Boeing's Spectrolab subsidiary has been working on making solar cells more and more efficient for years now, and it looks like it's now set to put its latest record-breaking cells into mass production. Those come in the form of the company's new C3MJ+ solar cells, which boast an average conversion efficiency of 39.2 percent, making them the most efficient mass produced cells to date. What's more, Spectrolab says that since the new cells are so similar to its current C3MJ production cells, it should be relatively easy for customers already using those to upgrade to the new cells. Still no word on a price, it seems, but the new cells should be available in January. And, yes, Spectrolab is also hard at work on breaking its own record -- it hopes to crack the 40 percent mark later in 2011.