Enhanced Photoluminescence and Stability of CH₃NH₃PbBr₃ Perovskite Nanocrystals with Protonated Melamine

Abstract The surface of CH₃NH₃PbBr₃ perovskite nanocrystals (PNCs) plays a critical role in determining their optical properties and stability. The introduction of capping ligands can enhance photoluminescence (PL), reduce non‐radiative recombination, and improve stability. Here, we report a facile synthesis of CH₃NH₃PbBr₃ PNCs with strong and highly stable green PL using melamine (Mela) as a simple and low‐cost capping ligand. The resulting CH₃NH₃PbBr₃/Mela PNCs have cubic phase crystal structure with an average particle size of 5.29±0.06 nm. The optical absorption and PL of the CH₃NH₃PbBr₃/Mela PNCs with narrow bandwidth can be tuned within the visible region, and the PL quantum yield (QY) reached 52.3% compared to 0.4% the pristine CH₃NH₃PbBr₃ PNCs. A synergistic effect between NH₃⁺ and the electron‐rich nitrogen atoms together with p‐p stacking capacity, likely contributes to enhance the PL by effectively passivating of the trap states of PNCs. Furthermore, melamine‐capped PNCs show high stability in protic solvents as a result of the steric bulkiness of the triazine rings, owing to the planar structure together with hydrogen bonding of melamine, which prevents solvent molecules from reaching and reacting with the core of PNCs. This study demonstrates a simple and effective approach for stabilizing PNCs for potential applications such as solar cells and LEDs.