Effects of hole carrier injection and transport in organic light-emitting diodes

In this paper, we examine the effects of hole carrier injection and mobility on both the electroluminescence (EL) quantum efficiency and the operating voltage of bilayer organic light-emitting diodes (OLED's). We find that hole-injection is limited by the nature of the hole injecting interface and significantly affects the operating voltage, but not the quantum efficiency of the OLED. Hole mobility is found not to affect the device quantum efficiency. We demonstrate the characteristics of an ideal ohmic contact by measuring space-charge-limited currents in a trap-free hole transporting polymer layer.