.; Zakharko, Y.; Schießl, S. P.; Backes, C.; Pfohl, M.; Flavel, B. S.; Zaumseil, J. Large scale, selective dispersion of long single-walled carbon nanotubes with high photoluminescence quantum yield by shear force mixing. Carbon 2016, 105, 593– 599,  DOI: 10.1016/j.carbon.2016.05.002

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   Large scale, selective dispersion of long single-walled carbon nanotubes with high photoluminescence quantum yield by shear force mixing

   Graf, Arko; Zakharko, Yuriy; Schiessl, Stefan P.; Backes, Claudia; Pfohl, Moritz; Flavel, Benjamin S.; Zaumseil, Jana

   Carbon (2016), 105 (), 593-599CODEN: CRBNAH; ISSN:0008-6223. (Elsevier Ltd.)

   Selective dispersion of semiconducting single-walled carbon nanotube (SWCNTs) with conjugated polymers typically involves harsh sonication methods that damage and shorten the nanotubes. Here, we use simple high speed shear force mixing (SFM) to disperse nearly monochiral (6,5) SWCNTs with poly[(9,9-dioctylfluorenyl-2,7-diyl)-alt-co-(6,6'-{2,2'-bipyridine})] (PFO-BPy) in toluene with high yield and in large vols. This highly scalable process disperses SWCNTs of exceptional quality with an av. tube length of 1.82 μm and an ensemble photoluminescence quantum yield (PLQY) of 2.3%. For the first time for SWCNTs, we describe and apply abs. PLQY measurements, without the need for any ref. emitter. We directly compare values for av. SWCNT length, PLQY, linewidth and Stokes shift to other dispersion methods, including bath and tip sonication, as well as other sorting methods such as gel chromatog. We find that SFM results in dispersions of longer SWCNT with higher av. PLQY than any other technique, thus making it an ideal method for sorting large amts. of long, high quality and purely semiconducting SWCNTs.
3. 3

   Samanta, S. K.; Fritsch, M.; Scherf, U.; Gomulya, W.; Bisri, S. Z.; Loi, M. A. Conjugated Polymer-Assisted Dispersion of Single-Wall Carbon Nanotubes: The Power of Polymer Wrapping. Acc. Chem. Res. 2014, 47 (8), 2446– 2456,  DOI: 10.1021/ar500141j

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   Conjugated Polymer-Assisted Dispersion of Single-Wall Carbon Nanotubes: The Power of Polymer Wrapping

   Samanta, Suman Kalyan; Fritsch, Martin; Scherf, Ullrich; Gomulya, Widianta; Bisri, Satria Zulkarnaen; Loi, Maria Antonietta

   Accounts of Chemical Research (2014), 47 (8), 2446-2456CODEN: ACHRE4; ISSN:0001-4842. (American Chemical Society)

   The future application of single-walled carbon nanotubes (SWNTs) in electronic (nano)devices is closely coupled to the availability of pure, semiconducting SWNTs and preferably, their defined positioning on suited substrates. Com. carbon nanotube raw mixts. contain metallic as well as semiconducting tubes of different diam. and chirality. Although many techniques such as d. gradient ultracentrifugation, dielectrophoresis, and dispersion by surfactants or polar biopolymers have been developed, so-called conjugated polymer wrapping is one of the most promising and powerful purifn. and discrimination strategies. The procedure involves debundling and dispersion of SWNTs by wrapping semiflexible conjugated polymers, such as poly(9,9-dialkylfluorene)s (PFx) or regioregular poly(3-alkylthiophene)s (P3AT), around the SWNTs, and is accompanied by SWNT discrimination by diam. and chirality. Thereby, the π-conjugated backbone of the conjugated polymers interacts with the two-dimensional, graphene-like π-electron surface of the nanotubes and the solubilizing alkyl side chains of optimal length support debundling and dispersion in org. solvents. Careful structural design of the conjugated polymers allows for a selective and preferential dispersion of both small and large diam. SWNTs or SWNTs of specific chirality. As an example, with polyfluorenes as dispersing agents, it was shown that alkyl chain length of eight carbons are favored for the dispersion of SWNTs with diams. of 0.8-1.2 nm and longer alkyls with 12-15 carbons can efficiently interact with nanotubes of increased diam. up to 1.5 nm. Polar side chains at the PF backbone produce dispersions with increased SWNT concn. but, unfortunately, cause redn. in selectivity. The selectivity of the dispersion process can be monitored by a combination of absorption, photoluminescence, and photoluminescence excitation spectroscopy, allowing identification of nanotubes with specific coordinates [(n,m) indexes]. The polymer wrapping strategy enables the generation of SWNT dispersions contg. exclusively semiconducting nanotubes. Toward the applications in electronic devices, until now most applied approach is a direct processing of such SWNT dispersions into the active layer of network-type thin film field effect transistors. However, to achieve promising transistor performance (high mobility and on-off ratio) careful removal of the wrapping polymer chains seems crucial, for example, by washing or ultracentrifugation. More defined positioning of the SWNTs can be accomplished in directed self-assembly procedures. One possible strategy uses diblock copolymers contg. a conjugated polymer block as dispersing moiety and a second block for directed self-assembly, for example, a DNA block for specific interaction with complementary DNA strands. Another strategy utilizes reactive side chains for controlled anchoring onto patterned surfaces (e.g., by interaction of thiol-terminated alkyl side chains with gold surfaces). A further promising application of purified SWNT dispersions is the field of org. (all-carbon) or hybrid solar cell devices.
4. 4

   Rother, M.; Brohmann, M.; Yang, S.; Grimm, S. B.; Schiessl, S. P.; Graf, A.; Zaumseil, J. Aerosol-Jet Printing of Polymer-Sorted (6,5) Carbon Nanotubes for Field-Effect Transistors with High Reproducibility. Adv. Electron. Mater. 2017, 3 (8), 1700080,  DOI: 10.1002/aelm.201700080

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5. 5

   Graf, A.; Murawski, C.; Zakharko, Y.; Zaumseil, J.; Gather, M. C. Infrared Organic Light-Emitting Diodes with Carbon Nanotube Emitters. Adv. Mater. 2018, 30 (12), 1706711,  DOI: 10.1002/adma.201706711

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6. 6

   Berger, F. J.; Higgins, T. M.; Rother, M.; Graf, A.; Zakharko, Y.; Allard, S.; Matthiesen, M.; Gotthardt, J. M.; Scherf, U.; Zaumseil, J. From Broadband to Electrochromic Notch Filters with Printed Monochiral Carbon Nanotubes. ACS Appl. Mater. Interfaces 2018, 10 (13), 11135– 11142,  DOI: 10.1021/acsami.8b00643

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   From Broadband to Electrochromic Notch Filters with Printed Monochiral Carbon Nanotubes

   Berger, Felix J.; Higgins, Thomas M.; Rother, Marcel; Graf, Arko; Zakharko, Yuriy; Allard, Sybille; Matthiesen, Maik; Gotthardt, Jan M.; Scherf, Ullrich; Zaumseil, Jana

   ACS Applied Materials & Interfaces (2018), 10 (13), 11135-11142CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)

   Dense layers of semiconducting single-walled C nanotubes (SWNTs) serve as electrochromic (EC) materials in the near-IR with high absorbance and high cond. EC cells with tunable notch filter properties instead of broadband absorption are created via highly selective dispersion of specific semiconducting SWNTs through polymer-wrapping followed by deposition of thick films by aerosol-jet printing. A simple planar geometry with spray-coated mixed SWNTs as the counter electrode renders transparent metal oxides redundant and facilitates complete bleaching within a few seconds through iongel electrolytes with high ionic conductivities. Monochiral (6,5) SWNT films as working electrodes exhibit a narrow absorption band at 997 nm (full width at half-max. of 55-73 nm) with voltage-dependent optical densities between 0.2 and 4.5 and a modulation depth of ≤43 dB. These (6,5) SWNT notch filters can retain >95% of max. bleaching for several hours under open-circuit conditions. Different levels of transmission can be set by applying const. low voltage (1.5 V) pulses with modulated width or by a given no. of fixed short pulses.
7. 7

   Ye, Y.; Bindl, D. J.; Jacobberger, R. M.; Wu, M.-Y.; Roy, S. S.; Arnold, M. S. Semiconducting Carbon Nanotube Aerogel Bulk Heterojunction Solar Cells. Small 2014, 10 (16), 3299– 3306,  DOI: 10.1002/smll.201400696

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   Semiconducting Carbon Nanotube Aerogel Bulk Heterojunction Solar Cells

   Ye, Yumin; Bindl, Dominick J.; Jacobberger, Robert M.; Wu, Meng-Yin; Roy, Susmit Singha; Arnold, Michael S.

   Small (2014), 10 (16), 3299-3306CODEN: SMALBC; ISSN:1613-6810. (Wiley-VCH Verlag GmbH & Co. KGaA)

   Using a novel two-step fabrication scheme, we form highly semiconducting-enriched single-walled carbon nanotube (sSWNT) bulk heterojunctions by first forming highly porous interconnected sSWNT aerogels (sSWNT-AEROs), followed by back-filling the pores with [6,6]-phenyl-C71-butyric acid Me ester (PC71BM). We demonstrate sSWNT-AERO structures with d. as low as 2.5 mg/cm3, porosity as high as 99.8%, and diam. of sSWNT fibers ≤10 nm. Upon spin coating with PC71BM, the resulting sSWNT-AERO-PC71BM nanocomposites exhibit highly quenched sSWNT photoluminescence, which is attributed to the large interfacial area between the sSWNT and PC71BM phases, and an appropriate sSWNT fiber diam. that matches the inter-sSWNT exciton migration length. Employing the sSWNT-AERO-PC71BM bulk heterojunction structure, we report optimized solar cells with a power conversion efficiency of 1.7%, which is exceptional among polymer-like solar cells in which sSWNTs are designed to replace either the polymer or fullerene component. A fairly balanced photocurrent is achieved with 36% peak external quantum efficiency in the visible and 19% peak external quantum efficiency in the near-IR where sSWNTs serve as electron donors and photoabsorbers. Our results prove the effectiveness of this new method in controlling the sSWNT morphol. in bulk heterojunction structures, suggesting a promising route for highly efficient sSWNT photoabsorbing solar cells.
8. 8

   Pfohl, M.; Glaser, K.; Graf, A.; Mertens, A.; Tune, D. D.; Puerckhauer, T.; Alam, A.; Wei, L.; Chen, Y.; Zaumseil, J. Probing the Diameter Limit of Single Walled Carbon Nanotubes in SWCNT: Fullerene Solar Cells. Adv. Energy Mater. 2016, 6 (21), 1600890,  DOI: 10.1002/aenm.201600890

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   There is no corresponding record for this reference.
9. 9

   Li, G.; Suja, M.; Chen, M.; Bekyarova, E.; Haddon, R. C.; Liu, J.; Itkis, M. E. Visible-Blind UV Photodetector Based on Single-Walled Carbon Nanotube Thin Film/ZnO Vertical Heterostructures. ACS Appl. Mater. Interfaces 2017, 9 (42), 37094– 37104,  DOI: 10.1021/acsami.7b07765

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   Visible-Blind UV Photodetector Based on Single-Walled Carbon Nanotube Thin Film/ZnO Vertical Heterostructures

   Li, Guanghui; Suja, Mohammad; Chen, Mingguang; Bekyarova, Elena; Haddon, Robert C.; Liu, Jianlin; Itkis, Mikhail E.

   ACS Applied Materials & Interfaces (2017), 9 (42), 37094-37104CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)

   UV photodetectors based on heterojunctions of conventional (Ge, Si, and GaAs) and wide bandgap semiconductors were recently demonstrated, but achieving high UV sensitivity and visible-blind photodetection still remains a challenge. Here, the authors used a semitransparent film of p-type semiconducting single-walled C nanotubes (SC-SWNTs) with an energy gap of 0.68 ± 0.07 eV in combination with a MBE grown n-ZnO layer to build a vertical p-SC-SWNT/n-ZnO heterojunction-based UV photodetector. The resulting device shows a current rectification ratio of 103, a current photoresponsivity ≤400 A/W in the UV range 230-370 to nm, and a low dark current. The detector is practically visible-blind with the UV-to-visible photoresponsivity ratio of 105 due to extremely short photocarrier lifetimes in the 1-dimensional SWNTs because of strong electron-phonon interactions leading to exciton formation. In this vertical configuration, UV radiation penetrates the top semitransparent SC-SWNT layer with low losses (10-20%) and excites photocarriers within the n-ZnO layer in close proximity to the p-SC-SWNT/n-ZnO interface, where electron-hole pairs are efficiently sepd. by a high built-in elec. field assocd. with the heterojunction.
10. 10

    Schuettfort, T.; Nish, A.; Nicholas, R. J. Observation of a type II heterojunction in a highly ordered polymer-carbon nanotube nanohybrid structure. Nano Lett. 2009, 9 (11), 3871– 6,  DOI: 10.1021/nl902081t

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    10

    Observation of a type II heterojunction in a highly ordered polymer-carbon nanotube nanohybrid structure

    Schuettfort, Torben; Nish, Adrian; Nicholas, Robin J.

    Nano Letters (2009), 9 (11), 3871-3876CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)

    We report a study of the electronic properties of the heterojunction between regioregular poly(3-hexylthiophene) (rrP3HT) and single-walled C nanotubes (SWNTs). Comparison of the spectroscopic data of nanotube dispersions in a range of polymers indicates significant changes in the nature of the obsd. SWNT excitons only in combination with rrP3HT. A detailed anal. concludes that a type II heterojunction between rrP3HT and small diam. s-SWNTs is formed, making these particular nanohybrids a promising material for org. photovoltaics.
11. 11

    Eckstein, A.; Karpicz, R.; Augulis, R.; Redeckas, K.; Vengris, M.; Namal, I.; Hertel, T.; Gulbinas, V. Excitation quenching in polyfluorene polymers bound to (6,5) single-wall carbon nanotubes. Chem. Phys. 2016, 467, 1– 5,  DOI: 10.1016/j.chemphys.2015.12.006

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    11

    Excitation quenching in polyfluorene polymers bound to (6,5) single-wall carbon nanotubes

    Eckstein, Angela; Karpicz, Renata; Augulis, Ramunas; Redeckas, Kipras; Vengris, Mikas; Namal, Imge; Hertel, Tobias; Gulbinas, Vidmantas

    Chemical Physics (2016), 467 (), 1-5CODEN: CMPHC2; ISSN:0301-0104. (Elsevier B.V.)

