KR101254949B1 - Solar cell comprising anti-reflective glass with superhydrophilic and antifogging properties - Google Patents

Abstract

According to the present invention, there is provided a solar cell including an antireflective glass substrate having a porous structure layer having nano-sized pores formed on its surface through an etching process. The depth of the layer of the porous structure in the thickness direction of the glass substrate is smaller than the wavelength of incident light, and preferably may be 1/4 or less of the wavelength of the incident light.

Description

SOLAR CELL COMPRISING ANTI-REFLECTIVE GLASS WITH SUPERHYDROPHILIC AND ANTIFOGGING PROPERTIES}

The present invention relates to a solar cell including anti-reflective (AR) glass, and more particularly to an anti-reflective glass substrate having both super-hydrophilicity and antifogging properties. It relates to a solar cell comprising.

Various methods have been developed to improve the antireflection of substrates that can be used in functional units such as thin film solar cells in optical and optical-electric devices. As substrates of the optical element and the optical-electric element, glass substrates are widely used because of low cost, high visible light transmittance, low coefficient of thermal expansion, high resistance to mechanical scratches and excellent barrier properties against water and oxygen.

In the case of forming an antireflective coating on a glass substrate to impart antireflective properties, for an ideal antireflective coating, (1) the thickness of the AR coating is 1/4 or less of the incident light wavelength; (2) The refractive index of AR coating needs to satisfy the conditions of about 1.22 or less.

Where the refractive index is expressed as n _c = (n _a n _g ) ^1/2 (n _c , n _a , n _g are the refractive indices of the coating, air and glass, respectively), and in general the refractive index of glass is approximately 1.50, so n _c The ideal value of is 1.22. However, high density thin film materials with refractive indices as low as 1.22 are not available.

Examples of low refractive index materials used in optical devices include silica (SiO ₂ ), calcium fluoride (CaF ₂ ) and magnesium fluoride (MgF ₂ ), but these refractive indices are 1.46, 1.44 and 1.39, respectively. Falls short of

An alternative option is to use a coating of porous structure, in which the coating material and the air form a composite layer. In this case, the refractive index n _eff of the composite layer is a value between the refractive index of the coating material and 1, which can be controlled by changing the fractional volume ratio.

Several methods have been implemented to realize such porous coatings on glass substrates. These methods include sol-gel, polymer and / or oxide colloidal monolayers or multilayers, selective etching and dissolution of separated copolymers. However, polymers suffer from the disadvantages of thermal, mechanical and chemical instability, and are incompatible with current electronic device manufacturing processes because they are sensitive to high temperatures and plasma. In addition, colloids have poor mechanical durability due to weak bonding with glass substrates. Other methods, including vacuum technology and lithography, have the disadvantage of being expensive. Moreover, in order to realize the antireflection property, since a separate coating layer must be formed on the glass, not only does the number of processes increase and the cost increases, but also a lot of effort is involved in material selection. Therefore, an inexpensive, simple and large area application method is important for producing a wide range of high performance and durable antireflective coatings.

On the other hand, during actual operation, particularly externally operated devices, performance may be degraded as dust or foreign matter adheres to the exposed surfaces thereof. For this reason, it is desirable to combine self cleaning and antireflective properties for use in outdoor photovoltaic devices, display devices, self-cleaning windows and vehicle windshields. For self-cleaning, the surface must have super-hydrophobicity or super-hydrophilicity, but AR and self-cleaning in the real visible region are competing with each other. I can't.

According to the Wenzel model and the Cassie-Baxter model, a large surface roughness is needed to meet the requirements of superhydrophobic or superhydrophilic, but such rough surfaces usually cause severe light scattering, which can lead to anti-reflective properties. Can't. Photo-responsive coatings (TiO ₂ , ZnO, etc.) may also cause superhydrophilicity, but the refractive index is too large.

Porous structures can be an attractive choice since they have been used to make AR coatings as well as superhydrophilic and / or hydrophobic layers. However, in order to realize a highly transparent self-cleaning AR coating, it is very important to reduce light scattering by controlling the pore size, but until now, these two properties have not been realized at the same time.

