Improved efficiency of organic light emitting devices using graphene oxide with optimized thickness as hole injection layer

Abstract Organic Light-Emitting Diodes (OLEDs) with graphene oxide (GO) as hole injection layer (HIL) have been demonstrated. The OLED devices possess structures of ITO/GO(x nm)/NPB(40 nm)/Alq 3 (70 nm)/LiF(0.5 nm)/Al(100 nm), it is found that as the thickness of GO-HIL is a 3.6 nm an optimal current efficiency of 4.4 cd/A and a brightness of 15,770 cd/m 2 were achieved, respectively, which are higher than that of reference device without GO-HIL layer (1 cd/A and 4735 cd/m 2 ). We reason that the improvement of electroluminescent (EL) intensity would be ascribed to the smoothed ITO surface and the reduced hole-injection barrier due to the high work function of GO layer. In terms of the impendence spectroscopy analysis of hole-only devices (HODs), for electrical character of device is mainly depends on the bulk resistance of the HODs. As a result, the optimized EL device offers fallen bulk resistances, finally, the improvement in EL performance was obviously realized.