    Fluorescence quenching of polyfluorene-based polymer (PFO-BPy) attached to single-wall carbon nanotubes (SWNT) has been investigated by means of fluorescence and transient absorption spectroscopy. Fluorescence of SWNT/PFO-BPy complex suspension in chlorobenzene decays nonexponentialy on a time scale from several to several hundreds of picoseconds, and experiences slower depolarization if compared with free polymer in soln. We attribute the slowly quenched and more polarized fluorescence to the polymer tail segments that are not in direct contact with the SWNT. Polymer fluorescence in SWNT/PFO-BPy solid films is quenched about 10 times faster than in suspensions. The initial excited state quenching in films occurs with a 2.3 ps time const., which we attribute to the polymer chains intimately attached to the SWNT. Slow changes of the spectroscopic properties of the SWNT/PFO-BPy suspensions with time revealed that their aging is assocd. with the desorption of polymers from SWNT, increasing their tendency to aggregate.
12. 12

    Amori, A. R.; Hou, Z.; Krauss, T. D. Excitons in Single-Walled Carbon Nanotubes and Their Dynamics. Annu. Rev. Phys. Chem. 2018, 69, 81– 99,  DOI: 10.1146/annurev-physchem-050317-014241

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    12

    Excitons in Single-Walled Carbon Nanotubes and Their Dynamics

    Amori, Amanda R.; Hou, Zhentao; Krauss, Todd D.

    Annual Review of Physical Chemistry (2018), 69 (), 81-99CODEN: ARPLAP; ISSN:0066-426X. (Annual Reviews)

    Understanding exciton dynamics in single-walled carbon nanotubes (SWCNTs) is essential to unlocking the many potential applications of these materials. This review summarizes recent progress in understanding exciton photophysics and, in particular, exciton dynamics in SWCNTs. We outline the basic phys. and electronic properties of SWCNTs, as well as bright and dark transitions within the framework of a strongly bound one-dimensional excitonic model. We discuss the many facets of ultrafast carrier dynamics in SWCNTs, including both single-exciton states (bright and dark) and multiple-exciton states. Photophys. properties that directly relate to excitons and their dynamics, including exciton diffusion lengths, chem. and structural defects, environmental effects, and photoluminescence photon statistics as obsd. through photon antibunching measurements, are also discussed. Finally, we identify a few key areas for advancing further research in the field of SWCNT excitons and photonics.
13. 13

    Bindl, D. J.; Arnold, M. S. Efficient Exciton Relaxation and Charge Generation in Nearly Monochiral (7,5) Carbon Nanotube/C60 Thin-Film Photovoltaics. J. Phys. Chem. C 2013, 117 (5), 2390– 2395,  DOI: 10.1021/jp310983y

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    13

    Efficient Exciton Relaxation and Charge Generation in Nearly Monochiral (7,5) Carbon Nanotube/C60 Thin-Film Photovoltaics

    Bindl, Dominick J.; Arnold, Michael S.

    Journal of Physical Chemistry C (2013), 117 (5), 2390-2395CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)

    N photovoltaic diodes based on bilayer heterojunctions between nearly monochiral, polymer wrapped (7,5) semiconducting carbon nanotube photoabsorbing films and C60 are reported. The internal quantum efficiencies (IQEs) for exciton dissocn. and subsequent charge collection at the nanotubes visible E22 and near-IR E11 and E11 + X resonances are 84% ± 7%, 85% ± 5%, and 84% ± 14%, resp. The high IQE at each transition shows that recombination losses during relaxation and/or direct dissocn. of hot E11 + X and E22 excitons are negligible. A peak external quantum efficiency (EQE) of 34% is achieved at the E11 transition. Zero-bias photoresponsivity is invariant up to short-circuit current densities of at least 23 mA cm-2, indicating negligible losses via trion, charge-exciton, and charge-charge recombination relaxation pathways. An open circuit voltage of 0.49 V and power conversion efficiency of 7.1% are achieved in response to monochromatic excitation of the diodes at the E11 transition. The high IQE across multiple spectral windows, invariant photoresponsivity, and attractive open circuit voltage relative to the 1.18 eV optical bandgap demonstrate the future promise of using monochiral and multichiral semiconducting carbon nanotube films for broadband solar photovoltaic applications.
14. 14

    Wang, J.; Peurifoy, S. R.; Bender, M. T.; Ng, F.; Choi, K.-S.; Nuckolls, C.; Arnold, M. S. Non-fullerene Acceptors for Harvesting Excitons from Semiconducting Carbon Nanotubes. J. Phys. Chem. C 2019, 123 (35), 21395– 21402,  DOI: 10.1021/acs.jpcc.9b06381

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    14

    Non-fullerene acceptors for harvesting excitons from semiconducting carbon nanotubes

    Wang, Jialiang; Peurifoy, Samuel R.; Bender, Michael T.; Ng, Fay; Choi, Kyoung-Shin; Nuckolls, Colin; Arnold, Michael S.

    Journal of Physical Chemistry C (2019), 123 (35), 21395-21402CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)

    Semiconducting single-walled carbon nanotubes (s-SWCNTs) are promising materials for solar energy conversion and photodetectors. Fullerenes and their derivs., being widely employed as electron acceptors in s-SWCNT photovoltaic devices, effectively dissoc. s-SWCNT excitons by forming heterojunctions with favorable energetic offsets. However, their limited tunability and poor co-processability with s-SWCNTs in blends have been major obstacles for further improving the device performance. Here, we investigate the exciton dissocg. capability of a series of non-fullerene acceptors (NFAs) based on indacenodithiophene and perylene diimides, by measuring internal quantum efficiency (QE) for exciton dissocn. and electron transfer in bilayer s-SWCNT/NFA devices. A max. internal QE of ∼50% is achieved with a (6,5) s-SWCNT/indacenodithiophene-based acceptor heterojunction. Our results indicate that non-fullerene acceptors with deeper electron affinities could potentially replace traditional fullerene acceptors in s-SWCNT photovoltaic devices.
15. 15

    Mollahosseini, M.; Karunaratne, E.; Gibson, G. N.; Gascon, J. A.; Papadimitrakopoulos, F. Fullerene-Assisted Photoinduced Charge Transfer of Single-Walled Carbon Nanotubes through a Flavin Helix. J. Am. Chem. Soc. 2016, 138 (18), 5904– 15,  DOI: 10.1021/jacs.5b13496

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    15

    Fullerene-assisted photoinduced charge transfer of single-walled carbon nanotubes through a flavin helix

    Mollahosseini, Mehdi; Karunaratne, Erandika; Gibson, George N.; Gascon, Jose A.; Papadimitrakopoulos, Fotios

    Journal of the American Chemical Society (2016), 138 (18), 5904-5915CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)

    One of the greatest challenges with single-walled carbon nanotube (SWNT) photovoltaics and nanostructured devices is maintaining the nanotubes in their pristine state (i.e., devoid of aggregation and inhomogeneous doping) so that their unique spectroscopic and transport characteristics are preserved. To this effect, we report on the synthesis and self-assembly of a C60-functionalized flavin (FC60), composed of PCBM and isoalloxazine moieties attached on either ends of a linear, C-12 aliph. spacer. Small amts. of FC60 (up to 3 M %) were shown to coassembly with an org. sol. deriv. of flavin (FC12) around SWNTs and impart effective dispersion and individualization. A key annealing step was necessary to perfect the isoalloxazine helix and expel the C60 moiety away from the nanotubes. Steady-state and transient absorption spectroscopy illustrate that 1% or higher incorporation of FC60 allows for an effective photoinduced charge transfer quenching of the encased SWNTs through the seamless helical encase. This is enabled via the direct π-π overlap between the graphene sidewalls, isoalloxazine helix, and the C60 cage that facilitates SWNT exciton dissocn. and electron transfer to the PCBM moiety. Atomistic mol. simulations indicate that the stability of the complex originates from enhanced van der Waals interactions of the flexible spacer wrapped around the fullerene that brings the C60 in π-π overlap with the isoalloxazine helix. The remarkable spectral purity (in terms of narrow ESii line widths) for the resulting ground-state complex signals a new class of highly organized supramol. nanotube architecture with profound importance for advanced nanostructured devices.
16. 16

    Balcı Leinen, M.; Berger, F. J.; Klein, P.; Mühlinghaus, M.; Zorn, N. F.; Settele, S.; Allard, S.; Scherf, U.; Zaumseil, J. Doping-Dependent Energy Transfer from Conjugated Polyelectrolytes to (6,5) Single-Walled Carbon Nanotubes. J. Phys. Chem. C 2019, 123 (36), 22680– 22689,  DOI: 10.1021/acs.jpcc.9b07291

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    16

    Doping-Dependent Energy Transfer from Conjugated Polyelectrolytes to (6,5) Single-Walled Carbon Nanotubes

    Balci Leinen, Merve; Berger, Felix J.; Klein, Patrick; Muehlinghaus, Markus; Zorn, Nicolas F.; Settele, Simon; Allard, Sybille; Scherf, Ullrich; Zaumseil, Jana

    Journal of Physical Chemistry C (2019), 123 (36), 22680-22689CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)

    Conjugated polymers exhibit strong interactions with single-walled carbon nanotubes (SWNTs). These enable the selective dispersion of specific semiconducting SWNTs in org. solvents and polymer-mediated energy transfer to the nanotubes followed by emission in the near-IR. Conjugated polyelectrolytes with ionic side-chains can add further functionalities to these nanotube/polymer hybrids such as dispersibility in polar solvents (e.g., methanol) and self-doping. Here, we demonstrate and investigate energy transfer from a range of conjugated polymers to preselected (6,5) SWNTs with varying spectral overlap between the optical transitions of the polymer and nanotube. We find evidence for increased backbone planarization of the polymers wrapped around the nanotubes. Furthermore, ambient p-doping of hybrids of anionic conjugated polyelectrolytes and (6,5) SWNTs blocks energy transfer in contrast to cationic polyelectrolytes. By addn. of a mild reducing agent, thus removing the p-doping, the energy transfer can be fully restored pointing toward an electron exchange mechanism. The p-doping of nanotube/polyelectrolyte hybrids in air and their doping-dependent emission and charge transport properties also become apparent in water-gated field-effect transistors based on such networks and might be useful for dual-signal sensing applications.
17. 17

    Stranks, S. D.; Yong, C.-K.; Alexander-Webber, J. A.; Weisspfennig, C.; Johnston, M. B.; Herz, L. M.; Nicholas, R. J. Nanoengineering Coaxial Carbon Nanotube–Dual-Polymer Heterostructures. ACS Nano 2012, 6 (7), 6058– 6066,  DOI: 10.1021/nn301133v

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    17

    Nanoengineering Coaxial Carbon Nanotube-Dual-Polymer Heterostructures

    Stranks, Samuel D.; Yong, Chaw-Keong; Alexander-Webber, Jack A.; Weisspfennig, Christian; Johnston, Michael B.; Herz, Laura M.; Nicholas, Robin J.

    ACS Nano (2012), 6 (7), 6058-6066CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)

    We describe studies of new nanostructured materials consisting of carbon nanotubes wrapped in sequential coatings of two different semiconducting polymers, namely, poly(3-hexylthiophene) (P3HT) and poly(9,9'-dioctylfluorene-co-benzothiadiazole) (F8BT). Using absorption spectroscopy and steady-state and ultrafast photoluminescence measurements, we demonstrate the role of the different layer structures in controlling energy levels and charge transfer in both soln. and film samples. By varying the simple soln. processing steps, we can control the ordering and proportions of the wrapping polymers in the solid state. The resulting novel coaxial structures open up a variety of new applications for nanotube blends and are particularly promising for implementation into org. photovoltaic devices. The carbon nanotube template can also be used to optimize both the electronic properties and morphol. of polymer composites in a much more controlled fashion than achieved previously, offering a route to producing a new generation of polymer nanostructures.
18. 18

    Kang, H. S.; Sisto, T. J.; Peurifoy, S.; Arias, D. H.; Zhang, B.; Nuckolls, C.; Blackburn, J. L. Long-Lived Charge Separation at Heterojunctions between Semiconducting Single-Walled Carbon Nanotubes and Perylene Diimide Electron Acceptors. J. Phys. Chem. C 2018, 122 (25), 14150– 14161,  DOI: 10.1021/acs.jpcc.8b01400

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    18

    Long-Lived Charge Separation at Heterojunctions between Semiconducting Single-Walled Carbon Nanotubes and Perylene Diimide Electron Acceptors

    Kang, Hyun Suk; Sisto, Thomas J.; Peurifoy, Samuel; Arias, Dylan H.; Zhang, Boyuan; Nuckolls, Colin; Blackburn, Jeffrey L.

    Journal of Physical Chemistry C (2018), 122 (25), 14150-14161CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)

    Nonfullerene electron acceptors have facilitated a recent surge in the efficiencies of org. solar cells, although fundamental studies of the nature of exciton dissocn. at interfaces with nonfullerene electron acceptors are still relatively sparse. Semiconducting single-walled carbon nanotubes (s-SWCNTs), unique 1-dimensional electron donors with mol.-like absorption and highly mobile charges, provide a model system for studying interfacial exciton dissocn. Here, the authors study excited-state photodynamics at the heterojunction between (6,5) s-SWCNTs and two perylene diimide (PDI)-based electron acceptors. Each of the PDI-based acceptors, hPDI2-pyr-hPDI2 and Trip-hPDI2, is deposited onto (6,5) s-SWCNT films to form a heterojunction bilayer. Transient absorption measurements demonstrate that photoinduced hole/electron transfer occurs at the photoexcited bilayer interfaces, producing long-lived sepd. charges with lifetimes exceeding 1.0 μs. Both exciton dissocn. and charge recombination occur more slowly for the hPDI2-pyr-hPDI2 bilayer than for the Trip-hPDI2 bilayer. To explain such differences, the potential roles of the thermodn. charge transfer driving force available at each interface and the different mol. structure and intermol. interactions of PDI-based acceptors are discussed. Detailed photophys. anal. of these model systems can develop the fundamental understanding of exciton dissocn. between org. electron donors and nonfullerene acceptors, which was not systematically studied.
19. 19

    Stranks, S. D.; Weisspfennig, C.; Parkinson, P.; Johnston, M. B.; Herz, L. M.; Nicholas, R. J. Ultrafast charge separation at a polymer-single-walled carbon nanotube molecular junction. Nano Lett. 2011, 11 (1), 66– 72,  DOI: 10.1021/nl1036484

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    19

    Ultrafast charge separation at a polymer-single-walled carbon nanotube molecular junction

    Stranks, Samuel D.; Weisspfennig, Christian; Parkinson, Patrick; Johnston, Michael B.; Herz, Laura M.; Nicholas, Robin J.

