Solution-processed vanadium oxide as an efficient hole injection layer for quantum-dot light-emitting diodes

PEDOT:PSS (polyethylene dioxythiophene: polystyrenesulfonate) is widely used as a hole injection layer (HIL) for various optoelectronic devices because of its high conductivity and high work-function. However, the acidic and hygroscopic nature of PEDOT: PSS are detrimental to the long-term stability of the devices. In this work, we develop a solution processed vanadium pentoxide (V2O5) as an alternative to the PEDOT: PSS. The sol-gel derived V2O5 is easily obtained by spin-coating the vanadium oxytriisopropoxide solution, followed by thermal annealing at 120 degrees C for 1 min. With the proposed V2O5 HIL, quantum dot light-emitting diodes (QLEDs) exhibit a maximum current efficiency of 10.91 cd A(-1) and a peak EQE of 7.25%, which are very close to those of devices with a conventional PEDOT: PSS HIL. Moreover, by substituting the problematic PEDOT: PSS with the inorganic V2O5, the stability/lifetime of the QLEDs is substantially improved. Our results demonstrate that the sol-gel derived V2O5 is an effective alternative to PEDOT: PSS for efficient, low cost and stable QLED devices.