Light redirecting composite film, method of making and use thereof

Abstract

The application discloses a light turning composite film, a preparation method and application thereof, and belongs to the field of light energy utilization. In view of the problem that the light energy of an existing solar cell module is seriously lost under low-angle light irradiation, the application provides a light turning composite film, which comprises a first diffusion functional layer, an intermediate bonding layer and a second diffusion functional layer arranged in sequence; a first microstructure diffusion zone is arranged on the first diffusion functional layer, a second microstructure diffusion zone is arranged on the second diffusion functional layer, the two microstructure diffusion zones are oppositely arranged, and the two diffusion functional layers are attached through the intermediate bonding layer; the refractive index difference of the two microstructure diffusion zones is less than or equal to 0.05, and the refractive index of the intermediate bonding layer is less than the refractive index of the two microstructure diffusion zones. The application is easy to meet the total reflection condition at the interface between the intermediate bonding layer and the upper and lower diffusion structure layers through a specific refractive index combination, so that the low-angle incident light is totally reflected at the interface and is efficiently guided to the active area of the cell piece, and the utilization rate of low-angle light is improved.

Description

Technical Field

[0001] This invention belongs to the field of light energy utilization technology, and more specifically, relates to a light-directing composite film, its preparation method, and its application. Background Technology

[0002] In solar cell modules, the gaps between cells cannot effectively utilize incident light energy, especially under low-angle illumination conditions, where light energy loss is particularly significant. Existing light-directing technologies mainly rely on the refractive effect of microstructure surfaces to change the light path, but this method suffers from high angle sensitivity and uneven light distribution. Although some multilayer composite optical films exist, they typically rely on large refractive index differences between layers to control the light path. This design imposes significant limitations on material selection and has complex fabrication processes. Furthermore, the capture efficiency of traditional structures for low-angle light still has room for improvement, particularly in applications during dawn / dusk and at high latitudes where performance is less than ideal. Therefore, there is a need to develop a novel light-directing structure that can more effectively capture low-angle light, has a simple fabrication process, and exhibits excellent optical performance.

[0003] For example, Chinese patent application CN201610375664.5, published on September 28, 2016, discloses a light-directing film, including a substrate layer, a microstructure layer disposed on the substrate layer, and a reflective layer covering the microstructure layer. The reflective layer is distributed in the non-cell area of ​​the photovoltaic module. The microstructure layer includes several horizontally and vertically arranged microstructure strips and microstructure areas disposed at the four corners of the cell. Both the microstructure strips and microstructure areas are serrated, including several microstructures. Each microstructure has a cross-section including at least two sides, and the reflective layer covers the sides of the microstructures. The angle between the microstructures and the length extension direction of the microstructure strips is 0~90°. The shortcomings of this patent are: if the serrated microstructure is not designed properly, it can easily lead to uneven light output, stray light spots or dispersion, affecting the light spot quality; and the serrated contour and side coverage of the microstructure require extremely high precision and consistency in the manufacturing process.

[0004] For example, Chinese patent application CN201820775718.1, published on March 19, 2019, discloses a directional reflective film and photovoltaic module. It includes a main film layer, a refractive functional layer, and an insulating layer. The refractive functional layer is located in the area of ​​the main film layer not covered by the solar cells. The insulating layer is located on top of the refractive functional layer or on the entire main film layer. The refractive functional layer consists of a substrate layer, a microstructure layer, and a reflective layer. The microstructure layer is located on one or both sides of the substrate layer, and the reflective layer is located on the surface of the microstructure layer. The drawback of this patent is that the metal reflective layer is prone to sulfurization and oxidation in humid and hot environments, leading to a sharp decrease in reflectivity. Although the design includes an insulating layer for protection, any micro-defects in the insulating layer can allow moisture and corrosive gases to penetrate, causing performance degradation of the reflective layer. Summary of the Invention

[0005] 1. The problem to be solved

[0006] To address the significant light energy loss in existing solar cell modules under low-angle illumination conditions, this invention provides a light-directing composite film, its preparation method, and its applications. This invention utilizes a specific refractive index combination of three layers in the composite film to easily satisfy total internal reflection conditions at the interface between the intermediate adhesive layer and the upper and lower diffusion structure layers. This allows low-angle incident light to undergo total internal reflection at the interface and be efficiently guided to the active region of the solar cell, significantly improving the utilization rate of low-angle light and thus minimizing the light energy loss problem in solar cell modules under low-angle illumination conditions.

