Aging effect on balance of carrier injection in polymer light-emitting diodes

We propose an approach to study the oxidation effect on the degradation process of phenyl-substituted polymer based light emitting diodes (LEDs) using acceleration aging of device in air. The poly(styrene sulfonate)-doped poly(3,4-ethylene dioxythiophene) (PEDOT) is used as hole transporting layer. We have made conventional balanced electron-hole injection together with electron and hole injection dominant devices. The acceleration aging of these devices in air was performed at a fixed current density that produces the maximum electroluminescence (EL) efficiency of the corresponding LEDs. The results show that the fast decrease of electron current in these devices with regard to the aging in air was mainly responsible for reduction of EL efficiency. This implies that the degradation of the polymer LED is due to the deterioration of the cathode contact for carrier injection.