Photovoltaic glass double-layer anti-reflection coating structure with adjustable refractive index bottom coating and preparation method of photovoltaic glass double-layer anti-reflection coating structure

Abstract

In order to solve the problems that in an existing photovoltaic glass double-layer anti-reflection coating, the refractive index of a bottom coating is difficult to regulate and control, and a surface coating needs to depend on high porosity to achieve the low refractive index, so that the surface hardness and the abrasion resistance are insufficient, a new double-layer anti-reflection coating design thought is provided. According to the invention, an inorganic oxide network structure formed by silicon-oxygen-titanium or silicon-oxygen-titanium-zirconium copolycondensation is introduced into the prime coat, so that the refractive index of the prime coat is effectively regulated and controlled on the premise of keeping the compactness and mechanical properties of the prime coat, and therefore, the refractive index of the prime coat can be effectively regulated and controlled under the condition that the porosity of the surface coat is not obviously improved. And completing refractive index matching between the double-layer coating. Based on the design, the anti-reflection effect of the photovoltaic glass surface can be achieved while the surface hardness, the wear resistance and the tempering stability are considered, the performance selection and rejection problem caused by a traditional double-plating technical route mainly for reducing the refractive index of a surface coating is solved, and good industrial application prospects are achieved.

Description

Technical Field

[0001] This invention relates to the field of functional coating technology for photovoltaic glass surfaces, specifically to a double-layer antireflective coating structure for photovoltaic glass, and more particularly to a double-layer antireflective coating structure with an adjustable refractive index for the base layer and its preparation method. This coating structure is suitable for application before tempering photovoltaic glass and can maintain stable optical performance and structural integrity after high-temperature tempering. Background Technology

[0002] With the rapid development of the photovoltaic industry, improving the photoelectric conversion efficiency of photovoltaic modules has become one of the important research directions in the field of photovoltaic glass technology. Reflection loss on the surface of photovoltaic glass will reduce the effective utilization rate of incident light energy. Therefore, forming an antireflection (AR) coating on the surface of photovoltaic glass to reduce interface reflection and improve light transmittance has become a widely adopted technical approach in the industry.

[0003] Existing antireflective coatings for photovoltaic glass mostly employ single-layer or multi-layer film structures. Taking a double-layer antireflective structure as an example, existing technologies generally achieve interference antireflection by matching the refractive index and thickness of a "bottom layer (relatively high refractive index / dense layer) + top layer (relatively low refractive index / porous layer)". For instance, Chinese patents CN101805135A / CN101805135B disclose a double-layer antireflective photovoltaic glass, whose structure includes a high refractive index oxide layer (such as TiO2, ZnO, ZrO2) and a low refractive index porous silicon oxide layer on top of it. However, in order to obtain a low refractive index top layer, this type of solution usually requires the introduction of a porous structure; although the porous structure is beneficial for reducing the refractive index and improving light transmittance, it often leads to a decrease in the mechanical strength and abrasion resistance of the film layer, thus making it more prone to scratches or wear during subsequent roll coating, handling, stacking, and module assembly of photovoltaic glass.

[0004] In addition, some existing technologies achieve antireflection by constructing nano-hollow particle / pore structures. For example, Chinese patent CN102617045A discloses a SiO2 antireflection film comprising a dense SiO2 layer and a SiO2 nano-hollow particle layer. This type of technology also relies on hollow / pore structures to achieve refractive index control, typically requiring precise control over particle structure, pore size, and filling. Under industrial conditions, fluctuations in pore structure control can affect film hardness, wear resistance, and optical consistency, thus impacting stable adaptation in automated production lines.

[0005] Furthermore, in order to improve the hardness and durability of the coating, existing technologies have proposed double-layer films to enhance strength. For example, Chinese patent CN105948533A discloses a high-strength double-layer anti-reflective film and claims that it can achieve higher pencil hardness.

[0006] However, the core of this type of technology is still mostly focused on the path of "achieving low refractive index and anti-reflection through pore / structure design" or "improving strength through composite / modification". It is still difficult to eliminate another key contradiction in the double-layer anti-reflection system - the insufficient adjustability of the refractive index of the bottom coating, which leads to the need to increase the porosity of the top coating in exchange for light transmittance - from the source of film system design.

[0007] Meanwhile, more complex dual-layer or composite layer designs have emerged in recent years. For example, Chinese patent CN116239311B proposes a dual-layer antireflective coating composed of a SiO2–TiO2 composite layer and a modified SiO2 composite layer. Such solutions often involve steps such as micelle templates and composite particle structures, resulting in a more complex process window and placing higher demands on online continuous coating and large-scale consistency control.

[0008] Foreign patents also frequently employ methods that rely on porous layers to achieve low refractive index and antireflective effects. For example, US Patent 8237047B2 discloses a method for preparing a sol-gel antireflective coating for photovoltaic glass, involving a system of porous SiO2 and siloxanes, followed by coating and heat treatment curing.

[0009] US Patent US20150104568A1 also discloses a method for preparing silica antireflective films based on TEOS, PEG, etc. The common thread in these approaches is that, to obtain a low refractive index, pores or organic pore templates are typically introduced. However, increasing porosity and introducing organic components often leads to a decrease in film hardness / wear resistance or a limited heat treatment window. Therefore, achieving long-term stability and high yield under industrial conditions of online roll coating before photovoltaic glass tempering and high-temperature tempering at 600–700℃ remains a challenge.

[0010] Japanese patents have also proposed multi-layer low-reflection film structures. For example, JP2013122949A discloses a low-reflection film for cover glass of solar cell modules, revealing the refractive index and film thickness range of the upper / middle / lower layers, wherein the refractive index of the upper layer can be as low as approximately 1.10–1.20. The realization of such ultra-low refractive index layers typically relies on higher porosity or stronger structural control, which may introduce risks of insufficient mechanical strength and wear resistance, and face higher surface damage sensitivity in continuous production and subsequent processes.

[0011] In the realm of European patents, there are also technologies that utilize "porous / gradient porosity" to achieve antireflection. For example, EP2752388A1 discloses the use of sol-gel to form porous metal oxide / silica antireflection coatings, and the ability to control the pore size to create a pore gradient structure. Another example is EP3071650A1, which relates to the composition and preparation method of porous antireflection coatings containing pore-forming agents.

[0012] Such antireflection methods still primarily rely on "porosity reduction to lower the refractive index," thus making it difficult to fundamentally avoid the structural contradiction of "increased porosity leading to decreased hardness and wear resistance." Furthermore, if multilayer or gradient structures are required to achieve broadband antireflection, the complexity of the process and the difficulty of controlling online mass production yield will increase. In addition, European patent EP3568379B1 mentions constructing single-layer or multilayer (including gradient refractive index) broadband antireflection film systems based on sol-gel. Multilayer stacking typically implies more stringent interlayer matching and process control, placing higher demands on adaptability for low-cost, large-area, and continuous production.

[0013] In summary, existing double / multilayer photovoltaic glass antireflection and anti-reflection technologies generally suffer from the following limitations: First, the bottom coating often uses a dense SiO2 layer (approximately 1.41–1.42) with a relatively fixed refractive index, resulting in a lack of "freedom in adjusting the refractive index of the bottom layer" in the film system design. Second, to further improve light transmittance, it is often necessary to reduce the refractive index by increasing the porosity of the top coating, thereby reducing the hardness and wear resistance of the top coating and making it more susceptible to scratches during automated production and handling of the modules. Third, some existing technologies rely on complex templates / multi-layer stacking, resulting in a narrow process window and significant difficulties in controlling the large-scale consistency of online roll coating and pre-tempering coating. Therefore, there is currently a lack of a technical solution that allows for continuous adjustment of the refractive index of the bottom coating in a double-layer structure. There is an urgent need for a technical solution that can improve the freedom of film system design, consider the mechanical properties of the top coating, and meet the requirements for tempering process compatibility while ensuring the double-layer antireflection and anti-reflection effect. Summary of the Invention

[0014] To address the problems existing in existing double-layer antireflective coatings for photovoltaic glass, such as fixed refractive index of the base layer, limited freedom of film system design, and forced increase of surface layer porosity to improve light transmittance, which leads to a decrease in coating hardness and wear resistance and makes it difficult to adapt to industrial production, the present invention aims to provide a double-layer antireflective coating structure for photovoltaic glass with adjustable base layer refractive index and its preparation method.

[0015] This invention introduces a refractive index-tunable undercoat layer into a dual-layer antireflective and anti-reflective coating structure, transforming the undercoat layer from a traditional optically inert layer into a functional layer participating in optical matching design. This achieves the antireflective and antireflective effect of the dual-layer coating system without significantly increasing the porosity of the topcoat. Consequently, while ensuring improved optical performance, it helps maintain the structural density and mechanical strength of the topcoat, and improves the coating's wear resistance and process adaptability.

