TT-Nb₂O₅ with dual-band modulation and exceptional performance retention for fast-responsive electrochromics

Independently modulating the transmittance of solar spectra, specifically within the visible and near-infrared light ranges, presents a significant prospect for windows that can effectively manage lighting and energy consumption in both buildings and electrical-vehicles. Electrochromic devices, capable of regulating the transmittance of visible and near-infrared light in response to external electrical stimuli, are considered as one of the ideal candidates for smart windows. However, electrochromic devices typically suffer from single-mode control (i.e. simultaneously varying the visible and near-infrared light), slow response and inadequate long-term durability. In this paper, we demonstrate that TT-Nb₂O₅ enables independent modulation of visible and near-infrared light and possesses rapid switching kinetics and exceptional cycling stability, i.e. no observed degradation of optical modulation after more than 10 000 cycles. The dual band modulation is attributed to a combination of progressive splitting and downward shift of Nb 3d conduction bands and rise of Fermi level as ion insertion proceeds. The open framework of the crystal structures accounts for the exceptional cycling stability. Simulation results based on assembled smart windows indicate a potential cooling energy saving of 160 GJ without compromising the outdoor view, or 225 GJ for a complete blocking of visible and near-infrared light can be achieved in hot climate zones.