265 Massachusetts Avenue, Cambridge, MA 02139 csf@cambridgesciencefestival.org

A Berry Efficient Solar Cell

A short walk through the Cambridge Science Festival will reveal an important fact: the festival is not just for science. It’s for technology, presentations of innovative ideas, and fun, hands-on activities. The CSF offers such a wide variety of activities that it has attracted cool, sometimes strange, modern technologies. Among the strangest is the blackberry solar cell – no, not a solar cell for the BlackBerry phone, we’re talking about the actual fruit – small seeded dark berries whose juice can be used to harvest energy from the sun. To see this technology in action and make a solar sell for yourself (for free!) head over to

the Cambridge Public Library at 449 Broadway between 12:30pm – 1:30pm or 2:00pm – 3:00pm for “The Blackberry Solar Cell: A green Chemistry Activity.” This activity is definitely for all ages.

If blackberries can be used to capture solar energy, what other unusual uses might fruit have? Perhaps a postage stamp made out of lemon rind, or a dress made out of apples?

An investigation of the many uses of fruit first reveals the most common uses: food, beverages, gifts and decorations. After all, where would we be without grape juice, fruit baskets, and holly at Christmas?

After a bit more research, increasingly unusual uses for fruit show up. Some uses seem to be completely unrelated to fruit. The following products are good examples: various type of pain killers – opium which contains morphine and codeine is made from the fruits of opium poppy; dyes – cherries and walnuts can be used as natural dyes; musical instruments – gourds are dried and hollowed out to make instruments; skin care products – supposedly, applesauce makes a great facial mask; and leather polish – banana rinds will do the trick!

Looking further into fruity practices, medicinal applications seem quite common. It is amusing, or possibly disturbing, that nearly every fruit has been claimed to have some medicinal benefit. Cranberries heal UTIs, rose apples are a brain and liver stimulant, figs cure warts, and goji berries boost your immune system. This widespread claim that “fruit is medicine” either suggests that fruits are generally good for one’s health and contain vitamins and minerals that promote wellness, or it suggests that people are desperate in the search for cures to yet incurable diseases. Most effects of fruit on health are not scientifically, clinically, or even methodically tested/proven to be beneficial. Therefore claims of healing fruit should be taken with a grain of salt whereas a product like a solar cell can be shown to work without doubt. Either way, it can’t be denied that fruit has had a large effect on the health of the world, whether as a medicine or simply a good source of nutrition.

After taking a look at some alternative uses of fruit, a blackberry solar cell is undoubtedly the most unique. Imagine a small electronic device whose materials include (1) indium tin oxide conducting glass, (2) iodide electrolyte solution, and (3) blackberry juice. That third ingredient is slightly shocking! However, the blackberry juice plays an important role in the solar cell, acting as a dye that first absorbs the light from the sun that the solar cell can then convert to electricity. If you’d like to see this for yourself, head over to the Blackberry Solar Cell event.

It’s pretty clear that fruit is not common in electronics. Why would someone think to use blackberry juice as a solar cell? In an increasingly green society, looking toward more natural and non-toxic materials is beneficial for the inventor and the environment. This presents an opportunity to introduce more natural products into modern technology, like trees grown for biomass to create renewable energy, or corn grown for ethanol. These green technologies already exist. What will be next?

Apple dress adapted from this photograph.



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