Metal Oxide Films as Charge Transport Layers for Solution-Processed Polymer Light-Emitting Diodes

Here, we discuss the use of metal oxide films as charge transport layers in polymer light-emitting diodes containing poly(9,9-dioctyl-9H-fluorene-2,7-diyl) (PFO) as emissive layer. A simple device architecture consisting of glass-ITO | poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) | poly(9-vinylcarbazole) (PVK) | PFO | Ca | Al was used as starting point. This device assembly allows the investigation of basic properties of polymeric emitting layers, but does not provide stable devices with high performances. Thus, a more complex, multilayered diode structure is needed. We pursuit that goal with focus on the use of low-cost, easily processed materials. At one side, solution-processed non-stoichiometric MoOx films were used to replace the PEDOT:PSS as hole transport layer. At the other interface, solution-processed ZnO films containing either the bare oxide or a ZnO/carbon dots composite were introduced as electron transport layer. By tunning the characteristics of the metal oxide films, the performance of the blue-emitting PFO-based polymer light-emitting diodes (PLEDs) was massively enhanced.