We are edging closer and closer to a world where buildings capture energy with rooftop solar panels as well as through thin, flexible solar panels that line the windows of buildings. Making these flexible panels wouldn’t be possible with today’s silicon-based solar cells, but a rather new material called perovskite is providing a cheaper, more efficient, and lightweight alternative that researchers believe could make solar technology ultra-efficient in the future. Made of calcium and titanium, perovskite has reached an efficiency of 21 percent in just three years of testing, something it took silicon-based solar panels 30 years to achieve.