Downconversion material, downconversion film, photovoltaic cell, and method for producing same

Abstract

The invention discloses a down-conversion material, a down-conversion film, a photovoltaic cell and a preparation method thereof, and belongs to the technical field of photovoltaics. The down-conversion material has a core-shell structure and comprises a core and a shell layer coating the core, wherein the core comprises quantum dots, and the shell layer comprises a hyperbranched polymer; the maximum emission peak of the emission spectrum of the quantum dot is larger than 380 nm and smaller than 780 nm, and the quantum efficiency of the quantum dot is not lower than 70%. According to the down-conversion material, the down-conversion film, the photovoltaic cell and the preparation method of the down-conversion material, the down-conversion film, the photovoltaic cell and the preparation method of the down-conversion film, the spectral response capability of a photovoltaic module can be improved by constructing a structural system with the quantum dots as the core and the hyperbranched polymer as the shell; the unique three-dimensional branched structure of the hyperbranched polymer can coat the quantum dots on a molecular level, so that the fluorescence attenuation problem of the quantum dots caused by oxygen, water vapor and a packaging aid is remarkably inhibited, and the chemical and optical stability of the quantum dots in hot-pressing packaging and outdoor environments is improved.

Description

Technical Field

[0001] The present invention belongs to the field of photovoltaic technology, and in particular relates to a down-conversion material, a down-conversion film, a photovoltaic cell and a preparation method thereof. Background Art

[0002] Solar cells, which use the photovoltaic effect to convert sunlight directly into electricity, have gained widespread commercial application worldwide due to their renewable, clean, and distributed power supply advantages. However, with the continuous advancement of photovoltaic technology, the conversion efficiency and packaging life of solar cells have become key factors restricting their further adoption.

[0003] However, the natural solar spectrum contains a significant amount of short-wavelength ultraviolet radiation, which can cause persistent damage to solar cell modules, particularly the cell structure, through multiple processes including light aging, thermal aging, and chemical degradation. This can lead to power output degradation. This long-term degradation induced by UV radiation has become a core technical bottleneck affecting the reliability and outdoor lifespan of photovoltaic modules.

[0004] To combat performance degradation caused by UV rays, existing technologies primarily employ two strategies. One is UV blocking, which involves adding UV absorbers or installing UV filters in the PV module encapsulation layer to remove UV light from the incident spectrum, thereby reducing damage to the cells and encapsulation materials. However, this blocking approach inevitably results in a loss of the incident spectrum, shielding some convertible photons, which in turn affects the photovoltaic conversion efficiency of the solar cell. Furthermore, the aging problem of the UV blocking film itself has not been effectively addressed, and performance degradation persists after long-term use.

[0005] Another approach is spectral down-conversion, which uses special materials to convert high-energy ultraviolet photons into visible or near-infrared photons with lower energy that are easily absorbed by solar cells. This approach theoretically preserves the utilization of ultraviolet light energy while avoiding its damage to the cell structure, and is therefore considered a more ideal approach. However, currently used down-conversion materials, such as organic fluorescent dyes, rare-earth-doped inorganic materials, and rare-earth coordination materials, all have different problems. For example, although organic fluorescent materials have adjustable absorption peaks, they have poor photostability and are easily degraded under ultraviolet irradiation; rare-earth inorganic materials are more stable, but have large particle sizes and poor dispersibility, which seriously affect the transmittance of the encapsulation layer; and rare-earth coordination materials are generally more expensive, and have limited absorption efficiency and fluorescence emission range, making it difficult to strike a balance between conversion efficiency and long-term stability.

[0006] Therefore, it is necessary to provide a new solution to the above technical problems. Summary of the Invention

[0007] The object of the present invention is to provide a down-conversion material, a down-conversion film, a photovoltaic cell and a preparation method thereof, which can improve the photoelectric conversion efficiency and have good stability.

[0008] To achieve the above objectives, the present invention provides the following technical solutions:

[0009] In a first aspect, the present invention provides a down-conversion material for a photovoltaic cell, wherein the down-conversion material has a core-shell structure, comprising a core and a shell layer coated outside the core; wherein the core comprises quantum dots, and the shell layer comprises a hyperbranched polymer; the maximum emission peak of the emission spectrum of the quantum dots is greater than 380 nm and less than 780 nm, and the quantum efficiency of the quantum dots is not less than 70%.

[0010] In one or more embodiments, the average size of the lower conversion material is 2 to 40 nm. The average size of the lower conversion material is 2 to 40 nm, including all numbers within this range and any range within this range, such as 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, 11 nm, 12 nm, 13 nm, 14 nm, 15 nm, 16 nm, 17 nm, 18 nm, 19 nm, 20 nm, 21 nm, 22 nm, 23 nm, 24 nm, 25 nm, 26 nm, 27 nm, 28 nm, 29 nm, 30 nm, 31 nm, The size of the down-conversion material in the present invention refers to the size of the whole core-shell structure including the shell. The down-conversion material is a core-shell structure, and the thickness of the outer shell has a less influence on the emission wavelength.

[0011] In one or more embodiments, the quantum dots are binary quantum dots or unit quantum dots; the binary quantum dots include at least one of the following components: MgO, MgS, MgSe, MgTe, CaO, CaS, CaSe, CaTe, SrO, SrS, SrSe, SrTe, BaO, BaS, BaSe, BaTe, ZnO, ZnS, ZnSe, ZnTe, CdO, CdS, CdSe, HgO, HgS, HgSe, HgTe, Al2O3, Al2S3, Al2Se3, Al2 Te3, Ga2O3, Ga2S3, Ga2Se3, Ga2Te3, In2O3, In2S3, In2Se3, In2Te3, SiO2, GeO2, SnO2, SnS, SnSe, SnTe, PbO, PbO2, PbS, PbSe, PbTe, AlN, AlP, AlAs, AlSb, GaN, GaP, GaAs, GaSb, InN, InP, InAs, InSb or BP; the unit quantum dot includes at least one of the following components: C, Si or Ge.

[0012] In one or more embodiments, the quantum dots are ternary quantum dots or quaternary quantum dots; the ternary quantum dots include at least one of the following components: CuGaO, CuGaS, CuGaSe, CuGaTe, CuInO, CuInS, CuInSe, CuInTe, CuAlO, CuAlS, CuAlSe, CuAlTe, AgGaO, AgGaS, AgGaSe, AgGaTe, AgInO, AgInS, AgInSe, AgInTe, AgAlO, AgAlS, AgAlSe, AgAlTe, CuSTe, CuSeTe, AgSTe, AgSeTe, CuZnTe, AgZnTe, ZnCdS, ZnCdSe, ZnCdTe, PbSSe, PbSTe, PbSeTe or ternary perovskite; the quaternary quantum dots include at least one of the following components: CdTeZnSe, CuInGaS, CuInGaSe or quaternary perovskite.

