The Michigan Engineer News Center

A window into the future of solar power

Windows in the buildings of the future could double as efficient solar cells.| Medium Read
EnlargeSolar powered windows
IMAGE:  Solar powered windows

Windows in the buildings of the future could double as efficient solar cells, and a new $1.3 project at the University of Michigan is working toward that goal.

Funded by the U.S. Department of Energy Solar Energy Technologies Office (SETO), researchers are developing semi-transparent, reliable, and efficient organic solar cells for integration into buildings and similar structures.

“There’s a lot of surface area on buildings that is sun facing. Why not use this to generate electricity?” said project leader Stephen Forrest, the Peter A. Franken Distinguished University Professor and renowned expert in organic photovoltaics.

Most commercial solar cells are based on silicon, a hard and opaque substance that is both abundant and inexpensive. They can be seen in solar farms and on roofs to provide a sustainable energy source that is friendly to the environment, and are now being integrated into buildings. However, there is another feature of buildings that is ripe for energy exploitation – windows.

Most building windows have a coating to reduce glare and lessen the amount of light that gets through to avoiding heating of interior spaces. About 50-70% of sunlight is lost in the process. Instead of coating the windows, transparent photovoltaic sheets would transform that heat into energy instead.

EnlargeThe image is viewed through an organic photovoltaic sheet. (Credit: Yongxi Li, Optoelectronic Components and Materials Group, Michigan Engineering)
IMAGE:  The image is viewed through an organic photovoltaic sheet. (Credit: Yongxi Li, Optoelectronic Components and Materials Group, Michigan Engineering)

Forrest’s group has already developed thin photovoltaic sheets that can be placed over windows with no reduction in clarity, thanks to the use of organic photovoltaics. He and his team have already achieved 8% efficiency in the lab, and plan to reach nearly 15% with 50% transparency in this new project.

“This project has the potential to play an integral role in harvesting significant amounts of energy that passes through city windows around the globe, thereby advancing green energy solutions and employment opportunities,” said Mike Hack, VP of Business Development for Universal Display Corporation, a world leader in OLED technologies.

Already thinking of the potential for future commercialization, Forrest envisions entire buildings newly constructed with the ability to gather the electricity generated by photovoltaic sheets integrated into the structure of the buildings.

“We’re developing plans for engagement with industry, and early acceptance of our technology for eventual installation and new constructions,” said Forrest.

“Because we are building these photovoltaics on a flexible substrate, they can be manufactured roll to roll, which means very fast production, high volume, and low cost,” said Forrest, who is always looking at the three pillars of efficiency, reliability, and cost. He believes all three will be met with this new technology, as well as environmental friendliness.

Forrest has a seasoned team comprised of graduate students and postdoctoral researcher, Dr. Yongxi Li, ready for the challenge. He credits Li with propelling this research into the future. “Li’s been pushing this for a long time,” said Forrest, “and I give him credit for relentlessly pursuing his goals.”

The project was selected as a part of the Energy Department’s FY2018 SETO funding program, an effort to invest in new projects that will lower solar electricity costs and support a growing solar workforce.

Andrej Lenert, a colleague of Forrest’s in the Department of Chemical Engineering, is funded under the same program. Lenert aims to reduce the heat lost when capturing solar thermal energy.

Forrest is also the Paul G. Goebel Professor of Engineering, a professor of electrical engineering and computer science, a professor of materials science and engineering, and a professor of physics.

About the Solar Energy Technologies Office
The U.S. Department of Energy Solar Energy Technologies Office supports early-stage research and development to improve the affordability, reliability, and performance of solar technologies on the grid. Learn more at

Solar powered windows
The image is viewed through an organic photovoltaic sheet. (Credit: Yongxi Li, Optoelectronic Components and Materials Group, Michigan Engineering)
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Catharine June
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  • Stephen Forrest

    Stephen Forrest

    Peter A. Franken Distinguished University Professor, Paul G. Goebel Professor of Engineering, Professor of Electrical Engineering and Computer Science; Professor of Materials Science and Engineering, Professor of Physics

  • Yongxi Li

    Yongxi Li

    Postdoctoral researcher

The electrons absorb laser light and set up “momentum combs” (the hills) spanning the energy valleys within the material (the red line). When the electrons have an energy allowed by the quantum mechanical structure of the material—and also touch the edge of the valley—they emit light. This is why some teeth of the combs are bright and some are dark. By measuring the emitted light and precisely locating its source, the research mapped out the energy valleys in a 2D crystal of tungsten diselenide. Credit: Markus Borsch, Quantum Science Theory Lab, University of Michigan.

Mapping quantum structures with light to unlock their capabilities

Rather than installing new “2D” semiconductors in devices to see what they can do, this new method puts them through their paces with lasers and light detectors. | Medium Read