Hybrid organolead halide perovskites have attracted tremendous attention due to their recent success as high efficiency solar cell materials and their fascinating material properties uniquely suitable for optoelectronic devices. However, the poor ambient and operational stability as well as the concern of lead toxicity greatly hamper their practical utilization. In this work, crystalline, all-inorganic and lead-free Cs₃Sb₂I₉ perovskite microplates are successfully synthesized by a two-step chemical vapor deposition method. As compared with other typical lead-free perovskite materials, the Cs₃Sb₂I₉ microplates demonstrate excellent optoelectronic properties, including substantial enhancements in the Stokes shift, exciton binding energy and electron-phonon coupling. Simple photoconductive devices fabricated using these microplates exhibit an ultra-fast response with the rise and decay time constants down to 96 and 58 μs, respectively. This respectable photoconductor performance can be regarded as a record among all the lead-free perovskite materials. Importantly, these photodetectors show superior thermal stability in a wide temperature range, capable to function reversibly between 80 and 380 K, indicating their robustness to operate under both low and high temperatures. All these results evidently suggest the technological potential of inorganic lead-free Cs₃Sb₂I₉ perovskite microplates for next-generation high-performance optoelectronic devices.

All-inorganic halide perovskites (IHP), CsPbX₃ (X = Cl, Br, I) exhibiting efficient optical emissions within the spectral range of 410 to 730 nm are potential candidates for many optoelectronic devices. Anion alloying of these IHPs is expected to achieve tunable emission wavelength covering the entire visible spectrum. Here, we developed a two-step chemical vapor deposition (CVD) process for growing quaternary IHP CsPbX₃ (X = Cl/Br and Br/I) alloys. By exploiting the fast diffusion of halide anions in IHPs, the alloy composition can be precisely controlled by the growth time of the respective layers once the growth of the individual ternary IHP is optimized. Hence complexities in the multi-parameter optimization in the conventional CVD growth of quaternary alloys can be mitigated. Using this process, we synthesized single crystalline, homogeneous and thermally stable CsPbCl_3(1-x)Br_3x and CsPbBr_3(1-x)I_3x perovskites alloy microplates and demonstrated continuously tunable emission covering the spectrum from 428 to 715 nm by varying the halide compositions in the alloys. These alloy microplates also exhibit room temperature amplified spontaneous emissions (ASE) along with strong photonic discharges from the microplate’s edges and hence are potentially useful as a gain medium as well as optical cavities for emissions with wavelengths covering the visible spectrum.