Lead-Free Halide Double Perovskites Nanomaterials: Fundamentals, Recent Advances and Perspectives

Lead-free halide double perovskites with the formula A2BI BIIIX6, and ordered vacancy perovskites, with the general formula A2BIVX6 have recently emerged as alternative materials for advancements in lead-halide perovskites. While the main obstacles to the development of lead-halide perovskites are the use of lead and the instability of the structure, halide double perovskites allow multiple metal combinations resulting from the replacement of the lead in single perovskites by two metal-complexes or alternating vacancy metal-complexes in their crystalline structure. Although many advances have already been made in lead-free halide double perovskites, there are still some challenges to be overcome, such as the indirect and high bandgap, and the transitions prohibited by parity, which are intrinsic features of their electronic structure, and result in low energy conversion efficiency and photoluminescence quantum yields as well. Emphasizing the need to review the results of the literature so far, considering the advances and challenges presented, this work involves a systematic and embracing bibliographical research on lead-free halide double perovskites, encompassing central aspects such as their historical evolution, crystalline structure, synthesis methods, challenges faced in the field, optoelectronic properties and perspectives for the development and application of these materials.