Pushing the Boundaries of Stability and Band Gap Pareto Front with High-Entropy Perovskites

Vacancy-ordered double perovskites (VODPs) have attracted particular attention following recently demonstrated high performance in solar cell devices. Besides mitigating toxicity concerns associated with the use of lead, the presence of formally tetravalent B sites in A₂B(IV)X₆ VODPs has been demonstrated to improve air and moisture stability relative to the divalent B sites in the conventional AB(II)X₃ perovskites. Substitutions at the B and X sites in A₂BX₆ give rise to emerging properties in the high-entropy VODPs which are not present in their pure counterparts. In this work, we employ high throughput density functional theory (DFT) calculations using the hybrid functional HSE06 to explore the structure-property relationships in high-entropy VODPs. Our results reveal that the B-site mixing can break the linear scaling between the bandgap and formation energy observed in the pure perovskites, and an optimal band gap of ~1.3 eV for single junction solar cell along with high stability can be readily achieved. This can be attributed to the weak coupling between the BX₆ octahedra in high entropy VODPs. As a result, the formation energy of the high-entropy perovskite is the average of the constituent pure perovskites, while the bandgap is determined by the minimum conduction band minimum (CBM) and maximum valence band maximum (VBM) of the constituent pure perovskites. Our study offers simple and practical guidelines for the experimental synthesis of new perovskites with improved photovoltaic performance.