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Small Exciton Binding Energies Enabling Direct Charge Photogeneration Towards Low‐Driving‐Force Organic Solar Cells
Author(s) -
Zhu Lingyun,
Zhang Jianqi,
Guo Yuan,
Yang Chen,
Yi Yuanping,
Wei Zhixiang
Publication year - 2021
Publication title -
angewandte chemie
Language(s) - English
Resource type - Journals
eISSN - 1521-3757
pISSN - 0044-8249
DOI - 10.1002/ange.202105156
Subject(s) - exciton , photoluminescence , organic solar cell , charge carrier , charge (physics) , binding energy , polarization (electrochemistry) , chemical physics , materials science , thermal , optoelectronics , chemistry , atomic physics , condensed matter physics , polymer , physics , quantum mechanics , meteorology , composite material
Organic solar cells (OSCs) with nonfullerene acceptors (NFAs) exhibit efficient charge generation under small interfacial energy offsets, leading to over 18 % efficiency for the single‐junction devices based on the state‐of‐the‐art NFA of Y6. Herein, to reveal the underlying charge generation mechanisms, we have investigated the exciton binding energy ( E b ) in Y6 by a joint theoretical and experimental study. The results show that owing to strong charge polarization effects, Y6 has remarkable small E b of −0.11–0.15 eV, which is even lower than perovskites in many cases. Moreover, it is peculiar that the photoluminescence is enhanced with temperature, and the energy barrier for separating excitons into charges is evidently lower than the thermal energy according to the temperature dependence of photoluminescence, manifesting direct photogeneration of charge carriers enabled by weak E b in Y6. Thus, charge generation in NFA‐based OSCs shows little dependence on interfacial driving forces.