    Nano Letters (2011), 11 (1), 66-72CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)

    We have investigated the charge photogeneration dynamics at the interface formed between single-walled carbon nanotubes (SWNTs) and poly(3-hexylthiophene) (P3HT) using a combination of femtosecond spectroscopic techniques. We demonstrate that photoexcitation of P3HT forming a single mol. layer around a SWNT leads to an ultrafast (∼ 430 fs) charge transfer between the materials. The addn. of excess P3HT leads to long-term charge sepn. in which free polarons remain sepd. at room temp. Our results suggest that SWNT-P3HT blends incorporating only small fractions (1%) of SWNTs allow photon-to-charge conversion with efficiencies comparable to those for conventional (60:40) P3HT-fullerene blends, provided that small-diam. tubes are individually embedded in the P3HT matrix.
20. 20

    Niklas, J.; Holt, J. M.; Mistry, K.; Rumbles, G.; Blackburn, J. L.; Poluektov, O. G. Charge Separation in P3HT:SWCNT Blends Studied by EPR: Spin Signature of the Photoinduced Charged State in SWCNT. J. Phys. Chem. Lett. 2014, 5 (3), 601– 606,  DOI: 10.1021/jz402668h

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    Charge Separation in P3HT:SWCNT Blends Studied by EPR: Spin Signature of the Photoinduced Charged State in SWCNT

    Niklas, Jens; Holt, Josh M.; Mistry, Kevin; Rumbles, Garry; Blackburn, Jeffrey L.; Poluektov, Oleg G.

    Journal of Physical Chemistry Letters (2014), 5 (3), 601-606CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)

    Single-wall carbon nanotubes (SWCNTs) could be employed in org. photovoltaic (OPV) devices as a replacement or additive for currently used fullerene derivs., but significant research remains to explain fundamental aspects of charge generation. ESR (EPR) spectroscopy, which is sensitive only to unpaired electrons, was applied to explore charge sepn. in P3HT:SWCNT blends. The EPR signal of the P3HT pos. polaron increases as the concn. of SWCNT acceptors in a photoexcited P3HT:SWCNT blend is increased, demonstrating long-lived charge sepn. induced by electron transfer from P3HT to SWCNTs. An EPR signal from reduced SWCNTs was not identified in blends due to the free and fast-relaxing nature of unpaired SWCNT electrons as well as spectral overlap of this EPR signal with the signal from pos. P3HT polarons. However, a weak EPR signal was obsd. in chem. reduced SWNTs, and the g values of this signal are close to those of C70-PCBM anion radical. The anisotropic line shape indicates that these unpaired electrons are not free but instead localized.
21. 21

    Ferguson, A. J.; Blackburn, J. L.; Holt, J. M.; Kopidakis, N.; Tenent, R. C.; Barnes, T. M.; Heben, M. J.; Rumbles, G. Photoinduced Energy and Charge Transfer in P3HT:SWNT Composites. J. Phys. Chem. Lett. 2010, 1 (15), 2406– 2411,  DOI: 10.1021/jz100768f

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    Photoinduced energy and charge transfer in P3HT:SWNT composites

    Ferguson, Andrew J.; Blackburn, Jeffrey L.; Holt, Josh M.; Kopidakis, Nikos; Tenent, Robert C.; Barnes, Teresa M.; Heben, Michael J.; Rumbles, Garry

    Journal of Physical Chemistry Letters (2010), 1 (15), 2406-2411CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)

    Using steady-state photoluminescence and transient microwave cond. (TRMC) spectroscopies, photoinduced energy and charge transfer from poly(3-hexylthiophene) (P3HT) to single-walled carbon nanotubes (SWNTs) are reported. Long-lived charge carriers are obsd. for excitons generated in the polymer due to interfacial electron transfer, while excitation of the SWNTs results in short-lived carriers confined to the nanotubes. The TRMC-measured mobility of electrons injected into the SWNTs exhibits a surprisingly small lower limit of 0.057 cm2/(V s), which we attribute to carrier scattering within the nanotube that inhibits resonance of the microwave elec. field with the confined carriers. The observation of charge transfer and the lifetime of the sepd. carriers suggest that the primary photoinduced carrier generation process does not limit the performance of org. photovoltaic (OPV) devices based on P3HT:SWNT composites. With optimization, blends of P3HT with semiconducting SWNTs (s-SWNTs) may exhibit promise as an OPV active layer and could provide good solar photoconversion power efficiencies.
22. 22

    Olivier, J. H.; Park, J.; Deria, P.; Rawson, J.; Bai, Y.; Kumbhar, A. S.; Therien, M. J. Unambiguous Diagnosis of Photoinduced Charge Carrier Signatures in a Stoichiometrically Controlled Semiconducting Polymer-Wrapped Carbon Nanotube Assembly. Angew. Chem., Int. Ed. 2015, 54 (28), 8133– 8138,  DOI: 10.1002/anie.201501364

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    22

    Unambiguous Diagnosis of Photoinduced Charge Carrier Signatures in a Stoichiometrically Controlled Semiconducting Polymer-Wrapped Carbon Nanotube Assembly

    Olivier, Jean-Hubert; Park, Jaehong; Deria, Pravas; Rawson, Jeff; Bai, Yusong; Kumbhar, Amar S.; Therien, Michael J.

    Angewandte Chemie, International Edition (2015), 54 (28), 8133-8138CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)

    Single-walled carbon nanotube (SWNT)-based nanohybrid compns. based on (6,5) chirality-enriched SWNTs ([(6,5) SWNTs]) and a chiral n-type polymer (S-PBN(b)-Ph4PDI) that exploits a perylenediimide (PDI)-contg. repeat unit are reported; S-PBN(b)-Ph4PDI-[(6,5) SWNT] superstructures feature a PDI electron acceptor unit positioned at 3 nm intervals along the nanotube surface, thus controlling rigorously SWNT-electron acceptor stoichiometry and organization. Potentiometric studies and redox-titrn. expts. det. driving forces for photoinduced charge sepn. (CS) and thermal charge recombination (CR) reactions, as well as spectroscopic signatures of SWNT hole polaron and PDI radical anion (PDI-.) states. Time-resolved pump-probe spectroscopic studies demonstrate that S-PBN(b)-Ph4PDI-[(6,5) SWNT] electronic excitation generates PDI-. via a photoinduced CS reaction (τCS≈0.4 ps, ΦCS≈0.97). These expts. highlight the concomitant rise and decay of transient absorption spectroscopic signatures characteristic of the SWNT hole polaron and PDI-. states. Multiwavelength global anal. of these data provide two charge-recombination time consts. (τCR≈31.8 and 250 ps) that likely reflect CR dynamics involving both an intimately assocd. SWNT hole polaron and PDI-. charge-sepd. state, and a related charge-sepd. state involving PDI-. and a hole polaron site produced via hole migration along the SWNT backbone that occurs over this timescale.
23. 23

    Kahmann, S.; Salazar Rios, J. M.; Zink, M.; Allard, S.; Scherf, U.; Dos Santos, M. C.; Brabec, C. J.; Loi, M. A. Excited-State Interaction of Semiconducting Single-Walled Carbon Nanotubes with Their Wrapping Polymers. J. Phys. Chem. Lett. 2017, 8 (22), 5666– 5672,  DOI: 10.1021/acs.jpclett.7b02553

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    23

    Excited-State Interaction of Semiconducting Single-Walled Carbon Nanotubes with Their Wrapping Polymers

    Kahmann, Simon; Salazar Rios, Jorge M.; Zink, Matthias; Allard, Sybille; Scherf, Ullrich; dos Santos, Maria C.; Brabec, Christoph J.; Loi, Maria A.

    Journal of Physical Chemistry Letters (2017), 8 (22), 5666-5672CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)

    We employ photoluminescence and pump-probe spectroscopy on films of semiconducting single-walled carbon nanotubes (CNTs) of different chirality wrapped with either a wide band gap polyfluorene deriv. (PF12) or a polythiophene with narrower gap (P3DDT) to elucidate the excited states' interplay between the two materials. Excitation above the polymer band gap gives way to an ultrafast electron transfer from both polymers toward the CNTs. By monitoring the hole polaron on the polymer via its mid IR signature, we show that also illumination below the polymer band gap leads to the formation of this fingerprint and infer that holes are also transferred toward the polymer. As this contradicts the std. way of discussing the involved energy levels, we propose that polymer-wrapped CNTs should be considered as a single hybrid system, exhibiting states shared between the two components. This proposition is validated through quantum chem. calcns. that show hybridization of the first excited states, esp. for the thiophene-CNT sample.
24. 24

    Dabera, G. D.; Jayawardena, K. D.; Prabhath, M. R.; Yahya, I.; Tan, Y. Y.; Nismy, N. A.; Shiozawa, H.; Sauer, M.; Ruiz-Soria, G.; Ayala, P. Hybrid carbon nanotube networks as efficient hole extraction layers for organic photovoltaics. ACS Nano 2013, 7 (1), 556– 65,  DOI: 10.1021/nn304705t

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    Hybrid Carbon Nanotube Networks as Efficient Hole Extraction Layers for Organic Photovoltaics

    Dabera, G. Dinesha M. R.; Jayawardena, K. D. G. Imalka; Prabhath, M. R. Ranga; Yahya, Iskandar; Tan, Y. Yuan; Nismy, N. Aamina; Shiozawa, Hidetsugu; Sauer, Markus; Ruiz-Soria, G.; Ayala, Paola; Stolojan, Vlad; Adikaari, A. A. Damitha T.; Jarowski, Peter D.; Pichler, Thomas; Silva, S. Ravi P.

    ACS Nano (2013), 7 (1), 556-565CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)

    Transparent, highly percolated networks of regioregular poly(3-hexylthiophene) (rr-P3HT)-wrapped semiconducting single-walled carbon nanotubes (s-SWNTs) are deposited, and the charge transfer processes of these nanohybrids are studied using spectroscopic and elec. measurements. The data disclose hole doping of s-SWNTs by the polymer, challenging the prevalent electron-doping hypothesis. Through controlled fabrication, high- to low-d. nanohybrid networks are achieved, with low-d. hybrid carbon nanotube networks tested as hole transport layers (HTLs) for bulk heterojunction (BHJ) org. photovoltaics (OPV). OPVs incorporating these rr-P3HT/s-SWNT networks as the HTL demonstrate the best large area (70 mm2) carbon nanotube incorporated org. solar cells to date with a power conversion efficiency of 7.6%. This signifies the strong capability of nanohybrids as an efficient hole extn. layer, and we believe that dense nanohybrid networks have the potential to replace expensive and material scarce inorg. transparent electrodes in large area electronics toward the realization of low-cost flexible electronics.
25. 25

    Deria, P.; Olivier, J. H.; Park, J.; Therien, M. J. Potentiometric, electronic, and transient absorptive spectroscopic properties of oxidized single-walled carbon nanotubes helically wrapped by ionic, semiconducting polymers in aqueous and organic media. J. Am. Chem. Soc. 2014, 136 (40), 14193– 9,  DOI: 10.1021/ja507457z

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    25

    Potentiometric, Electronic, and Transient Absorptive Spectroscopic Properties of Oxidized Single-Walled Carbon Nanotubes Helically Wrapped by Ionic, Semiconducting Polymers in Aqueous and Organic Media

    Deria, Pravas; Olivier, Jean-Hubert; Park, Jaehong; Therien, Michael J.

    Journal of the American Chemical Society (2014), 136 (40), 14193-14199CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)

    We report the first direct cyclic voltammetric detn. of the valence and conduction band energy levels for noncovalently modified (6,5) chirality enriched SWNTs [(6,5) SWNTs] in which an aryleneethynylene polymer monolayer helically wraps the nanotube surface at periodic and const. morphol. Potentiometric properties as well as the steady-state and transient absorption spectroscopic signatures of oxidized (6,5) SWNTs were probed as a function of the electronic structure of the aryleneethynylene polymer that helically wraps the nanotube surface, the solvent dielec., and nanotube hole polaron concn. These data: (i) highlight the utility of these polymer-SWNT superstructures in expts. that establish the potentiometric valence and conduction band energy levels of semiconducting carbon nanotubes; (ii) provide a direct measure of the (6,5) SWNT hole polaron delocalization length (2.75 nm); (iii) det. steady-state and transient electronic absorptive spectroscopic signatures that are uniquely assocd. with the (6,5) SWNT hole polaron state; and (iv) demonstrate that modulation of semiconducting polymer frontier orbital energy levels can drive spectral shifts of SWNT hole polaron transitions as well as regulate SWNT valence and conduction band energies.
26. 26

    Wu, J.; Zhang, S.; Lin, D.; Ma, B.; Yang, L.; Zhang, S.; Kang, L.; Mao, N.; Zhang, N.; Tong, L. Anisotropic Raman-Enhancement Effect on Single-Walled Carbon Nanotube Arrays. Adv. Mater. Interfaces 2018, 5 (3), 1700941,  DOI: 10.1002/admi.201700941

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27. 27

    Erck, A.; Sapp, W.; Kilina, S.; Kilin, D. Photoinduced Charge Transfer at Interfaces of Carbon Nanotube and Lead Selenide Nanowire. J. Phys. Chem. C 2016, 120 (40), 23197– 23206,  DOI: 10.1021/acs.jpcc.6b05571

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    27

    Photoinduced Charge Transfer at Interfaces of Carbon Nanotube and Lead Selenide Nanowire

    Erck, Adam; Sapp, Wendi; Kilina, Svetlana; Kilin, Dmitri

    Journal of Physical Chemistry C (2016), 120 (40), 23197-23206CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)

    Photoinduced generation of excitons and their nonradiative relaxation dynamics are simulated at the interface of (10, 0) carbon nanotubes (CNT) and a PbSe nanowire (NW). Possible pathways of photoinduced excitations are explored by combining a reduced d. matrix approach in the basis of Kohn-Sham orbitals and on-the-fly nonadiabatic couplings. A range of neutral photoexcitations localized on the CNT is followed by formation of charge transfer (CT) states involving PbSe NW. Depending on the wavelength of the incident light, the initial photoexcitation can be followed by two directions of charge transfer: either (PbSe)+(CNT)- or (PbSe)-(CNT)+. Excitation of a hot electron results in the CT state with an electron located at the NW and the hole at the CNT with shorter lifetime, while excitation of a hot hole leads to the CT state with an electron at the CNT and the hole at the PbSe having much longer lifetime. Obsd. ability to control the direction and the lifetime of the CT state makes the CNT/PbSe NW composites promising for photovoltaic applications.
28. 28

    Maruyama, S. 1D DOS (van Hove singularity). http://www.photon.t.u-tokyo.ac.jp/~maruyama/kataura/1D_DOS.htmlhttp://www.photon.t.u-tokyo.ac.jp/~maruyama/kataura/1D_DOS.html (accessed March 26, 2020).

