The progress in semiconducting lead-halide perovskite compounds within an unprecedentedly short time period drove their advancement for optoelectronic applications, among them tandem perovskite-based photovoltaic materials, low-dimensional (2D, 0D) quantum confined emitters. With the emergence of lead-halide perovskites, the necessity for a sustainable material and process strategy is arising. Recycling and closed cycle processes gain importance, especially in high priced segments using rare or precious raw materials.

Attempts to develop “green” perovskite compounds are currently concentrating on “lead-free” halide perovskites, with the Sn based perovskites as one leading structure. An alternative approach are double-cation perovskites AIMIMIIIX6, where A is an alkali cation, X is a halide, and a couple of MI+MIII represents an isovalent substitution of two PbII cations in the lead-halide (APbX3)2 perovskite structure. The double lead-free compounds combine the variability of A and X sites typical for APbX3 compounds with new possibilities of independent variation of both MI and MIII sites from corresponding pools of MI = Na+, K+, Ag+, Tl+, Au+, etc. and MIII = In3+, Bi3+, Sb3+, Fe3+, Au3+, etc. Among the double halide perovskites, compounds based on Bi and In with a general formula Cs2AgxNa1-xBiyIn1-yCl6 (or CANBIC by first letters of elements) have started to occupy an outstanding position due to the combination of compositional variability, stability, opportunities for sustainable material combinations and promising photoluminescence quantum yields. Along with variable parameters x and y, both Cs and Cl sites can also be varied and potentially substituted with analogs (for example, Cs for Rb or methylammonium, Cl for Br and I).

Recently, we reported on a relatively “green” single-step synthesis of luminescent CANBIC perovskites in 2-propanol:water mixtures and were able to demonstrate a semi-automatic synthesis on a robot-based pipetting platform. That opens the opportunity to systematically the huge parameter space of lead-free, multinary metal, cation and halide double perovskites is a systematic way. First data libraries are presented and characterized according to their optical properties. The talk will be concluded with an outlook, whether the synthesis platform can be made compatible for a Bayesian optimization process looking for the most promising optoelectronic lead-free perovskites.