Electronic Structure of Organic/organic Interface Depending on Heteroepitaxial Growth Using Templating Layer

Abstract

The electronic structure at organic-organic interface gives essential information on deviceperformance such as charge transport and mobility. Especially, the molecular orientation oforganic material can affect the electronic structure at interface and ultimately the deviceperformance in organic photovoltaics. The molecular orientation is examined by the changein ionization potential (IP) for metal phthalocyanines (MPc, M=Zn, Cu)/fullerene (C60)interfaces on ITO by adding the CuI templating layer through ultraviolet photoelectronspectroscopy measurement. On CuPc/C60 bilayer, the addition of CuI templating layerrepresents the noticeable change in IP, while it hardly affects the electronic structure ofZnPc/C60 bilayer. The CuPc molecules on CuI represent relatively lying down orientationwith intermolecular π-π overlap being aligned in vertical direction. Consequently, in organicphotovoltaics consisting of CuPc and C60 as donor and acceptor, respectively, the carriertransport along the direction is enhanced by the insertion of CuI templaing layer. In addition,optical absorption in CuPc molecules is increased due to aligned transition matrix elements. Overall the lying down orientation of CuPc on CuI will improve photovoltaic efficiency.