Pillalamarri Srikrishnarka
Dielectica traverses through the literature on this topic – and summarizes as they appear.
Key words: Electrochromic device, Vanadium Oxide, Flexible screen
Chennai, India: Whenever we hear the word photochromic device, what comes to our mind is photochromic glasses. The glasses change color to black/brown in the presence of sunlight and return to normal colorlessness in its absence. This active switching protects the users/wearers from the harsh sunlight and soothes their sight. A stimulus of light is given which in response a color change is observed, this response can be activated by other stimuli one such is potential, called as electrochromic device. Electrochromic devices are far more appreciable than conventional photochromic devices due to their vast applications. Especially for smart displays, flexible screens, military camouflage and etc. Conventionally, tungsten oxide particles have been used for electrochromic displays since their discovery back in 1969. “They possess high transmittance contrast, cyclic stability against high temperature and strong light.”
Color tunability of these particles is possible by doping, however, the entire process is time-consuming, could be expensive due to the need of additional material and also affect the overall transmittance of the system.
In this regard, Wang et al., scientists from the University of Science and Technology, China, proposed a simple yet, and scalable method for the fabrication of highly tunable nanowire assembly-based electrochromic devices. Initially, they have synthesized tungsten oxide (W18O49) nanowires and vanadium oxide (V2O5) nanowires. These nanowires were then mixed and allowed to self-assemble on a fluorine-doped indium tin oxide coated glass. This process of self-assembly was accomplished by the Langmuir-Blodgett method. Upon drying, the coated glass was tested under various external potentials varying from – 0.5 to 2 V.
Upon application of potential, drastic changes in the chromic response were observed based on the ratio of W18O49 and V2O5 mixture. Switchability of the colors were visualized as orange, green and gray, which could be possible by varying the potential. Furthermore, transmittance of the film was tuned by changing the concentration of active material. Having such precise control over switchability and transmittance, these assembled nanowires potentially could be used in the display screen and by varying the substrates, they could be potentially be used as flexible screens also.
References:
[1] J. L. Wang, J. W. Liu, S. Z. Sheng, Z. He, J. Gao, and S. H. Yu, Nano Lett. 2021, 21, 21, 9203–9209