Transparent Luminescent Solar Concentrators (LSCs)

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lsc
Comparison between standard glass, a thin film of Si QDs on a window, and a thick film of Si QDs all on a backdrop of the Minneapolis skyline.
Schematic of an LSC window tuning the transmitted light to a plant below.

LSCs can be used to make solar windows by attaching small-area solar cells to the edges of an optically transparent waveguide that has been doped or coated with luminescent materials. In this way, LSCs can support building-integrated photovoltaic applications that use these solar windows in the built environment. In addition, LSCs can be used in agrivoltaic settings, such as greenhouses outfitted with LSC roofs. In this application, the LSC can be utilized to intentionally tune the light that is transmitted through the roof and improve the growth of plants below, while also generating renewable electricity.

An LSC is similar to a large, flat optical fiber with luminescent species embedded within. They effectively capture light from all directions, downshift it to a longer wavelength, and guide the downshifted light to the edges of the matrix. The Kortshagen Group is researching ways to create silicon nanocrystal (Si NC)-based LSC devices through gas phase-deposition, solution-based spin coating, spray coating, and/or bulk polymerization of the nanocrystals (NC’s) directly in transparent polymers like PMMA.

The goal is to reduce light losses as much as possible by maintaining the Si NC's high ~60% downshifting efficiency, reducing scattering losses caused by a rough surface, and maintaining high stability of all device components. Silicon has the benefit of low overlap between absorption and emission spectra, reducing losses due to reabsorption, which is a major hurdle for other LSC fluorescent materials studied today. Different surface chemistries of Si NCs also lend themselves to different LSC preparation methods and wave guiding materials which must be explored.

This work is sponsored by the University of Minnesota and the Minnesota Environment and Natural Resources Trust Fund.