December 21, 2012
Stanford Engineers Unveil Peel And Stick Solar Panels
Brett Smith for redOrbit.com - Your Universe Online
Solar cells provide emissions-free power at a relatively low cost, but for all their benefits, the cells still have one major drawback — they are stiff, bulky and therefore limited in their application.
Until now, thin-film photovoltaic cells have had to be fixed on rigid silicon and glass substrates, which greatly limits their potential applications. The pursuit of alternative substrates that could allow for flexibility has been riddled with problems for years.
"Nonconventional or 'universal' substrates are difficult to use for photovoltaics because they typically have irregular surfaces and they don't do well with the thermal and chemical processing necessary to produce today's solar cells," said Xiaolin Zheng, a Stanford professor of engineering who co-authored the paper.
"We got around these problems by developing this peel-and-stick process, which gives thin-film solar cells flexibility and attachment potential we've never seen before, and also reduces their general cost and weight."
To create the new cells, a 300-nanometer film of nickel is placed on a silicon-silicon dioxide wafer. The solar cells are then deposited on the nickel layer and coated with a protective layer of polymer. A strip of thermal release tape is then placed on top of the solar cells to facilitate their transfer from the production wafer to a new substrate.
The process to apply the solar cells begins by submerging the wafer in room-temperature water and peeling back the edge of the thermal release tape. This allows water to seep between the nickel and silicon dioxide layers. Eventually, the solar cell layer is freed from its production substrate but still attached to the thermal release tape. The tape and solar cell are then heated to 90°C for several seconds before they can be applied to any surface using an adhesive. Finally, the thermal release tape is removed from the applied cells.
The newly developed cells differ from previous efforts in that they don´t require modifications of existing processes or materials.
"The main contribution of our work is we have done so without modifying any existing processes, facilities or materials, making them viable commercially. And we have demonstrated our process on a more diverse array of substrates than ever before," said lead author Chi Hwan Lee, a PhD candidate in mechanical engineering at Stanford.
"Now you can put them on helmets, cell phones, convex windows, portable electronic devices, curved roofs, clothing — virtually anything," Zheng added.
The researchers expect that the new application potential will expand beyond the realm of solar cells and into other electronic devices, like LCD displays.
"Obviously, a lot of new products — from 'smart' clothing to new aerospace systems — might be possible by combining both thin-film electronics and thin-film solar cells," observed Zheng. "And for that matter, we may be just at the beginning of this technology. The peel-and-stick qualities we're researching probably aren't restricted to Ni/SiO2. It's likely many other material interfaces demonstrate similar qualities, and they may have certain advantages for specific applications. We have a lot left to investigate."