[0007] 2. Technical Solution

[0008] To solve the above problems, the present invention adopts the following technical solution.

[0009] A light-directing composite film includes a first diffusion functional layer, an intermediate adhesive layer, and a second diffusion functional layer arranged sequentially from top to bottom; the first diffusion functional layer is provided with at least one first microstructure diffusion region, and the second diffusion functional layer is provided with at least one second microstructure diffusion region, the first microstructure diffusion region and the second microstructure diffusion region are arranged facing each other, and the first diffusion functional layer and the second diffusion functional layer are bonded together by the intermediate adhesive layer.

[0010] Wherein, the difference between the refractive index of the first microstructure diffusion region and the refractive index of the second microstructure diffusion region is ≤0.05, the refractive index of the intermediate adhesive layer is less than the refractive index of the first microstructure diffusion region and the refractive index of the intermediate adhesive layer is less than the refractive index of the second microstructure diffusion region.

[0011] Furthermore, the first diffusion functional layer includes a first PET substrate and a plurality of first microstructure diffusion regions disposed on the lower surface of the first PET substrate;

[0012] The second diffusion functional layer includes a second PET substrate and a plurality of second microstructure diffusion regions disposed on the upper surface of the second PET substrate;

[0013] Both the first microstructure diffusion region and the second microstructure diffusion region are made of optical resin, and the difference between the refractive index of the first optical resin used to prepare the first microstructure diffusion region and the refractive index of the second optical resin used to prepare the second microstructure diffusion region is ≤0.01.

[0014] Furthermore, both the first microstructure diffusion region and the second microstructure diffusion region are groove-shaped, and the first microstructure diffusion region is randomly arranged on the lower surface of the first PET substrate, while the second microstructure diffusion region is randomly arranged on the upper surface of the second PET substrate; wherein, random arrangement means that the parameters of the groove shape are randomly selected within a set range; wherein the parameters of the groove shape include depth, length and width.

[0015] Furthermore, the thicknesses of both the first PET substrate and the second PET substrate are 50μm to 75μm.

[0016] Furthermore, the difference between the refractive index of the intermediate adhesive layer and the refractive index of the first microstructure diffusion region is greater than or equal to 0.15; the difference between the refractive index of the intermediate adhesive layer and the refractive index of the second microstructure diffusion region is greater than or equal to 0.15.

[0017] Furthermore, the refractive index of the first microstructure diffusion region and the refractive index of the second microstructure diffusion region are both 1.60~1.65; the refractive index of the intermediate adhesive layer is 1.40~1.45.

[0018] Furthermore, the refractive index of the first microstructure diffusion region and the refractive index of the second microstructure diffusion region are both 1.62, and the refractive index of the intermediate adhesive layer is 1.42.

[0019] A method for preparing a light-directing composite film as described in any of the above technical solutions includes the following steps:

[0020] S1: Preparation of the first microstructure diffusion region: The first microstructure diffusion region is formed on the first diffusion functional layer by a molding method or an imprinting method;

[0021] S2: Preparation of the second microstructure diffusion region: The second microstructure diffusion region is formed on the second diffusion functional layer by a molding method or an imprinting method;

[0022] S3: Composite: Using a soft-press bonding machine, optical resin is applied as an adhesive to the surface of the first microstructure diffusion area or the second microstructure diffusion area. Then, the first diffusion functional layer and the second diffusion functional layer are aligned and bonded together, so that the first microstructure diffusion area and the second microstructure diffusion area are facing each other and bonded by resin. Finally, the mixture is cured to form an intermediate adhesive layer.

[0023] An application of a light-directing composite film as described in any of the above technical solutions, wherein the light-directing composite film is stacked between the glass cover plate and the solar cell of the solar cell module.

