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.