Ultrafast Energy Transfer Triggers Ionization Energy Offset Dependence of Quantum Efficiency in Low-bandgap Non-fullerene Acceptor Solar Cells
De Castro, Catherine S. P.
Khan, Jafar Iqbal
Dela Peña, Top Archie
Anjum, Dalaver H.
De Wolf, Stefaan
Anthopoulos, Thomas D.
Paleti, Sri Harish Kumar
KAUST DepartmentKAUST Solar Center (KSC)
Material Science and Engineering Program
Physical Science and Engineering (PSE) Division
KAUST Solar Center, Physical Sciences and Engineering Division (PSE), Materials Science and Engineering Program (MSE), King Abdullah University of Science and Technology (KAUST), Thuwal, Kingdom of Saudi Arabia
Material Science and Engineering
Imaging and Characterization Core Lab
Biological and Environmental Sciences and Engineering (BESE) Division
Chemical Science Program
Permanent link to this recordhttp://hdl.handle.net/10754/667742
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AbstractIn bulk heterojunction (BHJ) solar cells, the heterojunction interface between electron donor and acceptor drives the exciton-to-charge conversion, yet it also adds to energy and carrier losses. In principle, in low-bandgap non-fullerene acceptor (NFA) BHJs both electron affinity (EA) and ionization energy (IE) offsets should equally control the internal quantum efficiency (IQE). Allegedly, exciton-to-charge conversion is efficient even for close-to-zero offsets. Here, we rebut both notions and demonstrate that counterintuitively, the charge transfer from the exciton rather than the further charge separation is the limiting step controlled by the IE offset and secondly, that sizeable IE offsets are required to reach high exciton-to charge conversion efficiency. We find that efficient Förster Resonant Energy Transfer to the low bandgap acceptor precedes the charge transfer, which thus always occurs via hole transfer from the acceptor, hence the unimportance of the EA offset. We discuss the reasons for the threshold IE offset in terms of interface energetics and find that two physical parameters are sufficient to describe the evolution of the IQE with IE offset on a very large range of material systems. Our model also explain other experimental observations such as the difficulty of observing CT states emission and absorption in NFA based systems.
CitationGorenflot, J., Laquai, F., Firdaus, Y., De Castro, C., Harrison, G., Khan, J., … Paleti, S. (2021). Ultrafast Energy Transfer Triggers Ionization Energy Offset Dependence of Quantum Efficiency in Low-bandgap Non-fullerene Acceptor Solar Cells. Proceedings of the Online Conference on NFA-Based Organic Solar Cells: Materials, Morphology and Fundamentals. doi:10.29363/nanoge.nfasc.2021.002
SponsorsBased on work supported by the KAUST Office of Sponsored Research (OSR) under award nos. OSR-2018-CARF/CCF-3079 and OSR-CRG2018-3746. D.A. acknowledges funding from the BMBF grant InterPhase and MESOMERIE (grant nos. FKZ 13N13661, FKZ 13N13656) and the European Union Horizon 2020 research and innovation program ‘Widening materials models’ under grant agreement no. 646259 (MOSTOPHOS). D.A. also acknowledges the KAUST PSE Division for hosting his sabbatical in the framework of the Division’s Visiting Faculty program. A.M. acknowledges funding from the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement no. 844655 (SMOLAC).
Conference/Event nameProceedings of NFA-Based Organic Solar Cells: Materials, Morphology and Fundamentals (NFASC)