Photovoltaic backsheet and its preparation method and application

Abstract

The present invention belongs to the technical field of photovoltaic backsheets and provides a photovoltaic backsheet and its preparation method and application. The preparation method comprises: immersing a polyester film substrate in a prefabricated tris(hydroxymethyl)aminomethane-hydrochloric acid buffer solution having a dopamine concentration of 1-2.5 mg / mL and a pH of 8-9, allowing dopamine to self-oxidatively polymerize and deposit on the upper and lower surfaces of the polyester film substrate to form a first PDA bonding layer and a second PDA bonding layer, respectively; immersing the second PDA bonding layer in a prefabricated fluorocarbon resin aqueous solution (the fluorocarbon resin has a mass percentage content of 45-60%), and curing it to form a fluorocarbon resin coating on the lower surface of the second PDA bonding layer. The photovoltaic backsheet prepared by this preparation method has both good initial adhesion and long-term aging adhesion to the encapsulating film, excellent adhesion performance to the fluorocarbon resin coating, and excellent long-term UV resistance and corrosion resistance. The product quality is stable, and the preparation process is simple and the cost is low.

Description

Technical Field

[0001] The present invention relates to the technical field of photovoltaic backsheets, and in particular to a photovoltaic backsheet for offshore photovoltaic applications, a preparation method thereof, and applications thereof. Background Art

[0002] As a renewable energy source with enormous potential, offshore photovoltaic power generation faces unique challenges. One of these challenges is the potential for corrosion of photovoltaic modules in seawater. Corrosion is caused by the salt and humidity of seawater. Chloride ions in salt are particularly corrosive, attacking metal surfaces, especially in hot and humid outdoor environments, damaging the structure and performance of photovoltaic modules. Furthermore, moisture and salt spray in seawater can corrode non-metallic components such as the glass, backsheet, and frame of photovoltaic modules.

[0003] To enhance the corrosion and weather resistance of photovoltaic backsheets, existing technologies typically apply a fluorocarbon coating to the outer surface of the substrate used for photovoltaic backsheets. Biaxially oriented polyester film (BOPET), a photovoltaic backsheet substrate, offers excellent mechanical properties, heat resistance, UV resistance, and electrical insulation. However, polyester films like BOPET exhibit poor adhesion to fluorocarbon coatings (such as FEVE), which can easily cause the coating to fall off, compromising the corrosion and weather resistance of the photovoltaic backsheet.

[0004] Prior art, such as publication number CN114656856B, provides an aqueous fluorinated acrylate copolymer emulsion, its preparation method, and application to enhance the adhesion of a fluorocarbon coating to a PET substrate. The application method for this aqueous fluorinated acrylate copolymer emulsion comprises synthesizing a dopamine-modified aqueous fluorinated acrylate copolymer emulsion, then subjecting a PET film to plasma treatment, surface grafting of polyacrylic acid, and surface deposition of polydopamine. The dopamine-modified aqueous fluorinated acrylate copolymer emulsion is then roller-coated onto the surface of the PET film, dried, and rolled to produce a photovoltaic backsheet film. This improves the adhesion between the fluorocarbon coating and the PET film. However, the photovoltaic backplane film disclosed in publication number CN114656856B not only requires multiple steps to synthesize the dopamine-modified aqueous fluorinated acrylate copolymer emulsion, but also requires the PET film to undergo multiple process steps such as plasma treatment, surface grafting of polyacrylic acid, and surface deposition of polydopamine. The process steps are numerous, the cost is high, and the process conditions are complex, the quality is unstable, and it is not conducive to large-scale production and application.

[0005] Furthermore, the polarity and high crystallinity of polyester films also result in poor adhesion of polyester films such as BOPET to solar photovoltaic cell encapsulation films (such as EVA and POE). This is particularly true after aging in outdoor environments, such as high temperatures and humidity. The adhesion of polyester films such as BOPET to these films can decrease dramatically. Consequently, long-term outdoor use in photovoltaic modules can easily lead to delamination and other issues. Existing photovoltaic backsheet films, such as those disclosed in Publication No. CN114656856B, only improve the adhesion of the enhanced fluorocarbon coating to the PET substrate and do not further enhance the initial or long-term adhesion between the polyester film and encapsulation films such as EVA or POE. Consequently, this type of photovoltaic backsheet film is unlikely to further enhance the quality and service life of photovoltaic modules used in offshore photovoltaic applications. Summary of the Invention

[0006] The purpose of the present invention is to provide a photovoltaic backplane and a preparation method and application thereof in view of the deficiencies in the prior art.