[0013] For ternary quantum dots or quaternary quantum dots, the component ratio can be changed, for example but not limited to, for example, PbSSe includes PbS x Se 1-x , where x is any number less than 1 and greater than 0; such as CdSeS including CdSe 0.2 S 0.8 、CdSe 0.1 S 0.9 、CdSe 0.3 S 0.7 、CdSe 0.4 S 0.6and CdSe 0.5 S 0.5 .

[0014] Perovskites are generally represented by ABX3, where A represents a monovalent or divalent cation (such as Cs + 、MA + [CH3NH3 + ]、FA + [HC(NH2) 2+ ]、Ca 2+ 、Sr 2+ , Pb 2+ etc.), B represents a divalent or tetravalent metal cation (such as Pb 2+ 、Sn 2+ 、Ti 4+ 、Ge 2+ etc.), X represents an anion (such as O 2- 、Cl - Br - , I - It is understandable that when ABX3 represents perovskite, the meanings of the symbols A, B, and X are distinguished separately from those generally believed. For example, B is generally believed to be the boron element rather than a divalent or tetravalent metal cation, and MA contains three elemental components but is not considered a ternary ion but a unitary ion.

[0015] When ABX3 contains one A cation, one B cation, and one X anion, it is considered a ternary perovskite. When ABX3 has two different A cations, two different B cations, or two different X anions, it is considered a quaternary perovskite. By way of example and not limitation, the perovskite is selected from at least one of the following components: SrTiO3, BaTiO3, LaMnO3, CsPbI3, CsPbBr3, CsPbCl3, MaPbI3, MaPbBr3, MaPbCl3, FaPbI3, FaPbBr3, FaPbCl3, Cs2AgBiBr6, and LaCoO3.

[0016] In one or more embodiments, the core includes a modification layer coated on the surface of the quantum dot, and the modification layer includes an organic small molecule ligand or an inorganic material.

[0017] In one or more embodiments, the organic small molecule ligand contains one or more of oleic acid, oleylamine, butylamine, octylamine, dodecyl mercaptan, tri-n-octylphosphine, 1-octylphosphoric acid, octadecene, and coconut oil fatty acid diethanolamide; the inorganic material contains one or more of ZnS, CdS, Al2O3, TiO2, ZnO, CuO, and SiO2.

[0018] In one or more embodiments, the hyperbranched polymer comprises at least one of the following components: a polyphenyl hyperbranched polymer, a polyester hyperbranched polymer, a polyether hyperbranched polymer, a polyamide hyperbranched polymer, a polyurethane hyperbranched polymer, a polysiloxane hyperbranched polymer, a polycarbonate hyperbranched polymer, or a polyaryletherketone hyperbranched polymer.

[0019] In a second aspect, the present invention provides a lower conversion film comprising a transparent substrate and the aforementioned lower conversion material dispersed in the transparent substrate.

[0020] In one or more embodiments, the thickness of the lower conversion film is 20 to 1000 nm, and / or the transparent substrate is selected from one of EVA, POE, PVB, EVOH, and PLMA.

[0021] In a third aspect, the present invention provides a photovoltaic cell comprising a cell and the aforementioned lower conversion film covering the surface of the cell.

[0022] In a fourth aspect, the present invention provides a method for preparing a photovoltaic cell, comprising:

[0023] Quantum dot powder whose emission spectrum and quantum efficiency meet preset requirements is prepared into a quantum dot solution; the quantum dot solution is mixed with a hyperbranched polymer solution to obtain a down-conversion material solution; the solvent in the down-conversion material solution is removed to obtain a down-conversion material; the down-conversion material is blended with a resin matrix to form a film, and the film is laminated with the battery cell.

[0024] Compared with the prior art, the down-conversion material, down-conversion film, photovoltaic cell and preparation method thereof provided by the present invention achieve efficient absorption of ultraviolet light and re-emission of visible light by constructing a structural system with quantum dots as the core and hyperbranched polymers as the shell, thereby effectively expanding the available range of the solar spectrum and improving the spectral response capability of photovoltaic modules; the unique three-dimensional branched structure of the hyperbranched polymer can form a coating on the quantum dots at the molecular level, significantly suppressing the fluorescence attenuation problem of the quantum dots caused by oxygen, water vapor and encapsulation additives, and improving the chemical and optical stability of the quantum dots in hot pressing packaging and outdoor environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments described in the present invention. Those skilled in the art can also derive other drawings based on these drawings without inventive effort.

[0026] Figure 1Flowchart of a method for preparing a photovoltaic cell in one embodiment of the present invention. DETAILED DESCRIPTION

[0027] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0028] It should be noted that, unless otherwise indicated, all numbers used in this specification and claims to represent feature sizes, quantities, and physical properties should be understood as being modified by the term "about" in all cases. Therefore, unless otherwise indicated, the numerical parameters listed in the above specification and the appended claims are approximate values, and those skilled in the art will be able to appropriately change these approximate values ​​by utilizing the teachings disclosed herein to seek to obtain the desired properties. The use of numerical ranges expressed as endpoints includes all numbers within the range and any range within the range, for example, 1 to 5 includes 1, 1.2, 1.4, 1.55, 2, 2.75, 3, 3.80, 4 and 5, etc.

[0029] Amidst the ongoing advancements in photovoltaic technology, how to maintain solar cell efficiency while extending their service life has become a topic of widespread concern. Based on an in-depth analysis of the multiple aging issues facing existing photovoltaic modules in outdoor environments, the inventors focused on the profound impact of the ultraviolet (UV) wavelengths contained in natural sunlight on module performance.

[0030] Through research on existing technologies, the inventors discovered that although ultraviolet radiation itself has a certain energy potential, it cannot be effectively converted into electrical energy in the working unit of a solar cell. Instead, it mainly manifests as a destructive cumulative effect, especially in terms of aging of packaging materials, light decay of solar cells, and degradation of device structures. To this end, the industry has tried to reduce the damage of ultraviolet radiation to devices through barrier materials, but this solution inevitably loses a portion of the available spectrum, ultimately leading to a decrease in overall photoelectric conversion efficiency. Other studies have attempted to convert ultraviolet light into visible light for reuse through spectrum conversion materials, but the conversion materials used in actual applications have technical difficulties such as poor photostability, low conversion efficiency, or unsuitability for packaging processes, making it difficult for the overall solution to simultaneously meet the dual requirements of high conversion and high reliability.