[0016] Furthermore, this invention aims to provide a double-layer antireflective coating system suitable for pre-tempering coating of photovoltaic glass, which can withstand high-temperature tempering treatment at 600-700℃ while maintaining stable optical performance and structural integrity, in order to meet the requirements of online roll coating, continuous production and large-scale industrial applications of photovoltaic glass.

[0017] To achieve the above-mentioned objectives, the present invention adopts the following technical solution.

[0018] (I) Coating Structure Technical Solution

[0019] This invention provides a double-layer antireflective coating structure for photovoltaic glass, comprising a base coating and a top coating sequentially disposed on the surface of a photovoltaic glass substrate. The base coating is an inorganic film layer with adjustable refractive index, formed by an amorphous silicon-oxygen-titanium (and / or zirconium) oligomer network structure through co-hydrolysis and co-condensation reaction of silicon, titanium, and / or zirconium sources under acidic conditions. By adjusting the ratio of silicon to titanium and / or zirconium sources, the refractive index of the base coating can be continuously adjusted within the range of 1.45 to 1.70, preferably 1.55 to 1.68, and more preferably 1.60 to 1.66. The top coating, disposed above the base coating, is an inorganic antireflective layer with a refractive index of 1.28 to 1.35, preferably about 1.32. While achieving antireflective and antireflective functions, the top coating maintains a relatively dense structural characteristic, thereby possessing high mechanical strength and wear resistance.

[0020] Through the above-mentioned dual-layer structure design, the bottom coating layer is transformed from a traditional optically inert layer into a functional layer that participates in optical matching design, thereby achieving the anti-reflection and anti-reflection effect of the dual-layer coating system without relying on significantly increasing the porosity of the top coating layer.

[0021] (II) Optical parameters and film thickness design scheme

[0022] In a preferred embodiment of the present invention, the double-layer antireflective coating is designed with the visible light band as its core. Through the coordinated matching of the refractive index and film thickness of the base coating and the top coating, effective suppression of incident light reflection is achieved. Specifically, the thickness of the base coating is 70–130 nm, preferably 80–110 nm; the thickness of the top coating is 80–150 nm, preferably 95–125 nm. By selecting a base coating with a refractive index higher than that of a traditional silica base coating and matching it with a top coating with a refractive index of approximately 1.32, a transmittance improvement effect superior to traditional double-layer antireflective structures can be achieved while ensuring the density of the top coating structure.

[0023] (III) Preparation Method Technical Scheme

[0024] The present invention also provides a method for preparing the above-mentioned double-layer antireflective coating structure for photovoltaic glass, comprising the following steps:

[0025] Preparation of the primer sol: A silicon source, a titanium source, and / or a zirconium source are co-hydrolyzed under acidic conditions, and then further undergo a co-condensation reaction to form an oligomeric network structure sol containing silicon-oxygen-titanium (and / or zirconium) bonds; by adjusting the ratio of reactants and reaction conditions, the resulting sol is made suitable for film formation and has the target refractive index range.

[0026] Formation of the base coating: The base coating sol is applied to the surface of the photovoltaic glass substrate to form the base coating, and then dried or preheated to obtain a stable film structure.

[0027] Formation of the topcoat: A topcoat sol is applied to the surface of the base coating and dried to form the topcoat, thereby obtaining a double-layer antireflective coating structure.

[0028] Tempering treatment: The coated photovoltaic glass is sent into a tempering furnace and tempered at 600-700℃ to further densify the double coating and form a stable bond with the glass substrate, while maintaining its optical properties.

[0029] (iv) Process compatibility scheme for double-coating and tempering

[0030] The coating process for the double-layer antireflective coating on photovoltaic glass includes the following steps:

[0031] (1) Provide cleaned photovoltaic glass substrate;

[0032] (2) Apply the primer sol to the surface of the photovoltaic glass substrate by online roller coating and pre-bake it at 80-150℃ to make the primer layer semi-cured or dry, forming a uniform and continuous primer layer.

[0033] (3) After the base coating is pre-baked, the topcoat sol is applied to the surface of the base coating by online roller coating and pre-baked at 80-150°C to form a continuous topcoat.

[0034] (4) The photovoltaic glass with the base coating and top coating completed is sent into the tempering furnace and tempered at 600-700℃ to obtain a double-layer anti-reflective coating structure.

[0035] By using the above-mentioned step-by-step coating and pre-baking-tempering process, the stability of the double-layer coating structure can be ensured while avoiding coating leveling loss or interface defects caused by wet-on-wet construction. This process is suitable for continuous industrial production of online roller coating before tempering photovoltaic glass.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] (1) Significantly improves the design freedom of the double-layer antireflection and anti-reflection film system

[0038] This invention introduces an adjustable refractive index undercoat, freeing it from the traditional fixed-refractive-index silica dense layer and transforming it into a functional layer capable of participating in optical matching design. By adjusting the composition ratio of the silicon-oxygen-titanium (and / or zirconium) oligomeric network structure in the undercoat, the refractive index of the undercoat can be continuously controlled over a wide range, thereby providing more design freedom for the double-layer antireflection and anti-reflection coating system and breaking through the limitation of the unadjustable refractive index of the undercoat in traditional double-coating systems.

[0039] (2) Avoid over-reliance on high-porosity surface coatings to achieve a balance between optical and mechanical properties.

[0040] In existing double-layer antireflective coatings, improving light transmittance typically requires increasing the porosity of the topcoat to reduce the refractive index, which in turn leads to a decrease in coating hardness and abrasion resistance. This invention achieves good antireflective and antireflective effects by increasing the refractive index of the base coat and synergistically matching it with the topcoat, without significantly increasing the porosity of the topcoat. This helps maintain the structural density of the topcoat, thereby improving the coating's mechanical strength and abrasion resistance, and reducing the risk of scratches during production, handling, and assembly.

[0041] (3) It is beneficial to improve the process adaptability of double-layer coating in photovoltaic glass production.

[0042] Since the topcoat does not require an extremely high porosity structure, the double-layer antireflective coating of this invention has better stability in processes such as roll coating, cleaning, handling and stacking, and can better adapt to the process requirements of automated and continuous photovoltaic glass production lines, thereby improving production yield and consistency.

[0043] (4) It has good high-temperature tempering stability and is suitable for coating processes before tempering.

[0044] The base coating of this invention adopts a silicon-oxygen-titanium (and / or zirconium) oligomeric network structure, which can be further densified under high temperature conditions to form a stable inorganic network structure; the top coating maintains a relatively dense structure, so that the double coating system can withstand high temperature tempering treatment of 600-700℃ without significant optical performance drift or structural failure, and is suitable for industrial application scenarios of coating before tempering photovoltaic glass.

[0045] (5) Achieve excellent anti-reflection and anti-reflection effects and improve the power generation efficiency of photovoltaic modules.

[0046] By rationally matching the refractive index and film thickness of the base coating and the top coating, the double-layer antireflection coating of the present invention can effectively reduce the reflection loss on the surface of photovoltaic glass and improve the transmittance of visible light and near-infrared bands, thereby helping to improve the photoelectric conversion efficiency and long-term operating performance of photovoltaic modules.

[0047] (6) The process route is clear and easy to scale up and apply.

[0048] The double-layer antireflective coating structure and preparation method adopted in this invention can be achieved through mature processes such as online roll coating on existing photovoltaic glass production lines. The raw material system and process conditions are controllable, making it suitable for large-area, continuous production and showing good prospects for industrial application. Detailed Implementation

[0049] A double-layer antireflective coating structure for photovoltaic glass includes a base coating and a top coating sequentially disposed on the surface of a photovoltaic glass substrate. The base coating is an inorganic oxide network structure formed by silicon-oxygen-titanium co-condensation, whereby the inorganic oxide network structure is formed by the simultaneous hydrolysis and co-condensation reaction of a silicon source and a titanium source under acidic conditions. The top coating is a low-refractive-index, low-porosity inorganic coating with a refractive index lower than that of the base coating.

[0050] By adjusting the refractive index matching relationship between the base coating and the top coating, the anti-reflection and anti-reflection effects on the surface of photovoltaic glass can be achieved without significantly increasing the porosity of the top coating.

[0051] In the aforementioned double-layer antireflective coating structure, the refractive index of the base coating is 1.52 to 1.70.

[0052] In the aforementioned double-layer antireflective coating structure, the refractive index of the base coating is 1.58 to 1.66.

