Integrated Photovoltaic-Supercapacitor Systems: Structural Architectures, Materials Innovations, and Emerging Multifunctional Designs

Renewable energy technologies that simultaneously harvest and store energy are attracting increasing attention as next-generation power solutions for portable, wearable, and self-powered electronic systems. Among these technologies, monolithically integrated solar energy conversion and storage devices that combine solar cells (SCs) with supercapacitors into singular, encapsulated structures offer a promising pathway to address the intermittency of solar power while enabling compact and multifunctional energy platforms. This review systematically summarizes recent progress in monolithically integrated solar energy harvesting and storage systems, with particular emphasis on structural architectures, photovoltaic configurations, electrode/electrolyte engineering, and multifunctional device designs. The advantages and limitations of two-electrode, three-electrode, and shared-substrate configurations are critically compared in terms of internal resistance, power matching, fabrication complexity, mechanical flexibility, and overall energy conversion-storage efficiency. Recent advances in rigid, flexible, and fibrous integrated systems based on silicon, dye-sensitized, perovskite, organic, and quantum-dot solar cells are comprehensively discussed, alongside emerging developments in photorechargeable supercapacitors, electrochromic systems, and multifunctional photovoltaic–triboelectric hybrid devices. Particular attention is given to the roles of advanced materials, including graphene, carbon nanotubes, MXenes, conductive polymers, and other low-dimensional materials, in enhancing electrochemical performance, flexibility, and device stability. Current challenges associated with electrolyte compatibility, device mismatch, mechanical durability, long-term cycling stability, scalability, and performance standardization are further analyzed. Finally, future perspectives toward high-efficiency, mechanically robust, and commercially viable integrated energy systems for wearable electronics, smart textiles, and distributed energy applications are outlined.