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Carbon Nanotube Based Organic Solar Cells

Carbon Nanotube Based Organic Solar Cells. Arun Tej M. PhD Student EE Dept. and SCDT. Outline. Carbon Nanotubes Properties Useful for Solar Cells Efficiency Limiting Factors Nanotubes in Organic Solar Cells Results and Future Challenges. Carbon Nanotubes.

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Carbon Nanotube Based Organic Solar Cells

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  1. Carbon Nanotube Based Organic Solar Cells Arun Tej M. PhD Student EE Dept. and SCDT

  2. Outline • Carbon Nanotubes • Properties Useful for Solar Cells • Efficiency Limiting Factors • Nanotubes in Organic Solar Cells • Results and Future Challenges Arun Tej M, REACH - 2008

  3. Carbon Nanotubes • S. Iijima - MWNT (1990), SWNT (1993) • Rolled graphene sheet with end caps • Large aspect ratios • Unique properties • Finds applications in • Conductive plastics and adhesives • Energy storage • Efficient heat conduits • Structural composites • Biomedical devices • Numerous electronic applications Arun Tej M, REACH - 2008 www.applied-nanotech.com

  4. Nanotube Field Emission Display Arun Tej M, REACH - 2008 W.B. Choi, Samsung, APL, 1999

  5. Nanotube Random Access Memory Arun Tej M, REACH - 2008 Thomas Rueckes, Nantero, 2000

  6. Nanotube Liquid Flow Sensor Arun Tej M, REACH - 2008 A.K.Sood, IISc Bangalore, Science, 2003

  7. Nanotube Integrated Circuit Arun Tej M, REACH - 2008 5 Stage Ring Oscillator on one SWNT Z.Chen, IBM, 2006

  8. Nanotube Based Inorganic Solar Cell Arun Tej M, REACH - 2008 W.J.Ready, Georgia Tech, JOM, 2007

  9. Nanotube Properties Useful for Solar Cells • High carrier mobilities (~1,20,000 cm2 V-1 s-1) • Large surface areas (~1600 m2 g-1) • Absorption in the IR range (Eg: 0.48 to 1.37 eV) • Conductance - Independent of the channel length • Enormous current carrying capability – 109 A cm-2 • Semiconducting CNTs – Ideal solar cells • Mechanical strength & Chemical stability Arun Tej M, REACH - 2008

  10. Arun Tej M, REACH - 2008 Split-Gate device, Energy band diagram and I-V characteristics

  11. Efficiency Improvement with SWNTs Arun Tej M, REACH - 2008 Combine the advantages of Organics and SWNTs

  12. Nanotubes in Organic Solar Cells Arun Tej M, REACH - 2008 • Exciton dissociation sites • As electron acceptors in bulk heterojunction solar cells • Carrier transport • Thin transparent films of m-SWNTs as electrodes Chhowalla et al, APL, 2005 Wu et al, Science, 2004

  13. Results(1) Arun Tej M, REACH - 2008 Higher Efficiency Photoluminescence Quenching Arun Tej M, S.S.K.Iyer, and B.Mazhari, IEEE INEC, 2008, Shanghai

  14. Results(2) Arun Tej M, REACH - 2008 Trap filling behaviour Tunneling behaviour Arun Tej M, S.S.K.Iyer, and B.Mazhari, IEEE PVSC, 2008, San Diego

  15. Results(3) Arun Tej M, REACH - 2008 High Open Circuit Voltages with Bulk Heterojunction Devices Our Work To be published

  16. Future REACH (1) • Synthesis of stable organic compounds • Separate semiconducting and metallic SWCNTs • Aligned CNTs inside the semiconducting polymers give improved charge transport e- Arun Tej M, REACH - 2008 e- h+ e- e- h+ h+

  17. Future REACH (2) e- e- e- e- • Add nanoparticles, quantum dots, fullerenes etc to • the side walls of SWNTs h+ e- h+ h+ Arun Tej M, REACH - 2008 h+

  18. Future REACH (3) New device structures Arun Tej M, REACH - 2008 “A Solar Cell with Improved Light Absorption Capacity” S. Sundar Kumar Iyer and Arun Tej M. Patent Appln. No. 933/DEL/2006 Dt: 31st March, 2006

  19. Acknowledgements • Faculty, Staff and Students, SCDT • Prof. Ashutosh Sharma, Chemical Engineering Arun Tej M, REACH - 2008

  20. Thank You Arun Tej M, REACH - 2008

  21. Organic Solar Cell Schematic and energy diagram of a typical polymer solar cell and its operation Exciton diffusion e- Exciton dissociation Carrier transport Arun Tej M, REACH - 2008 Exciton formation Charge collection h+ Anode Donor Acceptor Cathode

  22. Arun Tej M, REACH - 2008

  23. Conjugated polymers • Conduction due to sp2– hybridised carbon atoms •  and  (pz-pz)bonds •  electrons are delocalised in nature giving high electronic polarisability • High absorption in the UV-Visible range of the solar spectrum Arun Tej M, REACH - 2008 H.Hoppe and N.S. Sariciftci, 2004

  24. Metallic SWNTs Arun Tej M, REACH - 2008

  25. Conductance is independent of the channel length. Arun Tej M, REACH - 2008

  26. Conductance through a barrier with transmission probability T. • Landauer Formula: • With N parallel 1D channels (subbands): • m-SWNTs: Only two subbands cross EF(N=2) • Source of R: Mismatch in the number of conduction channels in the SWNT and the macroscopic metal leads. Arun Tej M, REACH - 2008

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