Polymer light-emitting diodes with an emitting layer based on a nano-confined semiconducting polymer blend

Blending a visible light-emitting organic semiconductor with an insulator alleviates the trap-limited nature of the electron current. Solution-processed organic light emitting diodes (OLEDs) comprising such a blend as emissive layer exhibit a two-fold increase in luminous efficiency with only 10% semiconductor. This low content of semiconductor can only be achieved with polymeric emitters. Hence, polymer-LEDs are considerably more cost-effective than devices based on small molecular emitters. However, due to the reduced translational entropy, polymers typically exhibit a low miscibility. In principle, macro-phase separation can be avoided if the molecular weight is kept low, which is however disadvantageous due to low charge carrier mobilities. An alternative strategy is to impose a nano-confinement. We prepare aqueous nanodispersions of poly(p-phenylenevinylene)-based emitters, blended with polystyrene. Macro-phase separation is fully suppressed, as confirmed by scanning force microscopy. Despite the fact that fabricating OLEDs from aqueous nanoparticle dispersions poses considerable risks of strong field inhomogeneity and high leakage currents, we succeed in fabricating such devices highly reproducibly and at efficiencies similar to the non-particle based reference devices.