Solar Photoconversion to Photovoltaic Electricity and Solar Fuels: Forty Years of History, Progress, New Concepts, and Prognosis

Since the global oil crisis of 1973 that followed the Fujishima-Honda paper of 1972 showing that under certain conditions semiconductor photoelectrodes could be used to photolytically split H₂O into H₂ and O₂, there have been large international research and development efforts to produce cost effective  solar fuels, such as H₂ from H₂O splitting or renewable carbon-based fuels from the photoreduction of CO₂ with H₂O, as occurs in biological photosynthesis. Parallel efforts to develop cost effective solar electricity from photovoltaic cells were also accelerated. The intensity of both of these R&D efforts have waxed and waned over the ensuing 40 years depending upon political leadership, societal/political perceptions of the severity of the energy security problem and global climate change (and their respective relative priority), and the state of the national economy of nations funding R& D in this area. Over this rather significant time period there have been many importance advances in the associated and highly interdisciplinary science and technology, new innovations and concepts, and some persistently difficult technological barriers to penetrate that have prevented commercialization, especially in producing cost effective solar fuels.  The scientific and technological  history, advances, new concepts, persistent barriers, and present status of viable solar fuels and solar electricity production will be discussed.