Due to the intermittent nature of sunlight, practical solar energy utilization systems demand both efficient solar energy conversion and inexpensive large scale energy storage. We have developed hybrid solar-charged storage devices called solar flow batteries (SFBs) that integrate solar cells with redox flow batteries (RFBs). In these devices, photoexcited carriers collected at the semiconductor-liquid electrolyte interface convert the redox couples to charge up the RFB without external electric bias; which can be discharged to generate the electricity when needed. After developing and carefully matching silicon solar cells and III-V solar cells with various organic redox couples and optimizing the SFB designs, we have improved the solar-to-output electricity efficiency (SOEE) and the device lifetime of SFB devices. We have recently achieved a record SOEE of 20% with a 500-hour lifetime using high performance tandem perovskite/silicon solar cells. The design principles with a quantitative model for voltage matching solar cells with RFBs we have developed lay the pathways for achieving high performance and stability yet maintaining a low overall cost, which would make these SFB devices practical for distributed and standalone solar energy conversion and storage systems in remote locations.
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