Solution-processed WS2 and its doping in PEDOT:PSS for tailoring hole injection in near ultraviolet organic light-emitting diodes

Abstract

Solution-processed ethanol tungsten disulfide and its doping in poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) ( P E D O T : P S S + W S 2 ) for tailoring hole injection in near ultraviolet organic light-emitting diodes (NUV OLEDs) are investigated in detail. Raman spectrum, scanning electron microscopy, atomic force microscopy, x-ray/ultraviolet photoelectron spectroscopy, and impedance spectroscopy measurements show that W S 2 and its composites have superior film morphology and exceptional electronic properties. Using 2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole as the emitter and P E D O T : P S S + W S 2 as the hole injection layer, the NUV OLED produces short-wavelength emission peaking at 404 nm and full-width at half-maximum of 53 nm. The device also gives maximum radiance of 4.7 m W / c m 2 and external quantum efficiency of 2.1%, which are superior to counterparts using W S 2 , UV-ozone-treated W S 2 , and PEDOT:PSS. The hole injection ability is enhanced by using W S 2 , UV-ozone-treated W S 2 , PEDOT:PSS, and P E D O T : P S S + W S 2 in this order. The robust hole injection contributes to carrier balance and accounts for high device performance of the fabricated NUV OLEDs. Our results pave an alternative approach for advancing OLEDs and accelerating W S 2 applications.