Efficient solar cells

The Economist (Feb. 22) -- Even the best silicon solar cells – by far the most common sort – convert only a quarter of the light that falls on them. Silicon has the merit of being cheap: Manufacturing improvements have brought its price to a point where it is snapping at the heels of fossil fuels. But many scientists would like to replace it with something fundamentally better. John Rogers, a materials science and engineering professor, is one. The cells he has devised are indeed better. By themselves, he told this year’s meeting of the American Association for the Advancement of Science, they convert 42.5 percent of sunlight. Suitably tweaked, he says, their efficiency could rise to 50 percent. Their secret is that they are actually not one cell, but four, stacked one on top of another.