They look other worldly, like whimsical spaceships crafted from diamonds and glass by alien engineers. More fantastic still, these intricate crystalline creations are microscopic, and they are alive. However, these are not invaders from another planet. They are from Earth, and some creative researchers from Oregon State University think that these creatures may provide us with the next generation of solar cells needed to save our planet.
These microscopic living things are a type of single celled algae, called diatoms. They are commonly found in waters all over the world. What gives them their beautiful appearance and makes them useful for researchers is that they produce intricate shells made of silicon dioxide. These glass-like outer coverings come in a myriad of forms that range from simple to mind bogglingly complex.
Many of these shells are being studied to see if they have applications in the field of nanotechnology. This is the cutting edge area of science and engineering that deals with structures and even machines so small that they are measured in billionths of meters. In recent years, nanotechnology, or nanotech, has been the focus of a great deal of scientific and media attention, because it offers advances ranging from lighter, stronger materials to radically improved medical treatments.
One particular group of diatoms, known as Pinnularia, is able to produce silica structures that are generating a lot of nanotech interest, because they may offer us a new way to produce a more efficient type of solar cell. Conventional solar cells tend to be heavy, easily broken and will work only in relatively sunny weather. The Oregon State and Portland State team, consisting of Clayton Jeffryes, Timothy Gutu, Jun Jiao and Gregory L. Rorrer has found an innovative way to use the structures produced by the diatoms to manufacture something called dye-sensitized solar cells. In these cells, the incoming particles of light, or photons, bounce around and collide with dye particles, creating electricity. This type of cell has a number of advantages over the conventional type. They are lighter and made from more environmentally friendly materials. They are also more flexible, more robust, meaning longer lasting and harder to break, and unlike typical solar cells, they can operate in lower light conditions, such as on cloudy days.
Dye-sensitive solar cells can be manufactured now using conventional means, but the ones created with the help of the diatoms offer far higher efficiencies. In the first step of the process, a thin layer of the living diatoms is allowed to settle onto a conductive glass surface. Then the living material is removed, leaving behind a template of the silica skeletons. Next, the template is covered with nanoparticles of titanium dioxide, which act as a semiconductor. The result is a solar cell that provides all of the advantages of the ordinary dye-sensitive cells, but with three times the electrical output. According to Gregory L. Rorrer, one of the Oregon team members, “Conventional thin-film, photo-synthesizing dyes also take photons from sunlight and transfer it to titanium dioxide, creating electricity. But in this system the photons bounce around more inside the pores of the diatom shell, making it more efficient.”
The results of the Oregon State and Portland State team’s work appeared originally in ACS Nano, a publication of the American Chemical Society, and the Journal of Materials Research, a publication of the Materials Research Society. This is yet another creative example of using the wonders of nature, in this case the nano-sized shells of algae, to help us improve our world and reduce our impact upon it.