Researchers have designed polymers that can be patterned directly with light into OLED pixels far smaller than those used in today's displays - a step that could make screens and sensors dramatically sharper.
Making the pixels in an OLED display smaller has always run into the same wall: the methods used to pattern high-performance light-emitting materials don't work well at very small scales, and materials that do respond to light-based patterning have generally performed too poorly for real devices.
co-led by , Associate Professor of Polymer Chemistry at the Department of Chemistry, Faculty of Science, University of Helsinki, and Professor at ETH Zurich, addresses this by rethinking the polymers themselves. Senior lecturer from RMIT provided the theoretical support by computational modelling.
The team built star-shaped polymers with red, green or blue light-emitting cores, made using a controlled radical polymerization method called ATRP. Each arm of the polymer carries a segment that can crosslink when exposed to light. Wherever light hits the material - whether from a UV lamp or an electron beam - the polymer locks into place, while the surrounding, unexposed material can be washed away. Repeating this for each color builds a full-color pixel array directly, without the metal shadow masks used in conventional OLED manufacturing.
A hidden bottleneck
While developing the polymers, the team found that a small reactive group left at the end of each polymer chain - a residue of the synthesis process - was quietly dragging down device performance. Deactivating that end group raised the devices' efficiency twentyfold.
"This solved a bottleneck that had kept controlled radical polymerization out of organic optoelectronics," Bao says.
"Polymer structures that were considered unusable in this field for a long time turn out to work - once you deal with the end group."
Toward much sharper pixels
Because the light-patterning approach is compatible with electron-beam lithography, the team was able to fabricate pixels as small as 300 nanometers - roughly 10 to 100 times smaller than pixels in current OLED displays. For comparison, Apple's Vision Pro headset reaches a pixel density of 3,386 pixels per inch with 7.5-micrometre pixels; a 300-nanometre pixel would correspond to about 84,660 pixels per inch, some 25 times finer.
"We've basically developed a new class of long-chain molecules that can be manufactured into OLED pixels using direct light exposure," Bao explains.
"That could enable displays with much higher resolution, and sensors with higher sensitivity, along with other uses in optoelectronic devices."
What's next
The devices' operational lifetime is still shorter than that of materials used in commercial products, and improving this durability is a focus for further work. The team sees potential applications in augmented and virtual reality displays, flexible electronics and sensors.
Bao describes the work as a shift in how polymers are approached in OLED research more broadly, opening the door to polymer structures - and potentially more sustainable materials - that had previously been ruled out for optoelectronics.
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