Optimizing transmittance in WO3-based electrochromic films: advanced growth control via chemical bath deposition

Abstract

Tungsten trioxide (WO₃)-based electrochromic film is a promising component for all-solid-state electrochromic devices, which can be used in smart windows to control the indoor temperature and incident solar irradiation. However, its practical application suffers from significant challenges including slow switching kinetics, low cycling stability, and high production costs. To overcome these limitations, a mild chemical bath deposition approach is introduced. Through strategic control of reactants, the thickness of the WO₃ film and the constituent WO₃ nanosheets forming the film can both be systematically regulated. The optimized W₂ sample demonstrates remarkable electrochromic performance, achieving an optical modulation amplitude of ΔT = 67.85% at 620 nm along with good cycling stability, which was caused by its well-engineered hierarchical structure featuring a thin film configuration (430 nm) composed of ultrathin nanosheets (39.48 nm). This work points out a new strategy for modulating the optical properties of WO₃ electrochromic film through reactant control during a chemical bath deposition process, providing valuable insights for the rational design of high-performance smart windows.