Opportunities and challenges of lead-free metal halide perovskites for luminescence

Metal halide perovskites (MHPs) have been developed rapidly for application in light-emitting diodes (LEDs), lasers, solar cells, photodetectors and other fields in recent years due to their excellent photoelectronic properties, and they have attracted the attention of many researchers. Perovskite LEDs (PeLEDs) show great promise for next-generation lighting and display technologies, and the external quantum efficiency (EQE) values of polycrystalline thin-film PeLEDs exceed 20%, which is undoubtedly a big breakthrough in lighting and display fields. However, the toxicity and instabilities of lead-based MHPs remain major obstacles limiting their further commercial applications. The exploration and development of lead-free MHPs (LFMHPs) are regarded as the most facile strategies to solve these problems. Compared with lead-based perovskites, LFMHPs exhibit better stabilities and broadband emission. With continuous development of LFMHPs, their photoluminescence quantum yields (PLQYs) have reached 99%, facilitating their use as ideal emitters. In this review, the structures and features of LFMHPs are analyzed, and the preparation methods of LFMHPs with various structures and configurations are discussed. Then, the mechanisms and strategies for improving the emission performance of white LEDs based on LFMHPs are demonstrated. Finally, their challenges in commercial production and perspectives are prospected.