Nanometer-Thick Cs₂SnI₆ Perovskite–Polyethylene Glycol Dimethacrylate Composite Films for Highly Stable Broad-Band Photodetectors

Halide perovskites have drawn considerable attention as a remarkable material in advanced optoelectronics. However, toxicity and poor stability of halide perovskites are major challenges hindering commercialization in wide applications. Also, conventional perovskites made the fabrication of broad-band photodetectors difficult due to the limitations of low band gap tuning. Here, we propose a robust strategy to ensure nontoxicity and long-term stability of Cs2SnI6 perovskite with broad-band photoelectric properties by applying ultraviolet (UV)-cured polyethylene glycol dimethacrylate (PEGDMA). The oxygen lone pair electrons of PEGDMA capture the Cs+ cations of the CsI, which affects the Cs2SnI6 phase formed by optimizing the stoichiometric ratio of Cs+ and Sn4+. Moreover, the formation of a polymer network through UV-cured PEGDMA contributes to maintaining the highly stable Cs2SnI6 film with nanoscale thickness over a long period of time. In particular, a photoconductor with PEGDMA 5 wt %–Cs2SnI6, having a fairly low band gap (1.24 eV) can function as a broad-band photodetector that operates not only in the visible region but also in the near-infrared region. It shows excellent optical properties with a responsivity of 1.41 A/W and detectivity of 2.52 × 1010 Jones at 980 nm. These results demonstrate the significant potential of long-term phase engineering with nontoxic perovskites for broad-band optical applications.