A multispectral nanocluster doped multiple coating luminescent concentrator and method thereof

Abstract

The application discloses a kind of multispectral nanocluster doped multiple coating light concentrator and its method, including preparation substrate layer, preparation light emitting layer and preparation anti-reflection function layer, multispectral nanocluster doped light emitting layer is coated on substrate layer, anti-reflection function layer is coated on light emitting layer, the multispectral nanocluster is using Eu 3+ 、Tb 3+ 、Ce 3+ Ion or any combination thereof induced nanocluster of agglomerated polymer formation, the light emitting layer is obtained using multispectral nanocluster doped resin, for the absorption of incident short-wave light and conversion into characteristic emission light;The anti-reflection function layer is coupled to the outermost layer of light emitting coating, for limiting the light quantum conduction in coating, using different refractive index coating to limit the light quantum conduction in coating, to lock the fluorescent light quantum escape emitted by inner layer light emitting material, while, also can play the role of reducing interface reflection loss and improving the injection efficiency of incident light to light emitting layer.

Description

Technical Field

[0001] This invention relates to the field of solar concentrators and optoelectronic functional thin films, specifically to a light-emitting solar concentrator based on a europium-polymer nanocluster multi-shell structure and its preparation method. Background Technology

[0002] With the continued growth in energy demand and the gradual depletion of traditional fossil fuels, solar energy, as a clean and renewable energy source, has received widespread attention. Traditional photovoltaic power generation technology mainly relies on silicon-based or inorganic semiconductor materials to directly absorb sunlight and convert it into electricity. However, in building-integrated applications, it still faces problems such as high cost, large material usage, and limitations in transparency and appearance.

[0003] Luminescent solar concentrators (LSCs) absorb incident sunlight and re-emit it as long-wavelength light by introducing a luminescent medium into a transparent substrate. The photons are then transmitted to the edge of the device by total internal reflection within the substrate, where they are converted into electrical energy by small-area photovoltaic cells. This technology has the advantages of reducing the amount of photovoltaic materials used and being suitable for large-area transparent components.

[0004] Currently used luminescent media in LSC systems, such as organic dyes, quantum dots, or conjugated polymers, generally suffer from insufficient photostability, susceptibility to self-absorption or concentration quenching, and poor dispersibility and thermal stability in polymer matrices. While rare-earth luminescent materials offer advantages like narrow emission spectra and good photostability, their compatibility with polymer matrices is insufficient, their processing adaptability is limited, and their emission spectra do not match well with the absorption of edge photovoltaic devices. For traditional bulk-doped LSCs, the luminescent medium is uniformly dispersed throughout the matrix material. At high doping concentrations, this leads to a significant decrease in overall transmittance and an increase in self-absorption loss. Furthermore, the luminescent medium is prone to thermal decomposition or agglomeration during processing. Simultaneously, due to total internal reflection limitations, the photon injection waveguide efficiency within LSCs is low, and optical leakage easily occurs at the interface, further restricting the optical efficiency and practical applications of the devices.

[0005] To mitigate the transmittance reduction and processing difficulties caused by bulk doping, surface-coated LSCs are gaining increasing attention. By coating a transparent substrate with a luminescent coating, the luminescent medium can be concentrated in the surface area, achieving effective luminescence while maintaining the high transparency of the substrate.

[0006] However, existing coating-type LSC technology still has the following prominent problems: (1) Low optical coupling efficiency between the luminescent coating and the substrate: Traditional coating-type LSC usually adopts a single luminescent coating structure. There is a significant refractive index difference (Δn ≈ 0.5-0.6) between the luminescent coating and the air interface, which causes total internal reflection of the emitted light at the interface. A large number of photons escape from the device surface and are lost (the surface leakage rate can reach 50-80%). They cannot be effectively injected into the substrate waveguide for long-distance transmission, which seriously limits the edge photon collection efficiency; (2) High concentration aggregation of luminescent medium in the coating: In order to obtain sufficient luminescence intensity, a high concentration of luminescent medium (>5 wt%) is usually required in the coating. However, under high concentration conditions, organic dyes or quantum dots are prone to aggregation and concentration quenching. Rare earth complexes form micron-sized aggregates in the resin matrix due to poor compatibility, which leads to enhanced scattering, reduced transparency, and decreased luminescence efficiency; (3) Lack of active control methods for photon transmission path: Existing coated LSCs primarily rely on the refractive index of the substrate material for waveguide transmission. However, they lack effective control over the coupling process of emitted light into the substrate, especially in large-area devices. Photons are easily lost through the escape cone during transmission, limiting the effective transmission depth and causing a rapid decline in optical efficiency as the device size increases. Some studies have attempted to introduce anti-reflective coatings or low-refractive-index materials on the coating surface to reduce interface losses, but due to the lack of synergistic optimization design between the emitting layer and the anti-reflective layer, there is often a trade-off between luminescence intensity and optical coupling efficiency. Furthermore, existing luminescent coatings often use single rare-earth ions or organic dyes, resulting in narrow and singular emission spectra that cannot fully utilize the multi-band energy in the solar spectrum. Moreover, their spectral matching with different types of photovoltaic cells (such as silicon-based, perovskite, and organic thin-film cells) is limited.

