Dual-functional passivators for highly efficient and hydrophobic FA-based perovskite solar cells

Ionic defects and humidity instability are the main limitations to realize the commercialization of FA-based perovskite solar cells. To overcome these issues, here, we report a dual-functional molecular 2-Fluorothiophenol (FTP) to achieve high-quality FA-based perovskites with simultaneously efficient defects passivation and improved hydrophobicity. It is revealed that SH^¯ groups of FTP induce highly oriented crystallization toward (0 0 1) crystal plane of cubic-phase Cs_0.05FA_0.95PbI₃ perovskite structure, thus improving the charge carrier transport. Moreover, a strong Lewis acid-base interaction between the SH^¯ group and Pb²⁺ in perovskite is of great benefit to passivate the surface and grain boundary defects, with additional merit for improving humidity stability of the FA-based perovskite films in conjunction with the hydrophobic group of FTP. The introduction of FTP boosts the efficiency from 20.30% to 22.66% for 0.04 cm² solar cells and from 16.86% to 20.01% for 1.0 cm² devices. More importantly, the solar cells demonstrate excellent humidity stability, which can retain 90% of their original efficiency after being kept for 80 days under ambient air conditions.