High-Temperature Synthesis of Colloidal CH₃NH₃PbBr₃ Perovskite Nanoplatelets and Nanocubes

Colloidal CsPbX₃ (X: Cl, Br, I) and FAPbX₃ (FA: formamidinium) perovskite nanocrystals (NCs) are well explored for their size-, shape-, and surface-dependent optoelectronic properties. However, colloidal MAPbX₃ (MA: CH₃NH₃⁺, methylammonium) perovskite NCs are relatively less explored, even though MAPbBr₃ nanoplatelets were the first halide perovskite NCs reported in the literature. Often, the synthesis temperatures of MAPbBr₃ NCs are restricted to ∼65 °C, keeping in mind the thermal instability of the MA precursor solution. Here, we advance the synthesis of MAPbBr₃ NCs in a nonpolar medium by increasing the synthesis temperature in the range of 120–160 °C. Colloidal MAPbBr₃ nanoplatelets with thicknesses of 1.9 and 2.3 nm are prepared at 120 and 140 °C. It is to be noted that for the nanoplatelets, the molar ratio of MA:Pb is <1, along with a significant contribution from capping organic ligands. Further increases in the synthesis temperature to 160 °C lead to the formation of MAPbBr₃ nanocubes with a photoluminescence quantum yield of 70–80%. The temperature-dependent control of the size and shape of colloidal MAPbBr₃ NCs results in tuning the quantum confinement of excitons, yielding wavelength-tunable optical properties. This temperature-driven control of the size and shape of MAPbBr₃ NCs expands their potential for optoelectronic applications.