Interface-engineered monolithic photo-harvesting supercapatteries: Charge storage, transport mechanisms, and self-charging architectures

Monolithic photo-harvesting supercapatteries represent an emerging class of integrated energy devices that simultaneously convert solar energy and store it electrochemically within a single architecture. Unlike conventional photovoltaic–storage modules that rely on external wiring and suffer from resistive losses, monolithic configurations enable direct photon-to-stored-energy conversion through tightly coupled semiconductor–electrode interfaces. Recent studies report specific capacitances ranging from 300 to 1800 F g⁻¹, energy densities of 20–80 Wh kg⁻¹, and solar-to-stored energy efficiencies typically below 10%, highlighting both progress and remaining limitations. Despite significant advances in semiconductor photoabsorbers, conductive carbon frameworks, transition-metal compounds, and MOF-derived structures, key challenges persist. These include interfacial recombination of photocarriers, suboptimal band alignment between photoactive layers and storage electrodes, and limited long-term stability under illumination and electrolyte exposure. This review provides a critical interface-centric perspective on monolithic photo-harvesting supercapatteries, focusing on ion–electron coupling, band-structure alignment, and interfacial charge-transfer mechanisms rather than simply cataloguing materials. Recent developments in device architectures, including planar, lateral, and three-dimensional configurations, are analyzed in relation to charge-transport pathways and photo-modulated electrochemical performance. Finally, the review outlines future research directions for improving scalability, stability, and standardized benchmarking to advance these devices toward practical self-charging energy systems.