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3-D Solar Cells

The researchers from Georgia Tech Research Institute (GTRI) , USA have developed photovoltaic cells that trap light between their tower structures, which are about 100 microns tall, 40 microns by 40 microns square, 10 microns apart—and built from arrays containing millions of vertically-aligned carbon nanotubes. Conventional flat solar cells reflect a significant portion of the light that strikes them, reducing the amount of energy they absorb.

Because the tower structures can trap and absorb light received from many different angles, the new cells remain efficient even when the sun is not directly overhead. That could allow them to be used on spacecraft without the mechanical aiming systems that maintain a constant orientation to the sun, reducing weight and complexity – and improving reliability.

The ability of the 3D cells to absorb virtually all of the light that strikes them could also enable improvements in the efficiency with which the cells convert the photons they absorb into electrical current.

In conventional flat solar cells, the photovoltaic coatings must be thick enough to capture the photons, whose energy then liberates electrons from the photovoltaic materials to create electrical current. However, each mobile electron leaves behind a “hole” in the atomic matrix of the coating. The longer it takes electrons to exit the PV material, the more likely it is that they will recombine with a hole—reducing the electrical current.

Because the 3D cells absorb more of the photons than conventional cells, their coatings can be made thinner, allowing the electrons to exit more quickly, reducing the likelihood that recombination will take place. That boosts the “quantum efficiency” – the rate at which absorbed photons are converted to electrons – of the 3D cells.

Fabrication of the cells begins with a silicon wafer, which can also serve as the solar cell’s bottom junction. The researchers first coat the wafer with a thin layer of iron using a photolithography process that can create a wide variety of patterns. The patterned wafer is then placed into a furnace heated to 780 degrees Celsius. Hydrocarbon gases are then flowed into furnace, where the carbon and hydrogen separate. In a process known as chemical vapor deposition, the carbon grows arrays of multi-walled carbon nanotubes atop the iron patterns.

Once the carbon nanotube towers have been grown, the researchers use a process known as molecular beam epitaxy to coat them with cadmium telluride (CdTe) and cadmium sulfide (CdS) which serve as the p-type and n-type photovoltaic layers. Atop that, a thin coating of indium tin oxide, a clear conducting material, is added to serve as the cell’s top electrode.

In the finished cells, the carbon nanotube arrays serve both as support for the 3D arrays and as a conductor connecting the photovoltaic materials to the silicon wafer.

The researchers chose to make their prototypes cells from the cadmium materials because they were familiar with them from other research. However, a broad range of other photovoltaic materials could also be used, and selecting the best material for specific applications will be a goal of future research.

For more information, contact:

Mr. John Toon
Tel: 404-894-6986);
Kirk Englehardt
Tel: 404-407-7280);

Sector: Renewable Energy Technologies
Country: India
Area of Application: Photovoltaics, Renewable Energy sector
Keywords: 3-D solar cells
Advantages: 1. More light-trapping efficiency than existing models
Environmental aspects: Energy efficiency
Development Status: PilotPlant
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Technical specifications:
Transfer Terms:
  • Consultancy
  • Joint Venture
  • Technical services
  • Research Partnerships
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Your Contact Details:
Contact Person: APCTT (UNESCAP)
Asian and Pacific Center for Transfer of Technology (APCTT)
C-2, Qutab Instituational Area
City: New Delhi
Country: India
Zip/Pin Code: 110016

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