Organic light emitting devices with enhanced operational stability at elevated temperatures

Temperature dependence of electroluminescence degradation is studied in organic light emitting devices containing an emitting layer composed of a mixture of N,N′-di(naphthalene-1-yl)-N,N′-diphenyl-benzidine and tris(8-hydroxyquinoline)aluminum (AlQ3), doped with quinacridone green emitter. The emitting layer is sandwiched between hole and electron transport layers. Electroluminescence degradation in time is measured on devices operated at temperatures ranging from 22 to 100 °C. The devices demonstrated remarkable stability, even at elevated temperatures. From accelerated degradation tests, a device half-life of about 78 500, 18 700, and 8600 h can be projected for devices operated at 22, 70, and 100 °C, respectively, at an initial device luminance of 100 cd/m2. Activation energy for device degradation of 0.27 eV is consistent with the recently proposed degradation mechanism based on the unstable cationic AlQ3 species.