Photobatteries: Prospects and fundamental limitations

The need for autonomous off-grid energy sources has led to the development of "photobatteries," which combine the dual functionalities of light-energy harvesting and electrochemical energy storage within the same device architecture. Although several interesting devices and materials have been reported recently, there remains a wide disparity between proposed mechanisms and measurement methods between various publications. In this perspective, we highlight the current issues in the field and provide possible solutions and avenues for future developments. We focus on the requirements for autonomous photocharging to be possible and the need for standardized measurement protocols, especially in relation to decoupling thermal and optical effects. These protocols lay the framework for the stepwise fabrication of photobatteries—from photo-enhanced to fully photo-rechargeable systems. We also highlight prospective use cases of photobatteries; for example, there are substantial technological challenges that need to be addressed before grid-scale energy storage becomes viable, but in the short term, they might be attractive for small off-grid devices.