[0007] Based on this, the present invention discloses a method for preparing a photovoltaic backsheet, comprising the following preparation steps:

[0008] S1. Preparing a tris-hydrochloric acid buffer solution containing dopamine; wherein the pH value of the tris-hydrochloric acid buffer solution containing dopamine is 8-9, and the concentration of dopamine is 1-2.5 mg / mL;

[0009] S2. Immersing the polyester film substrate in a tris(hydroxymethylaminomethane)-hydrochloric acid buffer solution containing dopamine, so that dopamine is deposited on the upper and lower surfaces of the polyester film substrate via auto-oxidative polymerization in the alkaline tris(hydroxymethylaminomethane)-hydrochloric acid buffer solution. The surface of the polyester film substrate is rinsed with water and dried to form a first polydopamine adhesive layer and a second polydopamine adhesive layer on the upper and lower surfaces of the polyester film substrate, respectively.

[0010] S3, preparing a fluorocarbon resin aqueous solution; wherein the mass percentage of fluorocarbon resin in the fluorocarbon resin aqueous solution is 45-60%;

[0011] S4. Immersing the second polydopamine adhesive layer in a fluorocarbon resin aqueous solution and curing the solution to form a fluorocarbon resin coating on the lower surface of the second polydopamine adhesive layer.

[0012] The mechanism of dopamine undergoing auto-oxidative polymerization and deposition on the upper and lower surfaces of the polyester film substrate in an alkaline tris(hydroxymethyl)aminomethane-hydrochloric acid buffer solution is as follows:

[0013]

[0014] The photovoltaic backsheet produced in the present invention, characterized by its polydopamine adhesive layer (PDA adhesive layer, such as the first and second PDA adhesive layers), exhibits strong adhesion properties and a large number of polar functional groups, such as hydroxyl and amino groups. This significantly improves the initial adhesion and long-term aging adhesion (PCT 24h adhesion) between the photovoltaic backsheet (specifically the first PDA adhesive layer) and an encapsulating film such as EVA. It also significantly enhances the adhesion between the second PDA adhesive layer and the fluorocarbon resin coating. Consequently, the photovoltaic backsheet of the present invention effectively withstands the effects of complex environments during long-term aging, such as the high humidity and high corrosion conditions encountered in offshore photovoltaic applications. Furthermore, the preparation method of the present invention eliminates the following steps in the conventional photovoltaic backsheet film preparation process, such as that described in CN114656856B: the dopamine modification step of the aqueous fluorinated acrylate copolymer emulsion, and the treatment steps of the polyester film substrate, such as plasma treatment, surface grafting of polyacrylic acid, and surface deposition of polydopamine. The preparation method of the present invention also reduces the energy consumption and organic solvent usage during the corona and coating processes in conventional coating-based backsheet manufacturing processes. Therefore, the preparation method of the present invention can greatly simplify the preparation process of the photovoltaic backsheet, reduce costs, and ensure stable product quality, which is conducive to large-scale production and application.

[0015] Preferably, in step S1, tris(hydroxymethylaminomethane) is dissolved in a mixed solvent of methanol and water, 36-38% concentrated hydrochloric acid is added dropwise to adjust the pH value of the solution, and then dopamine is added, stirred to dissolve, and the volume is constant to prepare the tris(hydroxymethylaminomethane)-hydrochloric acid buffer solution containing dopamine;

[0016] The pH value of the dopamine-containing tris-hydrochloric acid buffer solution is 8.2-8.5, and the dopamine concentration thereof is 1.5-2 mg / mL.

[0017] Further preferably, in step S1, the pH value of the dopamine-containing Tris-hydrochloric acid buffer solution is 8.5, and the dopamine concentration thereof is 2 mg / mL.

[0018] As the immersion time increases, the deposition thickness of the PDA adhesive layer (such as the first PDA adhesive layer or the second PDA adhesive layer) on the surface of the polyester film substrate gradually increases, and finally the thickness of the PDA adhesive layer tends to be moderate. Therefore, in order to make the first PDA adhesive layer (or the second PDA adhesive layer) reach the expected thickness. Preferably, in step S2, the polyester film substrate is immersed in the tris-hydrochloric acid buffer solution containing dopamine for more than 24 hours. The thickness of the first polydopamine adhesive layer (i.e., the first PDA adhesive layer) and the second polydopamine adhesive layer (the second PDA adhesive layer) are both 40-70nm.

[0019] Further preferably, the thickness of the first polydopamine adhesive layer and the second polydopamine adhesive layer are both 65-68 nm (more preferably 65-66 nm).

[0020] Preferably, in step S2, the drying temperature is 30-70°C (such as 50°C), and the drying time is 2-5h (4h).

[0021] As the middle layer of the photovoltaic backsheet, the polyester film substrate provides support. This substrate must be resistant to high and low temperatures, possess stable mechanical properties, possess excellent electrical insulation, exhibit good creep resistance, fatigue resistance, friction resistance, and dimensional stability, and have low gas and vapor permeability. Therefore, the polyester film substrate is preferably at least one of BOPET and BOPEN films.

