Clues to Solar Cell Efficiency Found at Atomic Level

For the past 10 years, a family of materials called metal-halide perovskites, which can efficiently convert sunlight to electricity, has been shaking up solar cell research. Unlike traditional silicon solar cells, perovskites do not need to be manufactured under high temperature and with high purity, making them comparatively cheaper and easier to work with. More importantly, the efficiency of perovskite solar cells-a measure of how much solar energy they convert to electricity-has increased nearly six-fold since 2009, to more than 20 percent. That jump in efficiency is unmatched by any other solar cell material. The silicon-based solar technologies that have been around since the 1970s have similar efficiencies-around 20-25 percent. "Despite being a relatively new technology, perovskite solar cells are now almost as efficient as solar cell materials that have been around for decades. But we still don't know why perovskite solar cells work so well," says Marco Bernardi , assistant professor of applied physics and materials science in Caltech's Division of Engineering and Applied Science.