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Proceedings Paper

Toward singlet fission for excitonic solar cells
Author(s): Josef Michl; Arthur J. Nozik; Xudong Chen; Justin C. Johnson; Geeta Rana; Akin Akdag; Andrew F. Schwerin
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Paper Abstract

Sensitizer dyes capable of producing two triplet excited states from a singlet excited state produced by the absorption of a single photon would allow an increase of the efficiency of photovoltaic cells by up to a factor of 1.5, provided that each triplet injects an electron into a semiconductor such as TiO2. Although singlet fission in certain crystals and polymers was reported long ago, little is known about its efficiency in dyes suitable for use as sensitizers of photoinduced charge separation on semiconductors surfaces. Biradicaloids and large alternant hydrocarbons are desirable parent structures likely to meet the requirement E(T2), E(S1) > 2E(T1) for the excitation energies of the lowest excited singlet (S1) and the two triplet (T1, T2) states. We report results for 1,3-diphenylisobenzofuran, a model compound of the biradicaloid type. Its energy levels satisfy the desired relation, and in solution it shows no triplet formation by intersystem crossing. In the neat solid state, it forms triplets efficiently, and indirect evidence suggests that this is due to singlet fission. This appears to be the first compound displaying SF by design. When two such chromophores were combined into dimers, triplet formation yields of up to 9% were observed in polar solvents, possibly due to singlet fission, but possibly due to intersystem crossing. The triplet formation occurs in two steps, via an intermediate assigned as an intramolecular charge-transfer state and responsible for most of the observed excitation loss.

Paper Details

Date Published: 17 October 2007
PDF: 9 pages
Proc. SPIE 6656, Organic Photovoltaics VIII, 66560E (17 October 2007); doi: 10.1117/12.735591
Show Author Affiliations
Josef Michl, Univ. of Colorado at Boulder (United States)
Arthur J. Nozik, National Renewable Energy Lab. (United States)
Xudong Chen, Univ. of Colorado at Boulder (United States)
Justin C. Johnson, National Renewable Energy Lab. (United States)
Geeta Rana, Univ. of Colorado at Boulder (United States)
Akin Akdag, Univ. of Colorado at Boulder (United States)
Andrew F. Schwerin, Univ. of Colorado at Boulder (United States)


Published in SPIE Proceedings Vol. 6656:
Organic Photovoltaics VIII
Zakya H. Kafafi; Paul A. Lane, Editor(s)

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