2. 8 5.25 (M): No Class (Memorial Day) 5.27 (W): Energy and Nanotechnology 5.28 (Th): LAB: Solar Cell 9 6.01 (M): Project Presentations 6.03 (W): LAB: Antimicrobial Properties of NPs 6.04 (Th): Project Presentations / complete lab 10 6.08 (M): Battery/LED/MEMS 6.10 (W): BioNanoTechnology 6.11 (Th): Guest Lecture 11 6.15 (M): Safety and Ethics / Lab Check-out 6.17 (W): Final Exam (10:30 – 12:30)

3. Energy and Nanotechnology Nano 101

4. Scope of Energy and Nanotechnology Huge Scope Focus on: –Photovoltaics –Energy Storage –LEDs, Photonics

5. Photovoltaic Semiconductor device that can convert sunlight to electricity 1. Free electron from VB 2. Separate charges to create current

6. P-N Junction N- type has extra CB electrons P-type is missing VB electrons (has extra holes) Difference of potential drives separation of charges http://www.pveducation.org/pvcdrom/pn-junction/formation-pn-junction

7. Photovoltaic Efficiency Electrical energy out / Photon energy in Theoretical limit for 1 PN Junction, solar spectrum = 33.7% –Shockley-Queisser Limit –Blackbody Radiation –Radiative Recombination –Spectrum Losses Si – E g = 1.1 eV GaA – E g = 1.4 eV

8. Landscape of Photovoltaics

9. Multi-Junction/Concentrated Solar Cells The Top Performer

10. Why do we need new PV materials? Cost –Expensive manufacturing –Decreases w/ polysilicon but still high Aesthetics Flexibility

11. Thin Film PVs http://solopower.com/solutions-technology/thin-film-photovoltaics/ CIGS flexible solar cell CdTe E g = 1.5 eV

12. Dye-Sensitized Solar Cells No P-N junction Colored dye absorbs light, separates charges Electron injected into TiO 2, goes to back contact Redox couple re-oxidizes dye First published 1991, ~ 7% efficient http://www.rsc.org/Education/EiC/issues/2007Sept/HarnessingSolarEnergyGratzelCells.asp

13. Maximizing Performance TiO 2 –Nanostructures –Improvement w/ 1-D vs 2-D or 0-D –Oriented, crystalline structures –Hydrothermal synthesis Scientific Reports 3, Article number: 3004 doi:10.1038/srep03004

14. Maximizing Performance Dye –Absorb energy in the solar spectrum –Attach to TiO2 –Inject electrons into TiO2 –Favorable electronic states Nature Chemistry 6, 242– 247 (2014) Advances in Materials Science and Engineering Volume 2014 (2014), Article ID 974782 Zn Prophyrin Ru Complex Anthrocyanin

15. Maximizing Performance Electrolyte –Minimal light absorption –Proper energy levels –Stability http://www2.mpip- mainz.mpg.de/groups/laquai/Research/Organic%20Electronics/DSSC/print_html?lang=en Advances in Materials Science and Engineering Volume 2014 (2014), Article ID 974782 Dalton Trans., 2012,41, 3111-3115

16. Easy to make

17. Commercial Products GCell (UK) Sony Dyesol (Australia)

18. Perovskites Methylammonium lead tri-iodide Originally sensitizer for DSSC http://spectrum.ieee.org/green-tech/solar/perovskite-is-the-new- black-in-the-solar-world

19. Landscape of Photovoltaics

20. Perovskite Development Found to be ambipolar semiconductor –Good hole and electron mobility Nature Materials 13, 838–842 (2014)

21. Pervoskite Synthesis Spin-coat Pb precursur onto TiO 2 Soak in CH 3 NH 3 I precursor Crystallinity tuned by choice of solvents

22. Concerns Stability – water soluble, does not hold up to direct sunlight Toxicity False positive in efficiency measurements Commercialization – –Oxford Photovoltaics

23. Quantum Dot Solar Cells Good at absorbing light and separating charge Light absorption can be tuned QDs can be easily mass produced Problems: –Stability –Air-sensitive –High temp synthesis J. Phys. Chem. Lett., 2013, 4 (6), pp 908–918

24. QD-Sensitized Solar Cell Like DSSC, QD replaces dye J. Phys. Chem. Lett., 2013, 4 (6), pp 908–918

25. Multiple Exciton Generation 1 photon -> 2 carriers Potential for > 100% efficiency Can you extract the charges before they recombine? J. Phys. Chem. Lett., 2013, 4 (6), pp 908–918

26. Tandem Solar Cell Quantum dots of different sizes/compositions absorb more of the solar spectrum

27. Record QD Solar Cell PbS QDs Pyramid shaped electrodes Tuning angles tunes performance of the cell http://nanotechweb.org/cws/article/ tech/59810

28. Products Solterra (Arizona) –QD Tetrapod PVs Nanoco (UK) –CIGS and CIS QDs