21st April 2014 Transparent solar-powered windows made possible by quantum dot breakthrough The superior light-emitting properties of quantum dots can be applied to solar energy, helping to more efficiently harvest sunlight.
A house window that doubles as a solar panel could be on the horizon, thanks to recent work by Los Alamos National Laboratory researchers in collaboration with scientists from the University of Milano-Bicocca (UNIMIB), Italy. Their project demonstrates that superior light-emitting properties of quantum dots can be applied in solar energy by helping more efficiently harvest sunlight. Quantum dots are ultra-small nanocrystals of semiconductor matter that are synthesized with nearly atomic precision. Their emission colour can be tuned by simply varying their dimensions. Colour tunability is combined with high emission efficiencies approaching 100%. These properties have recently become the basis of a new technology – quantum dot displays – employed, for example, in the newest generation of the Kindle Fire e-reader. 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.
Lead researcher Victor 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 his colleague, Sergio Brovelli. To implement their concept, Los Alamos researchers created a series of cadmium selenide/cadmium sulfide (CdSe/CdS) quantum dots, which were then incorporated by the Italian team into large slabs of transparent polymer. The particles are tiny, only about 10 nanometres (nm) across. For comparison, human hairs are typically 50,000 nm wide. Spectroscopic measurements indicated virtually no losses to re-absorption on distances of tens of centimetres. Tests using simulated solar radiation demonstrated high photon harvesting efficiencies of around 10% per absorbed photon – achievable in nearly transparent samples – perfectly suited for utilisation as photovoltaic windows. These findings are published in Nature Photonics. According to a report earlier this year, the quantum dot and quantum dot display (QLED) markets are expected to see a 42-fold growth in the next five years, reaching $6.4 billion by 2019.
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