Silicon nanohole solar cells aim to make photovoltaics cost-competitive

May 07, 2010 By Lisa Zyga feature
These scanning electron microscope images show the silicon nanoholes at different scales, and (d) shows a cross-sectional view. Image credit: Peng, et al. ©2010 American Chemical Society.

(PhysOrg.com) -- Due to the increasing demand for renewable energy sources, photovoltaic solar cells have advanced significantly over the past decade. Since 2002, photovoltaic production worldwide has been doubling every two years, making it the world’s fastest-growing energy technology. However, the overall energy conversion efficiency of photovoltaics is still too low to be cost-competitive with fossil fuels, and so it has not been widely deployed.

In an attempt to change this, scientists have recently developed a novel solar cell that has a unique geometry of nanoholes with diameters of about 500-600 nanometers. By achieving a power conversion efficiency of 9.5%, the new design boasts a superior performance compared with its silicon counterparts, such as solar cells that incorporate nanowires, nanotubes, and other optically active nanostructures. The best of these designs has an efficiency of a little more than 5%.

The researchers of the new study, Kui-Qing Peng of Beijing Normal University, Shuit-Tong Lee of the City University of Hong Kong, and their coworkers, have published their results in a recent issue of the . In their experiments, the scientists used a combination of deep ultraviolet lithograpy and metal-catalyzed electroless etching of silicon to fabricate the nanoholes on .

As the researchers explain, the key to the improved performance of the nanohole solar cell is that the nanohole arrays have better absorption than nanowires. Particularly, the vertically configured radial p-n junctions enable the electric current to travel only short distances between junctions for efficient current flow. In addition, the nanohole solar cell has shown to have superior mechanical robustness compared with the fragile structures of solar cells that have free-standing nanowire p-n junctions. In the past, this fragility problem has caused serious setbacks for manufacturing photovoltaic applications.

“The nanohole geometry solar cells possesses a robust structure compared with fragile free-standing nanowire geometry, a better ability for capturing sunlight than nanowire arrays, and radial p-n junctions allowing for enhanced carrier collection,” Lee summarized to PhysOrg.com.

Overall, the results demonstrate that the nanohole geometry has the potential for energy-efficient and cost-efficient photovoltaic solar energy conversion. The scientists plan to further improve the performance in several ways, such as by improving the coupling of light into the device, employing surface passivation to minimize surface recombination, and incorporating better electrical contacts.

“High optical absorption plus better carrier collection efficiency in nanohole geometry solar cells can be fabricated with less silicon materials and lower quality silicon,” Lee said. “These benefits would lead to efficient and less expensive , offering potentially competitive performance with traditional silicon-wafer cells, as well as cost-competitiveness with in the future.”

Explore further: Discovery is key to metal wear in sliding parts (w/ Video)

More information: Kui-Qing Peng, et al. “High-Performance Silicon Nanohole Solar Cells.” J. Am. Chem. Soc. Doi:10.1021/ja910082y

4.5 /5 (26 votes)

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DaveGee
4.7 / 5 (3) May 07, 2010
If we add up all of the news items where it's stated they intend on making solar more affordable WITH all the news items where they start they intend on making solar more efficient...

...in five to ten years(tm) we'll see oceans of 200% efficient solar panels that producers will PAY YOU to take.

Sorry for the friendly-poke but how about just ONE story on something that is already in production. Just so all this 'news' stops sounding like the zany reports from OU nuts and 'all-magnetic motor' fools.

Finally this is NOT an attack on this SPECIFIC news story but just my over all feeling on the subject. :(
PieRSquare
3 / 5 (1) May 07, 2010
@DaveGee: I share your frustration with not seeing more stories about these new technologies in production (esp w/ power storage) but it all has to start w/ R & D. Some things will work out, some won't but it's worth the attempt regardless and it's worth reporting what is being done.
For there to be a story about cool new tech in production someone has to put it into production first, so it's not really Physorg's fault unless it happens and they fail to report it.
Most of the really cool stuff has been happening in the last 5 years so it's not surprising we haven't seen much in the real world yet.
kcameron
5 / 5 (1) May 07, 2010
What bothers me about these announcements is that they always understate current technology. 9.5% is supposed to be an efficiency breakthrough for silicon but the record is about 25% and monocrystalline commercial cells routinely are running about 20%. I don't see how the cost of this process can be lower than today's multicrystalline cells which run about 15%.

