Work function tunning of lithium-doped vanadium oxide for functioning as hole injection layer in organic light-emitting diodes

The hole-injection layer (HIL) plays an important role in the electroluminescent property of organic lightemitting diodes (OLEDs). In this paper, Li-doped VOx was prepared by solution processing under lowtemperature annealing conditions and used as a new kind of HIL in OLEDs. It demonstrated the best phosphorescent OLED performance when the molar ratio of Li:VOx was 3%. The turn-on voltage was 3.7 V, the maximum current efficiency (CE) was 69.5 cd A-1 and the maximum power efficiency (PE) was 48.4 lm center dot W- 1. In contrast to the OLEDs with pristine VOx as HIL, the CE and PE of the OLEDs with Li:VOx were increased by 14.7% and 40.7% respectively. Based on the Fowler-Nordheim tunneling mechanism, doping Li+ in VOx improved the efficiency of hole injection and balanced carriers by adjusting the work function, thereby improving the efficiency of the device. The experimental results indicated that Li-doped VOx film prepared by solution processing is a very potential material as the HIL of high-performance OLED.