Instructions for building your own Gratzel solar cell:

 

With a few simple materials you can create your own Grätzel solar cell.  This project is cross-curricular in nature; there is both chemistry and physics involved.  There is also some connections to biology as the cell energizes electrons similar to photosynthesis.

 

There are other instructions available and I've included a link to these.

 

 

For each step, I included pictures and have short video clips you can watch. The videos on are my youtube page under the Gratzel solar cell playlist.

 

Common Household Chemicals:
Distilled white vinegar
Ivory clear dishwashing detergent or Triton X-100
Distilled water

Basic Lab Apparatus and Accessories:
Mortar and Pestle
Glass stirring rod
Microscope slide
Dropper bottle or eyedropper
Washbottle
*Soft Graphite pencil or graphite stick
Candle
*Small binder clips (2 per cell)
Multimeter
Alligator clip leads (2 per cell)
Small Shallow dish or petri dish (one per dye)
Kleenex
Scotch Tape
Q-tips cotton swabs

Ingredients to make the dyes:
Blackberries
Raspberries

Speciality materials:
*Conductive glass slides (2 per cell)
*Nanocrystalline Titanium Dioxide (TiO2) powder
Ethanol or Isopropanol
*Triiodide electrolyte Solution

Kits are available with enough specialty materials to make 5 solar cells are available for purchase from:

http://ice.chem.wisc.edu/catalogitems/ScienceKits.htm#SolarCell

Those items from above in the kit are marked with an asterisk (*)


Procedure:

Wear Eye Protection and Chemical Gloves

Coat slides with nano Titanium Dioxide (these steps can be done ahead of time). [steps 1-5]

1. To make the nano Titanium Dioxide suspension, add 10 mL vinegar (or dilute acetic acid) gradually to 6 g Titanium Dioxide, stirring and grinding with a mortar and pestle until smooth and lump-free (about 5 minutes). You should have a smooth solution that looks like White-Out and is just barely thin enough to be taken up into an eyedropper. Add one drop of clear dishwashing detergent (Ivory) or a few drops of the Triton X-100 surfactant, mix lightly, and let sit for 15 minutes. This surfactant, and the grinding, helps break up the nanoparticles. The mix you obtain should have a smooth consistency, somewhat like latex paint. You may need a bit more of the Titanium Dioxide or vinegar to reach this consistency. This is enough mixture to coat more than one plate.

 

 

2. Determining the conducting side of one of your glass plates. Set the multimeter to measure resistance and choose a low scale [100 Ohms, for example]. Take the two ends of the multimeter leads and measure the resistance along the entire length of the glass plate. Do this for both sides of the glass plate. The conducting side will have a resistance of 20-30 Ohms and the non-conducting side will show infinite resistance (this may be displayed as a '1' on your multimeter). Having determined the conducting side, you are now ready to prepare your Titanium Dioxide coated plate.

 

3. Using scotch tape, tape the slide to the table, conducting side up. Tape along three sides of the glass so tape covers about 3 millimeters of the glass along those three edges and is securely attached to the table. Wipe off any fingerprints or oils using a tissue wet with ethanol or isopropanol (2-prop). Let dry.

 

4. Using the eyedropper add 3-5 drops of the Titanium Dioxide mixture to the top of the slide along a row. Deposit a uniform, thin layer across the unmasked portion of the slide. There are several ways to do this. Drawing a stir-rod horizontally down the slide works well or use a glass microscope slide to gently spread the mixture evenly over the exposed surface. Do not press too hard on the stir-rod or glass slide as this may cause breakage. Allow the slide to dry a few minutes before removing the tape. After a few minutes, remove the tape from the slide without scratching the coating.

 

5. Now we must sinter the coated slide. Sintering is a method for adhering the Titanium Dioxide particles together so they are touching one another. There are several documented ways to sinter the coated slide.

a) Turn on a Bunsen burner and set the flame to blue. Securely grip the glass slide along one of the uncoated edge, making sure the coated side is facing upwards. Hold the glass about 10 cm above the blue flame. The white Titanium Oxide coating will turn from a white color to brownish after approximately one minute and then gradually turn white again. At this point the sintering process is complete. This process should not take more than three minutes to complete. Allow the plate to cool down.

 

 

or


b) Heat the glass on a very hot hotplate in a hood for 10-20 minutes. The surface turns brown as the organic solvent and surfactant dries and burns off to produce a white or greenish titanium dioxide coating. (Note: this requires a plate that gets quite hot.) Allow the glass to slowly cool by turning off the hotplate. I had good luck with this method.

 

or

c) Put the glass slide in an oven broiler for about 60 minutes, coated side up to sinter the film. Make sure the slides turn yellow and then white again. Let it cool slowly to room temperature. I did not try this method.

