1. The Effect of Carbon Nanotubes in Polymer Photovoltaic Cells May 13, 2010 JESUS GUARDADO, LEAH NATION, HUY NGUYEN, TINA RO

2. Agenda Overview of Market Goal of Project Science & Design of Cell Fabrication Procedures Results Analysis Future Work

3. Current Market Projection for Photovoltaics Investments on the rise Photovoltatic capacity is increasing Avg growth rate >40% for past 5 years

4. Our Focus: Polymer Photovoltaic Cells (PPC) Increased market focus on diversifying solar technologies Potential fabrication advantages Low processing temperature Printable Unique application possibilities Light weight Flexible Current disadvantages Lifetime instability Lower efficiency

5. Polymer Photovoltaic Cell Efficiency Growth Crystalline Si Cells (Single and Multi-crystalline) Thin-Film Technologies (Amorphous Si:H) Organic Photovoltaics 5.4% 12.1% 24.7% 20.3%

6. Project Goals Add carbon nanotubes (CNTs) to increase cell photovoltaic response Make functional cells to validate photoresponse mechanism Match current polymer photovoltaic cell (PPC) cell efficiency

7. Focus: sw-CNTs SWCNT at 80,000x Single-walled carbon nanotubes Large surface area High e- affinity Aids cells Improve carrier transport Induces crystallinity Cost: +$8 per m 2

8. Cell Design Based on past research Cell parts: Active layer (with CNTs) Charge acceptors Electrodes FTO – Fluoride Tin Oxide

9. How It Works: Photons => Exitons Carbon Nanotubes: Charge transport Facilitate disassociation

10. How It Works: Electron => TiO 2 Hole => PEDOT

11. How It Works: Electrodes accept charges

12. Procedures Prepare Solutions Fabricate Samples Test Samples

13. Preparing the Solutions Mix P3HT and solvent Add varying conc. of CNTs CNTs => main variable Sonicate & centrifuge to debundle CNTs Evolution of the solutions

14. Device Fabrication Prepare substrate Clean FTO substrate Separate layers with tape Spin Coat Must optimize rpm 800 rpm for thick layers 1200 rpm for thin layers Deposit top electrode Thermal vapor deposition Taping pix here

15. Fabricated Cell

16. Tests UV-Vis on solutions Confirms semiconductor properties Open circuit voltage No light vs desk lamp Tests for photoresponse IV-Curve Determines cell performance

17. UV-Vis Spectroscopy samples with CNTs show increased photo- response compared to control cells absorption increases as the wt% CNTs increases

18. CNT Concentration vs. V oc Trend

19. I-V Curves Observed Behavior Resistors Short circuit Desired Behavior Diode

20. IV Curves: Round I Sample 4, Concentration 1 Fabrication: 4/6 Testing: 4/14, 4/27 Typical IV curve of our samples The symmetry about the 0V axis implies there is no bias in electron/hole travel

21. IV Curve: Round II

22. Summary Verified Expectations Sources of Error CNTs: with increasing wt % Visible and IR Absorption increased V oc increased Fabrication Variables Inter-layer penetration yielded short circuits Human imprecision Testing Variables Delay between fabrication and testing resulted in degraded samples Oxidation of materials Geng, J.; Zeng, T. Journal of the American Chemical Society 2006, 128, 16827-16833.

23. Future Work Fabrication & Testing Experiment with the engineering parameters for fabrication Standardize testing Materials Investigate the effects of the TiO 2 layer Study alternative materials to P3HT Explore different materials for the heterostructure’s layers

24. Acknowledgements Helen Zeng Yin-lin Xie Jill Rowehl Prof. Yet-Ming Chiang 3.042 – Materials Project Laboratory Staff Facilities: Institute of Soldier Nanotechnologies (ISN) Organic Nanostructure Electronics (ONE) Lab

25. Thank you. Questions? You may reach us at nanosol@mit.edu http://web.mit.edu/course/3/3.042/team1_10

26. Appendix

27. Renewable Energy Comparison

28. Current Progress & Future Schedule

29. Cost Estimation $/grammg/mLL/slideslides/meter$/meter 1000.18750.00014444.448.33 PRODUCTION COSTS, to be added to other company's approximation of $/meter CNT $15-20% cnts

30. SilverTiO2 Profilometry: Ag/TiO 2 Border Image

31. PEDOTACTIVE LAYER Profilometry: Active Layer/PEDOT Image