As a rule, most solar cells need to catch direct sunlight. Even those that work indoors can only do so much to generate power from artificial light sources. However, British researchers have found a clever (and decidedly) unusual way to harvest energy while inside: by imitating moths. They've created a graphene-based material that traps electromagnetic waves much like a moth's eye, making it one of the most energy-absorbent substances to date. With the right antennas, it could produce energy from not just sunlight, but any device that emits microwave or radio waves -- your smartphone could help power your smartwatch.