Researchers at MIT have developed a new type of solar cell that can harvest energy from heat as well as light. The prototype uses thermophotovoltaic technology with a top layer of carbon nanotubes and an underlying photonic crystal. Sunlight heats the nanotubes, causing the crystal to glow brightly and emit photons with enough energy to release electrons in the solar cell. This new design is over 4 times as effective as previous heat-sensitive solar cells and could eventually reach 20% efficiency, unlocking solar power's potential to provide renewable energy from more locations and for more hours each day.

1. Heat-Sensitive Solar Cells
By Dhruov Bhatia

2. Contents
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Future Prospects
Upcoming Technology
Modern Technology
Introduction
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6-7
4-5
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3. Modern Solar Cells
Photovoltaic (PV) cells are synonymous with
solar power, one of the leading forms of
modern renewable energy.
Fact: They provide close to 1% of the world’s
energy demand. Europe alone holds over a third
of this capacity.
This technology is quite inefficient when dealing
with large amounts of energy.
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4. How do PV cells work?
PV cells use electromagnetic radiation mainly in the form of visible light to
generate electricity.
Light is made of packets of energy called photons. When photons in sunlight
interact (or collide) with the atoms of the PV cell, electrons in these atoms gain
the energy of the photons.
Electrons are ‘excited’ and rise in energy
levels. If they gain enough energy, they will be
capable of carrying charge and forming a
current.
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Cross-section of a PV cell: The metallic conductors are used to carry
current. The silicon layers are used to provide electrons.

5. Shortcomings
• Photons in sunlight may possess different
frequencies and hence different amounts of energy,
which is sometimes insufficient to produce a
current.
• If an electron does not gain enough energy from a
photon, all of its excess energy is lost as heat or
emitted as another photon.
• Much energy is lost as heat before even reaching
the conducting material. In combination with the
above factors, the efficiency of a PV cell is capped
at about 33 - 35%. In practice, however, efficiency is
barely 15%.
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A PV facility: PV cells are extremely inefficient and ineffective in
darkness or cloud cover.

6. The Solution
Researchers at MIT have
developed a prototype
nanochip that uses
thermophotovoltaic (TPV)
technology.
These new cells are capable
of harvesting energy from
electromagnetic radiation
in the form of heat.
Photo courtesy of the
researchers
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7. The Details
• The new cell has an additional layer above the
PV cell, consisting of carbon nanotubes and
photonic crystal.
• Sunlight will be absorbed by the nanotubes at
the top, causing them to heat up.
• This heat causes the photonic crystal
underneath to glow very brightly and emit light.
• The crystal has been tuned to emit light whose
photons contain enough energy to release
more electrons in the PV cell below.
7Photo courtesy of the
Composition of the new model: The nanotube slit is 1 cm in
diameter. Further tests with a 10 cm slit will also be conducted.

8. The Future
• The device currently performs at an efficiency
of 3.2%, although the team believes it will reach
20% in time.
• This model is 4 times as effective as its
predecessors. Attempts at solar TPV have been
made before, but no prototype has crossed an
efficiency of 1%.
• TPV technology has an efficiency cap of over
80%. With future advancements, we will soon
be able to harness the true power of the sun.
Photo courtesy of the
researchers
A prototype in action: The middle layer is the photonic crystal,
which glows brightly when exposed to heat.
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9. Further Uses
• They can provide more power to homes and
commercial systems, thus saving space and
costs. *
• The technology works at lower light intensities
than PV cells, hence allowing for production for
more hours in the day.
• Facilities can also be built at more locations
where light intensity is lower throughout the
year, without fear of low effectiveness.
• This also allows for use in humid or dark
environments where heat is still abundant.
A modern solar farm: Upgrading existing solar farms could
provide a tremendous boost to their production capacity.
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10. References
https://en.wikipedia.org/wiki/Solar_power_by_country
http://news.mit.edu/2016/hot-new-solar-cell-0523
https://www.engadget.com/2014/01/21/heat-sensitive-solar-cell-could-lead-to-more-on-demand-ener/
http://news.mit.edu/2010/explained-bandgap-0723
https://science.nasa.gov/science-news/science-at-nasa/2002/solarcells
* Actual savings not known yet; project under development
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