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Solar Cells Get Boost from Quantum Dots

Photonics.com
Apr 2014
LOS ALAMOS, N.M. and MILAN, April 15, 2014 — The superior light-emitting properties of quantum dots can efficiently harvest sunlight and enhance solar energy, according to researchers from Los Alamos National Laboratory, in collaboration with the University of Milan-Bicocca, who say this could lead to development of windows that double as solar panels.


Quantum dot luminescent solar concentrator devices under ultraviolet illumination. Images courtesy of Los Alamos National Lab.


“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 at Los Alamos.

Such quantum dots are highly efficient and tout color-tunable emission and solution processability. However, an overlap in emission and absorption bands in the dots can cause significant light losses as a result of the dots reabsorbing a portion of the light they produce.

The researchers overcame this challenge through development of a luminescent solar concentrator device based on quantum dots with an artificially induced large separation between the emission and absorption bands.

These Stokes-shift dots represent cadmium selenide/cadmium sulfide (CdSe/CdS) structures, in which light absorption is dominated by an thick outer shell of CdS, while emission occurs from the inner core of a narrower-gap CdSe.

In their study, the researchers created a series of CdSe/CdS quantum dots and incorporated them into large (tens of centimeters) slabs of polymethylmethacrylate (PMMA). Subsequent spectroscopic measurements indicated virtually no losses to reabsorption at this size and distance.


Quantum dots are embedded in the plastic matrix and capture sunlight to improve solar panel efficiency.


Additionally, tests using simulated solar radiation demonstrated high photon harvesting efficiencies of approximately 10 percent per absorbed photon achievable in nearly transparent samples, making photovoltaic windows a possibility, the researchers said.

The work was funded by the Center for Advanced Solar Photophysics, which is part of the Energy Frontier Research Center under the US Department of Energy’s Office of Science. The research is published in Nature Photonics. (doi: 10.1038/nphoton.2014.54)

For more information, visit: www.lanl.gov


GLOSSARY
cadmium sulfide
An inorganic compound, yellow to orange in color, that fluoresces strongly enough when bombarded by a high-current-density electron beam to be used as a high-intensity light source.
quantum dots
Also known as QDs. Nanocrystals of semiconductor materials that fluoresce when excited by external light sources, primarily in narrow visible and near-infrared regions; they are commonly used as alternatives to organic dyes.  
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