Optical studies of polymer light-emitting diodes using electroabsorption measurements

We have studied the electrical fields in single-layer polymer light-emittin g diodes (LEDs) using electroabsorption (EA) spectroscopy. The materials un der investigation were PPV derivatives, namely poly(2,5-dialkoxy-para-pheny lene vinylene) and a precursor route poly(2-methoxy-5-ethyl(2'-hexyloxy)-pa ra-phenylene vinylene). The applied bias generates an opposing electric fie ld that decays over time. The magnitude of the reversed field increases as the applied DC bias is increased and can be as high as one-third of the app lied external field. The development of the internal field is less pronounc ed in vacuum than in air and it vanishes for devices prepared and tested un der inert conditions. (C) 2000 Elsevier Science S.A. All rights reserved.