Enhanced performances in inverted bottom-emission organic light-emitting diodes with KBH4-doped electron-injection layer

Abstract

We report that a potassium borohydride (KBH4)-doped 1,3,5-tri(m-pyrid-3-yl-phenyl)benzene (TmPyPB) layer can be utilized as an efficient electron-injection layer (EIL) for the inverted bottom-emission organic light-emitting diodes (IBE-OLEDs). The KBH4-doped EIL in the IBE-OLEDs having tris(2-phenylpyridine)iridium(III) as a green phosphorescent dopant show a lower turn-on voltage (similar to 7V) and about two times higher efficiency (similar to 13.9% and 44.5 cd A(-1) at 0.63 mA cm(-2)) compared with the device without the KBH4-doped EIL. Furthermore, the KBH4-doped EIL rarely affects the electroluminescence spectrum of the device. The KBH4-doped TmPyPB films with different doping ratios are also analyzed by using electron-only devices (EODs) and X-ray photoemission spectroscopy. As the doping ratio of the KBH4 increases, the current of the EOD and the amounts of potassium increase. This result indicates that the potassium improves the electron-injection ability of an organic electron-transport layer. Therefore, the KBH4-doped EIL can be utilized as an effective EIL in the inverted structure OLEDs. (C) 2014 WILEY-VCH Verlag GmbH Co. KGaA, Weinheim