[0007] Therefore, developing an LSC system that achieves high-concentration luminescence, low surface leakage, multispectral emission, and efficient optical waveguide transmission through multi-layer coating structure co-design combined with multispectral nano-aggregate luminescence technology is of great significance for breaking through the technical bottlenecks of existing coated LSCs, improving the optical efficiency of devices, and enhancing their practical application. Summary of the Invention

[0008] The purpose of this invention is to provide a multilayer coated solar concentrator based on multispectral nanoclusters and its preparation method. By designing and controlling the interface of coating a multilayer functional coating on the surface of a substrate skeleton, while ensuring transparency and processability, the invention improves luminous efficiency, reduces surface leakage loss, enhances photon coupling and transmission capabilities, and achieves efficient quantum light collection and conversion of light energy into electrical energy.

[0009] To achieve the above objectives, the present invention adopts the following technical solution: A method for fabricating a multispectral nanoaggregate-doped multi-coated light-emitting concentrator includes fabricating a substrate layer, a light-emitting layer, and an anti-reflection functional layer. The light-emitting layer, doped with multispectral nanoaggregates, is coated on the substrate layer, and the anti-reflection functional layer is coated on the light-emitting layer. The multispectral nanoaggregates are produced using Eu... 3+ 、Tb 3+ Ce 3+ The luminescent layer is formed by inducing the agglomeration of polymers with one or any combination of ions. It is obtained by doping resin with multispectral nano-agglomerates and is used to absorb incident short-wavelength light and convert it into characteristic emitted light. The anti-reflection functional layer is coupled to the outermost layer of the luminescent coating and is used to restrict the conduction of photons within the coating. Coatings with different refractive indices are used to confine the conduction of photons within the coating, thereby blocking the loss of photons emitted by the inner luminescent material. At the same time, it can also reduce interface reflection loss and improve the injection efficiency of incident light into the luminescent layer.

[0010] In the preparation method described above, the substrate layer is made of a single polymer sheet or a polymer sheet doped with the multispectral nanoclusters, wherein the polymer sheet includes polyester sheet, polyethylene sheet, polypropylene sheet or polycarbonate sheet.

[0011] The preparation method described above, specifically the preparation of the anti-reflective functional layer, involves dispersing a low-refractive-index fluoropolymer (PTFE, fluorinated polyacrylate, etc.) and its curing component in a predetermined mass ratio (e.g., 3:1) in an anhydrous solvent (e.g., anhydrous ethanol), and stirring until a stable low-refractive-index coating system is formed. The anti-reflective coating system is then applied to the surface of the luminescent layer via dip coating, with the coating thickness controlled at 10-100 μm (preferably 20-50 μm). After vacuum degassing (vacuum degree <0.1 MPa, time 10-20 minutes) and freeze-drying to remove the solvent, the coating is finally cured into a film (temperature 60-120℃, time 6-8 hours), forming a low-refractive-index, high-transparency anti-reflective functional layer. Without affecting transparency, this effectively suppresses photon leakage from the surface of the luminescent layer, reducing the surface leakage rate by 30-70%, and enhancing the coupling and transmission capability of emitted light into the polyester waveguide, increasing the effective transmission depth by 30-60%.

[0012] In the preparation method described above, the polymers induced to participate in the aggregation of the multispectral nanopolymers are: block polymers, including polystyrene-polyacrylic acid and polymethyl methacrylate-polyacrylic acid; random copolymers, including nitrile rubber; and homopolymers, including polyacrylonitrile.

[0013] The preparation method described above, wherein the preparation steps of the multispectral nanoaggregates are as follows: preparing a concentration of 1×10⁻⁶... -1 -1×10⁻ 6mol / L containing Eu 3+ 、Tb 3+ Ce 3+ A solution of a luminescent complex of one or any combination of ions is mixed with a polymer solution that can be induced to aggregate at 15-80°C. The mixture is stirred in an oil bath for 4-8 hours to complete the self-assembly reaction. The solvent is removed by rotary evaporation and the mixture is then vacuum dried to obtain nano-aggregate powder.

[0014] The luminescent coating is prepared by using a multispectral nano-aggregate doped resin, wherein the doping mass fraction of the nano-aggregates is 0.01–10.0 wt%.

[0015] Multispectral nanoclusters doped with multiple coatings to produce light-emitting concentrators according to any of the methods described.

[0016] The application of the light-emitting concentrator in photovoltaic cells: The light-emitting concentrator is processed into a plate or thin film structure of the required size, and photovoltaic cells are installed on its four sides or some sides. The size of the photovoltaic cells matches the size of the substrate edge. They are fixed by optical coupling adhesive or mechanical clamping, thus constructing a light-emitting solar concentrator device based on a multi-layer functional coating structure. Under sunlight or artificial light source irradiation, the incident light passes through the anti-reflection functional layer and enters the light-emitting coating. It is absorbed by the nano-aggregates and converted into characteristic emitted light (red, green, blue or multi-color light). The emitted light is transmitted to the edge through total internal reflection in the substrate waveguide, captured by the photovoltaic cells and converted into electrical energy.

