Probing Surface Electronic Potentials and Photovoltaic Effects of Self-Assembled Multilayers of Metal Phthalocyanine and Oligomeric Viologen on Conductive Substrates

Abstract

To probe the effects that self-assembled multilayers may have on electronic properties of a conductive surface, we carried out layer-by-layer depositions of organic/polymeric thin films on indium tin oxide (ITO) substrates. The organic/polymeric thin films were prepared by alternatively dipping ITO substrates in an oligomeric viologen or oligo(hexylene 4,4‘-bipyridinum dibromide) solution and a macrocyle NiPc or nickel phthalocyanine solution. A linear relationship, between the optical absorption at 634 nm from NiPc and 274 nm from oligomeric viologen and the number of depositions, was observed in the UV−vis spectra. The multilayer structures were characterized with X-ray reflectometry, which yielded an average mean thickness of 1.5−2.0 nm per layer-pair. Taking advantage of the conductive surfaces, we performed surface infrared (IR) spectroscopy on oligomeric viologen and NiPc multilayers at an external grazing-angle reflection configuration. IR spectra with polarization perpendicular to the conductive I...