Fraunhofer FEP and Heliatek: Conclusion of BMBF research project on transparent organic photovoltaic glass façades (TOP)


In December 2018, the BMBF-funded research project "Transparent Organic Photovoltaics (OPV) Glass Facade" (project name: TOP) ended as part of the funding initiative "Organic Electronics - Fundamentals of Technology and Application Scenarios." The aim of the joint project was to develop semi-transparent solar foils with a transparency of 15-30% at an efficiency of 8-10% and a suitable encapsulation. The consortium consisted of CreaPhys GmbH (Dresden), Fraunhofer FEP (Dresden), Fraunhofer ISE (Freiburg), Heliatek GmbH (Dresden) and the University of Ulm.

The TOP project, which lasted three years, addressed the central topic of energy supply in Germany and Europe. In Europe, approx. 20 million m² of glass surfaces are used each year for building facades (office buildings and public facilities). These areas are thus available for alternative energy generation without the need for separate areas. Up to now, these areas have not been usable with conventional photovoltaics, or only to a limited extent. Dimensionable solar films, which can be easily and extensively integrated and produced as transparent designs, are an attractive solution for windows, solar control glazing and transparent facades, for example.

At the University of Ulm, various series of new absorber materials were synthesised and further developed in the project, which on the one hand have improved light absorption properties and on the other have increased thermal stability, which is very important for the manufacturing process.

Creaphys has successfully demonstrated the purification of new absorber materials on the basis of a gas phase process. The scalability of a bulk material was promoted. In addition, processes for the purification of further new materials have been established, which are expected to enter the next stack generation of solar film.

Fraunhofer FEP optimised the semi-transparent conductive top contact and further developed the encapsulation technology to protect the cells from water vapour penetration.

Using the new absorber materials (University of Ulm, Heliatek), Heliatek has developed an organic solar cell with an efficiency of 8% and a transparency of 17.6%. Together with the partner Fraunhofer FEP, the proof-of-principle for a thin-film encapsulation process using the ALD process (atomic layer deposition) could also be demonstrated, which enables service life values of the solar films of over T95 (i.e. less than 5% degradation) after a period of 1000h at 85°C and 85% humidity.

At Fraunhofer ISE, the long-term stability of Heliatek solar cells was investigated in detail. At 85°C, the glass-encapsulated solar cells are stable for more than ten thousand hours and even UV light does not lead to any noticeable degradation.

At the end of the TOP project, a glass demonstrator measuring 20cm × 20cm was produced.

Heliatek is currently building a new production plant for volume production, which will be started up in 2019/20 and has an annual production capacity of up to 1 million m² of OPV film. Production in Germany also makes economic sense due to the highly productive roll-to-roll process.

The TOP project was funded by the Federal Ministry of Education and Research and was part of the funding programme "Photonik Forschung Deutschland" (funding code: 13N13706).

Caption: Organic solar film (photo: Silicon Saxony/Fraunhofer FEP)

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