Alcohol-free flocking liquid based on amphiphilic three-component system as well as preparation method and application of alcohol-free flocking liquid

Abstract

The invention relates to an alcohol-free flocking liquid based on an amphiphilic three-component system and a preparation method and application of the alcohol-free flocking liquid in the field of solar photovoltaic cell manufacturing consumables, and the flocking liquid is an oil-in-water emulsion and comprises the following components: 15-19.52 wt% of potassium hydroxide, 2.4-25 wt% of n-heptanoic acid and 60-78.08 wt% of water. The flocking liquid has wide-range temperature stability, and is not layered by high-rotating-speed centrifugation. The silicon wafer flocking agent is low in biotoxicity, clear and transparent in state, easy to clean and capable of being used for monocrystalline silicon wafer flocking, and the flocked silicon wafer is low in surface reflectivity.

Description

Technical Field

[0001] The invention relates to a consumable material used in the manufacture of solar photovoltaic cells, and in particular to a method for preparing a flocking liquid. Background Art

[0002] In order to achieve sustainable development of energy and environment, countries around the world have made solar photovoltaic power generation a key focus of new energy and renewable energy development, making the solar photovoltaic industry one of the fastest growing industries in the world. There are many types of solar photovoltaic cells. From the perspective of materials, solar photovoltaic cells can be divided into two categories: silicon semiconductors and multi-component conductors. Silicon semiconductor solar photovoltaic cells include monocrystalline silicon cells, polycrystalline silicon cells and amorphous silicon cells. Monocrystalline silicon cells are increasingly becoming a hot topic in photovoltaic industry research due to their high photoelectric conversion efficiency and mature integrated circuit technology.

[0003] The manufacturing process of conventional monocrystalline silicon solar photovoltaic cells is: monocrystalline silicon wafer - silicon wafer surface treatment - velvet preparation - diffusion junction - back junction removal - preparation of anti-reflection film - corrosion of the periphery - preparation of upper and lower electrodes - inspection and testing. The preparation of velvet, also known as flocking, is an extremely critical process in the manufacturing process of solar photovoltaic cells because it can form a "pyramid" structure on the surface of monocrystalline silicon, reduce the light reflectivity of the silicon-based surface, increase the short-circuit current of the photovoltaic cell, and thus improve its photoelectric conversion efficiency.

[0004] Flocking is the texturing of the surface of crystalline silicon, that is, reducing the light reflectivity by changing the surface structure of the silicon base. Taking the single crystal silicon alkali process as an example, its principle is OH - With single crystal silicon <100> The reaction rate of the surface is <111> The surface of the silicon substrate is several times or even dozens of times larger than that of the silicon substrate (its ratio is called the anisotropy factor AF), thereby forming a "pyramid" structure on the silicon-based surface and forming a light trap, thereby increasing the incident area and reflection times of light, and ultimately reducing the light reflectivity and improving the photoelectric conversion efficiency. The existing surface flocking methods include: chemical corrosion, reactive ion etching, photolithography, mechanical grooving, etc. Among them, although photolithography can produce a more regular velvet structure, it has always remained in the laboratory stage; photolithography and mechanical grooving can obtain lower silicon wafer surface reflectivity, but the slow production speed and high cost have become bottlenecks restricting its industrial production. The chemical corrosion method has been widely used in industrial production due to its low production cost, high efficiency and simple method. There are many types of flocking liquid used for chemical corrosion, and the following are common ones:

[0005] (1).NaOH(KOH)+H2O+isopropanol

[0006] (2).TMAH+H2O

[0007] (3).Na2CO3+NaHCO3+H2O

[0008] (4).Na3PO4+H2O

[0009] (5).Na2SiO3+H2O

[0010] The flocking liquid system of NaOH (KOH) + H2O + isopropyl alcohol (IPA) is currently the most commonly used flocking system in the industry. After etching the monocrystalline silicon wafer with NaOH (KOH) + H2O + isopropyl alcohol solution, an anti-reflection velvet surface with low surface reflectivity can be obtained. However, due to the low boiling point and volatility of isopropyl alcohol, the flocking effect is unstable, the repeatability is poor, and the "spotted" phenomenon occurs, which seriously affects the appearance and photoelectric conversion efficiency of the battery cell. Therefore, the development of an efficient and environmentally friendly alcohol-free flocking liquid has become a hot topic in the photovoltaic industry. As a result, alcohol-free flocking liquids such as TMAH + H2O and Na2CO3 + NaHCO3 + H2O have emerged. However, they ultimately failed to completely replace the isopropyl alcohol flocking liquid. For example, although TMAH (tetramethylammonium hydroxide) flocking liquid can obtain a lower reflectivity than isopropyl alcohol flocking liquid, it has the disadvantages of high cost and high pollution, and cannot be used in industrial production on a large scale; although Na2CO3+NaHCO3+H2O flocking liquid has low cost and is green and environmentally friendly, it cannot obtain a lower light reflectivity and cannot meet the needs of industrial production. Therefore, seeking a new type of efficient and environmentally friendly flocking liquid is still the goal of the current photovoltaic solar cell industry. Summary of the invention

