Direct observation of junction formation in polymer light-emitting electrochemical cells

Abstract
Electroabsorption (EA) measurements are used to determine the electric fields in polymer light-emitting electrochemical cells (LEC’s). The EA signals are measured as a function of the dc bias and are found to increase abruptly above a threshold voltage. The EA measurements are compared with the capacitance-voltage and current-voltage characteristics. Calculations using a model based on electrochemical junction formation are in agreement with all of the experimental observations. These results show unambiguously that the picture of electrochemical junction formation in LEC’s is correct.