[0024] 3. Beneficial effects

[0025] (1) By setting the refractive indices of the first and second microstructure diffusion regions to be similar and the refractive index of the intermediate adhesive layer to be the smallest, a stable “light-dense-light-sparse-light-dense” medium structure is formed at the interface between the intermediate adhesive layer and the upper and lower microstructure diffusion regions. This makes it easy for the light to meet the total internal reflection condition at the interface between the microstructure diffusion region and the intermediate adhesive layer when low-angle light is incident in the early morning, evening, winter or high latitude regions. This allows the low-angle incident light to be totally internally reflected at the interface and efficiently guided to the active area of ​​the battery cell, greatly improving the utilization rate of low-angle light. At the same time, for normal incident or high-angle light, since the refractive indices of the first and second microstructure diffusion regions are almost the same, the light can penetrate efficiently, maximizing the inherent high transmittance of the module under the best lighting conditions. By decomposing the light-directing function into two functional layers bonded together by the intermediate adhesive layer, the structure is clearly hierarchical and the function is well-defined. The intermediate adhesive layer achieves a strong physical bond, ensuring the integrity of the composite film and the reliability of long-term use.

[0026] (2) The first and second microstructure diffusion regions of the present invention are made of optical resin. Optical resin has the inherent characteristics of adjustable refractive index, good optical uniformity and extremely high transmittance. Furthermore, the refractive index difference between the first and second microstructure diffusion regions is limited to ensure that while realizing the low-angle light diversion function, it can also maintain a high transmittance for the incident light. At the same time, the two microstructure diffusion regions are formed on the PET substrate. The PET substrate has the characteristics of high strength, good stiffness, scratch resistance and good dimensional stability. This enables the entire composite film to effectively resist deformation and prevent the microstructure from being crushed or worn during subsequent transportation, lamination and long-term use, thus ensuring the durability and reliability of optical performance.

[0027] (3) The grooves in this invention are randomly arranged on the PET substrate. The random arrangement ensures that the structural parameters of some of the random grooves can match the extremely low-angle light in the early morning, the near-vertical light at noon, or the oblique light in the afternoon, so that they can undergo efficient total internal reflection. This makes the composite film no longer limited to improving the light utilization rate of a specific angle range, but achieves comprehensive and efficient capture of light with a wide range of incident angles from morning to night. Furthermore, when the two PET substrates are bonded together, the random structure does not require strict microstructure alignment, which greatly reduces the process difficulty and defect rate of large-scale production and saves production costs.

[0028] (4) The present invention makes specific limits on the refractive index of the two microstructure diffusion regions and the intermediate adhesive layer. If the refractive index is smaller, the angle of light diffusion will be smaller and the effect will be worse. The larger the refractive index difference, the better, but the cost will be higher accordingly. Therefore, the cost and performance are balanced. The thickness of the two PET substrates is also limited to avoid excessive thickness affecting the subsequent bonding process and causing uneven bonding. If the thickness is too thin, the precision requirements of the preparation machine are high, resulting in high cost.

[0029] (5) The preparation method of the present invention adopts mature PET substrate and soft pressing bonding process, combined with specific refractive index material selection, which makes it easy to achieve large-scale stable production; and when it is used in the field of solar cell modules, it can significantly improve the power output of solar cell modules under low angle illumination conditions, greatly extend the effective power generation time of the modules, improve the photoelectric conversion efficiency under non-vertical illumination conditions, and thus significantly increase the daily and annual power generation per unit area. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the structure of the light-directing composite film. Detailed Implementation

[0031] The present invention will now be further described with reference to specific embodiments and accompanying drawings.

[0032] A light-directing composite film includes a first diffusion layer, an intermediate adhesive layer, and a second diffusion layer arranged sequentially from top to bottom. The first diffusion layer has at least one first microstructure diffusion region, and the second diffusion layer has at least one second microstructure diffusion region. The first and second microstructure diffusion regions face each other, and the first and second diffusion layers are bonded together by the intermediate adhesive layer. It is worth noting that in this embodiment, the position and orientation of the two microstructure diffusion regions are not required; they can be randomly arranged on two corresponding diffusion layers. It is only necessary that the two microstructure diffusion regions face each other. This random arrangement allows light to propagate at a less uniform angle, resulting in more even light dispersion, i.e., diverging a point laser beam into a planar laser beam. This allows the light to diffuse fully while redirecting, forming uniform illumination on the solar cell and effectively reducing the risk of hot spots.

