Heteroatom co-doping engineering endows tungsten oxide with highly efficient dual-band electrochromic performance

Abstract

Dual-band electrochromic smart windows hold the capability to intelligently modulate visible and near-infrared light, playing an important role in photo-thermal regulation. However, the long response time and low optical modulation of electrochromic materials hinder their development. Herein, heteroatom (Mo and N) co-doped WO₃·xH₂O (x = 1, 2) with tunable structural water was prepared by in-situ oxidation from tungsten nitride. Impressively, Mo and N co-doped WO₃·H₂O film achieves the efficient dual-band electrochromic regulation, such as high optical modulation (633 nm: 75 %, 1200 nm: 78 %), fast response speed (633 nm: 6 s, 1200 nm: 5 s), high coloration efficiency (633 nm: 95.3 cm²/C, 1200 nm: 200.6 cm²/C), and good cycling stability. Experimental and theoretical results reveal that: 1) N doping increases the free carrier density of WO₃·H₂O and induces a blue shift in localized surface plasmon resonance. 2) Mo doping optimizes the microscopic morphology and conductivity, which significantly reduces the diffusion energy barriers of electrons and ions. Consequently, the synergistic effect of Mo and N co-doping endows WO₃·H₂O with excellent dual-band electrochromic properties. As a proof of concept, we further assembled electrochromic devices based on Mo and N co-doped WO₃·H₂O film, which shows excellent photothermal management capability. This work underlines dual heteroatoms engineering for tungsten oxide to realize efficient dual-band electrochromic performance, which will provide new insight into the design of dual-band electrochromic materials.