Silicon quantum dots with indirect bandgap photoluminescence are promising luminophores for large-area luminescent solar concentrators (LSCs). However, if commercially viable devices are to be achieved, silicon quantum dots must be dispersed within functional, light-guiding matrices such as acrylic slabs without losing their high photoluminescent quantum yield or succumbing to light-scattering agglomeration. With a goal of limiting scattering and producing functional LSC materials, we study silicon quantum dot/poly(methyl methacrylate) (PMMA) bulk polymerized composites. Ray-tracing Monte Carlo modeling predicts that scattering losses are significant for large-area silicon quantum dot LSCs unless the characteristic scattering length is at least as large as the LSC side length. We compare the effect of particle ligand choice on the nanocomposites, using particle loadings ranging from 0.06 to 0.50 wt %. We find that methyl 10-undecenoate functionalized silicon quantum dots in PMMA composites exhibit low levels of particle agglomeration, and thus light scattering, as compared to analogous silicon quantum dots capped with 1-dodecene. As a result, these ester-Si/PMMA composites show an improvement in light guiding compared to the alkane−Si composites, which is beneficial for future LSC applications.

Silicon quantum dots (Si QDs) are attractive, nontoxic luminophores for luminescent solar concentrators (LSCs). Here, we produced Si QD/poly(methyl methacrylate) (PMMA) films on glass by doctor-blading polymer solutions and achieved films with low light scattering at an order of magnitude higher Si QD weight fraction than has been achieved previously in the bulk. We suggest that the fast solidification rate of films as compared to slow bulk polymerization is an enabling factor in avoiding large agglomerates within the nanocomposites. Scanning electron microscopy confirmed that ∼100 nm or larger QD agglomerates exist in light-scattering films, and photoluminescence intensity measurements show that light scattering, if present, significantly reduces waveguiding efficiencies for LSCs. Nonscattering films fabricated in this work exhibit high ultraviolet absorption (>80%) paired with high visible transmission (>87%) and minimal visible haze (∼1%), making them well suited for semitransparent coatings for LSCs realized as solar harvesting windows.

Luminescent solar concentrators downshift and concentrate the incident solar spectrum onto adjacent solar cells. In this paper we study the combination of highly performing luminescent nanocrystals with photonic structures to guide light to the edge of the concentrator. While one approach is to use a wavelength-selective Bragg mirror to reduce escape cone losses, we find that this also requires nearly perfect mirrors and luminophore quantum yield. The key issue is that light is trapped inside the concentrator in modes that inefficiently propagate toward the edge, leading to luminophore reabsorption and losses to imperfect mirrors. To overcome this difficulty, we use modeling to study the use of meta-mirrors that shift propagating photons to larger angles, minimizing interactions with the reabsorbing luminophores and mirrors. We find that this design favors mirrors with small changes in angle, separated from the luminophore–polymer layer by an air gap. This research indicates that a combination of photonic structures can be used with imperfect luminescent materials and mirrors to enable high optical efficiency from luminescent concentrators.

Spectrally-selective mirrors improve the performance of luminescent solar concentrators (LSCs) by trapping emitted light within the waveguide. However, this beneficial property comes with a spectral restriction on incident sunlight that enters the concentrator. Especially for luminophores with overlap between the absorption and emission bands, design of the spectrally-selective mirrors requires a tradeoff between transmission of incident sunlight and trapping of luminescent photons. In this paper, we explore how the design of a spectrally-selective top mirror changes for LSCs containing luminophores of varying loading fractions, quantum yield, and overlap between the absorption and emission spectra, as well as LSCs with different back reflectors and lateral sizes. Using CdSe/CdS core/shell nanocrystals as the luminophore, we find that specific conditions favor different mirror designs. Mirrors designed to trap luminescent light have higher predicted performance than mirrors designed for sunlight transmission when the luminophore quantum yield is greater than 0.85, the luminophore optical density is less than 1.4 at 450 nm, the lateral size of the concentrator is greater than 10 cm, or there is low overlap between the luminophore absorption and emission. Mirrors optimized for either transmission or luminescence trapping have comparable performance for quantum yields less than 0.85, and the other conditions favor mirrors optimized for light transmission. For a LSC with unity quantum yield, a lateral size of 1 m×1 m, and a mirror designed to trap luminescent light, a concentration factor of 37× is possible, as compared to 10× for a LSC with an open top. This research indicates the importance of tailoring the design of the spectrally-selective top mirror to the properties of the luminophore and LSC.

Thin film luminescent solar concentrators are promising components of distributed power generation systems for building integrated photovoltaic applications. However, thin film geometries require high luminophore loading fractions to achieve sufficient absorption of sunlight, which, in the case of nanocrystal luminophores, can lead to aggregation and light scattering. In this work, we integrate CdSe/CdS nanocrystals into thin films of poly(cyclohexylethylene) at a range of loading fractions and characterize the composites with a combination of spectroscopic and simulation tools. We find that increased incident sunlight scattering is observed for the increasing luminophore loading fraction, but that the scattering is mostly limited to higher energy sunlight such that visible transmittance and haze of the samples are all greater than 89.7% and less than 8.3%, respectively. We then analyze the refractive index of the composite and show that the increase in loading fraction also affects the propagation of photoluminescence in the film, especially if the refractive index of the film is greater than that of the substrate. These studies show the importance of understanding the optical transport within thin films and provide design criteria to fabricate thin films for future implementation into building integrated photovoltaic applications.