Solution-processed WOx hole injection layer for efficient fluorescent blue organic light-emitting diode

Abstract

Solution-processed tungsten oxide (s-WOx) interfacial layer for efficient hole injection in fluorescent blue organic light-emitting diode (OLED) is demonstrated. The OLED using 2-methyl-9,10-bis(naphthalen-2-yl)anthracene (MADN) as emitter shows luminous efficiency of 3.3 cd/A, power efficiency of 2.5 lm/W and external quantum efficiency of 4.6% with Commission Internationale d'Eclairage (CIE) color coordinates of (0.154, 0.102). Using MADN doped 1-4-di-[4-(N,N-diphenyl)amino]styryl-benzene as emitter, luminous efficiency of 10.8 cd/A, power efficiency of 6.4 lm/W and external quantum efficiency of 7.2% with CIE color coordinates of (0.167, 0.283) are achieved. Atomic force microscopy and X-ray photoelectron spectroscopy show that s-WOx features superior film morphology and non-stoichiometry with slight oxygen deficiency. Current-voltage characteristics and impedance spectroscopy analysis indicate that s-WOx behaves slightly enhanced hole injection and accordingly contributes to improved device performance in comparison with conventional vacuum thermal evaporation WOx. Our results pave an alternative way for broadening WOx application with solution process and advancing fluorescent blue OLEDs.