Optimizing thin film solar concentrators

Solar concentrators direct and focus sunlight toward a specific spot such as at a solar cell. Thin film luminescent solar concentrators (LSCs) have promising applications in integrable photovoltaic applications for buildings. By combining the right luminophore and polymer matrix, LSCs could be used as glazes for windows that can remain semi-transparent, while absorbing and emitting light towards solar cells mounted to the edge of the windows. These applications generally require qualifications such as high optical clarity, high refractive index, resistance to weathering and high luminophore loading fractions.

To better understand how to most efficiently guide light toward the edge of the concentrator and develop design criteria to fabricate them for these potential solar applications, Connell et al. studied LSCs comprised of cadmium selenide/cadmium sulfide (CdSe/CdS) core/shell quantum dots which were fixed in a matrix of polymer poly(cyclohexylethylene) (PCHE). The authors chose to investigate the material due to its high glass transition temperature and mechanical properties which are favorable for building-integrated applications.

“These composites can be applied as thin coatings on glass to form windows or architectural panels. By tuning the refractive index of the composite, luminescent light can be directed more efficiently onto the solar cell,” author Vivian Ferry said.

Using spectroscopic and simulation tools, they found that an increased luminophore loading fraction increases the amount of sunlight scattering, but also affects the propagation of photoluminescence in the film, depending on the refractive index of the film relative to that of the substrate.

They believe designs can be further optimized by controlling loading fraction of the nanocrystals, thickness of the films, and refractive index.

Source: “CdSe/CdS – poly(cyclohexylethylene) thin film luminescent solar concentrators,” by Ryan Connell, John Keil, Colin Peterson, Marc A. Hillmyer, and Vivian E. Ferry, APL Materials (2019). The article can be accessed at https://doi.org/10.1063/1.5121441 .