Humidity‐Mediated Synthesis of Highly Luminescent and Stable CsPbX3 (X = Cl, Br, I) Nanocrystals

Herein, the synthesis of CsPbX 3 nanocrystals (NCs) is reported, and the effect of humidity during the synthesis of perovskite NCs is investigated. Generally, lead halide perovskite NCs degrade very quickly in the presence of moisture. Contrary to previous observations, it is found that the CsPbX 3 (X = Cl, Br, I) NCs synthesized in the presence of an optimal amount of humidity show higher stability and significantly improved optical properties. At optimum humidity, it is found that water vapor helps in healing the surface defects commonly present on the CsPbX 3 NCs, reduces the nonradiative pathways, and leaves behind the nearly perfect unit cell of CsPbX 3 in the solution. Due to the reduction in the surface states, this simple protocol increases photoluminescence quantum yield (PLQY) of NCs by more than 90%. CsPbBr 3 NCs synthesized at 30% relative humidity (RH) conditions retain their phase, shape, and size for more than 1 year with negligible reduction in PLQY under 65% RH conditions. Similar findings are observed for CsPbI 3 NCs, where the NCs are stable for 2 months. This synthesis approach offers a new pathway to synthesize high‐quality perovskite NCs with excellent optical properties and outstanding stability for optoelectronic applications.