1. Photovoltaics: What material is best for your needs Benjamin Glassy Mark Ziffer 6/6/2013

2. Review of Current-Voltage Relationship in p-n Junction Diode

3. Current-Voltage Relationship in p-n Junction Diode Under Illumination Carrier flow creates potential = V oc Bhattacharya, Pallab. Semiconductor Optoelectronic Devices. Upper Saddle River, NJ: Prentice Hall, 1997.

4. In organic heterojunction solar cells, photocurrent still generated at interfacial region. However, kinetic processes are very different. Hence, the need for a new ideal diode equation. Brabec, C. J., Sariciftci, N. S. and Hummelen, J. C. Adv. Funct. Mater., 2001, 11, 15–26 Giebink, N. C., Wiederrecht, G. P., Wasielewski, M. R. & Forrest, S. R. Physical Review B, 2010, 82, 155305

5. 1.Exciton generation in polymer (donor) and diffusion to the interfacial region 2.Charge transfer (CT) state at the interface forming polaron pair (PP) 3.New kinetic processes: -PP can recombine to ground state: “Geminate recombination” (k PPr ) -PP can separate to form free charges 4.Kinetic process: - Free charges can reform PP: “Bi-molecular recombination” (k rec n I p I ) Giebink, N. C., Wiederrecht, G. P., Wasielewski, M. R. & Forrest, S. R. Physical Review B, 2010, 82, 155305 Halls, Jonathan J. M., and Richard H. Friend. "Chapter 9: Organic Photovoltaic Devices." Clean Electricity from Photovoltaics. Ed. Mary D. Archer and Robert Hill. London: Imperial College, 2001. 377-445.

6. Steady State Polaron Pair Recombination Rate: Steady State Free Carrier Recombination Rate: J x = exciton diffusion rate at interface ζ = polaron pair density ζ eq =equilibrium PP population n I p I = Free electron density * free hole density

7. Lots of Equations Giebink, N. C., Wiederrecht, G. P., Wasielewski, M. R. & Forrest, S. R. Physical Review B, 2010, 82, 155305

8. Brabec, C. J., Sariciftci, N. S. and Hummelen, J. C. Adv. Funct. Mater., 2001, 11, 15–26 Deibel, C. & Dyakonov, V. Polymer–fullerene bulk heterojunction solar cells. Reports on Progress in Physics, 2010, 73

9. Servaites, J. D., Ratner, M. A. & Marks, T. J. Organic solar cells: A new look at traditional models. Energy & Environmental Science 4, (2011) Giebink, N. C., Wiederrecht, G. P., Wasielewski, M. R. & Forrest, S. R. Ideal diode equation for organic heterojunctions. I. Derivation and application. Physical Review B 82, (2010) Brabec, C. J., Sariciftci, N. S. and Hummelen, J. C., Plastic Solar Cells. Adv. Funct. Mater., 11: 15–26, (2001) Good References

10. Sticking with what you know Decades of silicon research for electronics applications

12. Awesome Solar News A solar-powered plane aiming to cross the US from the West Coast to East Coast has completed its third leg (landed in St Louis) Planning around-the-world flight in 2015 Single crystal silicon from SunPower Solarimpulse.com

13. Multijunction Solar Cells Current record efficiency is held by the National Renewable Energy Lab for the cell shown at the left These cells are very expensive to make. The main user of these high efficiency cells is NASA—weight and efficiency outweigh cost when sending things into space. www.nrl.navy.mil

14. Large-scale use Even commercial silicon cells require 2-3 years of use before they have saved any money. These kinds of figures for the more exotic device architectures and materials have a much longer period. What if the focus was on materials that made ok solar cells, but were super cheap.

15. Cost benefit analysis 23 semiconductor materials Assumed single junction devices Designed devices to achieve a single pass absorption of 85% Wadia, Cyrus; Alivisatos, A. Paul; Kammen, Daniel M. Environ. Sci. Technol. 2009, 43, 2072-2077

16. Figures of Merit Minimum material intensity: β Power Conversion Efficiency: η PCE was taken to be 100% of the single junction thermodynamic limit based upon Eg Wadia, Cyrus; Alivisatos, A. Paul; Kammen, Daniel M. Environ. Sci. Technol. 2009, 43, 2072-2077

17. Total Electricity Potential Calculation Annual electricity potential (TWh) A: annual production per mineral in metric tons C: capacity factor set at 0.2 H: number of hours per year β: metric tons per year Wadia, Cyrus; Alivisatos, A. Paul; Kammen, Daniel M. Environ. Sci. Technol. 2009, 43, 2072-2077

19. Cost Modeling Note: Does not take into account cost of processing material, only extraction Not enough data on more exotic materials investigated For materials with this data the ratio (C p /C e ) is highly uniform Wadia, Cyrus; Alivisatos, A. Paul; Kammen, Daniel M. Environ. Sci. Technol. 2009, 43, 2072-2077

22. Plastics? Necessary for niche application such as flexible solar cells Possible benefits Cheaper manufacturing Solution processable Very earth abundant Pitfalls Efficiencies Lifetime

23. Kalowekamo, Joseph; Baker, Erin Solar Energy 2009, 83, 1224-1231 Cost of module comparison Actual cost is not the issue….. Lifetime of the product is

24. Based on this research, the largest benefit would come from increasing lifetime dramatically from 5 to 10 or 15 years Could become competitive with inorganic PV Kalowekamo, Joseph; Baker, Erin Solar Energy 2009, 83, 1224-1231

25. What to consider Cost versus application Equipment availability Possibly subsidy from the government?

26. Any Questions???

27. V BI in an Organic Diode