A light guide film for a photovoltaic module and a photovoltaic module

Abstract

The application discloses a light guide film for a photovoltaic module, comprising a substrate layer, a microstructure layer and an optical modulation layer covering the same. The microstructure layer has a higher refractive index than the optical modulation layer, and the surface of the microstructure layer has symmetrically arranged intersecting optical surfaces. The light guide film is covered on a non-cell piece area of the photovoltaic module, and utilizes total reflection to totally reflect and deflect the normally incident light at the interface to the adjacent cell piece, so that the light energy of the non-light receiving area is recycled, and the power generation efficiency of the module is improved. The light guide film is visually invisible, and does not destroy the appearance consistency of the module.

Description

Technical Field

[0001] This invention relates to the field of photovoltaic module technology, and in particular to a light guide film for photovoltaic modules and a photovoltaic module. Background Technology

[0002] With the accelerated transformation of the global energy structure, photovoltaic power generation, as a core pillar of clean energy, is facing the dual challenges of improving power generation efficiency and reducing the cost per kilowatt-hour. The output power of a photovoltaic module directly depends on its effective light-receiving area and light energy utilization rate. In conventional modules, to accommodate the circuit connections between cells and reserve thermal expansion gaps, there are "dead zones" between adjacent cells that cannot generate electricity, typically accounting for 2-5% of the module's surface area. Sunlight shining into these gaps cannot be absorbed by the cells, directly causing light energy loss and restricting further improvements in the overall efficiency of the module.

[0003] To address the aforementioned issues, various light guiding technologies have been developed in the industry, which can be broadly categorized into two types: The first approach involves attaching an aluminum-coated light guide film to the gap between the solar cells on the module's backsheet glass. This film refracts and guides incident light from the gap to the light-receiving area of ​​the solar cells. While this approach can improve light utilization to some extent, because the aluminum-coated light guide film is placed under the gap between the solar cells, some light is easily reflected directionally to inefficiently light-receiving areas such as the sides and back of the solar cells, resulting in optical waste and failing to fully and effectively utilize the light in the module's optical dead zones.

[0004] The second approach involves depositing a white glaze layer on the back glass surface of the module or using a white backsheet structure, utilizing the principle of diffuse reflection to recover and reuse light from the optical dead zones of the module. This approach relies on scattering and diffuse reflection to disperse light to the edge of the cell, but the light path is disordered and random, the light propagation path within the encapsulation materials such as the encapsulation film is relatively long, and the proportion of light energy absorbed and lost by the encapsulation materials is relatively large, ultimately resulting in a relatively low overall light energy utilization efficiency.

[0005] More importantly, existing technologies mostly focus on the physical "light guiding" without fully considering integration with the module's appearance. For distributed photovoltaic and building-integrated photovoltaics (BIPV) applications that increasingly emphasize architectural aesthetics, the regularity and visual concealment of the module's appearance have become key requirements. Existing modules with obvious macroscopic structures or printed patterns have a stark contrast between their dark cells and highly reflective gap areas, creating a significant "mosaic" or "grid" visual effect that fails to meet the aesthetic requirements of the high-end market.

[0006] Therefore, the photovoltaic industry urgently needs an innovative optical solution. This solution must be able to efficiently capture and redistribute vertically incident light in the gaps between solar cells, while being highly invisible to the naked eye, without compromising the overall integrity and consistency of the module's appearance. This would improve power generation efficiency while meeting the market's dual expectations for high performance and aesthetics. Summary of the Invention

[0007] In view of the technical problems existing in the background art, the present invention proposes a light guide film for photovoltaic modules, comprising: Substrate layer; A microstructure layer is disposed on the substrate layer; And an optical modulation layer, covering the surface of the microstructure layer; The refractive index of the microstructure layer is higher than that of the optical modulation layer, and the light guide film can deflect and control the light rays that are incident on and penetrate the invisible light guide film, and guide them to a preset direction.

[0008] Furthermore, the substrate layer, microstructure layer, and optical modulation layer are stacked sequentially; the surface contour of the microstructure layer has at least two intersecting optical surfaces, the at least two intersecting optical surfaces are symmetrically arranged with respect to the thickness direction of the light guide film, and the included angle between the two intersecting optical surfaces is less than 66°.

