Lead-Free Perovskite Derivative Cs2SnCl6-xBrx Single Crystals for Narrowband Photodetectors

Lead‐free and stable Sn halide perovskites demonstrate tremendous potential in the field of optoelectronic devices. Here, the structure and optical properties of the “defect” perovskites Cs₂SnCl_6−xBr_x are reported, as well as their use as photodetector materials. Millimeter‐sized Cs₂SnCl_6−xBr_x single crystals are grown by the hydrothermal method, with the body color continuously changing from transparent to yellow and finally to dark red. Narrowband single‐crystal photodetectors using Cs₂SnCl_6−xBr_x crystals are presented, which show a high detectivity of ≈2.71 × 10¹⁰ Jones, with narrowband photodetection (full‐width at half‐maximum ≈45 nm) and high ion diffusion barriers. Moreover, the response spectra are continuously tuned from near violet to orange depending on the variation of the bandgap of the single crystals by changing the halide compositions. The strong surface charge recombination of the excess carriers near the crystal surfaces produced by short wavelength light elucidates the narrowband photodetection behavior. This work provides a new paradigm in the design of lead‐free, stable, and high‐performance perovskite derivatives for optoelectronics applications.