Perspectives and Design Principles of Vacancy-Ordered Double Perovskite Halide Semiconductors

Halide perovskite semiconductors such as methylammonium lead iodide (CH3NH3PbI3) have achieved great success in photovoltaic devices; however, concerns surrounding toxicity of lead and material stability have motivated the field to pursue alternative perovskite compositions and structures. Vacancy-ordered double perovskites are a defect-ordered variant of the perovskite structure characterized by an antifluorite arrangement of isolated octahedral units bridged by A-site cations. In this Review, we focus upon the structure-dynamics-property relationships in vacancy-ordered double perovskite semiconductors as they pertain to applications in photovoltaics, and we propose avenues of future study within the context of the broader perovskite halide literature. We describe the compositional and structural motifs that dictate the optical gaps and charge transport behavior and discuss the implications of charge ordering, lattice dynamics, and organic-inorganic coupling upon the properties of these materials. The design principles we elucidate here represent an important step toward extending our understanding of perovskite functionality to defect-ordered perovskites.