[0031] Based on this situation, the inventors proposed a new approach from the perspective of integrating material structure and function. This approach no longer relies solely on traditional absorption or filtering mechanisms, nor is it limited to the selection of traditional spectrum conversion material systems. Instead, it attempts to construct a new material unit that combines high conversion performance with high stability. In this approach, the inventors proposed coating or compounding the spectrum conversion functional material with a specific interface structure, so that while it has energy conversion capabilities, it can effectively resist the effects of chemically active components and high-energy photons in the external environment on its stability, thereby achieving long-term performance maintenance and overall improvement of device reliability.

[0032] The core concept of this approach is to structurally integrate functional units with high spectral conversion capabilities with polymer materials with multifunctional protection capabilities, and to achieve synergistic enhancement of spectral conversion and anti-aging capabilities by constructing a material composite system with certain interface regulation capabilities.

[0033] Specifically, to address the problems of ultraviolet light energy loss and insufficient material stability, the present invention uses quantum dot materials with excellent photoelectric properties as the down-conversion core, and uses their adjustable optical properties to efficiently convert ultraviolet light into a spectrum suitable for solar cell absorption. To further enhance the stability and light conversion efficiency of the quantum dot material, the present invention introduces a hyperbranched polymer material with a three-dimensional network structure as a protective layer. This hyperbranched polymer effectively coats the quantum dot material through its unique structure, blocking the erosion of the external environment (such as oxygen, chemical additives), reducing the optical and chemical defects on the surface of the quantum dot material, and thus improving long-term stability and light conversion efficiency.

[0034] In one embodiment of the present invention, a down-conversion material for a photovoltaic cell has a core-shell structure, comprising a core and a shell coating the core. The core-shell structure may include multiple cores or multiple shells. The core comprises quantum dots, and the shell comprises a hyperbranched polymer. The maximum emission peak of the quantum dots' emission spectrum is greater than 380 nm and less than 780 nm, and the quantum efficiency of the quantum dots is no less than 70%.

[0035] Quantum dots, as core materials, can be composed of elements from Groups II-VI or III-V. Their quantum confinement effect allows them to possess excellent optical properties, and their absorption and emission spectra can be precisely tuned through size control. The present invention selects quantum dots as cores, aiming to exploit their ability to efficiently absorb ultraviolet light (<380nm) and convert it into visible light (380-780nm), thereby achieving downconversion. This spectral conversion not only prevents UV damage to the cell materials but also converts UV energy, which would otherwise be underutilized by the photovoltaic cell, into absorbable visible light.

[0036] The quantum dot emission spectrum is limited to 380-780nm, ensuring that the converted spectrum closely matches the spectral response of photovoltaic cells (such as crystalline silicon cells, with an absorption peak between 400-1100nm), thereby maximizing photoelectric conversion efficiency. With a quantum efficiency requirement of no less than 70%, surface quantum dots have the ability to efficiently convert absorbed photons into emitted photons, reducing non-radiative losses and ensuring a high level of re-emission efficiency after absorbing ultraviolet light. This can significantly increase the effective photon count, thereby enhancing the overall photoelectric conversion capability of the component.

[0037] To address the problem of quantum dots being susceptible to corrosion from chemical components such as oxygen, moisture, and crosslinking agents during their application, which can lead to reduced luminescence efficiency, the present invention provides a shell layer around the quantum dots. This shell layer is composed of a hyperbranched polymer. The three-dimensional dendritic structure and multi-branched points of the hyperbranched polymer provide an ideal encapsulation environment for the quantum dots. With its low viscosity, high solubility, and porous network structure, the hyperbranched polymer can evenly disperse and securely encapsulate the nanoscale quantum dots, forming a physical and chemical protective layer.

[0038] Hyperbranched polymers have excellent solubility, coating and interface regulation capabilities due to their unique three-dimensional branched structure and rich functional end groups. Through this shell structure, quantum dots can be evenly dispersed in the polymer matrix, avoiding agglomeration and light scattering, improving optical uniformity, and at the same time forming a layer of polymer barrier that can block oxygen, moisture and chemical additives (such as peroxides, crosslinking agents) in the photovoltaic cell encapsulation film from contacting the quantum dots, preventing defects on the surface of the quantum dots due to oxidation or chemical reactions, thereby maintaining their photostability and down-conversion performance. Hyperbranched polymers passivate the surface of quantum dots, reducing non-radiative recombination caused by surface defects, further improving quantum efficiency and enhancing light conversion effects. In addition, the high optical transparency of hyperbranched polymers ensures that ultraviolet and visible light can pass through the shell with minimal scattering or absorption, maintaining the high transmittance of the down-conversion material.

[0039] Quantum Yield (QY) is a key indicator of how efficiently quantum dots convert absorbed photons into emitted photons. It is defined as the ratio of the number of emitted photons to the number of absorbed photons. In down-conversion applications in photovoltaic cells, quantum dots must efficiently convert high-energy ultraviolet light (<380nm) into visible light (380-780nm) to improve photoelectric conversion efficiency.

[0040] The photoelectric conversion efficiency of photovoltaic cells (such as crystalline silicon cells) is highly dependent on the utilization of incident light. Ultraviolet light is often wasted due to excessive energy or insufficient absorption. The goal of down-conversion materials is to maximize the conversion of ultraviolet light energy into visible light that can be absorbed by the cell. Therefore, the greater the quantum efficiency of quantum dots, the greater the improvement in the photoelectric conversion efficiency of photovoltaic cells.

[0041] Preferably, the average size of the down-conversion material is 2 to 40 nm. The down-conversion material has a core-shell structure. The average size of the core (quantum dot) determines its band structure, showing a significant quantum confinement effect. The band gap energy increases as the size decreases, thereby affecting its absorption and emission spectra, achieving an accurate match of the emission spectrum at 380 to 780 nm. This range covers visible light from blue (~450 nm) to red (~650 nm), ensuring that the converted spectrum matches the absorption range of the photovoltaic cell. The coating of the shell increases the size of the down-conversion material, but has little effect on its absorption and emission spectra. The coating of the shell is not infinite. It is understandable that when the shell is too thick, it has an effect on the refraction loss of light. On the other hand, the shell has little effect on the absorption and emission spectra, but it will have an impact on other factors such as luminous efficiency, such as increasing luminous efficiency. The size of 2 to 40 nm is much smaller than the wavelength of visible light (380 to 780 nm), which can effectively reduce Rayleigh scattering and maintain high transmittance. Further preferably, the average size of the down-conversion material is 2 to 30 nm.

