Towards Making Windows-Sized Semitransparent Solar Cells

Towards Making Windows-Sized Semitransparent Solar Cells

The University of Michigan has created a method to produce its extremely effective and semitransparent solar cells, which is a significant step toward delivering transparent solar cells to residential windows.

“In principle, we can now scale semitransparent organic solar cells to two meters by two meters, which brings our windows much closer to reality,” said Stephen Forrest, the Peter A. Franken Distinguished University Professor of Electrical Engineering and corresponding author of a study published in Joule.

Since conventional silicon-based solar cells are totally opaque, they are ideal for solar farms and roofs but would be useless for windows. Organic solar cells, on the other hand, can have a transparent light absorber made of a certain type of plastic.

Due to engineering difficulties including poor efficiency and limited lifetimes, organic solar cells have trailed behind their silicon-based counterparts in terms of energy production. However, new work out of Forrest’s lab has achieved record efficiencies of 10% with predicted lifetimes of up to 30 years.

As a result, the team is now focused on producing transparent solar cells. The electrical connections between the individual solar module cells at the micrometer size present a substantial barrier. The organic light absorbers are easily harmed by conventional cell patterning techniques that involve lasers.

Instead, they created a multistep peel-off patterning technique that produced resolution down to the micron level. They applied thin plastic films and cut them into incredibly tiny strips.

The layers of metal and biological material are then applied. The strips were then peeled off, resulting in extremely tiny electrical connections between the cells. Eight semitransparent solar cells, each measuring 4 cm × 0.4 cm and joined by 200 m wide interconnections, were combined to form a single 13 cm2 module.

In principle, we can now scale semitransparent organic solar cells to two meters by two meters, which brings our windows much closer to reality.

Stephen Forrest

7.3% was around 10% less efficient at converting power than the module’s individual solar cells. Similar efficiencies are anticipated for meter-scale panels as well because this minimal efficiency loss does not grow with module size.

The cells are suitable for use in commercial windows because they have a transparency that is almost 50% and a greenish tint. This same technology makes it simple to attain higher transparency levels, which are probably preferable for the home sector.

“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 and first author on the published research.

The flexible solar cell panel will eventually be positioned in between two window panes. These energy-generating window films should have an efficiency of 10% to 15% while being roughly 50% transparent. Forrest believes this can be achieved within a couple years.

“The research we are doing is derisking the technology so that manufacturers can make the investments needed to enter large scale production,” Forrest said.

According to him, the method can be applied to other biological electronic devices. In fact, his team is already using it to create white illumination with OLEDs.

The University of Michigan has filed for patent protection and is looking for collaborators to help commercialize the technology.

Along with teaching electrical and computer engineering, materials science and engineering, physics, and applied physics, Forrest holds the Paul G. Goebel Professor of Engineering title.

Co-authors Huang and former doctoral student Dejiu Fan (PhD EE 2020) designed and conducted the experiments. Co-author and assistant research scientist Yongxi Li assisted in the fabrication of the devices, which was accomplished in the Lurie Nanofabrication Facility.

Primarily the U.S. Department of Energy supported the research. Universal Display Corporation provided additional support. Forrest and U-M have a financial interest in Universal Display Corp.