Recent processes on light-emitting lead-free metal halide perovskites

Lead halide perovskites (LHPs) have great potential applications in light-emitting diodes (LEDs) for advanced displays and general lighting due to their excellent optical and electrical properties. However, LHPs suffer from toxicity and poor stability. Although the stability of the perovskites can be enhanced by reducing dimensionality, doping transition metal ions, encapsulating organic polymers, or building super-hydrophobic structures, the improved stability is limited and still cannot meet the needs for practical applications. To fundamentally solve the above issues, lead-free metal halide perovskites (LFMHPs) have been alternatively developed owing to their low toxicity, expected good stability and excellent optical properties. In this review, we thoroughly overview recent processes on the synthetic method, type, structure, morphology, and optical properties of LFMHPs with a strict perovskite structure as well as on their stabilities against water, light, or heat. We further highlight their preliminary achievements in display and lighting applications. Finally, we address remaining challenges in this exciting field and present our perspectives for further investigations on LFMHPs to enhance the performance and lifetime of LED devices.