Boosting Cu─In─Zn─S‐based Quantum‐Dot Light‐Emitting Diodes Enabled by Engineering Cu─NiOx/PEDOT:PSS Bilayered Hole‐Injection Layer

Abstract 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.