'Evolution' improves solar cell efficiency

US researchers say they've developed a new design for organic solar cells that could lead to more efficient, less expensive solar power. Using a mathematical algorithm based on natural evolution, researchers at Northwestern University identified a specific optimal geometrical pattern for capturing and holding light in thin-cell organic solar cells, a university release reported Friday. The geometry of the so-called scattering layer maximizes the amount of time light remains trapped within the cell to increase the amount of energy created, the researchers said. "We wanted to determine the geometry for the scattering layer that would give us optimal performance," mechanical engineering Professor Cheng Sun said. "But with so many possibilities, it's difficult to know where to start, so we looked to laws of natural selection to guide us." Researchers employed a genetic algorithm that mimics the process of natural evolution, applying it to dozens of random design elements that were "mated," producing "offspring" that were analyzed to determine their particular light-trapping performance. The resulting final pattern significantly increases the efficiency of an organic solar cell, they said.