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

Abstract

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 (VO_x) HIL through solution processing at low temperature for improving device performance. Compared to non-doped VO_x and Au-doped VO_x films, co-doping with an optimal molar ratio of Au and Li endows the VO_x 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 VO_x (Au,Li:VO_x) HIL. As a result, the device with the Au,Li:VO_x 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 VO_x 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 VO_x HIL with excellent hole-injection ability, which provides a promising avenue to enhance OLED performance.