Hole-injection properties of annealed polythiophene films to replace PEDOT-PSS in multilayered OLED systems

Hole-injection properties of annealed poly(alkoxy- and alkylthiophene) films in OLEDs were studied. Among them, annealed poly(3,3'-dihexyloxy-2,2'-bithiophene) (aPHOBT) film exhibited good hole-injection properties and a triple-layered OLED with the structure ITO/aPHOBT/PVK/Alq3/Mg-Ag (device I) showed much higher performance than a double-layered device without the aPHOBT layer (device II, ITO/PVK/Alq3/Mg-Ag). Device I was slightly inferior to a device having a PEDOT-PSS layeras the hole injector (device III, ITO/PEDOT- PSS/PVK/Alq3/Mg-Ag) in the low-intermediate region of the applied voltage (6-11 V), but gave comparable luminance to III when the applied voltage exceeded 11 V