Construction of highly transparent, flexible, and robust solid-state symmetric supercapacitors using NiO electrodes roughened by conformal atomic layer deposition

Transparent flexible supercapacitors (TFSCs) have received significant attention as a power source for modern high-tech wearable electronic gadgets. Although carbon nanomaterials have been employed to manufacture TFSCs, unsatisfactory electrochemical performance and poor optical transparency have restricted their commercial use. In the present study, a TFSC device with large areal capacitance, excellent cyclic stability, and high optical transparency was developed by enhancing the electronic conductivity of the pseudocapacitive material using atomic layer deposition (ALD). In this method, a conformal nickel oxide (NiO) layer whose roughness was readjusted according to its thickness was successfully fabricated on a flexible substrate. The NiO film exhibited a high areal capacitance of 1.51 mF cm−2 at an optical transparency of > 81 % when employed as a TFSC electrode, and it outperformed other state-of-the-art TFSC electrodes. The symmetric solid-state TFSC fabricated via the complete integration of these layers exhibited scalable areal capacitance and cyclic stability at a transmittance of 76 %. These findings demonstrate the potential of ALD-based NiO electrodes for use in sustainable and integrated supercapacitor applications.