Photosynthesis-Based Discovery Could Pave Way for More Efficient Artificial Solar Cells

According to a team of Researchers at Georgia State University, more efficient artificial solar cells could be designed using a natural process that occurs during photosynthesis.

Credit: Georgia State University

Plants and other organisms, such as cyanobacteria and algae convert solar energy into chemical energy during photosynthesis, which can subsequently be used as fuel for activities. In plants, solar energy causes an electron to quickly travel across the cell membrane. In artificial solar cells, the electron time and again returns to its starting point and the trapped solar energy is lost. In plants however, the electron almost never returns to its starting point, and this is why solar energy absorption in plants is extremely efficient. A process known as inverted-region electron transfer could contribute to inhibiting this “back electron transfer.”

This study’s findings, published in the journal Proceedings of the National Academy of Sciences, offer quantitative indication that inverted-region electron transfer is accountable for the extremely high efficiency related with solar energy conversion in photosynthesis.

Dr. Rudolph Marcus won the 1992 Nobel Prize in Chemistry for theoretical research on this phenomenon. But so far the mechanism has not been observed in natural photosynthetic systems. The Researchers examined photosynthetic reaction centers from the freshwater cyanobacterium species Synechocystis, which has the same photosynthetic mechanism as plants.

We were able to reveal the existence of the mechanism for the first time by inventing a method to allow us to successfully undertake the required challenging experiments. Our findings point to new ways on how one might think about designing artificial solar cells that can be used, for example, for producing hydrogen gas, which can be used as a clean and renewable fuel.

Dr. Gary Hastings, Lead Author and Professor, the Department of Physics and Astronomy, Georgia State University

Solar energy, the cleanest and most plentiful renewable energy source available, can be changed into thermal, electrical or chemical energy. By harnessing and converting a miniature fraction of the solar energy that reaches the earth yearly, humans’ increasing desire for energy may be satisfied, Hastings said. The United States solar market industry is working to increase the production of solar technology and bring down costs, but it faces certain challenges, according to the Solar Energy Industries Association.

“Plants convert solar energy ultra-efficiently, considerably more efficiently than any artificial solar cell,” Hastings said. “In photosynthesis, light comes in, an electron moves across a membrane and it doesn’t come back. The big problem with artificial systems is the electron does go back much of the time. That’s the real heart of why plants are so efficient at converting solar energy.

The details that underlie efficient solar energy conversion in plants are poorly understood. This is unfortunate, as detailed knowledge in this area is important to aid in quests to design economically viable artificial solar converters. Our work has revealed one design principle that is at play in efficient solar energy conversion in plants, and the hope is that this principle could be utilized in the design of new and better types of artificial solar cells.

Dr. Gary Hastings, Lead Author and Professor, the Department of Physics and Astronomy, Georgia State University

Dr. Hiroki Makita of Georgia State is the study’s Co-author.  The Qatar National Research Fund funded the study.

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