Drawn together by the force of nature, but pulled apart by the force of man -- it sounds like the setting for a love story, but it is also a basic description of how scientists have begun to make more efficient organic solar cells.
At the atomic level, organic solar cells function like the feuding families in Romeo and Juliet. There's a strong natural attraction between the positive and negative charges that a photon generates after it strikes the cell, but in order to capture the energy, these charges need to be kept separate.
When these charges are still bound together, they are known to scientists as an exciton. "The real question that this work tries to answer is how to design a material that will make splitting the exciton require less energy," said senior chemist Lin Chen of the U.S. Department of Energy's (DOE) Argonne National Laboratory.
Excitons can be thought of as a sort of "quasiparticle," Chen said, because they exhibit certain unique behaviors. When the two charged regions of the exciton -- the electron and a region known as a "hole" -- are close together, they are difficult to pry apart.
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