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nanotimes Research

10-10/11 :: October/November 2010

Solar Cells // German HZB Researchers Solve the Case of Lost Current in Organic Solar Cells

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ogether with Scottish researchers, scientists at Helmholtz-Zentrum Berlin (HZB) have deve-

loped a method that uses the magnetic finger- print of the charge-carrying particles to reveal exactly how electricity is being lost. They did so by manipulating the magnetic properties of these particles.

Being made from carbon compounds, organic solar cells are also known as plastic solar cells. The heart of the cell is a layer only a hundred milli- onth of a millimetre thick, made of two compon- ents, polymers and soccer ball-shaped fullerenes, mixed together.

When light strikes a layer of this mixture, the polymer component is set into an excited state, dubbed an exciton. When an exciton bumps into a fullerene, an electron jumps over to the soccer ball molecule and a “hole” remains behind in the polymer. So that current can flow, the electrons and holes must travel to their respectively opposi- te contacts.

The electrons travel via the fullerenes while the holes travel via the polymer chain. The holes, which scientists call polarons, can obstruct one another along their path and thus reduce the