[0011] The purpose of the present invention is to provide an alcohol-free flocking liquid based on an amphiphilic three-component system, which has good stability, is clear and transparent, is easy to clean, and has a lower surface reflectivity of a silicon wafer after flocking.

[0012] To this end, the technical solution of the present invention is: an alcohol-free flocking liquid based on an amphiphilic three-component system, wherein the flocking liquid is an oil-in-water emulsion, and the components include 15-19.52wt% potassium hydroxide, 2.4-25wt% n-heptanoic acid and 60-78.08wt% water.

[0013] Furthermore, the amount of potassium hydroxide used is 1 / 4 of the weight of water.

[0014] As a preferred embodiment of the present invention, the flocking liquid components include 16.67 wt% potassium hydroxide, 16.67 wt% n-heptanoic acid and 66.67 wt% water.

[0015] The preparation method of the alcohol-free flocking liquid based on the amphiphilic three-component system is prepared according to the following steps:

[0016] (1) Weighing 15-19.52 wt% of potassium hydroxide, 2.4-25 wt% of n-heptanoic acid and 60-78.08 wt% of water according to weight percentage; the water used is preferably ultrapure water;

[0017] (2) mixing solid potassium hydroxide with water, and stirring at room temperature and pressure to obtain a potassium hydroxide aqueous solution;

[0018] (3) adding n-heptanoic acid into the potassium hydroxide aqueous solution and stirring and dispersing the mixture uniformly, thereby obtaining the target product, an alcohol-free flocking liquid based on an amphiphilic three-component system.

[0019] The obtained alcohol-free flocking liquid based on the amphiphilic three-component system is used for flocking the surface of a single-crystal silicon wafer, with a flocking temperature of 75° C. and an etching time of 30 minutes.

[0020] The amphiphilic molecule heptanoic acid in the present invention has wetting and emulsifying effects, and can reduce the surface tension of the flocking liquid and improve the adsorption capacity of the flocking liquid on the surface of the silicon wafer. In the process of flocking on the surface of single crystal silicon, the coverage and size distribution of the "pyramid" structure on the silicon-based surface can be adjusted by changing the concentration of heptanoic acid, the temperature of the system, and the ratio of heptanoic acid to potassium hydroxide.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1. The flocking liquid of the present invention has the effect of low biological toxicity.

[0023] 2. It has a wide range of temperature stability and high-speed centrifugation without stratification.

[0024] 3. The flocking liquid is clear and transparent and easy to clean.

[0025] 4. Compared with the traditional IPA flocking process, the problem of unstable flocking effect caused by the low boiling point of IPA is overcome. At the same time, under the conditions of lower flocking temperature (75°C) and shorter reaction time (30min), the reflectivity of this flocking system is lower, especially at a wavelength of 800-1000nm, which is about 0.56-0.85 percentage points lower. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is KOH / n-C6H at 75°C of the present invention. 13 Phase diagram of the COOH / H2O amphiphilic three-component system.

[0027] In the figure, 1: O / W region; 2: W / O region; line a: KOH / H2O=1 / 4 (wt / wt-mass percentage, the same below), line b: C6H 13 COOH / KOH=1 / 1 (wt / wt); line c: C6H 13COOH / H2O=1 / 4 (wt / wt).

[0028] Figure 2 The present invention is a flow chart for preparing the novel alcohol-free flocking liquid.

[0029] Figure 3 The present invention is a flow chart of flocking a single crystal silicon surface with a novel flocking liquid based on a three-component system of amphiphilic molecules.

[0030] Figure 4 This is a scanning electron microscope (SEM) image of the new type of flocking liquid based on the amphiphilic molecule three-component system of the present invention and other types of flocking liquids tested on the surface of single crystal silicon. KOH / H2O is fixed at 1 / 4 (wt / wt). In the figure, a: original silicon wafer; b: KOH / H2O; c: KOH / C6H 13 COOH / H2O; d:KOH / IPA / H2O.

