Green-antisolvent-regulated distribution of p-type self-doping enables tin perovskite solar cells with an efficiency of over 14%

The kinetics of solvent-antisolvent interactions play very important roles in perovskite crystallization, and potentially influences the p-type self-doping in tin (Sn)-based perovskites but has not drawn any attention. Moreover, most of the frequently used antisolvents in Sn-based perovskites are toxic, weakening the strong motivation of developing environment-friendly perovskite light absorbers and devices. Herein, for the first time, we report a green diethyl carbonate (DEC) as an antisolvent, which is more compatible with the fabrication of Sn-based perovskites than the toxic chlorobenzene (CB). Time-driven steady-state absorption spectra reveal that the retarded kinetics of solvent-antisolvent interactions during antisolvent treatment with DEC slows down the crystallization of FASnI(3), enabling preferred crystal orientation and less high-dimensional extended defects. More importantly, this specific crystallization enables the heterogeneous distribution of Sn/I vacancies throughout the perovskite film, leading to a gradient distribution of p-type self-doping, i.e., reduced p-type self-doping at the upper surface, but gradually increased p-type self-doping from the upper surface to the bottom surface. The resulting gradient of the band structure of the perovskite film facilitates carrier transport and suppresses reverse charge accumulation at both interfaces. Consequently, a green-antisolvent-fabricated Sn-based device with a champion efficiency of 14.2% and excellent operational stability is achieved.