This work highlights key parameters required to make 12 inch square, and larger, quantum dot (QD) luminescent solar concentrators (LSC) for solar window applications. Our quantum dot solar windows are neutral in color and have a high optical power efficiency of 8% at 50% visible light transmittance (VLT). The windows use copper-indium-sulfide (CIS) quantum dots that are cheaper to make and less toxic than other QD materials. This makes them ideal for large area applications including safety inks and agricultural films in addition to solar windows. In an LSC, QDs absorb light and re-emit that light within the LSC. Due to total internal reflection (TIR), that re-emitted light channels to the edge of the LSC where the solar cells absorb and convert the light to electricity. Small defects in the LSC material reduce performance. This includes surface defects, defects in the polymer and QD aggregation in the polymer. A successful device must limit these defects.
High performance QDs, dispersing agents, and controlled resin curing are all important for manufacturing successful LSC materials and solar windows. Our CIS QDs have high QY and are stable in air at high temperatures. This allows formulation and curing of QD resins in air with minimum QY reduction. The high temperature stability also opens future opportunities for extrusion processes. In fact, we demonstrate that our CIS QDs can withstand 190°C for more than 10 minutes with minimal QY reduction. We incorporate QDs into windows as part of an interlayer in a glass laminate configuration where the laminate is made by a casting manufacturing technique. The glass has minimal surface defects which allows highly efficient TIR. Typically, the hydrophobicity of the QDs limits QD resin formulations to low viscosity, low adhesion, and low concentration formulations. However, by using dispersing agents and controlled curing techniques, we are able to formulate our resins with functionality similar to commercial polymers. For example, our resins use a variety of viscosity modifiers, plasticizers and adhesion promoters that allow scalable manufacture such as roll-to-roll coating and polymer casting. With these complex formulas, our QD LSCs with a VLT of 50% allow solar windows to be made with 29W/m2 as certified with testing at NREL.