Natural Selection Algorithm Used to Make Super Efficient Solar Cell Pattern

First Posted: Jan 25, 2013 04:02 PM EST
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A novel approach for the optimization of a solar cell pattern was chosen by researchers at Northwestern University. They aimed at designing an optimized geometric pattern of the scattering layer that would maximize the amount of time light remained trapped within the cell, thus leading to more efficient, less expensive thin-cell organic solar cells.

In order to do this, the two scientists employed a mathematical search algorithm based on natural evolution, that narrowed in on specific geometrical pattern by determining the ones optimal for capturing and holding light in the solar cells.

The researchers began with dozens of random design elements,"mated"them and then analyzed their offspring to determine their particular light-trapping performance. The procedure, which was carried out over more than 20 generations, also accounted for evolutionary principles of crossover and genetic mutation.

The resulting design seems to validate the selected approach, since it theoretically exhibits "a three-fold increase over the Yablonovitch Limit, a thermodynamic limit developed in the 1980s that statistically describes how long a photon can be trapped in a semiconductor." To prove this, the pattern will have to undergo experimentation, after being fabricated with partners at Argonne National Laboratory.

"We wanted to determine the geometry for the scattering layer that would give us optimal performance," said Cheng Sun, assistant professor of mechanical engineering in Northwestern's McCormick School of Engineering and Applied Science and co-author of the paper. "But with so many possibilities, it's difficult to know where to start, so we looked to laws of natural selection to guide us."

In the newly designed organic solar cell, light first enters a 100-nanometer-thick "scattering layer," a geometrically-patterned dielectric layer designed to maximize the amount of light transmitted into the cell. The light is then transmitted to the active layer, where it is converted into electricity.

A paper about the results, "Highly Efficient Light-Trapping Structure Design Inspired by Natural Evolution," was published in Scientific Reports, a publication of Nature.

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