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Researchers at Harvard apply a new twist to inorganic nanoscale photovoltaics

A team led by Charles M. Lieber of Harvard has developed a nanowire which is both conductive and photovoltaic. The wire, comprised of silicons, may be ideal for powering various nanoscale devices.

While nanoscale photovoltaics are not a new invention, Lieber's nanowires are both more efficient and more durable than others. The nanowires can convert up to 3.4 percent of received sunlight into electricity, and almost 5 percent in concentrated light. The wires also do not degrade under these conditions the way organic photovoltaics do.

The wire itself, like traditional amorphous silicon solar cells, uses three types of silicon. A core doped with B2H6 is first grown, then covered with a layer of pure silicon. A third layer, doped with PH3 follows, after which the wire is coated with a protective mask. This layering creates an electric field between the core and the outer silicon layer, with the pure silicon acting as a resistor. Photons striking the wire create electricity and holes in in the neutral layer, which then separate into the core and outer layer.

While the core of the wire is a single crystal, the outer layers are nanocrystalline. Lieber believes the nanocrystalline structure is the key to the the wire's enhanced absorption properties over that of single-crystal materials.

To gather electricity from the wires, the outer layers are first etched away to expose the core. Then, using lithography, metallic contacts are laid down and attached to the exposed wire.

The cells, Lieber says, are not ready for commercial application. Typical commercial solar cells have an efficiency of 12 to 18 percent, compared to the nanowire's 3.4 percent. Lieber plans to research ways to boost the efficiency of the wire, targeting a 10 to 15 percent yield. Even at these levels, the low production cost could make them viable in larger applications.

“It will have to be unique to be an economically viable application, some place where you want durability and flexibility, where if it gets destroyed, people don't care,” said Lieber.

The nanowires have already been used to power various electronics, including a nanoelectronic pH sensor and a cancer detector.

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Great!.. but....
By Screwballl on 10/25/2007 4:01:04 PM , Rating: 2
as with many new findings like this, some major company that could stand to lose a lot of money from this may end up buying this patent and burying it so they keep the money making patents of their own profitable...

I hate to see this happen but we will see.

RE: Great!.. but....
By KristopherKubicki (blog) on 10/25/2007 4:03:37 PM , Rating: 5
Yeah but submarining patents like that is a lot harder than you'd think.

Patenting technology and then never using it does not stand up in court in this country.

RE: Great!.. but....
By mcnabney on 10/25/2007 5:34:16 PM , Rating: 2
Do some research. Various oil conglomerates own many of the current generation battery patents. I didn't believe it either until I went looking. Cheap tech like this could literally be applied to every roof in the sunbelt, providing cheap electricity during the peak daytime loads. Somebody is making a killing building new powerplants and those profits could just as easily be used shape the future market by acquiring key patents.

RE: Great!.. but....
By johnsonx on 10/25/2007 6:01:36 PM , Rating: 2
Do some research. Various oil conglomerates own many of the current generation battery patents.

I should find that disturbing or nefarious because.....?

RE: Great!.. but....
By surt on 10/25/2007 6:15:31 PM , Rating: 2
High powered batteries would enable cheap all electric cars that could be solar/wind/coal charged.

RE: Great!.. but....
By KFeldman on 10/26/2007 1:20:17 AM , Rating: 2
Because the only reason why they have the patents is so that other companies cannot use that technology to mass-produce better batteries...?

RE: Great!.. but....
By clovell on 10/25/2007 6:04:30 PM , Rating: 2
Wow, that might actually be an argument if you would have made the point that these 'oil conglomerates' have somehow stifled battery R&D.

RE: Great!.. but....
By 16nm on 10/26/2007 1:33:18 AM , Rating: 2
Do some research. Various oil conglomerates own many of the current generation battery patents.

That means nothing.

oil companies are actually energy companies. they see the writing on the wall and know that other sources of energy must be found. believe me, today's largest energy companies will be tomorrows largest energy companies. The only thing that will be changing is the energy source.

