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

CsPbI 3 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 CsPbI 3 (α-CsPbI 3 ) is surrounded by hexagonal Cs 4 PbI 6 in the low temperature region, and the ratio of CsPbI 3 and Cs 4 PbI 6 increases with increasing the reaction temperature. The strong confinement effect of Cs 4 PbI 6 leads to the high PLQY (95%) of α-CsPbI 3 NCs when the reaction temperature is 120 °C. The confinement effect of Cs 4 PbI 6 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-CsPbI 3 NCs occur in low reaction temperature region, and α-CsPbI 3 NCs with high PLQY can be stored in air for 90 days when the reaction temperature is 180 °C.