Blueberries may be key to cheaper solar power

By Peter J. Brown
Bangor Daily News

Professor Aldo Di Carlo in the Department of Electronic Engineering at the University of Rome Tor Vergata in Italy is a big fan of blueberries. He likes them, but not only to eat.

When Di Carlo sees a blueberry, what he really sees is a potential energy source. He is leading a research team that is exploring the use of several dyes, including pigments derived from blueberries, to improve solar panel production. The research is focused on the role of organic semiconductors in what are known as dye-sensitized solar cells, or DSSCs.

Eliminating most if not all silicon in the solar panel production process is the primary objective. What might emerge is a much cheaper, semi-transparent solar panel that offers greater flexibility.

"Here in our lab in Rome, we are comparing different plant pigments. It is quite clear that chemical synthesis can produce artificial organic molecules that are able to significantly improve DSSC efficiency," he said, adding that hybrid DSSC and organic semiconductor research is under way in the United States as well as at various universities around the world.

The president of a large Maine blueberry company said he hadn’t heard of the research under way in Italy but was intrigued by it.

"Wyman’s is not aware of any research of this sort, nor of any large-scale dye uses for blueberries, but other processors may be more active in that customer arena," said Ed Flanagan, president of Jasper Wyman & Son in Milbridge, the nation’s largest supplier of wild blueberry products. "The potential for wild blueberries continues to amaze us, whether in terms of the scientific health properties of our little fruit or in an application of this sort."

Blueberries contain a high concentration of a natural pigment based on the anthocyanine molecule that can be used as the dye in question. However, other dark-colored fruits, including blackberries, are possible sources of this dye as well.

Extraction of the anthocyanine pigment is accomplished through a fairly simple and quick procedure involving chemical purification, according to Di Carlo.

As far as the spectral properties of natural pigments in general are concerned, these dark-colored fruits are almost in a class by themselves, outperforming most other plant species when it comes to the spectral absorption of sunlight. In other words, the absorption spectra of the dye derived from these fruits are superior when it comes to matching the spectral distribution of sunlight, according to Di Carlo.

"At the moment, the use of natural dyes in solar cells is quite compelling because it demonstrates that with simple, organic ingredients, one can create electrical power from sunlight," Di Carlo said.

Di Carlo acknowledges that the power conversion efficiencies achieved thus far by DSSCs fabricated with organic ingredients are considerably lower than the efficiencies achieved with optimized synthetic molecules. Existing silicon-based solar panels achieve an efficiency rate of roughly 15 percent, whereas solar panels made with blueberries achieve only 1 percent efficiency today. By using synthetic dyes, efficiency rates of 10 percent or more can be achieved.

So the research continues. And indeed, there appears to be more and more research activity under way worldwide each year involving innovative hybrid devices infused not only with fruit pigments, but also with chlorophyll, according to Di Carlo.

"This worldwide quest for novel energy sources is gaining momentum, and the search for natural sources of dyes is appealing for obvious reasons. At the moment, this exciting research proceeds only in university labs," he said.

Di Carlo added: "We believe that once we identify new, lower-cost processes which can purify and stabilize this blueberry dye extract, we will be helping not just to open the door to a new generation of solar panel technologies, but also to more efficient procedures for the mass-scale production of new dyes for food products and paint."

Peter J. Brown