Integrated pulsed photoconductivity of organic light-emitting diodes

We analyze the transient photoconductivity induced by short light pulses in organic light-emitting diodes (OLEDs) to characterize the charge transport dynamics with high time resolution over four time decades. We show how integrated pulsed photoconductivity (IPP) can be used as a diagnostic method for finished, packaged OLEDs to determine and characterize the presence of impurities or other effects that influence the efficiency of charge transport. We demonstrate the usefulness of the method by comparing a simple one-layer ${\mathrm{Alq}}_3$ device on indium tin oxide (ITO) to a device where a nanometer thin NPB film separates the ${\mathrm{Alq}}_3$ from the ITO. In the single-layer device a charge transport dynamics stretching over several decades is observed, probably due to ${\mathrm{Alq}}_3$ contamination by its direct contact with ITO.