Poly(methyl methacrylate) Films with High Concentrations of Silicon Quantum Dots for Visibly Transparent Luminescent Solar Concentrators

Unmasking Fluorinated Moieties on the Surface of Hydride-Terminated Silicon Nanoparticles

Despite the widespread use of hydrofluoric acid (HF) in the preparation of silicon surfaces, the true nature of fluorinated surface species remains unclear. Here, we employ an array of characterization techniques led by solid-state nuclear magnetic resonance spectroscopy to uncover the nature of fluorinated moieties on the surface of hydride-terminated silicon nanoparticles (H-SiNPs). A structural model that explains the observed trends in 19F and 29Si magnetic shielding is proposed and further supported by quantum chemical computations. Fluorine is incorporated into local oxidation domains on the surface and clustered at the interface of the oxide and surrounding hydride-terminated surface. Silicon sites capped by a single fluorine are also identified by their distinct 19F and 29Si chemical shifts, providing insight into how fluorine termination influences the electronic structure. The extent of fluorine passivation and the effects of fluorine on the optical properties of SiNPs are also discussed. Finally, challenges associated with Teflon contamination are highlighted that future explorations of nanomaterials may have to contend with.

A comprehensive dataset of photonic features on spectral converters for energy harvesting

Building integrated photovoltaics is a promising strategy for solar technology, in which luminescent solar concentrators (LSCs) stand out. Challenges include the development of materials for sunlight harvesting and conversion, which is an iterative optimization process with several steps: synthesis, processing, and structural and optical characterizations before considering the energy generation figures of merit that requires a prototype fabrication. Thus, simulation models provide a valuable, cost-effective, and time-efficient alternative to experimental implementations, enabling researchers to gain valuable insights for informed decisions. We conducted a literature review on LSCs over the past 47 years from the Web of ScienceTM Core Collection, including published research conducted by our research group, to gather the optical features and identify the material classes that contribute to the performance. The dataset can be further expanded systematically offering a valuable resource for decision-making tools for device design without extensive experimental measurements.

Achieving High-Efficiency Large-Area Luminescent Solar Concentrators

Luminescent solar concentrators (LSCs) are semitransparent windows that are able to generate electricity from sunlight absorption. LSCs have shown huge promise for realizing building-integrated photovoltaics (BIPV). Unfortunately, to date, the power conversion efficiency (PCE) of LSCs is still very low which dramatically hampers their practical applications. In this Perspective, We summarize and review the latest developments of LSCs by looking at different structures. Among others, we focus more on the next developments in the field of LSCs, i.e., the possibility of high PCE, large area, mass production, and durability needed for future industrial development. We hope to promote the application of uniform testing standards and to draw attention to industrial development, toxicity, and durability. Then, we will provide a critical assessment of the field of LSCs. Finally, the challenge and solution will be discussed.

Luminescence-guided and visibly transparent solar concentrators based on silicon quantum dots

In this work, we demonstrate a new tapered prism-shaped luminescent solar concentrator (LSC), which guides most of the luminescence toward one edge instead of four, for the solar window application. Only one Si photovoltaic (PV) strip attached to the light-emitting sidewall is needed to collect the luminescence, which further reduces PV material cost and avoids electrical mismatch. To achieve high visible transmission and mitigate reabsorption, colloidal silicon quantum dots (SiQDs) with ultraviolet-selective absorption and large Stokes shift are used as the fluorophores. With the SiQD concentration equal to 8 mg mL^-1, the SiQD-LSC as a solar window can attain a power conversion efficiency (PCE) equal to 0.27%, while ensuring high average visible transmission (AVT = 86%) and high color rendering index (CRI = 94 with AM1.5G as the incident spectrum). When adjusted to front-facing, the Si PV strip can harvest not only the direct sunlight but also the concentrated SiQD fluorescence guided from the LSC. As a result, the overall solar window PCE can be increased to 1.18%, and the PCE of the front-facing Si PV strip alone can be increased by 7% due to the luminescence guided from the SiQD-LSC.

Si-H Surface Groups Inhibit Methacrylic Polymerization: Thermal Hydrosilylation of Allyl Methacrylate with Silicon Nanoparticles

Hydrogen-terminated silicon nanoparticles (H-SiNPs) inhibit anerobic thermal autopolymerization of methacrylates. When heated to 100 °C under an inert atmosphere, allyl methacrylate (AMA) was stable for at least 95 h in the presence of 1.2 wt % H-SiNPs, exhibiting less than 0.15% conversion, whereas the neat monomer solidified within 24 h (over 10% conversion after 34 h). A mechanism is proposed that is based on H-transfer from SiNPs to the thermally activated methacrylic dimer biradical, quenching autopolymerization. An analysis of SiNPs isolated after heating in AMA reveals the grafting of ester groups. Thermal hydrosilylation offers a facile way to attach an allyl group to the surface of SiNPs.

