Performances enhancement in OLEDs by inserting ultrathin trilayer in electron injection structure and using MoO3 as hole buffer layer

In order to improve performance of Organic Light-emitting Diodes (OLEDs) in this paper, the electron injection is enhanced by inserting an ultrathin Alq3–LiF–Al trilayer in between the organic layer and the LiF/Al cathode, which is explained by the formation of a thin n-doped Alq3 layer that improves electron injection. At the same time, a buffer layer using MoO3 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 MoO3 is suitable to be used as buffer layer but also the interfacial doping effect of MoO3 induces interfacial charge transfer complex formation between MoO3 and NPB. At current density of 20 mA/cm2, compared with control device, the current efficiency, power efficiency and luminance of device using ultrathin Alq3–LiF–Al trilayer and MoO3 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 Alq3–LiF–Al trilayer and MoO3, it is found that efficient carrier balance can improve device performance remarkably.

Research highlights
► Ultrathin Alq3–LiF–Al trilayer is effective in facilitate electron injection.
► Hole injection is improved significantly due to using MoO3.
► Device performance is improved greatly after using ultrathin trilayer and MoO3.