Making Transparent Solar Cells Manufacturable

University of Michigan, Ann Arbor, MI

Xinjing Huang, a Ph.D. student in applied physics, demonstrates the semi-transparent view through the solar cell. The new manufacturing process could enable meter-scale electricity-producing windows. (Image: Silvia Cardarelli, Electrical and Computer Engineering)

Traditional silicon-based solar cells are completely opaque, which works for solar farms and roofs but would defeat the purpose of windows. However, organic solar cells, in which the light absorber is a kind of plastic, can be transparent.

In an important step toward bringing transparent solar cells to home windows, researchers at the University of Michigan have developed a way to manufacture highly efficient and semitransparent solar cells.

Organic solar cells have lagged behind their silicon-based cousins for energy-producing purposes due to engineering challenges such as low efficiency and short lifespans, but recent work out of the lab has achieved record efficiencies of 10 percent and estimated lifetimes of up to 30 years.

The team has turned its attention to making transparent solar cells manufacturable. A significant challenge is creating the micron-scale electrical connections between individual cells that comprise the solar module. Conventional methods that use lasers to pattern the cells can easily damage the organic light absorbers.

The new manufacturing process could enable meter-scale electricity-producing windows. Left: Schematic illustration of the peel-off patterning procedure. Middle: Microscopic image of light-absorbing semiconductor film on a glass substrate, patterned by peeling off a 10 μm wide polyimide (PI) strip. Right: Photo of the prototype module. (Image: Xinjing Huang, Optoelectronic Components and Materials Group)

Instead, the team developed a multistep peel-off patterning method that achieved micron-scale resolution. They deposited thin films of plastic and patterned them into extremely thin strips. Then, they set down the organic and metal layers. Next, they peeled off the strips, creating very fine electrical interconnections between the cells.

The group connected eight semitransparent solar cells, each 4 cm x 0.4 cm and separated by 200μm-wide interconnections, to create a single 13 cm² module. The power conversion efficiency of 7.3 percent was approximately 10 percent less than for the individual solar cells in the module.

This small efficiency loss does not increase with the size of the module; hence, similar efficiencies are expected for meter-scale panels as well. With a transparency nearing 50 percent and a greenish tint, the cells are suitable for use in commercial windows. Higher transparencies that are likely preferred for the residential market are easily achieved by this same technology.

Eventually, the flexible solar cell panel will be sandwiched between two window panes. The goal for these energy-generating window films is to be about 50 percent transparent with 10-15 percent efficiency. The team believes this can be achieved within a couple years.

The technique can also be generalized to other organic electronic devices including OLEDs for white lighting.

For more information, contact Kate McAlpine at This email address is being protected from spambots. You need JavaScript enabled to view it.; 734-647-7087.