South Korea\'s conglomerate SK Group said Monday that it will invest US$50 million in a U.S. firm developing next generation thin-film solar module technology. SK Innovation Co., the country\'s largest oil refinery, and SK Technology Innovation Center will invest in HelioVolt which owns the technology to produce thin-film solar modules with a semiconductor material compound made of copper, indium, gallium and selenium (CIGS), business group said. The thin-film CIGS solar module is known for high manufacturing efficiency with a simpler production process and less materials needed to make the finished product. SK Group said that it will decide whether to help the U.S. company market the technology after verifying its ability to mass-produce the material.