The resulting TiO2 layer is nanoporous, meaning that it has pores, like a sponge, which are only a few nanometers (10-9 m) wide. The TiO2 particles themselves are about 20 nm wide. The film is about 7-10 micrometers thick (the thickness of the Scotch tape). The sintered slides can be stored in air for later use.


 

Preparing the graphite (carbonized) glass slide. (step 6).

 

6. While the coated plates are cooling, prepare a second blank glass plate with a graphite or soot coating. Take a second glass slide and again find its conducting slide using a multimeter (see step 2 above). Wipe off any fingerprints or oils using a tissue wet with ethanol or isopropanol (2-prop). Let dry.

There are several ways to give the slide the graphite or soot coating:

Either a) or b) can be done or both. I did both.


a) Use a #2 pencil or graphite pencil to evenly coat the conducting surface with a layer of graphite. Leave a small section of the glass surface clear for later connecting with the alligator clip wire.

or

b) Using the tongs, pass the glass side conducting side down, through a candle flame to coat the conducting side with carbon (soot). For best results, pass the glass piece quickly and repeatedly through the middle part of the flame. Wipe off the carbon along the perimeter of three sides of the carbon-coated glass plate using a Q-tip cotton swab.

 

 


Preparing the dye and staining the Titanium Dioxide coated slide (steps 7-9)

7. There are many possible dyes that can be used. The following represent options given in directions obtained for the project. I used blackberries, raspberries, a blend of pomegranite-cranberry juice, chlorophyll, hibiscus tea, black tea, and a combination.

a) Berries
Blend or crush fresh in a blender or by hand, adding a tablespoon of water for every 10 blackberries. You will need about 10 milliliters of fruit solution. Boil gently for several minutes on a hot plate. One can use different berries: cranberries; strawberries; raspberries; pomegranate seeds; or bing cherries. If using frozen fruit, simply thaw and remove the juice from the bottom-no dilution or boiling is necessary. The berries provide anthocyanin, a pigment that gives the fruit color.

 

b) Hibiscus Tea
Weigh out 1g of hibiscus tea leaves and add them to 50ml of water in a 100ml beaker. Using a hot plate, allow the solution to boil for a couple of minutes. The solution will become an intense purple color.

c) Onion Skin
In a 100ml beaker, add 5 pieces of onion skin and 50ml of water. Using a hot plate, allow the solution to boil for a couple of minutes. The solution will become an intense yellow/orange color.

d) Turmeric Powder
Weigh out 0.3g of turmeric powder and add it to 50ml of water in a 100ml beaker. Using a hot plate, allow the solution to boil for a couple of minutes. The solution will become an intense yellow color.

e) Black tea
Place a black tea bag into beaker with 50ml of boiling water. Using a hot plate, allow the tea bag to boil in water for a couple of minutes. The solution will turn a brown color.

8. Now we must dye the coated Titanium Dioxide glass slide. Take the dye juice and place it in a shallow clean dish or petri dish. Put the Titanium Dioxide glass slide, coated side face down in the juice. It should be soaked in the dye for about 10 minutes until no white Titanium Dioxide can be seen and it takes the color of the dye.

 

 

9. Rinse the slides in water, then in isopropanol or ethanol, using a washbottle, and blot dry with a tissue. The isopropanol or ethanol acts to remove water from the porous Titanium Oxide coating. These dyed Titanium Dioxide coated slides should be used immediately once dry.

 


Final assembly of the solar cell (steps 10-11).

10. The solar cell is made from the two glass slides: the graphite slide and the dyed Titanium Oxide slide. Put the graphite-coated slide face down on top of the dyed-soaked Titanium Oxide slide. The two slides should be placed offset to allow room at the ends to place an alligator clips. This creates a 'sandwich.' Clamp the two glass plates together using binder clips or make clamps using paper clips.

 

 

 

11. Add a few drops of a triiodide electrolyte solution to the crease between the two slides. Capillary action will cause the KI3 solution to travel between the two plates and stain the entire inside of the slides. Carefully wipe any excess triiodide solution using a tissue.

 

 


Testing your Gratzel cell (step 12).

12. Use the sun, overhead projector, or a bright light for illuminating the solar cell. Attach the two alligator clip electrical wires to the overhanging edges of the glass slides (opposite the binder or paper clips). The wire attached to the Titanium Dioxide coated slide is the negative terminal. Attach the other end of the alligator clip to the negative lead of the multimeter. The graphite coated side is the positive lead of the solar cell. Attach the other end of the alligator clip from this end to the positive lead of the multimeter. Move the multimeter setting to read DC volts. The maximum voltage in direct sunlight can range between 0.1 and 0.5 Volts. You can also read the current by changing the multimeter to read DC current.

 

 


There are other activities available for students to do with their Grätzel solar cell. I have placed these in another link.


Alan D. Gleue

Lawrence High School

Lawrence High School Science Department

back to Mr. Gleue's home page


Created: June, 2008.
Modified: July, 2008.