Light-emitting electrochemical cells for large-area lighting applications

A light-emitting electrochemical cell is a type of organic electroluminescent device of particular interest for large-area lighting. We have assessed the potential applicability of different kinds of light-emitting electrochemical cells. For devices having a blend of an electroluminescent polymer and a polymer electrolyte as active layer, the obtainable efficiency and lifetime were found to be insufficient for practical applications. Light-emitting electrochemical cells with charged transition metal complexes as conducting and electroluminescent material sandwiched between ITO and Ag electrodes resulted in considerable improvement. For a yellow-emitting charged Ir complex, an efficacy of about 4 cd/A over a wide luminance range was obtained. Furthermore, we have studied the dependence of the performance on the active layer thickness, and we demonstrate that thick-layer light-emitting electrochemical cells can be operated at much lower voltage than organic light-emitting diodes.