  Using density functional theory (DFT)-based calculations, we propose a family
of metastable, as-yet unmade V5+ and Cr6+ double perovskite compounds with low
band gaps spanning much of the visible region of the solar spectrum. Through
analysis of a related set of measured optical gaps of d0 ABO3 perovskites and
A2B'BO6 double perovskites, an ad hoc procedure is developed to correct DFT and
many-body perturbation theory gaps, bringing them into quantitative agreement
with experiment for measured compounds, and predicting that V5+ and Cr6+ double
perovskites would have gaps ranging from approximately 1.1-2.4 eV,
significantly lower than previous materials studied in this class. DFT
calculations also establish that these V5+ and Cr6+ compounds are likely able
to be synthesized, either in bulk form or as epitaxial thin films. These
compounds would comprise a new class of semiconducting double perovskites for
potential use in solar energy conversion and other optoelectronic applications.
