Traditional photovoltaic solar cells use the sun’s energy to knock electrons away from the positive charges (holes) in doped silicon. In this manner, the two cannot recombine until the electrons have traveled the entirety of the circuit with an applied load. The University of Delaware have devised solar cells being far more efficient, as they could implement up to some six different material substrates to generate power from different parts of the solar spectrum. The solar light coming into the cell is concentrated 20 times and passes through a high-energy absorbing material (purple) to a reflective splitter that directs medium (green) and low (red) energy light to the other appropriate absorption materials.

from 09/07 Forbes.com