Using design principles to systematically plan the synthesis of hole-conducting transparent oxides: Cu3VO4 and Ag3VO4 as a case study

In order to address the growing need for p-type transparent conducting oxides (TCOs), we present a materials design approach that allows to search for materials with desired properties. We put forward a set of design principles (DPs) that a material must meet in order to qualify as a p-type TCO. We then start from two prototype p-type binary oxides, i.e., Cu2O and Ag2O, and define a large group of compounds in which to search for unique candidate materials. From this set of compounds, we extracted two oxovanadates, Cu3VO4 and Ag3VO4, which serve as a case study to show the application of the proposed materials selection procedure driven by the DPs. Polycrystalline Ag3VO4 was synthesized by a water-based hydrothermal technique, whereas Cu3VO4 was prepared by a solid-state reaction. The theoretical study of the thermochemistry, based on first-principles electronic structure methods, demonstrates that Cu3VO4 and alpha-Ag3VO4 are p-type materials that show intrinsic hole-producing defects along with a low concentration of hole-killing defects. Owing to its near-perfect stoichiometry, Ag3VO4 has a rather low hole concentration, which coincides with the experimentally determined conductivity limit of 0.002 S/cm. In contrast, Cu3VO4 is highly off stoichiometric, Cu3-xVO4 (x = 0.15), which raises the amount of holes, but due to its black color, it does not fulfill the requirements for a p-type TCO. The onset of optical absorption in alpha-Ag3VO4 is calculated to be 2.6 eV, compared to the experimentally determined value of 2.1 eV, which brings it to the verge of transparency.