A strategy of synergistic optimization: gold and lithium co-doped vanadium oxide as a hole-injection layer for high-performance OLEDs

The hole-injection layer (HIL) plays a critical role in the efficiency and stability of organic light-emitting diodes (OLEDs). However, inorganic HIL materials, such as transition metal oxides (TMOs), usually suffer the problems of low conductivity and mismatched work function at ITO/hole-transport layer (HTL) interfaces, which limits the hole-injection in OLEDs. In this paper, a gold (Au) and lithium (Li) co-doping strategy has been employed to fabricate a vanadium oxide (VOx) HIL through solution processing at low temperature for improving device performance. Compared to non-doped VOx and Au-doped VOx films, co-doping with an optimal molar ratio of Au and Li endows the VOx films with both higher electrical conductivity and proper work function matching with the ITO anode and HTL, which leads to efficient hole-injection and improved carrier balance in the device with the Au and Li co-doped VOx (Au,Li:VOx) HIL. As a result, the device with the Au,Li:VOx HIL shows a peak power efficiency of 50.2 lm W−1 and a maximum external quantum efficiency (EQE) of 19.9%, which are superior to those of the counterpart with the VOx HIL (34.4 lm W−1 and 18.1%). Meanwhile, the device shows distinguished stability. This work indicates that Au and Li co-doping is an effective method to obtain an efficient VOx HIL with excellent hole-injection ability, which provides a promising avenue to enhance OLED performance.