RAtional DEsign of blends for bulk heterojunction SOLar cells

Organic solar cells have recently reached an efficiency of >10%, and are considered interesting and complementary technology to inorganic solar cells. Organic solar cells are cost effective, bendable/stretchable, environmentally friendly and biocompatible. The goal of the RADESOL project was to reach a deeper understanding of the coupling between the materials structure (nanomorphology), processing and the performance of the solar cell. The research group of Prof. Breiby has specialist competence within X-ray diffraction and -microscopy. Within RADESOL, we have demonstrated that the architecture of organic solar cells can be imaged in 3D using coherent X-ray diffraction, with a resolution of about 100 nm. This is a breakthrough because there are no other techniques available which can image organic multilayers non-destructively and with similar contrast and spatial resolution. We have also shown that domains within the photoactive polymer blends can be imaged with X-ray microscopy in combination with fast calorimetry, which opens for future in-situ studies of the connection between processing and material structure. Domains in SiGe microwires were also studied, with results published in Nature Communications. An important success factor for RADESOL was the complementary competence of the project partners, which we will continue to appreciate in continued collaborations.

In spite of being a quite young research area, organic photovoltaics are showing an impressive development. Top efficiencies of over 10% have recently been demonstrated. However, for this technology to become a real and competitive energy source for the f uture, it is clear that a deeper understanding of the inter-relationships between material structure, nanomorphology and device performance is needed, and this based on generic insights on the fundamentals of said relationships. Only in this way power con version efficiencies of 15% or more can be achieved on a reasonable time scale. The consortium brought together in this project comprises leading groups of Flanders (Belgium), Portugal, and Norway concerning advanced materials synthesis and characterizati on. The main goal of the project is to unravel nanomorphology formation at the molecular level and its effect on device performance beyond the state-of-the-art by an integrated experimental effort and a unique combination of equipment and expertises, aimi ng at the study of blends via advanced thermal analysis, solid-state NMR, and X-ray diffraction and ptychography 3D imaging techniques, combined with analysis of the optoelectronic characteristics in photovoltaic devices. The results will lead to an integ rated model allowing for molecular structure engineering in function of the desired nanomorphology and thus wanted photovoltaic parameters. As all partners are strongly involved within the European research community active in organic photovoltaics via ne twork programs and National & European projects, dissemination of the insights achieved will strengthen the research impact of Europe and facilitate efforts to valorize European activities in organic electronics.