Photovoltaic backboard and preparation method and application thereof

Abstract

The invention belongs to the technical field of photovoltaic backboards, and provides a photovoltaic backboard and a preparation method and application thereof. The preparation method comprises the following steps: dipping the polyester film substrate in a prefabricated trihydroxymethyl aminomethane-hydrochloric acid buffer solution with dopamine concentration of 1-2.5 mg / mL and pH of 8-9, so that dopamine is auto-oxidized, polymerized and deposited on the upper surface and the lower surface of the polyester film substrate to respectively form the first PDA bonding layer and the second PDA bonding layer; and dipping the second PDA bonding layer in a prefabricated fluorocarbon resin aqueous solution (the mass percentage content of fluorocarbon resin is 45-60%), and curing to form a fluorocarbon resin coating on the lower surface of the second PDA bonding layer. The photovoltaic backboard prepared by the preparation method has relatively good initial cohesiveness and long-term aging cohesiveness to a packaging adhesive film, excellent adhesion to a fluorocarbon resin coating, excellent long-term ultraviolet resistance, corrosion resistance and the like, the product quality is stable, the preparation process is simple, and the cost is low.

Description

Technical Field

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

[0002] As a renewable energy source with great potential, offshore photovoltaic power generation faces unique challenges. One of them is the corrosion problem that photovoltaic modules may experience in seawater environments. Corrosion is caused by the salt in seawater and the humid climate. The chloride ions in the salt are particularly corrosive. They can corrode metal surfaces, especially in hot and humid outdoor environments, which can damage the structure and performance of photovoltaic modules. In addition, moisture and salt spray in seawater may also cause corrosion to non-metallic parts such as glass, back panels and frames used in photovoltaic modules.

[0003] In order to improve the corrosion resistance and weather resistance of photovoltaic backsheets, the existing technology usually sets a fluorocarbon coating on the outer surface of the photovoltaic backsheet substrate. As the photovoltaic backsheet substrate, biaxially oriented polyester film (BOPET) has excellent mechanical properties, heat resistance, UV resistance, and good electrical insulation properties. However, the adhesion performance of polyester films such as BOPET and fluorocarbon coatings (such as fluorocarbon resin coatings of FEVE) is not good, which easily causes the fluorocarbon coating to fall off and affects the corrosion resistance and weather resistance of the photovoltaic backsheet.

[0004] In the prior art, as shown in publication number CN114656856B, in order to enhance the adhesion performance of the fluorocarbon coating to the PET substrate, it provides an aqueous fluorinated acrylate copolymer emulsion and its preparation method and application. The application method of the aqueous fluorinated acrylate copolymer emulsion is: first synthesize the dopamine-modified aqueous fluorinated acrylate copolymer emulsion, then sequentially perform plasma treatment, surface grafting of polyacrylic acid and surface polydopamine deposition on the PET film, then roll-coat the dopamine-modified aqueous fluorinated acrylate copolymer emulsion on the surface of the PET film, dry it, and roll it up to obtain a photovoltaic backplane film; in this way, the adhesion between the fluorocarbon coating and the PET film is improved. However, the photovoltaic backplane film disclosed in publication number CN114656856B not only needs to go through multiple steps to synthesize the dopamine-modified aqueous fluorinated acrylate copolymer emulsion, but also needs to perform multiple process steps on the PET film, 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, which is not conducive to large-scale production and application.

[0005] In addition, the polarity and high crystallinity of polyester film will also make the adhesion of polyester film such as BOPET to the encapsulation film of solar photovoltaic cells (such as EVA encapsulation film, POE encapsulation film) generally poor, especially after aging in high temperature, humidity and other outdoor environments, the adhesion performance of polyester film such as BOPET to the encapsulation film will drop sharply; therefore, after being applied to photovoltaic modules, long-term use in outdoor environments is prone to problems such as interlayer delamination. However, the existing photovoltaic backplane film such as the publication number CN114656856B can only improve the adhesion performance of the enhanced fluorocarbon coating to the PET substrate, and does not further improve the initial adhesion and long-term aging adhesion between the polyester film and the encapsulation film such as EVA or POE; therefore, this photovoltaic backplane film is difficult to further improve the quality and service life of photovoltaic modules for 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: 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(hydroxymethyl)aminomethane-hydrochloric acid buffer solution containing dopamine, so that dopamine is deposited on the upper and lower surfaces of the polyester film substrate by self-oxidative polymerization in the alkaline tris(hydroxymethyl)aminomethane-hydrochloric acid buffer solution, washing the surface of the polyester film substrate with water, and drying, so as to form a first polydopamine bonding layer and a second polydopamine bonding layer on the upper and lower surfaces of the polyester film substrate, respectively; S3, preparing a fluorocarbon resin aqueous solution; wherein the mass percentage content of the 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.