[0031] Figure 5 This is a graph of the visible-infrared spectral reflectance of the new type of flocking liquid based on the amphiphilic molecule three-component system of the present invention and other types of flocking liquids tested on the surface of single crystal silicon. Fixed KOH / H2O = 1 / 4 (wt / wt). In the figure, a: original silicon wafer; b: KOH / H2O; c: KOH / C6H 13 COOH / H2O; d:KOH / IPA / H2O. DETAILED DESCRIPTION

[0032] The following examples further illustrate the acquisition process of the present invention and verify the technical effects of the present invention.

[0033] The study of how the state of a two-phase or multi-phase system changes with the change of variables such as temperature, pressure and concentration, and the use of graphics to represent the change of the system state, this kind of diagram is called a phase diagram. Phase diagrams have important theoretical guiding significance in studying the phase behavior between substances and in industrial production. Figure 1 is KOH / n-C6H at 75°C of the present invention. 13 Phase diagram of COOH / H2O amphiphilic molecule three-component system. In this invention, in view of a series of problems existing in current flocking liquid, a phase diagram is designed and used as a guide. Figure 1 It is known that the alcohol-free flocking liquid of the present invention has two clear zones, namely zone 1 (O / W type - oil-in-water emulsion) and zone 2 (W / O type - water-in-oil emulsion), and the weight percentage range of each component in the two zones is:

[0034] Zone 1: n-heptanoic acid is 0-47.49wt%, potassium hydroxide is 0-50wt%, and water is 46.24wt%-100wt%.

[0035] Zone 2: n-heptanoic acid is 62.54 wt% to 100 wt%, potassium hydroxide is 0 to 12.45 wt%, and water is 0 to 37.47 wt%.

[0036] Since the viscosity of the flocking solution in zone 2 is greater than that in zone 1, it is not conducive to the escape of hydrogen bubbles during the flocking process of single crystal silicon, and the high content of n-heptanoic acid and high cost are not conducive to large-scale industrial flocking. Therefore, the present invention selects the flocking solution from zone 1.

[0037] Figure 1 The solid lines a, b, and c represent the methods for preparing and screening flocking liquid samples. The preparation process is as follows: Figure 2 shown.

[0038] Example 1

[0039] The invention discloses an alcohol-free flocking liquid based on an amphiphilic three-component system. The flocking liquid is an oil-in-water emulsion, and the components include 16.67 wt % of potassium hydroxide, 16.67 wt % of n-heptanoic acid and 66.67 wt % of water.

[0040] The preparation method of the alcohol-free flocking liquid based on the amphiphilic three-component system is prepared according to the following steps:

[0041] (1) Weighing potassium hydroxide, n-heptanoic acid and ultrapure water according to the above weight percentages;

[0042] (2) mixing solid potassium hydroxide with ultrapure water, and stirring at room temperature and pressure to obtain a potassium hydroxide aqueous solution;

[0043] (3) adding n-heptanoic acid into the potassium hydroxide aqueous solution and stirring and dispersing the mixture uniformly, thereby obtaining the target product, an alcohol-free flocking liquid based on an amphiphilic three-component system.

[0044] The flocking liquid is used for flocking the surface of a single crystal silicon wafer, the flocking temperature is preferably 75° C., and the etching time is preferably 30 minutes.

[0045] like Figure 3 As shown, single crystal silicon flocking can be divided into three main processes: 1. Cleaning of single crystal silicon wafers; 2. Damage removal before flocking; 3. Flocking of single crystal silicon wafers.

[0046] The specific implementation is as follows:

[0047] 1. Cleaning of single crystal silicon wafers

[0048] A 0.5 cm×0.5 cm single crystal silicon wafer was placed in acetone and ethanol for ultrasonic cleaning for 20 min respectively, and finally placed in a large amount of high-purity deionized water for ultrasonic cleaning for 30 min, dried and set aside.

[0049] 2. Damage treatment before flocking

[0050] The silicon wafer treated in 1 is placed in a 20wt% KOH aqueous solution, maintained at a constant temperature of 80°C, the reaction time is 30s, and then washed with a large amount of high-purity deionized water and dried to obtain a single crystal silicon wafer treated for damage removal.

[0051] 3. Flocking of monocrystalline silicon wafers

[0052] The single crystal silicon wafer treated in step 2 is placed in the prepared new alcohol-free flocking liquid based on the amphiphilic molecule three-component system, maintained at a constant temperature of 75° C., the reaction time is 30 minutes, and then washed with a large amount of high-purity deionized water and dried.

