Directional crystallization of semiconducting homopolymers and novel donor-acceptor diblock copolymers for control of nanostructure and optoelectronic properties

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Donor-acceptor block copolymers are potentially promising materials for organic solar cells. By self-assembly they are able to form thermodynamically stable donor-acceptor nanostructures. Such nanostructures are a fundamental requirement for efficient photoinduced charge separation into holes and electrons. Compared to the usually used donor/acceptor blends, block copolymers offer increased control over the morphology and avoid morphological degradation.While basic understanding of the complex self-assembly behavior of donor-acceptor block copolymers has been achieved, current investigations are limited to a small number of model materials and the necessary alignment of the microphase structure has not been realized. This proposal addresses both of these issues. New optimized materials will be synthesized, and using these materials, we plan to explore interface induced, directed crystallization as a means to create well-aligned donor-acceptor nanostructures to ensure efficient charge transport. In order to address both of the interwoven aims, the project consists of a collaboration between two groups with suitable expertize.In the polymer chemistry part of the project, both side-chain functionalized and all-conjugated block copolymers with a P3HT donor block and new optimized acceptor blocks based on PCBM with low Tg and Polydiketopyrrolopyrrole respectively will be synthesized. The self-assembly of these materials in bulk will be studied beforehand to make sure that structure formation is driven by crystallization. In the polymer physics part, the prerequisites for obtaining fully oriented crystalline films will be investigated in a first part using model materials supplied by polymer chemistry. In a second step, the elaborated methods of directional crystallization and epitaxial orientation will be transferred to block copolymers to obtain films with oriented donor-acceptor nanostructure. Electrical characterization will be performed in a diode setup (SCLC) measurements giving information about vertical charge transport.