|Sandia National Laboratory, www.sandia.gov
Solar cells the size and shape of tiny, sparkling snowflakes and made of crystalline silicon could soon be less expensive and more efficient than current solar collectors pieced together from 6-in. wafers. The new cells measure 14 to 20-μm thick, one-tenth the thickness of ordinary wafers, yet perform at approximately the same efficiency as today’s larger cells. The new cells were made by engineers at Sandia National Laboratory, Albuquerque, N.M., using MEMS techniques common in today’s electronic foundries. The cells could be mass produced and added to a variety of objects — everything from tents to high-rises.
Because the cells use so little silicon, they have fewer mechanical defects, making them more reliable than conventional solar cells. They can also be made from commercial wafers of any size. And if one cell is defective, the rest can still be used. This contrasts with conventional practices where if one unit goes bad, the entire wafer often must be scrapped.
Each of these small cells is formed on a silicon wafer, etched, and then released inexpensively in hexagonal shapes. Electrical contacts are prefabricated on each cell at up to 130,000 contacts/hr using techniques borrowed from IC fabs and MEMS. Solar collectors, optical devices that increase the number of photons hitting the cell, can be added to these new cells. The collectors can be smaller with shorter focal lengths, and thus less expensive, than those for current PV cells.