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Black silicon could boost efficiency of traditional solar cells

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October 3, 2012

Dark silicon could improve efficiency in traditional solar cells by harvesting energy in t...

Dark silicon could improve efficiency in traditional solar cells by harvesting energy in the infrared spectrum (Image: Fraunhofer HHI)

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Researchers at the Fraunhofer Institute for Telecommunications have developed a system that allows solar cells to effectively harvest energy from the infrared spectrum, tapping into a source of energy that in the past has mostly been out of reach. The new technology, which promises to work well with commercially available solar cells, has the potential of becoming a standard in the solar panels of tomorrow.

When photons hit the surface of a solar cell, the energy they carry can be absorbed by a semiconductor. If the energy absorbed is higher than a set threshold – which is known as the energy gap, and depends on the semiconductor used – electrons are freed from the semiconductor and can be used to generate an electric current.

The electromagnetic spectrum (Image: Shutterstock)

The energy carried by a photon is proportional to its frequency. In silicon solar cells, photons in the infrared often don't carry enough energy to produce electricity, and IR light simply passes through the cell, unused. Red photons are carrying just enough energy to knock an electron loose and photons in the blue spectrum or beyond (UV light) are carrying too much energy – so part of it is used to free a single electron, but the rest is wasted as heat. The inability to fully extract the energy carried by a photon is the main reason why solar cells are so inefficient.

Over the past few years, researchers have produced solar cells that can absorb infrared and ultraviolet light more effectively. Now, researchers at Fraunhofer Institute have come up with a straightforward way to capture more energy from the infrared spectrum, developing something that could very well become standard technology in the solar cell of the near future.

The research is based on absorbing infrared light using what's known as black silicon. This material is made by using precision lasers to "zap" sulfur atoms into the silicon lattice in well-defined patterns.

The sulfur lowers the energy gap, and therefore allows much lower-energy photons to free electrons from the semiconductor. In theory, this should boost the solar cell's efficiency; unfortunately, though, the smaller energy gap also makes it easier for electrons to "travel" in the opposite direction, causing electricity to be lost once again.

The researchers at Fraunhofer set out to address this issue and came up with a conceptually simple yet ingenious solution. They chose to change the patterns of laser pulses that drive sulfur atoms into the silicon lattice, altering their conformation to maximize the number of electrons that can climb "up" the energy gap and become conductive, while minimizing the number of electrons that can go back "down" it.

Prototypes of the cells have shown that the mechanism can double the efficiency of black silicon, but the researchers are still looking to identify the configuration of sulfur atoms that can result in the best performance.

The next step will be to embed the cells with already existing commercial technology, and the good news is that the two are very much compatible, and seem to complement each other. By simply removing the back cover of a traditional solar cell and incorporating a layer of black silicon, the team has found that they can increase efficiency of such panels by about one percent.

The researchers are now planning to market a laser system that manufacturers can use to produce the black silicon themselves and include it in their products as standard.

Source: Fraunhofer HHI

About the Author
Dario Borghino Dario studied software engineering at the Polytechnic University of Turin. When he isn't writing for Gizmag he is usually traveling the world on a whim, working on an AI-guided automated trading system, or chasing his dream to become the next European thumbwrestling champion.   All articles by Dario Borghino
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7 Comments

One percent? Seriously? *1%* ???

So, I read thru this article with all the techno-babble and science-speak thinking, "Wow, this is great! A real breakthrough!" ... then get down to the improvement increment: frickin' ONE percent! How much time/energy/expense was dumped into this project? Guys, go outside with some windex and wipe down your panel, and you'll get one percent improvement! Sheesh.

MzunguMkubwa
4th October, 2012 @ 05:38 am PDT

In addition, as I was a "genius" in my college statistics class (compared to the Psychology majors, I mean), 1 percent is probably not within statistically significant parameters, methinks, perhaps.

Horatio Van Pewterschmidt
4th October, 2012 @ 10:13 am PDT

Going from 12% to 13% is a big difference. You won't get that by cleaning your panels.

Captain Obvious
4th October, 2012 @ 10:15 am PDT

If every "breakthrough" I have read about over the last 20 years had been incorporated in the solar cell they would be capturing 100% of light energy by now. But this latest research is promising, even if 1% is all they can add presently. This points to another problem, however. The research is using the Edison method: trial & error. I prefer the Tesla method: Understand the fundamental physics and save 100s of thousands of hours guessing.

voluntaryist
4th October, 2012 @ 12:32 pm PDT

Captain Obvious - An increase of 1 percentage point from 12% to 13% would represent an efficiency increase of 8.3%.

It was not clear from the article whether the increase amounted to 1% or to 1 percentage point - a very common ambiguity.

Yukonite
4th October, 2012 @ 01:18 pm PDT

From the linked article:

“We hope to be able to increase the efficiency of commercial solar cells – which currently stands at approximately 17 percent – by one percent by combining them with black silicon,”

That pretty clearly implies going from 17 to 18 percent efficiency, a 5.9% boost. How much time/energy/expense was dumped into criticizing this project? It always amazes me how so many armchair scientists on Gizmag think they're so much smarter than professional scientists, especially when they have no grasp whatsoever of the field and haven't even gone as far as to read any of the studies. It's one thing to doubt the work of "designers" and marketers, which we see way too often on this site, but actual scientific research isn't something that can be disproved by snarky skeptics.

Gadgeteer
4th October, 2012 @ 07:53 pm PDT

I have seen so many improvements in solar (in the lab at least) in coatings that focus the light for less tracking, more efficient trackers, in 3D , and in double-sided to catch the reflections off the roof structure, to new construction methods, and materials to catch more of the light spectrum, along with focusing lens, and cooling methods.....Why can't they all be used on the same cells to create truly impressive solar cells, That actually get released from the lab for sale and use? When do we get to use all of these improvements we keep hearing about?

kellory
26th October, 2012 @ 05:45 pm PDT
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