We investigated the interfacial electronic structures of indium tin oxide (ITO)/molybdenum trioxide (MoO3) /N, N′ -bis(1-naphthyl)- N, N′ -diphenyl- 1, 1′ -biphenyl- 4, 4′ -diamine (NPB) using in situ ultraviolet and x-ray photoemission spectroscopy to understand the origin of hole injection improvements in organic light-emitting devices (OLEDs). Inserting a MoO3 layer between ITO and NPB, the hole injection barrier was remarkably reduced. Moreover, a gap state in the band gap of NPB was found which assisted the Ohmic hole injection at the interface. The hole injection barrier lowering and Ohmic injection explain why the OLED in combination with MoO3 showed improved performance.
Bibliographical noteFunding Information:
This work was supported by Institute of Physics and Applied Physics (IPAP), Yonsei University, and BK21 project of the Korea Research Foundation (KRF).
All Science Journal Classification (ASJC) codes
- Physics and Astronomy (miscellaneous)