Lead-free halide double-perovskite nanocrystals: structure, synthesis, optoelectronic properties, and applications

In recent years, lead-free halide double perovskite nanocrystals (NCs) have emerged as potential alternatives to traditional lead-based halide perovskite NCs owing to their environmentally friendly nature, robust intrinsic thermodynamic stability, and rich and tunable optoelectronic properties. However, challenges remain regarding their optoelectronic properties, including low energy conversion efficiency, poor photoluminescence quantum yield, intrinsic and surface defects, indirect and wide bandgaps, and parity-forbidden transition. Herein, this review systematically introduces recent progress in lead-free halide double perovskite NCs, encompassing their crystal structures, electronic properties, and photoluminescent mechanisms. We emphasize strategies for enhancing their optoelectronic properties and stability through synthesis methods, alloying, and doping, aiming to improve the potential applications of these NCs in optoelectronic devices. Building upon these strategies, the preliminary applications of these NCs in LEDs are then emphasized. Building upon these strategies, the preliminary applications of these NCs in optoelectronic devices is then emphasized. Furthermore, the key challenges and future directions in the development of efficient and stable lead-free perovskite NCs are discussed, providing theoretical and technical guidance for further advancements.