It is known that reflection from the glass surface can be reduced by removing leachable components from the glass, leaving a porous skeletal layer. All such chemical treatments have the problem of using complex and acidic solutions optimized for virtually one particular type of glass, and high process temperatures (> 160 ° C). Moreover, in order to effectively reduce light reflection, a second treatment bath containing hazardous chemicals such as HF or fluoride is needed. In addition, there is a problem that the volume of the pores obtained through such a process is hardly controlled.

On the other hand, in a device such as a thin film solar cell, a glass substrate is essentially used. In the case of solar cells, it is necessary to increase the transmittance of light and to reduce the reflectance as much as possible, that is, to increase the antireflection property. That is, the solar cell efficiency can be improved by reducing the reflectance on the glass substrate surface as much as possible. However, in order to improve such anti-reflection characteristics as described above, conventionally, a coating having a reflection ring characteristic is simply formed on the glass substrate, or a coating composition which gives an anti-reflection effect is found and the glass substrate is used by using the composition. It is only at the level of coating (see, eg, Publication Nos. 10-2010-51090, 10-2010-19959). However, such a prior art forms a separate coating layer, which is accompanied with various problems as described above.

On the other hand, in the case of a windshield for a vehicle, if a frost or the like is formed, the view may be disturbed, which may cause a lot of difficulty in driving. In this regard, U.S. Patent Publication 2009-239017 discloses a film having antifogging properties on a glass surface to impart frost protection. However, this also requires a separate film layer, the same problem occurs as above.

As such, according to the related art, in order to give anti-reflection characteristics, anti-fogging characteristics, and self-cleaning characteristics to the glass, there are problems such as forming a coating layer made of a special coating or using harmful chemicals. Moreover, the method of imparting the above characteristics to one glass is not disclosed at all.

The present invention is to solve the problems shown in the prior art, one object of the present invention is to provide a solar cell comprising a glass that can increase the antireflection properties, that is, the transmittance is reduced and the reflectance without forming a separate coating layer on the glass To provide.

Another object of the present invention is to provide a solar cell comprising glass having effective antireflection properties using a simple and low cost method.

It is yet another object of the present invention to provide a solar cell comprising glass having antireflective properties without the use of hazardous chemicals such as HF or fluoride.

Still another object of the present invention is to provide a solar cell including glass having not only anti-reflective properties but also superhydrophilic and antifogging properties.

In order to achieve the above object, according to the present invention there is provided a solar cell comprising an anti-reflective glass substrate in which a layer of porous structure in which nano-sized pores are formed on the surface through an etching process.

In one embodiment, the depth of the layer of the porous structure in the thickness direction of the glass substrate is characterized by being smaller than the wavelength of incident light.

In one embodiment, the depth of the layer of the porous structure is characterized in that less than 1/4 of the wavelength of the incident light.

In one embodiment, the depth of the layer of porous structure is about 70 nm to 480 nm.

In one embodiment, the glass substrate of the porous structure is characterized by having anti-reflective properties, hydrophilic properties and anti-fogging properties.

In one embodiment, the glass substrate may be soda lime glass or aluminosilicate glass.

In one embodiment, the glass substrate may be soda lime glass containing 20% by mass or more of Na or aluminosilicate glass containing 20% by mass or less of aluminum.

In one embodiment, the alkaline solution can be used to form the porous structure.

In one embodiment, the alkaline solution may be a potassium hydroxide (KOH) solution.

According to the present invention, by forming a nano-sized porous structure on the surface through etching using an alkali bath, the reflectance is extremely reduced, the transmittance is increased, and may have superhydrophilicity and antifogging properties. In addition, there is no use of hazardous chemicals, no process for forming a separate coating layer is required, and anti-reflective and self-cleaning properties can be simultaneously achieved through etching at low temperatures.

