Morphological evolution of electrochromic nanosheet-structured nickel-cobalt oxide thin films

Abstract

• Nanosheet-structured Ni-Co oxide thin films were prepared by one-pot solution method. • Growth of nanosheets was dependent on the hexamethylenetetramine amounts. • Electrochromic Ni-Co oxide thin films had stainable and reversible color modulation. Nanosheet-structured nickel-cobalt (Ni-Co) oxide thin films were directly grown on the fluorine-doped tin oxide (FTO)-coated glass substrates using a facile one-pot solution method. The oxide thin films were composed of interconnected nanosheets with several nanometer order in width, and their structures were well-preserved with the increase in the growth time. Furthermore, the growth of nanosheets that were vertically aligned on the FTO/glass substrate was enhanced by increasing the amount of hexamethylenetetramine (HMT) to 20 mM. Subsequently, it slightly decreased when the HMT amount was further increased to 50 mM, and the loose-packed nanosheets were sparely distributed. The Ni-Co oxide sample prepared with 20 mM HMT exhibited a stainable and reversible color modulation from black to yellow under a relatively high cyclic voltammetry (CV) scan rate (50 mV/s, 1000 cycle). It also had a fast switching time less than ∼4 s with excellent color retention in an open-circuit condition.