Light-emitting electrochemical cells from oligo(ethylene oxide)-substituted polythiophenes:: Evidence for in situ doping

Oligo(ethylene oxide)-substituted polythiophenes mixed with a salt simultaneously act as a light-emitting layer and solid-state electrolyte in light-emitting electrochemical cells (LECs), Under an applied bias, p-doping of the electroluminescent polymer takes place at the anode. At the opposite electrode the cathode material is reduced. Since the work function of the electrode material is less important in an LEG, all-polymer devices, with poly(3,4-ethylene-dioxythiophene) as anode and cathode, can be built. The doping processes have been studied by in situ absorption spectroscopy in both sandwich configuration as well as on planar electrochemical cells.