LAUSR

Summary Practical application of hybrid Pb-based halide perovskites needs not only to fabricate high-quality film samples on a large scale but also to properly overcome the issues of Pb toxicity and materials instability. Finding new, stable, Pb-free perovskites currently attracts significant research interest. Among various strategies, hetero-substitution of Pb to form quaternary halide double perovskites represents a promising direction to keep the high structural (and likely electronic) dimensionality nature of perovskite lattice and meanwhile offers rich chemical compositions a degree of freedom for discovering new perovskite materials. We herein present a perspective that concisely reviews the progress of rational design of Pb-free halide double perovskites by both theoretical and experimental efforts as well as their current and potential applications in various optoelectronic categories. We also envision the future research directions to realize new materials by exploring broader chemical composition space and to better utilize existing materials by considering optoelectronic properties modulation.