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Nanowire dye-sensitized solar cells

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Nanowire dye-sensitized solar cells Sung Hwan Kim EE 235 Presentation 2 Outline Dye-Sensitized Cells(DSC) / Motivation Nanowire DSC Fabrication of Nanowires and Solar ... – PowerPoint PPT presentation

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Title: Nanowire dye-sensitized solar cells


1
Nanowire dye-sensitized solar cells
  • Sung Hwan Kim
  • EE 235 Presentation 2

2
Outline
  • Dye-Sensitized Cells(DSC) / Motivation
  • Nanowire DSC
  • Fabrication of Nanowires and Solar Cell
  • Results and Analysis
  • Summary and Conclusion

3
Dye-Sensitized Cells(DSC)
  • A type of photochemical cell that consists of an
    electrolyte sandwiched between a cathod and
    transparent anode
  • Anode is a thick film of nanoparticles (10µm
    TiO2) coated with a photosensitive
    dye(ruthenium-polypyridine)
  • Electrolyte(iodide solution) consists of redox
    couples
  • Giving up electrons(accepting holes) oxidizes
  • Accepting electrons changes from oxidized to
    reduced state
  • When sunlight enters through anode, photons
    strike the dye, injecting electrons into the
    conduction band of TiO2 film
  • Electrons are supplied to the dye from iodide
  • Oxidized iodide receives electron from cathod

4
Nanowire DSCs
  • Limitations of DSC
  • Electron transport in nanoparticle film(TiO2
    layer) is a trap-limited diffusion
    process(diffusivity Dn10-4cm2/sec) gt small
    diffusion length
  • Efficiency is limited by Ln in the film, surface
    area of the electrodes, and low absorbance near
    400-800nm where much of the solar spectrum is
    incident
  • Nanowire DSCs
  • For a single nanowire(ZnO), measured electron
    diffusivity(Dn) of 0.05-0.5cm2/sec is several
    hundred times larger than the highest reported
    diffusivity for TiO2
  • gt provides faster carrier extraction
  • Provides large surface area for dye loadings
  • Overall increase in carrier collection efficiency

5
Fabrication of Nanowires and Solar Cell
  • 3-4nm in diameter ZnO quantum dots deposited in
    FTO substrate and nanowires grown submerged in a
    complex solution
  • Thermally platinized FTO counter electrodes were
    used to sandwich nanowires separated by 40µm
    thick spacers
  • Internal space of the cell was filled with iodide
    electrolyte by capillary action

6
Results and Analysis
  • Solar cells were constructed for various surface
    areas(0.25-1.14cm2) and tested under 1
    Sun(100mA/cm2)
  • Jsc 5.35.85 mA/cm2
  • Voc 0.610.71V
  • FF 0.360.38
  • ? 1.21.5
  • FF for nanowire cells is relatively insensitive
    to device area
  • gt Nanowire cells are less affected by series
    resistance

7
Results and Analysis
  • Fill factor falls off with increasing light
    intensity owing to the development of a large
    photo-shunt gt efficiency is fairly constant
    above light intensity of 5mW/cm2
  • For nanoparticle cells, there is a rapid
    saturation and decline of the current with
    increasing roughness factor gt transport
    efficiency falls off above certain film thickness

8
Summary and Conclusion
  • Some thoughts
  • Lifetime of DSC solar cells
  • Semiconductor-electrolyte operation
  • gt susceptibility of semiconductor to
    photoenhanced corrosion?
  • Depends too heavily on dye loadings
  • Nanowire electrodes increase the rate of electron
    transport
  • Dye-sensitized solar cells are promising devices
    for inexpensive, large-scale solar energy
    conversion
  • Further work is required to accommodate the red
    region of the spectrum and to achieve higher dye
    loadings

9
(No Transcript)
10
Notes
  • Slide 3 electrolyte semiconductor or liquid //
    DSC low cost
  • Slide 3 , since drift transport is prevented by
    the ions in the electrolyte
  • Slide 4 At the electrodes, since drift is not
    possible, carriers diffuse(percolate) to the
    contacts with transit times in miliseconds gt
    small diffusion length
  • Roughness factor surface area x TiO2 weight
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