Effect of poly(3,4-ethylene dioxythiophene) on the built-in field in polymer light-emitting diodes probed by electroabsorption spectroscopy

Here we report electroabsorption (EA) measurements on light-emitting diodes (LEDs), fabricated with poly(4-4'-diphenylene diphenylvinylene) (PDPV) as the emissive layer in indium-tin oxide (ITO)/poly(3,4-ethylene dioxythiophene) (PEDOT):polystyrene sulfonic acid (PSS)/PDPV/Ca-Al and ITO/PDPV/Ca-Al structures. In the latter structure, the built-in potential, determined from nulling the EA signal, corresponds to the difference between the work functions of the electrodes. By incorporating a PEDOT:PSS film between the ITO electrode and the emissive layer we find that such a built-in voltage increases by 0.5 V. The correspondent lowering of the anodic barrier height at the PDPV interface is likely to be responsible for the improvement in device performance. (C) 2000 Elsevier Science S.A. All rights reserved.