in 2008 daniel ayoub the university of texas at austin department of chemical engineering
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Solar TechnologyIn 2008
Daniel Ayoub
The University of Texas at AustinDepartment of Chemical Engineering
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Introduction
Photovoltaic Cells Derived from Greek Language: φώς
“Phos” meaning light, and “voltaic” meaning electric
Brittanica
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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?
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Light
Initially Maxwell’s wave theory of light predicted energy would be proportional to light intensity
Einstein described light as composed of discrete quanta – photons.
E=hν
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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 efficiency=>Use 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
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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-cell4.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?id=cylindrical-solar-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. • Kevin Bullis, “Making Cheaper Solar Cells” MIT Technology Review, September 12, 2008. • Peter Fairley, “Fixing the Power Grid” MIT Technology Review, October 17, 2007. • Reuters on 2007 “Abu Dhabi to build $350m solar power plant” • Reuters on 2007 “Egypt invests $109mn in solar power”