Bio: Professor Müller-Buschbaum (b. 1966) carries out research in the field of functional materials, with a particular focus on energy materials, e.g. solar cells and batteries. Professor Müller-Buschbaum studied physics in Kiel and went on to earn his doctorate there in 1996. He then worked as a postdoctoral fellow at the Max Planck Institute for Polymer Research in Mainz and as visiting scientist at the Institut Laue-Langevin and the European Synchrotron Radiation Facility in Grenoble, France. He acquired his postdoctoral teaching qualification (Habilitation) in 2002 and headed the Chair of Functional Materials at the TUM Department of Physics, before his appointment as full professor in 2018. From 2018 to 2023 he was scientific director of the Forschungs-Neutronenquelle FRM-II and of the Heinz Maier-Leibnitz Zentrums MLZ. Since 2011, he has been the German representative at the European Polymer Federation and, since 2024, Deputy Editor of the journal ACS Applied Materials & Interfaces. He also heads the Bavarian key laboratory TUM.solar and the Network for Renewable Energies (NRG). Since 2024, he is member of the TUM sustainability board.

Abstract: Organic Solar Cell for Space Applications

Organic solar cells offer significant potential as a power source in space due to their exceptional properties. Their high absorbance in the visible spectrum allows the active layer thickness to be reduced to about a hundred nanometers. Combined with power conversion efficiencies of champion devices above 20%, this results in an outstanding power-to-weight ratio. Their solution processability significantly reduces manufacturing costs, making them an attractive, cost-effective alternative to current silicon or multi-junction gallium arsenide solar cells. However, numerous challenges must be addressed to make organic solar cells viable in space conditions, including high vacuum, extreme temperatures, and radiation. Moreover, the terrestrial handling before launch and the harsh launch conditions can impose challenges on organic solar cells.

We have developed a solar cell testing platform for sounding rocket flights [1], which allows the electrical characterization of organic solar cells at orbital altitudes [2]. Space flights are an ideal platform to investigate the behavior of solar cells in conditions that are characterized by ultra-high vacuum, strong UV solar irradiation, and the absence of oxygen or water outside Earth’s atmosphere. During a suborbital rocket flight, we measured the voltage-current response of organic solar cells under different illumination conditions.

Combining the solar cell measurements with irradiance data obtained from simultaneous light sensor measurements allows for deducing the performance parameters [3]. Our results show that the solar cells survived the harsh conditions during transport, the start preparation procedure, and the rocket launch, where the tested organic solar cells reached power conversion efficiencies comparable to the laboratory values. From a detailed post-flight characterization, we gain insights into the potential degradation mechanism of the new type of solar cells [4], with the target to better understand the individual influences of terrestrial handling, rocket launch, and space exposure.
[1] Reb et al. Rev. Sci. Instr. 92, 074501 (2021)
[2] Reb et al. Joule 4, 1880-1892 (2020)
[3] Reb et al. Solar RRL 6, 2200537 (2022)
[4] Reb et al. Solar RRL 7, 2300043 (2023