New processes suggest opportunities for cheaper high-performance solar cells

04/10/2018 |

Organic solar cells are affordable, abundant and have a lower environmental impact. Yet, they have struggled to convert as much electricity as traditional cells. A new study featured in Physical Review Letters suggests a solution that could boost organic solar cell efficiency.

Scientists of the Center for Computational Study of Excited-State Phenomena in Energy Materials (C2SEPEM) at the Department of Energy’s Lawrence Berkeley National Laboratory have found the source of a faster and more efficient energy carrying process. The process creates multiple carriers of electrical charge from one light particle in organic crystals important in these solar cells.

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The process, referred to as “singlet fission,” can significantly improve organic solar cell efficiency by converting energy from sunlight to electrical charges more quickly. Previous iterations of these cells would lose the energy to heat.

“We actually discovered a new mechanism that allows us to try to design better materials,” says Steven G. Louie, Director of C2SEPEM.

The singlet fission process is similar to nuclear fission. It involves splitting atomic nuclei to create two lighter atoms from a heavier one. During the splitting process, the material can carry twice as much charge and avoid energy loss.

“There’s a lot we still don’t understand about the fundamental physics of this process in crystalline materials that we are hoping to shed more light on,” says Jeffrey B. Neaton, Associate Director of C2SEPEM. “The computational method that we developed is very predictive, and we used it to understand singlet fission in a new way that may allow us to design materials even more efficient at harvesting light, for example.”

Past efforts had focused on a few molecules in the material but had oversimplified the process of singlet fission. This study takes a greater view of the material’s structure.

“It’s like trying to explain the ocean by either looking at it molecule by molecule, or looking at a whole wave,” says Felipe H. da Jornada, a co-lead author of the study with Sivan Refaely-Abramson, both of whom are postdoctoral researchers at Berkeley Lab and UC Berkeley. “Our approach directly captures the whole crystal.”

The main challenge now is to determine how to apply these findings to real-world applications on a large scale. Nevertheless, the increased understanding of the process suggests that this will occur sooner than later.

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