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Using molecules to capture solar energy

Using molecules to capture solar energy. Timothy Schmidt. The solar spectrum. 1000 W/m 2. Light is made of photons. Planck constant. Speed of light. Energy of photon. Wavelength. The solar spectrum. High energy photons. Low energy photons. Electrons absorb photons, get energy.

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Using molecules to capture solar energy

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  1. Using molecules to capture solar energy Timothy Schmidt

  2. The solar spectrum 1000 W/m2

  3. Light is made of photons Planck constant Speed of light Energy of photon Wavelength

  4. The solar spectrum High energy photons Low energy photons

  5. Electrons absorb photons, get energy unoccupied energy levels E electrons diamond

  6. Electrons absorb photons, get energy E unoccupied energy levels electrons silicon

  7. The solar spectrum 1000 W/m2

  8. single threshold solar cells unoccupied energy levels ~32% max V electrons

  9. Shockley-Queisser limit 35% SQ limit 6000K sun limit Si GaAs 25% efficiency CdTe CdS 15% Ge a-Si:H 5% 0.5 1.0 1.5 2.0 2.5 Band gap /eV

  10. the 3 generations of solar cell Thermodynamic Limit Single threshold (Shockley-Queisser limit)

  11. routes to circumventing Shockley-Queisser limit • using the low energy photons • upconversion • intermediate band cells • using all the photon’senergy • downconversion • multiple exciton generation • singlet Fission • hot carrier cells

  12. Electrons have “spin” Excited state S1 Ground state S0

  13. Electrons have “spin” Excited state T1 Ground state S0 Excited state S1

  14. Molecular photophysics! fluorescence (fast, allowed) absorption

  15. Molecular photophysics! Intersystem crossing absorption Phosphorescence (slow, forbidden)

  16. what is wrong with this picture?

  17. TTA triplet-triplet annihilation (TTA) sensitizer sensitizer S1 S1 S1 S1 ISC ISC T1 T1 T1 T1 S0 S0 S0 S0 emitter emitter

  18. Up-conversion Limiting efficiency of an Upconversion cell is about 50% cell Up-conversion unit

  19. select a sensitizer tetrakisquinoxalinoporphyrin palladium (II)

  20. ultrafast photoluminescence The compound only fluoresces while in S1 (only 10ps!) Measured fluorescence lifetime = 5ps Calculated fluorescence lifetime = 20ns Fluorescence yield = 0.025% Triplet yield may be 99.975%!

  21. select an emitter 100% fluorescence yieldused by others for TTA upconversion

  22. TTA emission kinetics

  23. prompt fluorescence vs upconversion laser laser upconversion fluorescence

  24. TTA yields pure rubrene ref mixture ref 33% 25%

  25. Nothing wrong with this picture!

  26. or this…

  27. ummmm?

  28. Dr Raphael “femtofingers” Clady Dr Nicholas J. Ekins-Daukes (NED) Now at Imperial College our man in London Murad Tayebjee Dennis Cheng

  29. $$ acknowledgements $$ University of Sydney University of NSW ARC LIEF ARC DP GCEP

  30. Application to a-Si realistic a-Si cell 100nm, 200nm or 300nm 1mm up-conversion unit

  31. Application to a-Si Modelled porphyrin absorption spectra Spectra transmitted through cell

  32. Application to a-Si +34%

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