Polymer-based OLEDs (organic light-emitting devices) have been held out as a kind of Holy Grail in lighting and display applications. Part of their unachievable-quest notoriety stems from the fact that they are expensive in part due to the complex processing involved. Nonetheless, they do possess the magical feature of being flexible.
Researchers at the University of California Los Angeles (UCLA) have developed just such an OLED material that can be twisted and folded and even stretched while remaining lit the entire time and could become the template for all future polymer OLEDs.
"Our new material is the building block for fully stretchable electronics for consumer devices," said Qibing Pei, a UCLA professor of materials science and engineering and principal investigator on the research, in a press release. "Along with the development of stretchable thin-film transistors, we believe that fully stretchable interactive OLED displays that are as thin as wallpaper will be achieved in the near future. And this will give creative electronics designers new dimensions to exploit."
The material, which was described in the journal Nature Photonics ("Elastomeric polymer light-emitting devices and displays"), owes at least part of its remarkable stretching capabilities to new transparent electrodes the researcher made out of silver nanowires that have been inlaid into the polymer.
Silver nanowires are currently being market by companies like Cambrios Technologies and Blue Nano for use as a replacement to indium tin oxide (ITO) as a transparent conductor to control display pixels.
In this latest application, the UCLA researchers found that when a single layer of an electro-luminescent polymer blend is sandwiched between the silver nanowire electrodes it was possible for the OLED to bend and stretch at room temperature.
As you can see from the video below, the researchers are able to bend and stretch the OLED into every conceivable shape and do it while in normal ambient conditions.
"The lack of suitable elastic transparent electrodes is one of the major obstacles to the fabrication of stretchable display," said Jiajie Liang, a postdoctoral scholar, in a press release. "Our new transparent, elastic composite electrode has high visual transparency, good surface electrical conductivity, high stretchability and high surface smoothness — all features essential to the fabrication of the stretchable OLED."
While the video demonstrates an OLED with just a solid block of light, the researchers have shown that they can create an OLED made up of different pixels, which opens up the possibility of stretch displays as well as new kinds of lighting.
The researchers were able to accomplish this pixel capability by arranging the silver nanowire-based electrodes into a cross-hatched pattern made up of one layer of columns and one layer of rows.
"While we perceive a bright future where information and lighting are provided in various thin, stretchable or conformable form factors, or are invisible when not needed, there are still major technical challenges," Pei conceded in the press release "This includes how to seal these materials that are otherwise sensitive to air. Researchers around the world are racing the clock tackling the obstacles. We are confident that we will get there and introduce a number of cool products along the way."