Endothermic Charge Separation Occurs Spontaneously in Non-Fullerene Acceptor/Polymer Bulk Heterojunction.

Autor: Rijal K; Department of Physics and Astronomy, University of Kansas, Lawrence, KS, 66045, USA., Fuller N; Department of Physics and Astronomy, University of Kansas, Lawrence, KS, 66045, USA., Rudayni F; Department of Physics and Astronomy, University of Kansas, Lawrence, KS, 66045, USA.; Department of Physics, Jazan University, Jazan, 45142, Saudi Arabia., Zhang N; Department of Materials Science and Engineering, City University of Hong Kong, Tat Chee Avenue, Kowloon, 999077, Hong Kong., Zuo X; X-ray Science Division, Argonne National Laboratory, Lemont, IL, 60439, USA., Berrie CL; Department of Chemistry, University of Kansas, Lawrence, KS, 66045, USA., Yip HL; Department of Materials Science and Engineering, City University of Hong Kong, Tat Chee Avenue, Kowloon, 999077, Hong Kong.; School of Energy and Environment, City University of Hong Kong, Tat Chee Avenue, Kowloon, 999077, Hong Kong.; Hong Kong Institute for Clean Energy, City University of Hong Kong, Tat Chee Avenue, Kowloon, 999077, Hong Kong.; Center of Super-Diamond and Advanced Films, City University of Hong Kong, Tat Chee Avenue, Kowloon, 999077, Hong Kong., Chan WL; Department of Physics and Astronomy, University of Kansas, Lawrence, KS, 66045, USA.
Jazyk: angličtina
Zdroj: Advanced materials (Deerfield Beach, Fla.) [Adv Mater] 2024 Aug; Vol. 36 (31), pp. e2400578. Date of Electronic Publication: 2024 May 31.
DOI: 10.1002/adma.202400578
Abstrakt: Organic photovoltaics (OPVs) based on non-fullerene acceptors (NFAs) have achieved a power conversion efficiency close to 20%. These NFA OPVs can generate free carriers efficiently despite a very small energy level offset at the donor/acceptor interface. Why these NFAs can enable efficient charge separation (CS) with low energy losses remains an open question. Here, the CS process in the PM6:Y6 bulk heterojunction is probed by time-resolved two-photon photoemission spectroscopy. It is found that the CS, the conversion from bound charge transfer (CT) excitons to free carriers, is an endothermic process with an enthalpy barrier of 0.15 eV. The CS can occur spontaneously despite being an endothermic process, which implies that it is driven by entropy. It is further argued that the morphology of the PM6:Y6 film and the anisotropic electron delocalization restrict the electron and hole wavefunctions within the CT exciton such that they can primarily contact each other through point-like junctions. This configuration can maximize the entropic driving force.
(© 2024 Wiley‐VCH GmbH.)
Databáze: MEDLINE
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