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 Cs 2 SnCl 6− x Br x are reported, as well as their use as photodetector materials. Millimeter‐sized Cs 2 SnCl 6− x Br 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 Cs 2 SnCl 6− x Br x crystals are presented, which show a high detectivity of ≈2.71 × 10 10 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.