Boosting Cu─In─Zn─S‐based Quantum‐Dot Light‐Emitting Diodes Enabled by Engineering Cu─NiOx/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 Cu²⁺ 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.