Reliability comparison of BTEL and bilayer organic LEDs

Organic structures consisting of two distinct layers (bilayer), a hole transport layer and an electron transport/emitter layer are compared to structures using a bipolar transport and emitting layer (BTEL). Reverse bias and different duty cycle did not significantly affect reliability. The BTEL structure had significantly improved reliability compared to the bilayer structure. The relative change in device voltage was found to be linearly proportional to the relative change in luminance and the constant of proportionality was a function of the contact. This constant of proportionality can be used as a figure of merit for voltage increase during operation. The BTEL structure also gives improved reliability at elevated temperature.