Stable Orthorhombic CsPbBr₃ Light Emitters: Encapsulation-Assisted In Situ Synthesis

Metal halide perovskite nanocrystals (PeNCs) are promising candidates for achieving Rec. 2020 with high color purity. However, the stability of PeNCs is inferior to that of conventional inorganic quantum dot emitters. Here, we developed a simple method using perhydropolysilazane (PSZ) to synthesize chemically stable CsPbBr 3 PeNCs while simultaneously encapsulating them in a SiO 2 matrix. During the synthesis, PSZ converts to SiO 2, encapsulates PeNCs, and forms stable Pb–O bonds with the orthorhombic CsPbBr 3 crystal. Unlike cubic CsPbBr 3 PeNCs synthesized by conventional colloidal synthesis, this encapsulation-assisted in situ synthesis provided orthorhombic CsPbBr 3 crystals with good control over the crystallization and with an average crystal size of 34.7 nm. Surprisingly, the resulting PeNC–PSZ composites showed a high photoluminescence quantum yield (PLQY) of 84.7% even without the use of organic ligands surrounding the PeNCs. The orthorhombic CsPbBr 3 PeNCs in situ-synthesized using PSZ assistance showed higher chemical stability than cubic CsPbBr 3 PeNCs synthesized by the conventional hot-injection method during storage under ambient conditions and in water and under continuous external energy (100 °C hot plate, UV excitation). Contrary to the common belief regarding the low stability of ionic perovskites in water, orthorhombic CsPbBr 3 PeNC in situ-synthesized using PSZ assistance retained >60% of the initial PL intensity even after long storage in water for >1100 h, which is more than 600 times longer than those of emitters that use PeNCs synthesized using the conventional hot-injection method.