1 is a photograph of SEM surface images with various etching times for glass substrate samples [(a): glass sample A, (b): glass sample B, (c): glass sample C].
2 shows the thickness of a nanosized porous layer formed in a glass sample over time of etching.
3 is a reflectance spectrum before and after etching of (a) glass sample A, and (b) transmittance spectrum before and after etching of glass sample A. FIG.
4 is a reflectance spectrum before and after etching of (a) glass sample B, and (b) transmittance spectrum before and after etching of glass sample B. FIG.
5 is a reflectance spectrum before and after etching of (a) glass sample C, and (b) a transmittance spectrum before and after etching of glass sample C. FIG.
6 shows the dynamic contact angles of the non-etched and etched states of glass sample A; (a) before etching, (b) after 0.5 hour etching, (c) after 1 hour etching, (d) after 2 hours etching, (e) after 4 hours etching, and (f) Shows antifogging properties of the etched glass substrate.
7 shows the dynamic contact angles of the non-etched and etched states of glass sample B, where (a) is before etching, (b) is after 0.5 hour etching, (c) is after 1 hour etching, and (d) is 2 hours etching After that, (e) shows the contact angle after 4 hours etching.
8 shows the dynamic contact angles of the non-etched and etched states of glass sample C, (a) before etching, (b) after 0.5 hour etching, (c) after 1 hour etching, and (d) 2 hours etching After that, (e) shows the contact angle after 4 hours etching.
9 shows the atomic ratio change (M / Si) changing as a function of the etching time of the glass substrate, where (a) represents Na / Si ratio and (b) represents Al / Si ratio.

Hereinafter, specific embodiments of the present invention will be described with reference to the accompanying drawings. In the following description, the description of technical constructions well known in the art will be omitted. Even if these explanations are omitted, those skilled in the art will readily understand the characteristic configuration of the present invention through the following description. In particular, in the following description, the glass is essentially contained in a solar cell such as a thin film solar cell, and description of the configuration of the solar cell including such a glass substrate is omitted. That is, the configuration of solar cells, including thin film solar cells, is well known and does not constitute the features of the present invention, and thus description thereof is omitted.

According to the present invention, a glass substrate having a porous surface layer having controllable wettability and AR properties by etching a conventional glass substrate in an alkaline solution (eg KOH) at low temperature (95 ° C.) and a method of manufacturing the same Initiate. The glass substrates produced exhibit increased transmittance (up to 97.7%) (ie lower reflectance), superhydrophilicity, magnetic cleaning and antifogging properties over a broad wavelength range.

Such glass substrates provide advantages for outdoor devices that require such a variety of properties, including anti-reflective properties such as thin film solar cells, display devices, automotive windshields, and the like. Tissue morphology and optical properties can be controlled through changes in etching time and glass composition.

Hereinafter, the present invention will be described in more detail with reference to specific experimental examples.

The inventors first of all have three types of glass substrates having the compositions shown in Table 1 [A: soda lime glass (relatively high Na content), B: lime soda glass (relatively low Na content), C: aluminosilicate Glass (relatively high Al content)], and experiments were carried out on the three glasses (content unit is% by mass).

Sample Kinds SiO ₂ Na ₂ O CaO MgO Al ₂ O ₃ Etc A Soda lime 61.58 27.42 2.09 7.12 1.49 0.30 B Soda lime 64.80 24.08 2.01 7.05 1.60 0.46 C Aluminosilicate 76.81 0.35 2.12 0.83 19.72 0.17

First, three glass substrate slides having the composition shown in Table 1 were washed with trichloroethylene, acetone and methanol under sonication and then rinsed with deionized water (DI). After drying in N ₂ gas, the glass substrate was etched by soaking in 50 mL of 0.1 M potassium hydroxide (KOH) solution for a predetermined time. These glass substrates were then placed in a water bath (95 ° C.) for different times. Finally, the glass substrates were removed and rinsed with deionized water.

The morphology of the etched glass surface was determined using FESEM (Hitachi S-4200), and the glass composition before and after etching was measured using an energy dispersive spectrum (EDS) (Oxford Instrumnets). UV-VIS-NIR transmittance and reflectance of the films were recorded with a spectrophotometer (Jasco V-570) for analysis of the optical properties. In addition, the static and dynamic contact angles (CA) of droplets of water were measured using a CA analyzer (Phoenix-300, SEO).

As is well known, the unetched glass surface is very smooth. However, the glass surface was etched as a result of supporting the glass in the alkaline solution (KOH in this experimental example) according to the above procedure. That is, the dense glass surface was divided into nanoflakes, with nanosized pores formed on both sides of the glass substrate. Tissue morphology and porous layer thickness can be controlled by varying etch time and glass composition (described below).

