Eco-Friendly Colloidal Quantum Dot-Based Luminescent Solar Concentrators

Heavy-Metal-Free Colloidal Quantum Dots: Progress and Opportunities in Solar Technologies

Colloidal quantum dots (QDs) hold great promise as building blocks in solar technologies owing to their remarkable photostability and adjustable properties through the rationale involving size, atomic composition of core and shell, shapes, and surface states. However, most high-performing QDs in solar conversion contain hazardous metal elements, including Cd and Pb, posing significant environmental risks. Here, a comprehensive review of heavy-metal-free colloidal QDs for solar technologies, including photovoltaic (PV) devices, solar-to-chemical fuel conversion, and luminescent solar concentrators (LSCs), is presented. Emerging synthetic strategies to optimize the optical properties by tuning the energy band structure and manipulating charge dynamics within the QDs and at the QDs/charge acceptors interfaces, are analyzed. A comparative analysis of different synthetic methods is provided, structure-property relationships in these materials are discussed, and they are correlated with the performance of solar devices. This work is concluded with an outlook on challenges and opportunities for future work, including machine learning-based design, sustainable synthesis, and new surface/interface engineering.

Vacuum-Boosting Precise Synthetic Control of Highly Bright Solid-State Carbon Quantum Dots Enables Efficient Light Emitting Diodes

Carbon quantum dots (C-dots) have emerged as efficient fluorescent materials for solid-state lighting devices. However, it is still a challenge to obtain highly bright solid-state C-dots because of the aggregation caused quenching. Compared to the encapsulation of as-prepared C-dots in matrices, one-step preparation of C-dots/matrix complex is a good method to obtain highly bright solid-state C-dots, which is still quite limited. Here, an efficient and controllable vacuum-boosting gradient heating approach is demonstrated for in situ synthesis of a stable and efficient C-dots/matrix complex. The addition of boric acid strongly bonded with urea, promoting the selectivity of the reaction between citric acid and urea. Benefiting from the high reaction selectivity and spatial-confinement growth of C-dots in porous matrices, in situ synthesize C-dots bonded can synthesized dominantly with a crosslinked octa-cyclic compound, biuret and cyanuric acid (triuret). The obtained C-dots/matrix complex exhibited bright green emission with a quantum yield as high as 90% and excellent thermal and photo stability. As a proof-of-concept, the as-prepared C-dots are used for the fabrication of white light-emitting diodes (LEDs) with a color rendering index of 84 and luminous efficiency of 88.14 lm W-1, showing great potential for applications in LEDs.

A Bifunctional Luminescent Whitening and Sensing Material Based on Photoluminescence and Mechanoluminescence

A bifunctional luminescent whitening and luminescent sensing composite material, BaMgAl12O17:Eu2+/polydimethylsiloxane (BAM/PDMS), that utilizes natural sunlight and mechanical energy is presented. By increasing the Eu2+ content, the photoluminescence (PL) excitation spectrum of the material shows a maximum redshift of 23 nm due to 5d level splitting of Eu2+, resulting in more spectral overlap with sunlight and an excellent PL whitening effect. Meanwhile, the self-recoverable mechanoluminescence (ML) of the material can be easily excited under mechanical stimuli due to contact electrification, exhibiting a unique stress sensing effect. Based on the unique features of PL whitening and ML sensing, the material is applied to model cars through a spray process, and the results demonstrate that the bifunctional BAM/PDMS material shows promising applications in automobile decoration.

Self-Trapped, Thermally Equilibrated Delayed Fluorescence Enables Low-Reabsorption Luminescent Solar Concentrators Based on Gold-Doped Silver Nanoclusters

Reabsorption-free luminescent solar concentrators (LSCs) are crucial ingredients for photovoltaic windows. Atomically precise metal nanoclusters (NCs) with large Stokes-shifted photoluminescence (PL) hold great promise for applications in LSCs. However, a fundamental understanding of the PL mechanism, particularly on the excited-state interaction and exciton kinetics, is still lacking. Herein, we studied the exciton-phonon coupling and singlet/triplet exciton dynamics for gold-doped silver NCs in a solid matrix. Following photoexcitation, the excitons can be self-trapped via strong exciton-phonon coupling. Subsequently, rapid thermal equilibration between the singlet and triplet states occurs due to the coexistence of small energy splitting and spin-orbit coupling. Finally, broadband delayed fluorescence with a large Stokes shift can be generated, namely, self-trapped, thermally equilibrated delayed fluorescence (ST-TEDF). Benefiting from superior ST-TEDF, we demonstrated efficient LSCs with minimized reabsorption.

