Recent Advances in All-Inorganic Lead-Free Three-Dimensional Halide Double Perovskite Nanocrystals

All-inorganic lead halide perovskite nanocrystals (NCs) have attracted extensive attention due to their three-dimensional (3D) structure, simple synthesis, and outstanding optical and electronic properties. However, the toxicity of lead and poor stability hindered their further development. Recently, air-stable, nontoxic, all-inorganic lead-free perovskite NCs have been developed and widely studied. Two Pb2+ ions can be replaced with monovalent B+ and trivalent B′3+ cations to form the halide double perovskite (DP) Cs2BB′X6 (B+ = Ag+, Na+, or Cu+; B′3+ = Bi3+, Sb3+, In3+, or Fe3+; X– = halogen anion) NCs, which are characterized by a 3D network similar to lead-based perovskite NCs and have potential to be excellent photoelectric materials. In this review, we present the recent advances in synthesis, optical properties, exciton dynamics, and optoelectronic applications of all-inorganic 3D halide DP NCs. In the end, the opportunities and challenges of all-inorganic 3D DP NCs have been proposed. This review not only provides a feasible idea for understanding the exciton dynamics in lead-free DP NCs but also guides the design and development of new, high-performance, stable lead-free DP NCs.