Low-temperature and solution-processable inorganic hole injection layer for flexible quantum-dot light-emitting diodes

A low-temperature solution-processable inorganic vanadium oxide (V₂O₅) hole injection layer (HIL) was synthesized for flexible quantum-dot light-emitting diodes (QLEDs). Efficient hole injection characteristics were observed in the hole-only devices; furthermore, the process temperature of V₂O₅ was as low as 30 °C. We investigated the source of the efficient hole injection behavior using ultraviolet and x-ray photoelectron spectroscopy. The density of gap states was found to increase in accordance with process temperature reduction. Therefore, QLEDs with low-temperature solution-processable V₂O₅ HILs were fabricated on a glass substrate, which showed excellent characteristics. The maximum luminance and luminous efficiency of the device were 56,717 Cd/m² and 4.03 Cd/A, respectively. Due to the low-temperature process of the V₂O₅ HIL, it was also possible to fabricate QLEDs on a flexible plastic substrate without mechanical or thermal deformation of the substrate. Our results suggest that the low-temperature V₂O₅ inorganic HIL is a feasible alternative to organic HILs for flexible QLEDs.