Boosting Cu─In─Zn─S-based Quantum-Dot Light-Emitting Diodes Enabled by Engineering Cu─NiO x /PEDOT:PSS Bilayered Hole-Injection Layer.

The imbalance of charge injection is considered to be a major factor that limits the device performance of cadmium-free quantum-dot light-emitting diodes (QLEDs). In this work, high-performance cadmium-free Cu─In─Zn─S(CIZS)-based QLEDs are designed and fabricated through tailoring interfacial energy level alignment and improving the balance of charge injection. This is achieved by introducing a bilayered hole-injection layer (HIL) of Cu-doped NiO x (Cu─NiO x )/Poly(3,4-ethylenedioxythiophene): poly (styrene sulfonate) (PEDOT:PSS). High-quality Cu─NiO x film is prepared through a novel and straightforward sol-gel procedure. Multiple experimental characterizations and theoretical calculations show that the incorporation of Cu 2+ ions can regulate the energy level structure of NiO x and enhance the hole mobility. The state-of-art CIZS-based QLEDs with Cu─NiO x /PEDOT:PSS bilayered HIL exhibit the maximum external quantum efficiency of 6.04% and half-life time of 48 min, which is 1.3 times and four times of the device with only PEDOT:PSS HIL. The work provides a new pathway for developing high-performance cadmium-free QLEDs.