NREL's Harin Ullal, who managed the research with TetraSun, said achieving 21% efficiency in just 18 months is unusual and indicative of the cell's disruptive technology. "That compares to 17% to 19% efficiency for screen-printed silicon cells," he said.
Ullal noted that the new technology, besides replacing expensive silver with abundant copper on the front contact grid, uses n-type silicon wafers, which have been doped with impurities that give them an excess of conductive electrons. (By contrast, p-type cells are doped to have more electron holes than electrons.) The n-type wafers can improve cell efficiency compared to the more common p-type wafers, which can suffer light-induced degradation. The innovations in the TetraSun cell structure design, corrosion resistance, and choice of n-type silicon material doping all added up to the efficiency gain of more than two absolute percent.
"By 2020, this technology could potentially reach the Energy Department's SunShot target of one dollar per watt for PV systems and about 6 cents per kilowatt hour for electricity generation," Ullal said.
Leading the team for TetraSun were Oliver Schultz-Wittmann, Denis DeCeuster, Adrian Turner, and Doug Crafts. In addition to Al-Jassim, Symko-Davies, and Ullal, NREL's team included Peter Hacke, Chunsheng Jiang, and Richard Mitchell.
First Solar built its worldwide reputation on cadmium telluride solar cells, which come from the second and sixth columns of the periodic tables. Those elements are costly by the pound, but require such thin layers that they can challenge silicon on price. But today, silicon continues to grab the lion's share of the solar market. With the acquisition of TetraSun, First Solar now is poised to have a presence in both
|Contact: David Glickson|
DOE/National Renewable Energy Laboratory