[0008] The mechanism of dopamine being deposited on the upper and lower surfaces of the polyester film substrate by self-oxidative polymerization in an alkaline tris(hydroxymethyl)aminomethane-hydrochloric acid buffer solution is as follows:

[0009] The photovoltaic backplane prepared by the present invention, the strong adhesion performance of its polydopamine adhesive layer (PDA adhesive layer for short, such as the first PDA adhesive layer, the second PDA adhesive layer) and a large number of polar functional groups such as hydroxyl and amino groups can greatly improve the initial adhesion and long-term aging adhesion (PCT24h adhesion) between the photovoltaic backplane (specifically the first PDA adhesive layer) and the packaging film such as EVA, and can greatly improve the adhesion performance between the second PDA adhesive layer and the fluorocarbon resin coating; Therefore, the photovoltaic backplane of the present invention can effectively resist the influence of complex environments during long-term aging, such as the damage caused by the high humidity and high corrosion environment faced by offshore photovoltaics. At the same time, the preparation method of the present invention can also omit the following steps in the preparation process of the existing photovoltaic backplane film such as CN114656856B: the dopamine modification step of the aqueous fluorinated acrylate copolymer emulsion, and the treatment steps such as plasma treatment, surface grafting of polyacrylic acid and surface polydopamine deposition on the polyester film substrate. The preparation method of the present invention can also reduce the energy consumption and organic solvent use in the corona and coating process in the traditional coating backplane processing technology. Therefore, the preparation method of the present invention can greatly simplify the preparation process of the photovoltaic backplane, reduce costs, and stabilize the product quality, which is conducive to large-scale production and application.

[0010] 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, dopamine is then added, stirred to dissolve, and the volume is fixed to obtain the tris(hydroxymethylaminomethane)-hydrochloric acid buffer solution containing dopamine; The pH value of the dopamine-containing tris-hydrochloric acid buffer solution is 8.2-8.5, and the dopamine concentration is 1.5-2 mg / mL.

[0011] 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.

[0012] 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 immersion time of the polyester film substrate in the tris(hydroxymethyl)aminomethane-hydrochloric acid buffer solution containing dopamine is more than 24h. 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.

[0013] More preferably, the thickness of the first polydopamine bonding layer and the second polydopamine bonding layer are both 65-68 nm (more preferably 65-66 nm).

[0014] Preferably, in step S2, the drying temperature is 30-70°C (such as 50°C), and the drying time is 2-5h (4h).

[0015] As the middle layer of the photovoltaic backsheet, the polyester film substrate plays a supporting role; the polyester film substrate needs to be resistant to high and low temperatures, have stable mechanical properties, excellent electrical insulation, good anti-creeping, fatigue resistance, friction resistance and dimensional stability, and low gas and vapor permeability. Therefore, preferably, the polyester film substrate is at least one of BOPET film and BOPEN film.

[0016] Further preferably, in step S2, the polyester film substrate is a BOPET film having a thickness of 260-300 μm (eg, 285 μm).

[0017] 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 auxiliary agent, and stirring them evenly; the fluorocarbon resin aqueous solution has a viscosity of 2500-4500 mPa·s at 23° C., and a fluorine content of 20-30%; The fluorocarbon resin is one or more of polytetrafluoroethylene, polyperfluoroethylene propylene, tetrafluoroethylene-perfluoroalkoxy vinyl ether copolymer, ethylene-tetrafluoroethylene copolymer, polychlorotrifluoroethylene, ethylene-chlorotrifluoroethylene copolymer and their derivatives; The auxiliary agent is one or more of a wetting agent, a dispersant, a defoaming agent, a thickener, and a multifunctional amine auxiliary agent.

