Advanced device architectures and tandem devices

Abstract

A single semiconductor junction photoelectrochemical (PEC) device could theoretically be capable of over 10 % conversion efficiency for photoelectrochemical hydrogen production via solar water splitting, but a single material capable of this performance has not yet been identified. An integrated tandem approach is more flexible regarding material choice, and can develop suitable photopotential for fuel production while also harvesting an appreciable amount of the solar spectrum. In this chapter a simple theoretical framework is presented to demonstrate how using two or more semiconductor junctions in tandem can allow a range of different material combinations to reach a device with over 10 % conversion efficiency, and up to 30 % even with large assumed losses in the device. In addition to the choice of semiconductor, the design geometry of a PEC tandem cell is also considered with respect to resistance losses due to membranes and ionic conduction. Key examples of operational tandem cells are also discussed together with technoeconomic considerations as a practical PEC tandem cell must optimize cost, longevity, and performance to compete with PV + electrolysis based approaches.