A nanocomposite of metal nanoclusters/OSTE is fabricated through off-stoichiometric thiol-ene polymerization, incorporating adamantanethiol-protected electrum nanoclusters Au_23-xAg_x(SAdm)₁₅ (where x = 7.44) along with the OSTE monomer. During the photopolymerization, there is a transforfation of the precursor nanoclusters and the nanocomposite achieves a maximum photoluminescence quantum yield of ≈73% at 740 nm and 60% at the 850 nm emission peak. The photophysical characteristics of nanocomposite AuAgNCs@OSTE are examined at both ambient and low temperatures, revealing an improved radiative recombination mechanism through the interactions with polymer radicals. This high photoluminescence quantum yield near-infrared-emitting AuAgNCs@OSTE material, distinguished by a larger Stokes shift, is utilized to fabricate luminescent solar concentrators measuring 5 × 5 × 0.13 cm³. Experimental measurements are conducted to determine the absorption coefficient, reabsorption coefficient, absorption cross-section, and volume concentration of the device. Additionally, theoretical evaluations of waveguiding efficiency and power conversion efficiency are performed and compared with quantum dot-based alternatives. The findings indicate that the metal NCs@OSTE nanocomposite has the potential to function as a highly efficient, heavy-metal-free nanophosphor, demonstrating superior overall performance for semi-transparent luminescent solar concentrator devices and being suitable for a broad range of light conversion applications in the NIR spectrum.

CuInS2/ZnS (CIS/ZnS) quantum dots (QDs) are extensively employed as fluorophores in luminescent solar concentrators (LSCs), due to their excellent optical properties and low toxicity. However, the power conversion efficiency (PCE) of LSCs employing CIS/ZnS QDs is significantly constrained by the energy losses from the overlap between the absorption and emission spectra. Herein, we propose a novel and facile approach to enlarge the Stokes shift of CIS/ZnS QDs using the off-stoichiometric thiol–ene (OSTE) polymers. Significantly, the photoluminescence (PL) spectrum of CIS/ZnS QDs in OSTE experienced a substantial redshift of 65 nm without compromising the PLQY. This resulted in a remarkably enlarged Stokes shift of 585 meV and a minimal spectral overlap integral of 0.126, marking the first instance of a nanocomposite featuring CIS/ZnS QDs with such an enlarged Stokes shift. Further investigation demonstrates that thiol monomers, characterized by a strong electron-donating property, altered the Cu+ defect energy states in CIS QDs, resulting in a significant redshift in the PL spectrum. Consequently, a certified record PCE of 1.36% was achieved for a large-area (29 × 29 cm2) LSC device with an average visible transmittance (AVT) of 51%, representing the highest PCE value for such devices. Our findings not only present a viable strategy for augmenting the efficiency of CIS/ZnS QD-based LSCs for building-integrated photovoltaics (BIPV) but also establish a new avenue for controlling the optical properties of QD/polymer nanocomposites for other optoelectronic devices.

This Letter introduces an analytical approach to estimate the waveguiding efficiency of large-area luminescent solar concentrators (LSCs), where the edges are covered by a var-ied number of mirrors and solar cells. The model provides physically relevant description in the whole range of optical (absorption, scattering) and geometrical (size) parameters of rectangular LSCs. A 19 x 19 cm2 silicon quantum dot -based LSC has been fabricated to verify the theory. Within an experimental error, the predicted waveguiding efficiency matched well the measured one. A critical LSC size, beyond which a part of the device turns inactive, has been deter-mined as N/& alpha; for N attached solar cells (one or two) and LSC material absorption coefficient & alpha;. This model provides a straightforward waveguiding analysis tool for large-area LSCs with different structural parameters relevant for both high concentration ratio and glazing applications.

