Improving the performance of quantum-dot light-emitting diodes via an organic-inorganic hybrid hole injection layer

Poly(3,4-ethylenedioxythiophene):poly(styrene-sulfonate) (PEDOT:PSS) is a commonly used material for the hole injection layer (HIL) in quantum-dot light-emitting diodes (QLEDs). In this work, we improved the performance of the QLED by using an organic-inorganic hybrid HIL. The hybrid HIL was prepared by mixing PEDOT:PSS with vanadium oxide (V₂O₅), which is a transition-metal oxide (TMO). The hole injection properties of PEDOT:PSS were improved according to the amount of V₂O₅ mixed into the PEDOT:PSS. The maximum luminance and current efficiency were 36 198 cd m^-2 and 13.9 cd A^-1, respectively, when the ratio of PEDOT:PSS and V₂O₅ was 10 : 1. Moreover, the operating lifetime exceeded 300 h, which is 10 times longer than the lifetime of the device with only PEDOT:PSS HIL. The improvement was analyzed using ultraviolet and X-ray photoelectron spectroscopy. We found that the density of state (DOS) of PEDOT:PSS near the Fermi energy level was increased by mixing V₂O₅. Therefore, the increase of DOS improved the hole injection and the performance of QLEDs. The result shows that the hybrid HIL can improve the performance and the stability of QLEDs.