Machine to weed out dud PV wafers could save solar industry billions

The National Renewable Energy Laboratory has developed a means to screen dud silicon wafers prior to the manufacture of photovoltaic cells, a technique that the lab claims could save the solar industry billions of dollars.

A wafer is a fragile, 180-micrometer layer of semiconductor substrate which is doped with impurities to create the crucial p-n junctions that enable the flow of electrical current. The problem, according to the NREL, is that between 5 and 10 percent of wafers break during the PV cell manufacturing process. Failure is caused by minuscule cracks that occur as the wafers themselves are made, an intensive procedure that begins with raw silica, and involves furnaces, chemical purification, and multi-wire sawing, among other things.

The cracks leave some wafers too fragile to survive the expensive process of fabricating PV cells, in which the wafers are doped, fitted with electrical contacts, coated, and sealed. Even a process as simple as moving a wafer from one stage of cell manufacture to the next can prove fatal. The later the stage of failure, the more expensive it is to the manufacturer.