Tailoring Eco-Friendly Colloidal Quantum Dots for Photoelectrochemical Hydrogen Generation

A photoelectrochemical (PEC) cell is able to realize effective solar-to-hydrogen energy conversion from water by using the semiconductor photoelectrode. Semiconducting colloidal quantum dots (QDs) with captivating features of size-tunable optoelectronic properties and broad light absorption are regarded as promising photosensitizers in solar-driven PEC systems. Up to now, different types of QDs have been developed to achieve high-efficiency PEC H2 generation, while the majority of state-of-the-art QDs-PEC systems are still fabricated from QDs consisting of heavy metals (e.g., Cd and Pb), which are extremely harmful to the human health and natural environment. In this context, substantial efforts have been made to mitigate the usage of highly toxic heavy metals and concurrently promote the development of alternative environment-friendly QDs with comparable features. This review presents recent advances of solar-driven PEC devices based on several typical environment-friendly QDs (e.g., carbon QDs, I-III-VI QDs and III-V QDs). A variety of techniques (e.g., shell thickness tuning, alloying/doping, and ligands exchange, etc.) to engineer these QD's optoelectronic properties and achieve high-efficiency PEC H2 production are thoroughly discussed. Furthermore, the critical challenges and future perspectives of advanced eco-friendly QDs-PEC systems in terms of QDs' synthesis, photo-induced charge kinetics, and operation stability/efficiency are briefly proposed.

Spatially Resolved Optical Efficiency Measurements of Luminescent Solar Concentrators

Luminescent solar concentrators (LSCs) are able to concentrate both direct and diffuse solar radiation, and this ability has led to great interest in using them to improve solar energy capture when coupled to traditional photovoltaics (PV). In principle, a large-area LSC could concentrate light onto a much smaller area of PV, thus reducing costs or enabling new architectures. However, LSCs suffer from various optical losses which are hard to quantify using simple measurements of power conversion efficiency. Here, we show that spatially resolved photoluminescence quantum efficiency measurements on large-area LSCs can be used to resolve various loss processes such as out-coupling, self-absorption via emitters, and self-absorption from the LSC matrix. Further, these measurements allow for the extrapolation of device performance to arbitrarily large LSCs. Our results provide insight into the optimization of optical properties and guide the design of future LSCs for improved solar energy capture.

Assessing the influence of microwave-assisted synthesis parameters and stabilizing ligands on the optical properties of AIS/ZnS quantum dots

Luminescent semiconductor quantum dots (QDs) are frequently used in the life and material sciences as reporter for bioimaging studies and as active components in devices such as displays, light-emitting diodes, solar cells, and sensors. Increasing concerns regarding the use of toxic elements like cadmium and lead, and hazardous organic solvents during QD synthesis have meanwhile triggered the search for heavy-metal free QDs using green chemistry syntheses methods. Interesting candidates are ternary AgInS₂ (AIS) QDs that exhibit broad photoluminescence (PL) bands, large effective Stokes shifts, high PL quantum yields (PL QYs), and long PL lifetimes, which are particularly beneficial for applications such as bioimaging, white light-emitting diodes, and solar concentrators. In addition, these nanomaterials can be prepared in high quality with a microwave-assisted (MW) synthesis in aqueous solution. The homogeneous heat diffusion and instant temperature rise of the MW synthesis enables a better control of QD nucleation and growth and thus increases the batch-to-batch reproducibility. In this study, we systematically explored the MW synthesis of AIS/ZnS QDs by varying parameters such as the order of reagent addition, precursor concentration, and type of stabilizing thiol ligand, and assessed their influence on the optical properties of the resulting AIS/ZnS QDs. Under optimized synthesis conditions, water-soluble AIS/ZnS QDs with a PL QY of 65% and excellent colloidal and long-term stability could be reproducible prepared.

