Exploring the Origin of Phase-Transformation Kinetics of CsPbI₃ Perovskite Nanocrystals Based on Activation Energy Measurements

Perovskite α-CsPbI₃ nanocrystals (NCs) with a high fluorescence quantum yield (QY) typically undergo a rapid phase transformation to a low-QY δ-CsPbI₃ 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 CsPbI₃ NCs (HMS-CsPbI₃) under ambient conditions. The reaction kinetics of the phase transformation of CsPbI₃ 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-CsPbI₃ NCs is found to be 14 times larger than that of CsPbI₃ NCs capped by olyelamine (OLA-CsPbI₃ NCs). According to density functional theory calculations, the bonding between HMS and CsPbI₃ NCs is stronger than that between OLA and CsPbI₃ NCs, preventing the subsequent phase transformation. Our study presents a clear pathway for achieving highly stable CsPbI₃ NCs for future applications.