Enhanced Photoluminescence and Stability of CH3NH3PbBr3 Perovskite Nanocrystals with Protonated Melamine

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.