[0053] In the above-mentioned double-layer antireflective coating structure, the refractive index of the top coating is 1.28 to 1.35.

[0054] In the aforementioned double-layer antireflective coating structure, the silicon source is selected from tetraethoxysilane, tetramethoxysilane, or a combination thereof.

[0055] In the above-mentioned double-layer antireflective coating structure, the titanium source is selected from tetrabutyl titanate, isopropyl titanate, or a combination thereof.

[0056] In the aforementioned dual-layer antireflective coating structure, the silicon source and the titanium source are in the same reaction system, and undergo simultaneous hydrolysis and co-condensation reaction under acidic conditions.

[0057] In the aforementioned double-layer antireflective coating structure, the titanium element in the bottom coating is introduced into the inorganic oxide network structure by chemical bonding, rather than by physical doping in the form of independent titanium oxide particles.

[0058] In the aforementioned dual-layer antireflective coating structure, the base layer further includes a zirconium source, making the inorganic oxide network structure a silicon-oxygen-titanium-zirconium co-condensation structure.

[0059] In the above-mentioned double-layer antireflective coating structure, the zirconium source is selected from butyl zirconate (CAS No. 1071-76-7), n-propyl zirconate (CAS No. 23519-77-9), or a combination thereof.

[0060] In the above-mentioned double-layer antireflective coating structure, the dry film thickness of the base coating is 80–110 nm.

[0061] In the above-mentioned double-layer antireflective coating structure, the dry film thickness of the top coating is 95–125 nm.

[0062] The aforementioned double-layer antireflective coating structure maintains structural and optical stability even after being tempered at 600–700°C.

[0063] In the aforementioned dual-layer antireflective coating structure, the base coating and the top coating are applied to the surface of the photovoltaic glass via online roller coating.

[0064] The aforementioned double-layer antireflective coating structure, wherein the base coating is prepared by the following method: under acidic conditions, a silicon source and a titanium source are added to the same reaction system for simultaneous hydrolysis reaction, and a co-condensation reaction occurs during the hydrolysis process to form a silicon-oxygen-titanium co-condensation inorganic oxide network structure.

[0065] In the aforementioned double-layer antireflective coating structure, the base coating and top coating are sequentially applied to the surface of the photovoltaic glass, followed by tempering treatment at 600–700°C.

[0066] A method for preparing a double-layer antireflective coating for photovoltaic glass includes the following steps:

[0067] (1) A base coating sol with adjustable refractive index is prepared by simultaneously hydrolyzing and co-condensing silicon and titanium sources under acidic conditions.

[0068] (2) The primer sol is applied to the surface of the photovoltaic glass substrate by online roller coating and pre-baked at 80-150°C to form a primer coating layer;

[0069] (3) After the base coating is pre-baked, the topcoat sol is applied to the surface of the base coating by online roller coating and pre-baked at 80-150℃ to form the topcoat.

[0070] (4) The photovoltaic glass with the base coating and top coating completed is sent into the tempering furnace and tempered at 600-700℃ to obtain a double-layer anti-reflection coating structure.

[0071] In the above-mentioned method for preparing a double-layer antireflective coating for photovoltaic glass, the silicon source is selected from one or more of tetraethoxysilane (TEOS) and tetramethoxysilane (TMOS), and the titanium source is selected from one or more of tetrabutyl titanate and tetraisopropyl titanate.

[0072] In the above-mentioned method for preparing a double-layer antireflective coating for photovoltaic glass, the pH of the simultaneous hydrolysis process is controlled between 2.0 and 3.0.

[0073] In the above-mentioned method for preparing a double-layer antireflective coating for photovoltaic glass, the refractive index of the base layer can be adjusted within the range of 1.52 to 1.66.

[0074] In the above-mentioned method for preparing a double-layer antireflective coating for photovoltaic glass, the dry film thickness of the bottom coating is 80–110 nm, and the dry film thickness of the top coating is 90–130 nm.

[0075] The present invention will be further described below with reference to specific embodiments. Any reasonable adjustments or modifications made to the embodiments by those skilled in the art without departing from the technical concept of the present invention should be understood as still falling within the protection scope of the present invention.

[0076] Example 1

[0077] I. Preparation of Topcoat

[0078] This embodiment provides a topcoat for a double-layer antireflective coating structure for photovoltaic glass. It is made by compounding hollow silica and solid silica with different particle sizes. While achieving a low refractive index, it avoids using an excessively high porosity structure, thus balancing optical and mechanical properties.

[0079] (1) Raw materials

[0080] Hollow silica sol A: solid content 20 wt%, average particle size approximately 30–60 nm

[0081] Solid silica sol B: solid content 30 wt%, average particle size approximately 5–30 nm

[0082] Tetraethoxysilane (TEOS)

[0083] Deionized water

[0084] Acidic catalysts (using nitric acid or hydrochloric acid as examples)

[0085] Alcohol solvents (mainly ethanol)

[0086] (2) Topcoat Sol Formulation

[0087] (Based on 100 g of finished topcoat working solution)

[0088]

[0089] The inorganic solids content corresponding to the above formula is approximately 4.5 wt%.

[0090] (3) Preparation method of topcoat sol

[0091] 1. Pre-hydrolysis of the binder phase

[0092] Add some ethanol to the reaction vessel, add TEOS under stirring, then add deionized water, and slowly add acidic catalyst to adjust the pH of the system to about 2.0 to 3.0. Continue stirring for 20 to 40 minutes to allow TEOS to undergo partial hydrolysis and form a silicon-oxygen oligomer binder phase.

[0093] 2. Add solid silica sol

[0094] Solid silica sol B is slowly added to the above pre-hydrolysis system and stirred at a medium speed for 15-30 minutes to fully mix the small-diameter solid silica particles with the binder phase, thereby enhancing the structural support of the film layer.

[0095] 3. Add hollow silica sol

[0096] Hollow silica sol A is added to the system in 2 to 3 portions and stirred evenly under low shear conditions to avoid damaging the hollow structure of the hollow silica particles.

[0097] 4. Adjustment and Aging

[0098] Add the remaining ethanol to adjust the solid content and viscosity of the system. After stirring evenly, let the sol stand for 2 to 8 hours and filter it through a 0.45 to 1.0 μm filter membrane to obtain a stable surface coating sol.

[0099] (4) Formation of the topcoat

[0100] The aforementioned topcoat sol was applied to the surface of the primer-treated photovoltaic glass using a roller coating method and dried at 80–150°C to form a uniform and continuous topcoat layer. The dry film thickness of the resulting topcoat layer was controlled at approximately 95–125 nm, and its refractive index was approximately 1.32.

[0101] By combining hollow silica and solid silica, the surface coating maintains a low refractive index while possessing a relatively dense microstructure, which is beneficial for improving the coating's hardness and wear resistance.

[0102] II. Preparation of the base coating (target refractive index n≈1.66)

[0103] In this embodiment, the undercoat layer is used to form the lower functional layer in the double-layer antireflective coating structure of photovoltaic glass. This undercoat layer is formed by co-hydrolyzing and co-condensing silicon and titanium sources under acidic conditions to form an amorphous oligomeric network structure containing silicon-oxygen-titanium bonds, thereby obtaining an inorganic film layer with adjustable refractive index suitable for high-temperature tempering processes.

[0104] (1) Raw materials

[0105] Silicon source: Tetraethoxysilane (TEOS)

[0106] Titanium source: Isopropyl titanate (TTIP)

[0107] Alcohol solvents: ethanol

[0108] Deionized water

[0109] Acidic catalyst: nitric acid or hydrochloric acid

[0110] (2) Primer sol formulation

[0111] (Based on 100 g of primer working fluid)

[0112]

[0113] In the above-mentioned primer sol, the mass of TEOS converted to SiO2 is approximately 1.33 g, the mass of isopropyl titanate converted to TiO2 is approximately 2.19 g, and the total inorganic solid content of SiO2 and TiO2 is approximately 3.5 wt%, which is suitable for forming a thin film primer coating in an online roll coating process.

[0114] (3) Preparation method of primer sol

[0115] 1. Pre-hydrolysis of silicon source

[0116] TEOS was added to a portion of ethanol, and deionized water was added under stirring. An acidic catalyst was then slowly added dropwise to adjust the pH of the system to 1.5–2.5. Stirring was continued for 20–40 min to allow TEOS to undergo partial hydrolysis and form silicon-oxygen oligomers.

[0117] 2. Introduction of titanium source and co-condensation

[0118] Under the condition of maintaining the acidity of the system, isopropyl titanate is slowly added to the above silicon source pre-hydrolysis system and stirred continuously, so that the titanium source and silicon-oxygen oligomer undergo co-hydrolysis and co-condensation reactions simultaneously, gradually forming an oligomeric network structure containing Si–O–Ti bonds.