[0033] Wherein, the difference between the refractive index of the first microstructure diffusion region and the refractive index of the second microstructure diffusion region is ≤0.05, the refractive index of the intermediate adhesive layer is less than the refractive index of the first microstructure diffusion region and the refractive index of the intermediate adhesive layer is less than the refractive index of the second microstructure diffusion region.

[0034] like Figure 1 As shown, in this embodiment, the refractive index of the first microstructure diffusion region is defined as n1, the refractive index of the second microstructure diffusion region is n2, and the refractive index of the intermediate adhesive layer is n3. n1 and n2 are the same or close, satisfying that the difference between them is ≤0.05; n3 < n1, and n3 < n2. The intermediate adhesive layer, located in the middle layer, has the smallest refractive index, while the upper and lower diffusion functional layers have larger refractive indices. This achieves a stable optically dense-optically sparse-optically dense dielectric structure at the interface between the intermediate adhesive layer and the upper and lower microstructure diffusion regions. When low-angle light is incident in the early morning, evening, winter, or high-latitude regions, this structure easily allows the light to meet the total internal reflection condition at the interface of the microstructure diffusion region or the intermediate adhesive layer, so that the low-angle incident light undergoes total internal reflection at the interface and is efficiently guided to the active area of ​​the solar cell, greatly improving the utilization rate of low-angle light. At the same time, for normal incident or high-angle light, since the refractive indices of the first and second microstructure diffusion regions are almost the same, the light can penetrate efficiently, maximizing the inherent high transmittance of the module under optimal lighting conditions. It achieves precise optical path management regardless of whether the light is at a low angle, normal incidence, or high angle, and takes into account light incident from all angles.

[0035] Furthermore, the intermediate adhesive layer not only achieves a strong physical bond, ensuring the integrity of the composite film and its long-term reliability, but also achieves efficient light redirection by setting the refractive index of the intermediate adhesive layer to match the refractive indices of the other two layers. This enables the intermediate adhesive layer to achieve a dual function. This multi-functional integrated design avoids complex multi-layer coatings or external components, reduces process complexity and manufacturing costs, and improves the weather resistance and stability of the product, making it more suitable for mass production and application.

[0036] In summary, this embodiment achieves efficient capture and redirection of low-angle incident light through a specific combination of three layers with different refractive indices, and its structural design is reasonable and easy to mass-produce.

[0037] In one specific embodiment, the first diffusion functional layer includes a first PET substrate and a plurality of first microstructure diffusion regions disposed on the lower surface of the first PET substrate; the second diffusion functional layer includes a second PET substrate and a plurality of second microstructure diffusion regions disposed on the upper surface of the second PET substrate.

[0038] The first microstructure diffusion region and the second microstructure diffusion region are both made of optical resin, and the material of the intermediate adhesive layer is also optical resin; and the difference between the refractive index of the first optical resin used to prepare the first microstructure diffusion region and the refractive index of the second optical resin used to prepare the second microstructure diffusion region is ≤0.01.

[0039] Specifically, in this embodiment, the structure of the two diffusion functional layers is further defined. The microstructure diffusion area is formed on the PET substrate, and PET is used as a carrier because it has the characteristics of high strength, good stiffness, scratch resistance and good dimensional stability. This makes it a skeleton support structure, so that the entire composite film can effectively resist deformation and prevent the microstructure from being crushed or worn during subsequent transportation, lamination and long-term use, thus ensuring the durability and reliability of optical performance.

