The resulting gradient of the band structure of perovskite film facilitates carrier transport and suppresses the reverse charge accumulation at both interfaces.

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 bottom surface. Time-drive steady-state absorption spectra reveal that the retarded kinetics of solvent-antisolvent interaction during antisolvent treatment of DEC slows down the crystallization of FASnI3, enabling preferred crystal orientation and less high-dimensional extended defects. Herein, for the first time, we report a green diethyl carbonate (DEC) as antisolvent, which is more compatible with the fabrication of Sn-based perovskites than the toxic chlorobenzene (CB). 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. The kinetics of solvent-antisolvent interaction play very important roles in perovskite crystallization, which potentially influences the p-type self-doping in the tin (Sn)-based perovskites but hasn't drawn any attention.

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