POLYMER LIGHT-EMITTING ELECTROCHEMICAL-CELLS - A THEORETICAL-STUDY OFJUNCTION FORMATION UNDER STEADY-STATE CONDITIONS

The performance of light-emitting electrochemical cells is studied und er steady-state conditions. The theoretical model presented is based o n the approach to electrodiffusion-reaction problems familiar with ele ctrochemical cells. However, some links with the traditional semicondu tor physics approach are also presented. The reversible redox electrod e reactions are considered to always be in thermodynamic equilibrium, and the distribution of the applied potential between the two electrod e/polymer interfaces and the active layer is carefully analyzed by the numerical solution of the transport equations. The theory is able to explain most of the experimental observations. Ln particular, the junc tion formation is proved to be a bulk process related to the electrodi ffusion and recombination reaction of polarons, thus explaining its ma croscopic nature. Current-voltage and light-voltage characteristics in qualitative agreement with experiment are found. The observed changes in the junction width and the electric field profile with applied vol tage are also accounted for. Some ideas for future work are also discu ssed.