Photovoltage at semiconductor-electrolyte junctions

Photoelectrochemical (PEC) cells based on an interfacial electric field formed at a semiconductor-electrolyte junction aim to achieve solar-driven water electrolysis at low cost and with low complexity. When targeting real devices with competitive efficiencies, one must critically understand the photovoltage demands on each photoabsorber as they relate to its band gap and its role in a tandem device. Now four decades after the first observations of PEC phenomena, device photovoltages remain below their target values for the most widely-studied materials, although innovative approaches have shown encouraging progress. This brief review summarizes the most recent advances in understanding and improving PEC device photovoltages.