[0040] Secondly, the difference in refractive index between the two microstructure diffusion regions is further limited, making their refractive indices nearly identical. According to optical principles, when light passes through multiple thin film interfaces consecutively, its overall reflectivity is closely related to the matching degree of the refractive indices of each layer. Since n1 ≈ n2 (difference ≤ 0.01), the amplitude and phase of the reflection of light at the first microstructure / adhesive layer interface are highly similar to those at the adhesive layer / second microstructure interface. This can produce a destructive interference effect in optics, thereby significantly reducing the reflection of the entire composite film on normally incident light and ensuring extremely high transmittance. Simultaneously, the material used to prepare the two microstructure diffusion regions is optical resin. Optical resins (such as acrylic, polyurethane acrylic, and silicone resins) have inherent characteristics of adjustable refractive index, good optical uniformity, and extremely high transmittance, enabling precise matching with the refractive index combination.

[0041] In one specific embodiment, both the first and second microstructure diffusion regions are groove-shaped, meaning that both microstructure diffusion regions are elongated grooves. The first microstructure diffusion regions are randomly arranged on the lower surface of the first PET substrate, and the second microstructure diffusion regions are randomly arranged on the upper surface of the second PET substrate. The random arrangement refers to the groove-shaped parameters being randomly selected within a set range. The groove-shaped parameters include depth, length, and width. It should be noted that in this embodiment, the set range for the groove-shaped parameters is: groove length: 50~200µm; groove depth: 12~26µm; groove width: 1.5~4µm.

[0042] The applicant wishes to emphasize that random arrangement means the arrangement of grooves on the PET substrate is irregular, without a specific logic or order; the parameters between two adjacent grooves can be identical, partially identical, or completely different; and the arrangement of opposing grooves on two PET substrates is also random, with opposing grooves either corresponding one-to-one or staggered. The core of this embodiment is random arrangement. Through the synergistic effect of random arrangement and total internal reflection mechanism, the composite film exhibits excellent response characteristics to light with a wide range of incident angles, significantly extending the effective power generation time; simultaneously, the random microstructure diffusion region allows light to diffuse fully while turning, forming uniform illumination on the solar cell and effectively reducing the risk of hot spots.

[0043] Meanwhile, this application selects elongated grooves as the microstructure diffusion region. When low-angle light is incident, its original propagation direction is first disrupted by the randomly distributed groove structure, resulting in sufficient diffusion. Subsequently, the light undergoes multiple reflections within the grooves, extending its propagation path. This process increases the probability that the light will eventually be adjusted to a near-vertical direction and reach the active area of ​​the solar cell. In this way, the final technical effect of effectively capturing low-angle incident light and using it for power generation is achieved. Furthermore, the grooves are easy to form, eliminating the need for complex molds and saving costs.

[0044] In one specific embodiment, the thicknesses of both the first PET substrate and the second PET substrate are 50μm to 75μm. The thickness of the two PET substrates is limited because if the substrates are too thick, it will affect the subsequent bonding steps between the two substrates, resulting in uneven bonding, a high defect rate, and high cost; if they are too thin, it will place higher precision requirements on the processing equipment, indirectly increasing cost and manufacturing difficulty.

[0045] In one specific embodiment, the difference between the refractive index of the intermediate adhesive layer and the refractive index of the first microstructure diffusion region is greater than or equal to 0.15; the difference between the refractive index of the intermediate adhesive layer and the refractive index of the second microstructure diffusion region is also greater than or equal to 0.15. If the refractive index difference between the intermediate adhesive layer and the microstructure diffusion region is too small, the angle of light diffusion will be small, resulting in a poorer effect; a larger refractive index difference is better, but the cost will be correspondingly higher. Therefore, considering the balance between cost and performance, it is clearly limited.

[0046] As a preferred embodiment, the refractive index of the first microstructure diffusion region and the refractive index of the second microstructure diffusion region are both 1.60~1.65; the refractive index of the intermediate adhesive layer is 1.40~1.45.

[0047] More specifically, the refractive index of the first microstructure diffusion region and the refractive index of the second microstructure diffusion region are both 1.62, and the refractive index of the intermediate adhesive layer is 1.42.

