Design of Metal-Halide Inverse-Hybrid Perovskites

We recently introduced a new class of perovskites, with inorganic anions on the A- and B-sites and an organic cation on the X-site, the so-called inverse-hybrid perovskites (IHPs). We found compounds that are predicted to be stable, possess large polarization, and span a wide range of electronic properties. Here, we present the materials search strategy that enabled these results. We demonstrate the design principles in terms of ion and site composition. Overall, we consider elements from most main groups of the periodic table, investigating their ability to form mono- or divalent anions in the framework of IHPs. We observe structural changes based on tolerance factor. Compounds are found in the perovskite or the related CaIrO3 structure, and different orientations of the employed organic cation (methylammonium) lead to different B···X···B bridging motifs. Furthermore, we demonstrate how the perovskite structure can be favored by interchanging B- and A-site anions and adjusting the ions within groups of the periodic table accordingly. Besides chalcogenide halides, we find that elements of groups XIII to XV can successfully form mono- or divalent anions by partly filling their valence p shell. Spin–orbit coupling in the heavier elements leads to interesting electronic motifs. Furthermore, while light divalent elements show a tendency toward protonation, this is suppressed by employing heavier elements of the same group. Evaluating the stability of these novel compounds also requires us to investigate largely unknown methylammonium compounds with mono- and divalent anions.