[0009] Furthermore, the refractive index n1 of the microstructure layer and the refractive index n2 of the optical modulation layer satisfy the following conditions: n1 ≥ 1.55 and n2 ≤ 1.50.

[0010] Furthermore, the refractive index n1 of the microstructure layer and the refractive index n2 of the optical modulation layer satisfy: 1.56≤n1≤1.60, and 1.35≤n2≤1.46.

[0011] Furthermore, the microstructure layer is a high-refractive-index UV-curable layer, and its material is selected from at least one of UV-curable high-refractive-index acrylate resin, aromatic sulfide type UV-curable high-refractive-index resin, phenylsiloxane modified UV-curable high-refractive-index resin, phenylphenol acrylate, aromatic sulfide polyfunctional acrylate, epoxy / cationic UV-curable high-refractive-index resin, and phenylsiloxane UV resin; the surface contour of the microstructure layer is integrally formed on the surface of the substrate layer by UV imprinting or etching process.

[0012] Furthermore, the microstructure layers are arranged in an array and integrated on the same substrate; the shape of the microstructure layer is a regular geometric shape or an irregular irregular shape. The regular geometric shape is selected from one or more combinations of isosceles triangular prisms, square pyramids, hemispheres, and V-grooves. The irregular irregular shape is a non-standard contour structure adapted to the light guide path design, and the shapes of the microstructure layers of adjacent light guide films can be the same or different.

[0013] Furthermore, the optical modulation layer is selected from magnesium fluoride, calcium fluoride, and silicon dioxide, and is formed on the surface of the microstructure layer by physical deposition or chemical deposition.

[0014] Furthermore, the substrate layer is a high-transmittance film material, selected from either polyethylene terephthalate or polypropylene; the thickness of the substrate layer is 23μm to 500μm, and the visible light transmittance is not less than 90%.

[0015] Furthermore, it also includes an adhesive layer disposed on the side of the substrate layer facing away from the microstructure layer; the adhesive layer is a hot melt adhesive or an optically transparent pressure-sensitive adhesive, and its thickness is 50 μm to 150 μm.

[0016] Furthermore, this application also proposes a photovoltaic module, which is assembled from top to bottom with a cover glass, an encapsulation layer and photovoltaic cells arranged in a matrix array, with light-transmitting gaps between adjacent groups of photovoltaic cells; characterized in that the photovoltaic module also integrates a light guide film, which is precisely arranged at the light-transmitting gaps between each cell.

[0017] The light guide film proposed in this invention, through the synergistic cooperation of a microstructure layer and a low-refractive-index modulation layer, utilizes total internal reflection to efficiently deflect and guide vertically incident light illuminating the gaps between solar cells to the light-receiving surface of the cells. This significantly recovers light energy loss in non-light-receiving areas, improving the overall power generation efficiency of photovoltaic modules. The light guide film employs transparent materials and a micron-level structure, making it highly invisible visually and preserving the overall integrity and consistency of the module's appearance, thus balancing performance improvement with aesthetic requirements. Simultaneously, its array design achieves coverage of the entire non-cell area within the gaps, eliminating blind spots for effective light loss, enhancing adaptability to scattered light, and maintaining the module's thin and lightweight characteristics without the need for complex external devices. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the light guide film structure; Figure 2 This is a schematic diagram of the optical path structure of the light guide film. Detailed Implementation

