Enhanced charge-carrier injection caused by molecular orientation

Current densities of hole-only devices based on alpha-sexithiophene (alpha-6T) and N-N'-diphenyl-N-N'-bis(1-naphthyl)-1, 1'-biphenyl-4,4'-diamine (alpha-NPD) increase 42 times at 1 V by rubbing alpha-6T with a Nylon cloth. Results of absorption spectroscopy with normal and oblique light incidence reveal that the rubbing induces a change from standing to lying orientations of alpha-6T in a film surface region. The increased current densities are attributed to enhanced alpha-6T-to-alpha-NPD hole injection due to the lying orientation. (C) 2011 American Institute of Physics. [doi:10.1063/1.3602925]