High Open‐Circuit Voltage and Efficiency CsPbI₃ Perovskite Solar Cells Achieved by Hole Transport Layer Modification

Abstract The lithium bis(trifluoromethane) sulfonimide salt (Li‐TFSI) and 4‐tert‐butylpyridine (t‐BP) codoped 2,2′,7,7′‐tetrakis(N,N‐di‐p‐methoxyphenylamine)‐9,9′‐spirobifluorene (Spiro‐OMeTAD) is a very classic and dominant hole transport layer (HTL) for the fabrication of high‐efficiency perovskite solar cells (PSCs). However, the PSCs based Spiro‐OMeTAD often shows poor stability due to the hygroscopic Li‐TFSI that is prone to ion migration, the volatile t‐BP, and the time‐consuming oxidation in air. Herein, hydrophobic 1,2‐Bis(perfluoropyridin‐4‐yl)disulfane (BPFPDS) is designed to optimize Spiro‐OMeTAD. The S‐Li, F‐Li, and N‐Li synergistic interaction between BPFPDS and Li‐TFSI inhibited Li⁺ ion migration, and the hydrophobic property of BPFPDS balanced the humidity sensitivity of Li‐TFSI, which prevented both Li⁺ ions and water molecules from corroding the perovskite layer. In addition, the F‐N superamolecular interaction between BPFPDS and t‐BP restricted the volatility of t‐BP, which indirectly prevented the migration of Li⁺ ions. As a result, the BPFPDS‐treated CsPbI₃ PSC engendered a respectable efficiency of 21.95% and an impressive open‐circuit voltage (V_OC) of 1.29 V. The BPFPDS‐treated devices sustained 96% and 98% of their efficiencies after aging in the air for 3000 h and tracking at maximum power point for 1200 h, respectively.