Markus Beck, the chief scientist at Solyndra, has defected to thin-film solar giant First Solar, according to sources.

The loss of Beck is a major loss for Solyndra, according to solar execs who heard about the switch. As chief scientist, Beck oversaw projects for improving the efficiency and performance of the company’s unusual, cylindrical copper, indium gallium selenide (CIGS) solar cells. His name is on various Solyndra patents.

“Beck was truly the key technical solar guy over there,� wrote one solar exec.

Both Solyndra and First Solar have not returned calls for comment. Beck, however, has arleady started at First Solar, say sources.

More soon.