[0019] This invention proposes a light guide film for photovoltaic modules. The light guide film includes a substrate layer 2, a microstructure layer 3 disposed on the substrate layer 2, and an optical modulation layer 4 covering the surface of the microstructure layer 3. The substrate layer 2 provides mechanical support for the entire light guide film and can be selected from high-transmittance polymer films such as polyethylene terephthalate or polypropylene to ensure efficient transmission of incident light. The microstructure layer 3 is attached to the surface of the substrate layer 2, and its core feature is a predetermined surface profile. The optical modulation layer 4 covers the profiled surface of the microstructure layer 3, forming a defined optical interface. In this three-layer stack, the refractive index of the microstructure layer 3 is set to be higher than that of the optical modulation layer 4; this refractive index difference is the physical basis for achieving total internal reflection guidance of light. When the light guide film covers a non-cell area of ​​the photovoltaic module, such as the gap 5 between adjacent cells 6 or above the busbar, light incident perpendicularly to this area sequentially penetrates the substrate layer 2 and enters the microstructure layer 3. Due to the significant refractive index difference between the microstructure layer 3 and the optical modulation layer 4, light undergoes total internal reflection or refraction at specific surface contours of the microstructure layer 3, forcibly deflecting and controlling its propagation direction, ultimately guiding it to the predetermined surface direction of the adjacent solar cell 6. In this way, solar energy that would otherwise be wasted or absorbed in areas outside the solar cell 6 is effectively recovered and converted into electrical energy, thereby improving the overall power generation of the photovoltaic module. Furthermore, because the microstructure size is on the micrometer scale and all constituent materials are transparent, the light guide film has a visually invisible effect, without compromising the original appearance integrity and consistency of the photovoltaic module.

[0020] Furthermore, as a further limitation of the aforementioned technical solution, this embodiment explicitly specifies the specific stacking order of each layer of the light guide film and the surface morphology of the microstructure layer 3. The substrate layer 2, microstructure layer 3, and optical modulation layer 4 are stacked sequentially; this order ensures the clarity and controllability of the light incident path. The surface profile of the microstructure layer 3 has at least two intersecting optical surfaces 41 and 42. These optical surfaces 41 and 42 are key geometric features for performing light deflection. To achieve optimal light guiding uniformity, these intersecting optical surfaces 41 and 42 are arranged symmetrically with respect to the thickness direction of the light guide film. (Reference) Figure 2Taking a common V-groove structure or triangular prism structure as an example, its two symmetrical sidewalls constitute the two intersecting optical surfaces 41 and 42. More importantly, the angle between these two intersecting optical surfaces 41 and 42 is limited to less than 66 degrees. This angle range is an optimal value obtained after optical simulation and experimental verification. When the angle is less than 66 degrees, combined with the refractive index difference of approximately 4% or more between the microstructure layer 3 and the optical modulation layer 4, it ensures efficient total internal reflection of most perpendicularly incident light rays, causing the light to be deflected and exit at a suitable angle, thereby achieving ideal light energy capture efficiency. For example, in actual production, this angle can be set to 62 degrees or less to match different combinations of material refractive indices.

[0021] Furthermore, this embodiment specifies the refractive index of the key optical parameters of the microstructure layer 3 and the optical modulation layer 4. To achieve a stable and efficient total internal reflection light guiding effect, the refractive index n1 of the microstructure layer 3 needs to be greater than or equal to 1.55, while the refractive index n2 of the optical modulation layer 4 needs to be less than or equal to 1.50. This numerical limitation ensures a sufficient refractive index gradient at the total internal reflection interface. For example, the microstructure layer 3 can be made of UV-curable acrylic resin with a refractive index of approximately 1.59, which exhibits excellent light transmittance and dimensional stability after curing. The matching optical modulation layer 4 can be made of magnesium fluoride material with a refractive index of approximately 1.38, which is much lower than that of the microstructure layer 3. With this combination of refractive indices, the critical angle for total internal reflection when light travels from the microstructure layer 3 to the optical modulation layer 4 is approximately 60 degrees. This creates a good synergistic effect with the aforementioned preferred angle of 62 degrees between the optical action surfaces 41 and 42, ensuring that the vast majority of incident light rays can meet the total internal reflection condition and are thus efficiently guided to the adjacent solar cell 6. This refractive index range is a reliable boundary derived from fundamental optical principles and extensive experimental data, ensuring the stability and repeatability of the light guide film solution under various practical conditions.

