Down the Line: Plastic Solar Cells
Researchers at Lawrence Berkeley National Laboratory and the University of California (Berkeley, CA) have developed a semiconductor-polymer photovoltaic material. They claim that it can be made in the same nearly infinite variety of shapes as pure polymers.
"The advantage of hybrid materials consisting of inorganic semiconductors and organic polymers is that potentially you get the best of both worlds," says Janke Dittmer, a staff scientist working on the project. "Inorganic semiconductors offer excellent, well-established electronic properties, and they are very well-suited as solar cell materials. Polymers offer the advantage of solution processing at room temperature, which is cheaper and allows for using fully flexible substrates, such as plastics."
The use of solar, or photovoltaic, cellsdevices that can absorb and convert light into electrical powerhas been limited because production costs are very high. "Even the fabrication of the simplest semiconductor cell is a complex process that has to take place under exactly controlled conditions, such as high vacuum and temperatures between 400 and 1,400 C," explains Dittmer.
Ever since the discovery of conducting plasticspolymers that feature conjugated double chemical bonds that enable electrons to move through themthere has been interest in using these materials in the fabrication of solar cells. According to Dittmer, plastic solar cells can be made in bulk quantities for a few cents each. However, the efficiency with which they convert light into electricity has been quite poor compared to the power-conversion efficiencies of semiconductor cells.
At the heart of all photovoltaic devices are two separate layers of materials: one with an abundance of electrons that functions as a "negative pole" and one with an abundance of electron holesvacant, positively charged energy spacesthat functions as a "positive pole." When photons from the sun, or some other light source, are absorbed, their energy is transferred to the extra electrons in the negative pole, causing them to flow to the positive pole and create new holes that start flowing to the negative pole. This electrical current can then be used to power other devices, such as pocket calculators.
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