Dye Sensitized Nanocrystalline Photovoltaic Cell

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Dye Sensitized Nanocrystalline Photovoltaic Cell

• Group 1 Luke, Matt, and Jeff

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Theory

• Schematic of Graetzel Cell

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Theory

• The adsorbed dye molecule absorbs a photon
  forming an excited state. dye
• The excited state of the dye can be thought of as
  an electron-hole pair (exciton).

• The excited dye transfers an electron to the
  semiconducting TiO2 (electron injection). This
  separates the electron-hole pair leaving the hole
  on the dye. dye
• The hole is filled by an electron from an iodide
  ion. 2dye 3I-? 2dye I3-

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Theory Charge Separation

• Charge must be rapidly separated to prevent back
  reaction.
• Dye sensitized solar cell, the excited dye
  transfers an electron to the TiO2 and a hole to
  the electrolyte.
• In the PN junction in Si solar cell has a
  built-in electric field that tears apart the
  electron-hole pair formed when a photon is
  absorbed in the junction.

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Objective

• Learn about the photovoltaic effect.
• Understand the Scherrer formula.

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Procedure TiO2 Suspension

• Begin with 6g colloidal Degussa P25 TiO2
• Incrementaly add 1mL nitric or acetic acid
  solution (pH 3-4) nine times, while grinding in
  mortar and pestle
• Add the 1mL addition of dilute acid solution only
  after previous mixing creates a uniform,
  lump-free paste
• Process takes about 30min and should be done in
  ventilated hood
• Let equilibrate at room temperature for 15
  minutes

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Procedure Deposition of TiO2 Film

• Align two conductive glass plates, placing one
  upside down while the one to be coated is right
  side up
• Tape 1 mm wide strip along edges of both plates
• Tape 4-5 mm strip along top of plate to be coated
• Uniformly apply TiO2 suspension to edge of plate
• 5 microliters per square centimeter
• Distribute TiO2 over plate surface with stirring
  rod
• Dry covered plate for 1 minute in covered petri
  dish

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Procedure Deposition of TiO2 Film

• Anneal TiO2 film on conductive glass
• Tube furnace at 450 oC
• 30 minutes
• Allow conductive glass to cool to room
  temperature will take overnight
• Store plate for later use

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Procedure Preparing Anthrocyanin Dye

• Natural dye obtained from green chlorophyll
• Red anthocyanin dye
• Crush 5-6 blackberries, raspberries, etc. in 2 mL
  deionized H2O and filter (can use paper towel and
  squeeze filter)

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Procedure Staining TiO2 Film

• Soak TiO2 plate for 10 minutes in anthocyanin dye
• Insure no white TiO2 can be seen on either side
  of glass, if it is, soak in dye for five more min
• Wash film in H2O then ethanol or isopropanol
• Wipe away any residue with a kimwipe

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Procedure Carbon Coating the Counter Electrode

• Apply light carbon film to second SnO2 coated
  glass plate on conductive side
• Soft pencil lead, graphite rod, or exposure to
  candle flame

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Procedure Assembling the Solar Cell

• Place two binder clips on longer edges to hold
  plates together (DO NOT clip too tight)
• Place 2-3 drops of iodide electrolyte solution at
  one edge of plates
• Alternately open and close each side of solar
  cell to draw electrolyte solution in and wet TiO2
  film
• Ensure all of stained area is contacted by
  electrolyte
• Remove excess electrolyte from exposed areas
• Fasten alligator clips to exposed sides of solar
  cell

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Procedure Measuring the Electrical Output

• Attach the black (-) wire to the TiO2 coated
  glass
• Attach the red () wire to the counter electrode
• Measure open circuit voltage and short circuit
  current with the multimeter.
• For indoor measurements, can use halogen lamp
• Make sure light enters from the TiO2 side
• Measure current-voltage using a 1 kohm
  potentiometer
• The center tap and one lead of the potentiometer
  are both connected to the positive side of the
  current
• Connect one multimeter across the solar cell, and
  one lead of another meter to the negative side
  and the other lead to the load

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Results

• Open circuit voltage 0.388 V

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Analysis Power

• Maximum Power 21 mW
• Active Area 0.7 in2 ? Max. power per unit area
  30 mW/in2

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Questions

• Approximate TiO2 particle size assume 25 nm
  diameter
• Number of TiO2 units per nanoparticle
• Volume of one nanoparticle 8.18 10-18 cm3
• Density of TiO2 4 g/cm3 ? Mass of one
  nanoparticle 3.27 10-17 g
• Molar mass of TiO2 79.87 g/mol ?moles of TiO2
  in one nanoparticle 4.10 10-19 moles
• 4.10 10-19 moles 6.022 1023
  molecules/mole 2.48 105 TiO2 units per
  nanoparticle
• Nanoparticle surface area per gram
• Number of nanoparticles per gram 1/(3.27
  10-17) 3.06 1016 nanoparticles
• Surface area of one nanoparticle 1.96 10-15
  m2
• Surface area per gram 3.06 1016
  nanoparticles/gram 1.96 10-15
  m2/nanoparticle 60.0 m2/gram

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Questions

• Fraction of atoms that reside on the surface
• Surface area of one particle 1.96 10-11 cm2
• Approximate atoms per unit area 1015 atoms/cm2
• Atoms on surface 1.96 10-11 cm2 1015
  atoms/cm2 1.96 104 atoms
• Fraction of atoms on surface (1.96
  104)/(2.48 105) 0.079
• Way to improve experiment
• Filter raspberry juice using a better filter
  system