Because the cells are only hundreds of micrometers in diameter they can be fabricated from commercial wafers of any size, including 300-mm and 450-mm wafers.
By Suzanne Deffree, Managing editor, news -- Electronic News, 12/23/2009
Scientists from Sandia National Laboratories have developed tiny glitter-sized PV (photovoltaic) cells that are 10 times smaller than conventional 6-in-by-6-in brick-sized cells, yet perform at about the same efficiency. As such, the scientists believe that the PV cells offer potential applications that range from satellites to remote sensing, and possibly to solar energy collecting clothing.
The cells -- from 14 to 20 micrometers thick, compared to a human hair that is approximately 70 micrometers thick -- are fabricated of crystalline silicon using MEMS techniques and are expected to eventually be less expensive and have greater efficiencies than current photovoltaic collectors that are pieced together with 6-in-sq solar wafers, according to Sandia.
“Eventually units could be mass-produced and wrapped around unusual shapes for building-integrated solar, tents, and maybe even clothing,” Greg Nielson, Sandia lead investigator, said in a statement. Sandia noted that that would make it possible for hunters, hikers, or military personnel in the field to recharge batteries for phones, cameras, and other electronic devices as they walk or rest.
Further, Sandia said that such microengineered panels could have circuits imprinted that would help perform other functions customarily left to large-scale construction with its attendant need for field construction design and permits.
“Photovoltaic modules made from these microsized cells for the rooftops of homes and warehouses could have intelligent controls, inverters, and even storage built in at the chip level,” Vipin Gupta, Sandia field engineer, said in the statement.
“One of the biggest scale benefits is a significant reduction in manufacturing and installation costs compared with current PV techniques,” Murat Okandan, Sandia researcher, added in the statement.
Part of the potential cost reduction comes about because the microcells require relatively little material to form well-controlled and highly efficient devices, the Sandia scientists said. According to Okandan, the cells use 100 times less silicon to generate the same amount of electricity compared to conventional 6-in-sq brick-sized cells. “Since they are much smaller and have fewer mechanical deformations for a given environment than the conventional cells, they may also be more reliable over the long term,” he said.
Because the cells are only hundreds of micrometers in diameter they can be fabricated from commercial wafers of any size, including 300-mm and 450-mm wafers, Sandia said.
Sandia noted that a commercial move to microscale PV cells would be a dramatic change from conventional silicon PV modules composed of arrays of 6-in-sq wafers. However, by bringing in techniques normally used in MEMS, electronics, and the LED industries, the change to small cells should be relatively straightforward, Gupta said.
Sandia explained that each cell is formed on silicon wafers, etched and then released in hexagonal shapes, with electrical contacts prefabricated on each piece, by borrowing techniques from ICs and MEMS.
Electricity presently can be harvested from the Sandia-created cells with 14.9% efficiency, while off-the-shelf commercial modules range from 13 to 20% efficiency.
Solar concentrators can be placed directly over each glitter-sized cell to increase the number of photons arriving to be converted via the photovoltaic effect into electrons. The small cell size means that cheaper and more efficient short focal length microlens arrays can be fabricated for this purpose, Sandia said.
High-voltage output is possible directly from the modules because of the large number of cells in the array, Sandia said, adding that that should reduce costs associated with wiring, due to reduced resistive losses at higher voltages.
The work is supported by the Department of Energy’s Solar Energy Technology Program and Sandia’s Laboratory directed R&D program, and has been presented at four technical conferences this year.
FROM HERE
http://www.edn.com/article/CA6712787.html
http://www.memsnet.org/news/
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