Quantum dot photovoltaics are not market ready just yet, but efficiency and production costs are quite attractive.  A new technique developed by University of Toronto Engineering Professor Ted Sargent and his research group could lead to significantly more efficient solar cells.

Sargent’s group has devised a new technique to improve efficiency in colloidal quantum dot photovoltaics, a technology that already projects inexpensive, more efficient solar cell technology. Quantum dot photovoltaics offers the potential for low-cost, large-area solar power – however these devices are not yet highly efficient in the infrared portion of the sun’s spectrum, which is responsible for half of the sun’s power that reaches Earth’s surface.

Colloidal Quantum Dot Solar Cell Artists View. Click image for the largest view.

Colloidal Quantum Dot Solar Cell Artists View. Click image for the largest view.

The group has their research describing the new technique published in the journal Nano Letters, “Jointly Tuned Plasmonic Excitonic Photovoltaics Using Nanoshells.”

The group’s solution is spectrally tuned, solution-processed plasmonic nanoparticles. These particles, the researchers say, provide unprecedented control over light’s propagation and absorption.

The new technique developed by Sargent’s group shows a possible 35% increase in the technology’s efficiency in the near-infrared spectral region, said co-author Dr. Susanna Thon. Overall, this could translate to an 11% solar power conversion efficiency increase, she says, making quantum dot photovoltaics even more attractive as an alternative to current solar cell technologies.

Thon explains the importance of colloidal quantum dot photovoltaics, “There are two advantages to colloidal quantum dots. First, they’re much cheaper, so they reduce the cost of electricity generation measured in cost per watt of power. But the main advantage is that by simply changing the size of the quantum dot, you can change its light-absorption spectrum. Changing the size is very easy, and this size-tunability is a property shared by plasmonic materials: by changing the size of the plasmonic particles, we were able to overlap the absorption and scattering spectra of these two key classes of nanomaterials.”

Sargent’s group achieved the increased efficiency by embedding gold nanoshells directly into the quantum dot absorber film. Though gold is not usually thought of as an economical material, other, lower-cost metals can be used to implement the same concept proved by Thon and her co-workers.

Thon said the current research provides a proof of principle. “People have tried to do similar work but the problem has always been that the metal they use also absorbs some light and doesn’t contribute to the
photocurrent – so it’s just lost light.”

More work needs to be done, she added. “We want to achieve more optimization, and we’re also interested in looking at cheaper metals to build a better cell. We’d also like to better target where photons are absorbed in the cell – this is important photovoltaics because you want to absorb as many photons as you can as close to the charge collecting electrode as you possibly can.”

The third party qualifier for the press release is Paul Weiss, Director of the California NanoSystems Institute.  Weiss explained the research is also important because it shows the potential of tuning nanomaterial properties to achieve a certain goal.

“This work is a great example of fulfilling the promise of nanoscience and nanotechnology,” Weiss says. “By developing the means to tune the properties of nanomaterials, Sargent and his co-workers have been able to make significant improvements in an important device function, namely capturing a broader range of the solar spectrum more effectively.”

Solar photovoltaics have fallen on hard times, partially due to simple inefficiency, political pushes followed by drops an the developed world’s economy doldrums.  Most of the problem is photovoltaics are quite expensive for the return and recovery of the capital costs.  When the economy recovers interest rates will push the capital expense backup gain to more normal rates delivering another blow.

Those build costs have to come way down and the ancillary equipment to transform the current to household or grid use needs to come down as well.

Year’s back the worry was could there be enough silicon production to keep up – we’re finally getting to the real issue, can photovoltaic get price competitive for the long haul.

This research lends real hope that it’s possible.


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