Over 16% efficiency organic photovoltaic cells enabled by a chlorinated acceptor with increased open-circuit voltages

• Published in: Nature communications Vol. 10; no. 1; pp. 2515 - 8
• Main Authors: Cui, Yong, Yao, Huifeng, Zhang, Jianqi, Zhang, Tao, Wang, Yuming, Hong, Ling, Xian, Kaihu, Xu, Bowei, Zhang, Shaoqing, Peng, Jing, Wei, Zhixiang, Gao, Feng, Hou, Jianhui
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 07.06.2019; Nature Publishing Group; Nature Portfolio
• Subjects: 639/624; 639/638; 639/638/298; 639/638/549; Absorption; Circuits; Efficiency; Energy conversion efficiency; Energy dissipation; Energy loss; Fluorination; Fullerenes; Halogenation; Humanities and Social Sciences; Molecular energy levels; multidisciplinary; Open circuit voltage; Photovoltaic cells; Photovoltaics; Science; Science (multidisciplinary); Short circuit currents; Short-circuit current; Solar cells; Voltage
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-019-10351-5

Broadening the optical absorption of organic photovoltaic (OPV) materials by enhancing the intramolecular push-pull effect is a general and effective method to improve the power conversion efficiencies of OPV cells. However, in terms of the electron acceptors, the most common molecular design strategy of halogenation usually results in down-shifted molecular energy levels, thereby leading to decreased open-circuit voltages in the devices. Herein, we report a chlorinated non-fullerene acceptor, which exhibits an extended optical absorption and meanwhile displays a higher voltage than its fluorinated counterpart in the devices. This unexpected phenomenon can be ascribed to the reduced non-radiative energy loss (0.206 eV). Due to the simultaneously improved short-circuit current density and open-circuit voltage, a high efficiency of 16.5% is achieved. This study demonstrates that finely tuning the OPV materials to reduce the bandgap-voltage offset has great potential for boosting the efficiency. Halogenation has proved an effective strategy to improve the power conversion efficiencies of organic solar cells but it usually leads to lower open-circuit voltages. Here, Cui et al. unexpectedly obtain higher open-circuit voltages and achieve a record high PCE of 16.5% by chlorination.