(Image source: ualberta laboratory official website)
According to foreign media reports, multi-color electrochromic displays are one of the very versatile applications because they do not need power to maintain a colored state. However, when operating a traditional electrochromic display, the simultaneous coloring of the counting layer will limit the color superposition effect, and an external voltage is required to trigger the coloring/decoloring process. Therefore, the traditional electrochromic display technology cannot achieve net zero energy consumption.
A research team led by Professor Abdulhakem Y. Elezzabi and Dr. Haizeng Li from the Ultrafast Optics and Nanophotonics Laboratory (Ultrafast Optics and Nanophotonics Laboratory) of the University of Alberta, Canada, developed a novel transparent multicolor electrochromic display concept. Sodium ion stabilized vanadium oxide (SVO) nanorods are used as electrochromic materials. SVO nanorods are compatible with simple rod coating methods, mixed with cellulose, and used to prepare electrochromic films. Due to the oxidizing nature of SVO, the added cellulose can be fully decomposed at low temperatures to avoid affecting electrical conductivity.
When inserting and extracting Zn2+, the SVO film exhibits reversible multi-color switching (orange⇄yellow⇄green). Inserting Zn2+ is full color/discharging, and extracting Zn2+ is decoloring/charging. Using this three-color electrochromic response of the SVO film, the zinc foil is sandwiched between two SVO electrodes to form an electrochromic display. This type of display can independently operate the electrochromic electrodes on the top and bottom, and use double electrochromic layers in the same or different color states to provide additional configuration flexibility for the device. Therefore, through the color superposition effect, the color range can be greatly expanded. The Zn-SVO electrochromic display constructed by the color superposition effect can switch a variety of colors, such as orange, amber, yellow, brown, and yellow-green, while maintaining a translucency of more than 30%.
More interestingly, the Zn-SVO electrochromic display has an off-circuit potential of 1.56 V, so self-coloring behavior can occur and it has an energy recovery function. This cut-off potential is generated by the oxidation-reduction potential difference between the zinc foil and the SVO electrode, which provides the driving force for activating zinc oxidation, for example, the driving force for stripping Zn into the electrolyte and reducing the SVO film, That is, insert Zn2+ into SVO. Therefore, the built-in voltage allows the display to switch from orange to green, including four intermediate colors, which is caused by the reduction of the SVO film when the LED is powered.
Based on these key characteristics, electrochromic displays have been significantly improved. Zn-SVO electrochromic displays are expected to be used in switchable filters, electrochromic tunable micro-optics and transparent displays. (Elisha)
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