This 300-nanometer-wide silicon wire (left) generates electricity from sunlight. Such nano­wire solar cells would initially be useful in tiny sensors, or in robots whose electronics might need built-in power. But arrays of microscopic wires could change the economics of solar power by enabling solar cells built from cheap materials such as low-grade silicon or even iron oxide--rust.

A number of such cheap materials absorb light and generate electrons, but defects in the materials usually "trap" the electrons before they can be collected. Microscopic wires, though, can be made thin enough to allow electrons to slip out easily and generate current, even if the material has defects. And the wires can be long enough to absorb plenty of photons from sunlight hitting them at an angle.