Excitons and Solar Energy

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Excitons and Solar Energy

• Shuhua Liang
• UTK Physics department

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Energy 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 Energy
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How to get energy from sun light?

• Use electron!
• (by shuhua)

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Energy band theory

• The problem of single electron approximation
• In experiment people find structure in energy
  gap.

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Excition and binding energy

• Binding energy
• Reduced mass

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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 Cell
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The disadvantage of Si cell

• Expensive
• 565.00 Weight 28.00 lbs
• Low efficiency (around 16)

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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

• Quantum Dot
• Size 2-10 nm
• Accommodate 5-1000electrons
• 2Dor 3D free electron model (depend on the shape)
• Structure
• coreshell
• (from Evident Technologies )

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How does it work?

• Larger and heavier quantum dots are at bottom

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How does it work?
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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 frequency

• Technically we can design the size of quantum dot
  to design the gap width.
• (from google)

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Thank You