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Volume 155, 2012

Excitons and charges at organic semiconductor heterojunctions

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Abstract

All-organic heterojunction solar cells now provide very high quantum efficiencies for charge generation and rapidly-improving power conversion efficiencies. Charge generation and separation however, must overcome the strong Coulomb interactions between electrons and holes in these materials that is manifest also through the large exchange energies usually observed. We show for a polymer–polymer system with low charge generation efficiency that this arises through intersystem crossing from the photogenerated charge-transfer state to a lower lying triplet state, mediated by the proton hyperfine interaction, and that the activation barrier for full separation of electrons and holes is of the order of 250 meV. We observe, using transient optical spectroscopy, the processes of charge separation, recombination and sweep-out in efficient polymer-fullerene devices. We report also on the process of singlet exciton fission to form a pair of triplet excitons in pentacene that can later be dissociated against a heterojunction formed with C60.

Article information


Submitted
05 Jul 2011
Accepted
08 Jul 2011
First published
12 Dec 2011

Faraday Discuss., 2012,155, 339-348
Article type
Paper

Excitons and charges at organic semiconductor heterojunctions

R. H. Friend, M. Phillips, A. Rao, M. W. B. Wilson, Z. Li and C. R. McNeill, Faraday Discuss., 2012, 155, 339 DOI: 10.1039/C1FD00104C

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