[0022] Further preferably, in step S2, the polyester film substrate is a BOPET film with a thickness of 260-300 μm (eg, 285 μm).

[0023] Preferably, in step S3, the fluorocarbon resin aqueous solution is prepared by mixing 38-53.5% water, 45-60% fluorocarbon resin, and the remainder of the additive, by mass percentage, and stirring uniformly; the fluorocarbon resin aqueous solution has a viscosity of 2500-4500 mPa·s at 23° C., and a fluorine content of 20-30%;

[0024] The fluorocarbon resin is one or more of polytetrafluoroethylene, polyperfluoroethylene propylene, tetrafluoroethylene-perfluoroalkoxy vinyl ether copolymer, ethylene-tetrafluoroethylene copolymer, polychlorotrifluoroethylene, ethylene-chlorotrifluoroethylene copolymer and derivatives thereof;

[0025] The auxiliary agent is one or more of a wetting agent, a dispersant, a defoaming agent, a thickener, and a multifunctional amine auxiliary agent.

[0026] Further preferably, in step S3, the fluorocarbon resin is ethylene-chlorotrifluoroethylene copolymer or tetrafluoroethylene-perfluoroalkoxyvinyl ether copolymer. Given the demanding operating environments and long-term stability requirements of photovoltaic backsheets, ether-based fluororesins such as FEVE are the preferred fluorocarbon resins due to their excellent outdoor weathering resistance, corrosion resistance, acid and alkali resistance, salt spray resistance, high temperature and humidity resistance, and excellent mechanical properties. The fluorocarbon resin has a water content of 50-55% by weight (more preferably 55%) and a water content of 43-48.5% by weight (e.g., 43.25%).

[0027] Preferably, in step S4, the curing temperature is 120-180° C. (such as 150° C.), the curing time is 2-8 min (such as 3 min); and the thickness of the fluorocarbon resin coating is 20-30 μm (such as 28 μm).

[0028] The present invention also discloses a photovoltaic backsheet, which is prepared by the method for preparing a photovoltaic backsheet described above in the present invention.

[0029] The present invention also discloses an application of a photovoltaic backboard, which is applied to a photovoltaic module; the first polydopamine adhesive layer is bonded to the back of a cell of the photovoltaic module via an encapsulating adhesive film.

[0030] Compared with the prior art, the present invention has at least the following beneficial effects:

[0031] The preparation method of the photovoltaic backsheet of the present invention comprises the following steps: firstly, a tris(hydroxymethylaminomethane)-hydrochloric acid buffer solution having a dopamine concentration of 1-2.5 mg / mL and a pH value of 8-9 is deposited on the upper and lower surfaces of a polyester film substrate to prepare a first PDA bonding layer and a second PDA bonding layer; and then, a fluorocarbon resin aqueous solution having a fluorocarbon resin content of 45-60% is used to prepare a fluorocarbon resin coating on the surface of the second PDA bonding layer. In this way, the photovoltaic backsheet produced by the present invention will not have the phenomenon of incomplete coverage and uneven thickness of the PDA adhesive layer or the fluorocarbon resin coating. The photovoltaic backsheet (specifically the first PDA adhesive layer) can show good initial adhesion and long-term aging adhesion (PCT24h adhesion) to the packaging film such as EVA, and the PDA adhesive layer (such as the second PDA adhesive layer) can also have excellent adhesion performance to the fluorocarbon resin coating. Furthermore, the photovoltaic backsheet of the present invention also has excellent long-term UV resistance, corrosion resistance and weather resistance. Therefore, the photovoltaic backsheet of the present invention is particularly suitable for use in offshore photovoltaic modules. The photovoltaic backsheet can effectively resist the influence of complex environments during the long-term aging process, such as the damage caused by the high humidity and high corrosion environment faced by offshore photovoltaics, which helps to further improve the quality and service life of photovoltaic modules.

[0032] Furthermore, the preparation method of the present invention can also omit the following steps in the existing photovoltaic backsheet film preparation process, such as the dopamine modification step of the aqueous fluorinated acrylate copolymer emulsion, and the treatment steps of the polyester film substrate, such as plasma treatment, surface grafting of polyacrylic acid, and surface polydopamine deposition. The preparation method of the present invention can also reduce the energy consumption and organic solvent usage during the corona and coating processes in traditional coating-type backsheet processing. Therefore, the preparation method of the present invention can greatly simplify the photovoltaic backsheet preparation process, reduce costs, and provide stable product quality, facilitating large-scale production and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a schematic diagram of the cross-sectional structure of a photovoltaic backsheet of the present invention.

[0034] Description of the accompanying drawings: BOPET substrate 1; PDA adhesive layer 2; fluorocarbon resin coating 3. DETAILED DESCRIPTION

[0035] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below in conjunction with specific embodiments.

