Unlike high-power consuming conventional displays that emit light, reflective displays or the so-called “electronic paper” use ambient light and consume much less energy. They lack behind, however, in color range and switching speed. Thus, electronic paper technology has been used predominantly for ebook readers and labels that are less demanding of these features. A group of English and Swedish scholars joined forces to overcome the setbacks. In research published in August 2021 in Advanced Materials, a weekly peer-reviewed scientific journal, they introduced a structural color technology that successfully achieved favorable video speed and image quality. The wide color spectrum in conventional displays results from the combination of red, green, and blue (RGB)-filtered subpixels. Under the leadership of Andreas Dahlin from the Department of Chemistry and Chemical Engineering of the Chalmers University of Technology in Gothenburg, Sweden, the researchers explored the potential of structural colors to generate the RGB subpixels in reflective displays. Conventional color is a result of the absorption of light. If an object appears red, it means a dye or pigment absorbs all other colors besides red. Structural color, however, results from the reflection of light from complex colorless nanostructures. Some examples in the natural world include butterflies’ wings and opals. Colors produced by chemical pigments remain unchanged regardless of the angle from which they are viewed. The colors produced by the multi-layered nanostructures, on the other hand, are iridescent; they appear different from different angles. Thus, making structural colors highly suitable for creating colored subpixels. It is important to note that the team did not use the widely popular liquid crystals. Instead, they used a broadband-absorbing polarization-insensitive electrochromic polymer to sustain a high level of reflectivity. The researchers started with thin alumina or aluminum films, on top of which they arranged nanoparticles and added an ultrathin gold coating. The created metamaterials boasted a large surface area and increased optical contrast. To regulate the brightness and visibility, the team finished with an opacity-changing conjugate polymer top coating.

1. Fast-Switching Structural Color to
Revolutionize Low-Power Displays
Andrew Kortyna

2. Introduction
Unlike high-power consuming conventional displays that emit light,
reflective displays or the so-called “electronic paper” use ambient light and
consume much less energy.
They lack behind, however, in color range and switching speed. Thus,
electronic paper technology has been used predominantly for ebook
readers and labels that are less demanding of these features.

3. A group of English and Swedish scholars joined forces to overcome the
setbacks. In research published in August 2021 in Advanced Materials, a
weekly peer-reviewed scientific journal, they introduced a structural color
technology that successfully achieved favorable video speed and image
quality.

4. The wide color spectrum in conventional displays results from the
combination of red, green, and blue (RGB)-filtered subpixels. Under the
leadership of Andreas Dahlin from the Department of Chemistry and
Chemical Engineering of the Chalmers University of Technology in
Gothenburg, Sweden, the researchers explored the potential of structural
colors to generate the RGB subpixels in reflective displays.

5. Conventional color is a result of the absorption of light. If an object
appears red, it means a dye or pigment absorbs all other colors besides
red. Structural color, however, results from the reflection of light from
complex colorless nanostructures. Some examples in the natural world
include butterflies’ wings and opals. Colors produced by chemical
pigments remain unchanged regardless of the angle from which they are
viewed. The colors produced by the multi-layered nanostructures, on the
other hand, are iridescent; they appear different from different angles.
Thus, making structural colors highly suitable for creating colored
subpixels.

6. It is important to note that the team did not use the widely popular liquid
crystals. Instead, they used a broadband-absorbing polarization-
insensitive electrochromic polymer to sustain a high level of reflectivity.

7. The researchers started with thin alumina or aluminum films, on top of
which they arranged nanoparticles and added an ultrathin gold coating.
The created metamaterials boasted a large surface area and increased
optical contrast. To regulate the brightness and visibility, the team
finished with an opacity-changing conjugate polymer top coating.

8. When the light resonated in the nanostructure, it reflected the RGB light,
thus making redundant high-energy-consuming light-emitting
components. Furthermore, changes in the thickness of the gold coating
and the thin films allowed for viewing the RGB coloration from any angle.

9. By changing the opacity of the conjugated polymer on top of each
subpixel from black to transparent, the scholars created the desired color
images, and thus, controlled the display. The polymer is black in its
natural state, while the oxidation of its monomers makes it transparent.
To switch between the two states, the researchers applied
electropolymerization, a process during which electrical current causes
the movement of ions within the polymer.

10. By adjusting the main factors influencing the switching, such as the
voltage, ions selection, movement, and monomer oxidation, the team
reached a switching speed of 10 to 50 milliseconds. Metamaterial
nanostructures enhance ion mobility. Thus, using them proved crucial for
achieving such high levels of speed and optical contrast.

11. In addition to the high switching speed, the team registered ultralow
energy consumption of less than one milliwatt per centimeter squared
(<1 mW cm−2), which surpasses even the high energy efficient organic
light-emitting diode (OLED) displays. The power consumption for static
images was also minuscule, less than one microwatt per centimeter
squared (<1 µW cm−2). Furthermore, the speed switching dramatically
increased the device's lifetime to higher than 107 cycles, an order of
magnitude higher than that of modern devices.

12. Dahlin and his team are yet to create a fully functional display utilizing
their technology. They will most probably integrate transistors that will
regulate the switching of the separate subpixels. The scholars are also
exploring ways to minimize the usage of gold in the created
metamaterial.