We present a method to synthesize stable and uniform high-quality perovskite nanocrystals (PNCs) by using excess halide to recover surface defects in CsPbBr₃/ZnS core/shell nanocrystals. Use of N-bromosuccinimide as a halide donor recovered surface halide vacancies of bare CsPbBr₃ PNCs during the growth of the ZnS shell, as confirmed by DFT calculations. This approach achieves a high photoluminescence quantum yield of nearly 1, and significantly increases the stability of PNCs under adverse conditions such as high humidity and elevated temperature. CsPbBr₃/ZnS PNC light-emitting diodes demonstrated outstanding luminous characteristics, with a remarkable external quantum efficiency of 12.77% and a maximum luminance of 1449 cd m^–2 at 517 nm. These characteristics of the PNCs will have a wide variety of applications and will help enable development of highly efficient optoelectronic devices.