Under the influence of light, electrons have been shown to move freely in layers of linked semiconductor nanoparticles. The breakthrough could lead to the development of cheap and efficient quantum dot solar cells, say researchers at Delft University of Technology's chemical engineering department and the Kavli Institute.

Right now, crystalline silicon solar panels are expensive to produce. Cheaper solar cells are available but are inefficient; e.g, an organic solar cell has a maximum efficiency of 8 percent, the researchers say. One way of increasing the efficiency of cheap solar cells is with the use of semiconductor nanoparticles, called quantum dots. In theory, the efficiency of these cells can be increased to 44 percent, in part because of an “avalanche effect” demonstrated by researchers from TU Delft and the FOM Foundation in the Netherlands in 2008.

In the current solar cells, an absorbed light particle can excite only one electron — creating an electron-hole pair — while in a quantum dot solar cell, a light particle can excite several electrons. The more electrons that are excited, the greater the efficiency of the solar cell.

Up to now, the creation of electron-hole pairs under the influence of light was demonstrated only within the limits of a quantum dot. To be usable in solar cells, it is essential that electrons and holes can move — this is what creates an electrical current that can be collected at an electrode.

Researchers now have demonstrated that the electron-hole pairs also can move as free charges between the nanoparticles. They linked nanoparticles together, using very small molecules, so that they were very densely clustered while still remaining separate from each other. The nanoparticles are so close together that every single light particle that is absorbed by the solar cell actually causes electrons to move.

The researchers published their findings in Nature Nanotechnology.

See also: QDs Improve Next-Gen Solar Cells by 6%

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