Performances enhancement in OLEDs by inserting ultrathin trilayer in electron injection structure and using MoO 3 as hole buffer layer

Abstract

In order to improve performance of Organic Light-emitting Diodes (OLEDs) in this paper, the electron injection is enhanced by inserting an ultrathin Alq 3–LiF–Al trilayer in between the organic layer and the LiF/Al cathode, which is explained by the formation of a thin n-doped Alq 3 layer that improves electron injection. At the same time, a buffer layer using MoO 3 was induced between m-MTDATA and N,N′-bis-[1-naphthy(-N,N′diphenyl-1,1′-biphenyl-4,4′-diamine)](NPB) to prompt hole injection because not only the Highest Occupied Molecular Orbital (HOMO) of MoO 3 is suitable to be used as buffer layer but also the interfacial doping effect of MoO 3 induces interfacial charge transfer complex formation between MoO 3 and NPB. At current density of 20 mA/cm 2, compared with control device, the current efficiency, power efficiency and luminance of device using ultrathin Alq 3–LiF–Al trilayer and MoO 3 were increased by 64%, 101% and 63% respectively, while driving voltage was reduced by 26%. After a series of single-carrier devices were made to analyze performance improvement of device using ultrathin Alq 3–LiF–Al trilayer and MoO 3, it is found that efficient carrier balance can improve device performance remarkably.