excitons and solar energy shuhua liang utk physics department utk physics department
DESCRIPTION
Solar Energy (from GCEP)TRANSCRIPT
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Excitons and Solar EneExcitons and Solar EnergyrgyShuhua LiangShuhua Liang
UTK Physics departmentUTK Physics department
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Energy ProblemEnergy Problem• Full list • Rank Company Revenues Profits ($ millions)• 1 Exxon Mobil 339,938.0 36,130.0• 2 Wal-Mart Stores 315,654.0 11,231.0• 3 Royal Dutch Shell 306,731.0 25,311.0• 4 BP 267,600.0 22,341.0• 5 General Motors 192,604.0 -10,567.0• 6 Chevron 189,481.0 14,099.0• 7 DaimlerChrysler 186,106.3 3,536.3• 8 Toyota Motor 185,805.0 12,119.6• 9 Ford Motor 177,210.0 2,024.0• 10 ConocoPhillips 166,683.0 13,529.0• (from FORTUNE top 500 companies 2006)
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Solar EnergySolar Energy
• (from GCEP)
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How to get energy from sun How to get energy from sun light?light?
• Use electron!
(by shuhua)
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Energy band theoryEnergy band theory• The problem of single electron
approximation• In experiment people find structure
in energy gap.
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Excition and binding energyExcition and binding energy2
_ 2_ _2Binding Energy
ground state radius
eEn a
-= e
• Binding energy
• Reduced mass
_ _ 0
1 1 1
reduced electron hole
electronground state radius
reduced
M M M
Ma a
M
= +
æ ö÷ç ÷= eç ÷ç ÷çè ø
2
_ 2_ _2Binding Energy
ground state radius
eEn a
-= e
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How to generate Current?How to generate Current?• Use two different type of material to separate the exciton (electron-hole)
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The first generation Si Solar CeThe first generation Si Solar Cellll
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The disadvantage of Si cell The disadvantage of Si cell • Expensive $565.00 Weight: 28.00 lbs
• Low efficiency (around 16%)
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Second generation solar cell Second generation solar cell 1)multiple junction photovoltaic cells
:high efficiency :high cost(from Sonny X. Li ) 2)Thin film :low efficiency :low cost
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Third Generation Third Generation • Quantum Dot• Size: 2-10 nm• Accommodate 5-1000electrons• 2Dor 3D free electron model (depend on the shape)• Structure: core&shell(from Evident Technologies )
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How does it work?How does it work?• Larger and heavier
quantum dots are at bottom
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How does it work?How does it work?
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Why Quantum Dot is good?Why Quantum Dot is good?• High efficiency due
to one photon can excite several electrons
• Energy gap decide the min frequency of light
• Can control the volt and current
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Quantum Dot can select Quantum Dot can select frequencyfrequency
• Technically we can design the size of quantum dot to design the gap width.
• (from google)
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Thank YouThank You