Fang et al. [45] reported highly narrowband photodetector based on a series of halide perovskite single crystals due to the strong surface-charge recombination-induced suppression of charge collection for shortwavelength excitation. By tuning the molar ratio of Cl/Br precursor, perovskite with different band gap can be produced. The device showed an ultra-narrow EQE peak with an FWHM of < 20 nm, and a detection limit down to 80 pW cm–2