Photoresponse and electroresponse studies of polymer light-emitting diodes

We have developed and applied a non-destructive and non-invasive technique, the saturated photovoltage (SPV), to measure the internal built-in potential, V-bi, in conducting polymer based light-emitting diodes (LED). We found that V-bi scales with the difference in work function between the two capping metal electrodes in a variety of polymer LEDs, independent of the constituent polymer. The SPV technique can be used as a diagnostic tool to study the polymer device quality and degradation. In addition, the photocurrent excitation spectra of polymer LEDs are shown to be sensitive to states in the gap and also to spectral features above the optical gap.