Sustainable Energy

Bumpy Coatings for Better Solar Cells

A simple method applies nanoscale texturing over large areas.

Nanoscale wires, pores, bumps, and other textures can dramatically improve the performance of solar cells, displays, and even self-cleaning coatings. Now researchers at Stanford University have developed a simpler, cheaper way to add these features to large surfaces.

Nanosphere smear: Using a spinning rod to deposit an ink suspension of silica nanospheres is a simple way to create bumpy, nanotextured coatings like these three.

Nanoscale structures offer particular advantages in devices that interact with light. For example, a thin-film solar cell carpeted with nano pillars is more efficient because the pillars absorb more light and convert more of it into electricity. Other nanoscale textures offer similar advantages in optical devices like display backlights.

This story is part of our September/October 2009 Issue
See the rest of the issue
Subscribe

The problem is scaling up to large areas, says Yi Cui, a Stanford professor of materials science and engineering who led the new work. “Many methods are really complex and don’t solve the problem,” says Cui. Lithography can be used to carve out nanoscale features with precise dimensions, but it’s expensive and difficult. Simpler techniques, such as spin-coating a surface with nanoparticles or using acids to etch it with tiny holes, don’t allow for much precision.

Cui’s group adapted a process that’s used commercially to manufacture flexible packaging. A rod wound with wires is used to evenly deposit a liquid coating containing silica nanospheres. The treated surface ends up with specific nanoscale structural properties.

Changing the size of the nanoparticles, using wires of different diameters, and applying subsequent chemical treatments can further modify the properties of the surface. The coating method is compatible with roll-to-roll processes used to print flexible devices on plastic, metal, and other materials, and it can also be used on rigid surfaces like glass.

In the journal Nano Letters, Cui reports that he and his group have made superhydrophobic surfaces and a proof-of-concept solar device. To make the solar cell, the researchers deposit metal and amorphous silicon on the bumpy surface. The result absorbs 42 percent more light than a flat surface that uses the same quantity of materials. Cui hopes the nanoscale texturing will make it possible to produce thin-film solar cells that use very little material but are still very efficient; he’s made such devices in the past using photolithography and other complex manufacturing techniques.

“This work demonstrates a simple yet effective method for achieving controlled assembly of nanospheres over large areas,” says Ali Javey, a professor of electrical engineering and computer science at the University of California, Berkeley. “It could present a route toward improved efficiencies in thin-film solar cells, without increasing the cost or the process complexity.”

L. Jay Guo, a professor of electrical engineering and computer science at the University of Michigan who is developing roll-to-roll printing systems, says that the method should be useful for solar cells and displays. “It uses a traditional wire-wound coating method, which is applicable to large-area substrates,” he says. But he believes that the process, which can apply the bumpy surfaces at 0.8 centimeters per second, may not be fast enough for industry unless the Stanford researchers can speed things up.

Cui is now taking the work in two directions. His group is tuning the size of the particles and the distance between them to determine which characteristics are best for solar cells. He’s also developing a coating for light-emitting diodes that he hopes will help liquid-crystal displays appear brighter.

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 Sustainable Energy

Can we sustainably provide food, water, and energy to a growing population during a climate crisis?

Want more award-winning journalism? Subscribe to Insider Basic.
  • 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 magazine 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.