Coupled Solar Battery with 6.9 % Efficiency

Abstract Solar‐to‐electrochemical energy storage in solar batteries is an important solar utilization technology comparable to solar‐to‐electricity (solar cells) and solar‐to‐fuel (photocatalytic cells) conversion. Unlike the indirect approach of integrated solar flow batteries combining photoelectrodes with redox‐electrodes, coupled solar batteries enable direct solar energy storage, but are hampered by low efficiency due to rapid charge recombination of materials and misaligned energy levels between electrodes. Herein, we propose a design for a coupled solar battery that intercouples two photo‐coupled ion transfer (PCIT) reactions through electron‐ion transfer upon co‐photo‐pumping of photoelectrochemical storage cathode and anode. We used a representative covalent organic framework (COF) to achieve efficient charge separation and directional charge transfer between two band‐matched photoelectrochemical storage electrodes, with a photovoltage sufficient for COF dual‐redox reactions. By pumping these electrodes, the coupled solar battery stores solar energy via two synergistic PCIT reactions of electron‐proton‐relayed COF oxidation and reduction, and the stored solar energy is released as electrochemical energy during COF regeneration in discharge while interlocking the loops. A breakthrough in efficiency (6.9 %) was achieved, adaptive to a large‐area (56 cm 2 ) tandem device. The presented photo‐intercoupled electron‐ion transfer (PIEIT) mechanism provides expandable paths toward practical solar‐to‐electrochemical energy storage.