Boosting efficiency of luminescent solar concentrators using ultra-bright carbon dots with large Stokes shift

Luminescent solar concentrators (LSCs) are able to collect sunlight from a large-area to generate electric power with a low cost, showing great potential in building-integrated photovoltaics. However, the low efficiency of large-area LSCs caused by the reabsorption losses is a critical issue that hampers their practical applications. In this work, we synthesized novel yellow emissive carbon dots (CDs) with a large Stokes shift of 193 nm, which exhibit nearly zero reabsorption. The quantum yield (QY) of the yellow emitting CDs is up to 61%. The yellow emitting CDs can be employed to fabricate high-performance large-area LSCs due to successful suppression of the reabsorption losses. The as-prepared LSCs are able to absorb 14% of the sunlight as the absorption of the CDs matches well with the sun's spectrum. The large-area LSC (10 × 10 cm²) with a laminated structure based on the yellow emitting CDs achieves an optical conversion efficiency (η_opt) of 4.56% and power conversion efficiency (η_PCE) of 4.1% under natural sunlight (45 mW cm^-2), which are significantly higher than other previously reported works with similar sizes. Furthermore, the prepared high-performance LSCs show good stability. This method of synthesizing novel CDs for high-efficiency LSCs provides a useful platform for future study and practical application of LSCs.

Low-Loss, High-Transparency Luminescent Solar Concentrators with a Bioinspired Self-Cleaning Surface

Luminescent solar concentrators (LSCs) have emerged as a disruptive technology that can potentially enable carbon-neutral buildings. The issues with current LSCs, however, are low optical efficiencies and limited long-term outdoor stability. Here we simultaneously address them by developing an LSC with aggregation-induced-emission (AIE) molecules embedded in a polydimethylsiloxane (PDMS) matrix. The AIE-emitter displayed a near unity emission quantum yield when embedded in the PDMS and the apparent absorption-emission Stokes shift reached 0.59 eV, effectively suppressing the reabsorption loss of waveguided photons inside an LSC. Moreover, the surface texture of the PDMS matrix was engineered using a bioinspired nanolithography method with a natural lotus leaf as the template. This allowed the fabricated AIE-PDMS LSC to inherit the superhydrophobic, self-cleaning properties of the leaf and meanwhile to possess a light-trapping capability. Our 100 cm² LSC, when coupled with commercial Si PVs, delivered efficient solar power conversion, high visible transmittance, and high working stability.

Mn-Doped Multiple Quantum Well Perovskites for Efficient Large-Area Luminescent Solar Concentrators

Luminescent solar concentrators (LSCs) can be used as large-area sunlight collectors, which show great potential in the application of building-integrated photovoltaic areas. Achieving highly efficient LSCs requires the suppression of reabsorption losses while maintaining a high photoluminescence quantum yield (PLQY) and broad absorption. Perovskites as the superstar fluorophores have recently emerged as candidates for large-area LSCs. However, highly emissive perovskites with a large Stokes shift and broad absorption have not been obtained up to now. Here, we devised a facile synthetic route to obtain Mn-doped multiple quantum well (MQW) Br-based perovskites. The Br-based perovskite host ensures broad absorption. Efficient energy transfer from the exciton to the Mn dopant produces a large Stokes shift and high PLQY simultaneously. By further coating the perovskites with Al₂O₃, the stability and PLQY are greatly elevated. A large area of liquid LSC (40 cm × 40 cm × 0.5 cm) is fabricated, which possesses an internal quantum efficiency (η_int) of 47% and an optical conversion efficiency (η_opt) reaching 11 ± 1%, which shows the highest value for large-area LSCs.

Highly Luminescent and Photostable Core/Shell/Shell ZnSeS/Cu:ZnS/ZnS Quantum Dots Prepared via a Mild Aqueous Route

An aqueous-phase synthesis of 3-mercaptopropionic acid (3-MPA)-capped core/shell/shell ZnSeS/Cu:ZnS/ZnS QDs was developed. The influence of the Cu-dopant location on the photoluminescence (PL) emission intensity was investigated, and the results show that the introduction of the Cu dopant in the first ZnS shell leads to QDs exhibiting the highest PL quantum yield (25%). The influence of the Cu-loading in the dots on the PL emission was also studied, and a shift from blue-green to green was observed with the increase of the Cu doping from 1.25 to 7.5%. ZnSeS/Cu:ZnS/ZnS QDs exhibit an average diameter of 2.1 ± 0.3 nm and are stable for weeks in aqueous solution. Moreover, the dots were found to be photostable under the continuous illumination of an Hg-Xe lamp and in the presence of oxygen, indicating their high potential for applications such as sensing or bio-imaging.

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.