[0022] Furthermore, this embodiment further optimizes the refractive index range of the microstructure layer 3 and the optical modulation layer 4 to achieve better optical performance and process matching. The refractive index n1 of the microstructure layer 3 is limited to between 1.56 and 1.60. Resin materials selected within this range exhibit balanced performance in terms of optical properties, mechanical properties, and compatibility with the imprinting process. The refractive index n2 of the optical modulation layer 4 is limited to between 1.35 and 1.46, for example, magnesium fluoride with a refractive index of 1.38 or silicon dioxide with a refractive index of 1.46 are selected. This narrower refractive index range ensures that the refractive index difference between the microstructure layer 3 and the optical modulation layer 4 is sufficiently stable, with a typical difference of around 0.18, which is much greater than the basic threshold of 0.05 that satisfies the total internal reflection condition. This preferred refractive index range not only ensures high total internal reflection guiding efficiency, but also provides more diverse and mature material options for the preparation of low refractive index modulation layers. For example, the refractive index can be precisely controlled within this range by vacuum evaporation or magnetron sputtering, thereby ensuring product performance while taking into account production feasibility and cost control.

[0023] Furthermore, this embodiment defines in detail the constituent materials and molding process of the microstructure layer 3. The microstructure layer 3 is made of a high-refractive-index material, specifically composed of a photocurable resin. The photocurable resin, such as an acrylate or epoxy acrylate system doped with high-refractive-index nanoparticles, can be rapidly cured under ultraviolet light irradiation to form a solid structure with high refractive index and excellent optical transparency. Its surface contour is not randomly formed, but is formed on the surface of the substrate layer 2 through a precise imprinting or etching process. Among them, the imprinting process is particularly suitable for large-scale, high-precision continuous production. In specific operation, firstly, a layer of liquid ultraviolet-curable resin with a high refractive index is uniformly coated on the surface of the substrate layer 2. Then, a precision-machined nickel template with the target microstructure (such as a V-groove array) etched on its surface is pressed onto the liquid resin under a certain pressure. The resin flows into the tiny grooves of the mold under pressure, replicating the microscopic pattern of the mold. Then, the resin is cured and shaped within seconds by ultraviolet irradiation. Finally, the mold is peeled off, resulting in a microstructure layer 3 with a precisely pre-defined contour formed on the surface of the transparent substrate layer 2. This process ensures the consistency of the microstructure, high alignment accuracy, and excellent mechanical strength.

[0024] Furthermore, this embodiment further describes the arrangement and specific shape of the microstructure layer 3. To achieve continuous, blind-spot-free light capture across the entire gap 5 region of the solar cell 6, multiple microstructure layers 3 are arranged in an array and integrated on the same substrate to form a continuous light-guiding plane. This array design ensures that incident light at any point within the coverage area can be effectively captured by adjacent microstructures. The shape of the microstructure layer 3 itself is highly flexible and can be a regular geometric shape, such as one or more combinations of isosceles triangular prisms, square pyramids, hemispheres, or V-grooves. For example, a single V-groove microstructure can provide two symmetrical intersecting optical surfaces 41 and 42. Irregular, non-standard structures can also be used, i.e., complex structures with non-standard contours designed to meet specific light-guiding path requirements or optical performance optimization goals. In actual array design, the microstructure layers 3 of adjacent light guide films can have the same shape to pursue uniformity of light spot and process uniformity, or they can be different. For example, microstructures with different angles or depths can be used in different areas of the array to cope with different incident light angle distributions or complex packaging environments, thereby achieving the optimal overall light guiding efficiency.

[0025] Furthermore, this embodiment provides a detailed description of the specific material selection and formation process of the optical modulation layer 4. The optical modulation layer 4 is selected from magnesium fluoride, calcium fluoride, or silicon dioxide. Magnesium fluoride is the preferred material due to its extremely low refractive index (approximately 1.38) and excellent ultraviolet-visible light transmittance. Calcium fluoride has similar low refractive index characteristics. Although silicon dioxide has a slightly higher refractive index (approximately 1.46), it is also an ideal choice for some specific applications due to its excellent chemical stability and good compatibility with encapsulation materials. This modulation layer is formed on the surface of the microstructure layer 3 by physical deposition or chemical deposition. Physical deposition methods, such as vacuum evaporation or magnetron sputtering, have the advantages of mature processes and dense film layers, enabling the formation of an extremely thin film with uniform thickness and steep interface on the surface of the microstructure layer 3 without filling the microstructure contour trenches. This film precisely defines the optical interface that produces total internal reflection. Chemical deposition methods, such as chemical vapor deposition, can achieve uniform coverage on complex shaped surfaces. Regardless of the method used, the modulation layer formed must be closely bonded to the surface of the microstructure layer 3 and maintain its own refractive index below the requirement of the microstructure layer 3 in order to constitute the necessary optical conditions for achieving total internal reflection.

