Long-lived charge separated states in nanostructured semiconductor photoelectrodes for the production of solar fuels

The efficient use of sunlight to drive the production of solar fuels requires the photogeneration of suitably long-lived charge separated states capable of driving the multi-electron chemistry of fuel synthesis. Here we discuss a range of promising material design approaches to increasing charge carrier lifetimes, focusing upon semiconductor photoelectrodes for water photolysis and carbon dioxide reduction. Parallels are drawn between the strategies deployed in the development of such artificial systems and those found in natural photosynthesis. We address the use of a range of junctions, including electrolyte/semiconductor, semiconductor/semiconductor and dye sensitized interfaces to provide the spatial separation of charges. A key consideration of the review is the design of such interfaces to achieve a sufficient increase in charge carrier lifetime with a high quantum yield, whilst minimising the energy loss associated with this lifetime gain.