[0036] Example 1

[0037] A method for preparing a photovoltaic backsheet according to this embodiment includes the following steps:

[0038] Step 1: First, 121.1 g of tris(hydroxymethyl)aminomethane is dissolved in a mixed solvent of methanol and water to prepare a mixed solution; 37% concentrated hydrochloric acid is then added dropwise to the mixed solution until the pH of the mixed solution reaches 8.0; then 2 mg of dopamine is added, stirred and dissolved, and the volume is adjusted to prepare a tris(hydroxymethyl)aminomethane-hydrochloric acid buffer solution with a dopamine concentration of 2 mg / mL and a pH of 8.0.

[0039] Step 2. Subsequently, a BOPET (biaxially oriented polyester film) substrate having a thickness of 285 μm was immersed in a tris(hydroxymethyl)aminomethane-hydrochloric acid buffer solution having a dopamine concentration of 2 mg / mL and a pH of 8.0 obtained in step 1 for 24 hours, so that dopamine was deposited on the upper and lower surfaces of the BOPET substrate through auto-oxidative polymerization in the alkaline tris(hydroxymethyl)aminomethane-hydrochloric acid buffer solution. The buffer solution and unreacted dopamine on the surface of the BOPET substrate were removed by rinsing with water. The BOPET substrate was then placed in an oven and dried at 50° C. for 4 hours to form an adhesive layer on both the upper and lower surfaces of the BOPET substrate, thereby obtaining a photovoltaic backsheet of this embodiment.

[0040] A photovoltaic backsheet of this embodiment, see Figure 1 , comprising: a BOPET substrate 1, with an adhesive layer deposited on both the upper and lower surfaces of the BOPET substrate 1; the adhesive layer is made of polydopamine (PDA), that is, the adhesive layer is a PDA adhesive layer 2. Therefore, the photovoltaic backsheet of this embodiment is a backsheet film material with a three-layer structure of PDA-BOPET-PDA (referred to as PDA-BOPET-PDA backsheet).

[0041] An application of a photovoltaic backsheet in this embodiment is applied to a photovoltaic module. In this case, the PDA adhesive layer 2 on the upper surface of the BOPET substrate 1 is bonded to the back of the cell of the photovoltaic module through the EVA packaging film.

[0042] Example 2

[0043] The photovoltaic backsheet, preparation method, and application of this embodiment are all referenced to Example 1. The difference between this embodiment and Example 1 is that:

[0044] In step 1 of this embodiment, the pH of the mixed solution was adjusted to 8.2, and the pH of the tris-hydrochloric acid buffer solution containing dopamine was also adjusted to 8.2. The remaining steps were similar to those of Example 1. Thus, a photovoltaic backsheet (which is a PDA-BOPET-PDA backsheet) of this embodiment was obtained.

[0045] Example 3

[0046] The photovoltaic backsheet, preparation method, and application of this embodiment are all referenced to Example 1. The difference between this embodiment and Example 1 is that:

[0047] In step 1 of this embodiment, the pH of the mixed solution was adjusted to 8.5, and the pH of the tris-hydrochloric acid buffer solution containing dopamine was also adjusted to 8.5. The remaining steps were similar to those of Example 1. Thus, a photovoltaic backsheet (PDA-BOPET-PDA backsheet) of this embodiment was obtained.

[0048] Example 4

[0049] The photovoltaic backsheet, preparation method, and application of this embodiment are all referenced to Example 1. The difference between this embodiment and Example 1 is that:

[0050] In step 1 of this embodiment, the pH of the mixed solution was adjusted to 9.0, and the pH of the tris(hydroxymethylaminomethane)-hydrochloric acid buffer solution containing dopamine was also adjusted to 9.0. The remaining steps were similar to those of Example 1. Thus, a photovoltaic backsheet (PDA-BOPET-PDA backsheet) of this embodiment was obtained.

[0051] Example 5

[0052] The photovoltaic backsheet, preparation method, and application of this embodiment are all based on Example 3. The difference between this embodiment and Example 3 is that:

[0053] In step 1 of this embodiment, after the pH of the mixed solution was adjusted to 8.5, 1 mg of dopamine was added, stirred and dissolved, and the volume was fixed to prepare a tris-hydrochloric acid buffer solution with a dopamine concentration of 1 mg / mL and a pH of 8.5.

[0054] In step 2 of this example, a 285 μm-thick BOPET substrate was immersed in a tris-hydrochloric acid buffer solution having a dopamine concentration of 1 mg / mL and a pH of 8.5, as in step 1. The remaining steps were similar to those in Example 3. This yielded a photovoltaic backsheet (PDA-BOPET-PDA backsheet) of this example.