Highly Luminescent and Stable Organic-Inorganic Hybrid Films for Transparent Luminescent Solar Concentrators

Here, a highly luminescent, stable, and visible-transparent organic-inorganic hybrid film was in situ synthesized in a siloxane-polyether (di-ureasil) sol-gel process by dissolving a 4-hydroxy-2-methyl-1,5-naphthyridine-3-carbonitrile (2mCND) ligand and a europium(III) ion. Doping a europium(III) complex into di-ureasil achieves an boost in photoluminescence quantum efficiency (PLQY) from 23.25 to 68.9%. In particular, the excellent photostability of the hybrid film was demonstrated after a 15 h aging experiment in strong UV-LED irradiation (∼468 mW/cm²). Compared to the polymethyl methacrylate (PMMA) matrix, di-ureasil containing a europium(III) complex shows an improved UV resistance, making it a promising candidate for various photonic applications. By integrating the hybrid film onto an acrylic substrate, a transparent luminescent solar concentrator (LSC) was fabricated, which reveals an optical conversion efficiency of ∼0.51% with a G factor of 3.1 at an optical transmission level of ∼90%. Such an LSC could be of particular interest in future transparent photovoltaic windows.

Optical and Physicochemical Characterizations of a Cellulosic/CdSe-QDs@S-DAB5 Film

CdSe quantum dots nanoparticles were coated with the thiolated (DiAminoButane based dendrimer) DAB dendrimer of fifth generation (S-DAB₅) and embedded in a highly hydrophilic regenerated cellulose (RC) film by simple dip-coating method (immersion in QD-dendrimer aqueous solution) as a way to get a flexible nano-engineered film (RC-4/CdSe-QDs@S-DAB₅) with high transparency and photoluminescence properties for different applications. Optical changes in the RC film associated with QDs inclusion were determined by spectroscopic ellipsometry (SE) measurements, which provide information on changes caused in the refraction index and the extinction coefficients of the film, as well as by light transmittance/reflectance curves and photoluminescence (PL) spectra. Impedance spectroscopy (IS) and other typical physicochemical techniques for material characterization (TEM, SEM and XPS) have also been used in order to have more complete information on film characteristics. A comparison of RC-4/CdSe-QDs@S-DAB₅ film optical characteristics with those exhibited by other RC-modified films depending on the type of dendrimer was also carried out.

Low-Cost Synthesis of Silicon Quantum Dots with Near-Unity Internal Quantum Efficiency

As a cost-effective batch synthesis method, Si quantum dots (QDs) with near-infrared photoluminescence, high quantum yield (>50% in polymer nanocomposite), and near-unity internal quantum efficiency were fabricated from an inexpensive commercial precursor (triethoxysilane, TES), using optimized annealing and etching processes. The optical properties of such QDs are similar to those prepared from state-of-the-art precursors (hydrogen silsesquioxane, HSQ) yet featuring an order of magnitude lower cost. To understand the effect of synthesis parameters on QD optical properties, we conducted a thorough comparison study between common solid precursors: TES, HSQ, and silicon monoxide (SiO), including chemical, structural, and optical characterizations. We found that the structural nonuniformity and abundance of oxide inherent to SiO limited the resultant QD performance, while for TES-derived QDs this drawback can be avoided. The presented low-cost synthetic approach would significantly favor applications requiring high loading of good-quality Si QDs, such as light conversion for photovoltaics.

Quantum dot assisted luminescent hexarhenium cluster dye for a transparent luminescent solar concentrator

A luminescent solar concentrator (LSC) is a solar-light harvesting device that concentrates light on a photovoltaic cell placed at the edge of an LSC panel to convert it into electricity. The nano-sized inorganic-organic cluster complex (dMDAEMA)₄[Re₆S₈(NCS)₆] (this refers to RMC where dMDAEMA is 2-dimethyl amino ethyl methacrylate) is a promising candidate for LSC luminophores due to its downshifted broad photoluminescence suitable for photovoltaic cells. However, the low quantum yield (QY) of RMC limits the performance. Here, zinc-doped CuGaS/ZnS core/shell quantum dots (ZQD) were used as energy transferring donor with high QY to improve the performance of the LSC. The two metal chalcogenide luminophores, RMC and ZQD, are chemically suitable for dispersion in an amphiphilic polymer matrix, producing a transparent waveguide with suppressed reabsorption and extended harvesting coverage of the solar spectrum. We achieved an η_opt of 3.47% and a PCE of 1.23% while maintaining greater than 80% transparency in the visible range. The high performance of this dual-dye LSC with suppressed reabsorption, and scattering losses is not only due to uniform dispersion of dyes in a polymer matrix, but also energy transfer from ZQD to RMC. This report suggests a new possibility for promising various multi-dye LSCs for use in building-integrated photovoltaic windows.