[0048] A method for preparing a light-directing composite film as described in any of the above embodiments includes the following steps:

[0049] S1: Preparation of the first microstructure diffusion region: The first microstructure diffusion region is formed on the first diffusion functional layer by a molding method or an imprinting method;

[0050] S2: Preparation of the second microstructure diffusion region: The second microstructure diffusion region is formed on the second diffusion functional layer by a molding method or an imprinting method;

[0051] S3: Composite: Using a soft pressure bonding machine, optical resin is applied as an adhesive to the surface of the first microstructure diffusion area or the second microstructure diffusion area. Then, the first diffusion functional layer and the second diffusion functional layer are aligned and bonded together, so that the first microstructure diffusion area and the second microstructure diffusion area are facing each other and bonded by resin. Finally, the intermediate adhesive layer is cured to form an intermediate adhesive layer. The curing method is ultraviolet light curing.

[0052] The preparation method of this invention uses a mature PET substrate and soft pressing lamination process, combined with the selection of specific refractive index materials, which makes it easy to achieve large-scale and stable production.

[0053] An application of the light-directing composite film as described in any of the above embodiments is disclosed, wherein the light-directing composite film is stacked between the glass cover and the solar cells of the solar cell module. When used in the field of solar cell modules, it can significantly improve the power output of the solar cell module under low-angle illumination conditions, greatly extend the effective power generation time of the module, and improve the photoelectric conversion efficiency under non-perpendicular illumination conditions, thereby significantly increasing the daily and annual power generation per unit area.

[0054] To further understand the effects of this application, the following examples and comparative cases are provided for illustration:

[0055] Example 1

[0056] A light-directing composite film is prepared by the following method:

[0057] S1: Preparation of the first microstructure diffusion region: On the lower surface of the first PET substrate with a thickness of 50μm, an acrylic resin with a refractive index n1 of 1.62 is coated by UV curing imprinting process, and imprinting is performed using a mold with a random elongated groove structure. After UV curing, the first microstructure diffusion region is formed.

[0058] S2: Preparation of the second microstructure diffusion region: On the surface of the second PET substrate with a thickness of 50μm, an acrylic resin with a refractive index n2 of 1.62 is coated using the same process. The resin is then imprinted using a mold with a random elongated groove structure and UV cured to form the second microstructure diffusion region.

[0059] S3: Composite: Using a soft-press laminating machine, UV-curable epoxy resin with a refractive index n3 of 1.42 is used as an adhesive and uniformly coated on the surface of the first microstructure diffusion region. Then, the second diffusion functional layer is aligned and laminated with the first diffusion functional layer. The intermediate adhesive layer is cured by UV irradiation to obtain a light-directing composite film.

[0060] Example 2

[0061] Based on the same principle as Example 1, the difference is that the refractive index n1 of the resin used in the first microstructure diffusion region is 1.61, the refractive index n2 of the resin used in the second microstructure diffusion region is 1.63, the refractive index n3 of the resin in the intermediate adhesive layer is still 1.42, and the rest of the steps are exactly the same.

[0062] Comparative Example 1

[0063] The basic structure is the same as in Example 1, except that there is only one diffusion functional layer and one adhesive layer. Random microstructure diffusion areas are formed by embossing on the lower surface of a 50μm thick PET substrate. The resin used for the microstructure diffusion areas has a refractive index of 1.62.

[0064] Comparative Example 2

[0065] The basic structure is the same as in Example 1, except that the refractive indices of the three layers are as follows: the refractive index n1 of the resin in the first microstructure diffusion region is 1.62, the refractive index n2 of the resin in the second microstructure diffusion region is 1.62, and the refractive index n3 of the resin in the intermediate adhesive layer is 1.52 (n3 < n1, n3 < n2).

[0066] Experimental tests were conducted on the light-directing composite films obtained in Examples 1-2 and Comparative Examples 1-2, and the results are shown in Table 1 below:

[0067] Table 1 Experimental Data

[0068]

[0069] As shown in Table 1, Embodiments 1 and 2 of this application exhibit significant performance advantages under low-angle illumination conditions, with relative power gains of 5.1% and 4.9% respectively, which are significantly better than the comparative examples. Compared with Comparative Example 1, the three-layer composite structure of this application greatly enhances the ability to capture low-angle light by constructing a total internal reflection interface. Compared with Comparative Example 2, the three-layer refractive index design of this application makes it easier to form total internal reflection conditions at the interface, which is the key to achieving efficient light redirection.

