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  • New Solar Cell Mimics Self-Repairing Plants
Jan 2011
WEST LAFAYETTE, Ind., Jan. 6, 2011 — Researchers are creating a type of solar cell designed to self-repair the same way natural photosynthetic systems in plants do, by using carbon nanotubes and DNA. The approach is aimed at increasing service life and reducing cost.

“We’ve created artificial photosystems using optical nanomaterials to harvest solar energy that is converted to electrical power,” said Jong Hyun Choi, an assistant professor of mechanical engineering at Purdue University.

The design exploits the unusual electrical properties of structures called single-wall carbon nanotubes, using them as “molecular wires in light-harvesting cells,” said Choi, whose research group is based at the Birck Nanotechnology and Bindley Bioscience centers at Purdue’s Discovery Park.

“I think our approach offers promise for industrialization, but we’re still in the basic research stage,” he said.

Photoelectrochemical cells convert sunlight into electricity and use an electrolyte — a liquid that conducts electricity — to transport electrons and create the current. The cells contain light-absorbing dyes called chromophores, chlorophyll-like molecules that degrade because of exposure to sunlight.

Jong Hyun Choi, an assistant professor of mechanical engineering at Purdue University, and doctoral student Benjamin Baker use fluorescence imaging to view a carbon nanotube. Their research is aimed at creating a type of solar cell that can self-repair the same way natural photosynthetic systems do. The approach might enable researchers to increase the service life and reduce costs for photoelectrochemical cells, which convert sunlight into electricity. (Image: Purdue University/Mark Simons)

“The critical disadvantage of conventional photoelectrochemical cells is this degradation,” Choi said.

The new technology overcomes this problem just as nature does: by continuously replacing the photodamaged dyes with new ones.

“This sort of self-regeneration is done in plants every hour,” he said.

The new concept could make possible an innovative type of photoelectrochemical cell that continues operating at full capacity indefinitely as long as new chromophores are added.

Findings were detailed in a November presentation during the International Mechanical Engineering Congress and Exhibition in Vancouver, British Columbia. The concept also was unveiled in an online article featured on the website for SPIE, an international society for optics and photonics.

The talk and article were written by Choi, doctoral students Benjamin A. Baker and Tae-Gon Cha, and undergraduate students M. Dane Sauffer and Yujun Wu.

The carbon nanotubes work as a platform to anchor strands of DNA. The DNA is engineered to have specific sequences of building blocks called nucleotides, enabling them to recognize and attach to the chromophores.

“The DNA recognizes the dye molecules, and then the system spontaneously self-assembles,” Choi said

When the chromophores are ready to be replaced, they might be removed by using chemical processes or by adding new DNA strands with different nucleotide sequences, kicking off the damaged dye molecules. New chromophores would then be added.

Two elements are critical for the technology to mimic nature’s self-repair mechanism: molecular recognition and thermodynamic metastability, or the ability of the system to continuously be dissolved and reassembled.

The research is an extension of work on which Choi collaborated with researchers at MIT and at the University of Illinois. The earlier work used biological chromophores taken from bacteria, and findings were detailed in a research paper published in November in the journal Nature Chemistry.

However, using natural chromophores is difficult, and they must be harvested and isolated from bacteria, a process that would be expensive to reproduce on an industrial scale, Choi said.

“So instead of using biological chromophores, we want to use synthetic ones made of dyes called porphyrins,” he said.

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solar cell
A device for converting sunlight into electrical energy, consisting of a sandwich of P-type and N-type semiconducting wafers. A photon with sufficient energy striking the cell can dislodge an electron from an atom near the interface of the two crystal types. Electrons released in this way, collected at an electrode, can constitute an electrical current.
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