[0017] According to the method for preparing photovoltaic cells using the light-emitting concentrator, the light-emitting concentrator is processed into a plate or thin film structure of the required size, and photovoltaic cells are installed on its four sides or some sides. The size of the photovoltaic cells matches the size of the substrate edge and is fixed by optical coupling adhesive or mechanical clamping, thus constructing a light-emitting solar concentrator device based on a multilayer functional coating structure. Under sunlight or artificial light source irradiation, the incident light passes through the anti-reflection functional layer and enters the light-emitting coating, is absorbed by the nano-aggregates and converted into characteristic emitted light. The emitted light is transmitted to the edge through total internal reflection in the substrate waveguide, is captured by the photovoltaic cells and converted into electrical energy.

[0018] The specific preparation steps for lanthanide ion nanoaggregates are as follows: (1) For Eu³⁺ nanopolymers (ETPAs, emitting red light): polystyrene-polyacrylic acid block copolymer (PS-PAA, number-average molecular weight Mn = 25000 g / mol), thiophene methane trifluoroacetone (TTA), o-phenanthroline (Phen), and EuCl₃·6H₂O are mixed in a molar ratio of PS-PAA:TTA:Phen:Eu³⁺ ​​= (1-3):(1-3):(1-3):(1-3) were dissolved in a mixed solvent of ethanol / dichloromethane (volume ratio (0-1):(1-0). EuCl3·6H2O was first stirred with TTA and Phen at 60℃ for 2 hours to fully coordinate them to form Eu(TTA)3Phen complex. Then PS-PAA was added, and the mixture was stirred in an oil bath at 15-80℃ (preferably 60-70℃) for 1-18 hours to complete the self-assembly reaction, forming nanospheres with Eu³⁺ complex as the core and PS-PAA as the shell. The solvent was removed by rotary evaporation and dried under vacuum (25-90℃, 8-72 hours) to obtain pale yellow Eu³⁺-induced nanoaggregate powder. After further grinding, ETPAs powder was obtained. Under 365 nm ultraviolet light excitation, ETPAs exhibited red light emission at 612-620 nm, with a luminescence quantum efficiency of 65-75%.

[0019] (2) For Tb³⁺ nanoaggregates (TTPAs, emitting green light): PS-PAA, TTA, Phen, and TbCl3·6H2O were dissolved in an ethanol / dichloromethane mixed solvent at the same molar ratio. First, TbCl3·6H2O was allowed to fully coordinate with the ligands to form a Tb(TTA)3Phen complex (the solution was light green). Then, PS-PAA was added, and the mixture was stirred in an oil bath at 30-80℃ for 6-8 hours to carry out a self-assembly reaction. After rotary evaporation and vacuum drying, light green Tb³⁺-induced nanoaggregate powder TTPAs was obtained. Under 365 nm ultraviolet light excitation, TTPAs exhibited green light emission at 545 nm. 5 D4→ 7 (F5 transition), the luminescent quantum efficiency can reach 55-65%.

[0020] (3) For Ce³⁺ nanoaggregates (CTPAs, emitting blue light): PS-PAA, TTA, Phen, and CeCl3·6H2O were dissolved in an ethanol / dichloromethane mixed solvent at the same molar ratio. CeCl3·6H2O was first fully coordinated with the ligands to form a Ce(TTA)3Phen complex. Then PS-PAA was added, and the mixture was stirred in an oil bath at 60-70℃ for 6-8 hours to carry out a self-assembly reaction. After rotary evaporation and vacuum drying, light blue Ce³⁺-induced nanoaggregate powder CTPAs was obtained. Under 365 nm ultraviolet light excitation, CTPAs exhibited blue light emission at 410-450 nm (5d→4f transition), with a luminescence quantum efficiency of 45-55%. By adjusting the mixing ratio of three nano-aggregates, Eu³⁺, Tb³⁺, and Ce³⁺, emission modulation from monochromatic to multicolor can be achieved, covering a wide spectral range from blue light 410 nm to green light 545 nm to red light 620 nm, meeting the needs of different application scenarios.

[0021] Preparation of luminescent coating: The coating composition for preparing coatings with different luminescent spectra includes: (1) Luminescent component: nano-aggregate powders (ETPAs, TTPAs, CTPAs) with different spectra (red, green, blue three primary colors or multicolor spectra composed of them) prepared in step three above, with a doping mass fraction of 0.01-10.0 wt% (preferably 3.0-4.0 wt%); (2) Adhesive resin composition: including but not limited to epoxy resin (such as bisphenol A type epoxy resin, polyamide-based epoxy resin, etc.), phenolic resin, urea-formaldehyde resin and other base materials, as well as corresponding curing agents (such as amine curing agents, acid anhydride curing agents, etc.); (3) Solvent: polar organic solvents such as N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), tetrahydrofuran (THF) are used to dissolve nano-aggregates and adjust the viscosity of the coating.

