The role of gap states on energy level alignment at an α-NPD/HAT(CN)6 charge generation interface

Abstract

We report the effect of gap states on energy level alignment in a typical organic charge generation interface of N,N-bis(1-naphthyl)-N,N-diphenyl-1,1-biphenyl-4,4-diamine (α-NPD)/hexaazatriphenylene−hexacarbonitrile [HAT(CN)6] by using ultraviolet and X-ray photoemission spectroscopy. The gap states tailed from the highest occupied molecular orbital (HOMO) onset of α-NPD dominate the Fermi level pinning at the α-NPD(<1.6nm)/HAT(CN)6 interface, which is favorable for charges generation upon bias operation and facilitates the electron injection from the HOMO-tail region of α-NPD to the lowest unoccupied molecular orbital (LUMO) region of HAT(CN)6.