Emerging perovskite solar cell technology has inspired extensive study of perovskite materials, with a recent focus on the search of stable and environmentally benign lead-free alternatives. The huge compositional space of the perovskites family necessitates rational strategies, for which predictive descriptors that relate target properties to a few key variables are crucial. Among others, ionic radius plays key roles on many important materials properties. In this work, to unlock the full potential of ionic radius for rational materials design (1) the widely used Shannon radii data set were consistently expanded to more than twice as large by extending to unusual oxidation states and arbitrary coordination, (2) new criterion for improved prediction of perovskites formability was proposed, (3) a general and predictive band gap physical descriptor with radius and normalized volume as inputs was discovered for a wide range of three-dimensional halide perovskites. These results offer new opportunities for perovskites design by exploiting radii.
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