Ascorbic acid-induced porous iodide layer for a high-purity two-step solution-processed tin-lead mixed perovskite photodetector

Tin (Sn)-lead (Pb) mixed halide perovskites have attracted widespread interest due to their wider response wavelength and lower toxicity than lead halide perovskites. Among the preparation methods, the two-step method more easily controls the crystallization rate and is suitable for preparing large-area perovskite devices. However, the residual low-conductivity iodide layer in the two-step method can affect carrier transport and device stability, and the different crystallization rates of Sn- and Pb-based perovskites may result in poor film quality. Therefore, Sn-Pb mixed perovskites are mainly prepared by a one-step method. Herein, a MAPb0.5Sn0.5I3-based self-powered photodetector without a hole transport layer is fabricated by a two-step method. By adjusting the concentration of the ascorbic acid (AA) additive, the final perovskite film exhibited a pure phase without residues, and the optimal device exhibited a high responsivity (0.276 A W−1), large specific detectivity (2.38 × 1012 Jones), and enhanced stability. This enhancement is mainly attributed to the inhibition of Sn2+ oxidation, the control of crystal growth, and the sufficient reaction between organic ammonium salts and bottom halides due to the AA-induced pore structure.