Electrochromic characteristics of porous nanosheet-structured nickel oxide films with cobalt and zinc dopants

Abstract Porous nanosheet-structured nickel oxide (NiO) films were directly prepared on conductive oxide substrates using a cost-effective and simple one-pot solution method. By incorporating cobalt (Co) dopant, the growth of vertically aligned nanosheet was promoted. However, zinc (Zn)-doped NiO film had the loose-packed nanosheet-structure with relatively low coverage on the surface of the substrate compared to the NiO and Co-NiO films. All the NiO films exhibited electrochromic properties. In the colored state, the NiO, Co-NiO, and Zn-NiO films were dark brown, black, and brown, respectively. In the bleached state, the NiO, Co-NiO, and Zn-NiO films were pale gray, pale yellow, and transparent, respectively. The switching time of the Co-NiO film (tc ~ 2 s, tb ~ 6 s) was slightly slower than those of the NiO (tc ~ 1 s, tb ~ 1 s) and Zn-NiO (tc ~ 1 s, tb ~ 2 s) films. However, it had better transmittance modulation (~58% at 700 nm) with excellent memory durability (increased by ~2% after 3,000 s) than the NiO and Zn-NiO films. Dopants could easily and effectively modify the electrochromic performance of NiO films.