Research progress of lead-free metal halide perovskites in white light-emitting diodes

White light-emitting diodes (WLEDs) are the core technology in solid-state lighting and display fields. However, the commercial GaN/YAG: Ce 3+ scheme suffers from bottlenecks such as insufficient color rendering index, limited color gamut, and reliance on rare earth resources, creating an urgent need for novel, high-efficiency, and environmentally friendly luminescent materials to overcome these limitations. Metal halide perovskites have emerged as ideal candidates for WLEDs due to their high defect tolerance, high photoluminescence quantum yield (PLQY), excellent solution processability, and broad spectral tunability. Nevertheless, the biotoxicity of lead-based perovskites severely hinders their commercialization. Consequently, green and environmentally benign lead-free metal halide perovskites (LFMHPs) have gained prominence. Through isovalent and heterovalent ion substitution strategies, LFMHPs form diverse crystal structures, including 3D perovskites, double perovskites, and low-dimensional derivatives. Their crystal structures directly determine the luminescent mechanisms: regular lattices support narrowband emission from free excitons (FEs), making them suitable for high-color-gamut three-primary-color devices; distorted or low-dimensional structures induce broadband emission from self-trapped excitons (STEs), providing a platform for single-component white LEDs. This review focuses on the core application demands of WLEDs, clarifying the intrinsic correlation between the crystal structure and exciton behavior of lead-free metal halide perovskites, exploring the regulatory mechanisms of narrowband/broadband luminescence, defining performance adaptation thresholds for high-color-gamut display and high-color-rendering lighting, comparing key regulation strategies, summarizing device construction pathways and core parameters of typical systems, and analyzing core bottlenecks in commercialization, aiming to provide theoretical support for next-generation green and high-performance WLED technologies.