Textiles create solar energy

Researchers from the Fraunhofer Institute for Ceramic Technologies and Systems (IKTS) have developed pliable, textile-based solar cells that could add a new dimension to photovoltaic energy generation. Instead of glass or silicon, the substrate for the solar cells is a woven fabric.

In addition to rooftop solar systems, other surfaces could be used to generate power. For example, truck or semitrailer tarps could produce the electricity needed to power cooling systems or other onboard equipment. Conventional building facades could be covered with photovoltaic textiles in place of concrete render; blinds used to provide shade in buildings with glass facades could be used to create hundreds of square metres of additional surface for producing power. This would enable a plethora of ways to harness solar energy.

Glass-fibre fabric as a solar-cell substrate

“There are a number of processes that enable solar cells to be incorporated in coatings applied to textiles,” explained Dr Lars Rebenklau, group manager for system integration and electronic packaging at Fraunhofer IKTS.

“That might sound easy, but the machines in the textile industry are designed to handle huge rolls of fabric — five or six metres wide and up to 1000 metres in length,” added Dr Jonas Sundqvist, group manager for thin-film technology at Fraunhofer IKTS.

Dr Rebenklau continued: “During the coating process, the textiles have to withstand temperatures of around 200°C. Other factors play a key role too: the fabric must meet fire regulations, have a high tensile strength and be cheap to produce. The consortium therefore opted for a glass-fibre fabric, which fulfils all of these specifications.”

An emphasis on standard processes

The research team faced the challenge of how to apply the wafer-thin layers that make up a solar cell — the bottom electrode, the photovoltaic layer and the top electrode — to the fabric. These layers are between one and 10 microns in thickness. By comparison, the surface of the fabric is like a mountain range.

The solution was to first apply a layer that levels out the peaks and troughs on the surface of the fabric. For this purpose, the researchers opted for a standard process used in the textile industry: transfer printing, which is also used to rubberise fabrics.

All other processes were adapted to be easily incorporated in standard production methods used in the textile industry. For example, the two electrodes — made from electrically conductive polyester — and the photovoltaic layer are applied by means of the common roll-to-roll method. The solar cells are then laminated with an additional protective layer to make them more robust.

Preparing fabric-based solar cells for market launch

The research team has already produced an initial prototype of the fabric-based solar cells.

“This has demonstrated the basic functionality of our textile-based solar cells,” Dr Rebenklau said. “Right now, they have an efficiency of between 0.1 and 0.3%.”

In a follow-up project, he and the team are seeking to push this over the 5% mark, at which point the textile-based solar cells would become commercially viable.

Silicon-based solar cells are significantly more efficient (10–20%). However, this new form of solar cell is not intended to replace the conventional type, merely offer an alternative for specific applications. In the coming months, the team will be investigating ways of enhancing the service life of the fabric-based solar cells.

If all goes according to plan, the first textile-based solar cells could be ready for commercialisation in around five years. This would fulfil the original goal of the PhotoTex project: to provide new stimulus for Germany’s textile industry and improve its competitiveness.

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