Interview: Printable Solar Cells for Flexible Solar Energy

6 April 2023

With innovative printable solar panels, researchers from the Helmholtz Association want to equip surfaces that are already in use with the added functionality photovoltaic (PV) power generation. The recently launched Solar TAP platform is intended to make the new technologies quickly and easily accessible to industry, society and consumers. In this interview, Prof. Christoph Brabec and Dr. Jens Hauch from HI ERN, a branch of Forschungszentrum Jülich, together with Prof. Eva Unger from Helmholtz-Zentrum Berlin (HZB) and Prof. Ulrich Lemmer from Karlsruhe Institute of Technology (KIT), explain the progress of various printable PV technologies and the potential multiple-use applications for photovoltaics they have in mind.

In order to achieve the climate targets in Germany and Europe, renewable energies must be massively expanded. For photovoltaics (PV), this means that solar modules would have to cover more than two percent of the land area in Germany. This does not necessarily require the development of new areas for solar parks. Thanks to lightweight, flexibly formable PV modules, it will be possible to use areas in agriculture or in the building sector in such a way that electricity from the sun can be generated on them at the same time, preferably creating an additional benefit for the application.

Through the Solar TAP innovation platform, Forschungszentrum Jülich, Helmholtz-Zentrum Berlin and Karlsruhe Institute of Technology aim to make these new PV technologies quickly and easily accessible to industry, society and consumers. The goal is new applications consisting of printed solar panels. Prof. Christoph Brabec of HI ERN, Prof. Eva Unger of Helmholtz-Zentrum Berlin (HZB), Prof. Ulrich Lemmer of Karlsruhe Institute of Technology (KIT) are coordinating the Solar TAP platform together with research manager Dr. Jens Hauch, HI ERN. Together, the scientists explain how far the technology has come and which applications they have in mind.

What technologies are involved in Solar TAP? What special properties do the corresponding PV modules have?

Prof. Christoph Brabec, HI ERN

Prof. Brabec (HI ERN): In Solar TAP we focus on so-called "emerging photovoltaic" technologies. These include technologies that differ from classical silicon and thin-film photovoltaics by relying on synthesized semiconductors - these include organic and perovskite semiconductors. These technologies have dramatically increased their light conversion efficiency over the past 5-10 years and have now caught up with silicon.

For perovskites, the peak efficiency in the lab is now 25.7 percent, while the record for silicon is 26.7 percent. Organic solar cells are close to exceeding 20 percent in laboratory test cells. But they offer extraordinary advantages when the absorption characteristics of solar cells need to be specifically tailored, for example, for color-attractive building-integrated PV or matching ideal light transmission for crop growth.

Prof. Unger (HZB): Organic and perovskite semiconductors have other advantages as well - they are defect-tolerant and can be easily processed from solution, and one can therefore print solar cells with them. This allows for low-cost, high-throughput manufacturing processes, even on flexible substrates.

Is this largely a dream of the future, or is the technology already ready for practical use?

Prof. Eva Unger, HZB

Prof. Unger: The technologies are still at an early stage, but there are already the first companies commercializing organic and perovskite-based solar cells and testing products in practice. Both technologies still have room for improvement and potential to catch up with the established solar cell technology based on silicon. But this is where there are great opportunities to develop PV products with these new technologies that can be used complementary to silicon PV. Helmholtz Association scientists and researchers are among the best in the world - especially in developing perovskite solar cells as an add-on technology to improve silicon solar cells.

The HI ERN colleagues add: In organic PV, we've made tremendous progress in recent years, and we want to leverage that potential to transfer the technologies quickly and efficiently to industry and society.

Which application areas do you have in mind?

Prof. Ulrich Lemmer, KIT

Prof. Lemmer (KIT): In Solar TAP, we want to focus in particular on "multi-benefit" photovoltaics. In order to achieve the goals of the German government for the expansion of photovoltaics in the next few years, we will have to massively expand installations in Germany, but also worldwide. In Germany alone, we will have to open up thousands of square kilometers of land for PV. Conflicts are inevitable. Therefore, we want to make areas usable for photovoltaics, which are already used for other functions and where PV brings additional advantages. Hence the term "multi-benefit". By far the greatest potential here is in agrivoltaics – that is, the combination of agriculture and photovoltaics. Here, PV can not only generate electricity, it can also be used to manage solar radiation or water, as well as protect against erosion and desiccation. Other interesting areas include, in particular, integration in facades. We can advance technologies for this very quickly and easily in research and development projects along a roadmap together with our industrial partners. Thanks to the funding for the innovation platform, we can get started immediately and implement overarching development projects in a targeted manner.

Prof. Brabec: This offer is very attractive to companies, as they can benefit directly from the Helmholtz centers' accumulated expertise in printed PV technologies. Joint research and development projects enable the smooth transfer of know-how and a direct economic utilization strategy of innovative PV products. This bidirectional transfer also enables the adaptation of PV products according to further aspects such as sustainability and social acceptance, which are important principles in Solar TAP.

Which industry partners are involved? Are concrete applications or prototypes already planned?

Dr. Jens Hauch, HI ERN

Dr. Hauch (HI ERN): In the application phase for the innovation platform, more than 45 industrial partners have already supported us. This is a very heterogeneous group of companies, ranging from small startups to large companies and agricultural enterprises. The first projects can start immediately. In Solar TAP, we have the possibility to produce modules for the demonstration projects in our "solar factory of the future". The first such projects are already being worked on. With a partner who grows raspberries and blackberries, we will investigate this season how these berries grow under semi-transparent organic solar modules. With a small company that develops specialty technologies for airships, we will investigate the suitability of lightweight and flexible solar modules to extend the range of these airships. With other companies, we are developing coating systems for printed solar cells or specialized measurement equipment which makes it possible to characterize extremely thin layers without contact. The projects and the companies have a wide range. But they have one thing in common - they have recognized the great potential of multi-benefit photovoltaics!


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  • Institute of Energy and Climate Research (IEK)
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  • Institute of Energy and Climate Research (IEK)
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Tobias Schlößer


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    Last Modified: 06.04.2023