[0055] Example 6

[0056] The photovoltaic backsheet, preparation method, and application of this embodiment are all based on Example 3. The difference between this embodiment and Example 3 is that:

[0057] In step 1 of this embodiment, after the pH of the mixed solution was adjusted to 8.5, 1.5 mg of dopamine was added, stirred and dissolved, and the volume was fixed to prepare a tris-hydrochloric acid buffer solution with a dopamine concentration of 1.5 mg / mL and a pH of 8.5.

[0058] In step 2 of this embodiment, a 285 μm-thick BOPET substrate was immersed in a tris-hydrochloric acid buffer solution having a dopamine concentration of 1.5 mg / mL and a pH of 8.5, as in step 1. The remaining steps were similar to those in Example 3. This yielded a photovoltaic backsheet (PDA-BOPET-PDA backsheet) of this embodiment.

[0059] Example 7

[0060] The photovoltaic backsheet, preparation method, and application of this embodiment are all based on Example 3. The difference between this embodiment and Example 3 is that:

[0061] In step 1 of this embodiment, after the pH of the mixed solution was adjusted to 8.5, 2.5 mg of dopamine was added, stirred and dissolved, and the volume was fixed to prepare a tris-hydrochloric acid buffer solution with a dopamine concentration of 2.5 mg / mL and a pH of 8.5.

[0062] In step 2 of this embodiment, a 285 μm-thick BOPET substrate was immersed in a tris-hydrochloric acid buffer solution having a dopamine concentration of 2.5 mg / mL and a pH of 8.5, as in step 1. The remaining steps were similar to those in Example 3. This yielded a photovoltaic backsheet (PDA-BOPET-PDA backsheet) of this embodiment.

[0063] Example 8

[0064] The method for preparing a photovoltaic backsheet of this embodiment, based on steps 1-2 of embodiment 3, further includes the following preparation steps:

[0065] Step 3. Prepare a fluorocarbon resin aqueous solution: add 53.25% deionized water, 0.25% wetting agent (BYK, BYK-3455), 0.4% dispersant (BYK, DISPERBYK-2155), 45% fluorocarbon resin FEVE (fluoroolefin-vinyl ether copolymer), 0.5% defoamer (Evonik, TEGO Foamex 810), 0.4% thickener (Dow, ASE-60), and 0.2% multifunctional amine additive (ANGUS, AMP-95 (2-amino-2-methyl-1-propanol)) in sequence, by mass percentage, adjust the pH to 8.5, stir evenly, and prepare a fluorocarbon resin aqueous solution.

[0066] Step 4: Immerse the PDA-BOPET-PDA backsheet of Example 3 on one side in the fluorocarbon resin aqueous solution of Step 3 for 3 minutes, and then place it in an oven at 150°C for curing for 3 minutes to prepare a fluorocarbon resin coating on the outer surface of one of the adhesive layers to obtain a photovoltaic backsheet of this embodiment.

[0067] A photovoltaic backsheet of this embodiment, see Figure 1 The photovoltaic backsheet of this embodiment comprises a BOPET substrate 1, with an adhesive layer deposited on both the upper and lower surfaces of the BOPET substrate 1. One of the adhesive layers (preferably the adhesive layer located on the lower surface of the BOPET substrate 1) also has a fluorocarbon resin coating 3 deposited on its outer surface. This adhesive layer is a PDA adhesive layer 2. Therefore, the photovoltaic backsheet of this embodiment is a four-layer backsheet film structure of PDA-BOPET-PDA-fluorocarbon resin coating (referred to as PDA-BOPET-PDA-fluorocarbon resin coated backsheet).

[0068] An application of a photovoltaic backsheet in this embodiment is applied to a photovoltaic module. In this case, the PDA adhesive layer 2 on the upper surface of the BOPET substrate 1 is bonded to the back of the cell of the photovoltaic module through the EVA packaging film.

[0069] Example 9

[0070] The photovoltaic backsheet, preparation method, and application of this embodiment are all referenced to Example 8. The difference between this embodiment and Example 8 is that:

[0071] In step 3 of this example, the fluorocarbon resin aqueous solution prepared contained 48.25% deionized water (by mass percentage, the same below) and 50% FEVE. The remaining conditions were similar to those of Example 8. This yielded a photovoltaic backsheet (a PDA-BOPET-PDA-fluorocarbon resin-coated backsheet) of this example.

[0072] Example 10

[0073] The photovoltaic backsheet, preparation method, and application of this embodiment are all referenced to Example 8. The difference between this embodiment and Example 8 is that:

[0074] In step 3 of this example, the fluorocarbon resin aqueous solution prepared contained 43.25% deionized water (by mass percentage, the same below) and 55% fluorocarbon resin (FEVE) content, with all other conditions being the same as in Example 8. This yielded a photovoltaic backsheet (PDA-BOPET-PDA-fluorocarbon resin coated backsheet) of this example.