[0022] The anti-reflective functional layer is disposed outside the light-emitting layer, and its refractive index is lower than that of the substrate layer, enhancing the coupling and transmission of emitted light into the interior of the substrate layer. A high-efficiency light-emitting layer and a low-refractive-index, high-transmittance polymer material are introduced onto the surface to act as a coating that emits light and confines photons within the coating layer, resulting in a light-emitting solar concentrator with a dual-layer functional film structure.

[0023] Coating and curing of the luminescent coating: The prepared luminescent coating is uniformly coated onto the surface of the substrate layer prepared in step one by means of dip coating, scraping coating, spraying or spin coating, with a coating thickness of 10-100 μm (preferably 20-50 μm). After coating, degassing is performed under vacuum conditions (vacuum degree <0.1 MPa, time 10-30 minutes) to remove air bubbles inside the coating and ensure the optical uniformity of the coating. Subsequently, drying is performed to remove residual solvent in a freeze-drying system or an oven at 80-120℃ (time 2-6 hours). Finally, curing is performed (temperature 80-150℃, time 8-12 hours) to form a luminescent layer with good adhesion, rich luminescent components, and high transparency on the substrate surface. The luminescent coating is mainly distributed in the surface area and is used to effectively absorb incident short-wavelength light and convert it into characteristic emitted light, while simultaneously coupling the emitted light into the substrate waveguide for transmission.

[0024] The described solar concentrator employs a functionally partitioned structural design. It selectively incorporates low-concentration (0.1-0.5 wt%) lanthanide ion nanoclusters into the substrate framework to form a luminescent waveguide layer. A luminescent coating containing a high concentration (3.0-4.0 wt%) lanthanide ion nanoclusters is then deposited on the surface of this waveguide layer. A low-refractive-index anti-reflective functional layer is further deposited outside the luminescent coating, forming a three-layer (doped substrate + luminescent layer + anti-reflective functional layer) or a three-layer multi-shell functional structure (single substrate + luminescent layer + anti-reflective functional layer). This layered design concentrates the luminescent medium in the surface region, achieving efficient light emission and waveguide transmission while maintaining high substrate transparency.

[0025] Furthermore, the concentrator, through the synergistic effect of the light-emitting layer and the anti-reflection functional layer, improves the coupling efficiency of incident light and the transmission capability of photons in the waveguide without changing the intrinsic light-emitting characteristics of the light-emitting center. The performance indicators of the concentrator are as follows: (1) Spectral coverage: Through the synergistic luminescence of Eu³⁺, Tb³⁺, and Ce³⁺ ternary lanthanide ions, the luminescence spectrum is in the broad band range of blue light 410 nm to green light 545 nm to red light 620 nm, which exactly matches the absorption spectrum of most different types of solar cells, especially the absorption of flexible polymer solar cells; (2) Optical quantum yield: Under 365 nm ultraviolet light excitation, the optical quantum yield of a single rare earth nanoaggregate can reach 45-75%, and the overall quantum yield of the multispectral composite system can reach 25-63%; (3) Surface leakage suppression: By introducing an anti-reflection functional layer, the surface leakage rate is reduced by 30-70%, which significantly suppresses escape cone loss; (4) Effective transmission depth: Compared with the single-layer structure, the multi-layer coating structure can improve the effective transmission depth of photons in the waveguide by 30-60%, which slows down the optical efficiency decay of large-area devices; (5) Photovoltaic conversion efficiency: After coupling with photovoltaic cells, the photovoltaic conversion efficiency of polymer solar cells can reach 5.5%, which is 40-60% higher than that without a concentrator.

[0026] The present invention has the following beneficial effects: The concentrator, through the synergistic effect of the luminescent layer and the anti-reflective functional layer, improves the coupling efficiency of incident light and the transmission capability of photons in the waveguide without altering the intrinsic luminescence characteristics of the luminescent center. The emission spectrum spans a broad band from 410 nm for blue light to 545 nm for green light to 620 nm for red light, precisely matching the absorption of most different types of solar cells, especially flexible polymer solar cells, achieving an optical quantum yield of 25-63%. By introducing the anti-reflective functional layer, the surface leakage rate is reduced by 30-70%, significantly suppressing escape cone loss. The effective transmission depth of photons within the waveguide is increased by 30-60%. The photoelectric conversion efficiency of the connected polymer solar cell can reach 5.5%. This technology has enormous development potential for the future development of flexible portable power generation systems. Multispectral synergistic luminescence and solar spectrum matching: This invention achieves broadband emission from blue light (410 nm) to green light (545 nm) and then to red light (620 nm) through the synergistic luminescence of Eu³⁺, Tb³⁺, and Ce³⁺ ternary lanthanide ion nanoclusters. Compared with a single rare earth ion system, it can make fuller use of the multi-band energy in the solar spectrum and achieve better spectral matching with different types of photovoltaic cells (silicon-based, perovskite, organic thin films, etc.), thereby improving the overall photoelectric conversion efficiency.

