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Engineered Quantum Dots Could Help Lower Solar Power Cost

Photonics.com
Jan 2018
LOS ALAMOS, N.M., Jan. 8, 2017 — A window architecture that includes two different layers of low-cost colloidal quantum dots tuned to absorb different parts of the solar spectrum could be used to build double-pane solar windows that generate electricity more efficiently while providing insulation and shading.

Spectral tunability of the quantum dots enables the creation of stacked multilayered luminescent solar concentrators (LSCs). Solar-spectrum splitting allows higher- and lower-energy photons to be processed separately. Enhanced performance is obtained through spectral splitting of incident sunlight, as in multijunction photovoltaics.

Engineered quantum dots used to power up double pane solar windows.

Researchers at Los Alamos National Laboratory are creating double-pane solar windows that generate electricity with greater efficiency and also create shading and insulation. It’s all made possible by a new window architecture that utilizes two different layers of low-cost quantum dots tuned to absorb different parts of the solar spectrum. Courtesy of Los Alamos National Laboratory.

A team at Los Alamos National Laboratory began by incorporating ions of manganese into quantum dots. The ions served as highly emissive impurities and were activated by the light absorbed by the quantum dots. Following activation, the manganese ions emitted light at energies below the quantum-dot absorption onset. This allowed for almost complete elimination of losses due to self-absorption by the quantum dots.

To transform a window into a tandem LSC, the researchers deposited a layer of highly emissive manganese-doped quantum dots onto the surface of the front glass pane, and a layer of copper indium selenide quantum dots onto the surface of the back pane. The front layer absorbed the blue and UV portions of the solar spectrum, while the rest of the spectrum was absorbed by the back layer. The quantum dots used in the front layer were virtually reabsorption-free.

Following absorption, the dots re-emitted photons at a longer wavelength. The re-emitted light was guided by total internal reflection to the glass edges of the window, where solar cells integrated into the window frame collected the light and converted it to electricity.

The researchers demonstrated a large-area tandem LSC based on two types of nearly reabsorption-free quantum dots, spectrally tuned for optimal solar-spectrum splitting. Their prototype device showed a high optical quantum efficiency of 6.4 percent for sunlight illumination and a solar-to-electrical power conversion efficiency of 3.1 percent. According to researchers, the efficiency gains made by using the tandem architecture over single-layer devices would increase if LSC size increased; and gains could reach more than 100 percent in structures with window sizes of more than 2500 cm.

“Because of the strong performance we can achieve with low-cost, solution-processable materials, these quantum-dot-based double-pane windows and even more complex luminescent solar concentrators offer a new way to bring down the cost of solar electricity,” said researcher Victor Klimov. “The approach complements existing photovoltaic technology by adding high-efficiency sunlight collectors to existing solar panels or integrating them as semitransparent windows into a building’s architecture.”

The research was published in Nature Photonics (doi:10.1038/s41566-017-0070-7).

GLOSSARY
nanophotonics
The study of how light interacts with nanoscale objects and the technology of applying photons to the manipulation or sensing of nanoscale structures.
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.
Research & TechnologyAmericaslight sourcesmaterialsphotovoltaicssolarnanonanophotonicsplasmonicsquantum dotscolloidal quantum dotssolar-spectrum splitting

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