Phase Regulation of CsPb₂Br₅/CsPbBr₃ Perovskite Nanocrystals by Doping with Divalent Cations: Implications for Optoelectronic Devices with Enhanced Stability and Reduced Toxicity

Inorganic metal halide perovskites are generally considered as highly attractive materials for optoelectronic application devices. Unfortunately, Pb-based perovskite nanocrystals (NCs) are unstable because of their sensitivity to water, oxygen, light, and thermal treatment, which seriously limits their practical application. Herein, the dual-phase CsPb2Br5/CsPbBr3 NCs were synthesized first, and then the dual-phase M2+-doped CsPb2Br5/CsPbBr3 NCs (M = Ca2+, Sr2+, and Ba2+) with low toxicity were simply and rapidly prepared at room temperature based on the CsPb2Br5/CsPbBr3 NCs. The Sr2+-doped samples show outstanding stability and photoluminescence quantum yield due to the elimination of structural distortion and lattice contraction caused by the almost equal radii of Sr2+ (1.18 Å) and Pb2+ (1.19 Å). Interestingly, with the increase in M2+ concentration, the dual-phase quasi-2D tetragonal CsPb2Br5/CsPbBr3 NCs gradually transformed into single-phase 3D cubic Cs(Pb/M)Br3. These high-performance perovskite luminescent materials are expected to be used in light-emitting devices and other optoelectronic devices.