Photovoltaic Cells Nanocrystalline Dye Sensitized Solar Cell Outline Cell Schematic Useful Physics Construction Procedure Preparation and
deposition of TiO2 (10-50 nm diameter) Preparation of dye and staining semi-conducter Carbon Coating counterelectrode Assemblage Electric Output
Data Analysis Conclusion Schematic of the Graetzel Cell Theory and Physics 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-] Electrons are collected from the TiO2 at the cathode. Redox mediator is iodide/triiodide (I-/I3-) The dashed line shows that some electrons are transferred from the TiO2 to Anode is covered with carbon catalyst and the triiodide and generate iodide. This reaction is an internal short circuit that injects electrons into the cell regenerating decreases the efficiency of the cell. the iodide.
Key Step 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. Chemical Note Triiodide (I3-) is the brown ionic species that forms when elemental iodine (I2) is dissolved in water containing iodide (I-). I2 I
I 3 Construction Procedure TiO2 Suspension Preparation TiO2 Film Deposition Anthrocyanin Dye Preparation and TiO2 Staining Counter Electrode Carbon Coating Solar Cell Assembly Preparing the 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 Deposition of the 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 Deposition of the TiO2 Film (cont.) 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 Preparation photos Mixing the TiO2 Safety first! Applying the TiO2 Working under the hood Examples: TiO2 Plate Good Coating: Bad Coating: Mostly even distribution Patchy and irregular
The thicker the coating, the better the plate will perform Preparing the 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) Dye Preparation Dye comes from black berries Crushing the berries
Staining the 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 Dry and store in acidified (pH 3-4) deionized H 2O in closed dark-colored bottle if not used immediately Filter and Staining the TiO2 Petri dish TiO2 glass 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 Can be performed while TiO2 electrode is being stained SnO2 pre-coated glass Assembling the Solar Cell Remove, rinse, and dry TiO2 plate from storage or staining plate
Place TiO2 electrode face up on flat surface Position carbon-coated counter electrode on top of TiO2 electrode Conductive side of counter electrode should face TiO2 film Offset plates so all TiO2 is
covered by carbon-coated counter electrode Uncoated 4-5 mm strip of each plate left exposed 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 Measuring the Electrical Output To measure solar cell under sunlight, the cell should be protected from UV exposure with a polycarbonate cover 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 Multimeter
light solar cell Testing Circuit Ammeter Voltmeter Photo Cell Potentiometer Measuring the Electrical Output Measure current-voltage using a 500 ohm
potentiometer The center tap and one lead of the potentiometer are both connected to the positive side of the current Connect one multi-meter across the solar cell, and one lead of another meter to the negative side and the other lead to the load Voltage 0.242
0.22 0.21 0.17 0.13 0.1 0.08 0.041 Current 0 0.003 0.004 0.006 0.008 0.01 0.012 0.016 Data Analysis
Plot point-by-point current/voltage data pairs at incremental resistance values, decrease increments once line begins to curve Plot open circuit voltage and short circuit current values Divide each output current by the measured dimensions of stained area to obtain mA/cm2 Determine power output and
conversion efficiency values VI characteristic Current 0.018 0.016 0.014 0.012 0.01 0.008 0.006 0.004 0.002 0
Series1 0 0.1 0.2 0.3 Voltage Open circuit voltage 0.242mV Excel generated plot of data Data Analysis Continued
Max Power Power curve 1.025W @ 0.14mV 0.0012 Max Power per unit area Photocell area = 34.2 cm2 Power, mA 0.001 0.0008 0.0006
Assumed size of 20nm: r = 10nm, density TiO2 = 3.84g/cm3 Volume of spherical particle = 4.19 * 10-18 cm3/particle Amount of TiO2=(4.19*10-18)cm3 *3.84g/cm3=1.61 * 1017g/particle SA= 1.26*10-11cm2/particle SA/g = 1.26*10-11/1.61*10-17 = 78m2/g atoms on surface/atoms in volume = 1.26*10-11cm2 * 1015cm2 / 4.19 * 10-18 * 1022.5 = 0.095 Procedure Improvements Filter dye Dont get light source too close to photocell while performing data acquisition Be sure TiO2 layer is uniform and not too thin
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