Solar cells in windows could turn buildings into power plants

Solar energy is one of our most promising renewable energy sources. However, today’s conventional solar cells are expensive to manufacture and difficult to integrate into surfaces like windows and façades. Now, research from Luleå University of Technology demonstrates how a new type of thin-film solar cell can be produced at a lower cost—enabling buildings to generate their own electricity without blocking outdaylight.

Traditional silicon-based solar cells dominate the market, but their production requires significant resources. Researchers are now turning their attention to thin, semi-transparent solar cells that can be integrated into buildings—allowing light to pass through while also generating electricity.
"Solar panels don’t have to be limited to rooftops. If we can integrate them into glass panels or façades, it opens the door to entirely new applications," says Pankaj Kumar, doctoral student in Experimental Physics at Luleå University of Technology.
"Buildings aren’t just major energy consumers—they also have enormous surfaces that we haven’t yet utilized for energy production. With this technology, every window can become a small power generator."

New Material with Low Environmental Impact

In his doctoral thesis, Pankaj Kumar focuses on a material called antimony sulfide (Sb₂S₃). It’s an inorganic compound made of antimony and sulfur that effectively captures sunlight and converts it into electricity—a property that makes it highly suitable for solar cells. The material is also non-toxic, inexpensive, and naturally occurring in the Earth’s crust.

One challenge with many existing solar technologies is their reliance on components that are toxic, costly, or unstable—hindering widespread and sustainable use. To address this, the researchers have been working to replace both the light-absorbing and conductive layers with more environmentally friendly alternatives.

By experimenting with different manufacturing methods and layer structures, they developed a range of solar cells with improved properties. Among the key improvements were replacing toxic materials with greener alternatives, improving the durability of the devices, and achieving record-breaking performance for ultrathin, semitransparent solar cells. For instance, they achieved an average visible transmittance (AVT) of over 20 percent while still generating electricity. This indicates that the cells are transparent enough to function as window glass, while still producing energy—an important step for real-world applications.

Pankaj Kumar shows an example of the thin-film solar cells developed by the researchers.

A Contribution to Energy-Smart Buildings of the Future

The thesis presents several techniques for creating thin and uniform films of antimony sulfide. Using a method called sputtering – a technique in which material is ejected from a source by ionized gas and deposited as a thin film – Pankaj Kumar succeeded in producing solar cells with good efficiency even at very low thicknesses..
"The idea is that the buildings of the future should be able to generate their own electricity without compromising on design or natural light. My results show that we are well on our way," says Pankaj Kumar.

Although the technology is not ready for the market just yet—mainly due to current scalability issues—ongoing research is focused on improving durability.

The potential societal impact remains significant: the ability to generate complementary electricity from building façades could help reduce both energy costs and environmental impact.
"We need to rethink how we produce and use electricity in everyday life. These solar cells show that it’s possible to combine energy efficiency with sustainability and aesthetics," says Pankaj Kumar.

• Experimental Physics