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SPIE Professional October 2015

Advances in flexible OLEDs

R&D Highlights: Recommended Reading

Researchers at Pohang University of Science and Technology (Republic of Korea) have demonstrated good electrical, optical, and mechanical performance in various organic materials that may make commercial use of organic LED (OLED) technology more feasible and closer to implementation.

cover of Journal of Photonics for EnergyReporting in the Journal of Photonics for Energy, the researchers discuss advances in three key areas for OLEDs — flexible electrodes, flexible encapsulation methods, and flexible substrates — that are desired for the next-generation of solid-state lighting.

OLEDs show promise as a future light source because of their thinness, light weight, energy efficiency, and use of environmentally benign materials. Companies such as Philips and LG Chemical have begun producing flat OLED panels that produce non-glare, UV-free light but very little heat, with no need for lampshades or diffusers.

If those panels were flexible, the technology could be bent into shapes, fit the interior or exterior curves of vehicles, even be incorporated into clothing.

“The future trend in OLEDs is to make them on plastic substrates for flexibility, durability, and light weight,” says SPIE Fellow Franky So, a professor at North Carolina State University (USA) and an associate editor of the journal.

Figure from article in Journal of Photonics for EnergyIn “Flexible organic light-emitting diodes for solid-state lighting,” Min-Ho Park and coauthors tested a variety of transparent electrodes as flexible alternatives to currently available devices based on indium tin oxide, which is brittle and expensive.

The schematic illustration of OLED structures, above, shows (a) conventional glass lid and (b) thin-film encapsulation.

The researchers identified next steps needed to make flexible solid-state lighting commercially feasible:

  • Develop a flexible electrode with high electrical conductivity, high bending stability, few defects, smooth surface texture, and high work function
  • Reduce the water-vapor transmission rate of materials used, to counter the vulnerability of OLEDs to moisture

OLEDs produce light by sending electricity through one or more thin layers of an organic semiconductor. The semiconductor is sandwiched between a positively charged electrode and a negatively charged one. These layers are deposited on a substrate and protected from exposure to air by a thin layer of encapsulants (traditionally glass).

The Pohang team demonstrated good performance with flexible electrodes fabricated using graphene, conducting polymers, silver nanowires, and dielectric-metal-dielectric multilayer structures.

Coauthors are Tae-Hee Han, Young-Hoon Kim, Su-Hun Jeong, Yeongjun Lee, Hong-Kyu Seo, Himchan Cho, and Tae-Woo Lee.

The Journal of Photonics for Energy covers fundamental and applied research areas focused on the applications of photonics for renewable energy harvesting, conversion, storage, distribution, monitoring, consumption, and efficient usage.

Editor-in-Chief Zakya Kafafi is adjunct professor in electrical and computer engineering at Lehigh University.

The journal is published digitally in the SPIE Digital Library, which contains more than 430,000 articles from SPIE journals, proceedings, and books, with approximately 18,000 new research papers added each year.

Source: dx.doi.org/10.1117/1.JPE.5.053599


DOI: 10.1117/2.4201510.09

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