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Transparent Display Shows Smooth Transitions over Broad Color Spectrum

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Researchers from Jilin University developed a transparent glass display with a high white-light contrast ratio that is able to smoothly transition between a broad spectrum of color when stimulated with electricity. The technology overcomes hurdles that face existing electrochromic devices by capitalizing on the interactions between metal ions and ligands.

Electrochromic displays are able to continuously and reversibly manipulate the properties of light through the application of electricity. These devices have been proposed for use in a wide variety of applications, including in windows, electronic price tags, billboards, rear-view mirrors, augmented reality, and artificial irises. Current devices, however, tend to have low contrast ratios, especially for white light, poor stability, and limited expression of color.

The Changchun team took a simple chemical approach; it used metal ions to induce a variety of switchable dyes to adopt particular structures. When the ions achieve the desired configurations, they are stabilized. To trigger color changes, the electrical field is applied to switch the valences of the metal ions, forming new bonds between the ions and the molecular switches.

“Different from the traditional electrochromic materials, whose color-changing motifs and redox motifs are located at the same site, this new material is an indirect-redox-color-changing system composed by switchable dyes and multivalent metal ions,” said Yu-Mo Zhang, associate professor of chemistry at Jilin University.

The researchers fabricated an electrochromic device by injecting a material containing metal salts, dyes, electrolytes, and a solvent into a sandwiched device with two electrodes and adhesive as spacers. They then put the device through a series of tests to evaluate its light spectrum and electrochemical properties. The device produced cyan, magenta, yellow, red, green, black, pink, purple, and gray-black while maintaining a high contrast ratio.

The prototype was also able to shift seamlessly from a colorless transparent display to black, a useful property for commercial applications, with high coloration efficiency, low transmittance change voltage, and a white-light contrast ratio that would be suitable for real transparent displays.

“The low cost and simple preparation process of this glass device will also benefit its scalable production and commercial applications,” Zhang said.

The researchers plan to optimize the device’s performance to meet the requirements of high-end displays for real-world application. Additionally, to avoid leakage of its liquid components, they intend to develop improved fabrication technologies that are able to produce solid or semi-solid electrochromic devices.

“We are hoping that more and more visionary researchers and engineers cooperate with each other to optimize the electrochromic displays and promote their commercialization,” Zhang said.

The research was published in Chem (www.doi.org/10.1016/j.chempr.2021.02.005).


Photonics Spectra
May 2021
GLOSSARY
ion
An atom that has gained or lost one or more electrons and, as a result, carries a negative or positive charge.
color
The attribute of visual experience that can be described as having quantitatively specifiable dimensions of hue, saturation, and brightness or lightness. The visual experience, not including aspects of extent (e.g., size, shape, texture, etc.) and duration (e.g., movement, flicker, etc.).
contrast
The apparent difference in brightness between light and dark areas of an image. For a light target against a dark background, contrast is computed as follows: where Lt is the luminance of the target and Lb is the luminance of the background.
Research & TechnologyDisplayselectrochromicelectrochromic deviceselectrochromic windowschemistryionionscolorContrastChemJilin UniversityYu-Mo ZhangAsia-PacificTech Pulse

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