Anhydride-Terminated Solid-State Carbon Dots with Bright Orange Emission Induced by Weak Excitonic Electronic Coupling

In this work, fluorescent solid carbon dots (CDs) welcome a new member, namely anhydride-terminated CDs, which have a photoluminescence quantum yield (PLQY) of 28% for orange-emitted CDs at 580 nm in powder form. For the first time, we revealed that the electronic coupling of the functional groups should be a crucial factor affecting the optical properties of solid CDs. Due to the negligible hydrogen bonding interaction between the anhydride groups, the electronic coupling of excitons between neighboring anhydride groups is weak, leading to a high PLQY of 28% and an immobile emission peak at 580 nm in solid state. Anhydride-terminated CDs can be partly converted into carboxyl-terminated CDs after dispersion in ethanol. However, the strong electronic coupling of carboxyl groups at high concentration generates the stacking mode of J-aggregates, giving rise to a red-shifted emission from 450 to 515 nm as well as quenched fluorescence in solid state. In comparison, a useful blue emission for solid-state CDs occurs from low sp² hybridized carbon atoms, which possess weak electronic coupling and a stationary emission band at 450 nm in both solution and solid state. By adjusting the feed ratio of the reactants, the relevant intensities between the emission from low sp² hybridized carbon atoms at 450 nm and the emission from anhydride groups at 580 nm can be controlled. As a result, single-component anhydride-terminated CD powder with tunable emission color from orange to white light can be achieved. As-prepared anhydride-terminated CDs can be used for fabricating light-emitting diodes (LEDs), white LEDs, and luminescent solar concentrators (LSCs).

Eco-Friendly and Efficient Luminescent Solar Concentrators Based on a Copper(I)-Halide Composite

Luminescent solar concentrators (LSCs) show great promise in reducing the cost of silicon solar cells due to their potential use for high-efficiency energy harvesting. Compared to narrow absorption organic dyes, quantum dots (QDs) are a favorable approach to acquire stable LSCs. However, the use of toxic heavy metals in QDs and the small Stokes shift largely restrict their development. Here, a toxic metal-free, highly luminescent ink based on a copper(I)-halide hybrid cluster is reported, whose quantum yield (QY) exceeds 68%. Under the interaction with halohydrocarbon, CuI and phenethylamine (PEA) can be easily dissolved and the ink can be facilely acquired. The obtained film exhibits strong orange light emission with a large Stokes shift. As a proof-of-concept experiment, (PEA)₄Cu₄I₄ has been used to fabricate LSCs. The as-prepared LSC (4 cm × 4 cm × 0.3 cm) exhibits an internal quantum efficiency (η_int) as high as 44.1%. After coupling to a solar cell, an optical conversion efficiency (η_opt) of 6.85% is acquired from this LSC. In addition, the LSC possesses high stability such as air stability, water stability, and photostability. These results demonstrate that the (PEA)₄Cu₄I₄ film can be employed as a promising candidate for large-area and high-efficiency LSCs.

Mechanism of morphology variations in colloidal CuGaS2 nanorods

Cu2-x S nanocrystals can serve as templates and intermediates in the synthesis of a wide range of nanocrystals through seeded growth, cation exchange, and/or catalytic growth. This versatility can facilitate and accelerate the search for environmentally benign nanocrystals of high performance with variable shapes, sizes, and composition. However, expanding the compositional space via Cu2-x S nanocrystals while achieving necessary uniformity requires an improved understanding of the growth mechanisms. Herein we address several unusual and previously unexplained aspects of the growth of CuGaS2 nanorods from Cu2-x S seeds as an example. In particular, we address the origin of the diverse morphologies which manifest from a relatively homogeneous starting mixture. We find that CuGaS2 nanorods start as Cu2-x S/CuGaS2 Janus particles, the majority of which have a {101̄2}/{101̄2} interface that helps to minimize lattice strain. We propose a mechanism that involves concurrent seed growth and cation exchange (CSC), where epitaxial growth of the Cu2-x S seed, rather than the anticipated catalytic or seeded growth of CuGaS2, occurs along with cation exchange that converts growing Cu2-x S to CuGaS2. This mechanism can explain the incorporation of the large number of anions needed to account for the order-of-magnitude volume increase upon CuGaS2 rod growth (which cannot be accounted for by the commonly assumed catalytic growth mechanism) and variations in morphology, including the pervasive tapering and growth direction change. Insights from the CSC growth mechanism also help to explain a previously puzzling phenomenon of regioselective nucleation of CuInSe2 on kinked CuGaS2 nanorods.

