Solar goes black: These two solar cells were fabricated on a silicon wafer treated to create an antireflective black silicon surface. The silvery areas around the cells are a different color because the highly absorbent black layer has been etched away.
Hao-Chih Yuan
A one-step process creates a highly antireflective layer for photovoltaics.
A simple chemical treatment could replace expensive antireflective solar cell coatings, bringing down the cost of crystalline silicon panels. The treatment, a one-step dip in a chemical bath, creates a highly antireflective layer of black silicon on the surface of silicon wafers, and it would cost just pennies per watt, say researchers at the National Renewable Energy Laboratory (NREL). They've used it to create black silicon solar cells that match the efficiency of conventional silicon cells on the market.
The crystalline silicon wafers used to make today's solar cells are treated to create a textured surface, then coated with an antireflective layer, usually silicon nitride, using high-vacuum processes. This additional layer increases the value of a solar cell by improving its efficiency--it suppress reflection so that more photons actually enter the silicon wafer instead of bouncing off its surface, increasing the flow of electricity off the cell. But the extra layer also adds to the expense. "We believe it can be cheaper," says Howard Branz, principal scientist in silicon materials and devices at NREL. Even with a coating, the best-quality silicon solar cells typically reflect 3 percent of the light that hits them. Branz's lab is developing inexpensive ways to create black silicon, which reflects almost no light.
Prototype solar cells made at NREL have the best efficiency ever reported for black silicon cells. Monocrystalline silicon cells with the black surface, and no additional antireflective coating, convert 16.8 percent of the light that hits them into electricity, about the same efficiency offered by a typical crystalline silicon solar cell coated with antireflective material. The previous record for black silicon cells was 13.9 percent.
To replace the vacuum-deposition processes used to treat the surface of a silicon wafer, Branz's lab developed a chemical process that can be performed at ambient temperature and pressure using equipment already on site at solar-panel factories. A wafer is submerged in a bath containing a water solution of hydrogen peroxide, hydrofluoric acid, and chloroauric acid, which is made up of hydrogen, chlorine, and gold. The small amount of gold in the acid bath acts as a catalyst for chemical reactions. It's not clear exactly what the chemical reactions are, but they lead to the formation of gold nanoparticles that drill nanoholes at varying depths into the wafer. Branz says the gold can be reused again and again.
A new form of silicon could create cheaper photo detectors that are easier to make in bulk.
The figure of 1 billion years is actually rather conservative. It is an estimate of the maximum time the Earth will remain inhabitable, due to the increasing solar output. But, on reflection, long before then we will have colonised other bodies in the solar system, and some of those further from the sun will remain inhabitable a lot longer. In fact creating mobile sustainable colonies is extremely likely within a much shorter period of time, so the figure of one billion years can be replaced by a much larger number, unless there is some unavoidable catastrophe that will exterminate all descendents of humans before then. Note that with efficient use of large energy supplies, all other resources are recyclable pretty much indefinitely.
Guest (aarontco)
For a long time people have been saying that, with sufficient interest and investment that solar PV could make great strides in efficiency and cost reduction. It is gratifying to see some many breakthroughs recently in this area. Photovoltaics are essentially a semiconductor technology and therefore, many of the tricks and techniques developed in other areas of electronics manufacturing can be exploited to build better solar panels.
Wherever man put his conscious effort with a goal in mind, we have results showing up. Solar energy is the current focus of the human mind. Congratulations on creating the possibility and we shall soon see the results. Thanks Katherine.
That controlled-fusion generation station ought to be coming on line any day now, right?
Articles says: "Even with a coating, the best-quality silicon solar cells typically reflect 3 percent of the light that hits them."
That means they absorb 97%. So absorbing 100% with black silicon is not much of an improvement. The story is the cost savings, not the performance improvement. Unless I'm totally misunderstanding this.
A 3% relative increase in the performance of solar cells is actually significant, especially if it can be obtained at lower cost. Where this technology would really be useful is to improve the absorption of lower-cost multicrystalline and ribbon Si cells, which cannot be effectively textured in any other economically viable way. There, the absorption would be reduced from 10% or more.
Possible impact on light-oxygen induced degradation?
Improving the reflective properties of solar cell coatings is clearly important to improving their efficiencies; but I wonder about the relationship to another factor that affects efficiency: the light-induced reaction with residual oxygen that occurs in the first 48 hours of operation. This can reduce efficiency by 3 - 5%. This oxygen, present from the time of manufacture, reacts with the dopant (Boron) in a light activated reaction. The coating method described in the article is said to result in tunnels of varying depths in the coating. These tunnels presumably are responsible for the improved optical properties. But it's reasonable to ask if they would also increase the coating's permeability to air, allowing for additional oxygen to diffuse into the cell over time. This could cause further efficiency degradation (beyond what occurs due to the oxygen initially present in the material).
Technology Review Magazine recently did an article on an anti-reflective solar cell coating that actually tied up the residual oxygen in the material, resulting in less efficiency loss due to degradation, as well as improved optical properties: A Safer Way to Coat Long-Lasting Solar Cells, Tyler Hamilton, January 27, 2010.
Investors would no doubt be interested in seeing a comparison of the two technologies, in terms of initial and long-term efficiencies.
Re: Possible impact on light-oxygen induced degradation?
So your saying that this new black coating could affect the operational life? I would think so, as well because it is black is will absorb more IR and thus get hotter, running less efficiently. I would be interested to see its operational life is reduced.
