Highly Efficient Hole Injection Using Polymeric Anode Materials for Small-Molecule Organic Light-Emitting Diodes



A novel, highly efficient hole injection material based on a conducting polymer polythienothiophene (PTT) doped with poly(perfluoroethylene-perfluoroethersulfonic acid) (PFFSA) in organic light-emitting diodes (OLEDs) is demonstrated. Both current–voltage and dark-injection-current transient data of hole-only devices demonstrate high hole-injection efficiency employing PTT:PFFSA polymers with different organic charge-transporting materials used in fluorescent and phosphorescent organic light-emitting diodes. It is further demonstrated that PTT:PFFSA polymer formulations applied as the hole injection layer (HIL) in OLEDs reduce operating voltages and increase brightness significantly. Hole injection from PTT:PFFSA is found to be much more efficient than from typical small molecule HILs such as copper phthalocyanine (CuPc) or polymer HILs such as polyethylene dioxythiophene: polystyrene sulfonate (PEDOT-PSS). OLED devices employing PTT:PFFSA polymer also demonstrate significantly longer lifetime and more stable operating voltages compared to devices using CuPc.