Temperature dependence of electroluminescence degradation in organic light emitting devices without and with a copper phthalocyanine buffer layer

Temperature dependence of electroluminescence degradation was investigated in two types of organic light emitting devices (OLEDs) based on tris(8-hydroxyquinoline) aluminum (AlQ3) emitter molecule, one without and another with copper phthalocyanine (CuPc) buffer layer at the hole-injecting contact interface. Electroluminescence degradation in time was measured for devices operated at 22 and 70 °C. Results unexpectedly showed that devices without the CuPc buffer layer demonstrated negligible change in half-life when operated at 22 or 70 °C, while devices with the CuPc layer showed the expected decrease in half-life when the temperature was increased. The results are explained within the framework of recently proposed OLED degradation mechanism, which identifies AlQ3 cations as unstable, leading to device degradation.