Moth eyes may hold key to more efficient solar cells

Feb 22, 2008 By Miranda Marquit feature
Moth eyes may hold key to more efficient solar cells
Picture of the structure of a moth eye. Credit: Peng Jiang

One of the difficulties with solar power is that solar cells are notoriously inefficient. Some of that inefficiency, says Peng Jiang, is due to the fact that silicon is reflective. Jiang, an assistant professor at the University of Florida, tells PhysOrg.com that there are “disadvantages to the anti-reflective coating currently used in solar cells.”

With a new process that looks to the structure of moth eyes for inspiration, Jiang hopes to address these disadvantages, improving the cost-efficiency of solar cells. “You want more of the sunlight absorbed, rather than reflected,” he says. Jiang and his collaborators, Chih-Hung Sun at the University of Florida, and Bin Jiang at Portland State University, share the results of their work in Applied Physics Letters: “Broadband moth-eye antireflection coatings on silicon.”

Moth eyes may hold key to more efficient solar cells
Silicon wafer with anti-reflection array, model after a moth eye. Credit: Peng Jiang

“Right now,” Jiang explains, “the bluish anti-reflective coating you see on solar cells is not very efficient beyond a narrow range.” He says that the wavelengths of light from the sun range from between 400 nm and 1400 nm. “Once you get below about 500 nm, and above 800 nm, reflection starts increasing.” Jiang points out that the optimal efficiency for the current technology works with wavelengths of around 600 nm.

Looking at the way moth eyes are structured gave Jiang and his co-authors an idea. “Moth eyes are not very reflective,” he points out. “We found our inspiration in nature, trying to mimic the natural nanostructure.”

Moth eyes have orderly bumps on their corneas. Jiang refers to these bumps as “nipples.” The nipples are in an array that creates a situation in which almost no reflection exists. While it was most likely an evolutionary defense against nocturnal predators, it can be adapted for use in solar cells, creating a situation in which most of the light from the sun is absorbed and efficiently utilized instead of reflected uselessly.

Jiang says that a method of spin coating is used to create the effect. Nanoparticles in a liquid suspension are placed on a silicon wafer, similar to those used in solar cells. As the wafer is spun, the force created distributes the nanoparticles in the liquid. A sort of mask is created that can be used as a template. Etching is used to transfer the nanoparticle structure onto the silicon wafer beneath.

“It is self-assembling,” Jiang says of the nanoparticle arrangement. “All of the particles are the same size. It’s like when you put glass beads in a box and then shake it. All of the beads arrange themselves into an array pattern.”

In addition to being technologically easy, the process is also inexpensive. “In addition to the inefficiency, these are the two main disadvantages of the current solar cell anti-reflective coating,” Jiang explains. “It is difficult to make, and it is an expensive process.”

Jiang points out that this process creates less than two percent reflection. This is a vast improvement over the 35 to 40 percent reflection rate seen without the anti-reflection coating layers. “This simple, cheaper process is also much more efficient.”

The next step, Jiang says, is manufacturing. “We think it is ready now,” he says. “We are close to a start-up company that could use this process to make solar cells.” And he also hopes to improve upon the design. “Right now, this is done with single crystalline silicon wafers. We hope to extend the technology to work on multi-crystalline silicon, which is where solar cell technology is moving in the future.”

“I don’t see much trouble with it though,” he continues. “Because of the simplicity of the process, there should be no reason it shouldn’t work. There should be no limitation to expansion.”

Copyright 2007 PhysOrg.com.
All rights reserved. This material may not be published, broadcast, rewritten or redistributed in whole or part without the express written permission of PhysOrg.com.

Explore further: The unifying framework of symmetry reveals properties of a broad range of physical systems

add to favorites email to friend print save as pdf

Related Stories

Sun powers complex cancer test for remote regions

Feb 21, 2014

From the sun, a solution: Cornell University and Weill Cornell Medical College researchers have remodeled an energy-intensive medical test – designed to detect a deadly skin cancer related to HIV infections ...

New solar cell is more efficient, less costly

Nov 11, 2013

(Phys.org) —American innovators still have some cards to play when it comes to squeezing more efficiency and lower costs out of silicon, the workhorse of solar photovoltaic (PV) cells and modules worldwide.

Recommended for you

What time is it in the universe?

16 hours ago

Flavor Flav knows what time it is. At least he does for Flavor Flav. Even with all his moving and accelerating, with the planet, the solar system, getting on planes, taking elevators, and perhaps even some ...

Watching the structure of glass under pressure

Aug 28, 2014

Glass has many applications that call for different properties, such as resistance to thermal shock or to chemically harsh environments. Glassmakers commonly use additives such as boron oxide to tweak these ...

Inter-dependent networks stress test

Aug 28, 2014

Energy production systems are good examples of complex systems. Their infrastructure equipment requires ancillary sub-systems structured like a network—including water for cooling, transport to supply fuel, and ICT systems ...

Explainer: How does our sun shine?

Aug 28, 2014

What makes our sun shine has been a mystery for most of human history. Given our sun is a star and stars are suns, explaining the source of the sun's energy would help us understand why stars shine. ...

User comments : 4

Adjust slider to filter visible comments by rank

Display comments: newest first

Nikola
5 / 5 (1) Feb 22, 2008
What effect would using this technology on telescope lenses have on light gathering ability and the resulting image? Does this work on other wavelengths?
earls
1 / 5 (1) Feb 22, 2008
oh eye see
Soylent
1 / 5 (1) Feb 23, 2008
"What effect would using this technology on telescope lenses have on light gathering ability and the resulting image?"

This is like putting a toilet window in front of the telescope. Your seeing will be less than good.
JZP
1 / 5 (1) Feb 26, 2008
For those interested in other exciting examples of bio-inspired engineering heading towards commercialization, Biomimetic Connections, LLC displays a PowerPoint presentation highlighting recent developments. This company specializes in helping companies with technology-transfer/licensing of biomimetic and bioinspired intellectual property (IP) being developed by universities and corporations worldwide.