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29. 29

    Park, K. H.; Lee, S.-H.; Toshimitsu, F.; Lee, J.; Park, S. H.; Tsuyohiko, F.; Jang, J.-W. Gate-enhanced photocurrent of (6,5) single-walled carbon nanotube based field effect transistor. Carbon 2018, 139, 709– 715,  DOI: 10.1016/j.carbon.2018.07.002

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    Gate-enhanced exciton-phonon coupling in photocurrent of (6,5) single-walled carbon nanotube based visible sensing field effect transistor

    Park, Ki Hong; Lee, Seung-Hoon; Toshimitsu, Fumiyuki; Lee, Jihoon; Park, Sung Heum; Tsuyohiko, Fujigaya; Jang, Jae-Won

    Carbon (2018), 139 (), 709-715CODEN: CRBNAH; ISSN:0008-6223. (Elsevier Ltd.)

    A visible sensing field effect transistor (FET) with a channel length of 100 nm for individual (6,5) single-walled carbon nanotubes (SWCNTs) is fabricated via a selective sorting method using 9,9-dioctyfluorenyl-2,7-diyl-bipyridine (PFO-BPy) polymer. The FET of the (6,5) SWCNTs shows p-type behavior with hundreds of on-off ratios and on-state cond. of 50±4.0 (Ω m)-1. In addn., the photocurrent of the FET of the (6,5) SWCNTs in the visible range increases (max. 200 times at 620 nm) with higher gate voltage. E22 transition and PFO-BPy transition are obsd. in the FET of the (6,5) SWCNTs without application of a gate voltage. Interestingly, exciton-phonon coupled E22 transition due to gate-doping (p-type), which has been reported in photoluminescence and absorption studies, is expected to occur in the photocurrent of the FET at neg. higher gate voltage (≤-4 V). In addn., the exciton-phonon coupled E22 transition is prominently observable when carrier concn. by gate doping becomes approx. two-hundred sixty times (260±43) larger than carrier concn. without application of a gate voltage. This demonstration would be useful for the development of SWCNT-based visible sensors with gate control in the SWCNT devices.
30. 30

    Manzoni, C.; Gambetta, A.; Menna, E.; Meneghetti, M.; Lanzani, G.; Cerullo, G. Intersubband exciton relaxation dynamics in single-walled carbon nanotubes. Phys. Rev. Lett. 2005, 94 (20), 207401,  DOI: 10.1103/PhysRevLett.94.207401

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    Intersubband Exciton Relaxation Dynamics in Single-Walled Carbon Nanotubes

    Manzoni, C.; Gambetta, A.; Menna, E.; Meneghetti, M.; Lanzani, G.; Cerullo, G.

    Physical Review Letters (2005), 94 (20), 207401/1-207401/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)

    We study exciton (EX) dynamics in single-walled carbon nanotubes (SWNTs) included in polymethylmethacrylate by two-color pump-probe expts. with unprecedented temporal resoln. In the semiconducting SWNTs, we resolve the intersubband energy relaxation from the EX2 to the EX1 transition and find time consts. of about 40 fs. The observation of a photoinduced absorption band strictly correlated to the photobleaching of the EX1 transition supports the excitonic model for primary excitations in SWNTs. We also detect in the time domain coherent oscillations due to the radial breathing modes at ≈250 cm-1.
31. 31

    Crochet, J. J.; Hoseinkhani, S.; Luer, L.; Hertel, T.; Doorn, S. K.; Lanzani, G. Free-carrier generation in aggregates of single-wall carbon nanotubes by photoexcitation in the ultraviolet regime. Phys. Rev. Lett. 2011, 107 (25), 257402,  DOI: 10.1103/PhysRevLett.107.257402

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    Free-Carrier Generation in Aggregates of Single-Wall Carbon Nanotubes by Photoexcitation in the Ultraviolet Regime

    Crochet, Jared J.; Hoseinkhani, Sajjad; Luer, Larry; Hertel, Tobias; Doorn, Stephen K.; Lanzani, Guglielmo

    Physical Review Letters (2011), 107 (25), 257402/1-257402/5CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)

    We present evidence for the generation of free carriers in aggregated single-wall carbon nanotubes by photoexcitation in the energetic range of the π π* transition assocd. with the M saddle point of the graphene lattice. The underlying broad absorption culminating at 4.3 eV can be fit well with a Fano line shape that describes strong coupling of a saddle-point exciton to an underlying free electron-hole pair continuum. Moreover, it is demonstrated that transitions in this energetic region autoionize into the continuum by detecting features unique to the presence of free charges in the transient transmission spectra of the continuum-embedded second sub-band exciton, S2.
32. 32

    Park, J.; Reid, O. G.; Blackburn, J. L.; Rumbles, G. Photoinduced spontaneous free-carrier generation in semiconducting single-walled carbon nanotubes. Nat. Commun. 2015, 6, 8809,  DOI: 10.1038/ncomms9809

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    Photoinduced spontaneous free-carrier generation in semiconducting single-walled carbon nanotubes

    Park Jaehong; Reid Obadiah G; Blackburn Jeffrey L; Rumbles Garry; Reid Obadiah G; Rumbles Garry; Rumbles Garry

    Nature communications (2015), 6 (), 8809 ISSN:.

    Strong quantum confinement and low dielectric screening impart single-walled carbon nanotubes with exciton-binding energies substantially exceeding kBT at room temperature. Despite these large binding energies, reported photoluminescence quantum yields are typically low and some studies suggest that photoexcitation of carbon nanotube excitonic transitions can produce free charge carriers. Here we report the direct measurement of long-lived free-carrier generation in chirality-pure, single-walled carbon nanotubes in a low dielectric solvent. Time-resolved microwave conductivity enables contactless and quantitative measurement of the real and imaginary photoconductance of individually suspended nanotubes. The conditions of the microwave conductivity measurement allow us to avoid the complications of most previous measurements of nanotube free-carrier generation, including tube-tube/tube-electrode contact, dielectric screening by nearby excitons and many-body interactions. Even at low photon fluence (approximately 0.05 excitons per μm length of tubes), we directly observe free carriers on excitation of the first and second carbon nanotube exciton transitions.
33. 33

    Soavi, G.; Scotognella, F.; Brida, D.; Hefner, T.; Späth, F.; Antognazza, M. R.; Hertel, T.; Lanzani, G.; Cerullo, G. Ultrafast Charge Photogeneration in Semiconducting Carbon Nanotubes. J. Phys. Chem. C 2013, 117 (20), 10849– 10855,  DOI: 10.1021/jp404009z

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    Ultrafast Charge Photogeneration in Semiconducting Carbon Nanotubes

    Soavi, G.; Scotognella, F.; Brida, D.; Hefner, T.; Spath, F.; Antognazza, M. R.; Hertel, T.; Lanzani, G.; Cerullo, G.

    Journal of Physical Chemistry C (2013), 117 (20), 10849-10855CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)

    Excitons are not the unique outcome of photoexcitation in single-walled C nanotubes (SWNTs). Expts. of transient photoinduced absorption suggest that charge carriers are formed with quantum yield of a few percent and that such species strongly affect the long-lived transient spectrum. Photogenerated charge carriers induce strong local elec. fields that shift by the Stark effect the 2nd subband exciton absorption in SWNTs, resulting in a characteristic deriv. shape of the transient absorption spectra.
34. 34

    Valkunas, L.; Ma, Y.-Z.; Fleming, G. R. Exciton-exciton annihilation in single-walled carbon nanotubes. Phys. Rev. B: Condens. Matter Mater. Phys. 2006, 73 (11), 115432,  DOI: 10.1103/PhysRevB.73.115432

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    Exciton-exciton annihilation in single-walled carbon nanotubes

    Valkunas, Leonas; Ma, Ying-Zhong; Fleming, Graham R.

    Physical Review B: Condensed Matter and Materials Physics (2006), 73 (11), 115432/1-115432/12CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)

    The femtosecond fluorescence and transient absorption kinetics recorded on selected semiconducting single-walled C nanotubes exhibit pronounced excitation-intensity-dependent decays as the result of exciton-exciton annihilation. A satisfactory description of the decays obtained at various excitation intensities, however, requires a time-independent annihilation rate that is valid only for extended systems with dimensionality >2 in conjunction with diffusive migration of excitons. The authors resolved this apparent contradiction by developing a stochastic model, in which the authors assumed that the exciton states in semiconducting nanotubes are coherent, and the multiexciton manifolds are resonantly coupled with other excited states, which decay by subsequent linear relaxation due to electron-phonon coupling. The formalism derived from this model enables a qual. description of the exptl. results for the (9,5), (8,3), and (6,5) semiconducting single-walled C nanotubes.
35. 35

    Ma, Y. Z.; Valkunas, L.; Dexheimer, S. L.; Bachilo, S. M.; Fleming, G. R. Femtosecond spectroscopy of optical excitations in single-walled carbon nanotubes: evidence for exciton-exciton annihilation. Phys. Rev. Lett. 2005, 94 (15), 157402,  DOI: 10.1103/PhysRevLett.94.157402

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    Femtosecond Spectroscopy of Optical Excitations in Single-Walled Carbon Nanotubes: Evidence for Exciton-Exciton Annihilation

    Ma, Ying-Zhong; Valkunas, Leonas; Dexheimer, Susan L.; Bachilo, Sergei M.; Fleming, Graham R.

    Physical Review Letters (2005), 94 (15), 157402/1-157402/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)

    Frequency-resolved femtosecond transient absorption spectra and kinetics measured by optical excitation of the 2nd and 1st electronic transitions of the (8,3) single-walled C nanotube species reveal a unique mutual response between these transitions. Based on the anal. of the spectra, kinetics, and their distinct amplitude dependence on the pump intensity obsd. at these transitions, these observations originate from both the excitonic origin of the spectrum and nonlinear exciton annihilation.
36. 36

    Wang, S.; Khafizov, M.; Tu, X.; Zheng, M.; Krauss, T. D. Multiple exciton generation in single-walled carbon nanotubes. Nano Lett. 2010, 10 (7), 2381– 6,  DOI: 10.1021/nl100343j

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    Multiple Exciton Generation in Single-Walled Carbon Nanotubes

    Wang, Shujing; Khafizov, Marat; Tu, Xiaomin; Zheng, Ming; Krauss, Todd D.

    Nano Letters (2010), 10 (7), 2381-2386CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)

    Upon absorption of single photons, multiple excitons were generated and detected in semiconducting single-walled carbon nanotubes (SWNTs) using transient absorption spectroscopy. For (6,5) SWNTs, absorption of single photons with energies corresponding to three times the SWNT energy gap results in an exciton generation efficiency of 130% per photon. Our results suggest that the multiple exciton generation threshold in SWNTs can be close to the limit defined by energy conservation.
37. 37

    O’Connell, M. J.; Bachilo, S. M.; Huffman, C. B.; Moore, V. C.; Strano, M. S.; Haroz, E. H.; Rialon, K. L.; Boul, P. J.; Noon, W. H.; Kittrell, C. Band Gap Fluorescence from Individual Single-Walled Carbon Nanotubes. Science 2002, 297 (5581), 593– 596,  DOI: 10.1126/science.1072631

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    Band gap fluorescence from individual single-walled carbon nanotubes

    O'Connell, Michael J.; Bachilo, Sergei M.; Huffman, Chad B.; Moore, Valerie C.; Strano, Michael S.; Haroz, Erik H.; Rialon, Kristy L.; Boul, Peter J.; Noon, William H.; Kittrell, Carter; Ma, Jianpeng; Hauge, Robert H.; Weisman, R. Bruce; Smalley, Richard E.

    Science (Washington, DC, United States) (2002), 297 (5581), 593-596CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)

    Fluorescence has been obsd. directly across the band gap of semiconducting carbon nanotubes. We obtained individual nanotubes, each encased in a cylindrical micelle, by ultrasonically agitating an aq. dispersion of raw single-walled carbon nanotubes in sodium dodecyl sulfate and then centrifuging to remove tube bundles, ropes, and residual catalyst. Aggregation of nanotubes into bundles otherwise quenches the fluorescence through interactions with metallic tubes and substantially broadens the absorption spectra. At pH less than 5, the absorption and emission spectra of individual nanotubes show evidence of band gap-selective protonation of the side walls of the tube. This protonation is readily reversed by treatment with base or UV light.
38. 38

    Bai, Y.; Bullard, G.; Olivier, J. H.; Therien, M. J. Quantitative Evaluation of Optical Free Carrier Generation in Semiconducting Single-Walled Carbon Nanotubes. J. Am. Chem. Soc. 2018, 140 (44), 14619– 14626,  DOI: 10.1021/jacs.8b05598

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    Quantitative Evaluation of Optical Free Carrier Generation in Semiconducting Single-Walled Carbon Nanotubes

    Bai, Yusong; Bullard, George; Olivier, Jean-Hubert; Therien, Michael J.

