Precursor chemistry towards highly efficient and phase-stable red emitting CsPbI₃ perovskite nanocrystals

All-inorganic cesium lead halide perovskite nanocrystals (CsPbX₃, X = Cl, Br, I) have attracted considerable scientific and technological interest due to their precise bandgap tunability, high color purity and efficient luminescence. Nevertheless, their poor stability in harsh conditions such as moisture, ultraviolet (UV) light irradiation and high temperature, is a major obstacle for their further commercial applications. Herein, by simply using a new type of precursor, namely "HPbX₃" (X = Cl, Br, I), we can achieve the coordination equilibrium for Pb precursors during reaction and obtain high-quality perovskite nanocrystals with tremendously enhanced luminous efficiency and chemical stability based on hot-injection method. The prepared α-CsPbI₃ nanocrystals exhibit an extremely high photoluminescence quantum yield of 96% and keep stable in air for more than two months without any post-synthesis treatment. Moreover, stability evaluations under UV light irradiation, water or thermal impact are also performed and the results show substantially improved stability of these nanocrystals as compared with the samples prepared using traditional PbI₂ as precursor. Through temperature-dependent (10–300 K) steady and transient spectral analysis combined with compositional measurements, it is revealed that the lower structural defect density, which is guaranteed by abundant halogen when using HPbX₃ as precursor, is the most important reason for such performance enhancement.