[0018] Further preferably, in step S3, the fluorocarbon resin is ethylene-chlorotrifluoroethylene copolymer or tetrafluoroethylene-perfluoroalkoxy vinyl ether copolymer. In view of the harsh use environment and long-term stability requirements of photovoltaic backsheets, ether-type fluororesins such as FEVE with excellent outdoor weather resistance, corrosion resistance, acid and alkali resistance, salt spray resistance, high temperature and humidity resistance and excellent mechanical properties have become the first choice of fluorocarbon resins. The mass percentage content of the fluorocarbon resin is 50-55% (more preferably 55%), and the mass percentage content of water is 43-48.5% (such as 43.25%).

[0019] 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).

[0020] The present invention also discloses a photovoltaic back panel, which is prepared by the method for preparing the photovoltaic back panel described above in the present invention.

[0021] The present invention also discloses an application of a photovoltaic backboard, wherein the photovoltaic backboard is applied to a photovoltaic module; the first polydopamine bonding layer is bonded to the back of a battery of the photovoltaic module through a packaging adhesive film.

[0022] Compared with the prior art, the present invention has at least the following beneficial effects: The preparation method of the photovoltaic back panel 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 backplane 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 backplane (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. Therefore, the photovoltaic backplane of the present invention also has excellent long-term UV resistance, corrosion resistance and weather resistance. Therefore, the photovoltaic backplane of the present invention is particularly suitable for use in offshore photovoltaic modules. The photovoltaic backplane 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.

[0023] At the same time, the preparation method of the present invention can also omit the following steps in the existing photovoltaic backplane film preparation process such as CN114656856B: the dopamine modification step of the aqueous fluorinated acrylate copolymer emulsion, and the treatment steps such as plasma treatment, surface grafting of polyacrylic acid, and surface polydopamine deposition on the polyester film substrate. The preparation method of the present invention can also reduce the energy consumption and organic solvent use in the corona and coating process in the traditional coating backplane processing technology. Therefore, the preparation method of the present invention can greatly simplify the preparation process of the photovoltaic backplane, reduce costs, and the product quality is stable, which is conducive to large-scale production and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of the cross-sectional structure of a photovoltaic back panel of the present invention.

[0025] Description of the accompanying drawings: BOPET substrate 1; PDA bonding layer 2; fluorocarbon resin coating 3. DETAILED DESCRIPTION

[0026] 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 implementation methods.

[0027] Example 1 A method for preparing a photovoltaic backsheet in this embodiment includes the following preparation steps: 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; then, 37% concentrated hydrochloric acid is added dropwise to the mixed solution until the pH of the mixed solution is 8.0; then, 2 mg of dopamine is added, stirred and dissolved, and the volume is fixed to prepare a tris(hydroxymethyl)aminomethane-hydrochloric acid buffer solution with a dopamine concentration of 2 mg / mL and a pH of 8.0.

[0028] Step 2. Subsequently, immerse a BOPET (biaxially oriented polyester film) substrate having a thickness of 285 μm in a tris(hydroxymethyl)aminomethane-hydrochloric acid buffer solution having a dopamine concentration of 2 mg / mL and a pH of 8.0 in step 1 for 24 hours, so that dopamine is deposited on the upper and lower surfaces of the BOPET substrate by self-oxidative polymerization in the alkaline tris(hydroxymethyl)aminomethane-hydrochloric acid buffer solution, and rinse with water to remove the buffer solution and unreacted dopamine on the surface of the BOPET substrate. Then, place the BOPET substrate in an oven and dry it at 50° C. for 4 hours to form a bonding layer on both the upper and lower surfaces of the BOPET substrate, thereby obtaining a photovoltaic backplane of this embodiment.

[0029] A photovoltaic backsheet of this embodiment, see Figure 1 , including: a BOPET substrate 1, and a bonding layer is deposited on the upper surface and the lower surface of the BOPET substrate 1; the material of the bonding layer is polydopamine (PDA for short), that is, the bonding layer is a PDA bonding layer 2. Therefore, the photovoltaic backplane of this embodiment is a backplane film material with a three-layer structure of PDA-BOPET-PDA (PDA-BOPET-PDA backplane for short).

[0030] An application of a photovoltaic back sheet 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.