    Journal of the American Chemical Society (2018), 140 (44), 14619-14626CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)

    Gauging free carrier generation (FCG) in optically excited, charge-neutral single-walled carbon nanotubes (SWNTs) has important implications for SWNT-based optoelectronics that rely upon conversion of photons to elec. current. Earlier investigations have largely provided only qual. insights into optically triggered SWNT FCG, due to the heterogeneous nature of commonly interrogated SWNT samples and the lack of direct, unambiguous spectroscopic signatures that could be used to quantify charges. Here, employing ultrafast pump-probe spectroscopy in conjunction with chirality-enriched, length-sorted, ionic-polymer-wrapped SWNTs, we develop a straightforward approach for quant. evaluating the extent of optically driven FCG in SWNTs. Owing to the previously identified trion transient absorptive hallmark (Tr+11 → Tr+nm) and the rapid nature of trion formation dynamics (<1 ps) relative to established free-carrier decay time scales (>ns), we correlate FCG with trion formation dynamics. Exptl. detn. of the trion absorptive cross section further enables evaluation of the quantum yields for optically driven FCG [Φ(Enn→h++e-)] as a function of optical excitation energy and medium dielec. strength. We show that (i) E33 excitons give rise to dramatically enhanced Φ(Enn→h++e-) relative to those derived from E22 and E11 excitons and (ii) Φ(E33→h++e-) monotonically increases from ∼5% to 18% as the solvent dielec. const. increases from ∼32 to 80. This work highlights the extent to which the nature of the medium and excitation conditions control FCG quantum yields in SWNTs: such studies have the potential to provide new design insights for SWNT-based compns. for optoelectronic applications that include photodetectors and photovoltaics.
39. 39

    Park, J.; Deria, P.; Olivier, J. H.; Therien, M. J. Fluence-dependent singlet exciton dynamics in length-sorted chirality-enriched single-walled carbon nanotubes. Nano Lett. 2014, 14 (2), 504– 11,  DOI: 10.1021/nl403511s

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    Fluence-Dependent Singlet Exciton Dynamics in Length-Sorted Chirality-Enriched Single-Walled Carbon Nanotubes

    Park, Jaehong; Deria, Pravas; Olivier, Jean-Hubert; Therien, Michael J.

    Nano Letters (2014), 14 (2), 504-511CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)

    Individualized, length-sorted (6,5)-chirality enriched single-walled C nanotubes (SWNTs) having dimensions of 200 and 800 nm, fs transient absorption spectroscopy, and variable excitation fluences that modulate the exciton d. per nanotube unit length, were used to interrogate nanotube exciton/biexciton dynamics. For pump fluences <30 μJ/cm2, transient absorption (TA) spectra of (6,5) SWNTs reveal the instantaneous emergence of the exciton to biexciton transition (E11→E11,BX) at 1100 nm; in contrast, under excitation fluences exceeding 100 μJ/cm2, this TA signal manifests a rise time (τrise ∼ 250 fs), indicating that E11 state repopulation is required to produce this signal. The fs transient absorption spectral data acquired at 900-1400 nm (near-IR) for (6,5) SWNTs, as a function of nanotube length and exciton d., reveal that over time delays of >200 fs exciton-exciton interactions do not occur over spatial domains >200 nm. The excitation fluence dependence of the E11→E11,BX transient absorption signal demonstrates that relaxation of the E11 biexciton state (E11,BX) gives rise to a substantial E11 state population, as increasing delay times result in a concomitant increase of E11→E11,BX transition oscillator strength. Numerical simulations based on a 3-state model are consistent with a mechanism whereby biexcitons are generated at high excitation fluences via sequential SWNT ground- and E11-state excitation that occurs within the 980 nm excitation pulse duration. These studies that study fluence-dependent TA spectral evolution show that SWNT ground→E11 and E11→E11,BX excitations are coresonant and provide evidence that E11,BX→E11 relaxation constitutes a significant decay channel for the SWNT biexciton state over delay times >200 fs, a finding that runs counter to assumptions made in previous analyses of SWNT biexciton dynamical data where exciton-exciton annihilation was assumed to play a dominant role.
40. 40

    Huang, L.; Krauss, T. D. Quantized Bimolecular Auger Recombination of Excitons in Single-Walled Carbon Nanotubes. Phys. Rev. Lett. 2006, 96 (5), 057407,  DOI: 10.1103/PhysRevLett.96.057407

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    Quantized Bimolecular Auger Recombination of Excitons in Single-Walled Carbon Nanotubes

    Huang, Libai; Krauss, Todd D.

    Physical Review Letters (2006), 96 (5), 057407/1-057407/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)

    Auger-like exciton-exciton annihilation in isolated single-walled C nanotubes (SWNTs) was studied by femtosecond transient absorption spectroscopy. The authors observe a quantization of the Auger recombination process and ext. dynamics for 2 and 3 electron-hole pair excited states. Further Auger recombination in SWNTs is a two-particle process involving strongly bound excitons and not a three-particle Auger process involving unbound electrons and holes. The authors thus provide explicit exptl. evidence for 1-dimensional discrete excitons in SWNTs.
41. 41

    Li, H.; Gordeev, G.; Garrity, O.; Reich, S.; Flavel, B. S. Separation of Small-Diameter Single-Walled Carbon Nanotubes in One to Three Steps with Aqueous Two-Phase Extraction. ACS Nano 2019, 13 (2), 2567– 2578,  DOI: 10.1021/acsnano.8b09579

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    Separation of Small-Diameter Single-Walled Carbon Nanotubes in One to Three Steps with Aqueous Two-Phase Extraction

    Li, Han; Gordeev, Georgy; Garrity, Oisin; Reich, Stephanie; Flavel, Benjamin S.

    ACS Nano (2019), 13 (2), 2567-2578CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)

    An aq. two-phase extn. (ATPE) technique capable of sepg. small-diam. single-walled carbon nanotubes in one, two, or at the most three steps is presented. Sepn. is performed in the well-studied two-phase system contg. polyethylene glycol and dextran, but it is achieved without changing the global concn. or ratio of cosurfactants. Instead, the technique is reliant upon the different surfactant shell around each nanotube diam. at a fixed surfactant concn. The methodol. to obtain a single set of surfactant conditions is provided, and strategies to optimize these for other diam. regimes are discussed. In total, 11 different chiralities in the diam. range 0.69-0.91 nm are sepd. These include semiconducting and both armchair and nonarmchair metallic nanotube species. Titrn. of cosurfactant suspensions reveal sepn. to be driven by the pH of the suspension with each (n,m) species partitioning at a fixed pH. This allows for an (n,m) sepn. approach to be presented that is as simple as pipetting known vols. of acid into the ATPE system.
42. 42

    Pfohl, M.; Tune, D. D.; Graf, A.; Zaumseil, J.; Krupke, R.; Flavel, B. S. Fitting Single-Walled Carbon Nanotube Optical Spectra. ACS Omega 2017, 2 (3), 1163– 1171,  DOI: 10.1021/acsomega.6b00468

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    Fitting Single-Walled Carbon Nanotube Optical Spectra

    Pfohl, Moritz; Tune, Daniel D.; Graf, Arko; Zaumseil, Jana; Krupke, Ralph; Flavel, Benjamin S.

    ACS Omega (2017), 2 (3), 1163-1171CODEN: ACSODF; ISSN:2470-1343. (American Chemical Society)

    In this work, a comprehensive methodol. for the fitting of single walled carbon nanotube absorption spectra is presented. Different approaches to background subtraction, choice of line profile, and calcn. of full width at half max. are discussed both in the context of previous literature and in contemporary understanding of carbon nanotube photophysics. The fitting is improved by the inclusion of exciton-phonon sidebands, and new techniques to improve individualization of overlapped nanotube spectra by exploiting correlations between the first and second order optical transitions and the exciton-phonon sidebands are presented. Consideration of metallic nanotubes allows an anal. of the metallic/semiconducting content and a process of constraining the fit of highly congested spectra of carbon nanotube solid films according to the spectral wts. of each (n,m) species in soln. is also presented, allowing for more reliable resolving overlapping peaks into single (n,m) species contributions.
43. 43

    Lüer, L.; Hoseinkhani, S.; Polli, D.; Crochet, J.; Hertel, T.; Lanzani, G. Size and mobility of excitons in (6, 5) carbon nanotubes. Nat. Phys. 2009, 5 (1), 54– 58,  DOI: 10.1038/nphys1149

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    Size and mobility of excitons in (6, 5) carbon nanotubes

    Lueer, Larry; Hoseinkhani, Sajjad; Polli, Dario; Crochet, Jared; Hertel, Tobias; Lanzani, Guglielmo

    Nature Physics (2009), 5 (1), 54-58CODEN: NPAHAX; ISSN:1745-2473. (Nature Publishing Group)

    Knowledge of excited-state dynamics in C nanotubes is determinant for their prospective use in optoelectronic applications. It is known that primary photoexcitations are quasi-one-dimensional excitons, the electron-hole correlation length ( exciton size') of which corresponds to a finite vol. in the phase space. This vol. can be directly measured by nonlinear spectroscopy provided the time resoln. is short enough for probing before population relaxation. Here, the authors report on the exptl. detn. of exciton size and mobility in (6, 5) C nanotubes. The samples are Na cholate suspensions of nanotubes (produced by the CoMoCat method) obtained by d.-gradient ultracentrifugation. By using sub-15 fs near-IR pulses to measure the nascent bleach of the lowest exciton resonance, the authors est. the exciton size to be 2.0 ± 0.7 nm. Exciton-exciton annihilation in samples is rather inefficient so that many excitons can coexist on a single nanotube.
44. 44

    Styers-Barnett, D. J.; Ellison, S. P.; Mehl, B. P.; Westlake, B. C.; House, R. L.; Park, C.; Wise, K. E.; Papanikolas, J. M. Exciton dynamics and biexciton formation in single-walled carbon nanotubes studied with femtosecond transient absorption spectroscopy. J. Phys. Chem. C 2008, 112 (12), 4507– 4516,  DOI: 10.1021/jp7099256

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    Exciton Dynamics and Biexciton Formation in Single-Walled Carbon Nanotubes Studied with Femtosecond Transient Absorption Spectroscopy

    Styers-Barnett, David J.; Ellison, Stephen P.; Mehl, Brian P.; Westlake, Brittany C.; House, Ralph L.; Park, Cheol; Wise, Kristopher E.; Papanikolas, John M.

    Journal of Physical Chemistry C (2008), 112 (12), 4507-4516CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)

    The authors used femtosecond transient absorption (TA) spectroscopy to examine the excited state dynamics of single-walled C nanotube (SWNT) bundles embedded in polymer matrixes. The SWNTs were excited by a femtosecond pump pulse centered at either 1800, 900, or 550 nm and probed using a white-light continuum extending from 400 to 750 nm. The authors obsd. a structured TA spectrum consisting of narrow induced transmission (IT) and induced absorption (IA) bands. The TA spectrum, which is independent of excitation wavelength, appeared on a time scale shorter than instrument response (200 fs) and persisted for up to 100 ps. TA spectra obtained at pump-probe delay times provided a window through which to monitor the exciton dynamics. The authors obsd. 3 distinct spectral signatures in the time-dependent data: (1) the decay of a broad photobleach, (2) the biphasic decay of narrow IT and IA features, and (3) a dynamical spectral shift of IA bands. These processes were attributed to plasmon relaxation, electron-hole recombination, and lattice relaxation assocd. with exciton self-trapping, resp. Anal. of the transient spectrum suggested that it arose from a nonlinear optical response of the SWNT, where excitons produced by the pump pulse modified the transition frequencies of subsequent carrier excitations. The result was IT bands (bleaches) at the ground state absorption frequencies, and assocd. with each were a corresponding red-shifted absorption band. These induced absorptions were attributed to the formation of biexcitons, 4-particle excitations that are produced through the sequential excitation of 2 closely spaced electron-hole pairs.
45. 45

    Park, J.; Deria, P.; Therien, M. J. Dynamics and transient absorption spectral signatures of the single-wall carbon nanotube electronically excited triplet state. J. Am. Chem. Soc. 2011, 133 (43), 17156– 9,  DOI: 10.1021/ja2079477

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    Dynamics and Transient Absorption Spectral Signatures of the Single-Wall Carbon Nanotube Electronically Excited Triplet State

    Park, Jaehong; Deria, Pravas; Therien, Michael J.

    Journal of the American Chemical Society (2011), 133 (43), 17156-17159CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)

    The authors use femtosecond-to-microsecond time domain pump-probe transient absorption spectroscopy to interrogate for the 1st time the electronically excited triplet state of individualized single-wall C nanotubes (SWNTs). These studies exploit (6,5) chirality-enriched SWNT samples and poly[2,6-{1,5-bis(3-propoxysulfonic acid Na salt)}naphthylene]ethynylene (PNES), which helically wraps the nanotube surface with periodic and const. morphol. (pitch length = 10 ± 2 nm), providing a self-assembled superstructure that maintains structural homogeneity in multiple solvents. Spectroscopic interrogation of such PNES-SWNT samples in aq. and DMSO solvents using E22 excitation and a white-light continuum probe enables E11 and E22 spectral evolution to be monitored concomitantly. Such expts. not only reveal classic SWNT singlet exciton relaxation dynamics and transient absorption signatures but also demonstrate spectral evolution consistent with formation of a triplet exciton state. Transient dynamical studies evince that (6,5) SWNTs exhibit rapid S1→T1 intersystem crossing (ISC) (τISC ∼20 ps), a sharp T1→Tn transient absorption signal (λmax(T1→Tn) = 1150 nm; full width at half-max. ≈ 350 cm-1), and a substantial T1 excited-state lifetime (τes ≈ 15 μs). Consistent with expectations for a triplet exciton state, T1-state spectral signatures and T1-state formation and decay dynamics for PNES-SWNTs in aq. and DMSO solvents, as well as those detd. for benchmark Na cholate suspensions of (6,5) SWNTs, are similar; likewise, studies that probe the 3[(6,5) SWNT]* state in air-satd. solns. demonstrate 3O2 quenching dynamics reminiscent of those detd. for conjugated arom. hydrocarbon excited triplet states.
46. 46

    Korovyanko, O. J.; Sheng, C. X.; Vardeny, Z. V.; Dalton, A. B.; Baughman, R. H. Ultrafast spectroscopy of excitons in single-walled carbon nanotubes. Phys. Rev. Lett. 2004, 92 (1), 017403,  DOI: 10.1103/PhysRevLett.92.017403

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    Ultrafast Spectroscopy of Excitons in Single-Walled Carbon Nanotubes

    Korovyanko, O. J.; Sheng, C.-X.; Vardeny, Z. V.; Dalton, A. B.; Baughman, R. H.