[0119] 3. Adjustment and Aging

[0120] Add the remaining ethanol to adjust the concentration and viscosity of the sol, continue stirring for 10-20 min, and then let the resulting sol stand for aging for 2-12 h to obtain a stable, transparent or nearly transparent base coat sol suitable for film formation.

[0121] (4) Formation of the base coating

[0122] The aforementioned primer sol was applied to the surface of a photovoltaic glass substrate via online roller coating and then dried or pre-baked at 80–150°C to form a uniform and continuous primer coating. After the topcoat was applied and the substrate underwent final tempering at 600–700°C, the optical properties of the primer coating remained stable, and no abnormal changes were observed, indicating that the formed co-condensation network structure has good thermal stability.

[0123] The dry film thickness of the base coating is controlled at approximately 80–110 nm.

[0124] (5) Performance of the primer coating

[0125] Testing revealed that the base coating formed in this embodiment is an amorphous inorganic film layer, with no independent TiO2 crystalline phase detected, indicating that the titanium component enters the silicon-oxygen network structure via co-condensation. The refractive index of the base coating is approximately 1.66, and it remained stable during subsequent tempering at 600–700°C without significant optical property drift or structural failure.

[0126] Comparative Example 1: Traditional SiO2 primer double-layer antireflective coating structure

[0127] I. Purpose of Comparison

[0128] This comparative example is used to illustrate the technical characteristics and optical performance of conventional double-layer antireflective coating structures commonly found in the prior art.

[0129] By comparing this comparative example with Example 1, while keeping the topcoat structure, formulation and process conditions completely consistent, only the material system and refractive index of the base coating are changed, thereby verifying the technical effect brought about by the present invention by increasing the refractive index of the base coating.

[0130] II. Preparation of the base coating (traditional SiO2 system)

[0131] (1) Raw materials

[0132] Silicon source: Tetraethoxysilane (TEOS)

[0133] Alcohol solvents: ethanol

[0134] Deionized water

[0135] Acidic catalyst: nitric acid or hydrochloric acid

[0136] (2) Primer sol formulation

[0137] (Based on 100 g of primer working fluid)

[0138]

[0139] In the aforementioned primer sol, the inorganic solid content of TEOS converted to SiO2 is approximately 1.7 wt%. In practical industrial applications, the inorganic solid content can be controlled at 3-4 wt% by adjusting the amount of TEOS used to meet the requirements of online roll coating.

[0140] (3) Preparation method of primer sol

[0141] TEOS was added to a portion of ethanol, and deionized water was added under stirring. An acidic catalyst was then slowly added dropwise to adjust the pH of the system to 1.5–2.5. Stirring was continued for 20–40 min to allow TEOS to undergo hydrolysis and condensation reactions, forming a silica sol system dominated by Si–O–Si bonds.

[0142] The remaining ethanol was then added to adjust the system concentration and viscosity, and the mixture was allowed to stand for 2–12 hours to age before the primer sol was obtained.

[0143] (4) Formation of the base coating

[0144] The above-mentioned primer sol is applied to the surface of the photovoltaic glass substrate by online roller coating and dried or pre-baked at 80-150°C to form a uniform and continuous primer coating.

[0145] The dry film thickness of the resulting base coating is controlled at approximately 80–110 nm, and its refractive index is approximately 1.42.

[0146] III. Preparation of Topcoat

[0147] The topcoat in this comparative example is exactly the same as that in Example 1. It adopts a low refractive index coating structure of hollow silica and solid silica composite. The refractive index of the topcoat is about 1.32, the solid content of the working liquid is controlled at 4 to 5 wt%, and the dry film thickness is about 95 to 125 nm.

[0148] IV. Double-layer coating structure and performance

[0149] In the double-layer antireflective coating structure formed by the above-mentioned base coating and top coating:

[0150] The refractive index of the base coating is n1 ≈ 1.42;

[0151] The refractive index of the surface coating is n2 ≈ 1.32;

[0152] The refractive index gradient is small, resulting in limited optical matching capability.

[0153] Under the same substrate, same topcoat structure and same process conditions, compared with Example 1, the double-layer coating structure of this comparative example is significantly insufficient in terms of light transmittance improvement. Its anti-transmittance effect is mainly limited by the fixed and unadjustable refractive index of the bottom coating.

[0154] V. Comparative Conclusions

[0155] A comparison between Comparative Example 1 and Example 1 shows that:

[0156] Traditional double-layer antireflective coatings typically use pure SiO2 as the base layer, which has a refractive index of approximately 1.42, thus lacking freedom in optical design.

[0157] With the same topcoat structure, it is difficult to further improve the overall antireflection effect of the double coating by relying solely on the traditional SiO2 undercoat.

[0158] In contrast, this invention achieves superior optical matching and anti-reflection effects by constructing a high refractive index undercoat with adjustable refractive index, without altering the pore structure and mechanical properties of the topcoat.

[0159] Comparative Example 2: A traditional double-layer antireflective coating structure using a high-porosity, low-refractive-index surface coating.

[0160] I. Purpose of Comparison

[0161] This comparative example illustrates another common design concept in the prior art: a double-layer antireflective coating, which improves the antireflective effect by further reducing the refractive index of the topcoat.

[0162] By comparing this comparative example with Example 1, and with the condition that the base coating still uses the traditional SiO2 system, we verify the problem of insufficient mechanical properties caused by simply increasing the porosity of the top coating to reduce the refractive index.

[0163] II. Preparation of the base coating (traditional SiO2 system)

[0164] The base coating in this comparative example is the same as that in Comparative Example 1, and was prepared using a pure SiO2 sol system.

[0165] Primer material: TEOS hydrolyzed silica sol

[0166] Refractive index of the primer: n1 ≈ 1.42

[0167] Inorganic solids content of the working fluid: 3-4 wt%

[0168] Dry film thickness: approximately 80–110 nm

[0169] The preparation method, coating process and drying conditions of the primer coating were kept the same as those of Comparative Example 1.

[0170] III. Preparation of the topcoat (high-porosity, low-refractive-index SiO2 topcoat)

[0171] (1) Structural characteristics of topcoat

[0172] The topcoat in this comparative example uses a high-porosity silica structure. By increasing the proportion of hollow structures or introducing a sol system with higher porosity, the effective refractive index of the topcoat is further reduced.

[0173] (2) Topcoat parameters

[0174] Topcoat material: High-porosity silica coating

[0175] Topcoat refractive index: n2 ≈ 1.25

[0176] Inorganic solids content of the working fluid: 4-5 wt%

[0177] Dry film thickness: approximately 95–125 nm

[0178] Compared to Example 1, this surface coating significantly improves the porosity of the film to achieve a lower refractive index, and its microstructure is more porous.

[0179] IV. Double-layer coating structure and performance

[0180] In the dual-layer antireflective coating structure consisting of the aforementioned base coating and high-porosity surface coating:

[0181] The refractive index of the base coating is n1 ≈ 1.42;

[0182] The refractive index of the surface coating is n2 ≈ 1.25;

[0183] The refractive index gradient is significantly larger than that in Example 1, which can improve the anti-reflection effect to a certain extent.

[0184] However, due to the significantly increased porosity of the topcoat, the film density and mechanical strength are significantly reduced.

[0185] V. Comparison Results and Conclusions

[0186] A comparison between Comparative Example 2 and Example 1 shows that:

[0187] By significantly reducing the refractive index of the surface coating, traditional technical approaches can achieve a certain degree of anti-reflection effect in optics.

[0188] However, this anti-reflective effect depends on the high porosity structure of the topcoat, which leads to a significant decrease in the hardness and wear resistance of the topcoat, making it prone to scratches or wear during the production, handling and assembly of photovoltaic modules.

[0189] In contrast, Example 1 optimizes the optical matching of the two layers by increasing the refractive index of the base coating, achieving an anti-reflection effect without significantly increasing the porosity of the top coating, thus balancing optical performance and mechanical reliability.

[0190] Example 2: A double-layer antireflective coating structure with a base coating refractive index of approximately n≈1.62.

[0191] I. Purpose of the Implementation Examples

[0192] Based on Example 1, this embodiment only adjusts the ratio of titanium source to silicon source in the base coating to reduce the effective refractive index of the base coating to about 1.62, thereby verifying the technical effect of the base coating refractive index being adjustable within a certain range in this invention.

[0193] Except for the primer coating ratio, the structure, coating process and tempering conditions of the other topcoat layers are consistent with those in Example 1.