Fluorescent probes are vital to cell imaging by allowing specific parts of cells to be visualized and quantified. Color-switchable probes (CSPs), with tunable emission wavelength upon contact with specific targets, are particularly powerful because they not only eliminate the need to wash away all unbound probe but also allow for internal controls of probe concentrations, thereby facilitating quantification. Several such CSPs exist and have proven very useful, but not for all key cellular targets. Here we report a pioneering CSP for in situ cell imaging using aldehyde-functionalized silicon nanocrystals (SiNCs) that switch their intrinsic photoluminescence from red to blue quickly when interacting with amino acids in live cells. Though conventional probes often work better in cell-free extracts than in live cells, the SiNCs display the opposite behavior and function well and fast in universal cell lines at 37 °C while requiring much higher temperature in extracts. Furthermore, the SiNCs only disperse in cytoplasm not nucleus, and their fluorescence intensity correlated linearly with the concentration of fed amino acids. We believe these nanosilicon probes will be promising tools to visualize distribution of amino acids and potentially quantify amino acid related processes in live cells. 

A concept of transparent “quantum dot glass”(TQDG) is proposed for a combination of a quantum dot(QD)-based glass luminescent solar concentrator (LSC) and itsedge-attached solar cells, as a type of transparent photovoltaics(TPVs) for building-integrated photovoltaics (BIPVs). Differentfrom conventional LSCs, which typically serve as pure opticaldevices, TQDGs have to fulfill requirements as both powergeneratingcomponents and building construction materials. In thiswork, we demonstrate large-area (400 cm2) TQDGs based onsilicon QDs in a triplex glass configuration. An overall powerconversion efficiency (PCE) of 1.57% was obtained with back-reflection for a transparent TQDG (average visible transmittance of84% with a color rendering index of 88 and a low haze ≤3%), contributing to a light utilization efficiency (LUE) of 1.3%, which isamong the top reported TPVs based on the LSC technology with similar size. Most importantly, these TQDGs are shown to havebetter thermal and sound insulation properties compared to normal float glass, as well as improved mechanical performance andsafety, which significantly pushes the TPV technology toward practical building integration. TQDGs simultaneously exhibit favorablephotovoltaic, aesthetic, and building envelope characteristics and can serve as a multifunctional material for the realization of nearlyzero-energy building concepts.

      Silicon (Si) serves as the basic material of the system-on-a-chip industry and photovoltaic panels nowadays. This is mostly thanks to its high abundance in the earth’s crust, thereby low cost, virtually non-toxicity, and superior stability. Nano-silicon, especially silicon quantum dots (Si QDs), is endowed by the quantum confinement effect with the ability to emit light efficiently under photoexcitation, different from the bulk counterpart. The bright photoluminescence (PL), first found in the 1990s, has paved the way for this nanomaterial to be applied for light conversions in the last decades, such as for biosensing/biolabeling, light emitting diodes and luminescent solar concentrators (LSCs). The latter is used to concentrate sunlight in the slab on the edge-attached solar cells by means of PL. This thesis, on the one hand, deepens the comprehension on the optical properties of Si QDs by single-dot spectroscopy; on the other hand, a low-cost mass synthesis of high-quality Si QDs is developed here, which favors high QD loading applications, demonstrated as large-area “quantum dot glass”. 

      First, the photo-physics mechanism behind PL was studied by single-dot spectroscopy, excluding the QD size inhomogeneity in the ensemble measurements. A new method was developed to fabricate large-area (~mm²) isolated oxide-passivated Si QDs on a silicon-on-insulator wafer. Linearly polarized PLs were observed on those single dots. System-limited PL linewidths, ~250 μeV, were measured at 10 K on QDs here, indicating a good quality of oxide shell endowed by high temperature annealing. Based on this method, it is possible to modify the ambient optical environment of QDs without tenuous alignments. With Si QDs residing on a metal membrane with an oxide spacer, the PL yields of single dots were enhanced ~10 times in average compared to those residing outside the membrane. Next, we have achieved, for the first time, direct observation on the temperature-dependent radiative lifetimes on single ligand-passivated Si QDs. Most importantly, these single-dot PL decays can be well-fitted mono-exponentially, indicating trap-free dynamics, as opposite to oxide-passivated counterparts.

      Secondly, a chemical synthesis method of ligand-passivated Si QDs by using triethoxysilane (TES) as precursors is introduced. The quantum yield of as-synthesized Si QDs is ~40% in solution and ~55% in Si QDs/polymer nanocomposites. Such QDs have near-unity internal quantum efficiency both in the liquid and solid phase. With a comparably good quality of Si QDs, the QD cost of this TES method is about an order of magnitude less expensive than that of the established HSQ method. 

