Photoelectrochemical Tandem Cells for Solar Water Splitting

In order to be economically competitive with simple "brute force" (i.e., PV + electrolyzer) strategies or the production of promising solar fuels, like H-2, from fossil fuels, a practical photoelectrochemical device must optimize cost, longevity, and performance. A promising approach that meets these requirements is the combination of stable and inexpensive oxide semiconductor electrodes in a tandem photoelectrochemical device. In this article, we give an overview of the field including an examination of the potential solar-to-fuel conversion efficiency expected in a device with realistic losses. We next discuss recent advances with increasing the performance of promising semiconductor electrode materials and highlight how these advances have led to state-of-the-art solar-to-chemical efficiencies in the 2-3% range in real devices. Challenges for further optimization are further outlined.