The key to using silicon in electronic devices such as transistors and solar cells lies in doping, or adding in small quantities of other elements, to create an excess of electrons (n-type) or positively charged holes (p-type) that change the material's conductivity. N-type and p-type silicon are butted together to form p-n junctions, the basic building blocks of electronic devices such as solar cells, light-emitting diodes, and transistors.
For years, researchers have tried to do something similar with quantum dots, tiny semiconductor crystals a few nanometers in diameter. Now, a team of Israeli researchers has reported success. They have doped indium arsenide quantum dots to create n-type and p-type materials. The advance, published in the journal Science, could lead to new types of efficient, cheap, and printable thin-film solar cells.
Quantum dots hold promise for low-cost solar cells because they can be made using simple, inexpensive chemical reactions. Scientists have calculated that quantum dots could be used to make thin-film photovoltaics that are at least as efficient as conventional silicon cells, and possibly more efficient. The higher possible efficiency is because nanocrystals made of certain semiconductors can emit more than one electron for every photon absorbed. Plus, tweaking their size and shape changes the colors of light they absorb. "We could tune the nanocrystal absorption to match the solar spectrum," says Uri Banin, a professor of chemistry at the Hebrew University of Jerusalem who led the new work.
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