[0075] Example 11

[0076] The photovoltaic backsheet, preparation method, and application of this embodiment are all referenced to Example 8. The difference between this embodiment and Example 8 is that:

[0077] In step 3 of this example, the fluorocarbon resin aqueous solution prepared contained 38.25% deionized water (by mass percentage, the same below) and 60% FEVE. The remaining conditions were similar to those of Example 8. This yielded a photovoltaic backsheet (PDA-BOPET-PDA-fluorocarbon resin-coated backsheet) of this example.

[0078] Comparative Example 1

[0079] A method for preparing a photovoltaic backsheet in this comparative example includes the following preparation steps:

[0080] Step 1: corona treatment is performed on a BOPET substrate with a thickness of 285 μm.

[0081] Step 2: Apply a layer of adhesive to the upper surface of the corona-treated BOPET substrate (i.e., the surface bonded to the packaging film) through a coating line.

[0082] After drying in step 3, a photovoltaic backsheet of this comparative example was obtained. The photovoltaic backsheet of this comparative example comprises a BOPET substrate and an adhesive layer applied to the upper surface of the BOPET substrate. The adhesive layer is made of a polyurethane adhesive (Dow Chemical, VORAMER™ PU 3200) and has a thickness of 60 μm.

[0083] Comparative Example 2

[0084] A method for preparing a photovoltaic backsheet in this comparative example includes the following preparation steps:

[0085] Step 1: corona treatment is performed on a BOPET substrate with a thickness of 285 μm.

[0086] Step 2: A layer of adhesive is applied to both the upper and lower surfaces of the corona-treated BOPET substrate via a coating line, and then a layer of 20 μm thick fluorocarbon resin coating is applied to the outer surface of one of the adhesive layers (the material of the fluorocarbon resin coating in this comparative example refers to the fluorocarbon resin coating in Example 8).

[0087] Step 3: Dry and cure at 150°C for 3 minutes to obtain a photovoltaic backsheet according to this comparative example (i.e., a conventional photovoltaic backsheet comprising an adhesive layer and a fluorocarbon resin coating). The photovoltaic backsheet according to this comparative example comprises a BOPET substrate, with an adhesive layer coated on both the upper and lower surfaces of the BOPET substrate. The outer surface of one of the adhesive layers (preferably the adhesive layer located on the lower surface of the BOPET substrate) is further coated with a fluorocarbon resin coating. The adhesive layer is made of a polyurethane adhesive (Sika, Sikaflex®-552), and the thickness of each adhesive layer is 60 μm.

[0088] Performance Testing

[0089] Samples were prepared and performance tested according to the standards GB / T31034-2014 (Insulating Backsheets for Crystalline Silicon Solar Cell Modules) and CQC3308-2013 (Technical Specifications for Backsheets for Photovoltaic Module Encapsulation). The following tests were conducted according to the standard GB / T2790: initial adhesion between the PDA adhesive layer of Examples 1-11 (or the adhesive layer of Comparative Examples 1-2) and the EVA encapsulation film, and adhesion after 24 hours of PCT (121°C, 100% humidity, 0.2 MPa) rapid aging. UV resistance testing at 300 kw / h was conducted according to the standard IEC61215-2. Cross-hatch adhesion testing was conducted between the PDA adhesive layer of Examples 1-11 (or the adhesive layer of Comparative Examples 1-2) and the fluorocarbon resin coating according to the standard GB / T9286-2021. The test results are shown in Tables 1-2:

[0090] Table 1

[0091]

[0092] Combined with the data in Table 1, we can see that:

[0093] (1) Compared with the adhesive layer for the existing photovoltaic backsheet in comparative example 1, the initial bonding strength between the PDA bonding layer and the EVA encapsulation film in Examples 1-7 is better, especially the PCT 24h bonding strength between the PDA bonding layer and the EVA encapsulation film in Examples 1-7 is more advantageous.

[0094] (2) As the pH value of the tris(hydroxymethylaminomethane)-hydrochloric acid buffer solution with a dopamine concentration of 2 mg / mL gradually increases (e.g., from pH 8.0 in Example 1 to pH 9.0 in Example 4), the thickness of the PDA adhesive layer deposited on the surface of the BOPET substrate also gradually increases.

