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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).
•
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
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.
Objective


Learn about the photovoltaic effect.
Understand the Scherrer formula.
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 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 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
• 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 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
• 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
•
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
•
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
Results
Current vs. Voltage
300
250
current (mA)
200
150
100
50
0
0
50
100
150
200
voltage (m V)

Open circuit voltage: 0.388 V
250
300
350
Analysis: Power
Pow er vs. Voltage
25
power (mW)
20
15
10
5
0
0
50
100
150
200
250
300
350
voltage (m V)


Maximum Power: 21 mW
Active Area: 0.7 in2  Max. power per unit area: 30 mW/in2
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 * 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
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 * 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