Standalone photo-rechargeable capacitor integrating DSSCs with a Bi//NiCo2S4 asymmetric supercapacitor for high-efficiency indoor and outdoor energy storage

Abstract

The integration of photovoltaics with electrochemical energy storage (EES) into monolithic photo-rechargeable systems represents a promising approach for sustainable, off-grid power sources, particularly in the context of the Internet of Things (IoT). Herein, we report a high-performance photo-capacitor (PC) constructed by coupling two series-connected dye-sensitized solar cells (DSSCs) with an asymmetric Bi//NiCo₂S₄ supercapacitor in a three-electrode configuration. Nickel cobalt sulfide (NiCo₂S₄) serves as a dual-function common electrode, providing both excellent electrocatalytic activity toward the I₃⁻/I⁻ redox reaction and high supercapacitive performance, while bismuth (Bi) is employed as a storage electrode, offering favorable energy alignment and wide operational potential. The optimized PC achieves a photovoltage exceeding 1.2 V under one-sun illumination and 0.9 V under 1000 lux LED illumination, with an areal capacitance of 170.4 mF cm⁻² and an overall energy-storage efficiency of 7.05% under low-intensity solar irradiation (30 mW cm⁻²). The device demonstrates excellent rate capability, long-term cycling stability, and superior performance under dim-light conditions, confirming its potential as a standalone power supply for both indoor and outdoor IoT applications. This work highlights a strategic combination of band alignment, electrode design, and three-terminal architecture to realize efficient, grid-free solar energy storage.