(447e) Electronic Surface Properties of Polymer Electrode Materials for Polymer Photovoltaics

Polyethylenedioxythiophene Polystyrenesulphonate (PEDOT:PSS) is a highly conducting transparent polymer mixture that is used as a hole carrying electrode for nearly all organic optoelectronic devices, including OLED's and solar cells. Despite numerous electrical and morphological studies, the mechanism for charge injection and extraction from PEDOT:PSS is poorly understood. For example, the work function of PEDOT:PSS changes little when additional organic layers are deposited onto it, where by contrast, metal electrodes will form surface dipole layers that greatly change the expected charge injection conditions. In order to investigate the interface between PEDOT:PSS and other conducting polymers, we fabricate complete devices, and later wash the polymers off of the PEDOT:PSS so that we can perform measurements of the PEDOT:PSS surface. We show that when heated, the PEDOT:PSS incorporates a variety of polymers onto its interface (including P3HT, MEH:PPV, F8BT, and APFO3) that change the work function, and allow for a reduction of injection and extraction barriers for mobile carriers to the adjoining layer. The listed polymers are insoluble in this interface layer. The method of incorporation is discussed as well as the implications for mixed interfaces in organic devices. Finally, we show that the prepared polymer surfaces can be incorporated into devices to raise and lower injection and extraction barriers in OLED's and organic solar cells.