Quantum dots make see-through solar cells a reality

May 8, 2014
Quantum dots make see-through solar cells a reality.

Researchers at Los Alamos National Laboratory have developed a way to magnify the amount of light that gets sent to solar cells using quantum dots to build luminescent solar concentrators (LSC).

The researchers embedded quantum dots in a transparent sheet of polymethylmethacrylate. Quantum dots are nanoscale bits of semiconducting material manufactured with atomic precision using colloidal chemistry. They shift the frequency of incoming light with near-100% efficiency, and the output color can be precisely tuned. When light hits the sheet of material, it is reradiated at longer wavelengths and guided toward the edge of the sheet. The edge is lined with solar cells designed to absorb light at the longer wavelength. So the LSC concentrates solar radiation from a larger area to focus it on a smaller solar cell, thus boosting its power output. One of the potential applications for this technology are transparent windows that also serve as solar cells for houses and buildings.

This schematic shows how quantum dots embedded in a plastic matrix capture sunlight and reradiate it to improve solar-panel efficiency.

An engineering challenge researchers had to overcome was the overlap between a dot’s emission and absorption bands, meaning it reabsorbs some of the light it reradiates, hampering its efficiency.

To solve that problem, the team needed to induce a relatively large separation between the emission and absorption frequencies (called a Stokes shift). The scientists managed this trick with engineered quantum dots made of cadmium selenide/cadmium sulfide (CdSe/CdS). The outer CdS shell controls absorption, while the inner core of CdSe controls emissions. There’s a large gap between absorption and emission frequencies; thus, little light is lost to reabsorption.

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