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Quantum dots take solar energy harvesting to new heights

Posted: 16 Apr 2014     Print Version  Bookmark and Share

Keywords:University of Milano-Bicocc  Los Alamos National Laboratory  solar energy  quantum dot  panel 

Los Alamos National Laboratory researchers, together with scientists from University of Milano-Bicocca (UNIMIB), Italy, have demonstrated superior light-emitting properties of quantum dots that can be applied in solar energy by helping harvest sunlight more efficiently. One probable application for the discovery is the creation of a window that doubles as a solar panel, the researchers stated.

"The key accomplishment is the demonstration of large-area luminescent solar concentrators that use a new generation of specially engineered quantum dots," said lead researcher Victor Klimov of the Center for Advanced Solar Photophysics (CASP) at Los Alamos.

Quantum dots are ultra-small bits of semiconductor matter that can be synthesised with nearly atomic precision via modern methods of colloidal chemistry. Their emission colour can be tuned by simply varying their dimensions. Colour tunability is combined with high emission efficiencies approaching 100 per cent. These properties have recently become the basis of a new technology, quantum dot displays, employed, for example, in the latest generation of the Kindle Fire e-reader.

Quantum dot LSC devices

Quantum dot LSC devices under UV illumination

A luminescent solar concentrator (LSC) is a photon management device, representing a slab of transparent material that contains highly efficient emitters such as dye molecules or quantum dots. Sunlight absorbed in the slab is re-radiated at longer wavelengths and guided towards the slab edge equipped with a solar cell.

Klimov explained, "The LSC serves as a light-harvesting antenna which concentrates solar radiation collected from a large area onto a much smaller solar cell, and this increases its power output."

"LSCs are especially attractive because in addition to gains in efficiency, they can enable new interesting concepts such as photovoltaic windows that can transform house facades into large-area energy generation units," said Sergio Brovelli, who worked at Los Alamos until 2012 and is now a faculty member at UNIMIB.

Because of highly efficient, colour-tunable emission and solution processability, quantum dots are attractive materials for use in inexpensive, large-area LSCs. One challenge, however, is an overlap between emission and absorption bands in the dots, which leads to significant light losses due to the dots re-absorbing some of the light they produce. To overcome this problem the Los Alamos and UNIMIB researchers have developed LSCs based on quantum dots with artificially induced large separation between emission and absorption bands (called a large Stokes shift).

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