Fast-switching quasi-solid state electrochromic full device based on mesoporous WO3 and NiO thin films

Abstract

Mesoporous tungsten trioxide (WO3) and nickel oxide (NiO) electrochromic (EC) thin films have been fabricated by sol-gel method with assistant of tri-block copolymer [PEO132PEO50PEO132] (F108). By controlling weight ratio of F108 and calcination temperatures, uniform and transparent mesoporous films are fabricated. Both WO3 and NiO films are comprised by nanoparticles with diameters of ca.10 nm, mesopores with pore size of approximately 6 nm are distributed in the films. The thickness of the films are ca. 400 nm. The as-prepared films have ultra-fast switching time during EC redox reactions. Applied with positive and negative voltages of 40 s respectively, the coloration/bleaching time of WO3 and NiO films are 5.7 s/2.3 s and 0.9 s/3.8 s, which is faster than that of comparative EC films fabricated by sol-gel method without F108 (coloration/bleaching time of WO3 and NiO films are 17.5 s/14.5 s and 13.6 s/4.9 s) and EC films fabricated by magnetron sputtering method (coloration/bleaching time of WO3 and NiO films are 29.4 s/21.3 s and 9.6 s/7.5 s). Quasi-solid state electrochromic device assembled with mesoporous WO3 and NiO thin films has excellent EC performance, such as fast switching speed (3.2/1.1 s for coloration/bleaching time), large optical modulation of about 45% (at 600 nm), high coloration efficiency (130.8 cm2/C at the wavelength of 600 nm) and good cycle stability. These excellent properties are derived from mesoporous channels in the films. For the mesoporous channels can shorten the diffusion paths and make it easier for ions to transport in films.