Building a solar cell from white paint and berries: a tutorial

When chemistry professor Hal Van Ryswyk invited the admission staff to test out the new first-year chem lab, we jumped at the opportunity. I mean -- solar cells from paint and berries? It didn't seem possible. And a chance to wear these stylish goggles again? Ah, high school flashbacks.




Unlike most actual labs at Mudd, Prof. Van Ryswyk had absolutely everything set up for us and guided us through the entire process step-by-step (normally we encourage students to actually read the directions). And since some of Prof. Van Ryswyk's research involves creating low-cost photovoltaics, this was a good introduction to how chemists are trying to save the planet. Here's the how-to, much of which is taken verbatim from the frosh chem lab handout:



1) Grind about .5 grams of nanocrystalline titanium dioxide (found in white paint).

2) Tape off three sides of a small piece of conductive glass, then spread on a thin layer of the nanocrystalline titanium dioxide. After the paint dries, pull off the tape, and place paint side up on an extremely toasty hot plate for twenty minutes. (You can see the hot plate in the foreground of the picture below.)

3) Heat a second piece of tin oxide glass, conducting side down, over a candle flame to coat the conducting side with carbon. (Tongs are very important for this step!) After the glass cools, wipe off three of the edges with a q-tip, trying to keep the shape similar to the paint on the other piece of glass.

4) Grind the berries of your choice! Thyra and I used bing cherries, Peter used raspberries, and Raissa used blackberries. Later, in the grand reveal, I'll tell you which worked best.

5) Staring helps the nanoparticles sinter faster.

6) Assemble your two glass plates into a sandwich with coated sides together, but offset so that uncoated glass extends beyond the sandwich. Attach with binder clips. It's nice to do this step with a professor, so that when you screw it up, as most of us did, he can fix your sandwich for you. Add a few drops of a triiodide solution to the edge of the plate.

7) Connect a multimeter using an alligator clip to each plate. Turn on the overhead projector.

8) Watch the computer measure the current and voltage produced by the solar cell. Have Prof. Van Ryswyk do the math calculations for you to find the overall efficiency of your cell. First-years, sorry, you have to do the math yourselves. Bring a calculator!

The big winner? Blackberries! Raissa's blackberries far outperformed the bing cherries (not your best bet for photovoltaics) and moderately outperformed the raspberries. In fact, Raissa's blackberry cell set a Mudd record and Prof. Van Ryswyk printed out an extra copy of the results for his lab. Go Raissa! Go blackberries! Antioxidants and photovoltaic potential all in one delicious package!