      Finally, the application of Si QDs in photovoltaic devices was demonstrated. A 9 × 9 × 0.6 cm³ LSC device based on Si QDs was fabricated, delivering ~7.9% optical power conversion efficiency under one standard sun. This performance is very similar to the state of the art of direct-bandgap semiconductor QDs. To further expand the application area of this kind of transparent photovoltaic devices, a concept of transparent “quantum dot glass” (TQDG) is introduced, fulfilling requirements as both power-generating components and building construction materials. A 20 × 20 × 1 cm³ TQDG device was fabricated with the overall power conversion efficiency up to 1.57% and the average visible transmittance 84%. The light utilization efficiency (LUE) is 1.3%, which is among the top reported TPVs based on the LSC technology with a similar size. Moreover, to facilitate the characterization of large-area LSC-like light-harvesting devices a new concept of an “optical center” is introduced. A procedure of whole device PCE estimates from optical center excitation measurements with basic laboratory instruments was provided, with a negligible error to the measured one by the conventional method.

This letter introduces a novel approach estimating the power conversion efficiency (PCE) of a square luminescent solar concentrator (LSC) by point excitations on the “optical centers” as proposed here. Predicted by theoretical calculations, photoluminescence emissions from these optical centers experience almost the same average optical path with those from the whole device under uniform illumination. This is experimentally verified by a 20 × 20 cm2 silicon quantum dots-based LSC, with a negligible error between the predicted PCE and the measured one. This method provides a convenient way to estimate the photovoltaic performance of large-area LSC devices with basic laboratory instruments.

As a cost-effective batch synthesis method, Si quantum dots (QDs) with nearinfrared photoluminescence, high quantum yield (>50% in polymer nanocomposite), and nearunity 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.

Luminescent solar concentrator (LSC) is a promising technology to integrate semitransparent photovoltaic (PV) systems into modern buildings and vehicles. Silicon quantum dots (QDs) are good candidates as fluorophores in LSCs, due to the absence of overlap between absorption and emission spectra, high photoluminescence quantum yield (PLQY), good stability, nontoxicity, and element abundance. Herein, LSCs based on Si QDs/polymer nanocomposites are fabricated in a triplex glass configuration. A special polymer matrix (off-stoichiometric thiol-ene, OSTE) is used, which improves Si nanocrystal quantum yield. Herein, a comprehensive investigation to improve the performance of LSCs by exploring different strategies under the guidance of a theoretical description is conducted. Among these strategies, the systematical enhancement of PLQY of the nanocomposite is achieved by tuning the thiol/allyl group ratio in the OSTE matrix. In addition, ligand selection and loading optimization for QDs reduce the total scattering loss in the device. Finally, an optical power efficiency of 7.9% is achieved for an optimized LSC prototype (9 x 9 x 0.6 cm(3), transmittance approximate to 62% at 500 nm) based on Si QDs/OSTE nanocomposite, which shows good potential of this material system in LSC fabrication.

A wafer-scale fabrication method for isolated silicon quantum dots (Si QDs) using standard CMOS technology is presented. Reactive ion etching was performed on the device layer of a silicon-on-insulator wafer, creating nano-sized silicon islands. Subsequently, the wafer was annealed at 1100 degrees C for 1 h in an atmosphere of 5% H(2)in Ar, forming a thin oxide passivating layer due to trace amounts of oxygen. Isolated Si QDs covering large areas (similar to mm(2)) were revealed by photoluminescence (PL) measurements. The emission energies of such Si QDs can span over a broad range, from 1.3 to 2.0 eV and each dot is typically characterized by a single emission line at low temperatures. Most of the Si QDs exhibited a high degree of linear polarization along Si crystallographic directions [110] abd [(1) over bar 10]. In addition, system resolution-limited (250 mu eV) PL linewidths (full width at half maximum) were measured for several Si QDs at 10 K, with no clear correlation between emission energy and polarization. The initial part of PL decays was measured at room temperature for such oxide-embedded Si QDs, approximately several microseconds long. By providing direct access to a broad size range of isolated Si QDs on a wafer, this technique paves the way for the future fabrication of photonic structures with Si QDs, which can potentially be used as single-photon sources with a long coherence length.