WO2001047033A1

WO2001047033A1 - Photoelectric transducer and substrate for photoelectric transducer

Info

Publication number: WO2001047033A1
Application number: PCT/JP2000/009056
Authority: WO
Inventors: Tsuyoshi Otani; Toshifumi Tsujino; Yasunori Seto; Masahiro Hirata; Katsuhiko Kinugawa; Tetsuro Kawahara
Original assignee: Nippon Sheet Glass Co., Ltd.
Priority date: 1999-12-20
Filing date: 2000-12-20
Publication date: 2001-06-28

Abstract

The invention provides a substrate for a photoelectric transducer, which comprises a transparent body having a principal surface covered with antireflection coating containing fine silica-base particles of particle size of greater than 300 nm. Preferably, the antireflection coating further contains silica-base particles different in particle size from the above-mentioned particles. A photoelectric layer consisting of crystalline silicon film may be formed on the substrate in order to obtain a thin-film photoelectric transducer with very high photoelectric efficiency.

Description

Description: Substrate for photoelectric conversion device and photoelectric conversion device provided with the same

The present invention relates to a substrate used for a photoelectric conversion device such as a solar cell panel. Further, the present invention relates to a photoelectric conversion device using the substrate.

Background art

Currently, photoelectric conversion devices generally used include a “thin film type” using amorphous silicon for the photoelectric conversion layer and a “crystal type” using silicon crystal. Thin-film type photoelectric conversion devices consist of a transparent conductive film such as tin oxide, zinc oxide or tin-doped indium oxide (IT〇) on one main surface of a transparent substrate such as a glass plate or a resin sheet, and an amorphous A photoelectric conversion layer made of silicon is further added to aluminum, silver, or zinc oxide.

(ΖηΟ ₂ ) and the like. On the other hand, the crystal-type photoelectric conversion device has a structure in which a photoelectric conversion element composed of a single-crystal silicon / polycrystalline silicon wafer is sandwiched between two substrates and sealed. The substrate on the light incident side must be transparent, and a glass plate is usually used (hereinafter, this transparent substrate is referred to as “cover glass”).

With the emergence of energy problems in recent years, photoelectric conversion devices, especially solar panels, have attracted public attention. Above all, the above-mentioned thin-film solar cell panel is considered to become the mainstream in the future because of the low energy cost at the manufacturing stage. Tin oxide films formed by methods involving thermal decomposition and oxidation of raw materials, such as chemical vapor deposition (CVD), are frequently used as transparent conductive films in thin-film photoelectric conversion devices. In addition, between the transparent conductive film and the transparent substrate, especially the glass plate, there is a force such as sodium contained in the glass plate. A base film is provided to prevent the components from diffusing into the transparent conductive film and lowering the electrical conductivity of the transparent conductive film (increase in resistance). A transparent thin film made of silica (Si〇, etc.) is preferably used for the underlayer. In order to increase the photoelectric conversion rate of the thin-film photoelectric conversion device, the transparent conductive film has a high transmittance (the photoelectric conversion layer More light), lower resistance (less loss when extracting the generated current), and contribution to light confinement in the photoelectric conversion layer. As a technique that can contribute to confinement, there is known a method of forming irregularities of an appropriate size on the surface of a transparent conductive film (Japanese Patent Application Laid-Open No. 58-57756).

Further, by improving components other than the transparent conductive film, the photoelectric conversion rate of the thin-film photoelectric conversion device can be increased. For example, by providing an anti-reflection film on a surface opposite to one main surface of the transparent substrate on which the transparent conductive film is formed, more light can be introduced into the photoelectric conversion layer. As such a reflection suppressing film, a single-layer film having a refractive index distribution is known. For example, when a film containing silica fine particles having a particle size of 50 nm is formed on a glass surface by a sol-gel method, The following literature5 shows that the solar transmittance is improved (2nd international Conierence on Coatiners on Glass, 1999, Elsevier Science, ISBN: 0-444-50247-5'255-260). Since high transmittance is naturally required for the antireflection film, fine particles having a relatively small particle size and uniform particle size as described in the above-mentioned literature have been used.

