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Department of Applied Physics Chalmers vägar mot en hållbar värld 2009 Photo- voltaics H 2 production & storage Fuel cells Photo-

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Presentation on theme: "Department of Applied Physics Chalmers vägar mot en hållbar värld 2009 Photo- voltaics H 2 production & storage Fuel cells Photo-"— Presentation transcript:

1 Department of Applied Physics Chalmers vägar mot en hållbar värld 2009 Photo- voltaics H 2 production & storage Fuel cells Photo- catalysis Emission cleaning Batteries Chalmers vägar mot en hållbar värld 2009 Ljus framtid för solenergi tack vare nano teknik ? Michael Zäch Chalmers tekniska högskola Institutionen för teknisk fysik

2 Department of Applied Physics Chalmers vägar mot en hållbar värld 2009 Några inledande tankar kring solenergi, solceller och nanoteknik Nanopartikelplasmoner – vad är det för något ? Nanopartikelplasmoner i solceller Innehåll

3 Department of Applied Physics Chalmers vägar mot en hållbar värld 2009 Energikällor Solen täcker världens årliga energibehov på en timma! Fotosyntes Vind Vatten Sol Kol Uran Gas Olja Världens energibehov (15 TW) cont.

4 Department of Applied Physics Chalmers vägar mot en hållbar värld 2009 Hur mycket är en TW? 1 TW = 1 Terawatt = 1’000 GW = 1’000 Gigawatt = 1’000’000 MW = 1’000’000 Megawatt = 1’000’000’000 kW = 1’000’000’000 kilowatt 1’000’000’000’000 W 1 W 1 kW 1 MW 1 GW 1 TW back

5 Department of Applied Physics Chalmers vägar mot en hållbar värld 2009 Si Solar Cell (1st Generation PV) Source: Surek, Tom - Solar Power - Today, Tomorrow, and Forever.pdf (NREL)

6 Department of Applied Physics Chalmers vägar mot en hållbar värld 2009 Monocrystalline Si Solar Cells (1st Generation Photovoltaics) E n-Si p-Si hole transport electron transport I R Essentially a p-n junction, with contacts to p- and n-sides Photons with E ≥ 1.12eV generate charge carriers (e-h pairs) in silicon Charges are separated by built-in electric field and driven through external load

7 Department of Applied Physics Chalmers vägar mot en hållbar värld 2009 Issues with 1st Generation PV Si has an indirect bandgap  low optical absorption  Si needs to be thick to absorb most of the light (>> 100  m) e-h pairs must diffuse to the junction region Minority carrier diffusion length (recombination rate) depends on material purity and crystallinity Efficient devices can only be made with very pure (solar-grade) Si, which is expensive and energy-intensive in the production The most widely used technique for making single-crystal silicon is the Czochralski process, in which a seed of single-crystal silicon contacts the top of molten silicon. As the seed is slowly raised, atoms of the molten silicon solidify in the pattern of the seed and extend the single- crystal structure. Czochralski process to make single-crystal Si

8 Department of Applied Physics Chalmers vägar mot en hållbar värld 2009 Dye-Sensitized Solar Cells (3rd Generation PV) Fundamental difference: light absorption occurs in a dye rather than in a semiconductor (i.e. it is separated from charge separation) Need rather thick layer of dye  use 3-D scaffold of mesoporous titania (Rather) cheap raw materials, and “simple” production process  cost advantages Efficiency is smaller than for Si cells (≈ 10%) Good price/performance ratio

9 Department of Applied Physics Chalmers vägar mot en hållbar värld 2009 Overview of State-of-the-Art LabModule (%)(%) Monocrystalline Si Polycrystalline Si Amorphous Si CIGS DSSC Organic5.4?

10 Chalmers vägar mot en hållbar värld 2009 Department of Applied Physics How small is a nm? 1 µm= one millionth of a meter 1 nm= one billionth of a meter ≈ 1/50,000 thickness of a hair If we shrunk all distances 110,000,000,000 times, the sun and earth would be separated by 1m. A football field would then be 1nm. Human hair thickness ~ 50 µm 110,000,000 km

11 Department of Applied Physics Chalmers vägar mot en hållbar värld 2009 Early Nanotechnology The Lycurgus Cup The British Museum 4th century AD Window of the Seasons, (Jan. and Feb.) Chartres Cathedral (France) 13th century (?)

12 Department of Applied Physics Chalmers vägar mot en hållbar värld 2009 Nanoparticle Plasmons Observed when electrons in metallic nanostructures oscillate collectively under the influence of an electric field (light) Resonance frequency of the oscillation (= color) can be tuned by varying particle size For particles in the size range ≈ nm, the resonance frequency falls into the visible regime  Metallic nanoparticles are good at absorbing and scattering sunlight E-fieldMetal sphere e - cloud

13 Department of Applied Physics Chalmers vägar mot en hållbar värld 2009 Solar Spectrum and Plasmons Wavelength [nm] Absorbance [a.u.] Particle ø:

14 Department of Applied Physics Chalmers vägar mot en hållbar värld 2009 p-Si n-Si Al-electrode 200µm 2000µm Polarized light I Model Si Solar Cell Au nanoparticles X Y Z

15 Department of Applied Physics Chalmers vägar mot en hållbar värld 2009 Enhancement = (Photocurrent with nanoparticles) (Photocurrent without nanoparticles) Hägglund, C., Zäch, M., Petersson, G., and Kasemo, B., Appl. Phys. Lett. 92 (2008) Optical properties Elliptical particles with two distinct NPPs (corresponding to long- and short axis) Light polarization can be used to “switch NPPs on and off”.

16 Department of Applied Physics Chalmers vägar mot en hållbar värld 2009 Photocurrent Photocurrent clearly polarization dependent Clear correlation with plasmon resonance peaks Net decrease of photocurrent at resonance (<1) Increase off resonance (>1) Hägglund, C., Zäch, M., Petersson, G., and Kasemo, B., Appl. Phys. Lett. 92 (2008) (Photocurrent with nanoparticles) (Photocurrent without nanoparticles) Wavelength [nm] s-polarized light p-polarized light // to minor axis// to major axis

17 Department of Applied Physics Chalmers vägar mot en hållbar värld 2009 TiO 2 Glass support Au/Ti-electrode ± V 10µm 2000µm Elongated Ag or Au nanoparticle Polarized light X Y Z Model DSSC Dye

18 Department of Applied Physics Chalmers vägar mot en hållbar värld 2009 Optical properties Polarization- dependent microextinction measurement Two clearly separated peaks corresponding to particle short and long axis P P

19 Department of Applied Physics Chalmers vägar mot en hållbar värld 2009 Photoconductance with Au particles Clear polarization dependence Clear correlation with plasmon peak Net increase of photoconductance with Au particles P P GG G // Hägglund et al, Applied Physics Letters (2008)

20 Department of Applied Physics Chalmers vägar mot en hållbar värld 2009 Plasmonic charge carrier generation in photovoltaic solar cells Far field effects Photoemission of charge carriers Near field effects Electromagnetic field influence on the charge carrier generation PV Schematic taken from Carl Hägglund’s PhD thesis

21 Department of Applied Physics BAKOM STÄNGDA DÖRRAR – 19 feb 2009 Acknowledgements EU, Mistra, SSF and Chalmers Foundation for financial support Collaborators in the Chemical Physics group Many of the students who attended the course TIF165 - “Nanotechnology for Sustainable Energy” And you for your attention ! Tack !


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