    Physical Review Letters (2004), 92 (1), 017403/1-017403/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)

    The fs dynamics were studied of photoexcitations in films contg. semiconducting and metallic single-walled C nanotubes (SWNTs), using various pump-probe wavelengths and intensities. Confined excitons and charge carriers with sub-ps dynamics dominate the ultrafast response in semiconducting and metallic SWNTs, resp. From the exciton excited state absorption bands and multiphoton absorption resonances in the semiconducting nanotubes, transitions between subbands are allowed; this unravels the important role of electron-electron interaction in SWNT optics.
47. 47

    Bai, Y.; Olivier, J. H.; Bullard, G.; Liu, C.; Therien, M. J. Dynamics of charged excitons in electronically and morphologically homogeneous single-walled carbon nanotubes. Proc. Natl. Acad. Sci. U. S. A. 2018, 115 (4), 674– 679,  DOI: 10.1073/pnas.1712971115

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    Dynamics of charged excitons in electronically and morphologically homogeneous single-walled carbon nanotubes

    Bai, Yusong; Olivier, Jean-Hubert; Bullard, George; Liu, Chaoren; Therien, Michael J.

    Proceedings of the National Academy of Sciences of the United States of America (2018), 115 (4), 674-679CODEN: PNASA6; ISSN:0027-8424. (National Academy of Sciences)

    The trion, a three-body charge-exciton bound state, offers unique opportunities to simultaneously manipulate charge, spin, and excitation in one-dimensional single-walled carbon nanotubes (SWNTs) at room temp. Effective exploitation of trion quasi-particles requires fundamental insight into their creation and decay dynamics. Such knowledge, however, remains elusive for SWNT trion states, due to the electronic and morphol. heterogeneity of commonly interrogated SWNT samples, and the fact that transient spectroscopic signals uniquely assocd. with the trion state have not been identified. Here, we prep. length-sorted SWNTs and precisely control charge-carrier-doping densities to det. trion dynamics using femtosecond pump-probe spectroscopy. Identification of the trion transient absorptive hallmark enables us to demonstrate that trions (i) derive from a precursor excitonic state, (ii) are produced via migration of excitons to stationary hole-polaron sites, and (iii) decay in a first-order manner. Importantly, under appropriate carrier-doping densities, exciton-to-trion conversion in SWNTs can approach 100% at ambient temp. Our findings open up possibilities for exploiting trions in SWNT optoelectronics, ranging from photovoltaics and photodetectors to spintronics.
48. 48

    Zhu, Z.; Crochet, J.; Arnold, M. S.; Hersam, M. C.; Ulbricht, H.; Resasco, D.; Hertel, T. Pump-Probe Spectroscopy of Exciton Dynamics in (6,5) Carbon Nanotubes. J. Phys. Chem. C 2007, 111 (10), 3831– 3835,  DOI: 10.1021/jp0669411

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    Pump-Probe Spectroscopy of Exciton Dynamics in (6,5) Carbon Nanotubes

    Zhu, Zipeng; Crochet, Jared; Arnold, Michael S.; Hersam, Mark C.; Ulbricht, Hendrik; Resasco, Daniel; Hertel, Tobias

    Journal of Physical Chemistry C (2007), 111 (10), 3831-3835CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)

    Exciton dynamics was studied in isopycnically enriched (6,5) nanotube-DNA suspensions using fs time-resolved pump-probe spectroscopy. The ground state recovery is characterized by a t-0.45 ± 0.03 power law behavior, indicative of a 1-dimensional diffusion-limited reaction that is tentatively attributed to subdiffusive trapping of dark excitons. Spectral transients of bright 0A0- singlet excitons within the E11 and E22 manifolds exhibit a photobleach (PB) and a photoabsorption (PA) signal of similar strength. The PA is blue-shifted with respect to the PB-signal by 7.5 meV and is attributed to a transition from the dark singlet exciton 0A0+ to a 0A0- + 0A0+ state within the 2 exciton E11 manifold.
49. 49

    Ma, Y.-Z.; Stenger, J.; Zimmermann, J.; Bachilo, S. M.; Smalley, R. E.; Weisman, R. B.; Fleming, G. R. Ultrafast carrier dynamics in single-walled carbon nanotubes probed by femtosecond spectroscopy. J. Chem. Phys. 2004, 120 (7), 3368– 3373,  DOI: 10.1063/1.1640339

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    Ultrafast carrier dynamics in single-walled carbon nanotubes probed by femtosecond spectroscopy

    Ma, Ying-Zhong; Stenger, Jens; Zimmermann, Jorg; Bachilo, Sergei M.; Smalley, Richard E.; Weisman, R. Bruce; Fleming, Graham R.

    Journal of Chemical Physics (2004), 120 (7), 3368-3373CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)

    Ultrafast carrier dynamics in individual semiconducting single-walled carbon nanotubes was studied by femtosecond transient absorption and fluorescence measurements. After photoexcitation of the second van Hove singularity of a specific tube structure, the relaxation of electrons and holes to the fundamental band edge occurs to within 100 fs. The fluorescence decay from this band is dependent on the excitation d. and can be rationalized by exciton annihilation theory. In contrast to fluorescence, the transient absorption has a distinctly different time and intensity dependence for different tube structures, suggesting a branching to emissive and trap states following photoexcitation.
50. 50

    Arias, D. H.; Sulas-Kern, D. B.; Hart, S. M.; Kang, H. S.; Hao, J.; Ihly, R.; Johnson, J. C.; Blackburn, J. L.; Ferguson, A. J. Effect of nanotube coupling on exciton transport in polymer-free monochiral semiconducting carbon nanotube networks. Nanoscale 2019, 11 (44), 21196– 21206,  DOI: 10.1039/C9NR07821E

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    Effect of nanotube coupling on exciton transport in polymer-free monochiral semiconducting carbon nanotube networks

    Arias, Dylan H.; Sulas-Kern, Dana B.; Hart, Stephanie M.; Kang, Hyun Suk; Hao, Ji; Ihly, Rachelle; Johnson, Justin C.; Blackburn, Jeffrey L.; Ferguson, Andrew J.

    Nanoscale (2019), 11 (44), 21196-21206CODEN: NANOHL; ISSN:2040-3372. (Royal Society of Chemistry)

    Semiconducting single-walled carbon nanotubes (s-SWCNTs) are attractive light-harvesting components for solar photoconversion schemes and architectures, and selective polymer extn. has emerged as a powerful route to obtain highly pure s-SWCNT samples for electronic applications. Here we demonstrate a novel method for producing electronically coupled thin films of near-monochiral s-SWCNTs without wrapping polymer. Detailed steady-state and transient optical studies on such samples provide new insights into the role of the wrapping polymer on controlling intra-bundle nanotube-nanotube interactions and exciton energy transfer within and between bundles. Complete removal of polymer from the networks results in rapid exciton trapping within nanotube bundles, limiting long-range exciton transport. The results suggest that intertube electronic coupling and assocd. exciton delocalization across multiple tubes can limit diffusive exciton transport. The complex relationship obsd. here between exciton delocalization, trapping, and long-range transport, helps to inform the design, prepn., and implementation of carbon nanotube networks as active elements for optical and electronic applications.
51. 51

    Figueroa Del Valle, D. G.; Moretti, L.; Maqueira-Albo, I.; Aluicio-Sarduy, E.; Kriegel, I.; Lanzani, G.; Scotognella, F. Ultrafast Hole Transfer from (6,5) SWCNT to P3HT:PCBM Blend by Resonant Excitation. J. Phys. Chem. Lett. 2016, 7 (17), 3353– 8,  DOI: 10.1021/acs.jpclett.6b01377

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    Ultrafast Hole Transfer from (6,5) SWCNT to P3HT:PCBM Blend by Resonant Excitation

    Figueroa del Valle, Diana Gisell; Moretti, Luca; Maqueira-Albo, Isis; Aluicio-Sarduy, Eduardo; Kriegel, Ilka; Lanzani, Guglielmo; Scotognella, Francesco

    Journal of Physical Chemistry Letters (2016), 7 (17), 3353-3358CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)

    Nowadays, SWCNTs are envisaged to enhance the charge sepn. or transport of conjugated polymer-fullerene derivs. blends. In this work we studied, by means of ultrafast transient absorption spectroscopy, three components blends in which com. available SWCNTs are added to the std. bulk heterojunction. We explored three different configurations that give rise to diverse interfacing scenarios. We found strong evidence of a direct hole transfer from photoexcited SWCNTs to the P3HT polymer. The transfer efficiency depends on the interface configuration. It is the highest for the blend where we achieve closer contact between the (6,5) SWCNTs and the polymer. When the polymer blend is deposited on top of the nanotube film or the nanotube film is deposited onto the polymer blend, the process is slowed down due to less or missing interfacing of the carbon nanotubes with the polymer chains. Addnl. we demonstrate a cascading effect in the electron path, which stabilizes charge sepn. by further transferring the electron left behind by hole transfer to the polymer to the adjacent (7,5) SWCNTs. Our results highlight the potential of semiconducting SWCNTs to improving the performance of org. solar cells.
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    Verissimo-Alves, M.; Capaz, R. B.; Koiller, B.; Artacho, E.; Chacham, H. Polarons in Carbon Nanotubes. Phys. Rev. Lett. 2001, 86 (15), 3372– 3375,  DOI: 10.1103/PhysRevLett.86.3372

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    Polarons in Carbon Nanotubes

    Verissimo-Alves, M.; Capaz, R. B.; Koiller, Belita; Artacho, Emilio; Chacham, H.

    Physical Review Letters (2001), 86 (15), 3372-3375CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)

    We use ab initio total-energy calcns. to predict the existence of polarons in semiconducting carbon nanotubes (CNTs). We find that the CNTs' band edge energies vary linearly and the elastic energy increases quadratically with both radial and with axial distortions, leading to the spontaneous formation of polarons. Using a continuum model parametrized by the ab initio calcns., we est. electron and hole polaron lengths, energies, and effective masses and analyze their complex dependence on CNT geometry. Implications of polaron effects on recently obsd. electro- and optomech. behavior of CNTs are discussed.
53. 53

    Jakubka, F.; Grimm, S. B.; Zakharko, Y.; Gannott, F.; Zaumseil, J. Trion Electroluminescence from Semiconducting Carbon Nanotubes. ACS Nano 2014, 8 (8), 8477– 8486,  DOI: 10.1021/nn503046y

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    Trion Electroluminescence from Semiconducting Carbon Nanotubes

    Jakubka, Florian; Grimm, Stefan B.; Zakharko, Yuriy; Gannott, Florentina; Zaumseil, Jana

    ACS Nano (2014), 8 (8), 8477-8486CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)

    Near-IR emission from semiconducting single-walled carbon nanotubes (SWNTs) usually results from radiative relaxation of excitons. By binding an addnl. electron or hole through chem. or electrochem. doping, charged three-body excitons, so-called trions, are created that emit light at lower energies. The energy difference is large enough to observe weak trion photoluminescence from doped SWNTs even at room temp. Here, we demonstrate strong trion electroluminescence from electrolyte-gated, light-emitting SWNT transistors with three different polymer-sorted carbon nanotube species, namely, (6,5), (7,5) and (10,5). The red-shifted trion emission is equal to or even stronger than the exciton emission, which is attributed to the high charge carrier d. in the transistor channel. The possibility of trions as a radiative relaxation pathway for triplets and dark excitons that are formed in large nos. by electron-hole recombination is discussed. The ratio of trion to exciton emission can be tuned by the applied voltages, enabling voltage-controlled near-IR light sources with narrow line widths that are soln.-processable and operate at low voltages (<3 V).
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    Matsunaga, R.; Matsuda, K.; Kanemitsu, Y. Observation of charged excitons in hole-doped carbon nanotubes using photoluminescence and absorption spectroscopy. Phys. Rev. Lett. 2011, 106 (3), 037404,  DOI: 10.1103/PhysRevLett.106.037404

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    Observation of charged excitons in hole-doped carbon nanotubes using photoluminescence and absorption spectroscopy

    Matsunaga, Ryusuke; Matsuda, Kazunari; Kanemitsu, Yoshihiko

    Physical Review Letters (2011), 106 (3), 037404/1-037404/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)

    The authors report the 1st observation of trions (charged excitons), three-particle bound states consisting of one electron and two holes, in hole-doped C nanotubes at room temp. When p-type dopants are added to C nanotube solns., the photoluminescence and absorption peaks of the trions appear far below the E11 bright exciton peak, regardless of the dopant species. The unexpectedly large energy sepn. between the bright excitons and the trions is attributed to the strong electron-hole exchange interaction in C nanotubes.
55. 55

    Eckstein, K. H.; Oberndorfer, F.; Achsnich, M. M.; Schöppler, F.; Hertel, T. Quantifying Doping Levels in Carbon Nanotubes by Optical Spectroscopy. J. Phys. Chem. C 2019, 123 (49), 30001– 30006,  DOI: 10.1021/acs.jpcc.9b08663

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    Quantifying Doping Levels in Carbon Nanotubes by Optical Spectroscopy

    Eckstein, Klaus H.; Oberndorfer, Florian; Achsnich, Melanie M.; Schoeppler, Friedrich; Hertel, Tobias

    Journal of Physical Chemistry C (2019), 123 (49), 30001-30006CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)

    Controlling doping is essential for the successful integration of semiconductor materials into device technologies. However, the assessment of doping levels and the distribution of charge carriers in carbon nanotubes or other nanoscale semiconductor materials is often either limited to a qual. attribution of being "high" or "low" or entirely absent. Here, we describe efforts toward a quant. characterization of doping in redox- or electrochem. doped semiconducting single-wall carbon nanotubes (s-SWNTs) using vis-NIR absorption spectroscopy. We discuss how carrier densities up to about 0.5 nm-1 can be quantified with a sensitivity of roughly 1 charge per 104 carbon atoms assuming inhomogeneous or homogeneous carrier distributions.
56. 56

    Heller, I.; Kong, J.; Williams, K. A.; Dekker, C.; Lemay, S. G. Electrochemistry at Single-Walled Carbon Nanotubes: The Role of Band Structure and Quantum Capacitance. J. Am. Chem. Soc. 2006, 128 (22), 7353– 7359,  DOI: 10.1021/ja061212k

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    Electrochemistry at Single-Walled Carbon Nanotubes: The Role of Band Structure and Quantum Capacitance

    Heller, Iddo; Kong, Jing; Williams, Keith A.; Dekker, Cees; Lemay, Serge G.

