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CNT Based Solar Cells MAE C187L

CNT Based Solar Cells MAE C187L. Joyce Chen Kari Harrison Kyle Martinez. Our Approach. An array of micro-sized “blocks” composed of single walled carbon nanotubes coated with photovoltaic materials and anti-reflective coating on a silicon wafer

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CNT Based Solar Cells MAE C187L

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  1. CNT Based Solar CellsMAE C187L Joyce Chen Kari Harrison Kyle Martinez

  2. Our Approach • An array of micro-sized “blocks” composed of single walled carbon nanotubes coated with photovoltaic materials and anti-reflective coating on a silicon wafer • The 3 dimensional surface causes light rays to be trapped inside the cell • This, combined with the anti-reflective surface reduces the percentage of reflected rays

  3. Our Approach

  4. Methodology • The single walled nanotubes are cheaper, easier to fabricate and have better electrical properties than multi walled nanotubes • Silicon based photovoltaic materials are cheaper than many alternatives, and proven to be successful and reliable • E-beam lithography and chemical vapor deposition were used where applicable because we are familiar with these processes

  5. Step 1: Silicon wafer

  6. Step 1: Silicon wafer • Clean a 2 inch silicon wafer with Acetone, Methanol and IPA • De-ionized water rinse • N2 blow dry

  7. Step 2a: E-beam Lithography:Spin Coating Photoresist

  8. Step 2a: E-beam Lithography:Spin Coating Photoresist • PMMA 495C2: 500 RPM for 5 seconds and 4000 RPM for 45 seconds • Soft bake Sample at 180C for 90 seconds

  9. Step 2b: E-beam Lithography:E-beam Patterning

  10. Step 2b: E-beam Lithography:E-beam Patterning • Make a pattern of 700 blocks x 700 blocks of 40um x 40um squares with 10 um gaps • Based on our limited knowledge, we would use the same parameters procedure as in Lab 1

  11. Step 2c: E-beam Lithography:Metal Deposition

  12. Step 2c: E-beam Lithography:Metal Deposition • Using chemical vapor deposition we would deposit a thin layer of iron oxide on top of the patterned resist and wafer

  13. Step 2d: E-beam Lithography:Photoresist Development and Metal Lift-Off

  14. Step 2d: E-beam Lithography:Photoresist Development and Metal Lift-Off • Soak PMMA developer for 30-40 sec • Isopropanol + MIBK at 3 to 1 volume ratio • Rinse in Isopropanol • Blow dry with N2

  15. Step 3: SWCNT Growth

  16. Step 3: SWCNT Growth • Place the wafer in a furnace heated to 1000C and pass an argon flow through the furnace • Replace the argon flow with a methane flow of 99% purity at a flow rate of 6150cm3/min under 1.25 atm for 10 minutes • Replace the methane flow with an argon flow and cool to room temperature

  17. Step 4: Photovoltaic Deposition

  18. Step 4: Photovoltaic Deposition • Using molecular beam epitaxy, deposit silicon phosphorus (n-type layer) and silicon boron (p-type layer) • Molecular beam epitaxy is a slow deposition of films taking place in a high vacuum

  19. Step 5: Anti-Reflective Coating Deposition

  20. Step 5: Anti-Reflective Coating Deposition • Use a Cooke Thermal Evaporator to deposit a layer of silicon monoxide on the solar cell • Program the Sigma Film Thickness mOnitor with these parameters • Density = 2.13 g/cm3 • Tooling = 126% • Z-ratio = 0.87

  21. Step 5: Anti-Reflective Coating Deposition • Fill a long tungsten boat with SiO fragments • Turn power up to 15% until boat beings to glow and stay there for 2 minutes • Switch on heating until and increase dial to 30% for 30 seconds, until deposition rate is between 0.3-0.5 angstroms/s • Slowly increase to 35%-40% • Once desirable thickness is obtained, close shutter and record thickness after 1 minute • Slowly reduce boat current to zero and switch of heating unit

  22. Cost Analysis • Iron Oxide $1.00/ounce • Silicon ~ $2.00/lb • Silicon monoxide ~ $1.45/g • Methane < $0.10/L • A typical solar cell costs ~$0.05/kwh • This cell uses less silicon, an expensive commodity, and should produce more energy per square meter – therefore we would expect it to cost at least the same, if not less per kwh

  23. Estimated Efficiency • A similar experiment obtained a 7% efficiency, while it is expected that  a 40% efficiency is possible • The addition of an anti-reflective coating can reduce the reflected light from 30% to 10%, which adds ~ 1% efficiency

  24. Lifespan • Current solar panels are rated ~ 30 years • It is still unknown how long carbon nanotubes will last, but we assume their lifespan is the same as the copper wires they are replacing, if not longer • This would make our solar cell life span also ~30 years

  25. Testing • Test in lab with UV light to determine kw per square meter • Test at different angles to the sun to determine the correct incident angle for maximum efficiency • Test in extreme temperatures, as well as in wind tunnels to determine structural stability

  26. References http://www.gtri.gatech.edu/casestudy/3d-solar-cells-boost-efficiency http://www.nanowerk.com/news/newsid=1763.php http://www.alfa.com/en/ge100w.pgm http://ostc.physics.uiowa.edu/~microfab/manuals/pdf/deposition-SiO.pdf http://blog.sciencenet.cn/upload/blog/file/2010/2/20102193247668823.pdf http://en.wikipedia.org/wiki/Photovoltaic_array http://en.wikipedia.org/wiki/Carbon_nanotubes_in_photovoltaics http://www.metalprices.com/FreeSite/metals/nickelalloy/nickelalloy.asp Lecture Slides and Lab Handouts

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