Light-emitting electrochemical cells based on ruthenium(II) using crown ether as solid electrolyte

Solid-state light-emitting devices have been fabricated from blends of lithium salt/18-crown-6 ether complex with a ruthenium(II) binuclear complex containing 1,6-bis[4-(4′-methyl-2,2′-bipyridyl)]hexane and regular 2,2′-bipyridine ligands. Orange light is emitted for low turn-on voltages, i.e. ranging from 2.5 to 3 V. The use of an additional PEDOT-PSS layer, obtained from an aqueous dispersion of poly(3,4-ethylenedioxythiophene) (PEDOT) and polystyrene sulfonate (PSS), on the indium tin oxide (ITO) anode has been investigated leading to improved operating lifetimes. By replacing the triflate salt by a derivative of a more delocalized anion, such as trifluorosulfonimide, turn-on rate is enhanced and the corresponding ionic conductivity allows to reach operating voltages in the neighborhood of the electrochemical gap of the Ru-based complex. However, whatever the case, device performances decrease upon operation within few hours. We report that the main degradation process involved in the decrease of the light emission intensity during device operation is based on an electrochemical degradation of the ruthenium complex, mainly a loss of capacity on the reduction side.