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January 4th, 2011

Self-repairing carbon nanotube solar cells mimic photosynthesis

Published on January 4th, 2011 | By: pwray@ceramics.org

Using carbon nanotubes combined with natural or synthetic biomaterials, researchers at Purdue University have demonstrated some new types of solar cell designed to self-repair. By mimicking natural photosynthesis in plants, the researchers believe they can increase the lifespan and reduce costs of the photoelectrochemical cells.

Their goal is to optimize donor-acceptor nanohybrid cells by making photovoltaic nanostructures with synthetic analogs to nature’s efficient charge-separation and regeneration processes.

In one approach, they used hybrid single-wall carbon nanotubes (with ruthenium-based complexes) and natural material, grafting photosynthetic reaction centers onto the SWCT, switching the photocurrent on and off by controlling the active and inactive (repairing) states:

In a story on the SPIE website, the researchers say that with the right triggering mechanism, these complexes dissociate from the nanotube. The damaged components are replaced before reassembly.

“Thus, the associated photoactive hybrid can be disassembled into photo-inactive and reassembled into photo-active states based on a single chemical signal. This process mimics that in biological systems, where damaged systems are disassembled, repaired, and reassembled to restore functionality.”

In a second approach, they used a chromophore made of porphyrin dye, phospholipids, short-stranded DNA/RNA sequences instead of natural photosystems in the carbon-nanotube hybrids. These synthetic materials are attractive for reasons of self-assembly, their ability for molecular recognition and their high affinity for the sp2 lattice of carbon nanotubes.

“By varying the size of the biomolecule, it is possible to control the intermolecular distance between donor and acceptor, a critical aspect in charge-separation and recombination kinetics. Additionally, by changing the local environment, the structure of the biomolecule can be altered, modifying the binding conditions with the donor and allowing for removal and replacement with fresh donor molecules for optimal photoconversion.”

The triggering mechanism is the introduction of a surfactant. Here, the complex consists recombinant proteins, a chromophore and a carbon nanotube that mimics the natural process of nature adding chlorophyll.

The basic cycle is that the components self-assemble into a platform for the attachment of light-converting proteins. Then, the addition of a surfactant triggers the materials to disassemble. When the surfactant is removed, the materials reassemble (with the DNA/RNA recognizing the chromophore) and the cycle starts over again for an unlimited number of cycles.

As in nature, the chromophore in this model will degrade, but when it needs to be replaced it can be removed by using chemical processes (or by adding new DNA strands with different nucleotide sequences that won’t recognize the damaged molecule) and new chromophores is then added.

They say the assembly is “thermodynamically metastable and can only transition reversibly if the rate of surfactant removal exceeds a threshold value. Only in the assembled state do the complexes exhibit photoelectrochemical activity.”

They say they achieved a photoconversion efficiency of 300%+ over 168 hours and foresee an “indefinite extension of the system lifetime.”

Jong Hyun Choi, an assistant professor of mechanical engineering at Purdue University, says, “We’ve created artificial photosystems using optical nanomaterials to harvest solar energy that is converted to electrical power . . . Instead of using biological chromophores, we want to use synthetic ones made of dyes called porphyrins . . . I think our approach offers promise for industrialization, but we’re still in the basic research stage.”

The research is being performed at the Birck Nanotechnology and Bindley Bioscience centers at Purdue’s Discovery Park. A paper about the early work was published in Nature Chemistry.

 


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