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Dye Sensitized Nanocrystalline Photovoltaic Cell. Group 1 – Luke, Matt, and Jeff. Theory. Schematic of Graetzel Cell. 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).

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dye sensitized nanocrystalline photovoltaic cell

Dye Sensitized Nanocrystalline Photovoltaic Cell

Group 1 – Luke, Matt, and Jeff

  • Schematic of Graetzel Cell
  • 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-]
theory charge separation
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.

  • Learn about the photovoltaic effect.
  • Understand the Scherrer formula.
procedure tio2 suspension
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
procedure deposition of tio 2 film
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
procedure deposition of tio 2 film8
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
procedure preparing anthrocyanin dye
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)
procedure staining tio 2 film
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
procedure carbon coating the counter electrode
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
procedure assembling the solar cell
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
procedure measuring the electrical output
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
  • Open circuit voltage: 0.388 V
analysis power
Analysis: Power
  • Maximum Power: 21 mW
  • Active Area: 0.7 in2  Max. power per unit area: 30 mW/in2
  • 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 * 10^23 molecules/mole = 2.48 * 10^5 TiO2 units per nanoparticle
  • Nanoparticle surface area per gram:
    • Number of nanoparticles per gram = 1/(3.27 * 10^-17) = 3.06 * 10^16 nanoparticles
    • Surface area of one nanoparticle = 1.96 * 10^-15 m2
    • Surface area per gram = 3.06 * 10^16 nanoparticles/gram * 1.96 * 10^-15 m2/nanoparticle = 60.0 m2/gram
  • 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 * 10^15 atoms/cm2 = 1.96 * 10^4 atoms
    • Fraction of atoms on surface = (1.96 * 10^4)/(2.48 * 10^5) = 0.079
  • Way to improve experiment:
    • Filter raspberry juice using a better filter system