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Engineered Quantum Dots Could Help Lower Solar Power Cost

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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).

Published: January 2018
Glossary
nano
An SI prefix meaning one billionth (10-9). Nano can also be used to indicate the study of atoms, molecules and other structures and particles on the nanometer scale. Nano-optics (also referred to as nanophotonics), for example, is the study of how light and light-matter interactions behave on the nanometer scale. See nanophotonics.
nanophotonics
Nanophotonics is a branch of science and technology that explores the behavior of light on the nanometer scale, typically at dimensions smaller than the wavelength of light. It involves the study and manipulation of light using nanoscale structures and materials, often at dimensions comparable to or smaller than the wavelength of the light being manipulated. Aspects and applications of nanophotonics include: Nanoscale optical components: Nanophotonics involves the design and fabrication of...
plasmonics
Plasmonics is a field of science and technology that focuses on the interaction between electromagnetic radiation and free electrons in a metal or semiconductor at the nanoscale. Specifically, plasmonics deals with the collective oscillations of these free electrons, known as surface plasmons, which can confine and manipulate light on the nanometer scale. Surface plasmons are formed when incident photons couple with the conduction electrons at the interface between a metal or semiconductor...
quantum dots
A quantum dot is a nanoscale semiconductor structure, typically composed of materials like cadmium selenide or indium arsenide, that exhibits unique quantum mechanical properties. These properties arise from the confinement of electrons within the dot, leading to discrete energy levels, or "quantization" of energy, similar to the behavior of individual atoms or molecules. Quantum dots have a size on the order of a few nanometers and can emit or absorb photons (light) with precise wavelengths,...
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