New Stable Cathode Materials for OLEDs (Phase I)

Investigating Organization
International Technology Exchange

Principal Investigator(s)
Terje Skotheim, taskotheim@aol.com, (520) 299-9533

Subcontractor
None

Funding Source
Small Business Innovation Research

Award
DOE Share: $99,800

Contract Period
7/1/03 - 4/30/04

NAC (nanostructured amorphous carbon) materials can be made electroactive by “doping” with a wide range of elements and compounds. The materials are deposited in a vacuum using plasma-enhanced chemical vapor deposition (PECVD) with the substrate at or near room temperature. The films can be deposited on a wide range of substrates, including polymeric and other organic substrates.

NAC films are dense and can be made pinhole-free at a thickness below 1 mm. They have excellent properties as corrosion protection coatings, implying that these films are effective barriers to water and oxygen. The work function can be varied by doping with elements with different electronegativities.

During Phase I, OLEDs were fabricated with a 100 nm thick emitter layer of Alq3 and a PEDOT:PSS hole conducting layer on ITO. The top layer was an Al-doped NAC cathode layer. The performance of these OLEDs were compared with that of OLEDs made with evaporated Al metal films as cathodes. Additionally, OLEDs were made in the reverse order with the emitter layer deposited on top of the NAC cathodes and with a thin, semi-transparent Au film as anode. The results fulfilled the objective of demonstrating the proof-of-principle that NAC coatings can be used as cathode materials. The Al-NAC cathodes had a turn-on voltage of ~8V vs. ~4V for cells with evaporated Al metal cathodes.

In addition, atomic force microscopy of the NAC coatings revealed that the ~1mm coatings that were used were atomically smooth and free of pinholes.

Content dated 2/08