(579c) Structural Characterization of Thin-Film Polymer/Fullerene Composites

The structural morphology assumed by conjugated polymer/fullerene composites has an important influence over the performance of photovoltaic devices produced from them. The efficiency of exciton dissociation and free carrier transport are both important factors to optimize with respect to thin-film morphology. In order to do so, a detailed model of structural components of these thin-film composites is necessary. Our work characterizing the structure of conjugated polymer/fullerene composites has shown that generally the films can be viewed as composed of three main phases:  a polymer aggregate phase, a fullerene aggregate phase, and a disordered polymer/fullerene phase. The concentration, distribution, and composition of these phases are directly tied to composition, how devices are processed and to the film treatment history. However, regardless of the specific thermal treatment we seek to show that the performance of the thin-film composite can be understood by examining its instantaneous morphology. Grazing Incidence Small Angle X-Ray scattering techniques provide detailed structural information about all the phases in these composites and therefore is a powerful technique through which the performance of these composites can be understood.