Optical nanomaterials allow solar cell to repair itself

West Lafayette, IN--Optical-nanomaterial-based solar cells created at Purdue University are designed to self-repair using carbon nanotubes and DNA, an approach aimed at increasing service life and reducing cost.

West Lafayette, IN--Optical-nanomaterial-based solar cells created at Purdue University are designed to self-repair using carbon nanotubes and DNA, an approach aimed at increasing service life and reducing cost.

The design exploits the electrical properties called single-walled carbon nanotubes, using them as "molecular wires in light-harvesting cells," as phrased by John Hyun Choi, an assistant professor of mechanical engineering at Purdue University.

In a photoelectrochemical cell, an electrolyte transports electrons and creates the current. The cells contain light-absorbing chromophores, chlorophyll-like molecules that unfortunately degrade upon exposure to sunlight. In the new technology, the photo-damaged chromophores are continuously replaced with new ones. As a result, a photoelectrochemical cell could continue operating at full capacity indefinitely, as long as new chromophores are added.

The findings were detailed in a November, 2010 at a presentation during the International Mechanical Engineering Congress and Exhibition (Vancouver, BC, Canada). The concept also was unveiled in an online article at SPIE's website.1

Molecular recognition
The carbon nanotubes work as a platform to anchor strands of DNA. The DNA has specific sequences of nucleotides that enable them to recognize and attach to the chromophores. "The DNA recognizes the dye molecules, and then the system spontaneously self-assembles," says Choi.

When the chromophores are ready to be replaced, they could be removed by using chemical processes or by adding new DNA strands with different nucleotide sequences, removing the damaged dye molecules. New chromophores could 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 that Choi collaborated on with researchers at the Massachusetts Institute of Technology (Cambridge, MA) and the University of Illinois (Urbana, IL). The earlier work used biological chromophores taken from bacteria; findings were detailed in a research paper published in November in the journal Nature Chemistry.2

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 says. "So instead of using biological chromophores, we want to use synthetic ones made of dyes called porphyrins," he notes.


REFERENCES:

1. http://spie.org/x41475.xml?ArticleID=x41475

2. http://www.nature.com/nchem/journal/v2/n11/abs/nchem.822.html

Posted by John Wallace

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