Due to its capability to dynamically modulate light and heat, electrochromism holds significant potential for applications in energy savings and displays. Enhancing the stability and reversibility of electrochromic materials and devices has always been one of the goals of electrochromism. Amorphous electrochromic oxides can reversibly change their optical properties upon cycling through ions/electrons intercalation, and ion trapping during long-term cycling is one of the leading causes of performance degradation.
Although potentiostatic and galvanostatic methods have been reported to effectively restore the performance of electrochromic amorphous oxides multiple times, both require high potential for a long duration, leading to the decomposition of the electrolyte and damage to other layers in the electrochromic devices. Therefore, neither method is compatible within a full device, and there is currently no better solution.
A research group led by Associate Professor Rui-Tao Wen from the Department of Materials Science and Engineering (MSE) at the Southern University of Science and Technology (SUSTech) has proposed a new ion detrapping technique. This photo-electrochemical synergistic detrapping method marks the first time performance rejuvenation has been successfully achieved in electrochromic thin films and devices.
Their research work, titled “Photo-electrochemical synergistically induced ion detrapping for electrochromic device rejuvenation”, has been published in the international journal Matter.
Figure 1. Ion detrapping in amorphous WO3 thin film under photo-electrochemical synergistic detrapping
The research team developed a new ion detrapping approach known as photo-electrochemical synergistic detrapping. Their findings showed that ultraviolet (UV) light irradiation combined with bias can achieve performance restoration for electrochromic oxides and devices. This study primarily focused on amorphous WO3 thin films and found that the photo-electrochemical synergistic method can rejuvenate the performance of amorphous WO3 thin films in a safe potential range. The wavelength and power of applied UV light, bias, and duration of photo-electrochemical synergistic detrapping can affect the ion detrapping effect. Additionally, the valley observed in the current density profile during the photo-electrochemical synergistic detrapping process can be considered a sign of ion detrapping.
Figure 2. Photo-electrochemical synergistic detrapping for performance restoration on a full electrochromic device
The study also indicates that photo-electrochemical synergistic detrapping (285 nm + 4.0 V) can rejuvenate other cathodic electrochromic oxides such as Nb2O5, TiO2, and Ta2O5. When using a wavelength of 405 nm, UV light can penetrate ITO glass. Therefore, 405nm+bias can rejuvenate the electrochromic performance of a full device with a configuration of glass/ITO/WO3/electrolyte/NiO/ITO/glass.
The finding provides a new strategy for extending the lifespan of electrochromic devices and other electrodes or devices operating based on ion intercalation.
Qinqi Zhou, a former master’s student from the Department of MSE at SUSTech and currently a Ph.D. student at Lund University, is the first author of the paper. Professor Rui-Tao Wen is the corresponding author. Other co-authors from the Department of MSE include doctoral student Peipei Shao, Dr. Renfu Zhang, former master’s student Siyuan Huang, Dr. Yiwen Zhang, Dr. Ying Zhu, and master’s student Menghan Yin, as well as Professor Gunnar Niklasson from Uppsala University.
Paper link: https://doi.org/10.1016/j.matt.2024.09.021
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