Exploring the Origin of Phase-Transformation Kinetics of CsPbI Perovskite Nanocrystals Based on Activation Energy Measurements.

Perovskite α-CsPbI nanocrystals (NCs) with a high fluorescence quantum yield (QY) typically undergo a rapid phase transformation to a low-QY δ-CsPbI phase, thus limiting their optoelectronic applications. In this study, organic molecule hexamethyldisilathiane (HMS) is used as a unique surfactant to greatly enhance the stability of the cubic phase of CsPbI NCs (HMS-CsPbI) under ambient conditions. The reaction kinetics of the phase transformation of CsPbI NCs are systemically investigated through in situ photoluminescence (PL), X-ray diffraction, and transmission electron microscope (TEM) measurements under moisture. The activation energy of HMS-CsPbI NCs is found to be 14 times larger than that of CsPbI NCs capped by olyelamine (OLA-CsPbI NCs). According to density functional theory calculations, the bonding between HMS and CsPbI NCs is stronger than that between OLA and CsPbI NCs, preventing the subsequent phase transformation. Our study presents a clear pathway for achieving highly stable CsPbI NCs for future applications.