Two-Dimensional Double Perovskites in the Dion–Jacobson Phase Alleviate Parity Forbidden Transitions for Photovoltaic Applications

Two-dimensional double perovskites have recently been identified as a potential class of materials for the improvement of halide-perovskite-based solar cell technology. The expanded set of utilizable B- and B′-site cations afforded to double perovskites, combined with tunable structural and electronic properties in two-dimensional perovskites, leads to a highly modifiable set of materials, which have yet to be explored. In this study, we investigate the structural, electronic, and thermoelectric properties of these materials and identify a number of key structure–property relationships governing their performance. In the process, we demonstrate a link between the relative electronegativities of the building components and the resultant geometric structures. Furthermore, we provide insights aimed toward alleviating concerns associated with parity forbidden transitions which plague many double perovskite systems. In addition, we identify a number of two-dimensional double perovskites including the mixed-oxidation state In25Tl75Cl-based system which displays optically active transitions as low as 1.41 eV across the Brillouin zone and indicators pointing toward stable experimental synthesis.