[0194] II. Preparation of the base coating (n≈1.62)

[0195] (1) Raw materials

[0196] Silicon source: Tetraethoxysilane (TEOS)

[0197] Titanium source: Isopropyl titanate (TTIP)

[0198] Alcohol solvents: ethanol

[0199] Deionized water

[0200] Acidic catalyst: nitric acid or hydrochloric acid

[0201] (2) Primer sol formulation

[0202] (Based on 100 g of primer working fluid)

[0203]

[0204] In the above formulation, the mass of TEOS converted to SiO2 is approximately 1.50 g, the mass of isopropyl titanate converted to TiO2 is approximately 1.80 g, and the total inorganic solid content of SiO2 and TiO2 is approximately 3.3 wt%, which meets the process requirements for online roll coating.

[0205] (3) Preparation method of primer sol

[0206] The preparation method of the primer sol is basically the same as that in Example 1, including the following steps:

[0207] TEOS was added to a portion of ethanol, deionized water was added under stirring, and an acidic catalyst was slowly added dropwise to control the pH of the system at 1.5–2.5 for pre-hydrolysis of the silicon source.

[0208] Under acidic conditions, isopropyl titanate is slowly added to allow the titanium source and silicon-oxygen oligomer to undergo co-hydrolysis and co-condensation reactions simultaneously, forming an oligomeric network structure containing Si–O–Ti bonds.

[0209] Add the remaining ethanol to adjust the viscosity and solid content of the sol, and let it stand for 2-12 hours to obtain a stable and transparent base coat sol.

[0210] (4) Formation and properties of the primer coating

[0211] The above-mentioned primer sol is applied to the surface of the photovoltaic glass substrate by online roller coating and dried or pre-baked at 80-150°C to form a uniform and continuous primer coating.

[0212] The dry film thickness of the resulting base coating is controlled at approximately 80–110 nm, and its refractive index is approximately 1.62.

[0213] The base coating remained stable during the subsequent tempering process at 600–700°C, without significant phase separation or optical property drift.

[0214] III. Preparation of Topcoat

[0215] The surface coating in this embodiment is exactly the same as in Example 1, employing a low-refractive-index coating structure composed of hollow silica and solid silica:

[0216] Refractive index of surface coating: n2 ≈ 1.32;

[0217] Inorganic solids content of the working fluid: 4–5 wt%

[0218] Dry film thickness: approximately 95–125 nm.

[0219] IV. Effects of the Implementation Examples

[0220] Compared with Example 1, this example reduces the refractive index of the base coating to about 1.62, and obtains different optical matching states while keeping the structure and mechanical properties of the top coating unchanged, further demonstrating the adjustability of the refractive index of the base coating in this invention.

[0221] This embodiment demonstrates that by adjusting the ratio of silicon source to titanium source in the base coating, the optical performance of the double-layer antireflection and anti-reflection coating can be flexibly designed within a certain range without relying on increasing the porosity of the top coating.

[0222] Example 3: A double-layer antireflective coating structure with a base coat refractive index of approximately n≈1.58

[0223] I. Purpose of the Implementation Examples

[0224] Based on Examples 1 and 2, this embodiment further reduces the ratio of titanium source to silicon source in the undercoat to reduce the effective refractive index of the undercoat to about 1.58.

[0225] This embodiment further verifies the technical effect of continuously adjustable refractive index of the base coating within a wide range in this invention. Except for the base coating ratio, the structure, coating process, and tempering conditions of the remaining top coatings are kept consistent.

[0226] II. Preparation of the base coating (n≈1.58)

[0227] (1) Raw materials

[0228] Silicon source: Tetraethoxysilane (TEOS)

[0229] Titanium source: Isopropyl titanate (TTIP)

[0230] Alcohol solvents: ethanol

[0231] Deionized water

[0232] Acidic catalyst: nitric acid or hydrochloric acid

[0233] (2) Primer sol formulation

[0234] (Based on 100 g of primer working fluid)

[0235]

[0236] In the above formulation, the mass of TEOS converted to SiO2 is approximately 1.61 g, and the mass of isopropyl titanate converted to TiO2 is approximately 1.57 g. The total inorganic solid content of SiO2 and TiO2 is approximately 3.2 wt%, which is still within a reasonable range suitable for online roll coating.

[0237] (3) Preparation method of primer sol

[0238] The preparation method of the primer sol is basically the same as that in Example 1, including the following steps:

[0239] TEOS was added to a portion of ethanol, deionized water was added under stirring, and the pH of the system was controlled at 1.5–2.5 by adding an acidic catalyst dropwise to pre-hydrolyze the silicon source.

[0240] Under acidic conditions, isopropyl titanate is slowly added to induce co-hydrolysis and co-condensation reactions between the titanium source and the silicon-oxygen oligomer, forming an oligomeric network structure containing Si–O–Ti bonds.

[0241] Add the remaining ethanol to adjust the sol concentration and viscosity, stir evenly, and let it stand for 2-12 hours to obtain a stable and transparent base coat sol.

[0242] (4) Formation and properties of the primer coating

[0243] The above-mentioned primer sol is applied to the surface of the photovoltaic glass substrate by online roller coating and dried or pre-baked at 80-150°C to form a uniform and continuous primer coating.

[0244] The dry film thickness of the resulting base coating is controlled at approximately 80–110 nm, and its refractive index is approximately 1.58.

[0245] During the subsequent tempering process at 600–700°C, the base coating maintained structural stability and did not show significant degradation in optical performance.

[0246] III. Preparation of Topcoat

[0247] The surface coating in this embodiment is exactly the same as in Embodiments 1 and 2, employing a low-refractive-index surface coating structure composed of hollow silica and solid silica:

[0248] Refractive index of surface coating: n2 ≈ 1.32;

[0249] Inorganic solids content of the working fluid: 4–5 wt%

[0250] Dry film thickness: approximately 95–125 nm.

[0251] IV. Effects of the Implementation Examples

[0252] Compared with Examples 1 and 2, this example further reduces the refractive index of the base coating to about 1.58, thereby forming a new double-layer optical matching state without changing the pore structure and mechanical properties of the top coating.

[0253] This embodiment further demonstrates that by adjusting the ratio of silicon source to titanium source in the undercoat, the present invention can flexibly design a double-layer antireflection and anti-reflection coating structure over a wide refractive index range without relying on a high-porosity surface coating to achieve optical gain.

[0254] Example 4: A double-layer antireflective coating structure with a base coat refractive index of approximately n≈1.52

[0255] I. Purpose of the Implementation Examples

[0256] Based on Examples 1 to 3, this embodiment further reduces the proportion of titanium source to silicon source in the undercoat, thereby reducing the effective refractive index of the undercoat to about 1.52, which is used to cover the lower limit range of the refractive index of the undercoat in this invention.

[0257] Except for the primer coating ratio, the structure, coating process and tempering conditions of the other topcoat layers are kept the same.

[0258] II. Preparation of the base coating (n≈1.52)

[0259] (1) Raw materials

[0260] Silicon source: Tetraethoxysilane (TEOS)

[0261] Titanium source: Isopropyl titanate (TTIP)

[0262] Alcohol solvents: ethanol

[0263] Deionized water

[0264] Acidic catalyst: nitric acid or hydrochloric acid

[0265] (2) Primer sol formulation

[0266] (Based on 100 g of primer working fluid)

[0267]

[0268] In the above formulation, the mass of TEOS converted to SiO2 is approximately 1.84 g, the mass of isopropyl titanate converted to TiO2 is approximately 1.18 g, and the total inorganic solid content of SiO2 and TiO2 is approximately 3.0 wt%, which is still suitable for forming a uniform film by online roll coating.

[0269] (3) Preparation method of primer sol

[0270] The preparation method of the primer sol is basically the same as that in Examples 1-3, including the following steps:

[0271] TEOS was added to a portion of ethanol, deionized water was added under stirring, and the pH of the system was controlled at 1.5–2.5 by adding an acidic catalyst dropwise to pre-hydrolyze the silicon source.

[0272] Under acidic conditions, isopropyl titanate is slowly added to induce co-hydrolysis and co-condensation reactions between the titanium source and the silicon-oxygen oligomer, forming an oligomeric network structure containing Si–O–Ti bonds.

[0273] Add the remaining ethanol to adjust the sol concentration and viscosity, stir evenly, and let it stand for 2-12 hours to obtain a stable and transparent base coat sol.

[0274] (4) Formation and properties of the primer coating

[0275] The above-mentioned primer sol is applied to the surface of the photovoltaic glass substrate by online roller coating and dried or pre-baked at 80-150°C to form a uniform and continuous primer coating.

[0276] The dry film thickness of the resulting base coating is controlled at approximately 80–110 nm, and its refractive index is approximately 1.52.