1 shows SEM images of glass substrates (Samples A, B, C) after etching for several different times (4 hours, 12 hours, 24 hours). Glass substrate sample A shows a uniform porous surface with a pore size of approximately 50 nm after etching up to 4 hours. When the etching time was increased to 12 hours, the nanoflakes were divided into smaller flakes, and after a longer etching time (24 hours), granular particles (100-200 nm) consisting of nanoflakes formed on the porous surface. .

Glass substrate sample B shows a very similar tissue morphology after etching, but the pore size and granular particles are two to three times larger than that of glass substrate sample A.

In contrast, glass substrate sample C shows different tissue morphology. Nanoflakes are very thick and large, with interstitical spaces formed between them. The surface roughness of glass substrate sample C is much larger than that of glass substrate samples A and B, and after a long etching time (24 hours), the nanoflakes were separated without forming any particles.

That is, the inventors have discovered that by etching the glass, a porous layer having nano-sized pores can be formed on the surface of the glass substrate, and the pore size of the porous layer can be controlled by changing the composition of the glass. . The thickness of the porous layer can be estimated from the cross-sectional SEM image (not shown).

2 shows the thickness of the porous layer of three glass substrates etched for several hours.

Referring to FIG. 2, the soda lime glass substrate samples (A, B) linearly increase in thickness of the porous layer, while the alumina silicate glass substrate sample (C) initially increases in thickness (<2 hours). It increases very slowly and linearly, but after 2 hours the etch rate tends to increase exponentially and eventually saturate.

After confirming that the porous structure can be formed on the surface of the glass substrate according to the above process, the present inventors evaluated the anti-reflection characteristics of the glass substrate having the porous structure. That is, reflectance and transmittance were measured for the glass substrate samples, and the results are shown in FIGS. 3 to 5.

In FIG. 3, (a) shows the change in reflectance with wavelength before and after etching of glass sample A, and (b) shows the change in transmittance with wavelength before and after etching of glass sample A. FIG. In FIG. 4, (a) shows the change in reflectance according to the wavelength before and after the etching of the glass sample B, and (b) shows the change in transmittance according to the wavelength before and after the etching of the glass sample B. In FIG. 5, (a) shows the change in reflectance with wavelength before and after etching of glass sample C, and (b) shows the change in transmittance with wavelength before and after etching of glass sample C.

First, in the case of glass substrate sample A, the glass substrate sample exhibits an average reflectance of about 9% in the 400-1500 nm range before etching. After etching for a short time (0.5 hour), the reflectance decreases over the entire range, and the reflectance rapidly decreases as the etching time increases. The lowest reflectance was obtained at around 630 nm after etching for 1.5 hours (0.95%). If the etching time exceeds 1.5 hours, the reflectance increased (reflectance increased, but its reflectance is low compared to unetched glass), which seems to be due to an increase in the thickness of the porous layer.

The decrease in reflectance can cause an increase in transmittance. This is because the size of the nanopores of the porous layer formed on the glass surface according to the present invention is much smaller than the visible light wavelength, especially when the size is smaller than 1/4 of the incident light wavelength, the scattering is prevented and the antireflection property is exhibited. Looking at the transmittance, the glass substrate sample A exhibits an average transmittance of 89% in the 400-1500 nm range before etching, and the transmittance increases over the entire range as the etching time increases. After 1.5 hours of etching, an optimized average transmittance of 94.5% and a maximum transmittance of 97.7% were observed at around 630 nm. As the etching time is further extended, the transmittance begins to decrease due to the increase in the thickness of the porous layer. Particles also act as scattering centers to reduce transmission.

In addition, in the case of the glass substrate sample B, since it has a similar composition to the glass substrate sample A, it has similar characteristics, but the maximum transmittance decreases to 95.7% (near 630 nm). Minimum reflectance is obtained (0.75%) at 640 nm for an etching time of 1.5 hours. In addition, the glass substrate sample C changes slowly in reflectance and transmittance with increasing etching time (up to 2 hours), and fluctuations in reflectance and transmittance as a function of wavelength are small. If the etching time exceeds 2 hours, the transmittance sharply decreases due to the increase in the thickness of the porous layer.

As such, it is clear that the initial composition of the glass substrate plays an important role in determining the antireflective properties.

