Sol-gel fabrication of NiO and NiO/WO3 based electrochromic device on ITO and flexible substrate

Abstract

Electrochromic devices (ECDs) with reversible transmittance change represent a promising alternative to smart windows. However, the low−cost facile fabrication of ECDs, particularly flexible devices, remains challenging. In this study, novel NiO is synthesized by a solid state method, and the as−prepared NiO is introduced as an electrochromic anodic layer and fabricated onto a transparent conductive electrode (indium tin oxide, ITO or flexible silver nanowires, AgNW) by a sol–gel spin coating and low temperature annealing (80 °C-150 °C). The solvent, thickness of NiO, and annealing temperature are evaluated to obtain higher ECD performance. NiO/ITO ECDs exhibit very high transmittance variation (ΔT = ~84%) at 700 nm with applied potentials of −3.0 and 0 V. The stability and transmittance variation of NiO/ITO are significantly improved in the presence of a WO3 cathodic electrode at lower applied voltages of 1.5 to 0 V. The low processing temperature of 80 °C demonstrates the potential of the flexible ECDs. The flexible NiO–WO3 device achieves a transmittance variation of ~38% at 700 nm with applied potential of 2.0 and 0 V, and retains the ECD performance. The application of low−cost solution−processed NiO and NiO/WO3−based ECDs in flexible transparent conductive electrodes provides a new pathway for the fabrication of optical devices and printed electronics.