Electrochromic properties of vertically aligned Ni-doped WO3 nanostructure films and their application in complementary electrochromic devices

Abstract

Tungsten trioxide (WO₃) is a promising electrochromic material for potential applications in architectural and automotive smart windows. Nanostructured WO₃ has attracted particular attention over the past few years due to its potential advantages in electrochromic properties. Herein, Ni-doped WO₃ nanostructured films were obtained by a seed-free hydrothermal method directly on transparent conducting substrates. The influences of Ni doping on the nanostructure and electrochromic properties of WO₃ films were investigated. Compared to pure WO₃ films, Ni doping can increase the crystal defects and induce significant changes in the nanostructure, thus affecting the electrochromic performance of WO₃ films. Low concentration Ni-WO₃ films exhibited a vertically aligned nanorods morphology, ultrahigh optical modulation (over 85% from 600 to 900 nm), high coloration efficiency (60.5 mc² C⁻¹ at 600 nm) and excellent cycling stability for about 5500 cycles. Finally, the complementary electrochromic device assembled with 1.5% Ni-WO₃ and NiO-based films exhibited vivid color change from transparent to black (x = 0.326, y = 0.369, Y_L% = 3.29%) with maximum transmittance of about 3.5% in the dark state.