Understanding the relationship between morphology and device performance in organic solar cells

Due to the rapidly increasing demand for clean energy, harnessing solar energy has been considered to be a promising way to solve the impending energy crisis. Among the various photovoltaic technologies, organic photovoltaics (OPV) are continuing to receive intensive interest with power conversion efficiencies of over 10% demonstrated recently. Solution processed organic solar cells have unique prospects for achieving low-cost energy harvesting via continuous roll-to-roll processing. A key requirement for fabricating high efficiency organic solar cells is the control of the thin-film morphology to facilitate efficient charge separation and collection. The active layer of an OPV device is based on a bulk heterojunction structure, consisting of an interpenetrating network of electron donor and electron acceptor. In this thesis, the application of a combination of synchrotron-based techniques enables a detailed characterization of polymer blend solar cells, providing an understanding of the relationship between the thin-film morphology and device performance. In particular, the effects of different thin-film treatments such as thermal annealing, anti-solvent treatment and the use of solvent additive to tune the blend morphology for optimized device performance are assessed.