(226f) Materials Design of Conjugated Block Copolymers for Photovoltaics

Weak intermolecular interactions and disorder at junctions of different organic materials limit the performance and stability of organic interfaces and hence the applicability of organic semiconductors to electronic devices.  We have demonstrated control of donor-acceptor heterojunctions through microphase-separated conjugated block copolymers.  When utilized as the active layer of photovoltaic cells, block copolymer-based devices demonstrate efficient photoconversion well beyond devices composed of homopolymer blends.  The 3% block copolymer device efficiencies are achieved without the use of a fullerene acceptor.  Resonant soft X-ray scattering and grazing-incidence X-ray diffraction results reveal that the efficient performance of block copolymer solar cells is due to self-assembly into mesoscale lamellar morphologies with primarily face-on crystallite orientations.  We can build on these initial results with the combination of Density Functional Theory, Molecular Dynamics simulations and polymer theory to design donor-acceptor block copolymers with control of charge transfer processes.  For example, interfaces in conjugated block copolymers are governed by chain flexibility and the interaction parameter.  As such, we can present strategies to design block copolymers with suppression of bimolecular recombination through the molecular composition and microstructure.