Research is good but there's no way they can make any legitimate claim to a breakthrough yet.
fixer
5 / 5 (1) May 07, 2010
I also agree with DaveGee, These constant updates sound like "look how clever I am".
How about "Look what we have available now"!
These things are always under development but rarely see daylight.
This is more about intellectual copyright than useful production.
Bite the bullet, people, and put your money where your mouth is!
matt_genuus_com
not rated yet May 07, 2010
The breakthrough is that they used a fundamentally different approach, and there's still plenty of room for improving efficiency.

Different approaches such as this one can sometimes be combined with others, resulting in advances much greater than the sum of the parts.
DaveGee
not rated yet May 07, 2010
Thanks for the comments... I'm glad I'm not alone feeling the way I do.

Now for the record... I'm 10000% pro science and the idea that governments AND (prosperous) individuals should be funding projects like this with as much zest as they do buying shiny new battleships and/or 4 story houseboats...

Perhaps I'm being somewhat selfish, I have a cancer that will likely take me before I turn 50 and sites like this one really give me HOPE .. the hope I need to 'keep on keepin on' and while cancer stores do have a personal interest, energy was ALWAYS my real joy to read about.

I guess I'd like to start seeing SOME 'pay-off' stories soon... Lab 'eureka' that remains lab 'eureka' simply isn't good enough!
labtvonline
not rated yet May 08, 2010
Even though the efficiency of this technology is slightly suspect, I still think it is a step in the right direction for the practicality of solar power. Nanotechnology is probably an everyday word for most of us on this site but I'm always shocked about when I have discussions with some of my friends, who I think are rather informed, who have no knowledge of the conquests that nanotechnology has already made. Just the other day I showed my friend and his kids a video about how, through the science of nanotechnology, the military has come up with a solar cell that is not only cheap and flexible but 10,000 times more efficient! It completely blew their minds. I'll post a link to the video if you would like to see it as it is rather relevant to this story as well.

http://www.ndep.u...ll-world
algaemasscsqrd
not rated yet May 08, 2010
The goal of nanotechnology R&D in silicon solar cells is to reduce grams/watt of silicon used in production. Crystalline Si typically (now ~7 grams/watt commercially) makes up half the cost of a solar panel. Also Silicon refining (purification)capacity is a bottleneck in mass production.
Efficiency is not the only parameter.
The hope is to reduce to up to
droid001
not rated yet May 08, 2010
People have become very impatient. Remember, how long it took until the LCD TV / Monitors has become a reality?
Alizee
May 08, 2010
This comment has been removed by a moderator.
GaryB
not rated yet May 08, 2010
from Wikipedia:

6% for amorphous silicon-based solar cells to 40.7% with multiple-junction research lab cells and 42.8% with multiple dies assembled into a hybrid package.[26] Solar cell energy conversion efficiencies for commercially available multicrystalline Si solar cells are around 14-19%.

It would be nice to place this into context. So, who cares about nano-wire efficiency which seems to be suspiciously low comparison here if the real comparison should be to multicrystalline techniques which (for all I know) may be cheaper.
DanRiches
5 / 5 (1) May 10, 2010
So with all these differing technologies which different companies hold patents on means that a final product (ie based on all the new "better" technology) may never actually be produced due to the fact that no one likes to share ideas. Research should go open source and then we'll see some improvements! Oh and 9.5% is awful, my BP Multicrystalline panels are ~19%
tpb
not rated yet May 13, 2010
Alizee,
Fossil fuel prices are artificially kept high, not low.
The actual cost per barrel of oil, in the tanker, in the middle east is about 4 to 6 dollars, not the 80 dollars we are paying.