Quantification of strain and its impact on the phase stabilization of all-inorganic cesium lead iodide perovskites

The high-temperature perovskite g-phase of CsPbI3 readily undergoes phase transition at ambient conditions to a low -temperature non-perovskite d-phase with a poorer optoelectronic performance, thus hindering commercialization of these materials in photovoltaics. Here, we present the epitaxial growth of CsPbI3 nanoplates on muscovite mica single-crystal substrates and demonstrate that the high-temperature phase stability of these nano plates is enhanced by a strained interface. Strain is measured as a function of nanoplate thickness on a single-particle level through spatially resolved structural and optical characterizations and is found to increase with decreasing thickness. From quantitatively tracking the CsPbI3 phase transition for thin (<400 nm) and thick (>400 nm) nanoplates, we observe a larger fraction of thin nano plates still maintaining their high-temperature phase after 1 month compared with their thick counterparts. These findings establish a relationship between strain and phase transition kinetics, which is critical for rational design of stable perovskite-based optoelectronic devices.