[0031] Example 2 A photovoltaic back sheet and a preparation method and application thereof of this embodiment are all referred to in Embodiment 1, and the difference between this embodiment and Embodiment 1 is that: In step 1 of this embodiment, the pH of the mixed solution is adjusted to 8.2, and the pH of the tris(hydroxymethyl)aminomethane-hydrochloric acid buffer solution containing dopamine is also adjusted to 8.2, and the rest is referred to Example 1. Thus, a photovoltaic backsheet (which is a PDA-BOPET-PDA backsheet) of this embodiment is obtained.

[0032] Example 3 A photovoltaic back sheet and a preparation method and application thereof of this embodiment are all referred to in Embodiment 1, and the difference between this embodiment and Embodiment 1 is that: In step 1 of this embodiment, the pH of the mixed solution is adjusted to 8.5, and the pH of the tris(hydroxymethyl)aminomethane-hydrochloric acid buffer solution containing dopamine is also adjusted to 8.5, and the rest is referred to Example 1. Thus, a photovoltaic backsheet (PDA-BOPET-PDA backsheet) of this embodiment is obtained.

[0033] Example 4 A photovoltaic back sheet and a preparation method and application thereof of this embodiment are all referred to in Embodiment 1, and the difference between this embodiment and Embodiment 1 is that: In step 1 of this embodiment, the pH of the mixed solution is adjusted to 9.0, and the pH of the tris(hydroxymethyl)aminomethane-hydrochloric acid buffer solution containing dopamine is also adjusted to 9.0, and the rest is referred to Example 1. Thus, a photovoltaic backsheet (PDA-BOPET-PDA backsheet) of this embodiment is obtained.

[0034] Example 5 A photovoltaic back sheet and its preparation method and application in this embodiment are all referred to in Example 3, and the difference between this embodiment and Example 3 is that: In step 1 of this embodiment, after the pH of the mixed solution is adjusted to 8.5, 1 mg of dopamine is added, stirred and dissolved, and the volume is fixed to prepare a tris(hydroxymethylaminomethane)-hydrochloric acid buffer solution with a dopamine concentration of 1 mg / mL and a pH of 8.5.

[0035] In step 2 of this embodiment, the BOPET substrate with a thickness of 285 μm is immersed in the tris(hydroxymethyl)aminomethane-hydrochloric acid buffer solution with a dopamine concentration of 1 mg / mL and a pH of 8.5 in step 1, and the rest is referred to Example 3. Thus, a photovoltaic backsheet (PDA-BOPET-PDA backsheet) of this embodiment is obtained.

[0036] Example 6 A photovoltaic back sheet and its preparation method and application in this embodiment are all referred to in Example 3, and the difference between this embodiment and Example 3 is that: In step 1 of this embodiment, after the pH of the mixed solution is adjusted to 8.5, 1.5 mg of dopamine is added, stirred and dissolved, and the volume is fixed to prepare a tris(hydroxymethyl)aminomethane-hydrochloric acid buffer solution with a dopamine concentration of 1.5 mg / mL and a pH of 8.5.

[0037] In step 2 of this embodiment, the BOPET substrate with a thickness of 285 μm is immersed in the tris(hydroxymethyl)aminomethane-hydrochloric acid buffer solution with a dopamine concentration of 1.5 mg / mL and a pH of 8.5 in step 1, and the rest is referred to Example 3. Thus, a photovoltaic backsheet (PDA-BOPET-PDA backsheet) of this embodiment is obtained.

[0038] Example 7 A photovoltaic back sheet and its preparation method and application in this embodiment are all referred to in Example 3, and the difference between this embodiment and Example 3 is that: In step 1 of this embodiment, after the pH of the mixed solution is adjusted to 8.5, 2.5 mg of dopamine is added, stirred and dissolved, and the volume is fixed to prepare a tris(hydroxymethylaminomethane)-hydrochloric acid buffer solution with a dopamine concentration of 2.5 mg / mL and a pH of 8.5.

[0039] In step 2 of this embodiment, the BOPET substrate with a thickness of 285 μm is immersed in the tris(hydroxymethyl)aminomethane-hydrochloric acid buffer solution with a dopamine concentration of 2.5 mg / mL and a pH of 8.5 in step 1, and the rest is referred to Example 3. Thus, a photovoltaic backsheet (PDA-BOPET-PDA backsheet) of this embodiment is obtained.

[0040] Example 8 The method for preparing a photovoltaic backsheet of this embodiment, based on steps 1-2 of embodiment 3, further includes the following preparation steps: Step 3, prepare 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), 0.2% multifunctional amine additive (ANGUS, AMP-95 (2-amino-2-methyl-1-propanol)) in sequence, adjust the pH to 8.5, stir evenly, and prepare the fluorocarbon resin aqueous solution.