Aqueous synthesis of composition-tuned defects in CuInSe2 nanocrystals for enhanced visible-light photocatalytic H2 evolution

The composition and defect tolerance of CuInSe₂ (CISe) quantum dots (QDs) provide a scaffold to design defects via tailoring the elemental ratio or distributions for boosting photocatalytic H₂ evolution (PHE). Herein, a ligand-assisted two-step aqueous method was developed to prepare defect CISe quantum dots for the first time. UV-vis, XPS, HRTEM, and HADDF investigations confirmed the typical double-absorption edges of copper vacancy defects and indium substituted at copper site defects in the structure constructed through initial synthesis tuned by Cu/In ratio and the ensued coarsening. The steady-transient PL suggested that the D-A recombination with prolonged PL lifetime dominated the emission of composition-optimized CuInSe₂ with the Cu/In ratio of 1/4 (CISe-1/4). Further transient photocurrent and electrochemical impedance spectroscopy investigations demonstrated that surface defects in the structure favor the carriers' separation/transportation. The CISe-1/4 exhibited a superior PHE rate of 722 μmol g^-1 h^-1, about 23 times higher than that of the initially synthesized CISe-1/4 nucleus (31 μmol g^-1 h^-1), with a maximum apparent quantum efficiency (AQE) of 1.3%. The analysis of energy levels and the coulombic interaction energy of electron-hole (J _e/h) based on Raman, extending UV-vis spectra investigations suggested that surface defects resulted in decreased J _e/h of CISe-1/4, favoring the enhanced PHE of this structure. This work is expected to provide a reference for designing effective non-noble metal I-III-VI photocatalysts.

A Study on an Organic Semiconductor-Based Indirect X-ray Detector with Cd-Free QDs for Sensitivity Improvement

In this paper, we studied the optimized conditions for adding inorganic quantum dots (QD) to the P3HT:PC₇₀BM organic active layer to increase the sensitivity of the indirect X-ray detector. Commonly used QDs are composed of hazardous substances with environmental problems, so indium phosphide (InP) QDs were selected as the electron acceptor in this experiment. Among the three different sizes of InP QDs (4, 8, and 12 nm in diameter), the detector with 4 nm InP QDs showed the highest sensitivity, of 2.01 mA/Gy·cm². To further improve the sensitivity, the QDs were fixed to 4 nm in diameter and then the amount of QDs added to the organic active layer was changed from 0 to 5 mg. The highest sensitivity, of 2.26 mA/Gy·cm², was obtained from the detector with a P3HT:PC₇₀BM:InP QDs (1 mg) active layer. In addition, the highest mobility, of 1.69 × 10⁻⁵ cm²/V·s, was obtained from the same detector. Compared to the detector with the pristine P3HT:PC₇₀BM active layer, the detector with a P3HT:PC₇₀BM:InP QDs (1 mg) active layer had sensitivity that was 61.87% higher. The cut-off frequency of the P3HT:PC₇₀BM detector was 21.54 kHz, and that of the P3HT:PC₇₀BM:InP QDs (1 mg) detector was 26.33 kHz, which was improved by 22.24%.

Improving power conversion efficiency in luminescent solar concentrators using nanoparticle fluorescence and scattering

Large-size luminescent solar concentrators (LSCs), which act as a complement to silicon-based photovoltaic (Si-PV) systems, still suffer from low power conversion efficiency (PCE). How to improve the performance of LSCs, especially large ones, is currently a hot research topic. Traditional LSCs have only a single transmission mode of fluorescence from the luminescent materials to the Si-PV, but here we introduce a new idea to improve the absorption of Si-PV by employing dual transmission modes of both fluorescence and scattering light. To prepare LSCs with dual mode transmission, Si-PV systems are coupled around the edges of a light-harvesting slice, which is prepared by ultraviolet light-induced polymerization of methyl methacrylate (MMA) solution containing both luminescent CsPbBr₃ and TiO₂ nanocrystals (NCs). When the sun light or incident light is coupled into the light-harvesting slice, CsPbBr₃ NCs can convert the incident light into fluorescence, and then partly transmit to Si-PV at the edges, where the light is finally converted into electrical energy. Besides the traditional fluorescence transmission mode, the addition of TiO₂ brings another transmission mode, namely the scattering of incident light to Si-PV, leading to an increase in PCE. In comparison to that of pure CsPbBr₃-based LSCs without the addition of TiO₂ (0.97%), the PCE of TiO₂-doped LSCs with a large size of 20 cm × 20 cm is improved to 1.82%. The maximal PCE appears for LSCs with a size of 5 cm × 5 cm, reaching 2.62%. The reported method of dual transmission modes is a new alternative way to improve the performance of LSC devices, which does not need to change the optical properties of luminescent materials. Moreover, the production process is simple, low-cost and suitable for preparing large area LSCs, further promoting the application of LSCs.

