Energy level alignments at the interface of N,N'-bis-(1-naphthyl)-N,N'-diphenyl-1,1′-biphenyl-4,4′-diamine (NPB)/Ag-doped In2O3 and NPB/Sn-doped In2O3

Abstract

The electronic structures of Ag-doped In2O3 (IAgO) and its energy level alignments with a N,N'-bis-(1-naphthyl)-N,N'-diphenyl-1,1′-biphenyl-4,4′-diamine (NPB) hole transport layer (HTL) were investigated using in situ ultraviolet and X-ray photoelectron spectroscopies (UPS and XPS). As compared to the conventional Sn-doped In2O3 (ITO), IAgO has less oxygen vacancies leading to a higher work function (WF). The lower hole injection barrier (Φh) from IAgO to a NPB HTL is observed, which is attributed mainly to its higher WF and interface dipoles. The UPS measurements reveal that the Φh is 0.87eV at NPB/IAgO while 1.11eV is at NPB/ITO. Therefore, IAgO could be an alternative transparent anode in organic optoelectronics.