Photoluminescence characteristics of organic molecules in the accelerated aging organic light-emitting diodes

We have employed the photoluminescent (PL) spectrum of an accelerated aging organic light-emitting diode (OLED) to investigate the mechanisms of molecular decomposition in the whole and each organic functional layer using a bevel-cutting and peel-off method. The devices were operated at a constant current density of 37mA/cm(2) and 70 degrees C until the luminance reached a half of the initial luminance. The results show a slight or even negligible degradation in PL intensity compared to unbiased devices, indicating that little cracked molecular structure and destroyed host-guest transfer mechanism occurred in organic materials of the biased device Scanning electron microscopy images of devices with bias demonstrated that the delamination at the interfaces of organic layers/Al and light-emitting layer/hole transport layer occurs. We concluded that the charges accumulated at the interface of the heterojunction formed between adjacent organic layers with different energy barriers in or near the emissive layer, as well as the cathode/organic layer, should be mainly responsible for the degradation of OLEDs. (C) 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim