Intelligent Machines

From the Labs: Materials

New publications, experiments and breakthroughs in materials science–and what they mean.

Self-Assembling Optics
Nanoparticles form sophisticated devices

Silver crystals: These octahedral silver nanoparticles suspended in ethanol are assembling into a large crystal. The density of the particles, which changes from top to bottom, determines what colors pass through.

Source: “Self-Organized Silver Nanoparticles for Three-Dimensional Plasmonic Crystals”
Peidong Yang et al.
Nano Letters
8: 4033-4038

This story is part of our January/February 2009 Issue
See the rest of the issue
Subscribe

Results: Researchers at the University of California, Berkeley, led by Peidong Yang, have shown that silver nanoparticles with very regular octahedral shapes pack together under the influence of gravity to form large crystals. The crystals’ optical properties can be varied by changing the amount of time the nanoparticles have to pack together, which affects the spacing between them.

Why it matters: Light striking the crystals causes the formation of what’s called a plasmon, a wave passing through the electrons at the crystals’ surfaces. Plasmonic crystals could be used to guide light in optical computers or to increase the sensitivity of chemical sensors. They could also serve as lenses for superhigh-resolution microscopy. Using conventional lithography to etch patterns in materials can achieve a similar effect but is more expensive.

Method: Using methods that Yang developed previously, the researchers grew silver nanoparticles in solution, then suspended them in ethanol inside a test tube. By allowing the nanoparticles to pack together for longer or shorter periods of time before evaporating the ethanol, the researchers produced densely and loosely packed crystals, whose optical properties they studied. The crystals transmitted particular bands of radiation while blocking others, and the frequency varied according to how tightly packed the crystals were.

Next steps: The Berkeley group plans to build a large plasmonic crystal on the surface of a six-inch wafer to establish that the crystals can be formed on a scale large enough for many of their potential applications.

Practical Plastic Solar Cells
New dyes and electrolytes improve efficiency of Grätzel cells

Source: “New Efficiency Records for Stable Dye-­Sensitized Solar Cells with Low-Volatility and Ionic Liquid Electrolytes”
Michael Grätzel et al.
Journal of Physical Chemistry C
112: 17046-17050

Results: Scientists at the Swiss Federal Institute of Tech­nology and the Chinese ­Academy of Sciences have used nonvolatile electrolytes and a new dye to improve the sta­bility of flexible dye-­sensitized solar cells (also called Grätzel cells) while achieving efficiencies of up to 10 percent.

Why it matters: Dye-­sensitized solar cells could be cheaper than conventional solar cells, because they’re made of inexpensive materials and can be printed rapidly. They can also be made flexible. But they have been difficult to manufacture and unreliable to operate, because the electrolytes that carry current within them are volatile and must be carefully encapsulated. By using nonvolatile electrolytes, the researchers have made Grätzel cells that are more reliable and potentially cheaper to manufacture. What’s more, the new dye allows the researchers to use the non­volatile electrolytes while maintaining efficiencies of near 10 percent, a level necessary to compete with conventional solar cells.

Method: The researchers coupled two previously synthesized nonvolatile electrolytes with a new dye that absorbs more light. That reduced both the amount of dye required and the thickness of the solar cells, making it easier for electrical charges to move out of the cell.

Next steps: The cells remain stable when exposed to light and high temperatures for 1,000 hours. The researchers are now testing them at higher temperatures, studying their long-term performance in a large solar panel, and working with corporate partners to commercialize the technology.

Cut off? Read unlimited articles today.

Become an Insider
Already an Insider? Log in.

Uh oh–you've read all of your free articles for this month.

Insider Premium

$179.95/yr US PRICE

More from Intelligent Machines

Artificial intelligence and robots are transforming how we work and live.

Want more award-winning journalism? Subscribe and become an Insider.

  • Insider Premium {! insider.prices.premium !}*

    {! insider.display.menuOptionsLabel !}

    Our award winning magazine, unlimited access to our story archive, special discounts to MIT Technology Review Events, and exclusive content.

    See details+

    What's Included

    Bimonthly home delivery and unlimited 24/7 access to MIT Technology Review’s website.

    The Download. Our daily newsletter of what's important in technology and innovation.

    Access to the Magazine archive. Over 24,000 articles going back to 1899 at your fingertips.

    Special Discounts to select partner offerings

    Discount to MIT Technology Review events

    Ad-free web experience

    First Look. Exclusive early access to stories.

    Insider Conversations. Join in and ask questions as our editors talk to innovators from around the world.

  • Insider Plus {! insider.prices.plus !}* Best Value

    {! insider.display.menuOptionsLabel !}

    Everything included in Insider Basic, plus ad-free web experience, select discounts to partner offerings and MIT Technology Review events

    See details+

    What's Included

    Bimonthly home delivery and unlimited 24/7 access to MIT Technology Review’s website.

    The Download. Our daily newsletter of what's important in technology and innovation.

    Access to the Magazine archive. Over 24,000 articles going back to 1899 at your fingertips.

    Special Discounts to select partner offerings

    Discount to MIT Technology Review events

    Ad-free web experience

  • Insider Basic {! insider.prices.basic !}*

    {! insider.display.menuOptionsLabel !}

    Six issues of our award winning magazine and daily delivery of The Download, our newsletter of what’s important in technology and innovation.

    See details+

    What's Included

    Bimonthly home delivery and unlimited 24/7 access to MIT Technology Review’s website.

    The Download. Our daily newsletter of what's important in technology and innovation.

/
You've read all of your free articles this month. This is your last free article this month. You've read of free articles this month. or  for unlimited online access.