Solar cells for buildings upgraded in new EU project
It looks like ordinary black glass, but the entire façade produces electricity. The Frodeparken apartment block in Uppsala is covered with thin-film solar cells developed from research at the University. Uppsala is also leading an international EU project on solar-cell technology that can be integrated into buildings.
Marika Edoff, Professor of Solid State Electronics, is the project coordinator. The kick-off meeting was held at the Ångström Laboratory in May, and in November another meeting took place, in Eindhoven, the Netherlands. The focus is on thin-film solar cells and how they can be made more efficient and integrated into buildings.
The dominant technology in the market uses silicon solar cells, which are manufactured on a large scale and thus at a lower cost. Thin-film solar cells are based on another technology and look different. They consist of microscopically thin films mounted on, for example, glass. The modules can be made into uniformly black building blocks, as on the Frodeparken façade.
“To compete with silicon solar cells, you have to go in for such huge production volumes that it’s hard for new entrants. We’ve therefore looked for a suitable niche where growth is possible,” says Edoff.
“In building integration, there are unique opportunities for thin-film solar cells, especially to look aesthetically different. With thin films, there are also ways of making solar cells flexible and lightweight.”
The EU cooperation includes, for example, a steel company that manufactures a steel substrate to which solar cells could be attached, so as to be made bendable and flexible.
The scientists’ challenge lies in making the materials thinner without impairing efficiency, which is currently 21%. To succeed, various optical techniques are used, such as incorporating mirrors in the thin layers so that twice as much light is absorbed.
“It may seem silly to make the layers even thinner, when the total thickness of the layers is already down to about three microns (micrometres), which you get if you take a hair and cut it into 20 slices. But we want to push it down further, reduce material usage by a factor of four and make the light-absorbing layers half a micrometre thick instead of two.”
During the development work, small samples are sent by post back and forth across Europe, Edoff recounts.
“The latest samples had received a layer from us and were then sent to Belgium, where more layers were added. Then they were sent to Portugal, where patterning of the layers was done, and came back to us so we could make measurements.”
Internationally, photovoltaic (PV) cells have had a major breakthrough in recent years. In countries such as Germany and Italy, rooftop solar cells are a common sight. Sweden is less advanced, but now the market is starting to grow here too, with various support systems for installing solar cells in buildings. This also generates prospects for solar-cell businesses and new jobs, Edoff thinks.
“Production is one thing, but it also provides many job opportunities in the building of facilities and in importing, mounting and installing solar cells. Through the EU project we can gather a range of skills, and we also hope to give solar cells a higher profile and lobby to bring about long-term solutions in Sweden.”
Edoff was a founder of the solar cell company Solibro GmbH and has worked for many years both as a researcher and within the company. When she started on thin-film solar cells in 1990, they had an efficiency of 10%. Now they have reached 21% – not far from the world record of 22.6%.
She attributes this success to the close collaboration between universities and companies.
“Various EU projects have been crucial in enabling the technology to progress this far, thanks to the cooperation they’ve fostered between companies and research groups. That’s been extremely important.”
CIGS solar cells consist of thin layers of four substances: copper, indium, gallium and (di)selenide. This semiconductor material is an outstandingly efficient light absorber that can be used to coat various types of substrate. The researchers are striving to attain the highest possible efficiency for the solar cells by using various materials and material combinations, and by modifying the manufacturing process.
The EU project ARCIGS-M (Advanced aRchitectures for ultra-thin high-efficiency CIGS solar cells with high Manufacturability) began in December 2016 and is coordinated from Uppsala University. It is a collaboration among 13 academic and business partners from five countries. The project has been granted EUR 4.5 million over the three years until 2019.