Utilization of a composite hole transporting layer and novel homogeneous double emitting layers for performance improvement and low efficiency roll-off in organic light-emitting diodes

• Composite hole transporting layer with novel homogenous double emitting layers.
• Balance of carrier distribution as well as the expansion of exciton formation zone.
• Blue OLEDs based on the structure of c-HTL and DELs exhibit improved performances.

Blue organic light-emitting devices (OLEDs) combing a composite hole transporting layer (c-HTL) and novel homogeneous double emitting layers (DELs) have been fabricated. The c-HTL plays a significant role of rectification in balancing the carriers’ injection concentration which matches well with the DELs structure. The DELs is consisted of two homogeneous hosts, such as 2-methyl-9,10-di(2-naphthyl) anthracene (MADN) and 9,10-di(2-naphthyl) anthracene (ADN). The optimal device presents the maximal current efficiency of 15.9 cd/A at 4.9 mA/cm2 and the minor efficiency roll-off of 13.4% under the driving voltage varying from 5 V to 10 V, respectively. Meanwhile, the device’s maximal current efficiency and the corresponding efficiency roll-off have been obviously improved by 55.9% and 63.9% compared with those of the conventional device. These results indicate that the homogeneous DELs not only greatly facilitate carriers’ injection into the emitting layer (EML), but also evenly modulate carriers’ distribution due to natural energy barrier of the interface. The transient photoluminescence decay of double hosts further illustrates that the DELs structure can increase the recombination ratio of electron–hole pairs and improve the exciton’s utilization. Additionally, the optimal device’ current density is reduced by 44.1% under the same luminance of 25,780 cd/m2 compared with that of the conventional device.