Electrochemically doped polymeric anode for improving the performance of molecular organic light-emitting diodes

The doping level of spin-coated poly(ethylenedioxythiophene):poly(styrenesulfonate) (PEDT:PSS) films was adjusted quantitatively by an electrochemical doping/dedoping process in toluenesulfonic acid containing solution. The increase in doping level leads to an improvement of hole injection from the PEDT:PSS/ITO (indium-tinoxide) anode to the hole transporting layer, which is attributed to the enhanced work function of PEDT. The performance of vapor-deposited tri(8-hydroxyquinoline) aluminum (Alq(3)) based organic light-emitting devices with these anodes is shown to depend strongly on the doping level of PEDT: PSS. The device, built on a highly oxidized anode by electrochemical modification (electrochemical equilibrium potential of 0.59 V vs Ag/AgCl), shows a reduction of the operating voltage by 2 V, as well as remarkable enhancement of the luminance compared to the device on a pristine polymer anode. (C) 2003 American Institute of Physics.