• Detailed view of a new, highly efficient solar cell pattern

    Credit: Courtesy of Northwestern University

    Detailed view of a new, highly efficient solar cell pattern

The hunt for a more efficient solar cell typically focuses on material technology, but a new renewable energy breakthrough is based on geometry.

Historically, conventional cells have been confined by a thermodynamic threshold called the Yablonovitch Limit, which dictates the quantity of time a photon will remain within a semiconductor. Based on experiments in manipulating the arrangement of a polymer layer on an organic solar cell, scientists at Illinois's Northwestern University’s McCormick School of Engineering and Applied Science have been able to transcend the Yablonovitch Limit by a factor of three.

With the intent to trap light as long as possible within the thin-film photovoltaic, the researchers created an algorithm to generate multiple patterns for the light-scattering layer of the cell. After 20 generations of development, the scientists arrived at a diagonal grid pattern with alternating holes and voids—the resulting successful arrangement.

“We wanted to determine the geometry for the scattering layer that would give us optimal performance,” said Cheng Sun, assistant professor of mechanical engineering at Northwestern. “But with so many possibilities, it’s difficult to know where to start, so we looked to laws of natural selection to guide us… Our approach is based on the biologically evolutionary process of survival of the fittest.”

This so-called "evolutionary" approach is rapidly becoming a method of choice for the optimization of material performance in both engineering and design, and may be seen at a much larger scale in the structures of architects such as Makoto Sei Watanabe. Given the versatility of the approach, it will be interesting to see how it can be applied in a more comprehensive way—from micro to macro scales—within the physical environment.

Blaine Brownell is a regularly featured columnist whose stories appear on this website each week. His views and conclusions are not necessarily those of ARCHITECT magazine nor of the American Institute of Architects.