High Stability and Temperature‐Dependent Photoluminescence of Orthorhombic CsPbI 3 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 (α‐CsPbI 3 ) with the most appropriate bandgap for light harvesting is thermodynamically unstable at room temperature and spontaneously transforms into the undesired orthorhombic δ‐CsPbI 3 . Here, a simple method is demonstrated to synthesize orthorhombic γ‐CsPbI 3 NCs using 3‐aminopropyl triethoxysilane molecules as capping ligands. The crystalline structure and morphology of these γ‐CsPbI 3 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 α‐CsPbI 3 NCs under the same condition. More importantly, temperature‐dependent PL spectra reveal that the exciton/electron–phonon coupling and exciton recombination process of these γ‐CsPbI 3 NCs strongly depend on their particle sizes. This finding may enable versatile design of stable γ‐CsPbI 3 NCs with different sizes meeting diverse demands for various applications.