[0277] The base coating remained structurally stable during the subsequent tempering process at 600–700°C, without any significant phase separation or optical performance failure.

[0278] III. Preparation of Topcoat

[0279] The surface coating in this embodiment is exactly the same as in Examples 1-3, employing a low-refractive-index surface coating structure composed of hollow silica and solid silica:

[0280] Refractive index of surface coating: n2 ≈ 1.32;

[0281] Inorganic solids content of the working fluid: 4–5 wt%

[0282] Dry film thickness: approximately 95–125 nm.

[0283] IV. Effects of the Implementation Examples

[0284] By reducing the refractive index of the base coating to approximately 1.52, this embodiment achieves another double-layer optical matching state while maintaining the structure and mechanical properties of the top coating.

[0285] This embodiment further demonstrates that the double-layer antireflective coating structure proposed in this invention can be designed over a wide range of refractive indices, and that even with a base coating refractive index close to that of the traditional SiO2 system, it can still achieve optical performance superior to the traditional double-coating scheme through structural design.

[0286] Example 5: High-refractive-index primer double-layer antireflective coating with Si–O–Ti–Zr co-condensation structure

[0287] I. Purpose of the Implementation Examples

[0288] This embodiment, based on embodiments 1-4, introduces a zirconium source to participate in the co-hydrolysis and co-condensation reactions of the silicon-titanium system, constructing a Si–O–Ti–Zr multi-element inorganic network structure to further improve the structural stability and high-temperature resistance of the undercoat. This embodiment verifies that the undercoat described in this invention not only achieves adjustable refractive index through the silicon-titanium system, but also further improves the structural stability of the coating during photovoltaic glass tempering processes at 600–700℃ by introducing zirconium.

[0289] II. Preparation of the base coating (Si–O–Ti–Zr, n≈1.66)

[0290] (1) Raw materials

[0291] Silicon source: Tetraethoxysilane (TEOS)

[0292] Titanium source: Isopropyl titanate (TTIP)

[0293] Zirconium source: n-propyl zirconate (CAS No. 23519-77-9) or n-butyl zirconate (CAS No. 1071-76-7)

[0294] Alcohol solvents: ethanol

[0295] Deionized water

[0296] Acidic catalyst: nitric acid or hydrochloric acid

[0297] (2) Primer sol formulation

[0298] (Based on 100 g of primer working fluid)

[0299]

[0300] In the above formulation, TEOS, titanate and zirconate are hydrolyzed and polycondensed to form SiO2, TiO2 and ZrO2 network units respectively, with the total inorganic solid content controlled at about 3.5 wt%, which is suitable for online roll coating process.

[0301] (3) Preparation method of primer sol

[0302] The preparation of the primer sol includes the following steps:

[0303] TEOS was added to a portion of ethanol, deionized water was added under stirring, and the pH of the system was controlled at 1.5–2.5 by adding an acidic catalyst dropwise, so that the silicon source would undergo pre-hydrolysis.

[0304] Under acidic conditions, isopropyl titanate is slowly added to induce co-hydrolysis and co-condensation reactions between the titanium source and the silicon-oxygen oligomer, forming a preliminary Si–O–Ti oligomer network.

[0305] Zirconate ester is then slowly added, allowing the zirconium source to further participate in the polycondensation reaction, forming a multi-component inorganic oligomer structure containing Si–O–Ti–Zr bonds;

[0306] Add the remaining ethanol to adjust the concentration and viscosity of the system, stir evenly, and let it stand for 2-12 hours to age, thus obtaining a stable and transparent primer sol.

[0307] (4) Formation and properties of the primer coating

[0308] The above-mentioned primer sol is applied to the surface of the photovoltaic glass substrate by online roller coating and dried or pre-baked at 80-150°C to form a uniform and continuous primer coating.

[0309] The dry film thickness of the resulting base coating is controlled at approximately 80–110 nm, and its refractive index is approximately 1.66.

[0310] After being tempered at 600–700℃ for photovoltaic glass, the base coating did not show obvious phase separation, crystal precipitation or optical performance degradation, exhibiting superior high-temperature structural stability compared to base coatings containing only silicon-titanium systems.

[0311] III. Preparation of Topcoat

[0312] The surface coating in this embodiment is exactly the same as in Examples 1-4, and uses a low refractive index surface coating formed by a composite of hollow silica and solid silica:

[0313] Refractive index of surface coating: n2 ≈ 1.32;

[0314] Inorganic solids content of the working fluid: 4–5 wt%

[0315] Dry film thickness: approximately 95–125 nm.

[0316] IV. Effects of the Implementation Examples

[0317] By introducing a zirconium source into the base coating and forming a Si–O–Ti–Zr co-condensation structure, this embodiment further improves the structural stability of the base coating under high-temperature tempering conditions while maintaining a high refractive index.

[0318] This embodiment demonstrates that the base coating of the present invention can not only achieve refractive index design by adjusting the ratio of silicon source to titanium source, but also enhance the heat resistance and structural integrity of the film by introducing zirconium element, thus making it more suitable for industrial application scenarios of online coating and pre-tempering coating of photovoltaic glass.

[0319] Comparative Example 3: A double-layer antireflective coating structure using TiO2 particles as a base coat for SiO2.

[0320] I. Purpose of Comparison

[0321] This comparative example illustrates a base coating technology that does not employ silicon-titanium co-hydrolysis and co-condensation reactions, namely, a scheme to improve the refractive index of the base coating by physically doping TiO2 nanoparticles into a traditional SiO2 sol system.

[0322] By comparing this comparative example with Examples 1-5, it is verified that it is difficult to obtain the structural uniformity, optical stability and high-temperature tempering adaptability achieved by the present invention by simply introducing titanium elements through particle doping.

[0323] II. Preparation of the base coating (TiO2 particle physical doping type)

[0324] (1) Raw materials

[0325] Silicon source: Tetraethoxysilane (TEOS)

[0326] Titanium source: Titanium dioxide nanoparticles (anatase or rutile, particle size 5–20 nm)

[0327] Alcohol solvents: ethanol

[0328] Deionized water

[0329] Acidic catalyst: nitric acid or hydrochloric acid

[0330] (2) Primer sol formulation

[0331] (Based on 100 g of primer working fluid)

[0332]

[0333] (3) Preparation method of primer sol

[0334] TEOS was added to a portion of ethanol, and deionized water was added under stirring. The pH of the system was controlled at 1.5–2.5 by adding an acidic catalyst dropwise, so that TEOS would undergo hydrolysis and condensation reaction to form SiO2 sol. TiO2 nanoparticles were pre-dispersed in ethanol and then added to the above SiO2 sol system after ultrasonic or high-speed dispersion treatment.

[0335] Continue stirring for 30–60 min to allow the TiO2 nanoparticles to form an apparent uniform dispersion in the sol. Then allow it to stand for 2–12 h to age, and obtain the primer sol.

[0336] (4) Formation and properties of the primer coating

[0337] The above-mentioned primer sol is applied to the surface of a photovoltaic glass substrate by online roller coating and dried or pre-baked at 80-150°C to form a primer coating.

[0338] The resulting base coating has a dry film thickness of approximately 80–110 nm and an initial refractive index of approximately 1.55–1.60.

[0339] III. Preparation of Topcoat

[0340] The surface coating in this comparative example is exactly the same as in Examples 1-5, employing a low-refractive-index surface coating structure composed of hollow silica and solid silica:

[0341] Refractive index of surface coating: n2 ≈ 1.32;

[0342] Inorganic solids content of the working fluid: 4–5 wt%

[0343] Dry film thickness: approximately 95–125 nm.

[0344] IV. Comparative Results and Problem Analysis

[0345] During the subsequent photovoltaic glass tempering process at 600–700℃, the undercoat layer with physical doping of TiO2 particles exhibited the following problems:

[0346] (1) Structural inhomogeneity: TiO2 nanoparticles are prone to agglomeration or crystal transformation under high temperature conditions, resulting in local refractive index inhomogeneity of the undercoating layer and affecting optical consistency;

[0347] (2) Insufficient optical performance stability: The refractive index and light transmittance of the base coating fluctuate significantly before and after tempering, making it difficult to meet the requirements of photovoltaic glass for stable anti-reflection effect;

[0348] (3) Poor interface compatibility: The relationship between TiO2 particles and SiO2 matrix is ​​mainly physical embedding, lacking stable chemical bonding, and is prone to micro-defects under thermal stress.

[0349] V. Comparative Conclusions

[0350] A comparison of Comparative Example 3 with Examples 1-5 shows that:

[0351] While physical doping with TiO2 nanoparticles can improve the refractive index of the undercoat to some extent, it is difficult to obtain uniform and stable optical properties.

