Synergistic Effect of Compositional Engineering and Graded Heterojunction Formation in Tin‐Halide Perovskites for Near‐Infrared Photodetectors

Abstract Tin (Sn)‐halide perovskites present significant potential as lead‐free alternatives for various optoelectronic applications. However, their performance is often hindered by oxidation and high defect densities. In this study, these challenges are addressed by combining compositional engineering with a C ₆₀ ‐based graded heterojunction (GHJ) strategy. The incorporation of methylammonium chloride (MACl) into formamidinium tin iodide (FASnI ₃ ) induces lattice contraction, enhances crystallinity, and reduces trap densities in ≈200 nm‐thick films, as confirmed by X‐ray diffraction (XRD), photoluminescence (PL), time‐resolved PL, and X‐ray photoelectron spectroscopy (XPS). Additionally, the introduction of C ₆₀ as a passivation layer further improves film quality, reflected in increased built‐in potential and reduced trap density. As a result, the optimized lead‐free perovskite photodetectors exhibit superior near‐infrared performance, achieving an external quantum efficiency of 63.4% and a specific detectivity of 1.38 × 10 ¹¹ Jones at 810 nm, alongside reduced noise levels and faster response times. These findings highlight the efficacy of integrating compositional engineering and GHJ formation to develop stable, high‐performance Sn‐halide perovskite devices for advanced near‐infrared photodetection applications.