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The chemical trends in the thermodynamic stability and band gaps of 980 A2B+B3+X6 halide double perovskites are revealed based on high-throughput first-principles calculations. To accurately predict the stability with respect to phase decomposition, all known metal halides in the Materials Project database are considered as the competing compounds. The energies above the convex hull show that only 112 of 980 double perovskites are stable and 27 double perovskites that had been predicted to be stable in the literature are actually unstable after considering more competing compounds. The stability of these double perovskites is determined mainly by A, X, and B+ elements and increases gradually as A becomes heavier (from Li to Cs) and X becomes lighter (from I to F). The band gaps are determined mainly by X, B+, and B3+ elements, decreasing monotonically as X becomes heavier while changing nonmonotonically as B+ and B3+ change. These chemical trends provide clear instructions for the design of double perovskites with good stability and suitable band gaps for various applications, i.e., through choosing heavier A cations (e.g., large organic cations), stable double perovskites can be designed with band gaps tunable in a wide range of 0–7 eV (infrared to ultraviolet); however, through choosing light X anions, stable double perovskites can be designed with only wide band gaps.
Zhang et al. (Mon,) studied this question.