Influence of electric fields on morphology and performance of compatibilized all-polymer solar cells
Final Report Abstract
This project has investigated new and efficient synthetic avenues towards all‐conjugated block copolymer architectures comprising both electron donor as well as electron acceptor blocks with carefully chosen and suitably aligned energy levels. P3HT was selected as donor block due to the possibility for quantitative and asymmetric end‐functionalization. As acceptor block PCDTBT was chosen on the basis of its electron transport properties and the favorably high open circuit voltage that can be achieved together with P3HT. Starting with, the synthesis of PCDTBT has been revised in very detail, including simplified syntheses, defect analysis and molecular weight control. Linear diblock copolymers of type PCDTBT‐b‐P3HT have been prepared and the influence of additional side chains on the pahse separation behavior in PCDTBT‐b‐P3HT has been investigated. Semifluorinated side chains in PCDTBT drastically enhance the Flory‐Huggins parameter with P3HT, leading to microphase separation in SF‐PCDTBT‐b‐P3HT. This finally also enables efficient compatibilization of blends of SF‐PCDTBT and P3HT, which opens up ways to use complex and cost intensive block copolymers as minority component in all conjugated polymer blends. Finally, new avenues towards graft copolymers of type PCDTBT‐g‐P3HT were successfully investigated. Overall, the outcome of this project clarifies some of the long‐standing questions in the field of all‐conjugated block copolymers for photovoltaics, and can thus be rated as extremely successful. Importantly, block copolymer alignment using electric fields, as originally proposed, is not required as P3HT domains in SF‐PCDTBT‐b‐P3HT were shown to orient in a face‐on fashion, suggesting the presence of vertically aligned pathways in thin films made of these block copolymers. Nevertheless, further structural investigation of SF‐PCDTBT‐b‐P3HT as well as PCDTBT‐g‐P3HT using TEM and SAXS remains to be done in to order to fully understand the phase behavior of these novel materials in thin film.
Publications
- Macromol. Rapid Commun. 2015, 36, 231
F. Lombeck, R. Matsidik, H. Komber, M. Sommer
(See online at https://doi.org/10.1002/marc.201400437) - Macromolecules 2015, 48, 7851–7860
Lombeck, F.; Komber, H.; Sepe, A.; Friend, R. H.; Sommer, M.
(See online at https://doi.org/10.1021/acs.macromol.5b01845) - On the Effect of Prevalent Carbazole Homocoupling Defects on the Photovoltaic Performance of PCDTBT:PC71BM Solar Cells. Adv. Energy Mater., Vol 6 Issue 21, November 9, 2016, 1601232
F. Lombeck, H. Komber, D. Fazzi, D. Nava, J. Kuhlmann, D. Stegerer, K. Strassel, J. Brandt, A. de Zerio Mendaza, C. Müller, W. Thiel, M. Caironi, R. H. Friend, M. Sommer
(See online at https://doi.org/10.1002/aenm.201601232)
