White organic LEDs and their recent advancements

White organic light emitting devices (WOLEDs) are being considered as substitutes for conventional white light sources. They are efficient solid-state lighting sources and their power efficiencies have surpassed those of the incandescent light sources, especially due to recent improvement in device architectures, molecular engineering in synthesis of new materials and the incorporation of electrophosphorescent emitters. This paper reviews the various approaches to achieve white light emission from organic light emitting diodes (OLEDs), their advantages, disadvantages and recent progress. The device architecture and problems related to various device designs have been discussed.