Order enables efficient electron-hole separation at an organic heterojunction with a small energy loss.
Ran, Niva A
Greehnam, Neil C
Bazan, Guillermo C
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Menke, S., Cheminal, A., Conaghan, P., Ran, N. A., Greehnam, N. C., Bazan, G. C., Nguyen, T., et al. (2018). Order enables efficient electron-hole separation at an organic heterojunction with a small energy loss.. Nature communications, 9 (1), 277. https://doi.org/10.1038/s41467-017-02457-5
Donor-acceptor organic solar cells often show low open-circuit voltages (VOC) relative to their optical energy gap (Eg) which limit power conversion efficiencies to around 12%. This energy loss is attributed, in part, to the offset in energy between Eg and that of intermolecular charge transfer (CT) states at the donor-acceptor interface. Here we study charge generation occurring in PIPCP:PC61BM, a system with a very low driving energy for initial charge separation (Eg−ECT~50 meV) and a high short-circuit internal quantum efficiency (ηIQE~80%). We track the strength of the electric field generated between the separating electron-hole pair by following the transient electroabsorption optical response, and find that while localised CT states are formed rapidly (<100 fs) after photoexcitation, free charges are not generated until 5 ps after photogeneration. In PIPCP:PC61BM, electronic disorder is low (Urbach energy < 27 meV) and we consider that free charge separation is able to out-compete trap-assisted non-radiative recombination of the CT state.
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External DOI: https://doi.org/10.1038/s41467-017-02457-5
This record's URL: https://www.repository.cam.ac.uk/handle/1810/271586
Attribution 4.0 International
Licence URL: http://creativecommons.org/licenses/by/4.0/
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