On the other hand, for glass, a low refractive index of about 1.22 is needed to minimize light reflection. Based on the effective medium theory, n _eff of a composite layer is calculated by the following equation (1).

Where n _c and n _Air are the refractive indices of the coating and air, and f is the filling factor. The porous layer has a lower n _eff because air is present in the interstitial space. If the n _eff of the composite layer is close to the ideal value of 1.22, the reflection can be reduced efficiently. In current applications, f is controlled by pore size, which is highly dependent on etching time and glass composition. Also, as the glass is gradually etched, the n _eff of the porous layer will gradually change from the top of the glass to the bottom. It also acts favorably over a wide range of antireflection effects (i.e., due to varying sizes of pores in the porous layer, the antireflective effect appears over a wide range).

This inventor also evaluated the wettability property about the glass substrate formed as mentioned above as follows.

The rough and porous nature of the etched glass surface can significantly increase hydrophilicity. The relationship between the apparent contact angle (CA) and the roughness of the liquid droplets on the surface is given by the Wenzel equation (2).

는 거친 표면 상에서 관찰된 외견상 접촉각(CA)이고, θ는 매끄러운 표면에서의 대응하는 접촉각이며, γ는 투영된 표면적에 대한 실제 표면적의 비로 정의되는 표면 거칠기이다. γ의 값은 다공성 물질의 경우 매우 큰데, 이는 액적이 유리 기판 표면 상에 떨어지는 경우 완전한 젖음을 예상할 수 있다는 것을 의미한다. 상기한 것과 같이 에칭한 유리 기판들의 젖음 거동은 500 frmaes/s(프레임 사이의 시간 간격은 2ms)의 캡처 속도로 동작하는 비디오 CA 도구를 이용하여 검사하였다.
In this formula,

Is the apparent contact angle (CA) observed on the rough surface, θ is the corresponding contact angle at the smooth surface, and γ is the surface roughness defined by the ratio of the actual surface area to the projected surface area. The value of γ is very large for porous materials, which means that full wetting can be expected if the droplets fall on the glass substrate surface. Wetting behavior of the etched glass substrates as described above was examined using a video CA tool operating at a capture rate of 500 frmaes / s (2 ms time interval between frames).

Droplet contact angles CA of glass substrates A, B, and C before and after etching are shown in FIGS. 6 to 8.

6 shows the dynamic contact angles of the non-etched and etched states of glass sample A, where (a) is before etching, (b) is after 0.5 hour etching, (c) is after 1 hour etching, and (d) is 2 hours etching After that, (e) shows the contact angle after 4 hours etching, and (f) shows the antifogging properties of the etched glass substrate. 7 shows the dynamic contact angles of the non-etched and etched states of glass sample B, where (a) is before etching, (b) is after 0.5 hour etching, (c) is after 1 hour etching, and (d) is 2 hours etching After that, (e) shows the contact angle after etching for 4 hours. 8 shows the dynamic contact angles of the non-etched and etched states of glass sample C, (a) before etching, (b) after 0.5 hour etching, (c) after 1 hour etching, and (d) 2 hours etching After that, (e) shows the contact angle after etching for 4 hours.

First, for glass substrate sample A, the initial contact angle of the droplet when it was in film contact with the glass substrate surface was 76 °, slowly decreased to 65 ° after about 0.1 s, and the final static contact angle was about 35 °. As the etching time increased (0-4 hours), the surface became more hydrophilic, which can be seen by the decrease of the initial contact angle. The contact angle also decreases quickly with time after the droplets fall to the surface.

In the present invention, the thickness of the porous layer plays an important role in obtaining a superhydrophilic surface. As the etching time increases from 0.5 hours to 4 hours (thickness increases from 70 nm to 480 nm), the wet time required for the droplets to be added to the surface is drastically faster (ie, as the etching time increases, the wet time becomes shorter). Loses). For samples etched for 4 hours, the contact angle could not be measured within 48 ms, because the contact angle is extremely small, which means that the glass of the present invention exhibits superhydrophilic properties (CA <5 °).

Superhydrophilicity originates from two things: 1) The porous structure allows water to spread over the surface and pass through it; 2) It is rich in hydrophilic Si-OH bonds generated during etching.

