An organic solar cell is a low-cost alternative to the silicon photovoltaic cells currently used to harness the Sun’s energy to produce clean, renewable electricity. The cells are actually a polymer sandwich — one layer contains electrons and the next layer is electron-poor. Tiny channels in the electron poor layer allow electrons to flow producing an electric current.
“Making organic solar cells more efficient is crucial to making them viable,” said David Ginger, University of Washington. And the key to improving solar cell efficiency is accurately modeling how electrons are flowing through the cell.
Many models that measure organic solar cell efficiency assume that the polymers in the solar cell sandwich are uniform. According to Ginger, this assumption is akin to trying to improve highway efficiency by increasing the speed limit without taking into consideration how on-ramps and off-ramps alter the flow of cars traveling along the highway. In reality, the polymers layers are pock-marked with small bubbles and channels that form during the baking process. These channels alter the characteristics of the polymer and change the way the electrons move, similar to the merging cars on a busy highway. But it is possible to alter the number and configuration of these channels simply by adjusting the backing time and temperature when making the polymer.
By understanding the configuration and shape of the nanoscale-size channels, engineers may be able to design a more efficient organic solar cell material.
Unfortunately, the channels and bubbles are difficult to study because they are tiny, on the order of the nanoscale – roughly 10,000 times smaller than a human hair. Ginger’s research team developed a creative way to measure currents through these tiny channels. They used a microscopic probe that resembles the needle on an old record player to record electrical currents from sections of the solar cell that are no more than 20 nanometers across.
Scientists hope that in the future these plastic solar cells will be added to bags and back packs to power small electrical items, like mp3 players, cell phones, and smart phones and, eventually, produce enough electricity to contribute to the electric grid.
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