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 C60-based graded heterojunction (GHJ) strategy. The incorporation of methylammonium chloride (MACl) into formamidinium tin iodide (FASnI3) 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 C60 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 × 1011 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.