[0070] The examples described herein are merely preferred embodiments of the invention and are not intended to limit the concept and scope of the invention. Any modifications and improvements made by those skilled in the art to the technical solutions of the invention without departing from the design concept of the invention should fall within the protection scope of the invention.

Claims

1. A light-directing composite film, characterized in that: It includes a first diffusion functional layer, an intermediate adhesive layer and a second diffusion functional layer arranged sequentially from top to bottom; the first diffusion functional layer is provided with at least one first microstructure diffusion region and the second diffusion functional layer is provided with at least one second microstructure diffusion region, the first microstructure diffusion region and the second microstructure diffusion region are arranged facing each other, and the first diffusion functional layer and the second diffusion functional layer are bonded together by the intermediate adhesive layer. Wherein, the difference between the refractive index of the first microstructure diffusion region and the refractive index of the second microstructure diffusion region is ≤0.05, the refractive index of the intermediate adhesive layer is less than the refractive index of the first microstructure diffusion region and the refractive index of the intermediate adhesive layer is less than the refractive index of the second microstructure diffusion region. The first diffusion functional layer includes a first PET substrate and a plurality of first microstructure diffusion regions disposed on the lower surface of the first PET substrate; The second diffusion functional layer includes a second PET substrate and a plurality of second microstructure diffusion regions disposed on the upper surface of the second PET substrate; Wherein, both the first microstructure diffusion region and the second microstructure diffusion region are made of optical resin, and the difference between the refractive index of the first optical resin used to prepare the first microstructure diffusion region and the refractive index of the second optical resin used to prepare the second microstructure diffusion region is ≤0.01; the optical resin is acrylic resin. Both the first and second microstructure diffusion regions are groove-shaped, with the first microstructure diffusion regions randomly arranged on the lower surface of the first PET substrate and the second microstructure diffusion regions randomly arranged on the upper surface of the second PET substrate. The random arrangement refers to the random selection of the groove parameters within a set range. The groove parameters include depth, length, and width, with groove length of 50~200um, groove depth of 12~26um, and groove width of 1.5~4um.

2. The light-directing composite film according to claim 1, characterized in that: The thicknesses of the first PET substrate and the second PET substrate are both 50μm to 75μm.

3. The light-directing composite film according to claim 1, characterized in that: The difference between the refractive index of the intermediate adhesive layer and the refractive index of the first microstructure diffusion region is greater than or equal to 0.15; the difference between the refractive index of the intermediate adhesive layer and the refractive index of the second microstructure diffusion region is greater than or equal to 0.

15.

4. The light-directing composite film according to claim 3, characterized in that: The refractive index of the first microstructure diffusion region and the refractive index of the second microstructure diffusion region are both 1.60~1.65; the refractive index of the intermediate adhesive layer is 1.40~1.

45.

5. The light-directing composite film according to claim 4, characterized in that: The refractive index of the first microstructure diffusion region and the refractive index of the second microstructure diffusion region are both 1.62, and the refractive index of the intermediate adhesive layer is 1.

42.

6. A method for preparing a light-directing composite film as described in any one of claims 1-5, characterized in that: Includes the following steps: S1: Preparation of the first microstructure diffusion region: The first microstructure diffusion region is formed on the first diffusion functional layer by a molding method or an imprinting method; S2: Preparation of the second microstructure diffusion region: The second microstructure diffusion region is formed on the second diffusion functional layer by a molding method or an imprinting method; S3: Composite: Using a soft-press bonding machine, optical resin is applied as an adhesive to the surface of the first microstructure diffusion area or the second microstructure diffusion area. Then, the first diffusion functional layer and the second diffusion functional layer are aligned and bonded together, so that the first microstructure diffusion area and the second microstructure diffusion area are facing each other and bonded by resin. Finally, the mixture is cured to form an intermediate adhesive layer.

7. An application of the light-directing composite film as described in any one of claims 1-5, characterized in that: It is applied in solar cell modules, and the light-directing composite film is stacked between the glass cover and the cells of the solar cell module.

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