Combination of a polyaniline anode and doped charge transport layers for high-efficiency organic light emitting diodes

Up to now, most organic light emitting diodes (OLEDs) have utilized inorganic materials as transport anodes. In this study, we show that conductive polymers are suitable for this purpose as well. Polyaniline anodes, with a conductivity of 200 S/cm, are used to inject holes into the adjacent organic layers. Due to electrical doping of the electron and hole transport layer with an intrinsic emission layer sandwiched in between (pin-OLED), the devices reach high luminance at low voltage. The phosphorescent emitters Ir(MDQ)(2)(acac) and Ir(ppy)(3), as well as the fluorescent emitter Spiro-DPVBi, are implemented within pin-OLEDs using a polyaniline anode. By the use of different host materials, a green double-emitting OLED is demonstrated and compared to the corresponding single emission layer device. Furthermore, a white OLED combining fluorescent and phosphorescent emitting layers is presented, reaching 8.9 lm/W at 1000 cd/m(2). The results demonstrate an efficient charge carrier injection from the polymer into the p-type doped hole transport layer, leading to good power efficiencies of the OLEDs. (c) 2007 American Institute of Physics.