Led by Professor Hideo Fujikake and Associate Professor Takahiro Ishinabe of the School of Engineering, the team overcame OLEDs' instability challenges by turning back to well established and stable LCD materials, albeit replacing the conventional thick and rigid glass substrates with plastic films only a few micrometres thin.
LC materials are cheap, do not deteriorate even when poorly protected by these flexible substrates and there are already well established production methods for large-area displays. The challenge to make rollable displays was to prevent uneven deformation of the display (and image distorsion) upon bending, due to the LC-filled gap between the two substrates.
The researchers developed a super-flexible LC device by bonding two ultra-thin transparent polyimide substrates about 10μm thick each (similar to food-wrapping cling film), maintained appart with robust polymer wall spacers.
The polymer wall spacers bonding substrates were formed by irradiating a twisted-alignment LC layer including monomer component with patterned ultra-violet light through single thin substrate. This allowed them researchers to stabilize the ultra-thin substrates via small pitch polymer walls.
They also demonstrated that the device uniformity could be kept without breaking spacers even after a roll-up test to a curvature radius of 3mm for rollable and foldable applications. The researchers envisage that large area high-resolution rollable displays could be manufactured at a much better yield than OLEDs, saying that fine pixel structures, including transparent electrodes and colour filters could be formed on top of these films.
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