Enhancing light extraction efficiency of organic light-emitting diodes by embedding tungsten trioxide islands or network structure pattern-transferred from a self-assembled deliquesce cesium chloride mask

We present a new and simple method to improve internal light out-coupling of organic light emitting diodes (OLEDs) by incorporating tungsten trioxide (WO₃) islands or network structure in the devices. These structures were pattern-transferred from a cesium chloride (CsCl) film that self-assembled into the islands or network structure as it deliquesced in air. The size and type of structures could be controlled with the thickness of the CsCl film, the relative humidity, the developing time and the developing temperature. The WO₃ patterned structures scattered light in the OLEDs devices to extract light trapped in the waveguide modes. As a result, the current efficiencies, external quantum efficiencies and power efficiencies of the WO₃ patterned OLEDs were increased compared with those of a conventional OLED without WO₃ layer. Operating voltages of the devices with WO₃ layer were significantly decreased because the WO₃ layer facelifted the hole injection of the devices.