Department of Physics, Engineering Physics & Astronomy

Department of Physics, Engineering Physics & Astronomy
Department of Physics, Engineering Physics & Astronomy

Studies of long-term and high-temperature operational stability of small molecule based OLEDs

Dr. Zoran D. Popovic
Xerox Research Center of Canada

Date: Wednesday, October 23, 2002
Time: 1:30 PM
Location: Stirling A


Recent advances in organic light emitting devices (OLEDs) led to the realization of many device structures showing enhanced operational stability, with a half-life often well in excess of 10,000 hours. The understanding of the mechanism of device degradation has been accomplished recently, but only for devices using AlQ3 electron transport and emitter molecule. In this presentation, after a general introduction to the OLED field, the experimental evidence for the degradation mechanism of AlQ3 based devices will be reviewed, showing that the hypothesis of an unstable AlQ3+ cation explains a large amount of experimental data. This hypothesis, however, explains not only the room temperature device degradation in time but also sheds light on temperature stability of OLEDs. Dependence of half-life of a series of devices with an emitter layer composed of a mixture of AlQ3 and different hole transport molecules (mixed emitter layer) will be discussed when they are operated at elevated temperatures. These results can also be explained in the framework of an unstable AlQ3+ species. An OLED structure containing a doped mixed emitter layer will be described, which shows extraordinary stability, half-life of 1200 hours at operating temperature of 70 C and initial luminance of 1650 cd/m2.