Composite Assembling of Oxide-Based Optically Transparent Electrodes for High-Performance Asymmetric Supercapacitors

Simultaneously achieving a transparent and high-energy density supercapacitor is a major challenge because of the trade-off between energy storage capacity and optical transparency of active electrode materials. Herein, we demonstrate a novel approach to construct an optically transparent asymmetric supercapacitor (Trans-ASC) by assembling positive (ZnO-SnO₂) and negative (TiO₂-SnO₂) composite thin-film electrodes on a conductive indium-doped tin oxide substrate via reactive DC magnetron cosputtering. The optical transmittance for both composite thin films is found to be 68% (ZnO-SnO₂) and 64% (TiO₂-SnO₂). Furthermore, electrochemical kinematics of the primed transparent electrodes are scrutinized in 0.5 M KOH electrolyte without affecting the transparency of active electrodes. The structural reliability of the electrodes aids the superb electrochemical performance to construct a Trans-ASC, TiO₂-SnO₂//ZnO-SnO₂, which works at a voltage of +1.2 V and attains a higher areal capacitance of 44.6 mF cm^-2 at 2 mA cm^-2. The assembled Trans-ASC delivers a maximum areal energy density of 8.75 μW h cm^-2 with an optimal areal power density of 570 μW cm^-2. Additionally, the capacitance retention of 81.6% and transparency of both electrodes remain almost the same (up to 60% for ZnO-SnO₂ and 62% for TiO₂-SnO₂) even after 10,000 charging-discharging cycles. These remarkable electrochemical properties and outstanding cycling stability of the designed Trans-ASC device make it a potential candidate for storing energy and for further use in transparent electronic devices.