Organic light-emitting electrochemical cells based on polyfluorene -: Investigation of the failure modes

The discovery of organic light-emitting electrochemical cells (OLECs) has opened new directions for organic light-emitting devices based on luminescent conjugated polymers. However, such systems face two major problems: slow turn-on speed and short lifetime. If the p-n time formation can be efficiently reduced by increasing the ionic conductivity of the active layer by simply adding salt-laden poly(ethylene oxide), especially when the salt is fully dissociated, short lifetimes remains a key issue. A study of the decay of the electroluminescence intensity vs. current ratio as a function of time is representative of the quantum efficiency and can be compared with the evolution of the cyclic voltammograms, representative of the system electroactivity. We report that the main degradation process involved in the decrease of the light emission intensity during device operation is based on a current-driven degradation of the semiconducting polymer, mainly a loss of capacity on the n'' side. Possibly this is associated with an irreversible reduction of the anions from the added salt. (C) 2001 The Electrochemical Society.