Spatially resolved electric fields in polymer light-emitting diodes using fluorescence lifetime imaging

Polymer light-emitting diode (LED) structures have been studied using fluorescence lifetime imaging (FLIM). FLIM allows one to image perturbations in the excited state of the luminescent polymer that lead to changes in its fluorescence lifetime. Observation of strong electric field induced luminescence lifetime quenching of a blue emitting polyfluorene type co-polymer enabled the spatial resolution of field strengths. For example, black spots (degradation induced defects in the LED) did not show any lifetime quenching upon applying an electric field in contrast to the surrounding polymer layer. Future applications of this technique in the field of thin film LEDs are suggested.