Subscribe to our free daily newsletters
  Solar Energy News  




Subscribe to our free daily newsletters



SOLAR DAILY
Stanford technology makes metal wires on solar cells nearly invisible to light
by Mark Shwartz for Stanford News
Stanford CA (SPX) Nov 30, 2015


Silicon pillars emerge from nanosize holes in a thin gold film. The pillars funnel 97 percent of incoming light to a silicon substrate, a technology that could significantly boost the performance of conventional solar cells. Image courtesy Vijay Narasimhan, Stanford University. For a larger version of this image please go here.

A solar cell is basically a semiconductor, which converts sunlight into electricity, sandwiched between metal contacts that carry the electrical current. But this widely used design has a flaw: The shiny metal on top of the cell actually reflects sunlight away from the semiconductor where electricity is produced, reducing the cell's efficiency.

Now, Stanford University scientists have discovered how to hide the reflective upper contact and funnel light directly to the semiconductor below. Their findings, published in the journal ACS Nano, could lead to a new paradigm in the design and fabrication of solar cells.

"Using nanotechnology, we have developed a novel way to make the upper metal contact nearly invisible to incoming light," said study lead author Vijay Narasimhan, who conducted the work as a graduate student at Stanford. "Our new technique could significantly improve the efficiency and thereby lower the cost of solar cells."

Mirror-like metal
In most solar cells, the upper contact consists of a metal wire grid that carries electricity to or from the device. But these wires also prevent sunlight from reaching the semiconductor, which is usually made of silicon.

"The more metal you have on the surface, the more light you block," said study co-author Yi Cui, an associate professor of materials science and engineering. "That light is then lost and cannot be converted to electricity."

Metal contacts, therefore, "face a seemingly irreconcilable tradeoff between electrical conductivity and optical transparency," Narasimhan added. "But the nanostructure we created eliminates that tradeoff."

For the study, the Stanford team placed a 16-nanometer-thick film of gold on a flat sheet of silicon. The gold film was riddled with an array of nanosized square holes, but to the eye, the surface looked like a shiny, gold mirror.

Optical analysis revealed that the perforated gold film covered 65 percent of the silicon surface and reflected, on average, 50 percent of the incoming light. The scientists reasoned that if they could somehow hide the reflective gold film, more light would reach the silicon semiconductor below.

Silicon nanopillars
The solution: Create nanosized pillars of silicon that "tower" above the gold film and redirect the sunlight before it hits the metallic surface.

Creating silicon nanopillars turned out to be a one-step chemical process.

"We immersed the silicon and the perforated gold film together in a solution of hydrofluoric acid and hydrogen peroxide," said graduate student and study co-author Thomas Hymel. "The gold film immediately began sinking into the silicon substrate, and silicon nanopillars began popping up through the holes in the film."

Within seconds, the silicon pillars grew to a height of 330 nanometers, transforming the shiny gold surface to a dark red. This dramatic color change was a clear indication that the metal was no longer reflecting light.

"As soon as the silicon nanopillars began to emerge, they started funneling light around the metal grid and into the silicon substrate underneath," Narasimhan explained.

He compared the nanopillar array to a colander in your kitchen sink. "When you turn on the faucet, not all of the water makes it through the holes in the colander, " he said. "But if you were to put a tiny funnel on top of each hole, most of the water would flow straight through with no problem. That's essentially what our structure does: The nanopillars act as funnels that capture light and guide it into the silicon substrate through the holes in the metal grid."

Big boost
The research team then optimized the design through a series of simulations and experiments.

"Solar cells are typically shaded by metal wires that cover 5-to-10 percent of the top surface," Narasimhan said. "In our best design, nearly two-thirds of the surface can be covered with metal, yet the reflection loss is only 3 percent. Having that much metal could increase conductivity and make the cell far more efficient at converting light to electricity."

For example, this technology could boost the efficiency of a conventional solar cell from 20 percent to 22 percent, a significant increase, he said.

The research team plans to test the design on a working solar cell and assess its performance in real-world conditions.

Covert contacts
Besides gold, the nanopillar architecture will also work with contacts made of silver, platinum, nickel and other metals, said graduate student and co-author Ruby Lai.

"We call them covert contacts, because the metal hides in the shadows of the silicon nanopillars," she said. "It doesn't matter what type of metal you put in there. It will be nearly invisible to incoming light."