[0027] Synergistic Effect of Multilayer Coating Structure: This invention constructs a multilayer coated solar concentrator structure based on nano-aggregates. By setting functional partitions of the luminescent medium within the surface luminescent coating and introducing an anti-reflection layer, synergistic control of incident light absorption, re-emission, and waveguide transmission processes is achieved. Compared to traditional bulk-doped LSCs, while maintaining high substrate transparency (transmittance >80%), it significantly improves luminescence intensity (2-3 times higher), reduces surface leakage loss (30-70% lower), and enhances effective transmission depth (30-60% higher), thereby greatly improving overall photon utilization efficiency and edge quantum collection efficiency.

[0028] In the aforementioned application, by comparing the single-layer polyester waveguide structure with the multi-shell structure that incorporates a luminescent coating and an anti-reflective functional layer, it is demonstrated that the multi-shell luminescent material significantly improves photon injection efficiency, light transmission capability, and edge photovoltaic coupling performance while maintaining high transparency.

[0029] Balancing High-Concentration Luminescence with Transparency: This invention employs surface coating technology to concentrate high-concentration nano-aggregates (3.0-4.0 wt%) in a surface luminescent coating, rather than uniformly dispersing them throughout the entire substrate. This effectively avoids the significant decrease in overall transmittance (down to <60%) and processing difficulties caused by traditional high-concentration bulk doping. Through this layered design, the luminescence intensity is greatly enhanced without significantly affecting the visible light transmittance of the substrate (still maintaining >80%), thereby improving the optical output capability and aesthetics of the luminescent solar concentrator.

[0030] Nanopolymer Structure Suppresses Concentration Quenching: This invention utilizes a polymer-induced self-assembly method to prepare lanthanide ion nanopolymers. Through the amphiphilic structure and steric hindrance effect of block copolymers, rare earth complexes are confined within 600-800 nm nanospheres, effectively isolating adjacent luminescent centers. Even at high concentrations (3-4 wt%), high luminescence quantum efficiency (>60%) is maintained, significantly suppressing the concentration quenching effect. Simultaneously, the nanopolymers are uniformly dispersed in the resin matrix, without forming micron-sized aggregates, exhibiting good optical uniformity and low scattering loss.

[0031] Simple process and wide applicability: The fabrication process of the multi-layer coated concentrator described in this invention is simple, employing conventional coating processes such as dip coating and curing, requiring no complex equipment and facilitating large-scale production. The coating technology is applicable to various transparent substrate materials (polyester, polyolefin, polycarbonate, etc.), and can be used to prepare concentrator devices of different areas (from cm² to m²) and shapes (flat plates, curved surfaces, etc.). Its applications are wide-ranging, including building-integrated photovoltaic windows, transparent roofs for agricultural greenhouses, and flexible portable power generation systems. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of a multi-layer coated light-emitting concentrator; Figure 2 This is a schematic diagram of the process of the present invention; Figure 3 TEM image of europium-polymer nanoclusters doped with polyester high-efficiency luminescent material; Figure 4 Fluorescence emission spectra of low-content (0.1–0.5 wt%) europium-polymer nanoclusters doped polyester waveguide structures and multi-shell structures formed by introducing a high-concentration epoxy luminescent coating (3–4 wt%) on the surface; Figure 5 Comparative results of optical performance tests on different polyester luminescent structures: (a) Surface reflection spectra of pure polyester waveguide structure, polyester waveguide structure with luminescent layer, and multi-shell structure with high-concentration luminescent coating and anti-reflection functional layer; (b) Curves showing the relationship between surface leakage ratio and in-plane transmission length for different structural samples under side illumination; (c) Depth resolution distribution of red edge emission intensity obtained at different acquisition positions under top illumination; (d) Simulated optical collection efficiency of multi-shell luminescent focusing structure under different device sizes and lengths.

[0033] Figure 6 Comparison of coupling efficiency between concentrators with different structures and solar cells; Detailed Implementation

[0034] The present invention will be described in detail below with reference to specific embodiments. Example 1

[0035] (1) Preparation of lanthanide-induced block copolymer nanoaggregates: Polystyrene-polyacrylic acid block copolymer (PS-PAA), Eu³⁺ and its complexes (TTA, Phen) powders were added to a suitable solvent mixture and stirred thoroughly in an oil bath at 60–70℃ for 8 hours to allow the components to fully dissolve and undergo a self-assembly reaction to form nanospheres. Subsequently, the solvent was removed by rotary evaporation and dried under vacuum to obtain ETPAS powder.

[0036] (2) Preparation of ETPAS@PET matrix: ETPAS powder and PET polyester powder were vacuum dried at 80℃ and 120℃ for 48 hours respectively to remove moisture. They were then thoroughly mixed and added to a twin-screw micro composite extruder for melt blending at 265–285℃. The mixture was then injection molded into a sheet with a size of 67×16×3 mm to obtain a polyester waveguide matrix (doped substrate layer) doped with 0.1–0.5wt% ETPAS.

[0037] The lanthanide element is Eu³⁺, which emits red light under excitation light, and the complex includes thiophene methane trifluoroacetone (TTA) and o-phenanthroline (Phen).

