Sulfur vs. tellurium: the heteroatom effects on the nonfullerene acceptors
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The effect of chalcogen heteroatom variation on donor materials has been systematically investigated. However, this effect on acceptors has rarely been explored. Herein, nonfullerene acceptors BFPSP and BFPTP were reported by simply changing the chalcogen atoms from S to Te. The differences between BFPSP and BFPTP in light absorption, energy levels, excited-state lifetimes, energy loss, charge mobilities, morphology, and photovoltaic properties were systematically investigated to understand the heteroatom effects. More importantly, the electroluminescence spectra, external quantum efficiency of photovoltaics and TD-DFT calculations revealed that the triplet excited state (T1) in energy of BFPTP equals to the charge transfer (CT) state in PBDB-T:BFPTP, which allows T1 excitons, generated by intersystem crossing, to split into free charges to contribute to the efficiency. This contribution provides a strategy for tuning the photophysical properties of nonfullerene acceptors and designing high performance triplet materials for OSCs.
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This work was supported by the National Natural Science Foundation of China (21774130, 21673054), the National Key Research and Development Program of China (2018FYA 0305800), the Key Research Program of Frontier Sciences, CAS (QYZDB-SSW-JSC046), Key Research Program of the Chinese Academy of Sciences (XDPB08-2), the Strategic Priority Research Program of Chinese Academy of Sciences (XDB28000000, XDB12020200), External Cooperation Programs of Chinese Academy of Sciences (211211KYSB20170014), Innovation Program of Aerospace Science and Technology, China Aerospace Science and Technology Corporation, One Hundred Talents Program of Chinese Academy of Sciences, and University of Chinese Academy of Sciences, the Ministry of Science and Technology (2017YFA0205004, 2016YFA0200700), Beijing Natural Research Foundation (4182076). We also thank Prof. Jianpu Wang, Dr. Qiming Peng, and Zewu Fu for magneto-photocurrent measurements.
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