In addition to silicon, this new technology can be used with other semiconducting materials for a variety of applications, including photosensors, light-emitting diodes and displays, transparent batteries, as well as solar cells.

"With most optoelectronic devices, you typically build the semiconductor and the metal contacts separately," said Cui, co-director of the Department of Energy's Bay Area Photovoltaic Consortium (BAPVC). "Our results suggest a new paradigm where these components are designed and fabricated together to create a high-performance interface."

A YouTube video of the experiment can be seen here


Thanks for being here;
We need your help. The SpaceDaily news network continues to grow but revenues have never been harder to maintain.

With the rise of Ad Blockers, and Facebook - our traditional revenue sources via quality network advertising continues to decline. And unlike so many other news sites, we don't have a paywall - with those annoying usernames and passwords.

Our news coverage takes time and effort to publish 365 days a year.

If you find our news sites informative and useful then please consider becoming a regular supporter or for now make a one off contribution.

SpaceDaily Contributor
$5 Billed Once


credit card or paypal
SpaceDaily Monthly Supporter
$5 Billed Monthly


paypal only

.


Related Links
Stanford University
All About Solar Energy at SolarDaily.com






Comment on this article via your Facebook, Yahoo, AOL, Hotmail login.

Share this article via these popular social media networks
del.icio.usdel.icio.us DiggDigg RedditReddit GoogleGoogle

Previous Report
SOLAR DAILY
Recurrent Energy Closes Financing for 100 MW Astoria Solar Power Project
Guelph, Canada (SPX) Nov 24, 2015
Canadian Solar reports that its wholly owned subsidiary, Recurrent Energy, one of North America's largest solar project developers, closed on a tax equity investment commitment with GE unit GE Energy Financial Services for the 100 megawatt (MWac) Astoria solar power project. Recurrent Energy also closed a debt facility for the Astoria project, currently under construction in California. Re ... read more


SOLAR DAILY
First biomethane injected into the grid at a farm in Den Bommel

New step towards producing cheap and efficient renewable fuels

EU clears clean British power plant

Algae could be a new green power source

SOLAR DAILY
High-tech Barbie stokes privacy fears

A row-bot that loves dirty water

China dreams of electric sheep at robot conference

NASA selects Northeastern for humanoid robot research

SOLAR DAILY
German power giant RWE to spin off renewables business

Big UK cities vow to run on green energy by 2050

SeaPlanner New Features Launched on Nordsee One Offshore Wind Farm

Moventas introduces breakthrough Extra Life technologies for wind industry

SOLAR DAILY
Volkswagen India to recall 323,700 cars over emissions scandal

French carmakers top European list of low CO2 emitters

Audi to spend 50 mn euros to repair diesel cars in US

German prosecutors say probing VW staff for tax evasion

SOLAR DAILY
HKUST scientists explain the theory behind Ising superconductivity

Price Declines Expected to Broaden the Energy Storage Market

Alberta to phase out coal

Dutch lawmakers approve plan to close coal power plants

SOLAR DAILY
Foreign groups seek to build Poland's first nuclear plant

Belgium extends lives of ageing nuclear reactors

Too Early to talk about status of Russia-Turkey joint projects

Nuclear agreement between Seoul, Washington comes into effect

SOLAR DAILY
Rich countries must not impose end to 'conventional energy': India PM

Commonwealth sets up $1 billion green finance facility

Fossil fuel divestment drive gathers momentum

China's carbon footprint grows with the good life

SOLAR DAILY
Amazon deforestation leaps 16 percent in 2015

Top civil servants probed over hardwood traffic in Gabon

Brazilian farmers learn to love Amazon's trees again

New York forest land may be peaking




Memory Foam Mattress Review
Newsletters :: SpaceDaily :: SpaceWar :: TerraDaily :: Energy Daily
XML Feeds :: Space News :: Earth News :: War News :: Solar Energy News






The content herein, unless otherwise known to be public domain, are Copyright 1995-2017 - Space Media Network. All websites are published in Australia and are solely subject to Australian law and governed by Fair Use principals for news reporting and research purposes. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. ESA news reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. All articles labeled "by Staff Writers" include reports supplied to Space Media Network by industry news wires, PR agencies, corporate press officers and the like. Such articles are individually curated and edited by Space Media Network staff on the basis of the report's information value to our industry and professional readership. Advertising does not imply endorsement, agreement or approval of any opinions, statements or information provided by Space Media Network on any Web page published or hosted by Space Media Network. Privacy Statement