Using a carbon nanotube instead of traditional silicon,
Cornell researchers have created the basic elements of a solar cell that
hopefully will lead to much more efficient ways of converting light to
electricity than now used in calculators and on rooftops.
The researchers fabricated, tested and measured a simple
solar cell called a photodiode, formed from an individual carbon nanotube.
Reported online Sept. 11 in the journal Science, the researchers—led by Paul
McEuen, the Goldwin Smith Professor of Physics, and Jiwoong Park,
assistant professor of chemistry and chemical biology—describe how their device
converts light to electricity in an extremely efficient process that multiplies
the amount of electrical current that flows. This process could prove important
for next-generation high efficiency solar cells, the researchers say.
"We are not only looking at a new material, but we
actually put it into an application—a true solar cell device," said first
author Nathan Gabor, a graduate student in McEuen's lab.
The researchers used a single-walled carbon nanotube, which
is essentially a rolled-up sheet of graphene, to create their solar cell. About
the size of a DNA molecule, the nanotube was wired between two electrical
contacts and close to two electrical gates, one negatively and one positively
charged. Their work was inspired in part by previous research in which
scientists created a diode, which is a simple transistor that allows current to
flow in only one direction, using a single-walled nanotube. The Cornell team
wanted to see what would happen if they built something similar, but this time shined
light on it.
Shining lasers of different colors onto different areas of
the nanotube, they found that higher levels of photon energy had a multiplying
effect on how much electrical current was produced.
Further study revealed that the narrow, cylindrical
structure of the carbon nanotube caused the electrons to be neatly squeezed
through one by one. The electrons moving through the nanotube became excited
and created new electrons that continued to flow. The nanotube, they
discovered, may be a nearly ideal photovoltaic cell because it allowed
electrons to create more electrons by utilizing the spare energy from the
light.
This is unlike today's solar cells, in which extra energy is
lost in the form of heat, and the cells require constant external cooling.
Though they have made a device, scaling it up to be
inexpensive and reliable would be a serious challenge for engineers, Gabor
said.
"What we've observed is that the physics is
there," he said.
The research was supported by Cornell's Center for Nanoscale
Systems and the Cornell NanoScale Science and Technology Facility, both
National Science Foundation facilities, as well as the Microelectronics
Advanced Research Corporation Focused Research Center on Materials, Structures
and Devices. Research collaborators also included Zhaohui Zhong, of the
University of Michigan, and Ken Bosnick, of
the National Institute for Nanotechnology at University of Alberta.
Study
abstract
Cornell University
