Crystalline-silicon panels—which make up about 90 percent of deployed photovoltaics—are expensive, and they’re already bumping up against efficiency limits in converting sunlight to electricity. So a few years ago, Michael S­aliba, a researcher at the Swiss Federal Institute of Technology in Lausanne, set out to investigate a new type of solar cell based on a family of materials known as perovskites. The first so-called perovskite solar cells, built in 2009, promised a cheaper, easier-to-process technology. But those early perovskite-based cells converted only about 4 percent of sunlight into electricity.

Saliba improved performance by adding positively charged ions to the known perovskites. He has since pushed solar cells built of the stuff to over 21 percent efficiency and shown the way to versions with far higher potential.

—Russ Juskalian