Application of Metal-Organic Frameworks and Covalent Organic Frameworks as (Photo)Active Material in Hybrid Photovoltaic Technologies

Metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) are two innovative classes of porous coordination polymers. MOFs are three-dimensional materials made up of secondary building blocks comprised of metal ions/clusters and organic ligands whereas COFs are 2D or 3D highly porous organic solids made up by light elements (i.e., H, B, C, N, O). Both MOFs and COFs, being highly conjugated scaffolds, are very promising as photoactive materials for applications in photocatalysis and artificial photosynthesis because of their tunable electronic properties, high surface area, remarkable light and thermal stability, easy and relative low-cost synthesis, and structural versatility. These properties make them perfectly suitable for photovoltaic application: throughout this review, we summarize recent advances in the employment of both MOFs and COFs in emerging photovoltaics, namely dye-sensitized solar cells (DSSCs) organic photovoltaic (OPV) and perovskite solar cells (PSCs). MOFs are successfully implemented in DSSCs as photoanodic material or solid-state sensitizers and in PSCs mainly as hole or electron transporting materials. An innovative paradigm, in which the porous conductive polymer acts as standing-alone sensitized photoanode, is exploited too. Conversely, COFs are mostly implemented as photoactive material or as hole transporting material in PSCs.

Visibly Transparent Solar Windows Based on Colloidal Silicon Quantum Dots and Front-Facing Silicon Photovoltaic Cells

We demonstrate luminescent solar concentrators (LSCs) based on colloidal silicon quantum dots (SiQDs) as UV-selective fluorophores and coupled with front-facing silicon photovoltaic cells for the solar window application. The visibly transparent LSC composed of a thin layer of liquid SiQD suspension sandwiched between two thin glass slabs constitutes the windowpane, while strips of silicon photovoltaic cells with their front surfaces adhering to the LSC rear surface form the window frame. Furthermore, the LSC perimeter is surrounded by reflecting mirrors for preventing the fluorescence from leaking out through the edges. The SiQDs dispersed in 1-octadecene selectively absorb UV light and re-emit red fluorescence with quantum efficiency about 40%. Owing to the negligible overlap between the absorbance and photoluminescence spectra, the reabsorption effect is insignificant. The front-facing silicon photovoltaic strips located at the window frame can produce electricity by harvesting not only solar radiation but also the SiQD-generated fluorescence propagating from the windowpane. For the SiQD-LSC with the total light absorbing area equal to 12 cm × 12 cm and the reflecting mirrors tilted 45°, an overall power conversion efficiency of 2.47% under simulated sunlight can be obtained of which about 6% is contributed by the SiQD fluorescence. Meanwhile, the SiQD-LSC retains high spectral quality with average visible transmission and color rendering index through the windowpane equal to 86% and 94, respectively.

Mn2+/Yb3+ Codoped CsPbCl3 Perovskite Nanocrystals with Triple-Wavelength Emission for Luminescent Solar Concentrators

Doping metal ions into lead halide perovskite nanocrystals (NCs) has attracted great attention over the past few years due to the emergence of novel properties relevant to optoelectronic applications. Here, the synthesis of Mn2+/Yb3+ codoped CsPbCl3 NCs through a hot-injection technique is reported. The resulting NCs show a unique triple-wavelength emission covering ultraviolet/blue, visible, and near-infrared regions. By optimizing the dopant concentrations, the total photoluminescence quantum yield (PL QY) of the codoped NCs can reach ≈125.3% due to quantum cutting effects. Mechanism studies reveal the efficient energy transfer processes from host NCs to Mn2+ and Yb3+ dopant ions, as well as a possible inter-dopant energy transfer from Mn2+ to Yb3+ ion centers. Owing to the high PL QYs and minimal reabsorption loss, the codoped perovskite NCs are demonstrated to be used as efficient emitters in luminescent solar concentrators, with greatly enhanced external optical efficiency compared to that of using solely Mn2+ doped CsPbCl3 NCs. This study presents a new model system for enriching doping chemistry studies and future applications of perovskite NCs.

