Stable Blue CsPbBr Perovskite Nanocrystals with Near-Unity Photoluminescence Quantum Yield by Surface Ligand Engineering.

All-inorganic cesium lead halide perovskites are emerging as a new promising candidate material in light-emitting diodes, photovoltaics, and photodetectors owing to their outstanding optical and electrical properties. However, blue perovskites still lag far behind the green and red analogues in terms of efficiency and stability. To avoid phase separation with mixed halide perovskite nanocrystals (e.g., CsPbBrCl), blue-emitting perovskites with a quantum confinement effect are very attractive. In this work, we designed a postsynthetic modification strategy with didodecyldimethylammonium bromide (DDAB) and lead bromide (PbBr) to achieve blue-emitting CsPbBr nanocrystals (NCs) with nearly perfect surface passivation and excellent stability. The synergistic effect of DDAB and PbBr inhibited the possible perovskite phase transformation caused by DDA, repaired the damaged [PbBr] octahedra after purification, and created a halide-rich environment on the surface of NCs, thus maximizing the passivation of surface vacancy defects. In addition, the relatively short-chain, proton-free DDAB partially replaced the original organic ligands on the surface of NCs, resulting in near-unity photoluminescence quantum yield (PLQY) and remarkable stability. After 14 days of continuous ultraviolet irradiation at 365 nm, the PLQY of NCs was close to 100% and the photoluminescence (PL) spectrum remained almost unchanged. The PLQY of NCs remained greater than 90% after either continuous heating in an oil bath at 80 °C for 14 days or storage in the air for 2 months. This study demonstrates an effective approach to obtaining highly bright and stable blue perovskite NCs, which is expected to be used in optoelectronic devices, and provides strategies for future surface ligand engineering of perovskites.