It is a good thing when a large energy company wants to invest in technologies that are relevant to its business.

Fossil fuels are on the way out. The only problem is that nobody knows what they will be replaced with. You mention solar, but its problem is cost and the fact that the sun disappears every night!! Until we can dramatically improve battery efficiency and reliability and make solar arrays much cheaper then solar is dead.

RE: Great!.. but....
By Samus on 10/25/2007 7:51:16 PM , Rating: 2
Patenting technology and then never using it does not stand up in court in this country.

Unless your NTP ;)

RE: Great!.. but....
By BVT on 10/26/2007 1:03:30 PM , Rating: 2

RE: Great!.. but....
By masher2 on 10/25/2007 5:13:21 PM , Rating: 2
Not to mention that aforementioned company could make ten times as much money by buying the patent, then exploiting the relevant technology to get a lead over their competitors.

RE: Great!.. but....
By Wightout on 10/25/2007 5:50:02 PM , Rating: 2
But in the interest of keeping people employed in the here and now, what are the odds that this will actually happen?

I heard rumors (completely unconfirmed) cold fusion research being almost altogether destroyed in attempt to keep both coal and oil in business. Not sure if this is true or not, but I wouldn't doubt it.

Will be interesting to see how patents get changed now that IBM has put in a request for a patent on the ability to patent. (lol)

RE: Great!.. but....
By Ringold on 10/25/2007 6:28:03 PM , Rating: 2
But in the interest of keeping people employed in the here and now, what are the odds that this will actually happen?

I fail to see the business logic here..

Lets say I have 10 guys mining coal, and make $100. I could go and buy this scientists patent, fire these coal miners, hire 2 young engineers to make the stuff, and make $1000 until the patent protection runs out or somebody else figures out how to do it better, at which point my profit falls to a more moderate amount.

But because I really, really like my coal miners I'm going to not bring the more profitable product to market?

Sorry, but CEO's aren't bleeding heart leftists. :P

Cold fusion research is probably being destroyed by the same people in the black helicopters after this sites owners:

Click the link fast, the Illuminati may take it down at any moment!

RE: Great!.. but....
By Wightout on 10/25/2007 7:25:29 PM , Rating: 2
Perhaps not from a business perspective. However from a politician's perspective the point of view may be a bit different.

Is there is a business reason we are not making more nuclear power plants? Because it is not safe? Becuase mining is? Gimme a break...

RE: Great!.. but....
By Ringold on 10/25/2007 10:57:40 PM , Rating: 1
No, there is no particular business reason we're not making new power plants. Utility companies would love to. The only thing stopping them is NIMBY environmentalists that do claim that nuclear is unsafe. This is pretty well established.. if you somehow thought American's above such FUD, it's even more prevalent in parts of Europe.

Mining gets grandfathered in, in my view, because it was occuring before society scorned difficult or dangerous work. Easy to ignore something when its an old thing that "always has been and always will be".

I really fail to see NIMBY environmentalists blocking solar power.. so I guess I fail to see your point.

RE: Great!.. but....
By ZmaxDP on 10/25/2007 11:02:00 PM , Rating: 2
Actually, there is a business reason(s).

1. Excessively steep code requirements for safety of the plants makes building them prohibitively expensive. (The government did pass these codes, but they are holding things back).

2. The amount of capital required means very few companies in the world can afford to build them.

3. All the lawsuits and other legal actions that come against companies that attempt to build them can add years and billions of dollars to the already high price.

RE: Great!.. but....
By drwho9437 on 10/25/2007 11:34:20 PM , Rating: 2
Wire technology is old stuff (used to be called Wisker). I think the basic synthesis of nanowires using VLS growth was patented as much as it could be in the 1970s. Those patents are dead. All Leiber group has done here is made a few axial clad wires (VLS followed by CVD again not patentable really) and then did ebeam (which costs a fortune) to make contacts. The Ebeam is ok here cause they are just try to show the efficiency of the wires in this kind of structure. They hint at better ways of doing it in the actual paper. I also note there is a major shortcoming to the way these are prepared other than the Ebeam, but I won't talk about it too much as they have a huge group of people at Harvard, and I just have me and another guy.