Glass substrates B and C show better hydrophilic properties because the layers are thicker and the pore size is larger. Unlike TiO ₂ -based coatings that exhibit photocatalytic properties, the superhydrophilicity of the glass etched according to the present invention does not require UV irradiation and thus can be used in the dark.

In addition, superhydrophilicity can also lead to antifogging properties. In ordinary glass, moisture condenses as separate droplets on the surface, scattering light. However, after etching as described above, the glass surface becomes hydrophilic, thus allowing the condensation to form a continuous thin film, thereby having the ability to prevent scattering and prevent frosting. Antifogging properties of the glass surface of the present invention were demonstrated by exposing the etched glass (Glass A, 4 hour etching) and the non-etched glass to low temperature (-10 ° C.) and then to steam (from boiling water), The result is shown in FIG. As expected, the glass that was not etched immediately became dim (FIG. 6 (f) right), but the etched glass remained transparent (FIG. 6 (f) left). In other words, it was confirmed that the glass etched according to the present invention exhibited superior antifogging properties as compared to the glass not etched.

Hereinafter, the mechanism which exhibits the characteristic of the glass etched as mentioned above is demonstrated more concretely.

Atoms in the glass form an extended three-dimensional network, with poor symmetry and periodicity. The cations in the glass are divided into three groups: (1) network formers (Si, Zr, B), (2) network modifiers (Na, Ca) and (3) intermediates. (Al, Mg) can be divided. For network formers and modifiers, the binding energy with oxygen is greater than 335 kJ / mol and less than 210 kJ / mol. For mesons, the binding energy is 210 to 335 kJ / mol.

The ratio of these cations in the glass is important when determining the corrosion behavior. The corrosion mechanism is not yet clear, but there are some reactions that occur during corrosion. Namely (1) hydration and hydrolysis, (2) ion exchange and (3) network reconstitution. Water molecules can react with the glass surface via a hydrolysis reaction that is essentially combined with a reverse condensation reaction, as represented by equation (3). The hydrolysis reaction may be accompanied by network decomposition (see Equation 4), which is released into a water-soluble species of solution such as Si (OH) ₄ , leaving large voids for further reaction.

In the present invention, the network decomposition reaction plays an important role due to the high concentration of OH ⁻ . Ion exchange is an exchange of the glass-modified character cations ^{(Na +, K +, Ca} 2 + , etc.) and both (protons), the protons, as shown in Equation 5 and 6, H ₂ O and / or H ₃ O ^It originates from water molecules in the form of ⁺ .

Silanol groups (Si-OH) produced through ion exchange can be condensed into the Si-O-Si network by dehydration, as shown by the inverse reaction of equation (3). This reconstructs the glass surface, forming a porous material similar to the aggregation of colloidal silica particles, which is called network reconstruction. Corrosion of the glass is initiated by a hydrolysis reaction, which opens the channel through which ion exchange will take place. Ion exchange reactions provide voids that allow water and ions to penetrate into the glass. Thus, corrosion occurs preferentially in the region near the modifier ions, and more modifier ions in the structure can cause more etching channels.

On the other hand, the present inventors measured the elemental composition change occurring during the etching using EDS spectra on the upper and lower surfaces of the glass substrates A, B, and C before and after etching. As shown in Table 1, the soda lime glass substrates A and B exhibit high concentrations of Na. The Na concentration (27.42%) in glass substrate A is slightly higher than the concentration in glass substrate B (24.08%). For glass substrate C (aluminosilicate glass), the Na concentration is much lower (0.35%) and the concentration of meso Al is very high compared to glass substrates A and B (19.72%). The Si content in these glass substrates is A (61.58%) <B (64.80%) <C (76.81%).

To compare the corrosion behavior of different cations, the change in the atomic weight ratio of M / Si (M refers to cations in the glass) as a function of etch time was calculated. FIG. 9 shows the atomic ratio change (M / Si) changing as a function of the etching time of the glass substrate, where (a) represents Na / Si ratio and (b) represents Al / Si ratio.

