A New Ingredient for Solar Cells - Raspberries

Solar cells basking in the sun

Lately, solar cells have been in the news almost as much as Brittany Spears (ok, well not that much). Between global warming, 100$ a barrel oil, and energy security, harvesting the rays from the sun has never been so in vogue. Traditional solar cells use expensive semiconductor grade silicon (the same material used in an Intel processor chip) and are exceptionally fragile. And although steady scientific and technical advances have helped solar cells harvest more and more light while hitting the wallet a little bit lighter, progress hasn't been fast enough to keep up with the demand for cheaper, more efficient cells.

To keep driving down the cost, a whole suite of new solar cell technologies has been rolling off the line ranging from “cheaper than coal” thin film solar cells to potentially dirt-cheap polymer based cells.

Titanium oxide particles with dye on surface

But there is another less sensationalized technology that is also making steady advancements in the solar world. This technology, dubbed the "dye sensitized" solar cell, uses titanium oxide nanoparticles with a thin layer of "dye" stuck to the particles' surface. The dye harvests the light and then transfers the energy into the titanium oxide. Next, the oxide transmits the energy to a conductive base layer that whisks away the generated electricity to the power grid, a light bulb, a Nintendo Wii or any other electrical device the heart desires.

The good news is that titanium oxide is cheap; it's the same material used in toothpaste and paint to produce that pleasing white color. The bad news is that the dye is pricey, although (fortunately) only tiny amounts are needed. In order to maximize solar energy harvesting, sophisticated dyes have been synthesized for optimal light absorbing. However, recent research has found a much more natural solution; enter the humble raspberry.

The humble raspberry and friends

It turns out that raspberry juice can harvest light in a manner similar to the more sophisticated dyes. Specifically, raspberry juice contains anthocyanins, a compound capable of both harvesting light and adhering to titanium oxide particles. The down side is that the efficiency (how well the solar cell converts sunlight into electricity) is exceptionally low and usually hovers around 1% (for reference, cells using artificial dyes have an efficiency of ~12%). Efforts are being made to perfect the fabrication techniques in order to increase the raspberry solar cell's efficiency, but it's unlikely that it would ever rival artificial dyes. Other fruits and berry juices such as cherries, blueberries, and pomegranate have also been successfully used as dyes.

While venture capitalists aren't exactly chomping at the bit to invest in these solar cells, it's a fascinating little bit of pop culture science. Who knew the raspberry would ever make such a contribution to the world of solar cell research?

For more information on the "raspberry" solar cell, check out these academic papers or these simple guides on how these cells can be constructed with the most basic tools.