Thanks
Dr. Glassman
www.GreenVineSolar.com
First, a 3% increase at low cost is huge in solar terms. Given that some of the best solar cells of any type in the lab are in the 20% ballpark, a cheap 3% gain of easily produced cells is huge.
Keep in mind, it's a 3% gain of "total available" energy, however it's actually a roughly 20% increase in comparison to the standard treatment.
20% more efficient in a town of 10,000 solar farm-powered homes means 2000 of those homes get "free" power compared to the standard AR treated black silicon cells.
Also mentioned, the boron/oxygen degradation issue, and coatings that deal with it (as well as other A/R coatings)... no reason is given in the article that those techniques can't be combined (it MIGHT not work, if the A/R coatings optically alter the benefits of the "tunnels" in the cells for instance)... but if the A/R coating/sealant can be combined with this production technique, no other reason to think the 3% gain can't be maintained.
I think you're misinterpreting the math here. The conversion efficiencies of PV, be it 20% or whatever, are relative to the absorbed light. Improving light adsorption from 97% to 100% would increase overall efficiency only by a factor of 3/97 or about 3.1%... assuming there aren't any wavelength dependent aspects of reflection that aren't presented in this article.
Why can't we just build 400 nuclear powerplants and call it a day? I like solar but I think we could be doing greater things than further engineering semiconductors.
There is nothing wrong with 400 more nukes except:
1. No one wants one in their backyard,
2. Utilities can not afford to build them, and;
3. No banks want to finance one.
We can solve 2. & 3. I am not so sure how we are going to solve 1.
Even if you could get the financing for your 400 nukes and built them you would hardly be able to call it a day. The average life span of a nuclear power plant is 40-50 years. That's a pretty darn short life for something so horrifically expensive that produces radioactive waste that will be around for thousands of years.
That solar panel on your roof will still be kicking out power as you try to figure out where you will get the money to build the next generation of nukes which would likely cost 3 times as much as the ones they would replace.
Nukes are not a sustainable solution.
GF
Instead of the 400 nuclear reactor suggestion, how about 400 milion solar panels? If placed on every house in the U.S., that would be about 4 per house. I am ready. Place panels on every building too. Just this one step would be huge. It would cost less than the proposed 400 nukes. It would provide free power and be non poluting and non-radioactive-byproduct producing.
And solar farms on desert land, Arizona, New Mexico, Texas, Ok?
Re: 400 nukes? 400M solar panels
I would like to know how much energy it would take to make all those silicon cells and their support structure. You might find you need those 400 nukes to make the solar cells
I think we should put the nuclear waste from these power plants in your back yard.
Yes that is really part of the problem isn't it. Where do we put the waste from 400 new units.
Many pro nuclear people say we should recycle the fuel and burn it in new mod IV/V reactors like high temperature gas cooled or thorium molten salt which of course could be done. This of course is a very good option since the resulting volume of waste will be significantly reduced. It probably also make financial sense. However, it appears to me we have not chosen to do this because:
No one, including the government, seems willing to bet billions and billions of dollars on a new reactor technology. I really shouldn't say new because molten salt reactors have been around for a long time. Maybe a better term is - we have chosen not to build them and there are several reasons why.
The primary reason as I see it is that wind and solar are both showing significant improvements in both power output and reliability. I believe many individuals in leadership positions are now beginning to believe that using renewable energy sources will soon become technically and financially possible. We are not there yet but we are fast approaching that point.
When we do there will no longer be a need for hundreds of new nuclear power plants but rather a limited number to provide base load power until we also solve the energy storage problem. When that happens we will no longer need nuclear, natural gas or coal burning power plants. How far away is this? - My guess is about 20-30 years - about 1/2 the lifetime of a nuclear unit.
So as a thinking individual, it is beginning to appear that maybe at best we will need nuclear for maybe 20-30 more years. We can extend the life of some of our existing plants, and build maybe a few new mod V units to burn up the existing waste or until renewables are ready to take over the load.
This is why I believe there is no real push for more nuclear - all of the people who have money or control money see the handwriting on the wall. Why invest billions in a dying technology.
Sorry this post is so long.
Right, along with squirrel driven generators.
http://www.instituteforenergyresearch.org/2010/03/09/expensive-solar-power-continues-to-be-built-in-the-u-s-why/
Could this process be used to increase the efficiency of solar collectors used to heat water?
No, no likely because silicon is not used for heat exchangers usually copper or aluminum would be used so the chemical reaction would be different as would the results of the reaction.
3D Vertical structures grown on the substrate can arrest the photons to greater extent. one such development is the growth of carbon nano tubes on the substrate.but due to the difficulties in the vertical growth of CNT's, the time for black silicon has come.Thanks for the researchers and students who worked on this topic.
Manufacturing in the United States is in trouble. That's bad news not just for the country's economy but for the future of innovation.
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sls1j
14 Comments
Activity
It certainly seems there is a lot of activity in the solar cell arena. I wonder how much is due to private investment and how much to government investment.
Brian
Ranch For Sale
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briang1621
171 Comments
Re: Activity
Good question, see this website for more details.
Link
Dr. Brian Glassman
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briang1621
171 Comments
Re: Activity
Actually, Black body are theoretically the best at adsorbing all energy, the closer to a black body you are the better. However, PVC only make good use of a limited spectrum. Hence, being black is good for the spectrum you want to absorb and bad for absorbing things like IR (heat).
Interestingly, I advocate Black body collectors use in solar technologies like solar troughs, and I even use it in my own revolutionary solar technology, if your interested check out my website (www.GreenVineSolar.com)
Thanks
Dr. Brian Glassman
Ph.D. in Innovation Management from Purdue University
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