Solar cells made with biodegradable components are extremely rare. Ayomi Perera, a Kansas State University doctoral student, created dye-sensitized solar cells out of a protein produced by bacteria and a dye less toxic than traditional dyes. This attractive new research might make solar power even greener.
Dye-sensitized solar cells have been around for decades, and although production is affordable, a few problems burden their potential. Their energy conversion efficiency is only about 11 percent. In the standard p-n junction photovoltaic cells, advances in technology have enabled commercial production of cells with efficiencies upward of 20 percent. In general, dye-sensitized cells continue to improve in efficiency and design, but Perera decided to focus on another problem—the dyes and solvents commonly used in dye-sensitized solar cells can be toxic to people and the environment.
Based on the principle of photosynthesis, the process in which plants convert sunlight into food, modern dye-sensitized cells are made of conductive glass with a porous layer of titanium dioxide nanoparticles covered in a molecular dye. The dye absorbs sunlight just as chlorophyll does in plants. With immersion in an electrolyte solution (often a corrosive material), a platinum-based catalyst adds the final component necessary to create electricity via the dye-sensitized cells.
Perera turned to bacteria for help in creating a less toxic version. Under the guidance of Professor Stefan Bossmann, Perera investigated the bacteria Mycobacterium smegmatis. The strain is relatively safe and easy to grow. It produces MspA, a protein which, when purified, has “so many applications due to its interesting surface chemistry,” according to Perera. Production of solar cells with a protein component became the focus of her research. The protein is mixed with an environmentally friendly dye, and a coat of the mixture is applied to the solar cells. Sunlight hits the dye, which produces electrons, and the protein transfers them in one direction, creating an electric current.