[0038] The polyester materials include not only polyethylene terephthalate (PET), but also PLA and other linear polyesters. Example 2

[0039] (1) Preparation of the luminescent layer: 8 mmol ETPAS was dissolved in 10 mL DMF and stirred at room temperature until homogeneous. Then, it was mixed with polyamide-based epoxy resin (component A) and hardener (component B) at a mass ratio of 5:2 to form a homogeneous coating. The coating was uniformly applied to the surface of the ETPAS@PET substrate and degassed under vacuum. After removing residual solvent in a freeze-drying system, the coating was cured for 12 hours to obtain a luminescent layer with good adhesion, optical uniformity, and a high concentration of ETPAS (approximately 3–4 wt%).

[0040] (2) Preparation of the anti-reflective functional layer: PTFE and fluorinated curing agent are dispersed in anhydrous ethanol at a mass ratio of 3:1 and stirred evenly to form a suspension. The suspension is then coated onto the surface of the aforementioned light-emitting layer by dip coating, followed by vacuum degassing and freeze-drying. Finally, the suspension is cured for 8 hours to form an anti-reflective functional layer with low refractive index and high transparency, which effectively suppresses edge light leakage.

[0041] The preparation of the europium-polymer nanoclusters doped polyester high-efficiency luminescent material, wherein the polyester material includes not only polyethylene terephthalate, but also PLA and other linear polyesters. Example 3

[0042] Experimental Objectives and Methods: To verify the optical performance of multi-shell structures in concentrators, this embodiment compares the prepared multi-shell luminescent polyester sample with a single-layer concentrator, and systematically studies the effects of different structures on optical efficiency, visible light transmittance, and coupling performance with solar cells.

[0043] Table 1: Optical efficiency, average visible light transmittance, and coupling efficiency with solar cells of multi-shell luminescent polyester samples and single-layer concentrators.

[0044]

[0045] Figure 2The overall fabrication process of the multi-shell luminescent material is illustrated. First, europium-polymer nanopolymers (ETPAs) are prepared using a solution self-assembly strategy. In the selected solvent system, the polystyrene (PS) segments are hydrophobic, and the polyacrylic acid (PAA) segments are hydrophilic. The carboxyl groups (–COOH) on the PAA molecular chains coordinate with Eu³⁺ ions through oxygen atoms, constructing a stable nanospherical coordination structure. Subsequently, ETPAs are melt-blended with polyethylene terephthalate (PET) to form a stable hybrid composite polyester waveguide layer (base layer) through synergistic interaction with the PET matrix. After the base layer is prepared, a high-concentration (approximately 3–4 wt%) ETPAs / epoxy resin luminescent coating is further coated on its surface to enhance short-wavelength light absorption and re-emission performance. Finally, a low-refractive-index fluoropolymer anti-reflective functional layer is introduced onto the surface of the luminescent layer to suppress photon leakage to the air side and promote the coupling and long-range transmission of emitted light into the waveguide, thereby constructing a functionally synergistic multi-shell luminescent material.

[0046] Figure 3 Transmission electron microscopy (TEM) images of europium ion-induced block copolymer nanoaggregates (ETPAs). Figure 3 As shown, the obtained nanoaggregates have a regular spherical structure, with particle sizes mainly distributed in the range of 600–800 nm. This indicates that ETAPs can form stable and uniform nanospheres during solution self-assembly, providing a basis for subsequent incorporation into a polyester matrix to construct multi-shell luminescent materials.

[0047] Figure 4 This paper presents the fluorescence emission spectra of ETPAs@PET hybrid luminescent polyester materials with different doping concentrations and their surfaces coated with high-concentration epoxy luminescent coatings. The results show that the low-doped (0.1–0.5 wt%) ETPAs@PET matrix exhibits a characteristic emission peak for Eu³⁺ ions at approximately 617 nm. The fluorescence intensity initially increases and then decreases with increasing doping concentration, reaching a matrix peak at 0.4 wt%. Furthermore, by dip-coating with high-concentration epoxy luminescent coatings (3.0, 3.5, and 4.0 wt%), the fluorescence intensity of the material is significantly enhanced, with the 3.5 wt% coating showing the strongest emission, reaching a level far exceeding that of the uncoated substrate. When the coating concentration increases to 4.0 wt%, the fluorescence decreases slightly, possibly due to a local concentration quenching effect. These results demonstrate that coating with a high-concentration luminescent layer can significantly improve the overall luminescence intensity while maintaining substrate transparency, providing an effective means for photon collection in multi-shell luminescent solar concentrators.

[0048] Figure 4b demonstrates the impact of different film structures on the optical transparency of the concentrator. The visible light transmittance of two types of samples was tested: one type consisted of a single-layer high-concentration epoxy luminescent coating (3.5 wt%) coated on an ETPAs@PET substrate; the other type featured a multi-shell structure, which involved introducing a low-refractive-index fluoropolymer anti-reflective layer on top of the high-concentration epoxy luminescent coating. The results showed that the transmittance of the single-layer film sample decreased compared to the substrate, mainly due to losses caused by the absorption and scattering of incident light by the high-concentration luminescent coating. In contrast, the multi-shell structure sample exhibited a significantly smaller decrease in transmittance, maintaining high overall transparency while achieving efficient luminescence. This comparison indicates that the multi-shell design, incorporating an anti-reflective functional layer, effectively improves transmittance while ensuring luminescence performance, providing technical support for the application of high-optical-efficiency luminescent solar concentrators.

