Active emitting layer thickness dependence and interfaces engineering studies on the performance of DOPPP white organic light emitting diodes

A type of double light-emitting layer highly efficient white organic light emitting diodes (WOLEDs) with the stacked structures of ITO/NPB(30 nm)/Rubrene(0.2 nm)/DOPPP(x nm)/Bphen(40 nm)/LiF(0.6 nm)/Al(100 nm) have been fabricated by a vacuum thermal evaporation method. Wherein the fluorescent dye 5,6,11,12-Tetraphenylnaphthacene (Rubrene) and 1-(2,5-dimethoxy-4-(1-pyrenyl)-phenyl) pyrene (DOPPP) work as the yellow light layer and blue light layer, respectively. The performances of a series of developed devices are investigated by regulating the DOPPP thickness and tailoring its corresponding interlayer interfaces. The optimized device with DOPPP thickness of 20 nm demonstrates the best light emitting performance. The maximum brightness is 13910 cd/m2 and the maximum current efficiency is up to 5.19 cd/A. With the increase of working voltage, the color coordinates migrate from (0.428, 0.433) to (0.382, 0.394), falling into the white light emitting scope. The light is changed from warm white light to neutral white light. When the thickness of DOPPP layer exceeds 20 nm, the efficiency and brightness tend to degrade slightly. The systematic investigations and complementary engineering studies upon the developed white WOLEDs also bring more opportunities to push the boundaries of current existing applications in an industrial level, e.g., flat panel display, human–machine interfaces lighting, and smart wearable devices etc.