Researchers at Linköping University have developed a method that may lead to new types of displays based on structural colors. The discovery opens the way to cheap and energy-efficient color displays and electronic labels. Structural colors can arise when light is internally reflected inside the material on a scale of nano­meters. This is usually referred to as inter­ference effects. An example found in nature are peacock feathers, which are funda­mentally brown but acquire their charac­teristic blue-green sheen from small structural features.

The color of each light-emitting diode depends on the molecules from which it is built, or in other words, its pigment. However, it is relatively expensive to manu­facture light-emitting diodes, and the global use of emissive displays consumes a lot of energy. Another type of display, reflective displays, is therefore being explored for purposes such as tablet computers used as e-readers, and elec­tronic labels. Reflective displays form images by controlling how incident light from the surroun­dings is reflected, which means that they do not need their own source of illu­mination. However, most reflective displays are intrin­sically mono­chrome, and attempts to create color versions have been rather complicated and have sometimes given poor results.

Shangzhi Chen at the Laboratory of Organic Electronics at Linköping University describes a new type of dynamic structural color image. “We have developed a simple method to produce structural colour images with electrically conducting plastics, or conducting polymers. The polymer is applied at nanoscale thick­nesses onto a mirror by a technique known as vapour phase polymerisation, after the substrate has been illuminated with UV light. The stronger the UV illu­mination, the thicker the polymer film, and this allows us to control the structural colors that appear at different locations on the substrate.”

The method can produce all colors in the visible spectrum. Further­more, the colors can be subsequently adjusted using electrochemical variation of the redox state of the polymer. This function has been popular for monochrome reflective displays, and the new study shows that the same materials can provide dynamic images in color using optical interference effects combined with spatial control of nanoscale thick­nesses. Magnus Jonsson, associate professor at the Labora­tory of Organic Electronics at Linköping University, believes that the method has great potential, for example, for appli­cations such as elec­tronic labels in colour. Further research may also allow more advanced displays to be manu­factured. 

“We receive increasing amounts of information via digital displays, and if we can contri­bute to more people gaining access to information through cheap and energy-efficient displays, that would be a major benefit. But much research remains to be done, and new projects are already under way”, says Magnus Jonsson. (Source: LIU)

Reference: S. Chen et al.: Tunable Structural Color Images by UV-Patterned Conducting Polymer Nanofilms on Metal Surfaces, Adv. Mat., online 5 July 2021; DOI: 10.1002/adma.202102451

Link: Laboratory of Organic Electronics, Dept. of Science and Technology (ITN), Linköping University, Norrköping, Sweden