Understanding the Effects of Fluorine Substitution in Lithium Salt on Photovoltaic Properties and Stability of Perovskite Solar Cells
Tai‐Sing Wu, Rongshan Zhuang, Rongjun Zhao, Rongmei Zhao, Lizhong Zhu, Gaoyuan Liu, Runtao Wang, Kanghong Zhao, Yong Hua
Abstract
Lithium bis(trifluoromethanesulfonyl)imide (Li-TFSI) additive is widely employed to improve the hole mobility of the hole-transporting layer (HTL) in perovskite solar cells (PSCs). However, the hygroscopic nature of Li-TFSI is not beneficial to the long-term stability of PSCs. Herein, a new more water-resistant Li-PFSI is used to replace Li-TFSI. As a result, the best power conversion efficiency (PCE) of 22.14% is achieved for Li-PFSI-treated PSCs, exceeding that of the control cell with Li-TFSI (20.25%). Importantly, the Li-PFSI-based cell shows impressive environmental and thermal stability. Moreover, we first comparatively investigate the effect of the amount of fluorine substitution in lithium salt (2F for Li-FSI, 6F for Li-TFSI, and 10F for Li-PFSI) on the HTL’s physical properties and their photovoltaic performance in PSCs. We found that more fluorine substitution can improve the HTL charge-carrier transfer and photovoltaic performance in PSCs. Our findings provide key missing information for designing new additives toward efficient and stable PSCs.