[0041] Step 4. Immerse the PDA-BOPET-PDA backplane 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 backplane of this embodiment.

[0042] A photovoltaic backsheet of this embodiment, see Figure 1, comprising: a BOPET substrate 1, a bonding layer is deposited on the upper surface and the lower surface of the BOPET substrate 1, and a fluorocarbon resin coating 3 is also deposited on the outer surface of one bonding layer (the bonding layer is preferably: the bonding layer located on the lower surface of the BOPET substrate 1); the bonding layer is a PDA bonding layer 2. Therefore, the photovoltaic backplane of this embodiment is a backplane film material with a four-layer structure of PDA-BOPET-PDA-fluorocarbon resin coating (referred to as PDA-BOPET-PDA-fluorocarbon resin coating backplane).

[0043] An application of a photovoltaic back sheet 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.

[0044] Example 9 A photovoltaic back sheet and a preparation method and application thereof of this embodiment are all referred to in Embodiment 8, and the difference between this embodiment and Embodiment 8 is that: In the fluorocarbon resin aqueous solution prepared in step 3 of this embodiment, the content of deionized water is changed to 48.25% (by mass percentage, the same below), and the content of fluorocarbon resin FEVE is changed to 50%, and the rest is referred to Example 8. Thus, a photovoltaic backsheet (which is a PDA-BOPET-PDA-fluorocarbon resin coated backsheet) of this embodiment is obtained.

[0045] Example 10 A photovoltaic back sheet and a preparation method and application thereof of this embodiment are all referred to in Embodiment 8, and the difference between this embodiment and Embodiment 8 is that: In the fluorocarbon resin aqueous solution prepared in step 3 of this embodiment, the content of deionized water is changed to 43.25% (by mass percentage, the same below), and the content of fluorocarbon resin FEVE is changed to 55%, and the rest is referred to Example 8. Thus, a photovoltaic backsheet (PDA-BOPET-PDA-fluorocarbon resin coated backsheet) of this embodiment is obtained.

[0046] Embodiment 11 A photovoltaic back sheet and a preparation method and application thereof of this embodiment are all referred to in Embodiment 8, and the difference between this embodiment and Embodiment 8 is that: In the fluorocarbon resin aqueous solution prepared in step 3 of this embodiment, the content of deionized water is changed to 38.25% (by mass percentage, the same below), and the content of fluorocarbon resin FEVE is changed to 60%, and the rest is referred to Example 8. Thus, a photovoltaic backsheet (PDA-BOPET-PDA-fluorocarbon resin coated backsheet) of this embodiment is obtained.

[0047] Comparative Example 1 A method for preparing a photovoltaic backsheet in this comparative example includes the following preparation steps: Step 1: corona treatment is performed on a BOPET substrate having a thickness of 285 μm.

[0048] 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.

[0049] Step 3: After drying, a photovoltaic backsheet of this comparative example is obtained. The photovoltaic backsheet of this comparative example comprises a BOPET substrate and an adhesive layer coated on the upper surface of the BOPET substrate; the adhesive layer is made of polyurethane adhesive (Dow Chemical, VORAMER™ PU 3200) with a thickness of 60 μm.

[0050] Comparative Example 2 A method for preparing a photovoltaic backsheet in this comparative example includes the following preparation steps: Step 1: corona treatment is performed on a BOPET substrate having a thickness of 285 μm.

[0051] Step 2: After passing through the coating line, a layer of adhesive is applied on the upper and lower surfaces of the corona-treated BOPET substrate, and then a layer of 20 μm thick fluorocarbon resin coating is applied on 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).

[0052] Step 3, drying and curing at 150°C for 3 minutes to obtain a photovoltaic backsheet of this comparative example (i.e., an existing photovoltaic backsheet containing an adhesive layer and a fluorocarbon resin coating). The photovoltaic backsheet of this comparative example comprises a BOPET substrate, the upper surface and the lower surface of the BOPET substrate are coated with an adhesive layer, and the outer surface of one of the adhesive layers (the adhesive layer is preferably: the adhesive layer located on the lower surface of the BOPET substrate) is also coated with a fluorocarbon resin coating; the material of the adhesive layer is a polyurethane adhesive (Sika, Sikaflex®-552), and the thickness of the single adhesive layer is 60μm.