    Journal of the American Chemical Society (2006), 128 (22), 7353-7359CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)

    The authors present a theor. description of the kinetics of electrochem. charge transfer at single-walled C nanotube (SWNT) electrodes, explicitly taking into account the SWNT electronic band structure. SWNTs have a distinct and low d. of electronic states (DOS), as expressed by a small value of the quantum capacitance. This greatly affects the alignment and occupation of electronic states in voltammetric expts. and thus the electrode kinetics. The authors model electrochem. at metallic and semiconducting SWNTs as well as at graphene by applying the Gerischer-Marcus model of electron transfer kinetics. The authors predict that the semiconducting or metallic SWNT band structure and its distinct van Hove singularities can be resolved in voltammetry, in a manner analogous to scanning tunneling spectroscopy. Consequently, SWNTs of different at. structure yield different rate consts. due to structure-dependent variations in the DOS. The rate of charge transfer does not necessarily vanish in the band gap of a semiconducting SWNT, due to significant contributions from states which are a few kBT away from the Fermi level. The combination of a nanometer crit. dimension and the distinct band structure makes SWNTs a model system for studying the effect of the electronic structure of the electrode on electrochem. charge transfer.
57. 57

    Zheng, M.; Diner, B. A. Solution Redox Chemistry of Carbon Nanotubes. J. Am. Chem. Soc. 2004, 126 (47), 15490– 15494,  DOI: 10.1021/ja0457967

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    Solution Redox Chemistry of Carbon Nanotubes

    Zheng, Ming; Diner, Bruce A.

    Journal of the American Chemical Society (2004), 126 (47), 15490-15494CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)

    UV/visible/NIR absorbance spectra were used to monitor electron transfer between small-mol. redox reagents and C nanotubes (CNTs). The oxidn. of (6, 5)-enriched nanotubes in H2O with K2Ir(Cl)6 reveals a valence electron d. of 0.2-0.4 e-/100 C atoms and a redn. potential of ∼800 mV vs. normal H electrode. The redn. potential of CNTs increases with increasing band gap and to decrease with the introduction of an anionic dispersant. In light of this newly revealed redox chem. of CNTs, probably the previously obsd. bleaching of the CNT absorbance spectrum at low pH is most likely a consequence of the oxidn. of the nanotubes by oxygen. These results demonstrate facile oxidn. and redn. of CNTs, provide a way to quantify the population of valence electrons, and point to possible applications of CNT in the catalysis of redox reactions.
58. 58

    Eckstein, K. H.; Hartleb, H.; Achsnich, M. M.; Schoppler, F.; Hertel, T. Localized Charges Control Exciton Energetics and Energy Dissipation in Doped Carbon Nanotubes. ACS Nano 2017, 11 (10), 10401– 10408,  DOI: 10.1021/acsnano.7b05543

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    Localized Charges Control Exciton Energetics and Energy Dissipation in Doped Carbon Nanotubes

    Eckstein, Klaus H.; Hartleb, Holger; Achsnich, Melanie M.; Schoeppler, Friedrich; Hertel, Tobias

    ACS Nano (2017), 11 (10), 10401-10408CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)

    Doping by chem. or phys. means is key for the development of future semiconductor technologies. Ideally, charge carriers should be able to move freely in a homogeneous environment. Here, the authors report on evidence suggesting that excess carriers in electrochem. p-doped semiconducting single-wall C nanotubes (s-SWNTs) become localized, most likely due to poorly screened Coulomb interactions with counterions in the Helmholtz layer. A quant. anal. of blue-shift, broadening, and asymmetry of the 1st exciton absorption band also reveals that doping leads to hard segmentation of s-SWNTs with intrinsic undoped segments being sepd. by randomly distributed charge puddles ∼4 nm in width. Light absorption in these doped segments is assocd. with the formation of trions, spatially sepd. from neutral excitons. Acceleration of exciton decay in doped samples is governed by diffusive exciton transport to, and nonradiative decay at charge puddles within 3.2 ps in moderately doped s-SWNTs. Probably conventional band-filling in s-SWNTs breaks down due to inhomogeneous electrochem. doping.
59. 59

    Hartleb, H.; Späth, F.; Hertel, T. Evidence for Strong Electronic Correlations in the Spectra of Gate-Doped Single-Wall Carbon Nanotubes. ACS Nano 2015, 9 (10), 10461– 10470,  DOI: 10.1021/acsnano.5b04707

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    Evidence for Strong Electronic Correlations in the Spectra of Gate-Doped Single-Wall Carbon Nanotubes

    Hartleb, Holger; Spaeth, Florian; Hertel, Tobias

    ACS Nano (2015), 9 (10), 10461-10470CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)

    The photophys. properties were studied of electrochem. gate-doped semiconducting single-wall C nanotubes (s-SWNTs). A comparison of luminescence (PL) and simultaneously recorded absorption spectra reveals that free-carrier densities correlate with the 1st sub-band exciton or trion oscillator strengths but not with PL intensities. A global anal. of the 1st sub-band exciton absorption was used for a detailed study of gate-doping, here of the (6,5) SWNT valence band. The data are consistent with a doping-induced valence band shift according to Δεv = n × b, where n is the free-carrier d., εv is the valence band edge, and b = 0.15 ± 0.05 eV nm. The authors also predict such band gap renormalization of 1-dimensional gate-doped semiconductors to be accompanied by a stepwise increase of the carrier d. by Δn = (32meffb)/(πℏ)2 (meff is effective carrier mass). The width of the spectroelectrochem. window of the 1st sub-band exciton of 1.55 ± 0.05 eV corresponds to the fundamental band gap of the undoped (6,5) SWNTs in the samples and not to the renormalized band gap of the doped system. These observations and a previously unidentified absorption band emerging at high doping levels in the Pauli-blocked region of the single-particle Hartree band structure provide clear evidence for strong electronic correlations in the optical spectra of SWNTs.
60. 60

    Kochi, J. K. Inner-sphere electron transfer in organic chemistry. Relevance to electrophilic aromatic nitration. Acc. Chem. Res. 1992, 25 (1), 39– 47,  DOI: 10.1021/ar00013a006

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    Inner-sphere electron transfer in organic chemistry. Relevance to electrophilic aromatic nitration

    Kochi, Jay K.

    Accounts of Chemical Research (1992), 25 (1), 39-47CODEN: ACHRE4; ISSN:0001-4842.

    A review with 47 refs. on the mechanism of electrophilic arom. nitration.
61. 61

    Connelly, N. G.; Geiger, W. E. Chemical Redox Agents for Organometallic Chemistry. Chem. Rev. 1996, 96 (2), 877– 910,  DOI: 10.1021/cr940053x

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    Chemical Redox Agents for Organometallic Chemistry

    Connelly, Neil G.; Geiger, William E.

    Chemical Reviews (Washington, D. C.) (1996), 96 (2), 877-910CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)

    A review, with >461 refs., showing how one-electron oxidants and reductants have been used in preparative chem. (incorporating both synthetic applications and generation of species for in situ characterization) in nonaq. solns., the usual media for organometallic ET reactions. The authors do not treat photochem.-generated reducing agents which, although generally transient species, may have advantages in some applications.
62. 62

    Aguirre, C. M.; Levesque, P. L.; Paillet, M.; Lapointe, F.; St-Antoine, B. C.; Desjardins, P.; Martel, R. The Role of the Oxygen/Water Redox Couple in Suppressing Electron Conduction in Field-Effect Transistors. Adv. Mater. 2009, 21 (30), 3087– 3091,  DOI: 10.1002/adma.200900550

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    The Role of the Oxygen/Water Redox Couple in Suppressing Electron Conduction in Field-Effect Transistors

    Aguirre, Carla M.; Levesque, Pierre L.; Paillet, Matthieu; Lapointe, Francois; St-Antoine, Benoit C.; Desjardins, Patrick; Martel, Richard

    Advanced Materials (Weinheim, Germany) (2009), 21 (30), 3087-3091CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)

    The similarities between the elec. behavior of carbon nanotube FETs and that of org. semiconductor FETs strongly suggest that the suppression of n-type cond. must have a common denominator. A mechanism was proposed that is based on electron transfer between SiO2 and adsorbed oxygen/water redox couple. According to this mechanism, n-type cond. will be suppressed in most org. semiconductor FETs fabricated on SiO2 substrates. Because the electron affinities of most org. semiconductors lie above the electrochem. potential of the aq. oxygen redox couple, it is natural that the electron transfer will favor the p-type cond.
63. 63

    Avery, A. D.; Zhou, B. H.; Lee, J.; Lee, E.-S.; Miller, E. M.; Ihly, R.; Wesenberg, D.; Mistry, K. S.; Guillot, S. L.; Zink, B. L. Tailored semiconducting carbon nanotube networks with enhanced thermoelectric properties. Nat. Energy 2016, 1 (4), 16033,  DOI: 10.1038/nenergy.2016.33

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    Tailored semiconducting carbon nanotube networks with enhanced thermoelectric properties

    Avery, Azure D.; Zhou, Ben H.; Lee, Jounghee; Lee, Eui-Sup; Miller, Elisa M.; Ihly, Rachelle; Wesenberg, Devin; Mistry, Kevin S.; Guillot, Sarah L.; Zink, Barry L.; Kim, Yong-Hyun; Blackburn, Jeffrey L.; Ferguson, Andrew J.

    Nature Energy (2016), 1 (4), 16033CODEN: NEANFD; ISSN:2058-7546. (Nature Publishing Group)

    Thermoelec. power generation, allowing recovery of part of the energy wasted as heat, is emerging as an important component of renewable energy and energy efficiency portfolios. Although inorg. semiconductors have traditionally been employed in thermoelec. applications, org. semiconductors garner increasing attention as versatile thermoelec. materials. Here we present a combined theor. and exptl. study suggesting that semiconducting single-walled carbon nanotubes with carefully controlled chirality distribution and carrier d. are capable of large thermoelec. power factors, higher than 340μW m-1 K-2, comparable to the best-performing conducting polymers and larger than previously obsd. for carbon nanotube films. Furthermore, we demonstrate that phonons are the dominant source of thermal cond. in the networks, and that our carrier doping process significantly reduces the thermal cond. relative to undoped networks. These findings provide the scientific underpinning for improved functional org. thermoelec. composites with carbon nanotube inclusions.
64. 64

    Holt, J. M.; Ferguson, A. J.; Kopidakis, N.; Larsen, B. A.; Bult, J.; Rumbles, G.; Blackburn, J. L. Prolonging Charge Separation in P3HT–SWNT Composites Using Highly Enriched Semiconducting Nanotubes. Nano Lett. 2010, 10 (11), 4627– 4633,  DOI: 10.1021/nl102753z

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    Prolonging Charge Separation in P3HT-SWNT Composites Using Highly Enriched Semiconducting Nanotubes

    Holt, Josh M.; Ferguson, Andrew J.; Kopidakis, Nikos; Larsen, Brian A.; Bult, Justin; Rumbles, Garry; Blackburn, Jeffrey L.

    Nano Letters (2010), 10 (11), 4627-4633CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)

    Single-walled C nanotubes (SWNTs) have potential as electron acceptors in org. photovoltaics (OPVs), but the currently low-power conversion efficiencies of devices remain largely unexplained. The authors demonstrate effective redispersion of isolated, highly enriched semiconducting and metallic SWNTs into poly(3-hexylthiophene) (P3HT). The authors use these enriched blends to provide the 1st exptl. evidence of the neg. impact of metallic nanotubes. Time-resolved microwave cond. reveals that the long-lived carrier population can be significantly increased by incorporating highly enriched semiconducting SWNTs into semiconducting polymer composites.
65. 65

    Sato, K.; Saito, R.; Jiang, J.; Dresselhaus, G.; Dresselhaus, M. S. Discontinuity in the family pattern of single-wall carbon nanotubes. Phys. Rev. B: Condens. Matter Mater. Phys. 2007, 76 (19), 195446,  DOI: 10.1103/PhysRevB.76.195446

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    Discontinuity in the family pattern of single-wall carbon nanotubes

    Sato, K.; Saito, R.; Jiang, J.; Dresselhaus, G.; Dresselhaus, M. S.

    Physical Review B: Condensed Matter and Materials Physics (2007), 76 (19), 195446/1-195446/7CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)

    The higher lying bright exciton energies (EM11,ES33,ES44,EM22,ES55,ES66,EM33) of single-wall C nanotubes are calcd. by solving the Bethe-Salpeter equation within an extended tight binding method. For smaller diam. nanotubes, some higher Eii excitonic states are missing. In particular, some Eii's on the 1-dimensional Brillouin zone (cutting line) are no longer relevant to the formation of excitons and are skipped in listing the order of the Eii values. Thus the family patterns show some discontinuities in k space and this effect should be observable in Raman G' band spectroscopy. The higher exciton energies ES33 and ES44 have a large chirality dependence due to many body effects, since the self-energy becomes larger than the binding energy. Thus the chirality dependence of the higher Eii comes not only from a single particle energy but also from many-body effects.
66. 66

    Chmeliov, J.; Narkeliunas, J.; Graham, M. W.; Fleming, G. R.; Valkunas, L. Exciton–exciton annihilation and relaxation pathways in semiconducting carbon nanotubes. Nanoscale 2016, 8 (3), 1618– 1626,  DOI: 10.1039/C5NR06853C

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    Exciton-exciton annihilation and relaxation pathways in semiconducting carbon nanotubes

    Chmeliov, Jevgenij; Narkeliunas, Jonas; Graham, Matt W.; Fleming, Graham R.; Valkunas, Leonas

    Nanoscale (2016), 8 (3), 1618-1626CODEN: NANOHL; ISSN:2040-3372. (Royal Society of Chemistry)

    We present a thorough anal. of one- and two-color transient absorption measurements performed on single- and double-walled semiconducting carbon nanotubes. By combining the currently existing models describing exciton-exciton annihilation-the coherent and the diffusion-limited ones-we are able to simultaneously reproduce excitation kinetics following both E11 and E22 pump conditions. Our simulations revealed the fundamental photophys. behavior of one-dimensional coherent excitons and non-trivial excitation relaxation pathways. In particular, we found that after non-linear annihilation a doubly-excited exciton relaxes directly to its E11 state bypassing the intermediate E22 manifold, so that after excitation resonant with the E11 transition, the E22 state remains unpopulated. A quant. explanation for the obsd. much faster excitation kinetics probed at E22 manifold, comparing to those probed at the E11 band, is also provided.
67. 67

    Harrah, D. M.; Schneck, J. R.; Green, A. A.; Hersam, M. C.; Ziegler, L. D.; Swan, A. K. Intensity-Dependent Exciton Dynamics of (6,5) Single-Walled Carbon Nanotubes: Momentum Selection Rules, Diffusion, and Nonlinear Interactions. ACS Nano 2011, 5 (12), 9898– 9906,  DOI: 10.1021/nn203604v

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    Intensity-Dependent Exciton Dynamics of (6,5) Single-Walled Carbon Nanotubes: Momentum Selection Rules, Diffusion, and Nonlinear Interactions

    Harrah, D. Mark; Schneck, Jude R.; Green, Alexander A.; Hersam, Mark C.; Ziegler, Lawrence D.; Swan, Anna K.