[0042] The components of the quantum dots can be selected according to actual needs, preferably binary quantum dots or unit quantum dots; the binary quantum dots include at least one of the following components: MgO, MgS, MgSe, MgTe, CaO, CaS, CaSe, CaTe, SrO, SrS, SrSe, SrTe, BaO, BaS, BaSe, BaTe, ZnO, ZnS, ZnSe, ZnTe, CdO, CdS, CdSe, HgO, HgS, HgSe, HgTe, Al2O3, Al2S3, Al2Se3, A l2Te3, Ga2O3, Ga2S3, Ga2Se3, Ga2Te3, In2O3, In2S3, In2Se3, In2Te3, SiO2, GeO2, SnO2, SnS, SnSe, SnTe, PbO, PbO2, PbS, PbSe, PbTe, AlN, AlP, AlAs, AlSb, GaN, GaP, GaAs, GaSb, InN, InP, InAs, InSb or BP; the unit quantum dot includes at least one of the following components: C, Si or Ge.

[0043] The components of the quantum dots can be selected according to actual needs, and are preferably ternary quantum dots or quaternary quantum dots; the ternary quantum dots include at least one of the following components: CuGaO, CuGaS, CuGaSe, CuGaTe, CuInO, CuInS, CuInSe, CuInTe, CuAlO, CuAlS, CuAlSe, CuAlTe, AgGaO, AgGaS, AgGaSe, AgGaTe, AgInO, AgInS, AgInSe, AgInTe, AgAlO, AgAlS, AgAlSe, AgAlTe, CuSTe, CuSeTe, AgSTe, AgSeTe, CuZnTe, AgZnTe, ZnCdS, ZnCdSe, ZnCdTe, PbSSe, PbSTe, PbSeTe or ternary perovskite; the quaternary quantum dots include at least one of the following components: CdTeZnSe, CuInGaS, CuInGaSe or quaternary perovskite.

[0044] In an exemplary embodiment, the core includes a modification layer coated on the surface of the quantum dot, and the modification layer includes an organic small molecule ligand or an inorganic material.

[0045] Preferably, the organic small molecule ligand contains one or more of oleic acid, oleylamine, butylamine, octylamine, dodecyl mercaptan, tri-n-octylphosphine, 1-octylphosphoric acid, and octadecene; and the inorganic material contains one or more of ZnS, CdS, Al2O3, TiO2, ZnO, CuO, and SiO2.

[0046] Due to unsaturated coordination, atoms on the surface of quantum dots are naturally prone to forming defect states. These defects can induce non-radiative recombination pathways, thereby reducing the fluorescence quantum efficiency and even exacerbating photodegradation. To this end, the surface can be passivated, that is, a modified layer is introduced to reduce the density of surface energy level traps and improve the photostability of quantum dots.

[0047] Small organic molecule ligands primarily refer to long-chain organic molecules that adsorb or coordinate to the surface of quantum dots during their synthesis, such as oleic acid, oleylamine, dodecyl mercaptan, tri-n-octylphosphine, 1-octylphosphonic acid, or octadecene. These small organic molecule ligands have two molecular structures: a polar ligand and a non-polar long-chain group. The former is used to coordinate with atoms on the surface of quantum dots (such as metal ions) to form stable surface complexes and inhibit surface defects; the latter forms a hydrophobic brush-like structure that provides steric hindrance in solution, preventing aggregation between quantum dots and thus improving their dispersibility in organic solvents or polymer matrices.

[0048] Inorganic material modification layers, such as ZnS, ZnO, CuO, and SiO2, achieve spatial confinement of electrons and holes by coating the quantum dot surface with an inorganic shell with a wide bandgap, reducing the rate of non-radiative recombination induced by surface states. For example, coating CdSe quantum dots with a layer of ZnS or ZnO can improve their luminescence efficiency and resistance to photooxidation.

[0049] The components of the hyperbranched polymer can be selected according to actual needs, and preferably include at least one of the following components: polyphenyl hyperbranched polymer, polyester hyperbranched polymer, polyether hyperbranched polymer, polyamide hyperbranched polymer, polyurethane hyperbranched polymer, polysiloxane hyperbranched polymer, polycarbonate hyperbranched polymer, polyaryletherketone hyperbranched polymer.

[0050] In one embodiment of the present invention, a lower conversion film is provided, which comprises a transparent substrate and the aforementioned lower conversion material dispersed in the transparent substrate. The lower conversion film structurally consists of a transparent substrate and the lower conversion material dispersed in the substrate.

[0051] As a carrier material, the transparent substrate not only provides the necessary mechanical support and film-forming structure, but also assumes the basic function of light transmission. Commonly used transparent substrates include EVA (ethylene-vinyl acetate copolymer), POE (polyolefin elastomer), PVB (polyvinyl butyral), EVOH (ethylene-vinyl alcohol copolymer) or PLMA (polylactide methacrylate) and other polymers with excellent optical properties, good flexibility and packaging adaptability. These materials have high light transmittance, low haze and good bonding properties. They can take into account the physical stability and heat sealing performance of the film material during the packaging process without interfering with the transmission of visible light flux.

[0052] The down-conversion material is evenly dispersed in the substrate in the form of functional nanostructured units. Its core function is to absorb high-energy ultraviolet photons and convert them into lower-energy visible photons through a fluorescence process, thereby improving the overall utilization efficiency of the incident light energy and alleviating the long-term damage of ultraviolet rays to photovoltaic cells and packaging materials.

[0053] Preferably, the thickness of the down-conversion film is 20 to 1000 nm. When the film thickness is less than 20 nm, the primary problem faced is insufficient loading of down-conversion materials. At this time, although nanomaterials such as quantum dots may still be embedded in the film, their quantity is far from enough to form a sufficient absorption cross-section, resulting in a significant decrease in the overall absorption rate of ultraviolet light, making it difficult to form an effective down-conversion effect. In addition, the ultra-thin film is easily affected by factors such as shear force, solvent evaporation rate and substrate adhesion during the preparation process, and process problems such as film breakage, uneven thickness or uncontrolled distribution may occur, seriously affecting the industrial adaptability and functional stability of the film.

[0054] When the film thickness exceeds 1000nm, quantum dots and other down-conversion materials themselves have certain absorption characteristics for visible light. If the material concentration is high and the film thickness is too large, the down-conversion film will produce obvious light absorption or even scattering in the visible light region, affecting the direct absorption of visible light by photovoltaic cells, and reducing the overall photoelectric conversion efficiency of the cell.

[0055] One embodiment of the present invention also provides a photovoltaic cell comprising a cell and the aforementioned lower conversion film covering the cell surface. In this structure, the cell still serves as the primary photoelectric conversion unit, fulfilling the core function of converting visible and near-infrared light into electrical energy, while the lower conversion film attached to its surface constitutes a spectral control layer, responsible for regulating and converting the shorter-wavelength, higher-energy ultraviolet light in natural light.

