Catching up with Sumika by Debra Vogler, senior technical editor, Photovoltaics World July 13, 2009 – Sumitomo Chemical Co., Ltd. and its U.S. subsidiary Sumika Electronic Materials, Inc., recently earned a supplier excellence award from one of the world’s largest microelectronics manufacturers. PV World caught up with Ken Campmann, GM of Sumika’s epi operations, before Intersolar North America, for an update on the company. Among the products Sumika offers for the worldwide solar market are GaAs-based epitaxial wafers, materials that enable volume production of a variety of end products including high-efficiency solar cells (where the company is currently working with several development partners), as well as cell phone power amplifiers and LEDs. The intent is to use epitaxial core competencies established over the years to produce and supply GaAs- and germanium-based wafers to partners. In 2003, Sumitomo purchased ATMI’s III-V epi division (which included Sumika) and put it together with the sales and marketing of Sumitomo Chemical’s IT-related businesses (e.g., photoresists) to form Sumika. The company recently branched out into solar applications, where it is working with a couple of different companies, Campmann told PV World. One is RSL Energy, a joint venture between Sumitomo Chemical and RoseStreet Labs formed in 2006 to develop and manufacture full spectrum solar cells. RSL Energy has patent licenses from both Lawrence Berkeley National Laboratory (the interband, or “I-band” solar cell technology) and Cornell University (an indium-nitride-based solar cell). Sumika is also working with other companies on a triple-junction cell grown on germanium. I-band technology uses a single semiconductor material that absorbs at three different wavelengths, vs. traditional CPV triple-junction technology that uses three different materials that each absorb at a different wavelength to cover the solar spectrum. Having just a single junction cell is simpler for manufacturing, noted Campmann. “You don’t have to worry about losses due to tunnel junctions — so you can make a single cell that covers the entire solar spectrum,” he noted. Dilute nitrides (III-V-based, with a bit of nitrogen) are one set of materials that are being evaluated for I-band solar cells. The biggest challenge, according to Campmann, is finding a material with good optical qualities that still has the properties required for absorbing three wavelengths. – D.V.