    ACS Nano (2011), 5 (12), 9898-9906CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)

    The exciton dynamics for an ensemble of individual, suspended (6,5), single-walled C nanotubes revealed by single color E22 resonant pump-probe spectroscopy for a wide range of pump fluences are reported. The optically excited initial exciton population ranges ∼5-120 excitons per ∼725 nm nanotube. At the higher fluences of this range, the pump-probe signals are no longer linearly dependent on the pump intensity. A single, predictive model is described that fits all data for 2 decades of pump fluences and 3 decades of delay times. The model introduces population loss from the optically active zero momentum E22 state to the rest of the E22 subband, which is dark due to momentum selection rules. In the single exciton limit, the E11 dynamics are well described by a stretched exponential, which is a direct consequence of diffusion quenching from an ensemble of nanotubes of different lengths. The obsd. change in population relaxation dynamics as a function of increasing pump intensity is attributed to exciton-exciton Auger de-excitation in the E11 subband and, to a lesser extent, in the E22 subband. From the fit to the model, an av. defect d. 1/ρ = 150 nm and diffusion consts. D11 = 4 cm2/s and D22 = 0.2 cm2/s are detd.
68. 68

    Perebeinos, V.; Tersoff, J.; Avouris, P. Scaling of Excitons in Carbon Nanotubes. Phys. Rev. Lett. 2004, 92 (25), 257402,  DOI: 10.1103/PhysRevLett.92.257402

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    Scaling of Excitons in Carbon Nanotubes

    Perebeinos, Vasili; Tersoff, J.; Avouris, Phaedon

    Physical Review Letters (2004), 92 (25, Pt. 1), 257402/1-257402/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)

    Light emission from C nanotubes is expected to be dominated by excitonic recombination. Here the authors calc. the properties of excitons in nanotubes embedded in a dielec., for a wide range of tube radii and dielec. environments. Simple scaling relations give a good description of the binding energy, exciton size, and oscillator strength.
69. 69

    Santos, S. M.; Yuma, B.; Berciaud, S.; Shaver, J.; Gallart, M.; Gilliot, P.; Cognet, L.; Lounis, B. All-Optical Trion Generation in Single-Walled Carbon Nanotubes. Phys. Rev. Lett. 2011, 107 (18), 187401,  DOI: 10.1103/PhysRevLett.107.187401

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    All-Optical Trion Generation in Single-Walled Carbon Nanotubes

    Santos, Silvia M.; Yuma, Bertrand; Berciaud, Stephane; Shaver, Jonah; Gallart, Mathieu; Gilliot, Pierre; Cognet, Laurent; Lounis, Brahim

    Physical Review Letters (2011), 107 (18), 187401/1-187401/5CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)

    We present evidence of all-optical trion generation and emission in pristine single-walled carbon nanotubes (SWCNTs). Luminescence spectra, recorded on individual SWCNTs over a large cw excitation intensity range, show trion emission peaks red shifted with respect to the bright exciton peak. Clear chirality dependence is obsd. for 22 sep. SWCNT species, allowing for detn. of electron-hole exchange interaction and trion binding energy contributions. Luminescence data together with ultrafast pump-probe expts. on chirality-sorted bulk samples suggest that exciton-exciton annihilation processes generate dissocd. carriers that allow for trion creation upon a subsequent photon absorption event.
70. 70

    Soavi, G.; Scotognella, F.; Viola, D.; Hefner, T.; Hertel, T.; Cerullo, G.; Lanzani, G. High energetic excitons in carbon nanotubes directly probe charge-carriers. Sci. Rep. 2015, 5, 9681,  DOI: 10.1038/srep09681

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    High energetic excitons in carbon nanotubes directly probe charge-carriers

    Soavi, Giancarlo; Scotognella, Francesco; Viola, Daniele; Hefner, Timo; Hertel, Tobias; Cerullo, Giulio; Lanzani, Guglielmo

    Scientific Reports (2015), 5 (), 9681CODEN: SRCEC3; ISSN:2045-2322. (Nature Publishing Group)

    Theory predicts peculiar features for excited-state dynamics in one dimension (1D) that are difficult to be obsd. exptl. Single-walled carbon nanotubes (SWNTs) are an excellent approxn. to 1D quantum confinement, due to their very high aspect ratio and low d. of defects. Here we use ultrafast optical spectroscopy to probe photogenerated charge-carriers in (6,5) semiconducting SWNTs. We identify the transient energy shift of the highly polarizable S33 transition as a sensitive fingerprint of charge-carriers in SWNTs. By measuring the coherent phonon amplitude profile we obtain a precise est. of the Stark-shift and discuss the binding energy of the S33 excitonic transition. From this, we infer that charge-carriers are formed instantaneously (<50 fs) even upon pumping the first exciton, S11. The decay of the photogenerated charge-carrier population is well described by a model for geminate recombination in 1D.
71. 71

    Shi, J.; Chu, H.; Li, Y.; Zhang, X.; Pan, H.; Li, D. Synthesis and nonlinear optical properties of semiconducting single-walled carbon nanotubes at 1 μm. Nanoscale 2019, 11 (15), 7287– 7292,  DOI: 10.1039/C8NR10174D

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    Synthesis and nonlinear optical properties of semiconducting single-walled carbon nanotubes at 1μm

    Shi, Jichao; Chu, Hongwei; Li, Ying; Zhang, Xiaodong; Pan, Han; Li, Dechun

    Nanoscale (2019), 11 (15), 7287-7292CODEN: NANOHL; ISSN:2040-3372. (Royal Society of Chemistry)

    Herein, we synthesized and extd. pure semiconducting single-walled carbon nanotubes (s-SWCNTs). Moreover, the nonlinear optical (NLO) properties, such as saturable absorption, two-photon absorption coeff., modulation depth and optical limitation, of s-SWCNTs were exptl. detd. using a high-energy 1064 nm nanosecond (ns) laser. Compared with the common SWCNTs, the s-SWCNTs demonstrated lower satn.intensity and lower two-photon absorption (TPA) coeff. The modulation depth of the s-SWCNTs was as high as 8.6%. Based on these parameters, the s-SWCNTs can be used as excellent saturable absorbers in pulsed laser applications.
72. 72

    Brady, G. J.; Joo, Y.; Singha Roy, S.; Gopalan, P.; Arnold, M. S. High performance transistors via aligned polyfluorene-sorted carbon nanotubes. Appl. Phys. Lett. 2014, 104 (8), 083107,  DOI: 10.1063/1.4866577

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    High performance transistors via aligned polyfluorene-sorted carbon nanotubes

    Brady, Gerald J.; Joo, Yongho; Singha Roy, Susmit; Gopalan, Padma; Arnold, Michael S.

    Applied Physics Letters (2014), 104 (8), 083107/1-083107/5CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)

    The authors evaluate the performance of exceptionally electronic-type sorted, semiconducting, aligned single-walled carbon nanotubes (s-SWCNTs) in field effect transistors (FETs). High on-conductance and high on/off conductance modulation are simultaneously achieved at channel lengths which are both shorter and longer than individual s-SWCNTs. The s-SWCNTs are isolated from heterogeneous mixts. using a polyfluorene-deriv. as a selective agent and aligned on substrates via dose-controlled, floating evaporative self-assembly at densities of ∼50 s-SWCNTs μm-1. At a channel length of 9 μm the s-SWCNTs percolate to span the FET channel, and the on/off ratio and charge transport mobility are 2.2 × 107 and 46 cm2 V-1 s-1, resp. At a channel length of 400 nm, a large fraction of the s-SWCNTs directly span the channel, and the on-conductance per width is 61 μS μm-1 and the on/off ratio is 4 × 105. These results are considerably better than previous soln.-processed FETs, which have suffered from poor on/off ratio due to spurious metallic nanotubes that bridge the channel. 4071 individual and small bundles of s-SWCNTs are tested in 400 nm channel length FETs, and all show semiconducting behavior, demonstrating the high fidelity of polyfluorenes as selective agents and the promise of assembling s-SWCNTs from soln. to create high performance semiconductor electronic devices. (c) 2014 American Institute of Physics.
73. 73

    Ehli, C.; Oelsner, C.; Guldi, D. M.; Mateo-Alonso, A.; Prato, M.; Schmidt, C.; Backes, C.; Hauke, F.; Hirsch, A. Manipulating single-wall carbon nanotubes by chemical doping and charge transfer with perylene dyes. Nat. Chem. 2009, 1 (3), 243– 9,  DOI: 10.1038/nchem.214

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    Manipulating single-wall carbon nanotubes by chemical doping and charge transfer with perylene dyes

    Ehli, Christian; Oelsner, Christian; Guldi, Dirk M.; Mateo-Alonso, Aurelio; Prato, Maurizio; Schmidt, Cordula; Backes, Claudia; Hauke, Frank; Hirsch, Andreas

    Nature Chemistry (2009), 1 (3), 243-249, s243/1-s243/6CODEN: NCAHBB; ISSN:1755-4330. (Nature Publishing Group)

    Single-wall carbon nanotubes (SWNTs) are emerging as materials with much potential in several disciplines, in particular in electronics and photovoltaics. The combination of SWNTs with electron donors or acceptors generates active materials, which can produce elec. energy when irradiated. However, SWNTs are elusive species when characterization of their metastable states is required. This problem mainly arises because of the polydispersive nature of SWNT samples and the inevitable presence of SWNTs in bundles of different sizes. Here, we report the complete and thorough characterization of an SWNT radical ion-pair state induced by complexation with a perylene dye, which combines excellent electron-accepting and -conducting features with a five-fused ring π-system. At the same time, the perylene dye enables the dispersion of SWNTs by π-π interactions, which gives individual SWNTs in soln. This work clears a path towards electronic and optoelectronic devices in which regulated elec. transport properties are important.
74. 74

    Dowgiallo, A.-M.; Mistry, K. S.; Johnson, J. C.; Blackburn, J. L. Ultrafast Spectroscopic Signature of Charge Transfer between Single-Walled Carbon Nanotubes and C₆₀. ACS Nano 2014, 8 (8), 8573– 8581,  DOI: 10.1021/nn503271k

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    Ultrafast Spectroscopic Signature of Charge Transfer between Single-Walled Carbon Nanotubes and C60

    Dowgiallo, Anne-Marie; Mistry, Kevin S.; Johnson, Justin C.; Blackburn, Jeffrey L.

    ACS Nano (2014), 8 (8), 8573-8581CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)

    The time scales for interfacial charge sepn. and recombination play crucial roles in detg. efficiencies of excitonic photovoltaics. Near-IR photons are harvested efficiently by semiconducting single-walled carbon nanotubes (SWCNTs) paired with appropriate electron acceptors, such as fullerenes (e.g., C60). However, little is known about crucial photochem. events that occur on femtosecond to nanosecond time scales at such heterojunctions. Here, we present transient absorbance measurements that utilize a distinct spectroscopic signature of charges within SWCNTs, the absorbance of a trion quasiparticle, to measure both the ultrafast photoinduced electron transfer time (τpet) and yield (.vphi.pet) in photoexcited SWCNT-C60 bilayer films. The rise time of the trion-induced absorbance enables the detn. of the photoinduced electron transfer (PET) time of τpet ≤ 120 fs, while an exptl. detd. trion absorbance cross section reveals the yield of charge transfer (.vphi.pet ≈ 38 ± 3%). The extremely fast electron transfer times obsd. here are on par with some of the best donor:acceptor pairs in excitonic photovoltaics and underscore the potential for efficient energy harvesting in SWCNT-based devices.
75. 75

    Howard, I. A.; Mauer, R.; Meister, M.; Laquai, F. Effect of Morphology on Ultrafast Free Carrier Generation in Polythiophene:Fullerene Organic Solar Cells. J. Am. Chem. Soc. 2010, 132 (42), 14866– 14876,  DOI: 10.1021/ja105260d

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    Effect of Morphology on Ultrafast Free Carrier Generation in Polythiophene:Fullerene Organic Solar Cells

    Howard, Ian A.; Mauer, Ralf; Meister, Michael; Laquai, Frederic

    Journal of the American Chemical Society (2010), 132 (42), 14866-14876CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)

    Despite significant study, the precise mechanisms that dictate the efficiency of org. photovoltaic cells, such as charge sepn. and recombination, are still debated. Here, we directly observe efficient ultrafast free charge generation in the absence of field in annealed poly(3-hexylthiophene):methanofullerene (P3HT:PCBM). However, we find this process is much less efficient in unannealed and amorphous regiorandom blends, explaining the superior short-circuit current and fill-factor of annealed regioregular P3HT:PCBM solar cells. We use transient optical spectroscopy in the visible and near-IR spectral region covering, but not limited to, the previously unobserved and highly relevant time scale spanning 1-100 ns, to directly observe both geminate and nongeminate charge recombination. We find that exciton quenching leads directly (time scale <100 fs) to two populations: bound charges and free charges. The former do not lead to photocurrent in a photovoltaic cell; they recombine geminately within 2 ns and are a loss channel. However, the latter can be efficiently extd. in photovoltaic cells. Therefore, we find that the probability of ultrafast free charge formation after exciton quenching directly limits solar cell efficiency. This probability is low in disordered P3HT:PCBM blends but approaches unity in annealed blends.