Solar technology has advanced in leaps and bounds over the past several years as traditionally expensive single-crystal silicon solar cells are eclipsed by organic solar cells (solar cells that use organic materials to absorb light and convert it into electricity). However researchers at Northwestern University have taken the next evolutionary step (literally) in the process by using a mathematical search algorithm based on natural evolution to pinpoint a specific geometric pattern that is optimal for capturing and holding light in thin-cell organic solar cells.

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Their team’s paper, “Highly Efficient Light-Trapping Structure Design Inspired by Natural Evolution,” was published in Scientific Reports. It describes how the new design could lead to more efficient, less expensive organic solar cells. The team’s method aims to increase efficiency by altering the thickness of the solar cell’s polymer layer and thus maximizing the amount of time light remains trapped within the cell. So far the team’s design has yielded a three-fold increase over the Yablonovitch Limit, a thermodynamic limit set in the 1980s which describes how long a photon can be trapped in a semiconductor.

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

“Due to the highly nonlinear and irregular behavior of the system, you must use an intelligent approach to find the optimal solution,” Chen said. “Our approach is based on the biologically evolutionary process of survival of the fittest.”

The team analyzed multiple designs in order to determine which had the best light-trapping performance. This process was then carried out over more than 20 generations, taking into account evolutionary principles of crossover and genetic mutation. The very fact that solar technology is ‘evolving’ and becoming more efficient each time is a remarkable achievement in itself.

+ Northwestern University