[0056] Please refer to Figure 1 As shown, an embodiment of the present invention further provides a method for preparing the aforementioned photovoltaic cell, which specifically includes the following steps:

[0057] S101: preparing a quantum dot solution from quantum dot powder whose emission spectrum and quantum efficiency meet preset requirements.

[0058] In step S101, quantum dot powders with emission spectra and quantum efficiency that meet pre-set standards are selected as the core material for downconversion. The quantum dots must have a high fluorescence quantum efficiency (at least 70%) and a main emission peak between 380 and 780 nm to ensure that they absorb ultraviolet light and convert it into visible light that can be effectively responded to by the cell.

[0059] Quantum dot powders that meet specific spectral response and quantum efficiency requirements are prepared into a stable solution system, laying the foundation for subsequent compounding with hyperbranched polymers and ultimately film formation. The core of this step is to select the appropriate quantum dot material and construct a uniformly dispersed liquid phase system to ensure good processability and optical consistency of the down-conversion functional unit.

[0060] In practice, commercially available or homemade quantum dot powders (such as CdSe, ZnS, and InP) can be selected. Their surfaces can be modified with small organic molecule ligands (such as oleic acid and oleylamine) to enhance solubility and stability. The quantum dot powder is prepared by adding it to an organic solvent (such as n-hexane, toluene, oleic acid, or octadecene) to a solution with a concentration of 50 to 200 mg / mL. To ensure uniform dispersion, mechanical stirring (500 to 1000 rpm), ultrasonic treatment (20-40 kHz, 5-15 minutes), or a combination of the two is typically used to promote dispersion.

[0061] The solution solvent is generally an organic solvent, and there can be many types of organic solvents, including but not limited to: n-hexane, n-octane, oleylamine, dodecyl mercaptan, oleic acid, octadecene, diphenyl ether, paraffin oil, methyl pyrrolidone, tri-n-octylphosphine oxide, toluene, ethylbenzene, dimethyl sulfoxide, isopropanol, 1-butanol, 1-pentanol, 1-octanol, dimethylformamide, tetramethylethylenediamine, ethyl acetate, butyl acetate, acetone, dibutyl phthalate, phenylcyclohexane, etc.; the organic solvent can be a pure solvent or a mixed solvent.

[0062] S102: Mixing the quantum dot solution with the hyperbranched polymer solution to obtain a down-conversion material solution.

[0063] In the specific implementation process, the hyperbranched polymer used preferably has good solubility and a highly branched structure so as to form a three-dimensional network to coat and physically isolate the quantum dots. Optional hyperbranched polymers include hyperbranched polyesters, hyperbranched polyaryletherketones, etc., which are soluble in ethanol, water or a mixed solvent thereof to form a stable polymer solution. For example, a 30 mg / mL hyperbranched polyester solution and a 100 mg / mL CdSe quantum dot n-hexane solution can be slowly added dropwise in a mass ratio of 1:1 and kept stirring to promote uniform mixing at room temperature or slightly heated (such as 40 ° C). Ultrasonic assisted dispersion can be used during the process to prevent quantum dot aggregation and improve coating efficiency.

[0064] In step S102, electrostatic, coordination, or van der Waals interactions between functional groups (such as carboxyl, hydroxyl, or amine) on the hyperbranched polymer chains and metal ions or ligands on the quantum dot surface create a soft interface structure at the nanoscale. This effectively inhibits aggregation, sedimentation, and fluorescence quenching of the quantum dots, even when they are in a stable dispersed state within the polymer matrix. This composite structure partially shields the chemical activity of the quantum dot surface, thereby improving its chemical and photostability in subsequent high-temperature environments such as hot pressing and crosslinking.

[0065] S103: removing the solvent in the lower conversion material solution to obtain the lower conversion material.

[0066] In step S103, the organic or mixed solvent in the down-conversion material solution formed in the previous step is removed to obtain a solid composite down-conversion material with quantum dots as the core and a hyperbranched polymer as the shell. This process completes the material's morphology transition from liquid to solid, giving the down-conversion material a certain structural stability, facilitating subsequent processing.

[0067] Methods for removing the solvent include heating for volatilization, reduced pressure concentration, vacuum drying, or rotary evaporation. For example, placing a uniformly mixed solution of the down-conversion material in a rotary evaporator and slowly removing the solvent at 40-60°C can quickly yield a semi-solid or powdered down-conversion material without destroying the fluorescence properties of the quantum dots. For systems with strong heat sensitivity, freeze drying or low-temperature vacuum drying under an inert atmosphere (such as nitrogen) can be used to further prevent heat-induced fluorescence quenching or molecular structure damage.

[0068] This process not only removes free solvent but also promotes the formation of a more stable adsorption or coating layer of the hyperbranched polymer on the surface of the quantum dots, making the entire composite structure denser and more thermally stable. In addition, this step also helps control the particle size distribution and dispersion state of the converted material, facilitating subsequent uniform blending with resins such as EVA or POE, and improving the optical uniformity and mechanical properties of the composite film.

[0069] S104: Blending the lower conversion material with the resin matrix to form an adhesive film, and laminating the adhesive film with the battery cell.

[0070] In step S104, the down-conversion material obtained in the previous stage is blended with a resin matrix to prepare a film with spectrum conversion function, and the film is integrated with the cell structure through a lamination process to construct a photovoltaic module with ultraviolet conversion capability.

[0071] In terms of specific implementation, the resin matrix can be selected from widely used encapsulation materials in the photovoltaic industry, such as EVA (ethylene-vinyl acetate copolymer), POE (polyolefin elastomer), and PVB (polyvinyl butyral). These materials have good transparency, flexibility, and heat-sealing properties. A powdered or semi-solid down-conversion material is added to the resin matrix at a specific mass ratio (e.g., 0.1-1 wt%) and then uniformly mixed through melt extrusion, hot-pressing blending, or solution casting to form a film with a thickness of 20-1000 nm.

[0072] After the adhesive film is prepared, it is encapsulated with the pre-arranged battery cells through a laminator. This can be done under vacuum, heating (such as 130-150°C) and a certain pressure (such as 0.4-0.6MPa), so that the adhesive film forms a dense bonding interface with the battery cells, glass cover or backplane at high temperature.

[0073] The present invention will be further described below with reference to specific embodiments.

