Thickness dependence of the trap states in organic thin film of N,N'-bis(naphthalen-1-yl)-N,N'-bis(phenyl) benzidine

The authors have investigated the relationship between the trap states (exponential trap distribution in energy and density) and the thickness of N,N'-bis(naphthalen-1-yl)-N,N'-bis(phenyl) benzidine (NPB). The thickness dependent hole mobility of NPB can be attributed to the trap states. The origin of deep trap states at thinner film can be attributed to both surface dipole of buckminsterfullerene and the interaction between NPB and indium tin oxide at the interface. The influence of interfacial trap states on charge drift mobility is getting weaker as the thickness increases and is negligible when the thickness of NPB is thicker than 300 nm. (C) 2007 American Institute of Physics.