[0049] To systematically investigate the impact of different light-emitting concentrator structures on photon management performance, comparative tests were conducted on the optical properties of three representative samples: pure polyester waveguide structures (PET), polyester waveguide structures with epoxy-based light-emitting layers (PET-LEC), and those further forming multi-shell structures (ETPAs@PET-LEC-ARF, high-concentration light-emitting coating + anti-reflective functional layer). Specific tests included surface reflection spectra, surface leakage, depth-resolution red-edge emission, and device optical collection efficiency.

[0050] like Figure 5 As shown in Figure a, the surface reflection spectra of the three types of samples indicate that the pure PET waveguide has the highest reflectivity throughout the entire measurement band. After the introduction of the luminescent layer, the surface reflection is significantly reduced, especially in the near-ultraviolet region (approximately 390 nm), indicating that incident photons are more easily injected into the waveguide. When ETPAs nanoaggregates are incorporated into the luminescent layer, the near-ultraviolet reflection further decreases, showing enhanced near-field absorption and re-emission. After further covering with an anti-reflection functional layer, the reflectivity of the multi-shell structure reaches the lowest level throughout the entire band, while photons within the waveguide are more effectively captured and transmitted.

[0051] Figure 5 b shows the variation of surface leakage with in-plane transmission length for samples with different structures under side illumination. The results show that the pure PET sample has the most severe surface leakage, indicating that photons are easily lost from the escape cone. After introducing the luminescent layer, the leakage is significantly reduced, indicating that photons are effectively confined at the luminescent layer-PET interface. Further doping with ETPAs nanoclusters further reduces the leakage, which is attributed to the scattering-recapture effect of the nanoclusters, which helps near-critical angle photons re-enter the guided mode. The multi-shell structure shows the lowest leakage over the entire transmission length, proving that the low refractive index anti-reflection layer and optical tunneling work synergistically to effectively suppress surface optical loss.

[0052] To evaluate the impact of optical tunneling on red edge light transmission, the depth-resolved red emission intensity (approximately 612 nm) at different acquisition locations was measured under top illumination. The results are as follows: Figure 5 As shown in c. The red light signal of the pure PET sample is weak and mainly confined to the surface area; after the introduction of the emitting layer, the red light intensity is significantly enhanced, but it is still concentrated on the surface; the ETPAs@PET-EL sample shows that the red light emission center migrates to the depth of the waveguide, proving that photons are no longer confined to the surface propagation path, and the optical tunneling effect is verified; the multi-shell structure sample exhibits the highest red light intensity across the entire depth range, indicating that the photon injection and long-range transmission efficiency are optimal.

[0053] Figure 5 d shows the simulated optical collection efficiency (η) of the multi-shell light-emitting focusing structure under different device sizes and lengths. opt The results show that the sample η with the introduced light-emitting layer opt Significantly higher than pure PET waveguides, while multi-shell structure samples not only have the highest η opt Moreover, the efficiency decays the slowest with increasing transmission length, further verifying the effectiveness of the optical tunneling-assisted photon management strategy in enhancing the capture, transmission, and utilization of red photons.

[0054] Figure 6 The current-voltage (I-V) characteristics of a multi-shell light-emitting solar concentrator coupled with a photovoltaic cell were demonstrated. The photoelectric conversion efficiency was compared under different material structures and doping conditions. (1) In PET concentrators with simple doping of ETPAs, different doping amounts (0.1, 0.2, 0.3, 0.4 wt%) showed significant differences. The efficiency was highest when doped with 0.3 wt%, followed by 0.2 wt%, 0.4 wt%, and 0.1 wt%, indicating that the appropriate doping amount can achieve the best balance between luminous intensity and light transmittance.

[0055] (2) After coating a single layer of high-concentration epoxy luminescent coating (3.0, 3.5, 4.0 wt%) on the PET substrate surface, the photoelectric conversion efficiency was further improved. The 3.5 wt% epoxy coating performed best, followed by 3.0 wt%, while the 4.0 wt% coating showed a slight decrease, mainly due to the high-concentration quenching effect leading to a decrease in luminescent efficiency.

[0056] (3) A multi-shell structure was adopted, namely, a high-concentration epoxy luminescent coating (3.5 wt%) was coated on a PET substrate doped with the optimal concentration of ETPAs (0.3 wt%), and a low-refractive-index fluoropolymer anti-reflective layer (ARF) was introduced to further optimize photon injection, transmission, and edge collection efficiencies. The results showed that the 20 μm thick ARF layer achieved the highest photoelectric conversion efficiency, followed by the 50 μm thick ARF layer, both significantly better than the sample without ARF. These results verify that by rationally designing the multi-shell structure and controlling the doping concentration and coating thickness, the photoelectric conversion performance of the luminescent solar concentrator can be significantly improved.

