Study of the electronic structure of the interfaces between 2-TNATA and MoOx

In order to understand the characteristics of ohmic hole-contacts for the inverted/conventional organic light emitting devices, a hole-only device with all ohmic contacts, which is composed of glass/ITO/MoOx/4,4,4-tris[2-naphthyl-phenyl-amino]triphenylamine (2-TNATA)/MoOx/Al, the elements of the electronic structures of MoOx-on-2-TNATA interface and 2-TNATA-on-MoOx interface were investigated by photoemission spectroscopy, with regards to interface energetics, formative mechanism, and a potential charge carrier injection. The electronic structures revealed that the behavior of the interface between MoOx and 2-TNATA was different whether MoOx was deposited on (2-TNATA) or vice versa. The bottom interfaces of 2-TNATA-on-MoOx in this hole-only devices showed no hole-injecting barrier height (Phi(h)B) when the thickness of 2-TNATA was deposited in the range of 0.1 to 5.0 nm on the 10.0 nm-thick MoOx thin films. This has been explained to be attributed to both metal-induced gap states and a chemical reaction at the interfaces. The top interfaces of MoOx-on-2-TNATA in this hole-only device structure also showed no Phi(h)B when a hole was injected from the MoOx-on-2-TNATA interfaces to cathode. The hole-ohmic property in the top interfaces depends on interface dipole by the formation of charge transfer complexes as well as interdiffusion of MoOx into the 2-TNATA film in these interfaces.