[0352] In contrast, this invention constructs a stable Si–O–Ti or Si–O–Ti–Zr network structure through co-hydrolysis and co-condensation reactions of silicon, titanium (and zirconium) sources at the molecular or oligomerization level, fundamentally solving the problems of structural stability and optical consistency under high-temperature tempering conditions.

[0353] Therefore, the solution described in Comparative Example 3 cannot achieve the technical effects of the present invention.

[0354] Comparative Example 4: Si–Ti primer double-layer antireflection and anti-reflection coating structure prepared by asynchronous co-hydrolysis process

[0355] I. Purpose of Comparison

[0356] This comparative example illustrates a method for preparing a base coating that does not employ the simultaneous co-hydrolysis and co-condensation reaction of silicon and titanium sources. Specifically, the method involves first hydrolyzing either the silicon or titanium source separately, and then mixing them to form a base coating sol.

[0357] By comparing this comparative example with Examples 1-5, it is verified that even if the raw materials are the same, it is difficult to obtain the uniform and stable Si–O–Ti network structure and corresponding technical effects described in this invention if simultaneous co-hydrolysis and co-condensation are not achieved.

[0358] II. Preparation of the base coating (non-synchronous co-hydrolysis)

[0359] (1) Raw materials

[0360] Silicon source: Tetraethoxysilane (TEOS)

[0361] Titanium source: Isopropyl titanate (TTIP)

[0362] Alcohol solvents: ethanol

[0363] Deionized water

[0364] Acidic catalyst: nitric acid or hydrochloric acid

[0365] (2) Primer sol formulation

[0366] (Based on 100 g of primer working fluid)

[0367]

[0368] The overall inorganic solid content was approximately 3.3 wt%, which is close to that of Example 2, and was used to exclude the influence of solid content differences on the results.

[0369] (3) Non-synchronous co-hydrolysis preparation method

[0370] The primer sol was prepared using the following asynchronous hydrolysis process:

[0371] 1. Separate hydrolysis of silicon source: TEOS is added to a portion of ethanol, deionized water is added and an acidic catalyst is added dropwise to control the pH of the system at 1.5-2.5, so as to fully hydrolyze and condense TEOS to form a silica sol mainly composed of Si–O–Si bonds.

[0372] 2. Addition of titanium source afterward: Add isopropyl titanate directly to the SiO2 sol system formed above and disperse it under stirring conditions to allow the titanium source to undergo subsequent hydrolysis reaction;

[0373] 3. Add the remaining ethanol to adjust the sol concentration and viscosity, stir evenly, and let it stand for 2–12 h to obtain the primer sol. During this preparation process, the silicon source and titanium source did not undergo simultaneous hydrolysis and co-condensation reactions in the same reaction stage.

[0374] (4) Formation and initial properties of the base coating

[0375] The above-mentioned primer sol is applied to the surface of a photovoltaic glass substrate by online roller coating and dried or pre-baked at 80-150°C to form a primer coating.

[0376] The resulting base coating has a dry film thickness of approximately 80–110 nm and an initial refractive index of approximately 1.58–1.62.

[0377] III. Preparation of Topcoat

[0378] The surface coating in this comparative example is exactly the same as in Examples 1-5, using a low refractive index surface coating formed by a mixture of hollow silica and solid silica:

[0379] Refractive index of surface coating: n2 ≈ 1.32;

[0380] Inorganic solids content of the working fluid: 4–5 wt%

[0381] Dry film thickness: approximately 95–125 nm.

[0382] IV. Comparative Results and Problem Analysis

[0383] During the subsequent photovoltaic glass tempering process at 600–700℃, the base coating prepared using a non-synchronous co-hydrolysis process exhibited the following problems:

[0384] 1. Inhomogeneous chemical structure: Due to the asynchronous reaction between the silicon source and the titanium source, the undercoat is dominated by Si–O–Si and local Ti–O–Ti structures, with a low proportion of true Si–O–Ti bonds;

[0385] 2. Insufficient thermal stability: The thermal shrinkage behavior of different structural regions varies during the tempering process, which can easily lead to microscale structural inhomogeneity or optical property drift.

[0386] 3. Poor refractive index stability: There is a significant change in the refractive index of the base coating before and after tempering, resulting in poor repeatability of the double-layer anti-reflection and anti-reflection effects.

[0387] V. Comparative Conclusions

[0388] A comparison of Comparative Example 4 with Examples 1-5 shows that even using the same silicon and titanium sources, it is difficult to construct a stable and uniform Si–O–Ti network structure without simultaneous co-hydrolysis and co-condensation reactions. In contrast, the present invention significantly improves the formation ratio of Si–O–Ti bonds in the undercoat by simultaneously co-hydrolyzing and co-condensing the silicon and titanium sources under acidic conditions, thereby achieving superior optical stability and high-temperature tempering adaptability. Therefore, the technical solution described in Comparative Example 4 cannot achieve the technical effects of the present invention.

[0389] Film thickness optimization and process tolerance analysis of double-layer antireflective coating

[0390] In the dual-layer antireflective coating structures described in Examples 1-5 and Comparative Examples 1-4, the refractive indices of the base coating and the top coating are determined by the material system. Under the premise that the refractive indices are basically fixed, the antireflective and antireflective effect of the dual-layer coating is also closely related to the thickness of each layer. To further illustrate the film thickness adaptability and process tolerance range of the dual-layer coating structure in practical industrial applications, supplementary explanations are provided regarding the film thickness optimization of the dual-layer coating and its impact on light transmittance.

[0391] In this invention, the double-layer coating is preferably designed with the comprehensive light transmittance performance in the visible and near-infrared bands as the design objective. Combining the spectral response characteristics of photovoltaic modules, the 550–650 nm band is selected as the central wavelength range for anti-reflection design. Within this band, the film thickness of the base coating and the top coating can be initially designed according to the quarter-wavelength anti-reflection principle, and on this basis, a film thickness window suitable for industrial coating can be formed through process control.

[0392] With a refractive index of approximately 1.32, the dry film thickness of the topcoat is preferably controlled within the range of 104–124 nm. Within this thickness range, even with some film thickness fluctuations, the topcoat can still maintain a good anti-reflection effect in the visible light band, while also achieving high film density and surface hardness.

[0393] For the base coating, when its refractive index is in the range of approximately 1.52 to 1.66, the dry film thickness of the base coating is preferably controlled within the range of 82 to 109 nm. The specific target thickness can be adjusted accordingly with changes in the refractive index of the base coating. Within the above thickness range, the base coating and the top coating work synergistically to effectively reduce the reflection loss on the glass substrate surface, enabling the double-layer coating to achieve a stable increase in transmittance under solar spectral weighting conditions.

[0394] Comparative tests of different film thickness combinations revealed that, under a fixed refractive index, even slight deviations in the thickness of a single film layer can alter the optical interference state of the double-layer coating, resulting in corresponding fluctuations in transmittance. For the refractive index combination used in this invention, when the thickness deviation of the top or bottom coating is controlled within ±5 nm, the average transmittance change of the double-layer coating typically does not exceed approximately 0.15%; when the thickness deviation is controlled within ±10 nm, the average transmittance change typically does not exceed approximately 0.30%. This transmittance fluctuation range is within the acceptable engineering range for photovoltaic glass antireflection applications.

[0395] Therefore, within the aforementioned film thickness window range, the double-layer antireflective coating of the present invention is not sensitive to film thickness fluctuations, exhibiting a wider process tolerance platform, and is able to adapt to film thickness differences caused by changes in viscosity, linear speed, rolling pressure, or solvent evaporation rate in industrial coating methods such as online roll coating and spray coating.

[0396] In actual production, the thickness of the dry film can be controlled by adjusting the inorganic solid content of the coating solution, the coating speed, the roller gap, and the drying conditions. Preferably, the inorganic solid content of the topcoat coating solution is controlled at 4-5%, and the inorganic solid content of the bottomcoat coating solution is controlled at 3-4%. Under these conditions, the above-mentioned film thickness range can be obtained relatively stably, and the stability of the film structure and refractive index can be maintained during the subsequent tempering treatment at 600-700℃.

[0397] In summary, this invention, by rationally designing the film thickness and process tolerance of the base coating and top coating based on refractive index matching, enables the double-layer antireflective coating to achieve stable and repeatable light transmittance improvement while maintaining high surface hardness and tempering stability, demonstrating good industrial application value.

[0398] Table 1 shows the performance comparison results of the double-layer antireflective coating (original glass transmittance: 91.6-91.8%).

