Regensburg 2007 – scientific programme

Parts | Days | Selection | Search | Downloads | Help

DS: Fachverband Dünne Schichten

DS 16: Organic Light Emitting Diodes (SYOE 9)

DS 16.4: Talk

Wednesday, March 28, 2007, 15:15–15:30, H32

Lifetime enhancement of organic top and bottom light-emitting diodes — •Michael Hofmann, Philipp Wellmann, Tobias Canzler, and Jan Birnstock — Novaled AG, Tatzberg 49, Dresden, Germany

Recent efforts regarding the development of organic light-emitting diodes (OLEDs) resulted in a major stability enhancement. Crucial factors are the improved metal electrodes and the introduction of an edge passivation layer preventing electrical shorts at the border of the anode contact. We present latest data on long-living top-emitting OLEDs with doped transport layers reaching 100.000 h for green and 12.000 h for blue devices at 500 cd/m^2.

Still the lifetime of blue OLEDs remains challenging because the stability of the emitter material itself is limited. Additionally, structures which generate high energy excitons place further demands on the adjacent transport and interlayer materials. A sensing layer method is applied to locate the position of the recombination zone. It contains a green emitter selected to quench blue excitons. The thin sensing layer is sandwiched in the predominantly electron-conducting emission layer (EML). In case of a high electron supply, the recombination zone is close to the EBL/EML interface and 6 nm wide. We conclude that this can be shifted away from the interface by an adjusted electron supply. The reduced stress on the surrounding organic materials and the broadening of recombination zone to 15 nm increases device stability. The presented blue bottom-emitting OLED with modified electron supply has a significantly increased lifetime of 18.000 h at 500 cd/m^2.