RF-sputtered Al-doped ZnO-based transparent electrochemical capacitors developed as a structural energy storage to replace double-glazed window for a smart building

Abstract

Structural energy storage combines energy storage with structural strength, reducing weight, saving space, and improving efficiency. Among various types, transparent structural energy storage shows strong potential for seamless integration into windows, screens, surfaces, consumer electronics, and automotive applications. Developing new electrode designs with environmentally abundant materials is essential to achieving global decarbonization goals and the net-zero target. In this work, we developed a transparent electrochemical capacitor (TEC) as a structural energy storage using aluminum-doped ZnO (AZO) film prepared by radio frequency sputtering on an indium-doped tin oxide (ITO) glass. We observed that the excellent electrical properties of the AZO film including high carrier concentration 6.54 × 1020 cm−3, Hall mobility 25.8 cm2 V−1 s−1, and resistivity 3.7 × 10−4 Ω cm contributed to enhancing the electrochemical performance of the TEC. The prepared transparent AZO exhibits a high specific capacitance of 44.4 μF cm−2 at 1 mV s−1 for a three-electrode study in a liquid electrolyte. The TEC fabricated using gel electrolyte shows a specific capacitance of 5.93 μF cm−2 at 1 mV s−1. We observed that both the electrochemical double-layer capacitance and pseudo-capacitance contributed to the charge storage in TEC, which was measured using Dunn's method. The double-glazed window shape of the TEC exhibits its promising potential for implementation as structural energy storage in smart buildings. We demonstrated TEC performance under various temperatures (−10 to 30 °C), its transparency of about 85% in the visible light range, and its integration capabilities with solar cells. This TEC aims to develop a structural element for smart buildings or autonomous electric vehicles.