Geometry effects on luminescence solar concentrator efficiency: analytical treatment

Luminescence solar concentrators act as semitransparent photovoltaic cells of interest for modern urban environments. Here, their efficiencies were analytically derived for different regular unit shapes as simple, integral-free expressions. This allowed analysis of the shape and size effect on the device performance. All regular shapes appear to have a similar efficiency as revealed by optical path distribution formulas, despite differences in the perimeter length. Rectangles of the same area feature higher efficiency due to reduced average optical path. It comes with the cost of a longer perimeter, and the relation between these two is provided. An explicit formula for the critical size of an LSC unit, above which its inner part becomes inactive, has been obtained. For square geometry with matrix absorption coefficient α this critical size is ∼2.7/α, corresponding to 70-90 cm for common polymer materials. Obtained results can be used for treatment of individual units as well as for analysis of tiling for large areas.

Highly transparent and luminescent gel glass based on reabsorption-free gold nanoclusters

Luminescent and transparent composites formed by embedding luminophores in a solid matrix are essential components for several photonic applications, such as luminescent solar concentrators (LSCs) and luminescent down-shifting/conversion layers. For these applications, the optical losses, including reabsorption and scattering need to be minimized, while the photoluminescence (PL) emission must be stable against outdoor environments. Here, highly transparent and luminescent aluminosilicate glass doped with surface-engineered gold nanoclusters (AuNCs) was prepared without involving toxic elements and hazardous solvents. Such an AuNC@glass composite with a high loading (∼14 wt%) exhibits a unique absorption profile; near-unity absorptance in the absorption range but near-zero reabsorption in the emission region, and thus generates bright PL emission with negligible reabsorption losses. Meanwhile, the PL quantum yield was enhanced (from ∼1% to ∼14%) without sacrificing the Stokes shift, while still maintaining high optical transparency. In addition, they have high stability due to the effective protection of rigid inorganic matrices, and thus would be eco-friendly candidates for further preparation of efficient and reabsorption-free LSCs.

Visible-Transparent Luminescent Solar Concentrators Based on Carbon Nanodots in the Siloxane Matrix with Ultrahigh Quantum Yields and Optical Transparency at High-Loading Contents

Visible-transparent luminescent solar concentrators (VT-LSCs) can be integrated with solar cells for designing solar glasses. Recently, rare-earth complexes, semiconductor nanocrystals, and carbon nanodots (CNDs) have been applied in developing VT-LSCs. However, several challenges still existed, such as quantum yields (QYs) at high-loading contents, scattering/reabsorption losses, and stability. Here, highly luminescent and visible-transparent composites based on organosilane-functionalized CNDs (Si-CNDs) cross-linked in the siloxane matrix were prepared. The composites with a high-loading content (∼10 wt %) possess ultrahigh QYs of ∼94% due to surface passivation, cross-linking-enhanced emission, and negligible inter-CND energy transfer. Moreover, they still appear exceptionally transparent and, thus, are suitable for VT-LSCs. Eco-friendly VT-LSCs without colored tinting were fabricated, yielding high internal and external quantum efficiencies of ∼66% and ∼3.9%. Our demonstration would pave a bright way for the utilization of eco-friendly VT-LSCs in solar glasses.

Effect of co-sensitization of InSb quantum dots on enhancing the photoconversion efficiency of CdS based quantum dot sensitized solar cells

The effect of co-sensitization of CdS and InSb Quantum Dots (QDs) on the enhancement of efficiency of Quantum Dots Sensitized Solar Cells (QDSSCs) has been investigated. InSb is synthesized by a facile solvothermal method using indium metal particles and antimony trichloride as precursors. From TEM images the average particle size of InSb was found to be less than 25 nm. The I–V data showed photoconversion efficiency (PCE) of 0.8% using InSb QDs as a sensitizer layer for QDSSC. However, co-sensitization of InSb QDs and CdS QDs on the TiO₂ photoanode in QDSSCs showed an enhanced PCE of 4.94% compared to that of CdS sensitized solar cells (3.52%). The InSb QD layer broadens the light absorption range with reduced spectral overlap causing an improvement in light harvesting along with suppression of surface defects which reduced the recombination losses. As a result, co-sensitized TiO₂/CdS/InSb QDSSC exhibits a greatly improved PCE of 4.94%, which is 40% higher than that of TiO₂/CdS (3.52%) based QDSSCs due to improved light absorption with low recombination losses.

