Professor Dawn Bonnell the director of the Nano/Bio Interface Center at the University of Pennsylvania and her colleagues have demonstrated the transduction of optical radiation to electrical current in a molecular circuit.  The system uses an array of nano-sized molecules of gold that respond to electromagnetic waves by creating surface plasmons to induce and project electrical current across molecules, similar to that of photovoltaic solar cells.

The team’s the results may provide a technological approach for higher efficiency energy harvesting with a nano-sized circuit that can potentially power itself with sunlight.  The system might also be developed for computer data storage. Traditional computer processing represents data in binary form, either on or off, a computer that used such photovoltaic circuits could store data corresponding to wavelengths of light.

The team fabricated an array of light sensitive, gold nanoparticles, linking them on a glass substrate. Minimizing the space between the nanoparticles to an optimal distance the researchers used optical radiation to excite conductive electrons, called plasmons, to ride the surface of the gold nanoparticles and focus light to the junction where the molecules are connected. This plasmon effect increases the efficiency of current production in the molecule by a factor of 400 to 2000 percent, which can then be transported through the network to the outside world.

Metal Nanoparticle Light Driven Generator. Click image for more info.

It works by optical radiation exciting a surface plasmon and where the nanoparticles are optimally coupled, a large electromagnetic field is established between the particles and captured by gold nanoparticles. The particles then couple to one another, forming a percolative path across the opposing electrodes. The size, shape and separation distance can be tailored to engineer the region of focused light. When the size, shape and separation of the particles are optimized to produce”resonant” optical antennae, enhancement factors of thousands might result.

The team demonstrated that the magnitude of the photoconductivity of the plasmon-coupled nanoparticles could be tuned independently of the optical characteristics of the molecule, a result that has significant implications for future nanoscale optoelectronic devices.

Bonnell says in the Penn press release, “If the efficiency of the system could be scaled up without any additional, unforeseen limitations, we could conceivably manufacture a one-amp, one-volt sample the diameter of a human hair and an inch long.”  It seems incredible; a watt per her dimensions would require a large gathering lens focused on a tiny device.

The study has been published in the current issue of the journal ACS Nano. The team includes Bonnell, David Conklin and Sanjini Nanayakkara of the Department of Materials Science and Engineering in the School of Engineering and Applied Science at Penn; Tae-Hong Park of the Department of Chemistry in the School of Arts and Sciences at Penn; Parag Banerjee of the Department of Materials Science and Engineering at the University of Maryland; and Michael J. Therien of the Department of Chemistry at Duke University.

This research is at the leading, bloody sharpest edge of photon to energy research.  It’s interesting as rather than relying on light stimulating silicon or the parts of light’s spectrum stimulating various dyes, the light triggers what seems like a cascade of light energy with the electromagnetic field descending between the molecules stimulating current.  With the bulk of photovoltaic research going to the maximum accumulation of light wave spectrum energy, tuning for photons seems unique even as surface plasmons have already been engineered into a variety of light-activated devices such as biosensors.

This is very encouraging research.  The idea of plastering solar collectors on a 1:1 ratio of area seems expensive, thus any development that could lead to simpler light concentration and higher efficiency harvesting is very worthwhile.


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