Lead‐Free Metal Halide Perovskite Nanocrystals: Challenges, Applications, and Future Aspects

Abstract Lead halide perovskite materials have shown strong promise in energy harvesting and generation over the past five years. However, their poor ambient stability and lead toxicity issues hinder optoelectronic applications. In the quest for alternatives, metal halide perovskites with lower toxicity and more stable metals have recently emerged. The divalent Pb²⁺ could be replaced with isoelectronic Sn²⁺, but Sn²⁺ tends to oxidize rapidly in presence of air to Sn⁴⁺, forming a defect in the structure. However, Sn²⁺‐based perovskites have been stabilized in 2D structures. Recently Sn⁴⁺ based halide perovskites nanocrystals with have been reported with poor luminescence. The replacement of Pb²⁺ with isoelectronic trivalent elements (Sb³⁺, Bi³⁺) results in A₃B₂X₉ type defect‐order perovskite structure, which shows promises for optoelectronic applications. The perovskite nanocrystals of Sb, Bi have been reported in the form of dimers and layered structures. In addition to these, double perovskites, where two divalent Pb²⁺ are replaced with a monovalent and a trivalent cation have been reported very recently. In this Focus Review, we give a brief summary of different non‐lead perovskite nanocrystals starting from synthesis, characterization, stability, properties to applications, along with potential future directions.