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 light-emitting diodes (OLEDs). In this paper, Li-doped VO x was prepared by solution processing under low-temperature 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:VO x 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∙W −1 . In contrast to the OLEDs with pristine VO x as HIL, the CE and PE of the OLEDs with Li:VO x were increased by 14.7% and 40.7% respectively. Based on the Fowler-Nordheim tunneling mechanism, doping Li + in VO x 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 VO x film prepared by solution processing is a very potential material as the HIL of high-performance OLED. • The solution-processed Li-doped VOx was investigated as the hole injection layer of OLED. • Li can effectively reduce the valence of V, reduce the work function, and make its energy level adapt between ITO and HTL. • Li:VO x film has good film morphology and excellent photoelectric properties. • Li:VO x has a strong hole injection performance. • The mechanism of Li:VO x improving device performance is systematically clarified.