solar cell

http://en.wikipedia.org/wiki/Solar_cell
A solar cell (also called a photovoltaic cell) is an electrical device that converts the energy of light directly into electricity by the photovoltaic effect.

http://en.wikipedia.org/wiki/Photoelectric_effect
Electrons can absorb energy from photons. If the photon energy is absorbed, some of the energy liberates the electron from the atom, and the rest contributes to the electron's kinetic energy as a free particle.

Interesting…

http://www.extremetech.com/extreme/175377-carbon-nanotubes-harvest-the-suns-energy-as-heat-for-better-solar-cells
The key to this new technology is taking all the wavelengths of light that silicon can’t absorb, and converting them to something it can absorb.
Unlike a regular solar cell, this process doesn’t immediately result in electricity generation. Instead, the absorber material heats up in response to the light and directs that heat energy into the photonic crystal layer.
This technology comes with the added benefit of being able to store the absorbed light as thermal energy for on-demand power generation when the sun isn’t shining.

Cool… right???