Physical origins of high photoluminescence quantum yield in α-CsPbI3 nanocrystals and their stability

CsPbI3 nanocrystals (NCs) with photoluminescence quantum yield (PLQY) larger than 90% have been synthesized at different temperature regions, and the physical origins for high PLQY were investigated. HRTEM images show that cubic phase CsPbI3 (α-CsPbI3) is surrounded by hexagonal Cs4PbI6 in the low temperature region, and the ratio of CsPbI3 and Cs4PbI6 increases with increasing the reaction temperature. The strong confinement effect of Cs4PbI6 leads to the high PLQY (95%) of α-CsPbI3 NCs when the reaction temperature is 120 °C. The confinement effect of Cs4PbI6 is weakened with increasing reaction temperature, which leads to the decrease of PLQY at 140 °C. However, non-radiative recombination is suppressed due to the microstructure improvement with further increasing the reaction temperature, and PLQY as high as 97% is achieved at 180 °C. Stability testing shows that fast degradation of α-CsPbI3 NCs occur in low reaction temperature region, and α-CsPbI3 NCs with high PLQY can be stored in air for 90 days when the reaction temperature is 180 °C.