Impedance study of the charge leakage phenomenon in ITO-free graphene-super-yellow light-emitting diode

The construction of hybrid organic-inorganic systems is usually aimed at increasing the electrical conductivity and modifying the work function of transparent and conductive electrodes. Here, we describe the fabrication and photoelectrical studies of a light-emitting diode incorporating graphene/molybdenum oxide as an anode and poly(para-phenylene vinylene) copolymer as an organic emitting layer. We observed increased hole injection from the anode relative to electron injection from the cathode, as well as undesirable hole-electron recombination at the graphene-polymer interface responsible for a significant charge leakage. Modeling the multilayer structure of organic light emitting diodes using electrical equivalent circuits based on the results of impedance spectroscopy measurements, we analyzed the electronic processes in the graphene/metal-oxide/organic layer junction. We developed a complex mathematical model to analyze and interpret impedance data. The original method that we present here provides a way to monitor the charge density of the main charge carriers as well as the leaked ones. The work paves the way towards understanding the interface charge transport phenomena in multilayer systems, in particular polymer light-emitting diodes.