[0053] Technical effect verification 1:

[0054] The surface morphology of the flocked single crystal silicon wafer was observed using a field emission scanning electron microscope (SEM). Figure 4 ), and its reflectivity was measured by UV-visible-near infrared absorption spectrometer ( Figure 5 ). In KOH / C6H 13 In the COOH / H2O flocking system, when the flocking liquid composition is C6H 13 COOH: 16.67wt%, KOH: 16.67wt%, H2O: 66.67wt%, etching time is 30min, reaction temperature is 75℃, the reflectivity of the best anti-reflection suede is 10.02%, which is 0.56-0.85 percentage points lower than the reflectivity of the traditional IPA process, and the reflectivity of the suede is weakly dependent on the spectrum between 700-1000nm.

[0055] On the basis of Example 1, KOH / H2O=1 / 4 (wt / wt) was fixed, and C6H 13 COOHwt%, and the reflectivity of the single crystal silicon wafer samples after flocking with each flocking liquid was tested, as shown in Table 1.

[0056] Table 1 Composition of flocking liquid and reflectivity after flocking

[0057] serial number KOHwt% <![CDATA[C6H 13 COOHwt%]]> <![CDATA[H2Owt%]]> Reflectivity % 1 20 0 80 12.05 2 19.52 2.4 78.08 10.88 3 18.8 6 75.2 10.27 4 18 10 72 10.18 5 16.67 16.67 66.66 10.02 6 16 20 64 10.16 7 15.6 22 62.4 10.65 8 15 25 60 10.39 9 14.4 28 57.6 12.25 10 13.80 31 55.2 12.71

[0058] As can be seen from Table 1, when KOH / H2O=1 / 4 (wt / wt), potassium hydroxide 15-19.52wt%, heptanoic acid 2.4-25wt% and water 60-78.08wt%, the prepared flocking liquid has a corresponding reflectivity of less than 11wt%, which is an alcohol-free flocking liquid with excellent performance.

[0059] KOH / C6H 13The flocking process of COOH / H2O alcohol-free flocking liquid is simple, and the flocking temperature and flocking time are lower than those of the commercial IPA process. At the same time, heptanoic acid has low toxicity and a high boiling point, which solves the major problems in the traditional IPA process. It is a new, efficient and environmentally friendly flocking liquid with great development potential.

[0060] The flocking liquid has low biological toxicity, temperature stability in a wide range, and no stratification during high-speed centrifugation.

[0061] The present invention is not limited to the above-mentioned embodiments. On the basis of the technical solution disclosed in the present invention, technicians in this field can make some substitutions and deformations to some technical features therein according to the disclosed technical content without creative labor, and these substitutions and deformations are all within the protection scope of the present invention.

Claims

1. An alcohol-free flocking liquid based on an amphiphilic three-component system, characterized in that: The flocking liquid is an oil-in-water emulsion, and its components include 15-19.52 wt % of potassium hydroxide, 2.4-25 wt % of n-heptanoic acid and 60-78.08 wt % of water.

2. The alcohol-free flocking liquid based on the amphiphilic three-component system according to claim 1, characterized in that: The amount of potassium hydroxide used is 1 / 4 of the weight of water.

3. The alcohol-free flocking liquid based on the amphiphilic three-component system according to claim 1, characterized in that: The flocking liquid components include 16.67 wt % potassium hydroxide, 16.67 wt % n-heptanoic acid and 66.67 wt % water.

4. The method for preparing alcohol-free flocking liquid based on an amphiphilic three-component system according to claim 1, characterized in that: Prepare as follows: (1) Weigh 15-19.52wt% potassium hydroxide, 2.4-25wt% heptanoic acid and 60-78.08wt% water according to weight percentage; (2) mixing solid potassium hydroxide with water, and stirring at room temperature and pressure to obtain a potassium hydroxide aqueous solution; (3) Add n-heptanoic acid to the potassium hydroxide aqueous solution and stir to disperse it evenly, thereby obtaining the target product, an alcohol-free flocking liquid based on an amphiphilic three-component system.

5. The method for preparing alcohol-free flocking liquid based on amphiphilic three-component system according to claim 1, characterized in that: The water used was ultrapure water.

6. The use of the alcohol-free flocking liquid based on the amphiphilic three-component system according to claim 1, characterized in that: The flocking liquid is used for flocking the surface of a single crystal silicon wafer, the flocking temperature is 75° C., and the etching time is 30 minutes.

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