Breakthrough in Solar Nano Technology
by Christine Lepisto, Berlin on 02.10.08
A chemistry professor at UC Santa Cruz, working with teams from California, Mexico and China, has published a paper reporting a breakthrough which may improve the conversion efficiency of incoming light photons to electrical current by as much as three times.
The material developed by Jin Zhang relies on two existing technologies from the field of nanotechnology. One is the use of nitrogen doped metal oxide nanoparticles. The other method uses nanosize crystals, "quantum dots", to increase solar energy conversion by injecting electrons into the metal oxide film.
Dr. Zhang combined the two concepts to produce a film both doped with nitrogen and electron-injected by quantum dots. Scientists measure the effectiveness of solar panels by the "incident photon to current conversion efficiency", IPCE for short. Using this measure, the new film is up to three times more effective at converting solar energy to electrical current. The trick is to make it easier for the current to flow by helping it hop around. It is a little bit like how it would be easier for you to walk upstairs if the stairs are built with many smaller risers as opposed to trying to walk up steps which are each several feet high. The ideal solar panel will be a one-story house: everything on the same level.
An interview with Dr. Zhang in CleanTech helps to put the scope of this new discovery into perspective. The films developed for this paper have an overall efficiency of only 1%. Currently, commercially available silicon solar panels have efficiencies topping out at 20 to 30%. But that is not the point declares Dr. Zhang.
The point is that these panels could become a cheaper alternative. So even if the new nanostructures only achieve 10 or 15% efficiency, they could beat out silicon on volume. Dr. Zhang also compares the toxicity of materials used in the manufacturing of the nano materials. The main film material is titanium oxide, which is substantially less toxic to work with than the silicon process. The new material also uses cadmium, a toxic heavy metal. Dr. Zhang points out that there is no solution which is free of chemicals. The trick is to use the chemicals without human or environmental exposures, thereby producing a material that is itself environmentally beneficial by breaking our reliance on fossil fuels. Breakthroughs like the work of Dr. Zhang, hairy solar panels, and 40% efficient solar pave the way to an alternate future.
Via ::CleanTech
Note that the efficiency of a solar celll is dependent on more than one factor; IPCE is just part of the game.
A big part of making solar cells more efficient is getting the charge out of the cell. Quantum dots help create a lot of electron-hole pairs but those holes usually close quickly, making less charge available externally. This remains one of the primary challenges to technologies such as the one presented above.
I don't get it. At the top you say the new solar panels could be up to 3 times as efficient as current ones. But then at the bottom it says the new panels are only 1% efficient. Well, which one is it? Are they more or less efficient then current panels?
Where did the author get his information?? Current solar cell efficiencies range from 12 to 15% maximum, not the 20 to 30% he claims. And yes, what does he mean by 3 times more efficient when the new design clearly isn't? Treehugger shouldn't publish items that are so obviously full of errors!
This is a response to the questions posed by the other commentors:
Q1. Marlo sees a discrepancy between the "3x more efficient" statement and the "1% as efficient as current technologies" statement.
A1. There two statements appear to me to be different measurements, and therefore are not comparable. In paragraph 1, they are measuring the efficiency of the conversion. In the fourth paragraph, it is measuring the actual proof-of-concept solar cell he developed in his lab. In a lab environment, and with his skill set and tools, he is probably set up to develop proof-of-concept designs, and not final production-quality applications of the technology. (The author could have clarified this a bit...)
Q2. Phil contests the "20-20% efficiency" claims of current solar cell technologies, and counters that it is more like 12-15%.
A2. True, a single solar cell laying in the sun will probably only hit 12-15% efficiency. (This is called "one sun insolation".) However, with light-focusing techniques, that same solar cell can reach 20-30% efficiency. There are also claims someone has surpassed the "40% efficient barrier" that has been plaguing people for a while.
So in an optimum installation, with all the added doodads and efficiencies, people can get 20-30% efficiency. (See this article for more info: http://www.renewableenergyaccess.com/rea/news/story?id=46765 )
I hope this is helpful to everyone!
- CJ