Highly efficient photo-supercapacitor based on Mg-doped NiOx/SnO2 p-n heterojunction

A photo-supercapacitor is a device that captures and stores renewable solar energy. Metal oxide-based photo-supercapacitors with p-n junctions have attracted significant attention for application in self-powered electronic devices. In this study, we utilized a NiO_x/SnO₂ p-n heterojunction electrode to achieve a capacitance of 180 mF/cm² in a 1 M aqueous KOH solution at a current density of 1 mA/cm². The n-type layer was synthesized from SnO₂ nanostructures via a simple hydrothermal method on an FTO substrate, while the p-type layer was created by forming a NiO_x thin film through spin-coating. When exposed to visible light, Mg doping in the p-type layer enhanced the supercapacitor electrode performance. The capacitance, cathodic, and anodic current densities of the NiO_x/SnO₂ p-n heterojunction increased by 60 %, 62 %, and 65 %, respectively, compared to the SnO₂ electrode. This approach presents a novel design and material composition for photo-supercapacitor fabrication, enabling the development of single-body structures with comparable performance to more complex configurations.