Optoelectronic energy conversion is very likely to be a key technology for a sustainable energy future. This broad field encompasses photovoltaics (PV, sunlight-to-electricity conversion), photoelectrochemistry (PEC, sunlight-to-fuel conversion through electronic processes), and light emitting diodes (LEDs, electricity-to-light conversion). All these technologies are based on similar fundamental processes: Light absorption and emission, electron-hole separation and recombination, and their transport to/from electrode materials. Although technology-specific requirements exist, PV, PEC, and LEDs exhibit a common thread. They all require a semiconductor material combining a high light absorption coefficient α, long photocarrier lifetimes τ, and high photocarrier mobilities μ. For simplicity, we will refer to such ideal materials as "high-quality semiconductors" throughout this paper. Current materials research efforts in this field are especially targeted at the discovery and development of semiconductors with relatively wide band gaps, often above 1.5 eV. The main reason is the lagging performance of wide band gap sub-cells in cost-effective multi-junction PV and PEC technologies, as well as the location of the low-photon-energy edge of the visible region in LEDs (around 1.6 eV).