[0057] It should be understood that those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A method for preparing a multispectral nano-aggregate doped multi-coated light-emitting concentrator, characterized in that, The process includes preparing a substrate layer, a light-emitting layer, and an anti-reflective functional layer. The light-emitting layer, doped with multispectral nanoaggregates, is coated onto the substrate layer, and the anti-reflective functional layer is coated onto the light-emitting layer. The multispectral nanoaggregates are prepared using Eu... 3+ 、Tb 3+ Ce 3+ The luminescent layer is formed by inducing the agglomeration of polymers with one or any combination of ions. It is obtained by doping resin with multispectral nano-agglomerates and is used to absorb incident short-wavelength light and convert it into characteristic emitted light. The anti-reflection functional layer is coupled to the outermost layer of the luminescent coating and is used to restrict the conduction of photons within the coating. Coatings with different refractive indices are used to confine the conduction of photons within the coating, thereby blocking the loss of photons emitted by the inner luminescent material. At the same time, it can also reduce interface reflection loss and improve the injection efficiency of incident light into the luminescent layer.

2. The preparation method according to claim 1, characterized in that, The substrate layer is made of a single polymer sheet or a polymer sheet doped with the multispectral nanoclusters, wherein the polymer sheet includes polyester sheet, polyethylene sheet, polypropylene sheet or polycarbonate sheet.

3. The preparation method according to claim 1, characterized in that, Preparation of the anti-reflective functional layer: A low-refractive-index fluoropolymer and its curing components are dispersed in an anhydrous solvent at a predetermined mass ratio and stirred until a stable low-refractive-index coating system is formed. The anti-reflective coating system is then applied to the surface of the luminescent layer by dip coating, with the coating thickness controlled at 10-100 μm. After vacuum degassing and freeze-drying to remove the solvent, the coating is finally cured into a film, forming a low-refractive-index, high-transparency anti-reflective functional layer. Without affecting transparency, this layer effectively suppresses photon leakage from the surface of the luminescent layer, reducing the surface leakage rate by 30-70%, and enhances the coupling and transmission capability of emitted light into the polyester waveguide, increasing the effective transmission depth by 30-60%.

4. The preparation method according to claim 1, characterized in that, The polymers induced to participate in aggregation in the multispectral nanoaggregates are: block polymers, including polystyrene-polyacrylic acid and polymethyl methacrylate-polyacrylic acid; random copolymers, including nitrile rubber; and homopolymers, including polyacrylonitrile.

5. The preparation method according to claim 1, characterized in that, The preparation steps of the multispectral nanoaggregates are as follows: Prepare a concentration of 1×10⁻⁶ -1 -1×10⁻ 6 mol / L containing Eu 3+ 、Tb 3+ Ce 3+ A solution of a luminescent complex of one or any combination of ions is mixed with a polymer solution that can be induced to aggregate at 15-80°C. The mixture is stirred in an oil bath for 4-8 hours to complete the self-assembly reaction. The solvent is removed by rotary evaporation and the mixture is then vacuum dried to obtain nano-aggregate powder.

6. The preparation method according to claim 1, characterized in that, The luminescent coating is made of a resin doped with multispectral nano-aggregates, with a doping mass fraction of 0.01–10.0 wt%.

7. A multispectral nanoaggregate doped multi-coated light-emitting concentrator prepared by the method according to any one of claims 1-6.

8. The application of the light-emitting concentrator according to claim 7 in photovoltaic cells, characterized in that, The light-emitting concentrator is fabricated into a plate or thin film structure of the required size, and photovoltaic cells are installed on its four sides or some sides. The size of the photovoltaic cells matches the size of the substrate edge and is fixed by optical coupling adhesive or mechanical clamping. This completes the construction of a light-emitting solar concentrator device based on a multi-layer functional coating structure. Under sunlight or artificial light source irradiation, the incident light passes through the anti-reflection functional layer and enters the light-emitting coating. It is absorbed by the nano-aggregates and converted into characteristic emitted light. The emitted light is transmitted to the edge through total internal reflection in the substrate waveguide, where it is captured by the photovoltaic cells and converted into electrical energy.

9. The method for preparing photovoltaic cells using the light-emitting concentrator according to claim 7, characterized in that, The light-emitting concentrator is fabricated into a plate or thin film structure of the required size, and photovoltaic cells are installed on its four sides or some sides. The size of the photovoltaic cells matches the size of the substrate edge and is fixed by optical coupling adhesive or mechanical clamping. This completes the construction of a light-emitting solar concentrator device based on a multi-layer functional coating structure. Under sunlight or artificial light source irradiation, the incident light passes through the anti-reflection functional layer and enters the light-emitting coating. It is absorbed by the nano-aggregates and converted into characteristic emitted light. The emitted light is transmitted to the edge through total internal reflection in the substrate waveguide, where it is captured by the photovoltaic cells and converted into electrical energy.

10. A photovoltaic cell prepared by the method according to claim 9.

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