Experimental determination of excitonic structure in polythiophene

Sakurai, Kouhei; Tachibana, Hiroaki; Shiga, Natsuki; Terakura, C.; Matsumoto, Mutsuyoshi; Tokura, Y.

doi:10.1103/physrevb.56.9552

Cited by 83 publications

(80 citation statements)

References 24 publications

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“…13 and 14 that situation II yields results in good agreement with the experiments of Ref. 32. The optical gap of 1.49 eV in situation III is smaller than in situation II and too small in comparison with experiment.…”

Section: A Polythiophene "Pt…supporting

confidence: 80%

Electronic and optical excitations in crystalline conjugated polymers

2002

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We calculate the electronic and optical excitations of crystalline polythiophene and polyphenylenevinylene, using the GW approximation for the electronic self-energy and including excitonic effects by solving the electron-hole Bethe-Salpeter equation. We compare with our earlier calculations on an isolated polythiophene chain and polymer chains embedded in a dielectric medium. Surprisingly, we find for the crystalline calculations optical gaps and exciton binding energies that are significantly smaller than present experimental values. We attribute the disagreement to the fact that the quantum-mechanical coherence between polymer chains, present in the calculations, is absent in most experimental situations. We discuss possible reasons for this absence. Our general conclusion is that the picture of a polymer chain in a dielectric medium is most appropriate in describing the present experimental data on electronic and optical excitations in conjugated polymers.

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Section: A Polythiophene "Pt…supporting

confidence: 80%

Electronic and optical excitations in crystalline conjugated polymers

2002

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“…78,82 In D-A molecules, a triplet formation is observed following the back electron transfer. 80 Relatively small ΔE ST have been reported for conjugated polymers with planar backbone structures including highly ordered regioregular P3OT films (ΔE ST = 0.45 eV) 85 and the ladder type MeLPPP in benzene solution (ΔE ST = 0.54 eV). 63 Thus, the polymer triplet energy, E T , for these polymers is estimated as ~ 1.5 eV.…”

Section: -----<<< Scheme 1 >>>-----mentioning

confidence: 99%

Charge Carrier Formation in Polythiophene/Fullerene Blend Films Studied by Transient Absorption Spectroscopy

et al. 2008

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Abstract:We report herein a comparison of the photophysics of a series of polythiophenes with ionization potentials ranging from 4.8 to 5.6 eV as pristine films and when blended with 5 wt% 1-(3-methoxycarbonyl)propyl-1-phenyl-[6,6]C 61 (PCBM). Three polymers are observed to give amorphous films, attributed to a non-planar geometry of their backbone whilst the other five polymers, including poly(3-hexylthiophene), give more crystalline films. Optical excitation of the pristine films of the amorphous polymers is observed by transient absorption spectroscopy to give rise to polymer triplet formation. For the more crystalline pristine polymers, no triplet formation is observed, but rather a short-lived (~ 100 ns), broad photoinduced absorption feature assigned to polymer polarons. For all polymers, the addition of 5 wt% PCBM resulted in 70 -90% quenching of polymer photoluminescence (PL), indicative of efficient quenching of polythiophene excitons. Remarkably, despite this efficient exciton quenching, the yield of dissociated polymer + and PCBM − polarons, assayed by the appearance of a long-lived, powerlaw decay phase assigned to bimolecular recombination of these polarons, was observed to vary by over two orders of magnitude depending upon the polymer employed. In addition to this power-law decay phase, the blend films exhibited short-lived decays assigned, for the amorphous polymers, to neutral triplet states generated by geminate recombination of bound radical pairs and, for the more crystalline polymers, to the direct observation of the geminate recombination of these bound radical pairs to ground. These observations are discussed in terms of a two-step kinetic model for charge generation in polythiophene/PCBM blend films analogous to that reported to explain the observation of exciplex-like emission in poly(p-phenylenevinylene)-based blend films. Remarkably, we find a excellent correlation between the free energy difference for charge separation (ΔG CS rel ) and yield of the long-lived charge generation yield, with efficient charge generation requiring a much larger ΔG CS rel than that required to achieve efficient PL 3 quenching. We suggest this observation is consistent with a model where the excess thermal energy of the initially formed polarons pairs is necessary to overcome their coulomb binding energy. This observation has important implications for synthetic strategies to optimize organic solar cell performance, as it implies that, at least devices based on polythiophene/PCBM blend films, a large ΔG CS rel (or LUMO level offset) is required to achieve efficient charge dissociation.4

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“…We assume the same atomic geometry for the ground and excited states, i.e., the coupling between electronic and lattice degrees of freedom is neglected. Experimental data 18 indicate that energy shifts due to lattice relaxations are of the order of 0.1 eV in PT. DFT-LDA calculations 27 predict a holepolaron relaxation energy of 0.04 eV for 16T (nT is an oligomer consisting of n thiophene-rings͒.…”

Section: Methodsmentioning

confidence: 99%

“…However, the luminescence spectrum of Ref. 18 can be fully understood in terms of the 1 B u exciton decay and its vibronic side bands, which means that such defects are either rare or that excitons trapped by such defects decay nonradiatively.…”

Section: Crystalline Polythiophenementioning

confidence: 99%

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Ab initioprediction of the electronic and optical excitations in polythiophene: Isolated chains versus bulk polymer

et al. 2000

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initio prediction of the electronic and optical excitations in polythiophene : isolated chains versus bulk polymer. Physical Review B, 61(23), 15817-15826. DOI: 10.1103/PhysRevB.61.15817 General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from the public portal for the purpose of private study or research.• You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal ? Take down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. We calculate the electronic and optical excitations of polythiophene using the GW ͑G stands for one-electron Green function, W for the screened Coulomb interaction͒ approximation for the electronic self-energy, and include excitonic effects by solving the electron-hole Bethe-Salpeter equation. Two different situations are studied: excitations on isolated chains and excitations on chains in crystalline polythiophene. The dielectric tensor for the crystalline situation is obtained by modeling the polymer chains as polarizable line objects, with a long-wavelength polarizability tensor obtained from the ab initio polarizability function of the isolated chain. With this model dielectric tensor we construct a screened interaction for the crystalline case, including both intra-and interchain screening. In the crystalline situation both the quasiparticle band gap and the exciton binding energies are drastically reduced in comparison with the isolated chain. However, the optical gap is hardly affected. We expect this result to be relevant for conjugated polymers in general.

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Experimental determination of excitonic structure in polythiophene

Cited by 83 publications

References 24 publications

Electronic and optical excitations in crystalline conjugated polymers

Electronic and optical excitations in crystalline conjugated polymers

Charge Carrier Formation in Polythiophene/Fullerene Blend Films Studied by Transient Absorption Spectroscopy

Ab initioprediction of the electronic and optical excitations in polythiophene: Isolated chains versus bulk polymer

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