University of Michigan Ph.D. student Xinjing Huang demonstrates the semi-transparent view through the solar cell. Credit: Silvia Cardarelli, Electrical and Computer Engineering, University of Michigan.

Making it clear: Michigan researchers’ window solar cell breakthrough

Transparent solar cells got a step closer to being used on home windows, thanks to an advancement at the University of Michigan. Researchers there figured out a method for manufacturing their flexible, semi-transparent solar cells.

A clear evolution

Typical solar cells are opaque, which works on solar farms or rooftop installations. But they aren’t suited for window installations. Organic solar cells are an emerging technology that contain a plastic light absorber, which can be transparent and has potential for use in windows.

Most organic solar cells are less energy efficient and have shorter lifespans than silicon-based models. The U-M researchers have been perfecting their organic solar cells over the last several years to achieve greater efficiency. Recently, they achieved 10% efficiency and an estimated lifespan of 30 years.

Developing a manufacturing process

After achieving the record level of cell efficiency, the U-M team began focusing on a scalable method for manufacturing the devices. Creating the tiny electrical connections between individual solar cells, which comprise an entire solar module, is challenging. Conventional methods involve lasers, but that can damage the organic light absorbers.

A series of images demonstrates a new manufacturing process that could enable electricity-producing windows. Credit: Xinjing Huang, Optoelectronic Components and Materials Group, University of Michigan.
A series of images demonstrates a new manufacturing process that could enable electricity-producing windows. Credit: Xinjing Huang / Optoelectronic Components and Materials Group / University of Michigan

The U-M researchers developed a peel-off patterning method that works at the tiny scale needed for electrical connections. They put down thin, patterned plastic films and peeled off certain strips, leaving other strips that create the desired pattern. 

The team created micron-scale connections in this way for eight semi-transparent solar cells that each measure 4 cm x 0.4 cm. They achieved power conversion efficiency of 7.3%, which is a small efficiency loss. The loss does not change with the size of the solar module, so large-scale panels are not expected to be less efficient than the small test models.

This style of manufacturing can be used for other devices as well. The researchers are already trying it for OLED lighting.

Home applications

So far, the U-M team’s organic solar cells are nearly 50% transparent and have a greenish tint, which makes them suitable for commercial settings but not for most homes. The manufacturing method they developed will still work on higher transparency modules in the future. 

“The research we are doing is derisking the technology so that manufacturers can make the investments needed to enter large scale production,” Stephen Forrest, University of Michigan electrical engineering professor, said in a news release.

The researchers expect to reach their desired transparency and efficiency goals — 50% and 10% to 15%, respectively — in the next couple years. Eventually, the flexible solar cells will be sandwiched between two layers of window glass and will be usable in home settings.

What’s next

“It is now time to get industry involved to turn this technology into affordable applications,” said Xinjing Huang, U-M doctoral student in applied physics. 

The university has applied for a patent for this manufacturing technique and is seeking partners to bring the technology to market.