Efficient and Stable Inverted Quantum Dot Light-Emitting Diodes Enabled by An Inorganic Copper-Doped Tungsten Phosphate Hole-Injection Layer.

Inorganic interfacial buffer layers have widely been employed for efficient and long lifetime optoelectronic devices due to their high carrier mobility and excellent chemical/thermal stability. In this paper, we developed a solution-processed inorganic tungsten phosphate (TPA) as hole injection layer (HIL) in inverted quantum dot light-emitting diodes (QLEDs) achieving a high external quantum efficiency (EQE) of up to ∼20%. Further, the copper ions are doped into tungsten phosphate (Cu:TPA) which leads to an enhancement in hole injection due to increased hole mobility and conductivity of TPA as well as decreased hole injection barrier, enabling better charge balance in QLEDs and lower turn-on voltage from 5 to 2.5 V. Compared with the devices using conventional organic poly(3,4-ethylenedioxythiophene):poly(styrene-sulfonate) (PEDOT:PSS) HIL, the half-lifetime of Cu:TPA-based devices is over 3000 h at an initial brightness of 100 cd m-2, almost 5-fold operating lifetime enhancement.