2, Laboratory of Organic and Macromolecular Chemistry (IOMC), Friedrich Schiller University Jena, Jena, , Germany
3, Institute of Thermodynamics and Fluid Mechanics, Technische Universität Ilmenau, Ilmenau, , Germany
4, Linz Institute for Organic Solar Cells (LIOS), Johannes Kepler University Linz, Linz, , Austria
5, Institute of Polymeric Materials and Testing, Johannes Kepler University, Linz, , Austria
Aggregation of organic semiconductors positively impacts the device performance of polymer-based bulk heterojunction solar cells. Aggregation and specifically intermolecular electronic coupling leads to extended absorption spectra by formation of new absorption bands. Furthermore, it has been demonstrated that more ordered domains of organic semiconductors improve the free charge carrier generation and also reduces the recombination of free charges located in the ordered phases due to energy relaxation. Finally, aggregation enhances charge carrier transport and lifetimes, resulting in an improved charge extraction under operating conditions.
The advantage of controlling the aggregation in solution is a higher reproducibility of bulk heterojunction domain sizes – largely independent of local drying conditions which are varying for different casting techniques during film formation. Furthermore, pre-aggregation in solution makes post-processing techniques mostly evitable and, hence, simplifies the production process of the solar cell devices.
In this study, progress in controlling polymer aggregation in solution by introduction of anti-solvent additives is reported. The impacts of polymer aggregation on parameters determining photovoltaic performance were investigated. Various spectroscopic and structure revealing methods were applied in order to further elucidate correlations between device properties and conformational state of materials and interfaces.