Side Chain Engineering of a Non-Fused Ring Electron Acceptor for Improved Thermal and Photo-Stability

Side Chain Engineering of a Non-Fused Ring Electron Acceptor for Improved Thermal and Photo-StabilityJulia Hönigsberger a, Barbara Muhry a, Bettina Schlemmer a, Thomas Rath a, Gregor Trimmel aa Institute for Chemistry and Technology of Materials (ICTM), NAWI Graz, Graz University of Technology, Stremayrgasse 9, 8010 Graz, AustriaInternational Conference on Hybrid and Organic PhotovoltaicsProceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV24)València, Spain, 2024 May 12th - 15thOrganizer: Bruno EhrlerOral, Julia Hönigsberger, presentation 198DOI: https://doi.org/10.29363/nanoge.hopv.2024.198Publication date: 6th February 2024Organic photovoltaics is a promising emerging technology for solar energy conversion due to low production cost, large area roll-to-roll production possibilities, flexibility, lightweight, and semitransparency.[1-2] Most organic solar cells contain non-fullerene acceptors with large fused-ring systems. However, the production of these acceptors is due to their synthetic complexity costly and often involves toxic materials and solvents. Non-fused electron acceptors are an alternative, since they require fewer synthesis steps, are cheaper to produce, and still have the required planarity of the molecule. In our work, we have successfully synthesized derivatives of the COTIC-4F acceptor comprising a cyclopentadithiophene core, thiophene linkers and fluorinated IC end groups. The molecules B1 and B2 differ from the COTIC-4F molecule in their side chains (hexyl instead of 2-ethylhexyloxy) attached to the thiophene linker. In B2, we additionally changed the position of the hexyl chain at the thiophene ring from 3 to 4. By this modification, we expected an increased photostability due to structural confinement mitigating photoisomerization and photooxidation of the molecule.[3] The NFAs B1 and B2 reveal higher optical band gaps (1.31 eV) than COTIC-4F (1.1 eV).[4] In bulk heterojunction organic solar cells in conventional architecture, power conversion efficiencies of 9.59% were obtained for solar cells with the PTB7-Th:B1 absorbers and 9.94% for PTB7-Th:B2 based absorber layers. The higher performance of the B2 based solar cells is most presumably due to a more balanced hole and electron mobility and higher exciton dissociation probabilities. In addition, we investigated the stability of these materials and solar cells in detail. For instance, we studied the change of absorption properties of B1 and B2 films under continuous solar simulator illumination in ambient conditions and obtained a significantly decreased fading in absorption intensity of the B2 film. Moreover, PTB7-Th:B1 and PTB7-Th:B2 based solar cells were tested under various conditions (shelf life at room temperature and 65 °C, continuous illumination) and found that the PTB7-Th:B2 solar cells show a significantly higher photostability (t80: ~600 h) as well as higher thermal stability (t80: ~600 h) compared to the B1 based solar cells, which reveal t80-times of only ~125 h under both testing conditions. This work reveals that the investigated modification in the NFA design does not only lead to improved photostability but also to increased stability at elevated temperatures, which we will investigate in more detail also for other non-fused NFA structures in the near future. References:[1] Luke, J., Yang, E.J., Labanti, C. et al. Key molecular perspectives for high stability in organic photovoltaics. Nat Rev Mater. 2023, 8, 839–852.[2] Yi, J., Zhang, G., Yu, H. et al. Advantages, challenges and molecular design of different material types used in organic solar cells. Nat Rev Mater. 2024, 9, 46–62.[3] Liu, ZX., Yu, ZP., Shen, Z. et al. Molecular insights of exceptionally photostable electron acceptors for organic photovoltaics. Nat Commun. 2021, 12, 3049.[4] Jaewon Lee, Seo-Jin Ko, Hansol Lee, Jianfei Huang, Ziyue Zhu, Martin Seifrid, Joachim Vollbrecht, Viktor V. Brus, Akchheta Karki, Hengbin Wang, Kilwon Cho, Thuc-Quyen Nguyen, and Guillermo C. Bazan ACS Energy Letters. 2019, 4, 6, 1401-1409.© FUNDACIO DE LA COMUNITAT VALENCIANA SCITOnanoGe is a prestigious brand of successful science conferences that are developed along the year in different areas of the world since 2009. Our worldwide conferences cover cutting-edge materials topics like perovskite solar cells, photovoltaics, optoelectronics, solar fuel conversion, surface science, catalysis and two-dimensional materials, among many others.MATSUSPreviously nanoGe Spring Meeting (NSM) and nanoGe Fall Meeting (NFM), MATSUS is a multiple symposia conference focused on a broad set of topics of advanced materials preparation, their fundamental properties, and their applications, in fields such as renewable energy, photovoltaics, lighting, semiconductor quantum dots, 2-D materials synthesis, charge carriers dynamics, microscopy and spectroscopy semiconductors fundamentals, etc.International Conference on Hybrid and Organic PhotovoltaicsInternational Conference on Hybrid and Organic Photovoltaics (HOPV) is celebrated yearly in May. The main topics are the development, function and modeling of materials and devices for hybrid and organic solar cells. The field is now dominated by perovskite solar cells but also other hybrid technologies, as organic solar cells, quantum dot solar cells, and dye-sensitized solar cells and their integration into devices for photoelectrochemical solar fuel production.Asia-Pacific International Conference on Perovskite, Organic Photovoltaics and OptoelectronicsThe main topics of the Asia-Pacific International Conference on Perovskite, Organic Photovoltaics and Optoelectronics (IPEROP) are discussed every year in Asia-Pacific for gathering the recent advances in the fields of material preparation, modeling and fabrication of perovskite and hybrid and organic materials. Photovoltaic devices are analyzed from fundamental physics and materials properties to a broad set of applications. The conference also covers the developments of perovskite optoelectronics, including light-emitting diodes, lasers, optical devices, nanophotonics, nonlinear optical properties, colloidal nanostructures, photophysics and light-matter coupling.International Conference on Perovskite Thin Film Photovoltaics Perovskite Photonics and OptoelectronicsThe International Conference on Perovskite Thin Film Photovoltaics Perovskite Photonics and Optoelectronics (NIPHO) is the best place to hear the latest developments in perovskite solar cells as well as on recent advances in the fields of perovskite light-emitting diodes, lasers, optical devices, nanophotonics, nonlinear optical properties, colloidal nanostructures, photophysics and light-matter coupling.