[0095] When the pH value of the tris-hydrochloric acid buffer solution with a dopamine concentration of 2 mg / mL increases to 9.0 (as in Example 4), the growth of the thickness of the PDA bonding layer tends to be flat. At this time, PDA begins to have a tendency to locally aggregate on the surface of the BOPET substrate, making the surface of the PDA bonding layer uneven, resulting in uneven thickness of the PDA bonding layer. Therefore, if the pH value of the tris(hydroxymethylaminomethane)-hydrochloric acid buffer solution with a dopamine concentration of 2 mg / mL continues to increase (i.e., the pH value of the tris(hydroxymethylaminomethane)-hydrochloric acid buffer solution with a dopamine concentration of 2 mg / mL is too high), the uneven thickness of the PDA adhesive layer will easily increase, which will greatly affect the quality of the photovoltaic backsheet. Furthermore, when such a photovoltaic backsheet is used in a photovoltaic module, the PDA adhesive layer will not only fail to significantly increase the initial bonding strength and PCT24h bonding strength between the PDA adhesive layer and the EVA encapsulation film, but such an extremely uneven PDA adhesive layer will increase the risk of cell fragmentation during lamination, and will easily lead to local delamination between the layers of the photovoltaic module, affecting the application effect of the photovoltaic backsheet in the photovoltaic module.

[0096] However, when the pH value of the 2 mg / mL dopamine-Tris-HCl buffer solution is low (as in Example 1), the PDA adhesive layer struggles to form a continuous film, which can lead to incomplete coverage of the PDA adhesive layer on the surface of the BOPET substrate. This can cause a decrease in the initial adhesion and PCT 24-hour adhesion between the PDA adhesive layer and the EVA encapsulation film. Therefore, if the pH value of the 2 mg / mL dopamine-Tris-HCl buffer solution continues to decrease (i.e., the pH value of the 2 mg / mL dopamine-Tris-HCl buffer solution is too low), the PDA adhesive layer can exhibit extremely incomplete coverage of the BOPET substrate surface, significantly impacting the quality of the photovoltaic backsheet. Furthermore, when such a photovoltaic backsheet is used in a photovoltaic module, this extremely incomplete PDA adhesive layer significantly increases the risk of poor interlayer adhesion, impacting the performance of the photovoltaic backsheet in the module.

[0097] (3) As shown in Examples 3 and 5-7, when the concentration of dopamine in the tris-hydrochloric acid buffer solution gradually increases, the thickness of the PDA adhesive layer deposited on the surface of the BOPET substrate also gradually increases. However, if the concentration of dopamine in the tris-hydrochloric acid buffer solution is too low or too high (e.g., less than 1 mg / mL or greater than 2.5 mg / mL), the PDA adhesive layer deposited on the surface of the BOPET substrate may have extremely incomplete coverage or extremely uneven thickness, thereby affecting the quality of the photovoltaic backsheet and, in turn, the application effect of the photovoltaic backsheet in photovoltaic modules.

[0098] Therefore, when the pH value of the tris(hydroxymethylaminomethane)-hydrochloric acid buffer solution containing dopamine is 8.5 and the concentration of dopamine is 2 mg / mL (as shown in Example 3), the PDA adhesive layer deposited on the surface of the BOPET substrate does not have incomplete coverage and uneven thickness, and the initial bonding strength and PCT24h bonding strength between the PDA adhesive layer and the EVA encapsulation film are both large. Therefore, the quality of the photovoltaic backsheet of Example 3 is the best, and its application in photovoltaic modules will help further improve the quality and service life of photovoltaic modules.

[0099] Table 2

[0100]

[0101] Combined with the data in Table 2, we can see that:

[0102] (4) Compared with the existing photovoltaic backsheet containing an adhesive layer and a fluorocarbon resin coating as in Comparative Example 2, the photovoltaic backsheet containing a PDA adhesive layer and a fluorocarbon resin coating of Examples 8-11 has better UV300kw / h UV resistance and adhesion.

[0103] (5) Increasing the fluorocarbon resin FEVE content in the fluorocarbon resin aqueous solution (as shown in Examples 8-11) will increase the thickness of the fluorocarbon resin coating obtained after curing. However, if the fluorocarbon resin FEVE content in the fluorocarbon resin aqueous solution is too low or too high (e.g., less than 45% or greater than 60%), the fluorocarbon resin coating obtained on the surface of the PDA adhesive layer may have extremely incomplete coverage or extremely uneven thickness, thereby affecting the quality of the photovoltaic backsheet and, in turn, the application effect of the photovoltaic backsheet in the photovoltaic module.

[0104] In summary, the photovoltaic backsheet preparation method of the present invention utilizes a tris(hydroxymethylaminomethane)-hydrochloric acid buffer solution with a dopamine concentration of 2 mg / mL and a pH of 8.5 to deposit a PDA adhesive layer on the surface of a BOPET substrate. Furthermore, a fluorocarbon resin coating is formed on the surface of the PDA adhesive layer using an aqueous fluorocarbon resin solution with a fluorocarbon resin FEVE content of 50-55% (preferably 55%) (as shown in Examples 9-10). As such, the photovoltaic backsheets prepared in Examples 9-10 avoid incomplete coverage and uneven thickness of the PDA adhesive layer or fluorocarbon resin coating, exhibit good initial adhesion and long-term aging adhesion (PCT 24h adhesion) to encapsulating films such as EVA, and the PDA adhesive layer also exhibits excellent adhesion to the fluorocarbon resin coating. Furthermore, the photovoltaic backsheets of the present invention also exhibit excellent long-term UV resistance, corrosion resistance, and weather resistance. Therefore, the photovoltaic backsheets of Examples 9-10 of the present invention are particularly suitable for use in photovoltaic modules, helping to further improve the quality and service life of photovoltaic modules.

