All-inorganic cesium lead bromide (CsPbBr 3 ) nanocrystals are one of the prominent members of the metal halide perovskite family of semiconductor materials, which possess considerable stability and excellent optoelectronic properties leading to a multitude of their potential applications in solar cells, light-emitting devices, photodetectors, and lasers. Hot-injection strategy is a popular method used to synthesize CsPbBr 3 nanocrystals, which provides a convenient route to produce them in the shape of rather monodisperse nanocubes. As in any synthetic procedure, there are different factors like temperature, surface ligands, precursor concentration, as well as necessary postpreparation purification steps. Herein, we provide a comprehensive hot-injection synthesis protocol for CsPbBr 3 nanocrystals, outlining intrinsic and extrinsic factors that affect its reproducibility and elucidating in detail the precursor solution preparation, nanocrystal formation and growth, and postpreparative purification and storage conditions to allow for the fabrication of high-quality green-emitting material.

Herein, the synthesis of CsPbX3 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 CsPbX3 (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 CsPbX3 NCs, reduces the nonradiative pathways, and leaves behind the nearly perfect unit cell of CsPbX3 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%. CsPbBr3 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 CsPbI3 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.