Four-mode Dual-band Electrochromic Properties in Amorphous WO<sub>3</sub> Film

Abstract WO 3 is an excellent dual-band electrochromic material that can selectively modulate the transmittance of visible light and near-infrared light under the driving voltage.However due to the influence of ion embedding depth and polariton transition mechanism only three optical modulation modes-'bright cold and dark' -are typically achievable.In this work amorphous WO 3 films were prepared and by controlling the annealing temperature and driving potential four optical modes-"bright " "dark " "cool " and "warm" -were successfully realized.The maximum optical contrast reached 77.4% and 82.2% in the visible and near-infrared bands respectively with an average response time of 11. 7 s.XPS and in-situ spectroscopy analysis showed that the formation of W 3+ and metallic W local states is the key mechanism for the "warm" mode.However deep ion trapping and excessive potential be yond the material' s stable range lead to poor reversibility of this mode.This study overcomes the multi-mode regula tion limitations of traditional dual-band devices and the revealed polariton-ion synergistic mechanism provides theo retical guidance for developing highly reversible four-mode devices.It also holds significant potential for applications such as building energy-saving.