Procedure * You must wear gloves and safety glasses during this lab.

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1 LAB: Dye- Sensitized Solar Cells Lab Report Due April 25, 2011 Summary: In this lab, you will construct three nanocrystalline dye- sensitized solar cells. You will then measure and compare your solar cells under different lighting conditions. * Materials - 3 conductive slides coated with Titanium Dioxide - 3 conductive slides (no TiO2 coating) - 6 binder clips - 1 HB pencil - Multimeter - 2 wire leads - Iodide electrolyte solution - 1 ml pipette - Cotton swabs - Raspberries - Blackberries - Deionized Water - Ethanol (ethyl alcohol) - 2 coffee filters - 2 plastic cups (1 blue and 1 red) - 1 plastic spoon - Petri dishes - 10 ml graduated cylinder Procedure * You must wear gloves and safety glasses during this lab. A. Preparing the Dye You will make three different dyes, one from raspberries, one from blackberries, and one from equal parts of raspberries and blackberries. To make the raspberry and blackberry dyes: 1. In one side of a petri dish, add 5-6 raspberries (OR 3-4 blackberries), and 1-2 ml of deionized water. 2. Crush the berries using a spoon or fork until the mixture is soupy. 3. Pour the crushed berries into a coffee filter over the other side of the Petri dish. Gently squeeze the filter so that the liquid dye flows into the Petri dish. Be careful not to tear the filter. For the third dye, combine equal parts of the two strained dyes in another Petri dish. B. Building the Cell 1. Each group should have 6 slides, enough to make 3 solar cells. 3 of these slides have already been coated with titanium dioxide. These can be identified by the white rectangle of titanium dioxide film. Be careful not to touch the coated side of the glass. Handle the slides by their edges. 2. Place each titanium dioxide coated slide face down in the petri dishes containing your dye, one per dish, and leave them for approximately ten minutes. The titanium dioxide film should absorb the dye. If white titanium dioxide can still be seen on either side of the slide after the initial soak, place the slide back in the dye for five more minutes. 3. While your slide is soaking, prepare the counter electrode slides (3 of them). Using the * Solar cell kits from Some images taken from 1

2 multimeter, set to ohms, identify which side is conductive; the reading of the conductive side will be between 10 and 30 ohms. Take the graphite pencil and apply a heavy film to the entire conductive side of the slide. Be careful not to miss any spots. FOLLOW STEPS 4 6 FOR EACH SLIDE, ONE AT A TIME. The dyed slides must not be exposed to the air for too long, so for each slide, complete these three steps in under 60 seconds. 4. When the dyed slide is ready, remove it from the dye. Rinse the dyed slide with deionized water and then with ethanol. The ethanol pulls any excess water trapped in the dyed titanium dioxide. Blot the slide dry with a paper towel but make sure not to damage the titanium dioxide layer. 5. Place the dye- stained slide on the counter, with the titanium dioxide side face up. Place the graphite coated slide face down on top of dyed slide so that the conductive sides are facing each other. Offset the glass slides so that all of the titanium dioxide is covered and the 5mm strip not coated by titanium dioxide is exposed. 6. Place the two binder clips where the slides overlap (the arrows in the picture on the right) to hold the cell together. AFTER COMPLETING STEPS 4-6 FOR ALL THREE SLIDES, MOVE ON TO STEP Add one to two drops of electrolyte solution to one edge of the slides. Alternately open and close the binder clips so the solution is drawn into the cell by capillary action. Make sure that all of the dyed titanium dioxide is contacted by the electrolyte. Wipe off excess electrolyte from exposed areas of the glass using cotton swabs dampened with ethanol. C. Collecting Measurements Attach leads to cell as shown below (DO NOT remove the binder clips). Then attach the probes from the micrometer to the other ends of the leads. Determine which side of the solar cell should be facing the light source by checking which side produces the most current and voltage. 2

3 1. Which slide is the negative electrode and which slide is the positive electrode? 2. Record the current and voltage for each solar cell when in direct sun, when in the shade and when under the lights in the room. Be sure to record the correct units with your measurements. Direct Sun R.5 V,.43 V,.4 V,.37 V,.1 V B.34 V,.46 V,.3 V,.17V M.45 V,.53, V,.41 V,.36 V.69 ma, 1.27 ma, 10 ma,.26 ma,.6 ma.69 ma,.65 ma,.15 ma.004 ma.56 ma,.31 ma,.2 ma,.8 ma Shade R.27 V,.069 V,.37 V,.161 V,.03 ma,.015 ma, 0 B.12 V,.23 V,.003 ma M.32 V,.29 V.003mA Indoors 3. With your most powerful solar cell, record the current and voltage when the solar cell is directly facing the sun and facing at a 75- degree angle to the sun. Include the units with your measurements. If you do not have measurements for this question, make an educated guess as to what you think would happen when the solar cell is turned towards the sun and turned away from the sun. You do not need to provide numbers, just a qualitative description. 3

4 4. With the spectroscope, look at the spectrum of the direct sunlight through each of the colored cups and list what colors/bands you see. (DO NOT LOOK DIRECTLY AT THE SUN) 5. Record the current and voltage for each cell when covered by each of the different colored cups. Include the units with your measurements. 6. Switch solar cells with another group, and measure the voltage and current in direct sun. Include the units with your measurements. When you are done, switch back. Use the underlined values from question 2 as your measurements for another group. 7. Can you use one of your solar cells to light up a red LED? A white LED? You should be able to answer these questions without actually trying to light up the LEDs. First make a hypothesis about whether each LED will light (YES or NO), and then get the LEDs from Darby or Stacy to test your hypotheses. Make your hypotheses based on your values from question 2 in direct sun and explain why you think they are correct. D. Cleanup 1. Place all used fruit, paper, and plastic forks and spoons in the trash. 2. Wash all glassware with soap and water. Finish with a deionized water rinse. 3. Disassemble your solar cells and rinse them with ethanol. 4. Return all materials to the appropriate locations. Additional Questions for Lab Report 1. Which solar cell produced the most power in direct sun? (Power = current * voltage) Give some scientific reasoning as to why this solar cell produced the most power? Indicate which values of current and voltage you are using for each cell. 2. Did the measurements of your solar cells match the measurements of the other group s solar cells (within a small margin of error)? If not, give some reasons why this could happen? Compare your measurements to the underline measurements from the table in Step 2 above. If you were not able to collect a measurement for a particular cell, explain why this happened. 3. Assuming that the insolence in direct sun is 200 W/m^2 and that each solar cell is 2 cm by 2cm, compute the efficiency of each of your solar cells. Show your work.. Indicate which values of current and voltage you are using for each solar cell. 4

5 4. How did the change in the angle of the solar cell affect the current and voltage? Based on this observation, how important do you think it is to have solar cells that can be repositioned based on the location of the sun? Is it worth the extra resources and energy needed to support this feature? Answer this as best you can given on your understanding of solar cells. If you don t have any or enough quantitative data (from your measurements) to base your answer on, describe what kind of data you would need to answer this question and why you would need it. 5. How did covering the cells with the colored cups affect the current and voltage of each solar cell? Was each solar cell affected in the same way? What do you think caused this change in voltage and current? 5