Innovative Approach to Bismuth-Antimony-Iodide Double Perovskite PV Absorbers via Anion Exchange and Solide-State Reactions

This work focuses on the development of advanced synthesis protocols for lead-free Cs2AgBi(Sb)Br6 perovskites and their conversion into lower-bandgap Cs2AgBi(Sb)I6 perovskite PV absorbers by using an innovative combination of mild anion exchange with a solid-state reaction between intermediate iodide derivatives. High-throughput robot-assisted experimentation is applied for the optimization of the synthesis conditions, targeting the highest yields of Cs2AgBi(Sb)I6 perovskites (ca. 90 mass%) with the lowest bandgap (1.78 eV). We provide new insights into the pathways, mechanisms, and dynamics of the formation of iodide double perovskites, reporting stable lead-free double iodide perovskites crystallized in a non-conventional tetragonal symmetry.