Solar cells on the roofs have long been common practice, as have large solar parks. In the future, however, it is planned to use areas that were previously unsuitable for energy generation. Truck tarpaulins, for example, could supply the trailers self-sufficiently with the electricity that the driver consumes during the journey and at rest areas or that is needed at logistics locations for truck location. In addition, entire building fronts could contribute to power generation by not plastering them as before, but covering them with power-generating textiles. With glass facades, shading textiles such as roller blinds could convert hundreds of square meters into power generation areas.
This is made possible by textile, flexible solar cells developed by researchers from the Fraunhofer Institute for Ceramic Technologies and Systems IKTS - together with the Fraunhofer Institute for Electronic Nano Systems ENAS, the Saxon Textile Research Institute e.V. and the companies erfal GmbH & Co. KG, PONGS Technical Textiles GmbH, Paul Rauschert GmbH & Co. KG and GILLES PLANEN GmbH. "We can manufacture solar cells directly on technical textiles using various coating processes," explains Dr. Lars Rebenklau, group leader for system integration and AVT at Fraunhofer IKTS. In other words, the researchers do not use glass or silicon as in conventional solar modules, but rather textiles as substrates. "However, this is anything but easy - after all, the plants in the textile processing companies are huge with fabric widths of five to six meters and fabric lengths of a thousand meters. What's more, the textiles have to withstand temperatures of around 200 degrees Celsius during coating," adds Dr. Jonas Sundqvist, group leader for thin-film technologies at Fraunhofer IKTS. Other requirements such as fire protection regulations, high stability and a favorable price are also elementary for the production of solar cells. "In the consortium, we have therefore decided on a glass fiber fabric that meets all these requirements," says Rebenklau.
Another challenge was the application of the various layers of a solar cell to the fabric - i.e. the base electrode, the photovoltaic layer and the cover electrode. Compared with these layers, which are only one to ten micrometers thick, the surface of a textile resembles a huge mountain. The researchers therefore use a trick: they first apply a levelling layer to the textile, which compensates for mountains and valleys. To do this, they use transfer printing - a standard process in the textile industry that is also used for gumming. From the outset, the researchers have also designed all other production processes in such a way that they can be easily integrated into the production lines of the textile industries: they apply electrodes made of electrically conductive polymer as well as the photovoltaic layer using the conventional roll-to-roll process. In order to make the solar cell as robust as possible, the researchers also laminate a protective layer onto it.
The research team has already produced the first prototype. "We were able to show that our textile solar cell works in itself," says Rebenklau. "Its efficiency is currently between 0.1 and 0.3 percent. In a follow-up project, the engineer and his colleagues are now working on increasing the efficiency to over 5 percent - because from this value the textile solar cell pays off. Silicon cells achieve significantly higher efficiency values of 10 to 20 percent. However, the novel cell is not intended to compete with conventional cells, but to complement them in a meaningful way. The researchers also want to investigate and optimize the service life of the textile solar cell in the coming months. If everything works as hoped, the textile solar cell could come onto the market in about five years. Then the original goal of the PhotoTex project would be achieved: to find new ideas for Germany as a textile location and to increase the competitiveness of this industrial sector.