NREL Thin-Film Solar Cell Achieves Record Efficiency

March 26, 2008

The prospect for alternatives to crystalline silicon solar cells brightened considerably on March 24, when DOE's National Renewable Energy Laboratory (NREL) announced that it has created a thin-film solar cell with a record efficiency. NREL created the solar cell from thin films of semiconducting materials made from alloys of cadmium, indium, copper, and selenium, or CIGS. The cell achieved a record thin-film conversion efficiency of 19.9%, that is, the cell is able to convert 19.9% of the sunlight hitting it into electricity. Although solar cells have been built with much higher efficiencies using expensive processes and multiple layers of semiconductors, the more common crystalline silicon solar cells have achieved at most efficiencies of 20.3%, which is quite close to the NREL achievement with the thin-film CIGS solar cell. CIGS solar cells involve applying a thin film of semiconductor material to an inexpensive substrate such as glass, plastic, flexible foil, or stainless steel. See the NREL press release.

While crystalline silicon solar cells currently dominate the solar cell market, their growth has been hampered in recent years by a lack of the polysilicon from which they are made. A recent report from Frost & Sullivan concluded that the polysilicon supply would catch up with demand by the end of this year, with the four top producers boosting their annual production by more than 17,000 tons, an increase of more than 50%. By the end of 2009, Frost & Sullivan expects the majority of the world's polysilicon supply to be going toward solar cells rather than computer chips, representing a fundamental shift in the silicon market. A BCC Research report released in December 2007 estimated global shipments of solar cells and modules at 2,875.1 megawatts in 2007 and expected shipments to increase by 28.6% this year, reaching 3,697.3 megawatts. The report anticipates continued annual growth of 30% per year, reaching 13,724.4 megawatts by 2013. See the press releases from Frost & Sullivan and BCC Research.

Thin-film solar cells are already supplying a portion of the solar cell market, and their influence is growing. First Solar, a manufacturer of cadmium telluride (CdTe) thin-film solar cells, is now the largest U.S.-based manufacturer of solar cells, with 277 megawatts of annual capacity and plants under construction that will increase its annual capacity to 910 megawatts by next year. Early this month, Global Solar Energy opened a CIGS plant in Tucson, Arizona, with an annual capacity of 40 megawatts, while startup company AVA Solar, Inc. announced plans to build a CdTe manufacturing plant in northern Colorado. Looking ahead, Konarka Technologies, Inc. has demonstrated its ability to produce organic (polymer) solar cells using inkjet printing techniques, while a report from NanoMarkets predicts that the use of printing technologies and roll-to-roll manufacturing (the type used for printing newspapers) will cause rapid growth of thin-film solar cells. See the First Solar Web site; the press releases from Global Solar, AVA Solar, and Konarka; and the NanoMarkets report (PDF 125 KB). Download Adobe Reader.