Lead-free tin halide perovskites: progress, photophysics, and applications in next-generation optoelectronics

Metal halide perovskites have transformed the landscape of photovoltaics (PVs) and optoelectronics due to their remarkable optical and electronic properties. Although lead (Pb)-based halide perovskites have shown exceptional power conversion efficiency and superior photoluminescence properties, environmental concerns about Pb toxicity have prompted research into Pb-free alternatives. Fortunately, among the Pb-free candidates, tin (Sn)-based halide perovskites (Sn-HPs) have emerged as potential candidates. Sn-HPs have an optimal bandgap, high charge carrier mobility, and long-lived hot carriers. However, the inherent instability of Sn²⁺, which readily oxidizes to Sn⁴⁺, poses significant challenges, leading to unintentional p-type doping, thereby degrading perovskites solar cells performance. Despite these challenges, recent progress in the stabilization of Sn²⁺, improvement of thin-film quality, and advancement in device engineering has significantly enhanced the performance and reliability of Sn-HPs. In this review, we systematically discuss the fundamental photophysical properties and strategies to mitigate intrinsic defects in tin halide perovskites across various structural modifications. Furthermore, advanced spectroscopic techniques, such as time-resolved spectroscopy, ultrafast transient absorption, and hot-carrier (HC) dynamics, enhance understanding of fundamental carrier dynamics and the potential of HC-based optoelectronic devices. Subsequently, we present recent advancements in achieving stable and efficient performance in light-emitting diodes, photodetectors, and PV technology, and provide perspectives on future developments.