[0026] Furthermore, this embodiment specifies the material, thickness, and optical properties of the substrate layer 2. The substrate layer 2, serving as the basic support for the light guide film, is made of a high-transparency film material, specifically polyethylene terephthalate (PET) or polypropylene. PET film is an ideal substrate for industrial production due to its excellent mechanical strength, good dimensional stability, high temperature resistance, and relatively low cost. The thickness of the substrate layer 2 is controlled between 23 micrometers and 500 micrometers. When the thickness of the substrate layer 2 is 23 micrometers, the light guide film exhibits excellent overall flexibility, making it particularly suitable for bonding to photovoltaic modules with curved or irregularly shaped structures. When the thickness of the substrate layer 2 is 500 micrometers, the light guide film has stronger mechanical support, facilitating positioning and handling in automated lamination processes. A preferred thickness is 50 micrometers or 125 micrometers, achieving a good balance between flexibility and ease of handling. More importantly, the visible light transmittance of the substrate layer 2 must be greater than or equal to 90%. This high transmittance ensures that the maximum amount of incident light can pass through the substrate layer 2 smoothly and reach the underlying microstructure layer 3 and optical modulation layer 4 for guidance, thereby avoiding the absorption or reflection loss of light energy by the substrate layer 2 itself.

[0027] Furthermore, to facilitate the installation and fixation of the light guide film, this embodiment adds an adhesive layer 1 to the light guide film. This adhesive layer 1 is disposed on the side of the substrate layer 2 facing away from the microstructure layer 3. During installation, the side with the microstructure layer 3 and the optical modulation layer 4 faces the gap 5 of the solar cell 6, while the adhesive layer 1 is located on the outside of the substrate layer 2, used to firmly adhere the entire light guide film to the inner surface of the cover glass 7 of the photovoltaic module or the upper encapsulation material. The adhesive layer 1 is a hot melt adhesive or an optically transparent pressure-sensitive adhesive. Hot melt adhesive melts at high temperatures during the photovoltaic module lamination process and solidifies after cooling, providing high-strength adhesion. Optically transparent pressure-sensitive adhesive is tacky at room temperature and can be directly adhered by applying pressure, facilitating rework and manual assembly. Regardless of the type used, to provide sufficient and uniform adhesive strength and avoid poor adhesion or air bubbles due to insufficient adhesive, the thickness of the adhesive layer 1 is controlled between 50 micrometers and 150 micrometers, preferably 75 micrometers or 100 micrometers. The adhesive layer 1 itself must also have excellent light transmittance, UV aging resistance, and damp heat resistance to ensure the reliability of the photovoltaic module during its long outdoor service life.

[0028] Further, refer to Figure 1 This embodiment proposes a photovoltaic module, which is assembled from top to bottom with a cover glass 7, an encapsulation layer 8 and photovoltaic cells 6 arranged in a matrix array, with light transmission gaps between adjacent groups of photovoltaic cells; the photovoltaic module also integrates a light guide film, which is precisely arranged at the light transmission gaps between each cell.

[0029] The key improvement of this invention lies in the provision of the aforementioned light guide film array at these gaps 5. This light guide film array is precisely positioned and embedded within the encapsulation layer 8 during manufacturing, covering directly above the gaps 5 of the solar cells 6. When sunlight shines on the surface of the photovoltaic module, the cover glass 7 transmits the light into the encapsulation layer 8. A portion of the light directly illuminates the surface of the solar cell 6 and generates electrical output. The remaining portion of the light, which would otherwise illuminate the ineffective gaps 5, is incident on the light guide film array covering them. This light guide film array then functions, causing the light to pass sequentially through the substrate layer 2 and undergo total internal reflection at the interface between the microstructure layer 3 with symmetrical optical surfaces 41 and 42 and the low-refractive-index optical modulation layer 4. The propagation direction of the light is thus completely deflected, ultimately illuminating the surface of the adjacent solar cell 6, where it is absorbed and converted into electrical energy. Through this integrated design, photovoltaic modules can effectively recover light energy from the cell gaps, which account for 2% to 5% of the module's surface area, without changing the standard lamination process, adding external devices, or sacrificing aesthetics, thus achieving a significant increase in the module's output power per unit area.

