Dye Sensitized Nanocrystalline Photovoltaic CellGroup 1 Luke, Matt, and JeffTheorynSchematic of Graetzel CellThe 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-TheoryTheory: Charge SeparationCharge 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.ObjectivenLearn about the photovoltaic effect.nUnderstand the Scherrer formula.Procedure: TiO2 Suspension1.Begin with 6g colloidal Degussa P25 TiO22.Incrementaly add 1mL nitric or acetic acid solution (pH 3-4) nine times, while grinding in mortar and pestle3.Add the 1mL addition of dilute acid solution only after previous mixing creates a uniform, lump-free paste4.Process takes about 30min and should be done in ventilated hood5.Let equilibrate at room temperature for 15 minutesProcedure: Deposition of TiO2 FilmAlign two conductive glass plates, placing one upside down while the one to be coated is right side upTape 1 mm wide strip along edges of both platesTape 4-5 mm strip along top of plate to be coatedUniformly apply TiO2 suspension to edge of plate5 microliters per square centimeterDistribute TiO2 over plate surface with stirring rodDry covered plate for 1 minute in covered petri dishProcedure: Deposition of TiO2 FilmAnneal TiO2 film on conductive glassTube furnace at 450 oC30 minutesAllow conductive glass to cool to room temperature; will take overnightStore plate for later useProcedure: Preparing Anthrocyanin DyeNatural dye obtained from green chlorophyllRed anthocyanin dyeCrush 5-6 blackberries, raspberries, etc. in 2 mL deionized H2O and filter (can use paper towel and squeeze filter)Procedure: Staining TiO2 FilmSoak TiO2 plate for 10 minutes in anthocyanin dyeInsure no white TiO2 can be seen on either side of glass, if it is, soak in dye for five more minWash film in H2O then ethanol or isopropanolWipe away any residue with a kimwipeProcedure: Carbon Coating the Counter ElectrodeApply light carbon film to second SnO2 coated glass plate on conductive sideSoft pencil lead, graphite rod, or exposure to candle flameProcedure: Assembling the Solar CellPlace 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 platesAlternately open and close each side of solar cell to draw electrolyte solution in and wet TiO2 filmEnsure all of stained area is contacted by electrolyteRemove excess electrolyte from exposed areasFasten alligator clips to exposed sides of solar cellProcedure: Measuring the Electrical OutputAttach the black (-) wire to the TiO2 coated glassAttach the red (+) wire to the counter electrodeMeasure open circuit voltage and short circuit current with the multimeter.For indoor measurements, can use halogen lampMake sure light enters from the TiO2 sideMeasure current-voltage using a 1 kohm potentiometerThe center tap and one lead of the potentiometer are both connected to the positive side of the currentConnect one multimeter across the solar cell, and one lead of another meter to the negative side and the other lead to the loadResultsnOpen circuit voltage: 0.388 VAnalysis: PowernMaximum Power: 21 mWnActive Area: 0.7 in2 Max. power per unit area: 30 mW/in2QuestionsnApproximate TiO2 particle size: assume 25 nm diameternNumber of TiO2 units per nanoparticle:nVolume of one nanoparticle = 8.18 * 10-18 cm3nDensity of TiO2 4 g/cm3 Mass of one nanoparticle = 3.27 * 10-17 gnMolar mass of TiO2 = 79.87 g/mol moles of TiO2 in one nanoparticle = 4.10 * 10-19 molesn4.10 * 10-19 moles * 6.022 * 1023 molecules/mole = 2.48 * 105 TiO2 units per nanoparticlenNanoparticle surface area per gram:nNumber of nanoparticles per gram = 1/(3.27 * 10-17) = 3.06 * 1016 nanoparticlesnSurface area of one nanoparticle = 1.96 * 10-15 m2nSurface area per gram = 3.06 * 1016 nanoparticles/gram * 1.96 * 10-15 m2/nanoparticle = 60.0 m2/gramQuestionsnFraction of atoms that reside on the surface:nSurface area of one particle = 1.96 * 10-11 cm2nApproximate atoms per unit area = 1015 atoms/cm2nAtoms on surface = 1.96 * 10-11 cm2 * 1015 atoms/cm2 = 1.96 * 104 atomsnFraction of atoms on surface = (1.96 * 104)/(2.48 * 105) = 0.079nWay to improve experiment:nFilter raspberry juice using a better filter system