April 17, 2013
Stanford, Department Of Energy Demonstrate Peel-And-Stick Solar Cells
redOrbit Staff & Wire Reports - Your Universe Online
Stanford University and the Department of Energy´s National Renewable Energy Laboratory (NREL) have developed a peel-and-stick solar cell that could one day be used to charge mobile phones and power a variety of other small devices.
Peel-and-stick, or water-assisted transfer printing (WTP), technologies were developed by the Stanford group, and have been used before for nanowire based electronics. However, the Stanford-NREL team has conducted the first successful demonstration using actual thin film solar cells, said NREL principal scientist Qi Wang.
The team showed that thin-film solar cells less than one-micron thick can be removed from a silicon substrate used for fabrication by dipping them in water at room temperature. After exposure to heat of about 90°C for a few seconds, they can then attach to nearly any surface.
The collaboration began last year when Wang met Stanford´s Xiaolin Zheng at a conference at which Wang was giving a presentation about solar cells and Zheng was discussing her peel-and-stick technology. Zheng quickly realized that the NREL had the type of solar cells that could be easily made on Stanford´s peel off substrate.
The amorphous silicon cells are fabricated on nickel-coated Si/SiO2 wafers. A thermal release tape attached to the top of the solar cell serves as a temporary transfer holder. An optional transparent protection layer is then spin-casted in between the thermal tape and the solar cell to prevent contamination when the device is dipped in water. The result is a thin strip much like a bumper sticker, allowing the user to peel off the handler and apply the solar cell directly to a surface.
“It´s been a quite successful collaboration,” Wang said.
“We were able to peel it off nicely and test the cell both before and after. We found almost no degradation in performance due to the peel-off.”
Zheng said the partnership with NREL was a critical component for the current work.
“NREL has years of experience with thin film solar cells that allowed us to build upon their success,” she said.
The cells can be mounted to almost any surface because almost no fabrication is required on the final carrier substrates, she said.
This ability to adhere to a universal substrate is uncommon, since most thin-film cells must be affixed to a special substrate.
The peel-and-stick approach allows the use of flexible polymer substrates and high processing temperatures. The resulting flexible, lightweight, and transparent devices then can be integrated onto curved surfaces such as military helmets, portable electronics, transistors and sensors.
In the future, the researchers plan to test peel-and-stick cells that are processed at higher temperatures, which will offer even greater power.
A paper about the work, entitled “Peel and Stick: Fabricating Thin Film Solar Cells on Universal Substrates,” was published online in the journal Scientific Reports, a subsidiary of the journal Nature.
Image 2 (below): TFSCs at different stages of the peel-and-stick process. Credit: Chi Hwan Lee, Dong Rip Kim, In Sun Cho, Nemeth William, Qi Wang & Xiaolin Zheng. Scientific Reports doi:10.1038/srep01000