Revealing nanocrystal growth within CsPbI_2xBr_3-x perovskite thin films

Inorganic lead halide perovskites have greatly impacted the optoelectronics field due to their band-tunability and solution-processability in high performance light emitting diodes (LEDs). However, the bulk material is unstable under room temperature which tends to phase segregate under ambient or device operational conditions. Recent breakthrough has successfully demonstrated a stabilized CsPbX₃ phase at room temperature by fabricating into nanostructured crystals (NC). Further, photo-physical property enhancement is attributed to the nano-scale structure control which are thus the most promising candidate for the lighting applications. It is therefore critical to systematically understand the structure of the CsPbX₃ NC synthesized via controlled approach and connect that with device operation efficiency and stability. In this study, we systematically investigated the synthetic approach to obtain room temperature stabilized mixed halide nanocrystals, focusing on the effect of the molar ratio between Cs source and Pb source on the optical performance in the mixed CsPbI₂Br perovskite thin films. The findings revealed the nanocrystal growth mechanism of the in situ processed perovskite layer which enabled us to fabricate bright and efficient red perovskite LEDs.