1. Excitons and Solar Energy Shuhua Liang UTK Physics department UTK Physics department

2. 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)

3. Solar Energy (from GCEP)

4. How to get energy from sun light? Use electron! (by shuhua)

5. Energy band theory The problem of single electron approximation In experiment people find structure in energy gap.

6. Excition and binding energy Binding energy Reduced mass

8. How to generate Current? Use two different type of material to separate the exciton (electron-hole)

9. The first generation Si Solar Cell

10. The disadvantage of Si cell Expensive $565.00 Weight: 28.00 lbs Low efficiency (around 16%)

11. Second generation solar cell 1)multiple junction photovoltaic cells :high efficiency :high cost (from Sonny X. Li ) 2)Thin film :low efficiency :low cost

12. 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 )

13. How does it work? Larger and heavier quantum dots are at bottom

14. How does it work?

15. 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

16. Quantum Dot can select frequency Technically we can design the size of quantum dot to design the gap width. (from google)

17. Thank You