Highly efficient tandem organic light-emitting diodes based on SubPc:C60 bulk heterojunction as charge generation layer

High efficiency tandem organic light-emitting diodes (OLEDs) were realized using an organic bulk heterojunction (BHJ) as charge generation layer (CGL) consisted of boron subphthalocyanine chloride (SubPc) and fullerene (C60). The results showed that the SubPc:C60 based CGL is a promising connecting unit for the fabrication of high efficiency tandem OLEDs with 2.64 folds enhancement in a current efficiency of 63.6 cd/A, compare to the corresponding single-unit OLEDs. The efficiency enhancement of tandem OLEDs is attributed to better charge carrier balance derived from the optimized charge transport pathways and reduced interface energy barrier. It showed that the charge generation ability and charge transport characteristics of CGL were strongly dependent on SubPc:C60 mixing ratio and corresponding film morphology, which was verified by the charge extracting analysis. Additionally, the highest occupied molecular orbital energy level of SubPc is compatible for most of hole transporting layer to minimize the hole injection barrier and suppress the hole accumulation and charge recombination in tandem OLEDs.