Home > Press > Stanford technology makes metal wires on solar cells nearly invisible to light
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. CREDIT: Vijay Narasimhan, Stanford University |
Abstract:
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."
###
On Dec. 1, Cui and Narasimhan will discuss the new nanopillar technology at the fall meeting of the Materials Research Society in Boston. For details visit: www.mrs.org/fall2015/
The study was supported by the BAPVC and the Global Climate and Energy Project at Stanford.
This article was written by Mark Shwartz, Precourt Institute for Energy at Stanford University.
####
For more information, please click here
Contacts:
Mark Shwartz
650-723-9296
Copyright © Stanford University
If you have a comment, please Contact us.Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.
Related News Press |
News and information
Simulating magnetization in a Heisenberg quantum spin chain April 5th, 2024
NRL charters Navy’s quantum inertial navigation path to reduce drift April 5th, 2024
Discovery points path to flash-like memory for storing qubits: Rice find could hasten development of nonvolatile quantum memory April 5th, 2024
Good as gold - improving infectious disease testing with gold nanoparticles April 5th, 2024
Display technology/LEDs/SS Lighting/OLEDs
Utilizing palladium for addressing contact issues of buried oxide thin film transistors April 5th, 2024
Light guide plate based on perovskite nanocomposites November 3rd, 2023
Simple ballpoint pen can write custom LEDs August 11th, 2023
Videos/Movies
New X-ray imaging technique to study the transient phases of quantum materials December 29th, 2022
Solvent study solves solar cell durability puzzle: Rice-led project could make perovskite cells ready for prime time September 23rd, 2022
Scientists prepare for the world’s smallest race: Nanocar Race II March 18th, 2022
Visualizing the invisible: New fluorescent DNA label reveals nanoscopic cancer features March 4th, 2022
Sensors
Discoveries
Chemical reactions can scramble quantum information as well as black holes April 5th, 2024
New micromaterial releases nanoparticles that selectively destroy cancer cells April 5th, 2024
Utilizing palladium for addressing contact issues of buried oxide thin film transistors April 5th, 2024
Materials/Metamaterials/Magnetoresistance
Nanoscale CL thermometry with lanthanide-doped heavy-metal oxide in TEM March 8th, 2024
Focused ion beam technology: A single tool for a wide range of applications January 12th, 2024
Announcements
NRL charters Navy’s quantum inertial navigation path to reduce drift April 5th, 2024
Discovery points path to flash-like memory for storing qubits: Rice find could hasten development of nonvolatile quantum memory April 5th, 2024
Interviews/Book Reviews/Essays/Reports/Podcasts/Journals/White papers/Posters
Simulating magnetization in a Heisenberg quantum spin chain April 5th, 2024
Discovery points path to flash-like memory for storing qubits: Rice find could hasten development of nonvolatile quantum memory April 5th, 2024
Energy
Development of zinc oxide nanopagoda array photoelectrode: photoelectrochemical water-splitting hydrogen production January 12th, 2024
Shedding light on unique conduction mechanisms in a new type of perovskite oxide November 17th, 2023
Inverted perovskite solar cell breaks 25% efficiency record: Researchers improve cell efficiency using a combination of molecules to address different November 17th, 2023
The efficient perovskite cells with a structured anti-reflective layer – another step towards commercialization on a wider scale October 6th, 2023
Battery Technology/Capacitors/Generators/Piezoelectrics/Thermoelectrics/Energy storage
What heat can tell us about battery chemistry: using the Peltier effect to study lithium-ion cells March 8th, 2024
A battery’s hopping ions remember where they’ve been: Seen in atomic detail, the seemingly smooth flow of ions through a battery’s electrolyte is surprisingly complicated February 16th, 2024
Events/Classes
Researchers demonstrate co-propagation of quantum and classical signals: Study shows that quantum encryption can be implemented in existing fiber networks January 20th, 2023
Grants/Sponsored Research/Awards/Scholarships/Gifts/Contests/Honors/Records
Discovery points path to flash-like memory for storing qubits: Rice find could hasten development of nonvolatile quantum memory April 5th, 2024
Chemical reactions can scramble quantum information as well as black holes April 5th, 2024
Photonics/Optics/Lasers
With VECSELs towards the quantum internet Fraunhofer: IAF achieves record output power with VECSEL for quantum frequency converters April 5th, 2024
Nanoscale CL thermometry with lanthanide-doped heavy-metal oxide in TEM March 8th, 2024
Optically trapped quantum droplets of light can bind together to form macroscopic complexes March 8th, 2024
HKUST researchers develop new integration technique for efficient coupling of III-V and silicon February 16th, 2024
Solar/Photovoltaic
Development of zinc oxide nanopagoda array photoelectrode: photoelectrochemical water-splitting hydrogen production January 12th, 2024
Shedding light on unique conduction mechanisms in a new type of perovskite oxide November 17th, 2023
Inverted perovskite solar cell breaks 25% efficiency record: Researchers improve cell efficiency using a combination of molecules to address different November 17th, 2023
Charged “molecular beasts” the basis for new compounds: Researchers at Leipzig University use “aggressive” fragments of molecular ions for chemical synthesis November 3rd, 2023
The latest news from around the world, FREE | ||
Premium Products | ||
Only the news you want to read!
Learn More |
||
Full-service, expert consulting
Learn More |
||