InSb co-sensitized QDSSCs showed relatively higher efficiency (4.94%) than CdS based QDSSCs (3.52%) due to improved light absorption with low recombination losses.

High-performance laminated luminescent solar concentrators based on colloidal carbon quantum dots

Luminescent solar concentrators (LSCs) are light-weight, semitransparent and large-area sunlight collectors for solar-to-electricity conversion. To date, carbon quantum dots (C-QDs) have attracted a lot of attention due to their size/shape/composition tunable optical properties, high quantum yield, excellent photostability, lower toxicity and simple synthetic methods using earth-abundant and low-cost precursors. However, due to the overlap between their absorption and emission spectra, it is still challenging to fabricate high-efficiency LSCs based on C-dots. In this work, we used C-QDs to fabricate semi-transparent large-area laminated LSCs (10 × 10 cm²). C-QDs have the absorption spectrum ranging from 300 to 550 nm with a Stokes shift of 0.6 eV. By optimizing the concentration of C-QDs, the laminated LSC exhibits a highest η _opt of 1.6%, which is 1.6 times higher than that of a single-layer LSC (100 mW cm^-2). In addition, the laminated LSC exhibits a power conversion efficiency of 0.7% under natural sunlight illumination (62 mW cm^-2) with excellent photostability. These findings suggest that laminated structured LSCs could be used for efficient solar energy harvesting compared to single layer or tandem structured LSCs based on colloidal C-QDs.

Fiber-Spinning-Chemistry Method toward In Situ Generation of Highly Stable Halide Perovskite Nanocrystals

All-inorganic halide perovskite nanocrystals (PNCs) have drawn increasing attention owing to their splendid optical properties. However, such nanomaterials suffer from intrinsic instability, greatly limiting their practical application. Meanwhile, environmental regulation has restricted the emissions of volatile organic compounds (VOCs), initiating a search for alternative approaches to PNC synthesis and film forming. Herein, fiber-spinning chemistry (FSC) is proposed for easy-to-perform synthesis of highly stable PNC fibrous films. The FSC process utilizes spinning fibers as reactors, reducing the generation of VOCs. This method enables the fabrication of CsPbX3 (X = Cl, Br, I) PNCs/poly(methyl methacrylate)/thermoplastic polyurethanes fibrous films at room temperature in one step, exhibiting tunable emission between 450 and 660 nm. Significantly, the in situ generation of PNCs in hydrophobic core-shell nanofibers results in highly improved fluorescence stability. PNCs/polymer fibrous films keep constant in photoluminescence (PL) after storage at atmosphere for 90 d and retain 82% PL after water immersion for 120 h (vs fluorescence quenching in 10 d in air or 5 h in water for pristine PNCs). The PNCs/polymer fibrous films endowed with superior optical stability and great flexibility show promising potentials in flexible optoelectronic applications. This work paves a facile way toward high-performance nanoparticles/polymer fibrous films.

A Critical Review on Enhancement of Photocatalytic Hydrogen Production by Molybdenum Disulfide: From Growth to Interfacial Activities

Ultrathin 2D molybdenum disulfide (MoS₂ ), which is the flagship of 2D transition-metal dichalcogenide nanomaterials, has drawn much attention in the last few years. 2D MoS₂ has been banked as an alternative to platinum for highly active hydrogen evolution reaction because of its low cost, high surface-to-volume ratio, and abundant active sites. However, when MoS₂ is used directly as a photocatalyst, contrary to public expectation, it still performs poorly due to lateral size, high recombination ratio of excitons, and low optical cross section. Besides, simply compositing MoS₂ as a cocatalyst with other semiconductors cannot satisfy the practical application, which stimulates the pursual of a comprehensive insight into recent advances in synthesis, properties, and enhanced hydrogen production of MoS₂ . Therefore, in this Review, emphasis is given to synthetic methods, phase transitions, tunable optical properties, and interfacial engineering of 2D MoS₂ . Abundant ways of band edge tuning, structural modification, and phase transition are addressed, which can generate the neoteric photocatalytic systems. Finally, the main challenges and opportunities with respect to MoS₂ being a cocatalyst and coherent light-matter interaction of MoS₂ in photocatalytic systems are proposed.

Enhancing the luminescence of carbon nanodots in films by tailoring the functional groups through alkylamine-functionalization and reduction

The luminescence of carbon nanodots in films was enhanced by tailoring functional groups because the energy levels could be significantly simplified.