Metal oxide nanomaterials have a wide range of applications in renewable energy conversion and storage. Many are used as electron transport materials in heterojunction solar cells while others are used directly as light absorbers and catalysts for energy storage reactions such as water splitting. Even further, metal oxides represent a large fraction of electrode materials used in Li-ion batteries which can store solar energy for later use. Copper delafossites (CuMO₂) are a unique class of materials capable of achieving all three of these feats. The layered structure of these materials, with Cu(I) atoms sandwiched between M(III)O₆ octahedra, along with the tunability of the M(III) atom create a wide range of functionality. Our group has been particularly interested in the delafossite CuGaO₂ for applications as a charge transport layer in p-type heterojunction solar cells. Detailed physical characterization and electrochemical studies of these materials reveal the existence and impact of copper vacancies in the crystalline lattice. These vacancies allow for rapid charge transport in CuGaO₂ but also introduce a large concentration of recombination trap sites that can be detrimental to solar energy conversion. The importance of these fundamental studies in terms of materials design for delafossite hole transport layers will be discussed throughout.