[0074] Example 1

[0075] Take 10g of CdSe blue quantum dot solid particles (the quantum dots have an average size of 4nm, a maximum emission peak of 450nm in the emission spectrum, and a quantum efficiency of 91%), add 100mL of cyclohexane solvent, and heat and stir to prepare a 100mg / mL quantum dot solution. Take 30g of hyperbranched polymer, use ethanol and water as a mixed solvent, and heat and stir to prepare a 100mg / mL hyperbranched polymer solution. The hyperbranched polymer is a hyperbranched polyester compound, specifically a hyperbranched bis-MPA polyester-64-hydroxy product produced by Sigma-Aldrich.

[0076] The quantum dot solution was dropped into the hyperbranched polymer solution, with the ratio of the quantum dot solid weight to the hyperbranched polymer weight being 1:10, and the solution was heated and stirred to obtain a down-conversion material solution.

[0077] The down-conversion material solution was heated to remove the solvent to prepare a down-conversion material (average size of 10 nm). The down-conversion material was mixed with an EVA resin matrix. Based on 100 parts of the EVA resin, 0.1 parts of the down-conversion material, 0.1 parts of a peroxide crosslinking agent, 0.1 parts of a co-crosslinking agent, and 0.2 parts of a silane coupling agent were added to prepare a single-layer film. The single-layer film thickness was 100 nm.

[0078] Photovoltaic cell samples were prepared by laminating a single layer of adhesive film with a cell sheet. These samples were then tested according to the test method specified in IEC 61215. The peroxide crosslinker was tert-butyl peroxycarbonate-2-ethylhexyl ester, the co-crosslinker was trimethylolpropane trimethacrylate, and the silane coupling agent was γ-(methacryloyloxy)propyltrimethoxysilane.

[0079] Example 2

[0080] Compared with Example 1, the quantum dots are replaced by: CdSe green quantum dot solid particles (the average size of the quantum dots is 7 nm, the maximum emission peak of the emission spectrum is 550 nm, and the quantum efficiency is 85%), and the other preparation conditions are the same as Example 1.

[0081] Example 3

[0082] Compared with Example 1, the quantum dots are replaced by: CdSe red quantum dot solid particles (the average size of the quantum dots is 10 nm, the maximum emission peak of the emission spectrum is 645 nm, and the quantum efficiency is 70%), and the other preparation conditions are the same as Example 1.

[0083] Example 4

[0084] Compared with Example 1, the hyperbranched polymer was replaced by a poly(aryletherketone) hyperbranched polymer, and the other preparation conditions were the same as those of Example 1. The poly(aryletherketone) hyperbranched polymer was synthesized using 5-phenoxyisophthalic acid as a raw material.

[0085] The polyaryletherketone hyperbranched polymer was synthesized as follows: 0.6 g of 5-phenoxyisophthalic acid was added to 3.6 ml of PPMA solution (a solution prepared by mass ratio of methanesulfonic acid and phosphorus pentoxide of 1:12) and stirred at 110 ° C for 10 hours under a nitrogen atmosphere. After the reaction was completed, the resulting solution was poured into 200 mL of water, the precipitated polymer was collected, washed with water, and then the polymer was placed in 200 mL of water and stirred at 70 ° C for 12 hours. The polymer was then collected and vacuum dried. Finally, the crude product was purified by precipitating it from DMF into methanol to obtain a polyaryletherketone hyperbranched polymer (denoted as Hyper-PEK-COK).

[0086] Example 5

[0087] Compared with Example 1, the hyperbranched polymer was replaced with a polyaryletherketone hyperbranched polymer, and the other preparation conditions were the same as those in Example 1.

[0088] The polyaryletherketone hyperbranched polymer was synthesized as follows: 0.2 g of the polyaryletherketone hyperbranched polymer (Hyper-PEK-COK) in Example 4 and 1 g of toluene were dissolved in 5 ml of PPMA solution, heated to 50 ° C and stirred, and reacted for 24 hours. The reaction solution was then poured into 400 mL of water, the system was neutralized with sodium bicarbonate solution, the precipitate was filtered, and washed with a large amount of water and methanol in turn. Finally, the crude product was purified by precipitating it from DMF into methanol to obtain a polyaryletherketone hyperbranched polymer (denoted as Hyper-PEK-TOL).

[0089] Example 6

[0090] Compared with Example 1, except that the thickness of the prepared single-layer film is 150 nm, the other preparation conditions are the same as those of Example 1.

[0091] Example 7

[0092] Compared with Example 1, except that the thickness of the prepared single-layer film is 300 nm, the other preparation conditions are the same as those of Example 1.

[0093] Example 8

[0094] Compared with Example 1, the hyperbranched polymer was replaced by a hyperbranched polyamide polymer, and the other preparation conditions were the same as those of Example 1. The hyperbranched polyamide polymer was a commercially available product with the brand name HyPer HPN202.

[0095] Example 9

[0096] Compared with Example 1, the hyperbranched polymer was replaced by a hyperbranched polyamide polymer, and the other preparation conditions were the same as those of Example 1. The hyperbranched polyamide polymer was a commercially available product with the brand name HyPer HPN10.

[0097] Example 10

[0098] Take 10g of CdS blue quantum dot solid particles (the quantum dots have an average size of 2.5nm, an emission spectrum maximum emission peak of 430nm, and a quantum efficiency of 88%), add 100mL of cyclohexane solvent, and heat and stir to prepare a 100mg / mL quantum dot solution. Take 30g of hyperbranched polymer, use ethanol and water as a mixed solvent, and heat and stir to prepare a 100mg / ml hyperbranched polymer solution. The hyperbranched polymer is a hyperbranched polyester compound, specifically a hyperbranched bis-MPA polyester-64-hydroxy product produced by Sigma-Aldrich.

[0099] The quantum dot solution was dropped into the hyperbranched polymer solution, with the ratio of the quantum dot solid weight to the hyperbranched polymer weight being 1:10, and the solution was heated and stirred to obtain a down-conversion material solution.

[0100] The down-conversion material solution was heated to remove the solvent to prepare the down-conversion material. The down-conversion material was mixed with an EVA resin matrix. Based on 100 parts of the EVA resin, 0.1 parts of the down-conversion material, 0.1 parts of a peroxide crosslinking agent, 0.1 parts of a co-crosslinking agent, and 0.2 parts of a silane coupling agent were added to prepare a single-layer film. The single-layer film had a thickness of 100 nm.

[0101] Photovoltaic cell samples were prepared by laminating a single layer of adhesive film with a cell sheet. These samples were then tested according to the test method specified in IEC 61215. The peroxide crosslinker was tert-butyl peroxycarbonate-2-ethylhexyl ester, the co-crosslinker was trimethylolpropane trimethacrylate, and the silane coupling agent was γ-(methacryloyloxy)propyltrimethoxysilane.