Monte Carlo simulation of a LSC based on stacked layers of fiber arrays with core-coating different absorbing properties

In this work, a Monte Carlo ray-tracing model for the simulation and optimization of a fiber Luminescent Solar Concentrator (LSC) based on stacked layers of fiber arrays is developed and validated. The fiber LSC efficiency improvements are compared against a conventional planar LSC. We developed a new model to analyze the performance of different configurations of bulk-doped fibers and fibers constituted by a doped coating and a passive core. These configurations are analyzed also varying fiber packing geometry diameters, and length. Due to the exceptionally low absorption coefficient of the silica fibers (α_wg ≈ 10^-4 cm^-1), concentration factors of up to 1.9 are predicted when dimensions are scaled over 1 m², which improve more than twice the maximum concentration factor ever reported. These results serve as a preliminary theoretical study for the future development of a new LSC design based on flexible silica micro-fibers coated with Si-QDs doped poly(lauryl methacrylate) (PLMA) layers.

White-light emission from the quadruple-stranded dinuclear Eu(iii) helicate decorated with pendent tetraphenylethylene (TPE)

The hybrid film doped with a quadruple-stranded Eu³⁺ helicate displayed tuneable emission and white light.

Utilizing host-guest interaction enables the simultaneous enhancement of the quantum yield and Stokes shift in organosilane-functionalized, nitrogen-containing carbon dots for laminated luminescent solar concentrators

Solar energy can be harvested using luminescent solar concentrators (LSCs) incorporated with edge-mounted solar cells without sacrificing their see-through visibility, thus facilitating the development of solar windows. Eco-friendly carbon dots (CDs) are promising alternatives to heavy-metal-containing quantum dots in LSC applications. Unfortunately, their solid-state quantum yield (QY) at high optical density (required by laminated LSCs) is still low (<30%) and the Stokes shift is only moderate (<100 nm). Here, we studied the host-guest interaction between aminosilane-functionalized, nitrogen-containing CDs (Si-NCDs) and a silica matrix for preparing efficient laminated LSCs. We found that a sol-gel-derived silica matrix with vacuum treatment can efficiently suppress the direct nonradiative transition of the absorbing states and selectively enhance the long-wavelength-emitting surface states. Therefore, the formed Si-NCDs@silica composites simultaneously exhibited high QYs (>60%) and large Stokes shifts (>200 nm) even at a high loading content (∼10 wt%), while still exhibiting high optical transparency. Moreover, unlike conventional QY reduction upon increasing the excitation wavelengths, such high QY values can be maintained over all excitation wavelengths in the absorption region. Benefiting from these photophysical properties, efficient laminated LSCs were simply prepared, yielding a high optical efficiency of ∼4.4%.

Poly(N-Isopropylacrylamide)-Functional Silicon Nanocrystals for Thermosensitive Fluorescence Cellar Imaging

Silicon nanocrystals (Si NCs) have received surging interest as a type of quantum dot (QD) due to the availability of silicon in nature, tunable fluorescence emission properties and excellent biocompatibility. More importantly, compared with many group II-VI and III-V based QDs, they have low toxicity. Here, thermoresponsive poly(N-isopropylacrylamide) (PNIPAAm)-functional Si NCs were firstly prepared for thermoresponsive detection of cancer cells. Si NCs were prepared under normal pressure with excellent water solubility. Then folic acid was bonded to the silicon nanocrystals through the reaction of amino and carboxyl groups for specific recognition of cancer cells. The folic-acid-modified silicon crystals (Si NCs-FA) could be modified by a one-pot copolymerization process into PNIPAAm nanospheres during the monomer polymerization process (i.e., Si NCs-FA-PNIPAAm) just by controlling the temperature below the lower critical solution temperature (LCST) and above the LCST. The results showed that the Si-FA-PNIAAm nanospheres exhibited not only reversible temperature-responsive on-off fluorescence properties, but also can be used as temperature indicators in cancer cells.