It may be possible soon to charge cell phones, change the tint on windows, or power small toys with peel-and-stick versions of solar energy cells, thanks to a partnership between Stanford University and the U.S. Department of Energy's National Renewable Energy Laboratory (NREL).
A scientific paper, "Peel and Stick: Fabricating Thin Film Solar Cells on Universal Substrates," appears in the online version of Scientific Reports, a unit of the British scientific journal Nature.
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, but the Stanford-NREL partnership has conducted the first successful demonstration using actual thin film solar cells.
The university and NREL 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. Then, after exposure to heat of about 90°C for a few seconds, they can attach to almost any surface.
NREL's cells could be made easily on Stanford's peel off substrate. NREL's amorphous silicon cells were 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 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: the user can peel off the handler and apply the solar cell directly to a surface.
Cells can be mounted to almost any surface because almost no fabrication is required on the final carrier substrates.
The cells' ability to adhere to a universal substrate is unusual; 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 and portable electronics, transistors and sensors.
In the future, the collaborators will test peel-and-stick cells that are processed at even higher temperatures and offer more power.
NREL is the U.S. Department of Energy's primary national laboratory for renewable energy and energy efficiency research and development. NREL is operated for DOE by the Alliance for Sustainable Energy, LLC.