The origin of the hole injection improvements at indium tin oxide/molybdenum trioxide/N,N-bis(1-naphthyl)-N,N-diphenyl-1,1-biphenyl- 4,4-diamine interfaces
Journal Article

Published: Friday, August 01, 2008
Citation: Applied Physics Letters, Volume 93, Number 4, Pages 43308
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Authors (1 total): S. Cho

Abstract: 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.