This review article addresses areas where solid-state chemistry concepts can contribute to the on-going search for a "magic bullet" inorganic semiconductor that can efficiently split water or reduce CO2. First, a methodology to visualize complex ternary oxide combinations is outlined using 31 examples based on copper in both +1 and +2 oxidation states. Then the synthetic aspects are reviewed followed by a discussion of the structural characteristics. The optoelectronic aspects are considered next, culminating the review with the state-of-the-art in the practical applicability of these materials in solar fuels photogeneration and environmental (e.g., azo dye) remediation. (C) The Author(s) 2018. Published by ECS.