2 replies to this topic

[Reno]

Solar panels that continuously repair themselves.

Nagging little things start to plague your existence .. a sprained ankle one year, a stiff calf every morning the next. A few too many beers and slowly a spare tire starts to inflate uncontrollably around your middle. Suddenly you’re forty and will never be able to run as fast as you could half a lifetime ago. Eek!

Wouldn’t it be nice to be a solar panel instead? Not only could you laze around in the sun all day but once in a while a chap will come along and clean you. If you’re very lucky, you may be one of the snazzy self-healing solar panels MIT have invented .. that would really be cool!

Modern solar panels degrade and become less efficient over both the long term and during periods of prolonged sunshine. This is because the chemical bonds in the molecules which convert sunshine to energy wear out with use .. so the more persistently sunny it is, the quicker your efficiency deteriorates.

However this isn’t the case for plants. Within each chloroplast (the cells within which photosynthesis takes place) the proteins responsible are broken and down and reformed while the plant is creating energy from sunlight. This keeps the chemical bonds fresh and so ensures the chloroplasts continue to operate at near maximum efficiency.

It was this which gave Michael Strano, associate professor of chemical engineering at MIT, his brainwave. “If plants can do this, why can’t we mimic them?” he reasoned. Some time and some clever jiggery poker later, we have the Death Defying Solar Panel.

In essence his solution works in three simple stages. First of all, a specific set of molecules is mixed together: these have been engineered to spontaneously bond with one another to produce a sunshine-to-energy conversion substance. Secondly a liquid is added to this substance which breaks it back down into the constituent parts; then finally the resultant soup is passed through a filter which removes the liquid and allows the light converting substance to reform with fresh chemical bonds.

Initial trials are promising: the bind-unbind-bind process has been run continuously for 14 hours within a prototype solar cell with no drop off in electricity generation efficiency. The next stage is to increase the concentration of the solution in the cell to start to output meaningful amounts of electricity.

The invention has been hailed by Philip Collins, associate professor of experimental and condensed-matter physics at the University of California, as a breakthrough in nanotechnology. He said: “One of the remaining differences between man-made devices and biological systems is the ability to regenerate and self-repair. Strano’s work … suggests that ‘nanotechnology’ is finally preparing to advance beyond simple nanomaterials and composites into this new realm.”

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[Reno]

Cheaper, Better Solar Cell Is Full of Holes

Scientists at the United States National Renewable Energy Laboratory (NREL) have made a breakthrough that will likely lead to lower-cost solar cells that are more efficient than the ones used today. The NREL scientists developed a new low-cost etching technique that can put a trillion holes in a silicon wafer the size of a compact disc, turning the silicon wafer darker as the tiny holes deepen, until it is almost black, and thus able to absorb nearly all the colors of light the sun throws at it. Each wafer can be made in about three minutes at room temperature, or less than a minute at 100 degrees F. The team found that the black-silicon etching result could be achieved using chloroauric acid, instead of colloidal gold nanoparticles, which are much more expensive, and with the same results. According to Howard Branz, the principal investigator for the project, "Chloroauric acid is much cheaper than colloidal gold. In essence, by skipping a few steps, they were able to make gold nanoparticles from the chloroauric acid at the same time as they were etching holes into the silicon with the gold they had made." This one-step process is also a lot easier on the environment as it does not require dangerous silane gas, or cleaning gases such as nitrogen trifluoride, both of which contribute to global warming. R&D Magazine recently awarded the NREL team one of its R&D 100 awards, which recognize the most significant scientific breakthroughs of the year, for its Black Silicon Nanocatalytic Wet-Chemical Etch. The article can be viewed online at the link below.

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[Reno]

Forcing mismatched elements together could yield better solar cells

In what could be a step toward higher efficiency solar cells, an international team including University of Michigan professors has invalidated the most commonly used model to explain the behavior of a unique class of materials called highly mismatched alloys.

Highly mismatched alloys, which are still in the experimental stages of development, are combinations of elements that won't naturally mix together using conventional crystal growth techniques. Professor Rachel Goldman compares them to some extent to homogenized milk, in which the high-fat cream and low-fat milk that would naturally separate are forced to mix together at high pressure.

New mixing methods such as "molecular beam epitaxy" are allowing researchers to combine disparate elements. The results, Goldman says, are more dramatic than smooth milk.
"Highly mismatched alloys have very unusual properties," Goldman said. "You can add just a sprinkle of one element and drastically change the electrical and optical properties of the alloy."

Goldman is a professor in the departments of Materials Science and Engineering, and Physics. Her team included other U-M physicists and engineers as well as researchers from Tyndall National Institute in Ireland.

Solar cells convert energy from the sun into electricity by absorbing light. However, different materials absorb light at different wavelengths. The most efficient solar cells are made of multiple materials that together can capture a greater portion of the electromagnetic radiation in sunlight. The best solar cells today are still missing a material that can make use of a portion of the sun's infrared light.

Goldman's team made samples of gallium arsenide nitride, a highly mismatched alloy that is spiked with nitrogen, which can tap into that underutilized infrared radiation.

The researchers used molecular beam epitaxy to coax the nitrogen to mix with their other elements. Molecular beam epitaxy involves vaporizing pure samples of the mismatched elements and combining them in a vacuum.

Next, the researchers measured the alloy's ability to convert heat into electricity. They wanted to determine whether its 10 parts per million of nitrogen were distributed as individual atoms or as clusters. They found that in some cases, the nitrogen atoms had grouped together, contrary to what the prevailing "band anti-crossing" model predicted.

"We've shown experimentally that the band anti-crossing model is too simple to explain the electronic properties of highly mismatched alloys," Goldman said. "It does not quantitatively explain several of their extraordinary optical and electronic properties. Atomic clusters have a significant impact on the electronic properties of alloy films."

If researchers can learn to control the formation of these clusters, they could build materials that are more efficient at converting light and heat into electricity, Goldman said.

"The availability of higher efficiency thermoelectrics would make it more practical to generate electricity from waste heat such as that produced in power plants and car engines," Goldman said.

This research is newly published online in Physical Review B ("Nitrogen composition dependence of electron effective mass in GaAs1-xNx").

This research is funded by the National Science Foundation, the Science Foundation Ireland, and the Center for Solar and Thermal Energy Conversion, an Energy Frontier Research Center funded by the U.S. Department of Energy.

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Edited by Reno, 10 September 2010 - 04:09 AM.