Degradation Mechanism of Organic Light-emitting Diodes

Abstract

Organic light-emitting diodes （OLEDs） have attracted much attention due to their huge potential applications in the field of lighting and display. In the past three decades， the efficiency and lifetime of OLED devices have been greatly improved. However， improving device lifetime is still one of the urgent problems to be solved for commercial applications. In order to further improve the stability of the device， it is necessary to study the intrinsic degradation mechanism intensively. In this paper， using examples in both small molecule and polymer OLEDs， the degradation mechanisms in two types of devices are examined. Some of the extrinsic and intrinsic degradation mechanisms in OLEDs are reviewed， and recent works on degradation studies of both small-molecule and polymer OLEDs are presented. For small-molecule OLEDs， some studies show that the degradation of devices is consistent with defect formation due primarily to exciton-polaron annihilation reactions， others show that degradation is closely linked to interactions between excitons and positive polarons， which lead to its aggregation near the interface and thus destroy the interface. For polymer OLEDs， the luminance loss and voltage rise dependence on time and current density are consistent with hole trap formation due to exciton-free hole interactions. Meanwhile， this paper summarizes some current effective solutions to increase the lifetime， which will play a positive role in the subsequent development of OLED devices with higher efficiency and longer lifetime.