High Stability and Temperature‐Dependent Photoluminescence of Orthorhombic CsPbI3 Perovskite Nanoparticles

High thermal stability of all-inorganic perovskite nanocrystals (NCs) offers their potential application in various fields such as solar cells and light-emitting diodes. However, the cubic cesium lead iodide (alpha-CsPbI3) with the most appropriate bandgap for light harvesting is thermodynamically unstable at room temperature and spontaneously transforms into the undesired orthorhombic delta-CsPbI3. Here, a simple method is demonstrated to synthesize orthorhombic gamma-CsPbI3 NCs using 3-aminopropyl triethoxysilane molecules as capping ligands. The crystalline structure and morphology of these gamma-CsPbI3 NCs hardly change after exposure to ethanol even though they are capped with fewer ligands. Their high stability is also demonstrated by retaining their photoluminescence (PL) intensity after heating/cooling cycles in the range of 295-375 K, in contrast to a quick destruction of alpha-CsPbI3 NCs under the same condition. More importantly, temperature-dependent PL spectra reveal that the exciton/electron-phonon coupling and exciton recombination process of these gamma-CsPbI3 NCs strongly depend on their particle sizes. This finding may enable versatile design of stable gamma-CsPbI3 NCs with different sizes meeting diverse demands for various applications.