[0399] 1) Relative gain to bare glass: The increase in average light transmittance compared to uncoated photovoltaic glass substrates;

[0400] 2) Traditional double plating is a mass-produced conventional SiO2 base coating double-layer structure;

[0401] 3) All test samples were single-sided double-layer coating and tempered at 600–700℃.

[0402] Performance Comparison Analysis

[0403] Based on uncoated photovoltaic glass (average transmittance 91.6-91.8%), the transmittance gain of the traditional SiO2 undercoat double-layer antireflection and antireflection structure under mass production conditions is typically +2.2-2.4%, corresponding to an average transmittance of approximately 93.8-94.1% for tempered glass.

[0404] As shown in Table 1, the traditional double-coating scheme represented by Comparative Example 1 has limited optical matching capability due to the fixed refractive index of the base coating (≈1.42), and its light transmittance improvement is close to the engineering limit of this structure.

[0405] Comparative Example 2: By further reducing the refractive index of the surface coating, the light transmittance gain can be increased to +2.3 to 2.5%. However, this solution relies on a high porosity surface coating structure, which leads to a decrease in surface hardness to 2H and insufficient wear resistance, which is not conducive to the actual production and use of photovoltaic modules.

[0406] Although Comparative Examples 3 and 4 improved the refractive index of the undercoat by introducing titanium, the uniformity of the undercoat structure and high-temperature stability were insufficient due to the use of TiO2 particle physical doping or asynchronous co-hydrolysis processes, respectively. Their transmittance gain was still mainly concentrated in the range of +2.2% to 2.5%, failing to break through the engineering bottleneck of the traditional double-plating scheme.

[0407] In contrast, Examples 1-5 of this invention achieve simultaneous co-hydrolysis and co-condensation of silicon, titanium (and zirconium) sources under acidic conditions to construct Si–O–Ti or Si–O–Ti–Zr undercoatings with adjustable refractive index and uniform structure. This allows the double-layer coating to achieve a stable transmittance gain of +2.5 to 2.8% while maintaining the dense structure and high hardness (above 5H) of the topcoat. The overall performance is significantly better than that of the comparative schemes.

[0408] This invention addresses the problems of insufficient surface hardness and wear resistance in existing double-layer antireflective coatings for photovoltaic glass, where the refractive index of the base layer is difficult to control and the top layer relies on high porosity to achieve a low refractive index. A novel design approach for a double-layer antireflective coating is proposed. This invention introduces an inorganic oxide network structure formed by silicon-oxygen-titanium or silicon-oxygen-titanium-zirconium co-condensation into the base layer. While maintaining the density and mechanical properties of the base layer, this allows for effective control of its refractive index, achieving refractive index matching between the two layers without significantly increasing the porosity of the top layer. Based on this design, this invention can achieve antireflective and antireflective effects on the photovoltaic glass surface while maintaining surface hardness, wear resistance, and tempering stability. It overcomes the performance trade-offs inherent in traditional double-coating techniques that primarily focus on reducing the refractive index of the top layer, and has promising prospects for industrial application.

[0409] Data related to Examples 1-5:

[0410]

[0411] Comparative data for Examples 1–4:

[0412]

[0413] Table 1

[0414]

Claims

1. A photovoltaic glass double-layer antireflective coating structure with an adjustable refractive index undercoat, characterized in that, The coating comprises a base coating and a top coating sequentially disposed on the surface of a photovoltaic glass substrate, wherein: the base coating is an inorganic oxide network structure formed by silicon-oxygen-titanium co-condensation, the inorganic oxide network structure is formed by the simultaneous hydrolysis and co-condensation reaction of silicon source and titanium source under acidic conditions, and the titanium element in the base coating is introduced into the inorganic oxide network structure by chemical bonding; the top coating is a low refractive index and low porosity inorganic coating, the refractive index of which is lower than that of the base coating.

2. The double-layer anti-reflective coating structure according to claim 1, characterized in that, The refractive index of the base coating is 1.52 to 1.70, and the refractive index of the top coating is 1.28 to 1.

35.

3. The double-layer anti-reflective coating structure according to claim 1, characterized in that, The silicon source is selected from tetraethoxysilane, tetramethoxysilane, or a combination thereof; the titanium source is selected from tetrabutyl titanate, isopropyl titanate, or a combination thereof.

4. The double-layer anti-reflective coating structure according to claim 1, characterized in that, The base coating is an amorphous silicon-oxygen-titanium-zirconium inorganic oxide network structure formed by co-hydrolysis and co-condensation reactions of silicon, titanium and zirconium sources under acidic conditions.

5. The double-layer anti-reflective coating structure according to claim 4, characterized in that, The zirconium source is selected from butyl zirconate, n-propyl zirconate, or a combination thereof.

6. The double-layer anti-reflective coating structure according to claim 1, characterized in that, The dry film thickness of the base coating is 80–110 nm, and the dry film thickness of the top coating is 95–125 nm.

7. A method for preparing a primer sol, characterized in that, Includes the following steps: 1) Pre-hydrolysis of silicon source TMOS or TEOS, which serves as the silicon source, is added to a portion of ethanol. Deionized water is then added under stirring conditions, and an acidic catalyst is slowly added dropwise to adjust the pH of the system to 1.5–2.

5. Stirring is continued for 20–40 min to allow partial hydrolysis of the silicon source, forming silicon-oxygen oligomers. 2) Introduction of titanium source and co-condensation Under the condition of maintaining the acidity of the system, isopropyl titanate or tetrabutyl titanate, which serves as the titanium source, is slowly added to the above-mentioned silicon source pre-hydrolysis system and stirred continuously, so that the titanium source and silicon-oxygen oligomer undergo co-hydrolysis and co-condensation reactions simultaneously, gradually forming an oligomeric network structure containing Si–O–Ti bonds. 3) Adjustment and aging Add the remaining ethanol to adjust the concentration and viscosity of the sol, continue stirring for 10-20 min, and then let the resulting sol stand for aging for 2-12 h to obtain a stable, transparent or nearly transparent base coat sol suitable for film formation.

8. The method for preparing the primer sol as described in claim 7, characterized in that, Based on 100g of primer sol, the amount of silicon source used is 4.60-6.40g, the amount of titanium source used is 7.80-4.20g, the amount of deionized water used is 2.50g, the acidic catalyst is nitric acid or hydrochloric acid, and the remainder is ethanol.

9. A method for preparing a double-layer antireflective coating structure for photovoltaic glass, characterized in that, Includes the following steps: (1) A base coating sol with adjustable refractive index is prepared by simultaneously hydrolyzing and co-condensing silicon and titanium sources under acidic conditions. (2) The primer sol is applied to the surface of the photovoltaic glass substrate by online roller coating and pre-baked at 80-150°C to form a primer coating layer; (3) After the base coating is pre-baked, the topcoat sol is applied to the surface of the base coating by online roller coating and pre-baked at 80-150℃ to form the topcoat. (4) The photovoltaic glass with the base coating and top coating completed is sent into the tempering furnace and tempered at 600-700℃ to obtain a double-layer anti-reflective coating structure.

10. The method for preparing the double-layer antireflective coating structure for photovoltaic glass as described in claim 9, characterized in that, The preparation method of the topcoat sol includes the following steps: 1) Pre-hydrolysis of the binder phase Add some ethanol to the reaction vessel, add TEOS under stirring, then add deionized water, and slowly add acidic catalyst to adjust the pH of the system to about 2.0 to 3.

0. Continue stirring for 20 to 40 min to allow TEOS to undergo partial hydrolysis and form a silicon-oxygen oligomer binder phase. 2) Add solid silica sol Solid silica sol with a solid content of 30 wt% and an average particle size of about 5 to 30 nm was slowly added to the above pre-hydrolysis system and stirred for 15 to 30 min to fully mix the small-diameter solid silica particles with the binder phase in order to enhance the structural support of the film. 3) Add hollow silica sol Hollow silica sol with a solid content of 20 wt% and an average particle size of about 30-60 nm was added to the system in 2-3 portions and stirred evenly under low shear conditions to avoid damaging the hollow structure of the hollow silica particles. 4) Adjustment and aging Add the remaining ethanol to adjust the solid content and viscosity of the system. After stirring evenly, let the sol stand for 2 to 8 hours and filter it through a 0.45 to 1.0 μm filter membrane to obtain a stable surface coating sol. Based on 100g of surface-coated sol, the amount of hollow silica sol used is 9.50-11.50g, the amount of solid silica sol used is 5.50-7.50g, the amount of TEOS used is 0.80-2.50g, the amount of deionized water used is 0.50-0.80g, the acidic catalyst is nitric acid or hydrochloric acid, and the remainder is ethanol.

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