TU Chemnitz: Major progress in printed solar cells

In 2011, the working group led by Prof. Dr. Arved Hübler from the Institute of Print and Media Technology at Chemnitz University of Technology published the first solar cell printed on paper - already a great success at the time. "The feasibility was demonstrated, but with a power efficiency of only 1.7 percent and a very reduced durability, the values were not yet convincing," says Hübler. His working group has now succeeded in printing solar cells with an efficiency of nine percent and significantly improved durability. The yield in the production of the well-functioning cells is already over 88 percent, which is already very high.

Hübler explains the production process in the research laboratory: "Organic semiconductors are located in the central, photoactive layer of the solar cell and convert incident light into a stream of electrons. The cells printed at Chemnitz University of Technology use the polymer mixture PM6:Y12, which is embedded in five additional layers. With the help of these layers, the electrical power generated can be harnessed. The layers are printed like a magazine page on a web press. Liquid printing inks are placed on top of each other and dried. However, these layers are not used for their color, but for their electrical functions."

• Ageing tests as part of a cross-university research collaboration

This success was achieved as part of the research group "POPULAR - Printed & Stable Organic Photovoltaics with Non-Fullerene Acceptors" funded by the German Research Foundation (DFG). Prof. Dr. Carsten Deibel, Chair of Optics and Photonics of Condensed Matter at Chemnitz University of Technology and spokesperson for the DFG research group, reports that the solar cells printed in Chemnitz were taken directly to the project partners at the University of Erlangen-Nuremberg for durability testing. There they are currently undergoing accelerated ageing. After six weeks, these aged solar cells can be compared with fresh solar cells printed at Chemnitz University of Technology in order to determine the causes of ageing. These investigations are carried out in the working group at the Institute of Physics at Chemnitz University of Technology and by other members of the POPULAR team in Dresden, Bayreuth and Potsdam. The results are incorporated into evaluations using simulation programs for the printed solar cells. The knowledge gained helps in the development of new organic semiconductors, which is located at the Institute of Chemistry at Chemnitz University of Technology.

• Printed solar cells have great market potential

According to Hübler, printed solar cells are a promising candidate for the next generation of solar cells. "Despite their very energy-intensive production, today's solar cells are relatively inexpensive because they are produced in China using extremely cheap coal-fired electricity. However, the next generation of technology must produce much more efficiently, which is where printing comes in, says the Chemnitz professor. In his opinion, square kilometers of solar cells can be printed on paper or film and brought to market in a short space of time with little energy input. "Potential markets are already known. Climate change requires more and more shading, for example in agriculture. Kilometers of solar panels can simply be pulled across the fields and cleared away later. However, the service life of the printed solar cells must be right for a successful application," says Hübler. With the work of the POPULAR research group, fundamental questions can now be clarified in order to lay the foundation for a next-generation solar cell industry - hopefully in Germany again.

• Background: DFG research group "Printed & stable organic photovoltaics with non-fullerene acceptors - POPULAR" under the leadership of Chemnitz University of Technology

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 a leader 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 Chemnitz University of Technology, is the spokesperson for the DFG research group, which involves 14 scientists from several universities in Germany and the UK. The common goal is to produce organic solar cells using printing processes suitable for mass production and to understand and improve them using complementary experiments and simulations.