[0053] Performance Testing Samples were prepared and performance tested according to the standards GB / T31034-2014 (Insulating backsheet for crystalline silicon solar cell modules) and CQC3308-2013 (Technical specifications for backsheet for photovoltaic module encapsulation). Among them, the following tests were performed according to the standard GB / T2790: the initial adhesion between the PDA adhesive layer of Example 1-11 (or the adhesive layer of Comparative Example 1-2) and the EVA encapsulation film, and the adhesion after 24 hours of rapid aging treatment with PCT (121°C, 100% humidity, 0.2MPa). UV300kw / h UV resistance test was performed according to the standard IEC61215-2. The cross-cut adhesion test between the PDA adhesive layer of Example 1-11 (or the adhesive layer of Comparative Example 1-2) and the fluorocarbon resin coating was performed according to the standard GB / T9286-2021. The test results are shown in Table 1-2: Table 1

[0054] Combining the data in Table 1, we can see that: (1) Compared with the adhesive layer for the existing photovoltaic backsheet in Comparative Example 1, the initial bonding force between the PDA bonding layer of Examples 1-7 and the EVA encapsulation film is better, especially the PCT 24h bonding force between the PDA bonding layer of Examples 1-7 and the EVA encapsulation film is more advantageous.

[0055] (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 bonding layer deposited on the surface of the BOPET substrate also gradually increases.

[0056] When the pH value of the tris(hydroxymethylaminomethane)-hydrochloric acid buffer solution with a dopamine concentration of 2 mg / mL increases to 9.0 (as in Example 4), the thickness of the PDA bonding layer tends to grow slowly. At this time, PDA begins to have a tendency to aggregate locally 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 (that is, 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 bonding layer will easily increase, which will greatly affect the quality of the photovoltaic backplane; and further, when such a photovoltaic backplane is applied to a photovoltaic module, the PDA bonding layer will not only not significantly increase the initial bonding force and PCT24h bonding force between the PDA bonding layer and the EVA encapsulation film, but such an extremely uneven PDA bonding layer will increase the risk of cell fragmentation during lamination, and will easily lead to local delamination between layers in the photovoltaic module, affecting the application effect of the photovoltaic backplane in the photovoltaic module.

[0057] When the pH value of the tris(hydroxymethylaminomethane)-hydrochloric acid buffer solution with a dopamine concentration of 2 mg / mL is relatively low (such as in Example 1), the PDA adhesive layer is not easy to form a continuous film layer, which easily leads to incomplete coverage of the PDA adhesive layer on the surface of the BOPET substrate, resulting in a decrease in the initial bonding force and PCT24h bonding force between the PDA adhesive layer and the EVA encapsulation film. Therefore, if the pH value of the tris(hydroxymethylaminomethane)-hydrochloric acid buffer solution with a dopamine concentration of 2 mg / mL continues to decrease (that is, the pH value of the tris(hydroxymethylaminomethane)-hydrochloric acid buffer solution with a dopamine concentration of 2 mg / mL is too low), the PDA adhesive layer will have an extremely incomplete coverage defect on the surface of the BOPET substrate, which will greatly affect the quality of the photovoltaic backplane; and when such a photovoltaic backplane is applied to a photovoltaic module, the extremely incomplete coverage of the PDA adhesive layer will greatly increase the risk of poor interlayer bonding, affecting the application effect of the photovoltaic backplane in the photovoltaic module.

[0058] (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 (such as less than 1 mg / mL or greater than 2.5 mg / mL), the PDA adhesive layer prepared on the surface of the BOPET substrate will have extremely incomplete coverage or extremely uneven thickness, which will affect the quality of the photovoltaic backsheet and further affect the application effect of the photovoltaic backsheet in the photovoltaic module.

[0059] 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 will not have incomplete coverage and uneven thickness, and the initial bonding force and PCT24h bonding force between the PDA adhesive layer and the EVA encapsulation film are both large. Therefore, the quality of the photovoltaic backplane of Example 3 is the best, and its application in photovoltaic modules will help to further improve the quality and service life of photovoltaic modules.

[0060] Table 2

[0061] Combined with the data in Table 2, we can see that: (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 bonding layer and a fluorocarbon resin coating in Examples 8-11 has better UV300kw / h UV resistance and adhesion.

