Powered Paint: Nanotech Solar Ink Brian A. Korgel Department of Chemical Engineering, Texas Materials Institute,

1. Hot Science - Cool Talks Vol. 69 Powered Paint: Nanotech Solar Ink Brian A. Korgel Department of Chemical Engineering, Texas Materials Institute, Center for Nano- and Molecular Science and Technology The University of Texas at Austin korgel@che.utexas.edu December 3, 2010

2. To Lower the Cost of Solar Energy…

3. To Lower the Cost of Solar Energy… Change the way solar cells are made Slow, high temperature vacuum processes

4. To Lower the Cost of Solar Energy… Change the way solar cells are made Print like newspaper Slow, high temperature vacuum processes

5. To Lower the Cost of Solar Energy… Change the way solar cells are made Print like newspaper Slow, high temperature vacuum processes Photovoltaic Paints…?

6. To Lower the Cost of Solar Energy… Change the way solar cells are made Brittle and heavy

7. To Lower the Cost of Solar Energy… Change the way solar cells are made Light and flexible Brittle and heavy

8. A Photovoltaic Device How it works:

9. A Photovoltaic Device How it works: A semiconductor Start with a semiconductor… (Examples of semiconductors include silicon, GaN, germanium…)

10. A Photovoltaic Device How it works: Photons (Light) A semiconductor The semiconductor absorbs the light from the sun

11. In the semiconductor, electrons are tied up in bonds between atoms

12. But when the semiconductor absorbs a photon Photon (Light)

13. But when the semiconductor absorbs a photon, a free electron is created Photon energy “excites” an electron

14. But when the semiconductor absorbs a photon, a free electron is created and a hole Excited electron leaves behind a hole

15. Both the electron and hole can move to create a photogenerated electrical current across the semiconductor e- Excited electron and hole can move to create a current h+

16. A Photovoltaic Device How it works: Photons (Light) Semiconductor 2 e- h+  Light absorption creates an electron and hole

17. A Photovoltaic Device How it works: Both the electron and hole can move Photons (Light) Semiconductor 2 e- h+ But…need a force that will separate the electron and hole to create an electric current

18. A Photovoltaic Device How it works: Photons (Light) Semiconductor 2 e- h+ Another semiconductor layer is needed

19. A Photovoltaic Device How it works: n-type Photons (Light) Semiconductor 2 e- h+ p-type The two semiconductors form a p-n junction

20. A Photovoltaic Device How it works: n-type Photons (Light) e- h+ p-type The two semiconductors form a p-n junction that separates the electron and hole; this is the photovoltaic effect

21. A Photovoltaic Device How it works: Photons (Light) e- h+ Electrical power can be generated

22. A Photovoltaic Device How it works: Metal (anode) Photons (Light) e- h+ Metal (cathode) But we need metal electrodes on each side to extract the charge

23. A Photovoltaic Device How it works: Metal (anode) Photons (Light) e- h+ And a mechanical support

24. ç A Photovoltaic Device How it works: Photons (Light) e- h+ This is the basic design of every solar cell

25. What’s wrong with the existing technology?

26. What’s wrong with the existing technology? A Solar Farms of PVs (of silicon)

27. What’s wrong with the existing technology? It’s too expensive

28. What’s wrong with the existing technology? It’s too expensive Production cost of energy (DOE, 2002)

29. What’s wrong with the existing technology? To compete with fossil fuels: • Need < $1/Wp module cost • Current cost is $4.27/Wp • Cost of power from fossil fuels is <¢4-10/kWh • -Solar power stands at ¢20/kWh

30. What’s wrong with the existing technology? • Need < $1/Wp module cost • Current cost is $4.27/Wp • -Corresponds to ~¢20/kWh 55% of the cost is in manufacturing the module SolarBuzz.com Kazmerski LL, J Electron Spectroscopy, 2006; 150:103–135.

31. Silicon dominates the solar cell market

32. Silicon dominates the solar cell market It’s relatively expensive

33. Silicon dominates the solar cell market It’s relatively expensive and mature

34. The Cost of Silicon http://pubs.usgs.gov/fs/2002/fs087-02/

35. The Cost of Silicon The cost of silicon is high http://pubs.usgs.gov/fs/2002/fs087-02/

36. The Cost of Silicon Processing silicon is energy intensive http://pubs.usgs.gov/fs/2002/fs087-02/

37. The Cost of Silicon 2009, $4.27/W 2010, $3.59/W http://pubs.usgs.gov/fs/2002/fs087-02/

38. Silicon PV’s work well and dominate the market Estimated 14,000 MW capacity in 2010

39. Silicon PV’s work well and dominate the market, but are too expensive for the long-term Estimated 14,000 MW capacity in 2010

40. There are new Technologies on the Horizon:

41. There are new Technologies on the Horizon: Source IEA PVPS CdTe-based thin film solar cells: First Solar claims to have built modules at $0.98/W Rooftop First Solar CdTe panels

42. There are new Technologies on the Horizon: Organic materials-based solar cells Roll-to-roll processing of polymer-based solar cells (Mekoprint A/S) Konarka

43. There are new Technologies on the Horizon: But the cost of solar energy still needs to be reduced by about a factor of 10.

44. Can we make a “solar” paint that can convert sunlight energy into electricity? Solar paint? 100 nm

45. First, we need an ink: Copper indium gallium selenide: CIGS

46. First, we need an ink:  Develop a chemical synthesis of CIGS nanocrystals

47. N2 TC First, we need an ink:  Develop a chemical synthesis of CIGS nanocrystals oleylamine, 240oC CuInSe2 nanocrystals CuCl + InCl3 + 2Se

48. 15 – 20 nm diameter CuInSe2 nanocrystals 48

50. Metal n-type semiconductor Nanocrystal ink Metal Glass or plastic support