[0102] Example 11

[0103] Compared with Example 10, except that the thickness of the prepared single-layer film is 150 nm, the other preparation conditions are the same as those of Example 10.

[0104] Example 12

[0105] Compared with Example 10, except that the thickness of the prepared single-layer film is 50 nm, the other preparation conditions are the same as those of Example 10.

[0106] Example 13

[0107] Compared with Example 10, except that the thickness of the prepared single-layer film is 20 nm, the other preparation conditions are the same as those of Example 10.

[0108] Example 14

[0109] Compared with Example 10, except that the thickness of the prepared single-layer film is 1000 nm, the other preparation conditions are the same as those of Example 10.

[0110] Example 15

[0111] Compared with Example 10, except that the hyperbranched polymer is replaced by a polyaryletherketone hyperbranched polymer (Hyper-PEK-COK), the other preparation conditions are the same as those of Example 10.

[0112] Example 16

[0113] 10g of homemade perovskite quantum dots and 30g of a hyperbranched polymer were mixed in a mixture of ethanol and water with heating and stirring to create a 100mg / ml hyperbranched polymer solution. The hyperbranched polymer was a hyperbranched polyester compound, specifically Sigma-Aldrich's hyperbranched bis-MPA polyester-64-hydroxy product.

[0114] The homemade perovskite quantum dots were obtained as follows: First, a Cs-oleate solution was prepared. Cesium acetate (0.315 g), 10 ml of octadecene (ODE), and 1 ml of oleic acid (OA) were placed in a 50 ml three-necked flask and evacuated at room temperature for 60 minutes. The flask was then heated to 100°C under a nitrogen atmosphere, evacuated for another 60 minutes, and finally heated to 140°C until all the cesium acetate was dissolved in the ODE. Second, a crude solution of CsPbBr3 nanocrystals was prepared. Lead bromide (0.069 g), 0.5 ml of OA, and 0.5 ml of oleylamine (OLA) were placed in a 50 ml three-necked flask. 5 ml of ODE was added, the solution was evacuated for 60 minutes, heated to 120°C, and evacuated for another 60 minutes. When the solution was heated to 160-180°C, 0.4 ml of the Cs-oleate solution was rapidly injected, resulting in a crude solution of CsPbBr3 nanocrystals coated with OA and OLA. Finally, the CsPbBr3 nanocrystals were purified to obtain a n-hexane solution. 5 ml of n-hexane was added to the crude solution of CsPbBr3 nanocrystals and centrifuged at 3000 rpm for 3 minutes. The supernatant was then extracted, 15 ml of methyl acetate was added to it, and the mixture was centrifuged at 8000 rpm for 5 minutes. Finally, the precipitate was dispersed in 2 ml of n-hexane. The separation and centrifugation were repeated three times. Finally, the product was redispersed in 2 ml of n-hexane to obtain a n-hexane solution of CsPbBr3 nanocrystals.

[0115] A n-hexane solution of CsPbBr3 nanocrystals was dropped into a hyperbranched polymer solution, with the ratio of the solid weight of quantum dots to the weight of the hyperbranched polymer being 1:10, and a down-conversion material solution was obtained under heating and stirring.

[0116] The down-conversion material solution was heated to remove the solvent to prepare a down-conversion material (average size of 30 nm). The down-conversion material was mixed with an EVA resin matrix. Based on 100 parts of the EVA resin, 0.1 parts of the down-conversion material, 0.1 parts of a peroxide crosslinking agent, 0.1 parts of a co-crosslinking agent, and 0.2 parts of a silane coupling agent were added to prepare a single-layer film. The single-layer film thickness was 100 nm.

[0117] Photovoltaic cell samples were prepared by laminating a single layer of adhesive film with a cell sheet. These samples were then tested according to the test method specified in IEC 61215. The peroxide crosslinker was tert-butyl peroxycarbonate-2-ethylhexyl ester, the co-crosslinker was trimethylolpropane trimethacrylate, and the silane coupling agent was γ-(methacryloyloxy)propyltrimethoxysilane.

[0118] Example 17

[0119] Compared with Example 16, except for the different preparation method of the homemade perovskite quantum dots, the other preparation conditions are the same as those of Example 16.

[0120] The homemade perovskite quantum dots of this example were obtained as follows: First, a Cs-oleate solution was prepared. Cesium acetate (0.315 g), 10 ml of octadecene (ODE), and 1 ml of oleic acid (OA) were placed in a 50 ml three-necked flask. The flask was vacuumed at room temperature for 60 minutes, then heated to 100°C under a nitrogen atmosphere, vacuumed for another 60 minutes, and finally heated to 140°C until all the cesium acetate was dissolved in the ODE.

[0121] Secondly, a crude solution of CsPbBr3 nanocrystals is prepared. In this embodiment, a hot injection method is used to prepare CsPbBr3 nanocrystals (OPA-CsPbBr3) coated with 1-octyl phosphoric acid. First, 1-octyl phosphoric acid (0.1 g), trioctyl phosphine oxide (TOPO, 1 g) and lead bromide (0.069 g) are placed in a 50 ml three-necked flask, 5 ml of ODE is added, and the mixture is evacuated for 30 minutes. Secondly, the flask is heated to 100°C and evacuated for another 30 minutes. Then, the solution is heated to 160-180°C under a nitrogen atmosphere, and 0.4 ml of Cs-oleate solution is quickly injected. After reacting for 5 seconds, the flask is quickly immersed in an ice-water bath to terminate the reaction. A crude solution of CsPbBr3 nanocrystals coated with 1-octyl phosphoric acid is obtained. Finally, the n-hexane solution of CsPbBr3 nanocrystals is purified. 5 ml of n-hexane was added to the crude solution of CsPbBr3 nanocrystals and centrifuged at 3000 rpm for 3 minutes. The supernatant was then extracted, 15 ml of methyl acetate was added, and the solution was centrifuged again at 8000 rpm for 5 minutes. Finally, the precipitate was dispersed in 2 ml of n-hexane. This separation and centrifugation process was repeated three times. Finally, the product was redispersed in 2 ml of n-hexane to obtain a n-hexane solution of CsPbBr3 nanocrystals.

[0122] Example 18

[0123] Compared with Example 17, except that the hyperbranched polymer is replaced by poly(aryletherketone) hyperbranched polymer (Hyper-PEK-COK), the other preparation conditions are the same as those of Example 17.

[0124] Comparative Example 1

[0125] Compared with Example 1, the hyperbranched polymer was replaced by a linear polyester polymer, and the other preparation conditions were the same as those of Example 1. The linear polyester polymer was polyethylene terephthalate (PET).

