Solvent-free tandem solar cells

Researchers from the Optoelectronic Thin-Film Materials Junior Research Group at the Department of Sustainable Systems Engineering (INATECH) at the University of Freiburg and the Fraunhofer Institute for Solar Energy Systems ISE have developed a new, fully solvent-free manufacturing process for perovskite-silicon tandem solar cells. Their findings have now been published in the renowned scientific journal Joule.

Perovskite-silicon tandem solar cells are considered a promising technology for the next generation of highly efficient solar cells. However, conventional manufacturing processes rely on solvents, which present a number of challenges, including the solubility of the starting materials, their toxicity, as well as the homogeneity and compatibility of individual process steps. The Freiburg research team has now succeeded in overcoming these challenges entirely, paving the way for a more sustainable and potentially more scalable manufacturing process.

At the heart of the project is the fabrication of the perovskite layer using physical vapor deposition (PVD) and other solvent-free, industrially scalable processes. The perovskite layer was deposited through sequential evaporation. To gain a better understanding of crystal formation during deposition and the subsequent annealing process, the research team led by Mohamed A. A. Mahmoud and Dr. Juliane Borchert monitored the process using in-situ X-ray diffraction (XRD). In addition, the researchers investigated the influence of the surface structure of silicon substrates on the formation of the perovskite layer. For these specialized measurements, the Freiburg scientists collaborated with researchers from Martin Luther University Halle-Wittenberg, Universidad Pablo de Olavide in Seville, Spain, King Abdullah University of Science and Technology in Saudi Arabia, and the ODTÜ-GÜNAM Research Center in Türkiye.

A key distinguishing feature of the work is the development of the world’s first fully solvent-free perovskite-silicon tandem solar cell. At the same time, the use of in-situ XRD in collaboration with Martin Luther University Halle-Wittenberg (MLU) during the evaporation and annealing processes provides new insights into the underlying crystallization processes. These findings provide an important foundation for further optimizing the technology and for its future industrial implementation.

“We have succeeded in eliminating all solvents from the manufacturing process of the wide-bandgap perovskite top cell and integrating this technology into the world’s first fully solvent-free perovskite-silicon tandem solar cell,” says Mohamed A. A. Mahmoud.

„Thanks to excellent collaboration with researchers from four different countries, we were able to combine various measurement techniques to gain a detailed understanding of the processes taking place during the deposition of the perovskite thin films,“ says Dr. Juliane Borchert. “Perovskite-silicon tandem solar cells have great potential to become the next generation of highly efficient solar cells. For them to make the transition from the laboratory to industrial manufacturing, it is essential to identify the optimal combination of deposition methods that enables reliable, large-scale, and high-throughput production. With this solvent-free tandem solar cell, we are laying an important foundation for achieving this goal.”

This research was funded by the Vector Foundation, the German Research Foundation (DFG), the Federal Ministry for Economic Affairs and Energy, and the Spanish Ministry of Universities.

Link to the article in the journal Joule: https://www.cell.com/joule/fulltext/S2542-4351(26)00330-2

Contact:

Dr. Juliane Borchert
Head of the „Optoelektronic Thin-Film Materials“ research group oft he Department of Sustainable Systems Engineering (INATECH) at the University of Freiburg
Head of the „Perovskite Materials and Interfaces” research group at the Fraunhofer Institute for Solar Energy Systems ISE, Freiburg
Tel.: +4976145885475
E-Mail: juliane.borchert@inatech.de

Mohamed A. A. Mahmoud
PhD Researcher
Fraunhofer Institute for Solar Energy Systems ISE & University of Freiburg
Freiburg im Breisgau, Germany
Email: mohamed.mahmoud@ise.fraunhofer.de

Kerstin Steiger-Merx
Representative Marketing & PR
University of Freiburg
Tel.: 0761/203-8056
E-Mail: steiger-merx@tf.uni-freiburg.de