[0030] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A light guide film for photovoltaic modules, characterized in that, include: Substrate layer (2); A microstructure layer (3) is disposed on the substrate layer (2); And an optical modulation layer (4) covering the surface of the microstructure layer (3); The refractive index of the microstructure layer (3) is higher than that of the optical modulation layer (4), and the light guide film can deflect and control the light rays that are incident on and penetrate the invisible light guide film, and guide them to a preset direction.

2. The light guide film according to claim 1, characterized in that, The substrate layer (2), the microstructure layer (3) and the optical modulation layer (4) are stacked in sequence; the surface contour of the microstructure layer (3) has at least two intersecting optical surfaces (41, 42), the at least two intersecting optical surfaces (41, 42) are symmetrically arranged with respect to the thickness direction of the light guide film, and the included angle between the two intersecting optical surfaces (41, 42) is less than 66°.

3. The light guide film according to claim 1, characterized in that, The refractive index n1 of the microstructure layer (3) and the refractive index n2 of the optical modulation layer (4) satisfy the following: n1≥1.55 and n2≤1.

50.

4. The light guide film according to claim 1, characterized in that, The refractive index n1 of the microstructure layer (3) and the refractive index n2 of the optical modulation layer (4) satisfy: 1.56≤n1≤1.60, and 1.35≤n2≤1.

46.

5. The light guide film according to claim 1, characterized in that, The microstructure layer (3) is a high-refractive-index UV-curable layer, and its material is selected from at least one of UV-curable high-refractive-index acrylate resin, aromatic sulfide type UV-curable high-refractive-index resin, phenylsiloxane modified UV-curable high-refractive-index resin, phenylphenol acrylate, aromatic sulfide multifunctional acrylate, epoxy / cationic UV-curable high-refractive-index resin and phenylsiloxane UV resin; the surface contour of the microstructure layer (3) is integrally formed on the surface of the substrate layer (2) by UV imprinting or etching process.

6. The light guide film according to claim 1, characterized in that, The microstructure layers (3) are arranged in an array and integrated on the same substrate; the shape of the microstructure layers (3) is a regular geometric shape or an irregular irregular shape. The regular geometric shape is selected from one or more combinations of isosceles triangular prisms, square pyramids, hemispheres, and V-grooves. The irregular irregular shape is a non-standard contour structure adapted to the light guide path design, and the shapes of the microstructure layers (3) of adjacent light guide films can be the same or different.

7. The light guide film according to claim 1, characterized in that, The optical modulation layer (4) is selected from magnesium fluoride, calcium fluoride, and silicon dioxide, and is formed on the surface of the microstructure layer (3) by physical deposition or chemical deposition.

8. The light guide film according to claim 1, characterized in that, The substrate layer (2) is a high-transmittance film material, and the material is selected from either polyethylene terephthalate or polypropylene; the thickness of the substrate layer is 23μm to 500μm, and the visible light transmittance is not less than 90%.

9. The light guide film according to claim 1, characterized in that, It also includes an adhesive layer (1) disposed on the side of the substrate layer (2) facing away from the microstructure layer (3); the adhesive layer (1) is a hot melt adhesive or an optically transparent pressure-sensitive adhesive, and its thickness is 50 μm to 150 μm.

10. A photovoltaic module, comprising, from top to bottom, a cover glass (7), an encapsulation layer (8), and photovoltaic cells (6) arranged in a matrix array, wherein there is a light-transmitting gap between adjacent groups of photovoltaic cells; characterized in that, This photovoltaic module also integrates a light guide film as defined in claim 1, wherein the light guide film is precisely arranged in the light transmission gap between each cell.

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