[0105] Although the preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they become aware of the basic creative concepts. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the embodiments of the present invention.

[0106] The technical solution provided by the present invention is introduced in detail above. Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there may be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A method for preparing a photovoltaic backsheet, characterized in that: The method comprises the following preparation steps: S1. Preparing a tris-hydrochloric acid buffer solution containing dopamine; wherein the pH value of the tris-hydrochloric acid buffer solution containing dopamine is 8-9, and the concentration of dopamine is 1-2.5 mg / mL; S2. Immersing the polyester film substrate in a tris(hydroxymethylaminomethane)-hydrochloric acid buffer solution containing dopamine, so that dopamine is deposited on the upper and lower surfaces of the polyester film substrate via auto-oxidative polymerization in the alkaline tris(hydroxymethylaminomethane)-hydrochloric acid buffer solution. The surface of the polyester film substrate is rinsed with water and dried to form a first polydopamine adhesive layer and a second polydopamine adhesive layer on the upper and lower surfaces of the polyester film substrate, respectively. S3, preparing a fluorocarbon resin aqueous solution; wherein the mass percentage of fluorocarbon resin in the fluorocarbon resin aqueous solution is 45-60%; S4, immersing the second polydopamine adhesive layer in a fluorocarbon resin aqueous solution and curing the solution to form a fluorocarbon resin coating on the lower surface of the second polydopamine adhesive layer; In step S3, the fluorocarbon resin aqueous solution is prepared by mixing 38-53.5% water, 45-60% fluorocarbon resin and the remainder of the additive, and stirring them uniformly; the fluorocarbon resin is fluorocarbon resin FEVE; In step S4, the curing temperature is 120-180°C and the curing time is 2-8 minutes; The polyester film substrate is at least one of a BOPET film and a BOPEN film.

2. The method for preparing a photovoltaic backsheet according to claim 1, wherein: In step S1, tris(hydroxymethylaminomethane) is dissolved in a mixed solvent of methanol and water, 36-38% concentrated hydrochloric acid is added dropwise to adjust the pH value of the solution, dopamine is added, stirred to dissolve, and the volume is constant to prepare the tris(hydroxymethylaminomethane)-hydrochloric acid buffer solution containing dopamine; In step S1, the pH value of the tris-hydrochloric acid buffer solution containing dopamine is 8.2-8.5, and the concentration of dopamine is 1.5-2 mg / mL.

3. The method for preparing a photovoltaic backsheet according to claim 2, wherein: In step S1, the pH value of the dopamine-containing tris-hydrochloric acid buffer solution is 8.5, and the dopamine concentration is 2 mg / mL.

4. The method for preparing a photovoltaic backsheet according to claim 1, wherein: In step S2, the polyester film substrate is immersed in the tris-hydrochloric acid buffer solution containing dopamine for more than 24 hours; the drying temperature is 30-70° C., and the drying time is 1-5 hours; The thickness of the first polydopamine bonding layer and the second polydopamine bonding layer are both 40-70 nm.

5. The method for preparing a photovoltaic backsheet according to claim 4, characterized in that: In step S2, the polyester film substrate is a BOPET film with a thickness of 260-300 μm; the thickness of the first polydopamine adhesive layer and the second polydopamine adhesive layer are both 65-68 nm.

6. The method for preparing a photovoltaic backsheet according to claim 1, wherein: In step S3, the fluorine content of the fluorocarbon resin aqueous solution is 20-30%; The auxiliary agent is one or more of a wetting agent, a dispersant, a defoaming agent, a thickener, and a multifunctional amine auxiliary agent.

7. The method for preparing a photovoltaic backsheet according to claim 6, characterized in that: In step S3, the mass percentage content of the fluorocarbon resin is 50-55%, and the mass percentage content of water is 43-48.5%.

8. The method for preparing a photovoltaic backsheet according to claim 1, wherein: In step S4, the thickness of the fluorocarbon resin coating is 20-30 μm.

9. A photovoltaic backsheet, characterized in that: It is prepared by the method for preparing a photovoltaic backsheet according to any one of claims 1 to 8.

10. The application of a photovoltaic backsheet according to claim 9, characterized in that: The photovoltaic backboard is applied to a photovoltaic module; the first polydopamine adhesive layer is bonded to the back of the battery of the photovoltaic module through a packaging film.

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