In the case of the glass substrate A, the Na ratio decreases drastically, and the Al ratio gradually increases as the etching time becomes longer. In the case of glass substrate B, the change in Na ratio tends to be slightly slower than that of glass substrate A, decreasing and finally saturating after a long etching time. For glass substrate C, the Na ratio is stable at very low concentrations after etching. In the glass substrates A and B, the Al ratio is low and slightly increases after etching. In the case of glass substrate C, the Al ratio is very high and decreases with longer etching time. Saturation behavior is also observed after a long etch time.

In soda lime glass substrates (A, B), a rapid decrease in Na ratio indicates fast ion exchange. The binding energy between Na ions and non-bridge oxygen is low (94 kJ / mol) and can be easily attacked compared to Si-O-Si bonds (443 kJ / mol). Al-O bond energy is high (330-422 kJ / mol), which is relatively resistant to ion exchange. Thus, the atomic ratio of Al in the soda lime glass substrates A and B shows only a very small change during etching. In the case of the aluminosilicate glass substrate C, the Na content is so low that the etching channel will be initiated by the dissolution of Al. Therefore, as the etching becomes longer, the ratio of Al decreases significantly.

The tissue morphology can be determined by the composition of the glass. In soda lime glass substrates (A, B), the ratio of Na is high, which is first attacked by ion exchange. Following this process, water molecules diffuse through the pores left by the reaction and undergo hydrolysis and dissolution reactions. Etching selectively occurs much faster at the original Na ion location, and pores may be formed at this location after the new network is formed. Thus, for the soda lime glass substrate A with a higher Na content, the number of pores is much higher and the pore size is smaller compared to the soda lime glass substrate B with a lower Na content. In the aluminosilicate glass substrate C, the Na content is very low, and etching is more likely to occur at the Al site. Thus, compared to soda lime glass, the number of pores is much smaller and the pore size is larger.

The analysis results are summarized as follows. To etch the glass, a etchable solution such as an alkali bath (KOH in the example) is used and the process temperature is relatively low (about 95 ° C.). Etched glass shows nanoporous surfaces on both sides. Over a wide wavelength range, reflections have been efficiently reduced and transmittances have increased. Porous antireflective layers have less angular dependence and thus have an antiglare effect, which is important in many devices such as displays. The process does not require an additional porous coating on the glass, which can provide an advantage for mechanical stability (eg wear resistance). Also, no HF or fluoride is used. In addition, the surface exhibits superhydrophilic properties and antifogging effects are also demonstrated, providing advantages for devices operating outdoors such as in high humidity environments or underwater. Tissue morphology, composition, surface and optical properties are well controlled by varying the original composition and etching time.

On the other hand, the present invention also relates to various external operating devices comprising an antireflective glass substrate manufactured by the above-described method. Since the antireflection glass substrate is the same as the configuration of the above-described embodiment, overlapping description is omitted. The external operating device may be one of a photovoltaic device comprising a glass, a solar cell device, a display device, a self-cleaning window and a vehicle windshield.

While the present invention has been described with reference to the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. That is, the present invention can be variously modified and modified within the scope of the following claims, all of which are within the scope of the present invention. Accordingly, the invention is limited only by the claims and the equivalents thereof.

Claims (9)

A solar cell comprising antireflective glass,
The glass includes a glass layer of a porous structure having nano-sized pores integrally formed on the surface through an etching process, wherein the glass layer of the porous structure is not a separate coating layer formed on the surface of the antireflective glass. And the surface of the glass is etched through the etching process and formed of the same material as the antireflective glass. The solar cell of claim 1, wherein a depth of the layer of the porous structure in the thickness direction of the glass is smaller than a wavelength of incident light. The solar cell of claim 2, wherein the depth of the layer of the porous structure is 1/4 or less of a wavelength of incident light. The solar cell of claim 1, wherein a depth of the layer of the porous structure is 70 nm to 480 nm. The solar cell of claim 1, wherein the glass of the porous structure has anti-reflective properties, hydrophilic properties, and anti-fogging properties. The solar cell according to any one of claims 1 to 5, wherein the glass is soda lime glass or aluminosilicate glass. The solar cell according to claim 6, wherein the glass is soda lime glass containing 20% by mass or more of Na or aluminosilicate glass containing 20% by mass or less of aluminum. The solar cell according to claim 7, wherein the porous structure is formed using an alkaline solution. The solar cell of claim 8, wherein the alkaline solution is a potassium hydroxide (KOH) solution.

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