Enhanced Brightness and Efficientcy in Polymer Light-Emitting Diodes (PLED) Using Alq(subscript 3) Electron-Transporting Layer

Abstract

We report that an electron-transporting layer of Alq(subscript 3) is interposed between a cathode of Al and an emissive layer of Polyfluorene (PF) which can significantly improve electroluminescence efficiency in a polymer light emitting diode (PLED). The difference of the turn-on voltage is about 2.5 V for with and without insertion of a thin Alq(subscript 3) layer, which greatly improves the EL performance compared with the devices without an Alq(subscript 3) layer. The thickness of Alq(subscript 3) is 10nm, which is resulted in the smooth energy barrier height on PLED and promoted electron injection in the cathode section. The average surface roughness of Alq(subscript 3) under thickness 10 nm is the smallest about 0.790 nm. Besides, the turn-on voltage of luminescence with Alq(subscript 3) defined by 3.51 cd/㎡ is 5 V. A maximum luminescence is obtained at 361.8 cd/㎡. The emission area is 1.5×0.3 cm(superscript 2). The devices show the yellow-green light emission with a peak at about 536 nm. The color coordinate in CIE chromaticity is (0.39, 0.57).