RE: Great!.. but....
By KFeldman on 10/26/2007 1:35:19 AM , Rating: 2
Only if the company holding the patent is stupid enough to sell...

And before you ask "if the technology is so good, why doesn't the company holding the patent just use it to bring new (better) products to market?", the answer is also pretty simple:

They will. When and only when they determine that doing so will increase their profits. Energy companies don't push dirty sources because they're evil. They push them simply because (at this point) that is what maximizes their profits.

But the fact that they are holding on to key patents in "competing" energy sources (or storage methods, etc) reduces competition, which slows down innovation and drives prices up.

Nice but...
By DeepBlue1975 on 10/25/2007 6:41:42 PM , Rating: 2
I'd prefer research oriented towards getting higher efficiency solar cells even if they cost more, than unbearable poor efficiency ones which cost much less.

If they could combine dirt cheap price with high efficiency, that's what I'd call awesome.

As for this, I find it as a good step that could help solar cell technology becoming more massive (provided they are still so cheap when they attain a normal efficiency) and as such paving the way for more research.

RE: Nice but...
By Treckin on 10/25/2007 8:18:00 PM , Rating: 2
If they could make them better for less, that would be cool, essentially?


RE: Nice but...
By drwho9437 on 10/25/2007 11:28:52 PM , Rating: 2
Sadly there are physical limits to the quantum efficiency of a solar cell. Even with detailed band engineering and multilayer cells you can only do so much.

Effectively the reason high efficiency cell aren't worth it is they cost more. The cost more require a lot more energy and materials to make.

These nanowires are grown much in the same way your LCD panel on your laptop is made. It is more or less CVD type costs, but with a lot of advantages.

So what if it costs more it will pay for itself later? Not necessarily. Radiation damages solar cells. Polymer cells are the most sensitive to this as they have fragile low energy carbon bonds, but even single crystal cells can be damaged. Every kind dies eventually.

I have to disclose I am another researcher in the nanowire field, in fact I'm working along similar lines to this group at the moment at another major University.

RE: Nice but...
By 16nm on 10/26/2007 1:41:14 AM , Rating: 2
I think solar arrays will keep getting more efficient and cheaper. It's batteries that must improve. Imagine how many of today's batteries it would take to hold enough power to supply Los Angeles for one night. Then what would happen if the following day it rained and the batteries were unable to fully recharge... We need to have enough capacity for several days without full sun. Solar may one day work but that day is far from now.

Of course, I forgot about the Energizer Bunny. I guess if we ever need more juice we can just add him to the power grid. LOL

What would einstein say...?
By jtemplin on 10/25/2007 8:13:26 PM , Rating: 2
What in the quantum photoelectric effect???


RE: What would einstein say...?
By drwho9437 on 10/25/2007 11:22:42 PM , Rating: 2
I hope you are being sarcastic as the photoelectric effect was an early indication of the need for a new theory for light.

Comprise != Compose
By KFeldman on 10/26/2007 1:52:18 AM , Rating: 2
The wire, comprised of silicons [...]

I'm pretty sure you mean "composed", not "comprised". The whole comprises the parts; the parts compose the whole. It's a frequent error, but an easy one to fix.

RE: Comprise != Compose
By Visual on 10/26/2007 4:47:30 AM , Rating: 2
isn't it "the whole comprises of the parts" ?
so, "The wire, comprising of silicons"?

Possible Mistake
By Goty on 10/25/2007 6:00:19 PM , Rating: 3
I'm not entirely positive, but I'm pretty sure that describing the silicon layer in between the two doped layers as a resistor is erroneous. The silicon would act as a dielectric and the two doped layers would act as the cathode/anode; i.e. the whole wire would act as a resistor, not just one layer.

"The whole principle [of censorship] is wrong. It's like demanding that grown men live on skim milk because the baby can't have steak." -- Robert Heinlein

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