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Carbon-Based Solar Cells

Chabot College Guest Lecture Michael Vosgueritchian PhD Candidate Prof. Zhenan Bao’s Group 2-19-2013. Carbon-Based Solar Cells. Research Overview. Carbon and Organic Electronics. Current Energy. World demand is 15 TW (15 trillion Watts) Enough power for 15 billion 100W light bulbs

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Carbon-Based Solar Cells

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  1. Chabot College Guest Lecture Michael Vosgueritchian PhD Candidate Prof. ZhenanBao’s Group 2-19-2013 Carbon-Based Solar Cells

  2. Research Overview • Carbon and Organic Electronics

  3. Current Energy • World demand is 15 TW (15 trillion Watts) • Enough power for 15 billion 100W light bulbs • US 26% (even though 5% of population) Source: cleantech.org

  4. Sustainable Energy • Wind Energy • Solar Energy • Ocean Energy • Geothermal Energy • Biofuel • In ~1 hr we get enough solar power to power the earth for a year! Source: Sandia National Lab

  5. Solar Radiation and Market • Enough • <1% of landmass enough to provide energy demand

  6. Solar Cells NREL.com • Technologies • Crystalline Si – 27.6% • Thin-Film • CIGS – 20.4% • CdTE – 18.3% • α- Si - 13.4% • OPVs – 11.1% • Nanotechnology • Quantum Dots – 7.0% • Carbon based PVs (CPVs) – 1.2%* (~0.5%) • Other: GaAs, dye-sensitized, etc. Konerka GE

  7. Best Cell Efficiencies

  8. Solar Cell Uses and Considerations • Applications • Industrial • Commercial • Home • Portable • Considerations • Cost/efficiency • Materials • Lifetime • Niche applications NREL.com

  9. Portable Solar Cells • Uses • Power portable electronic devices • Lighting • Transportation • Lighting Africa Project • Main failure due to cracks in the solar cells Krebs et al. Energy Environ. Sci., 2010,3, 512-525

  10. Transparent Electrodes (TEs) • Materials that offer high conductivity and high transparency, usually in thin film form Displays Solar Cells • LEDs • Touch Screens • Energy Storage • Sensors • Transistors Sony.com Konarka.com

  11. Why do we Need New Alternative Electrodes? • Replace ITO • Enable flexible (stretchable) organic electronics Images from Google

  12. Carbon PVs (CPVs) • New class of solar cells • First demonstration of all-C solar Cell • Stability • Chemical/Environmental: water/O2, heat, etc. • Physical: strains, flexible/stretchable devices • Potential for cheap solar cells • Solution processable • Roll-to-roll fabrication • Lightweight • Near-infrared absorption • Tandem cells

  13. Carbon Nanomaterials • Fullerenes – 0D • Discovered in 1985 (C60) • C60, C70, C84 • Films – n-type semiconducting • Carbon Nanotubes (CNTs) – 1D • Discovered in 1991 • Single and multi-walled • Semiconducting or Metallic • Graphene – 2D • Discovered in 2004 • 2010 Nobel Prize • Metallic/transparent

  14. Solar Cell Operation • Short Circuit Current (Jsc) • High absorption • Low recombination • Open circuit voltage (Voc) • Optimum band gap • Fill factor (FF) • Reduce parasitic resistances

  15. CPV Structure • Design of first demonstration of all-Carbon solar cell • Bilayer active layer: P3DDT sorted CNTs, C60 • Electrodes • Anode: ITO/PEDOT  reduced graphene oxide (rGO) • Cathode: Ag  n-doped CNTs M. Vosgueritchian et al. ACS Nano, 2012, 6 (11), pp 10384–10395

  16. Film Fabrication Spin-Coating Spray-Coating Roll-to-roll Coater Konerka.com

  17. Sorting of SC-SWNTs • Solution based method to selective sort SWNTs • Semiconducting selectivity by P3DDT • Can be solution deposited: spin-coating, spray coating, etc. • Absorbs in the infrared (IR) Lee, H. W. et al. Nature Communication 2011, 2, 541

  18. Active Layer • Bilayer of sorted SWNTs and C60 • SWNT spin coated from solution • C60 evaporated in vacuum Absorption Spectrum M. Vosgueritchian et al. ACS Nano, 2012, 6 (11), pp 10384–10395

  19. Anode – Graphene • Can make large area electrodes • Smooth (2D) structure • Can be made highly conductive (30 ohms/sq at 90%) Bae et al., Nature Nanotechnology 5, 574–578 (2010) 

  20. Reduced Graphene Oxide Oxidation thermal reduction Deposit on Surface by spin-coating Reduced Graphene Oxide (rGO) • rGO– 2D • Solution Processable • 102-103Ω/□ at ~80% T • Cheap H. Becerrilet al. ACS Nano, 2008, 2 (3), pp 463–470

  21. Cathode – n-doped SWNT TE • Use stretchable SWNT films on PDMS as the cathode for all-carbon solar cells instead of metal • Need n-doping: DMBI organic dopant • Previously used as electrodes in pressure an strain sensors • Spray-coated from solution M. Vosgueritchian et al. Nature Nanotech, 2008, 2 , pp 788-792

  22. Device Performance • With traditional electrodes • ~0.5% Efficiency for full spectrum • ~0.2% Efficiency in the IR • With carbon electrodes • ~0.01% Efficiency full and IR

  23. Improving Performance • Electrodes • Improve conductivity • Long Term • Introduce flexibility • Test stability • All solution-processable • Theoretical Efficiency of ~9-10% • Morphological Issues • Smoothen films: roughness/aggregates can cause leakage/shorting • Contact Issues • Better contact between films: better charge transport, decrease recombination • Active Layer Materials • Use variety of SWNTs: increase absorption • Heterojunctions • Thicker films Heterojunction

  24. Absorption Issues • SWNTs absorb mostly in the infrared • Film thickness only about 5 nm • Different deposition process

  25. Summary • First demonstration of all-carbon Solar Cell • Sorted-SWNTs used as light absorber • C60 used to separate excitons • Carbon electrodes replace traditional ITO/metal electrodes • Lots of work needs to be done! • Acknowledgments • Prof. ZhenanBao • Dr. Marc Ramuz • Dr. GhadaKoleilat • Evan Wang Ben Naab

  26. QUESTIONS?

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