A perspective on photoelectrochemical storage materials for coupled solar batteries

Abstract

Solar-to-electrochemical energy storage in solar batteries is an important solar utilization technology alongside solar-to-electricity (solar cell) and solar-to-fuel (photocatalysis cell) conversion. Integrated solar batteries that integrate photoelectrodes with redox-electrodes realize indirect solar energy storage based on dual energy matching (photo-carriers and redox couples) and two distinct processes (electricity generation and redox reaction). In contrast, the emerging coupled solar batteries allow direct solar energy storage via a photo-coupled ion transfer at photoelectrochemical storage electrode materials with both light harvesting and redox activity. However, issues of rapid charge recombination of these photoelectrochemical storage materials and misaligned band energy of the devices have resulted in a limited efficiency that hampers the development of coupled solar batteries. In this review, we describe how photoelectrochemical storage materials and coupled solar batteries can be designed to promote the coupling between photogenerated charges and redox reactions for high efficiency. We discuss the characteristics of recent photoelectrochemical storage materials in coupling basic functions such as light harvesting and redox activity, along with new approaches to promote charge separation. We also assess the mechanisms and limitations of current device design (e.g., photo-assisted and photo-charged solar batteries), based on which opportunities for a new device with matched band alignments are proposed. Finally, we translate these mechanistic insights and key metrics into standardized protocols for future modifications, innovations, and ultimately, commercialization of coupled solar batteries.