Details

Autor(en) / Beteiligte

• Lee, Tsung-Hsun
• Huang, Jung-Chun-Andrew
• Pakhomov, Georgi L'vovich
• Guo, Tzung-Fang
• Wen, Ten-Chin
• Huang, Yi-Shun
• Tsou, Chuan-Cheng
• Chung, Chia-Tin
• Lin, Ying-Chang
• Hsu, Yao-Jane

Titel

Organic-Oxide Cathode Buffer Layer in Fabricating High-Performance Polymer Light-Emitting Diodes

Ist Teil von

• Advanced functional materials, 2008-10, Vol.18 (19), p.3036-3042

Ort / Verlag

Weinheim: WILEY-VCH Verlag

Erscheinungsjahr

2008

Quelle

Wiley Online Library All Journals

Beschreibungen/Notizen

• Spin‐casting or thermal evaporation in vacuum of a salt‐free, neutral, organic‐oxide ultra‐thin film as a buffer layer with an aluminum (Al) cathode has become an alternative approach for fabricating high‐performance organic and polymer light‐emitting diodes (O/PLEDs). [Guo et al., Appl. Phys. Lett. 2006, 88, 113501 and Appl. Phys. Lett. 2006, 89, 053507] The electroluminescence efficiency of phenyl‐substituted poly(para‐phenylene vinylene) copolymer‐based PLEDs is 0.16 cd A−1 when Al is used as the device cathode, but is approximately two orders of magnitude higher, 14.53 cd A−1, when an organic oxide/Al composite cathode is used. The polymer/metal junction in PLEDs with and without depositing an ultra‐thin organic oxide interlayer is studied by X‐ray photoelectron spectroscopy. Experimental results indicate that the deposition of an Al electrode causes the oxidation at the surface of the light‐emissive polymer layer. Introducing an organic‐oxide cathode buffer layer suppresses the oxidation and the diffusion of the Al atoms into the functional polymer layer. The formation of a carbide‐like (negative carbon) thin layer, which accompanies interfacial interactions, is critical to the injection of electrons through the Al cathode. The balanced charge injection is responsible for the substantially improved device performance. This process is specific to the organic oxide/Al interface, as revealed by a comparison with similar device configurations that have Ag as the electrode, in which no significant interaction in the interface is observed. The origin of ethylene‐oxide functionalized cathode buffer layer in fabricating high‐performance PLEDs is discussed. The reaction of PEGDE layer with thermally evaporated Al suppresses the diffusion of Al into the light‐emissive polymer layer, potentially inhibiting oxidization and generation of metal‐induced EL quenching sites near the recombination zone. The salt‐free, neutral PEGDE interfacial layer can be easily integrated with manufacturing procedures.