[0126] Comparative Example 2

[0127] Compared with Example 1, the hyperbranched polymer is replaced by a linear poly(phenylene ether ketone) polymer, and the other preparation conditions are the same as those of Example 1. Linear poly(phenylene ether ketone) polymer polyetheretherketone (PEEK).

[0128] Comparative Example 3

[0129] A similar method to Example 1 is used, except that the film does not contain quantum dot material.

[0130] Comparative Example 4

[0131] Compared with Example 1, the lower conversion material was replaced by a rare earth complex europium-benzoic acid-o-phenanthroline, and the other preparation conditions were the same as those in Example 1.

[0132] Comparative Example 5

[0133] Compared with Example 1, the quantum dots were changed to CdS, the hyperbranched polymer was replaced by a linear polyphenylene ether ketone polymer, and the other preparation conditions were the same as those in Example 1.

[0134] Test method: Adopt the test method of IEC61215. Adopt stricter test, and the radiation measurement is 30kwh / m 2 .

[0135] The test results are shown in Table 1:

[0136] Table 1

[0137]

[0138]

[0139] When the attenuation exceeds 3%, the product's performance is considered poor, and below 3%, it is considered excellent. The embodiments of the present invention have an attenuation of substantially less than 2.5%, while the comparative examples have an attenuation performance exceeding or significantly exceeding 3%.

[0140] In summary, the down-conversion material, down-conversion film, photovoltaic cell and preparation method thereof provided by the present invention achieve efficient absorption of ultraviolet light and re-emission of visible light by constructing a structural system with quantum dots as the core and hyperbranched polymers as the shell, thereby effectively expanding the available range of the solar spectrum and improving the spectral response capability of photovoltaic modules; the unique three-dimensional branched structure of the hyperbranched polymer can form a coating on the quantum dots at the molecular level, significantly suppressing the fluorescence attenuation problem of the quantum dots caused by oxygen, water vapor and encapsulation additives, and improving the chemical and optical stability of the quantum dots in hot pressing packaging and outdoor environments.

[0141] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the invention can be embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the invention is defined by the appended claims, not the foregoing description, and all variations within the meaning and range of equivalents of the claims are intended to be included therein. Any reference sign in a claim should not be construed as limiting the claim to which it relates.

[0142] In addition, it should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A down-conversion material for photovoltaic cells, characterized in that: The down-conversion material has a core-shell structure, comprising a core and a shell layer covering the core; The core comprises quantum dots, and the shell comprises a hyperbranched polymer; the maximum emission peak of the emission spectrum of the quantum dots is greater than 380 nm and less than 780 nm, and the quantum efficiency of the quantum dots is not less than 70%.

2. The down-conversion material according to claim 1, characterized in that The average size of the lower conversion material is 2-40 nm.

3. The down-conversion material according to claim 1, characterized in that The quantum dots are binary quantum dots or unit quantum dots; the binary quantum dots include at least one of the following components: MgO, MgS, MgSe, MgTe, CaO, CaS, CaSe, CaTe, SrO, SrS, SrSe, SrTe, BaO, BaS, BaSe, BaTe, ZnO, ZnS, ZnSe, ZnTe, CdO, CdS, CdSe, HgO, HgS, HgSe, HgTe, Al2O3, Al2S3, Al2Se3, Al2Te3, Ga 2O3, Ga2S3, Ga2Se3, Ga2Te3, In2O3, In2S3, In2Se3, In2Te3, SiO2, GeO2, SnO2, SnS, SnSe, SnTe, PbO, PbO2, PbS, PbSe, PbTe, AlN, AlP, AlAs, AlSb, GaN, GaP, GaAs, GaSb, InN, InP, InAs, InSb or BP; the unit quantum dot includes at least one of the following components: C, Si or Ge.

4. The down-conversion material according to claim 1, characterized in that The quantum dots are ternary quantum dots or quaternary quantum dots; the ternary quantum dots include at least one of the following components: CuGaO, CuGaS, CuGaSe, CuGaTe, CuInO, CuInS, CuInSe, CuInTe, CuAlO, CuAlS, CuAlSe, CuAlTe, AgGaO, AgGaS, AgGaSe, AgGaTe, AgInO, AgInS, AgInSe, AgInTe, AgAlO, AgAlS, AgAlSe, AgAlTe, CuSTe, CuSeTe, AgSTe, AgSeTe, CuZnTe, AgZnTe, ZnCdS, ZnCdSe, ZnCdTe, PbSSe, PbSTe, PbSeTe or ternary perovskite; the quaternary quantum dots include at least one of the following components: CdTeZnSe, CuInGaS, CuInGaSe or quaternary perovskite.

5. The down-conversion material according to claim 1, characterized in that The core includes a modification layer coated on the surface of the quantum dot, and the modification layer includes organic small molecule ligands or inorganic materials.

6. The down-conversion material according to claim 5, characterized in that The organic small molecules contain one or more of oleic acid, oleylamine, butylamine, octylamine, dodecyl mercaptan, tri-n-octylphosphine, 1-octylphosphoric acid, and octadecene; the inorganic materials contain one or more of ZnS, CdS, Al2O3, TiO2, ZnO, CuO, and SiO2.

7. The down-conversion material according to claim 1, characterized in that The hyperbranched polymer comprises at least one of the following components: polyphenyl hyperbranched polymer, polyester hyperbranched polymer, polyether hyperbranched polymer, polyamide hyperbranched polymer, polyurethane hyperbranched polymer, polysiloxane hyperbranched polymer, polycarbonate hyperbranched polymer, polyaryletherketone hyperbranched polymer.

8. A lower conversion film, characterized in that: The method comprises a transparent substrate and the down-conversion material according to any one of claims 1 to 7 dispersed in the transparent substrate.

9. The lower conversion film according to claim 8, characterized in that: The thickness of the lower conversion film is 20 to 1000 nm, and / or the transparent substrate is selected from one of EVA, POE, PVB, EVOH, and PLMA.

10. A photovoltaic cell, characterized in that: The invention comprises a battery cell and a lower conversion film as claimed in claim 8 or 9 covering the surface of the battery cell.

11. A method for preparing a photovoltaic cell according to claim 10, characterized in that: include: The quantum dot powder whose emission spectrum and quantum efficiency meet the preset requirements is prepared into a quantum dot solution; mixing the quantum dot solution with the hyperbranched polymer solution to obtain a down-conversion material solution; removing the solvent from the down-conversion material solution to obtain the down-conversion material; The lower conversion material is mixed with a resin matrix to form an adhesive film, and the adhesive film is laminated with the battery cell.

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