A UK-based micro-engineering specialist says the commercial development of flexible OLEDs is now “a large step closer”, thanks to the recent completion of a project in which it was involved.
Epigem has played a key role in an EU project to deliver a new form of lighting, the so-called flexible OLED (Organic LED) as a member of the ‘Flex-o-Fab’ consortium.
The Redcar-based company supplied substrates that were used to evaluate the mechanical properties of amorphous zinc-tin oxide (ZTO) and polycrystalline aluminium-doped zinc oxide (AZO) films that form a part of the OLED anode. These transparent conducting oxide (TCO) films were deposited onto the substrates with and without embedded metal grids.
This involved producing the anode film based on Epigem’s existing Epimesh product. Epimesh film has been developed as a flexible electrode (anode/cathode) with very low sheet resistance combined with high optical transparency.
The film comprised an ultra-fine metal mesh embedded into a polymer coating which is adhesively bonded onto one side of a flexible carrier film. Surface resistance is very low, typically in the range 0.4 to 1.5 ohm/square, depending on the mesh pitch. Light transmission through the metal grid and polymer layers is typically above 90 percent.
Two types of flexible substrates were used in the study by Flex-o-Fab partner EPFL, based on a 125 µm thick PET foil coated with 10 µm thick UV-cured adhesive layer followed by 4 µm thick epoxy resin layer, without and with a hexagonal nickel + gold grid (PET and PET-Ni/Au grid respectively). The 6 µm wide and 4 µm thick metal grid lines were embedded in the epoxy layer, forming a hexagonal grid with a 300 µm pitch size.
Resistance to mechanical bending or stretching is an important parameter when developing electrodes for flexible applications. Micro-crack formation and delamination of thin-film TCOs under mechanical load degrade the electrical and optical performance of the device and may lead to further degradation with the formation. Epigem says its embedded electrodes significantly improved the performance of the TCOs under mechanical stress when compared to non-embedded configurations
The Flex-o-Fab project created a pilot-scale manufacturing chain for flexible OLEDs, and used it to develop reliable production processes. Funded through the EU’s 7th Framework Programme (FP7-ICT-2012, grant 314362), the project strengthened Europe’s leading position in the lighting industry by achieving significant progress towards making flexible OLEDs a commercial reality, opening the doors for many new forms of lighting.
Flex-o-Fab is a collaborative research project between twelve European companies and organisations, including Epigem.
Tim Ryan, Managing Director of Epigem, said: “This has been a fantastic project and brings commercial development of flexible OLEDs a large step closer. We are really excited to have been involved in these innovative developments and that our Epimesh conducting film performed so effectively in increasing our understanding the applications of roll-to-roll lighting foils.”