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Current research led by TU Chemnitz contributes to a deeper understanding of why slow electrons reduce the efficiency of organic solar cells – Publications in the renowned journals Reports on Progress in Physics and Advanced Energy Materials
Researchers from the Chair of Optics and Photonics of Condensed Matter (led by Prof. Dr. Carsten Deibel) at the Chemnitz University of Technology and other partner institutions are currently working intensively on solar cells made from novel organic semiconductors that can be produced using established printing processes. The scientists are collaborating interdisciplinarily to fundamentally understand these photovoltaic cells made from organic semiconductors to further improve them. This is taking place within the framework of the Research Unit "Printed & Stable Organic Photovoltaics with Non-Fullerene Acceptors - POPULAR", funded by the German Research Foundation, of which Prof. Deibel is the spokesperson.
"Organic solar cells can be produced very easily and cheaply using printing processes," says the Chemnitz physics professor. In contrast to established solar modules made of crystalline silicon, however, the current flow in organic solar cells is very slow. "Due to the production of the solar cells from a kind of ink, the organic, light-absorbing layers are very disordered. Therefore, the current flow is very slow," explains Deibel. A consequence of the slow transport of light-generated electrons and holes is the so-called transport resistance, which reduces the fill factor of the solar cells and thus the power.
Deeper Understanding: Transport Resistance Limits the Performance of Organic Solar Cells
To better understand the performance characteristics of organic solar cells, Deibel and his scientific assistant Maria Saladina have produced and thoroughly investigated different types of organic solar cells and uncovered the negative influence of transport resistance. The current-voltage characteristics under illumination, which result from the interplay of charge generation by light, recombination of electron and holes, and charge transport, were measured. Theycontain information on the power efficiency of the solar cells. These measurements were compared with the so-called suns-Voc method, which allows to construct an alternative current-voltage curve that is not limited by charge transport losses such as transport resistance. "Transport resistance is a result of the slow charge carriers in the disordered solar cells processed from organic ink. Thus, the charge carriers get in their own way and lead to a loss of fill factor and thus power," says Saladina.
Publications in the Journals "Reports on Progress in Physics" and "Advanced Energy Materials"
The research results were published in the renowned journal "Reports on Progress in Physics" (88, 038001 (2025)) (https://doi.org/n687). Although the optimization of organic solar cells must be re-evaluated due to these new results, there is no fundamental obstacle to producing highly efficient, printed organic solar cells. In a perspective article, written by Chen Wang, Carsten Deibel, and Maria Saladina together with renowned co-authors from various German universities and published in the journal Advanced Energy Materials, the physical origin of transport resistance and its significance for solar cells is explained in detail. "In recent years, charge transport has been continuously improved without the research community knowing the exact relationship between fill factor losses and transport resistance," says Deibel. Saladina adds: "In addition to recombination, transport resistance is also determined by the shape of the density of states of organic solar cells. This shows that we are step by step understanding the physical foundations of these photovoltaic devices better and better." These results have been achieved within the framework of the DFG Research Unit POPULAR, which continues to work on understanding and improving printed organic solar cells.
Background: DFG Research Group "Printed & Stable Organic Photovoltaics with Non-Fullerene Acceptors - POPULAR" under the leadership of TU Chemnitz
The research group "Printed & Stable Organic Photovoltaics with Non-Fullerene Acceptors - POPULAR" (FOR 5387), funded by the German Research Foundation with around five million euros, is leading in the field of optoelectronic characterization of organic solar cells. Prof. Dr. Carsten Deibel, holder of the Chair of Optics and Photonics of Condensed Matter at TU Chemnitz, is the spokesperson for the DFG Research Unit, which involves 14 scientists from several universities in Germany and Great Britain. The common goal is to produce organic solar cells using mass-production-compatible printing processes and to understand and improve them with complementary experiments and simulations.
Maria Saladina, phone +49 (0)371 531-34046, email maria.saladina@physik.tu-chemnitz.de, and Prof. Dr. Carsten Deibel, phone +49 371 531-34878, email deibel@physik.tu-chemnitz.de
Maria Saladina, Carsten Deibel: Transport resistance dominates the fill factor losses in record organic solar cells. Reports on Progress in Physics, 88, 038001 (2025). DOI: https://doi.org/n687
Chen Wang, Carsten Deibel, Maria Saladina, et al: Transport resistance dominates the fill factor losses in record organic solar cells. Advanced Energy Materials, 2405889 (2025). DOI: https://doi.org/10.1002/aenm.202405889
Maria Saladina, Carsten Deibel, and Chen Wang (r.) from the Chair of Optics and Photonics of Condens ...
Photo: Martin Mellendorf
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Maria Saladina, Carsten Deibel, and Chen Wang (r.) from the Chair of Optics and Photonics of Condens ...
Photo: Martin Mellendorf
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