[0062] (5) Increasing the content of fluorocarbon resin FEVE in the fluorocarbon resin aqueous solution (as shown in Examples 8-11), the thickness of the fluorocarbon resin coating obtained after curing also increases. However, if the content of fluorocarbon resin FEVE in the fluorocarbon resin aqueous solution is too small or too large (such as less than 45% or greater than 60%), the fluorocarbon resin coating obtained on the surface of the PDA bonding layer will have extremely incomplete coverage or extremely uneven thickness, which will affect the quality of the photovoltaic backsheet and further affect the application effect of the photovoltaic backsheet in the photovoltaic module.

[0063] In summary, the preparation method of the photovoltaic backsheet of the present invention is to deposit a PDA bonding layer on the surface of the BOPET substrate using a tris(hydroxymethyl)aminomethane-hydrochloric acid buffer solution with a dopamine concentration of 2 mg / mL and a pH value of 8.5, and then use a fluorocarbon resin aqueous solution with a fluorocarbon resin FEVE content of 50-55% (preferably 55%) to prepare a fluorocarbon resin coating on the surface of the PDA bonding layer (as shown in Examples 9-10); in this way, the photovoltaic backsheet prepared in Examples 9-10 will not have the phenomenon of incomplete coverage and uneven thickness of the PDA bonding layer or the fluorocarbon resin coating, and will show good initial adhesion and long-term aging adhesion (PCT24h adhesion) to the encapsulation film such as EVA, and the PDA bonding layer also has excellent adhesion performance to the fluorocarbon resin coating, and 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 such as Examples 9-10 is particularly suitable for use in photovoltaic modules, which helps to further improve the quality and service life of photovoltaic modules.

[0064] Although the preferred embodiments of the present invention have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. 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.

[0065] The technical solution provided by the present invention is introduced in detail above. Specific examples are used in this article to illustrate the principle and implementation mode 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 will be changes in the specific implementation mode 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(hydroxymethyl)aminomethane-hydrochloric acid buffer solution containing dopamine, so that dopamine is deposited on the upper and lower surfaces of the polyester film substrate by self-oxidative polymerization in the alkaline tris(hydroxymethyl)aminomethane-hydrochloric acid buffer solution, washing the surface of the polyester film substrate with water, and drying, so as to form a first polydopamine bonding layer and a second polydopamine bonding layer on the upper and lower surfaces of the polyester film substrate, respectively; S3, preparing a fluorocarbon resin aqueous solution; wherein the mass percentage content of the 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.

2. The method for preparing a photovoltaic backsheet according to claim 1, characterized in that: 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 fixed to obtain the tris(hydroxymethylaminomethane)-hydrochloric acid buffer solution containing dopamine; The pH value of the dopamine-containing tris-hydrochloric acid buffer solution is 8.2-8.5, and the dopamine concentration is 1.5-2 mg / mL.

3. The method for preparing a photovoltaic backsheet according to claim 2, characterized in that: In step S1, 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.

4. The method for preparing a photovoltaic backsheet according to claim 1, characterized in that: In step S2, the polyester film substrate is immersed in the tris(hydroxymethyl)aminomethane-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 polyester film substrate is at least one of a BOPET film and a BOPEN film; 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 back sheet 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, characterized in that: In step S3, the fluorocarbon resin aqueous solution is prepared by mixing 38-53.5% water, 45-60% fluorocarbon resin and the remaining additives, and stirring them evenly; the fluorine content of the fluorocarbon resin aqueous solution is 20-30%; The fluorocarbon resin is one or more of polytetrafluoroethylene, polyperfluoroethylene propylene, tetrafluoroethylene-perfluoroalkoxy vinyl ether copolymer, ethylene-tetrafluoroethylene copolymer, polychlorotrifluoroethylene, ethylene-chlorotrifluoroethylene copolymer and their derivatives; 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 back sheet according to claim 6, characterized in that: In step S3, the fluorocarbon resin is ethylene-chlorotrifluoroethylene copolymer or tetrafluoroethylene-perfluoroalkoxy vinyl ether copolymer; 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 back sheet according to claim 1, characterized in that: In step S4, the curing temperature is 120-180° C., the curing time is 2-8 min; and 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 back panel as described in any one of claims 1 to 8.

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

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