Efficient\nand Stable Inverted Quantum Dot Light-Emitting\nDiodes Enabled by An Inorganic Copper-Doped Tungsten Phosphate Hole-Injection\nLayer

Abstract

Inorganic interfacial\nbuffer layers have widely been employed for\nefficient and long lifetime optoelectronic devices due to their high\ncarrier mobility and excellent chemical/thermal stability. In this\npaper, we developed a solution-processed inorganic tungsten phosphate\n(TPA) as hole injection layer (HIL) in inverted quantum dot light-emitting\ndiodes (QLEDs) achieving a high external quantum efficiency (EQE)\nof up to ∼20%. Further, the copper ions are doped into tungsten\nphosphate (Cu:TPA) which leads to an enhancement in hole injection\ndue to increased hole mobility and conductivity of TPA as well as\ndecreased hole injection barrier, enabling better charge balance in\nQLEDs and lower turn-on voltage from 5 to 2.5 V. Compared with the\ndevices using conventional organic poly­(3,4-ethylenedioxythiophene):poly­(styrene-sulfonate)\n(PEDOT:PSS) HIL, the half-lifetime of Cu:TPA-based devices is over\n3000 h at an initial brightness of 100 cd m^–2, almost\n5-fold operating lifetime enhancement.