Molecular organic light-emitting diodes with temperature-independent quantum efficiency and improved thermal durability

We demonstrate efficient and thermally stable molecular light-emitting diodes based on a multilayered structure that consists of two hole transport layers with high glass-transition temperatures, and an emitting layer doped with a highly fluorescent dye. Stable device operation was achieved up to 90 degrees C. By using an emitting layer doped with a highly fluorescent dye, the electroluminescence quantum efficiency reaches 2.2% and does not decrease with increasing temperature in contrast to a device with an undoped emitting layer. The luminous efficiency at 100 cd/m(2) increases from 4.6 lm/W at room temperature to 7.5 lm/W at 90 degrees C. The half-decay time of the initial luminance (similar to 800 cd/m(2)) of the devices is 3200 h (room temperature) and 200 h (80 degrees C) at constant dc current (10 mA/cm(2)). (C) 1999 American Institute of Physics. [S0003-6951(99)01747-7].