Degradation of organic electroluminescent devices. Evidence for the occurrence of spherulitic crystallization in the hole transport layer

Electroluminescent devices show major promise for the next generation of flat panel displays. These devices consist of a hole transport material in conjunction with an electron transport material, sandwiched between electrodes of different work function. This paper provides the first evidence of the crucial role of spherulitic crystallization of the hole transport material in the degradation of organic electroluminescent, devices. The evolution and growth of nonemissive dark spots are studied using a combination of atomic force microscopy, electron microscopy, and energy-dispersive X-ray analysis. Spherulites are imaged and shown to nucleate from a 1 mu m defect on the indium tin oxide anode. These spherulites cause the device to delaminate, and this results in a decrease in the luminescence around the defect and, finally, the failure of the electroluminescent device.