Solar Technology

1
Solar Technology

• In 2008

Daniel Ayoub
The University of Texas at Austin Department of
Chemical Engineering
2
Introduction

• Photovoltaic Cells
• Derived from Greek Language f?? Phos meaning
  light, and voltaic meaning electric

Brittanica
3
Introduction

• First discovered in 1839 by French physicist A.E.
  Becquerel.
• First solar cell build in 1883 by Charles
  Fritts with gold on selenium. Produced a current.
• But why did this work?

4
Light

• Initially Maxwells wave theory of light
  predicted energy would be proportional to light
  intensity
• Einstein described light as composed of discrete
  quanta photons.
• Eh?

5
Light

• A photon above a certain threshold frequency
  (energy) is able to eject a single electron.
• The Photovoltaic Effect

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Light

• 1921 Albert Einstein Nobel Prize in Physics
• Quantum Revolution

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Solar Cells General
Source How stuff works
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Solar Cells P-n Junction

• What is a p-n junction?

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Materials P-type

• Addition of trivalent impurities usually from
  group IIIA.
• Hole-rich material
• Boron, Aluminum, Gallium, etc..
• E.g. Diffuse B2H6 gas into silicon

Source Hyperphysics
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Materials N-type

• Addition of pentavalent impurities usually from
  group 5A.
• Electron-rich material
• Phosphorus, Arsenic, Antimony, etc..
• E.g. Diffuse PH3 gas into silicon

Source Hyperphysics
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Solar Cells Band Gap

• ?E between Valance band and Conduction band
• Available carriers only in conduction band

Source Wikipedia
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Materials P-n Junction

• Carrier Diffusion
• Depletion Region at interface
• E-Field

Source Wikipedia
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Solar Cells

• Photons above band gap energy create free
  electron-hole pairs.
• E-Field will send free electron from P to N side

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Solar Cells

• Disrupts electrical neutrality
• Collect electrons. Pass through external circuit
  to do work.
• Recombine with respective holes back in P-type

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Solar Cells General
Source How stuff works
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Solar Cells Today

• First Generation
• Single Junction
• Expensive
• Theoretical max efficiency 33 (average 15)
• 1/Watt

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Solar Cells Today

• Second Generation (Now)
• Alternative manufacturing techniques
• Thin-Films
• CVD
• Electroplating
• Defects reduce efficiencygtUse Multi-layer
• CdTe, CIGS, etc
• Typical layer efficiency of 7-10
• Replace 80cents of Si with 1 cent of thin-film
  material

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Solar Cells HelioVolt (Austin, TX)

• FASST Process cheaper
• 10-14 power conversion efficiency

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Solar Cells Power Generation
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Solar Cells Power Generation
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Solar Cells Cool Stuff

• Solyndra
• Cylindrical Tubes
• Thin-film CIGS coating
• Paint roof white
• Collect 20 more light
• 2x energy density claim
• Low installation cost(1/2)

Source Scientific American
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Solar Cells The Future

• Third Generation Solar Cells
• Current Research targeting 30-60 efficiencies!
• July 2007, U Delaware set 42.8 efficiency record
  (1994 previous record of 24.7)
• Exploit other frequencies of light
• Multi-junction cells
• Cheaper manufacturing processes

23
References

• Hyperphyisics The Doping of Semiconductors
  http//hyperphysics.phy-astr.gsu.edu/hbase/Solids/
  dope.html Retrieved Nov. 10th, 2008.
• Wikipedia. Solar Cell. http//en.wikipedia.org/
  wiki/Solar_cells/. Retrieved Nov. 10, 2008
• Scott Aldous, How Stuff Works. How Solar Cells
  Work. http//science.howstuffworks.com/solar-cell
  4.htm. Retrieved Nov. 10, 2008.
• David Biello, Scientific American. Cylindrical
  Solar Cells Give a Whole New Meaning to Sunroof
  http//www.sciam.com/article.cfm?idcylindrical-so
  lar-cells-give-new-meaning-to-sunroof
• Carl Gutierrez, Forbes Magazine, Market Scan,
  First Solar Goes Supernova November, 2008
• Ed. P. Capper, Properties of Narrow-Gap
  Cadmium-Based Compounds INSPEC, IEE, London,
• UK, 1994.
• Kim J et al. Efficient Tandem Polymer Solar
  Cells Fabricated by All-Solution Processing.
• Science, 2008.
• Antonio Luque and Steven Hegedus. Handbook of
  Photovoltaic Science and Engineering.
• John Wiley and Sons. 2003
• M.A. Green et al. Crystalline Silicon
  Thin-Film Solar cell Modules. Solar Energy,
  2004.
• Fthenakis, Renewable Sustainable Energy
  Reviews," Vol. 8, 2004
• V M Life Cycle Impact Analysis of Cadmium in
  CdTe PV Production pp 303 334,
• Plastics Background Information for
  Teachers. American Plastics Council, 2006.
• Stefan Lovgren, National Geographic News,
  Spray-On Solar-Power Cells Are True
• Breakthrough January, 2005.
• "New Ways to Catch Rays" NOVA Website,
  November, 2008.
• Steven Latham "Saved by the Sun", NOVA on PBS.
  Courtesy of SCHOTT. April 2007.