Furthermore, the use of crystalline silicon such as microcrystal or polycrystal for the photoelectric conversion layer has attracted attention as a technique for dramatically increasing the photoelectric conversion rate of a thin film photoelectric conversion device.

However, the above technology has the following problems. The above transparent group The technology to increase the transmissivity by forming an anti-reflection film on one main surface of the body has a well-established feeling, as long as there is no fundamental component change such as using new materials that have never existed before However, it is considered difficult to expect effects beyond those shown in the above literature.

Therefore, in order to increase the photoelectric conversion rate of the thin-film photoelectric conversion device, it is conceivable to increase the surface irregularities of the transparent conductive film so as to generate more light confinement in the photoelectric conversion layer. However, it has been reported that when the surface roughness of the transparent conductive film increases, the crystal growth of the crystalline silicon is hindered (Technical Digest of the International PVSEC-11, Sapporo, Hokkaido, Japan, 1999, 231- 232). This means that in a photoelectric conversion device using crystalline silicon for the photoelectric conversion layer, light confinement in the photoelectric conversion layer can be sufficiently generated by means similar to the conventional photoelectric conversion layer made of amorphous silicon. That is, there is a limit to the performance improvement.

Disclosure of the invention

The present invention has been made in view of the above problems. Its purpose is to suppress more light to the photoelectric conversion layer and to suppress light confinement in the photoelectric conversion layer without depending on surface irregularities of the transparent conductive film. Another object of the present invention is to provide a substrate for a photoelectric conversion device including the same. Another object of the present invention is to provide a thin-film photoelectric conversion device having a photoelectric conversion layer made of crystalline silicon by using this substrate and having extremely high photoelectric conversion efficiency.

The present invention provides a substrate for a photoelectric conversion device in which a reflection suppressing film containing fine particles mainly composed of silica having a particle diameter of 30 O nm or less is formed on the main surface of a transparent substrate.

In this photoelectric conversion device substrate, the particle size of the fine particles is from 300 to 60 O nm. It is suitable.

Further, in this substrate for a photoelectric conversion device, it is preferable that the antireflection film contains fine particles mainly composed of silica having a different particle diameter from fine particles mainly composed of silica having a particle diameter of 300 nm or more.

In the substrate for a photoelectric conversion device, the particle diameter of fine particles mainly composed of silica having different particle diameters is preferably 50 to: I 50 nm.

In the photoelectric conversion device substrate of the present invention, it is preferable that the fine particles exist in a region of 60% or more of the main surface of the transparent substrate. Further, a transparent conductive film having a haze ratio of 10% or less may be formed on a surface opposite to the main surface of the transparent substrate. The present invention also provides a photoelectric conversion device provided with the substrate described above.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a cross-sectional view of one embodiment of the substrate for a photoelectric conversion device of the present invention. FIG. 2 is a schematic view showing an apparatus for producing a glass plate and a transparent conductive film. FIG. 3 is an example of a diffusion transmission spectrum of a tin oxide film.

FIG. 4 is an example of the diffusion transmission spectrum of the photoelectric conversion device substrates of Examples 1 to 3.

FIG. 5 is a diagram illustrating a state in which the surface of the antireflection film manufactured in Example 2 is observed by SEM.

Embodiment of the Invention

Hereinafter, embodiments of the present invention will be described in detail. However, it is not limited to the following embodiment.

FIG. 1 is a cross-sectional view of one embodiment of the present invention. In this photoelectric conversion device substrate, an underlayer film 1 and a transparent conductive film 2 mainly composed of tin oxide are formed in this order on one main surface of a transparent substrate 5, and silica is mainly formed on the opposing surface. An antireflection film 6 composed of fine particles (hereinafter referred to as “silicone fine particles”) and a binder (not shown) is formed. This photoelectric conversion device In the substrate for use, irregularities due to silica fine particles 7 and 8 are formed on the surface of the antireflection film 6.

Hereinafter, the reflection suppressing film 6 that contributes to the reflection suppression and scattering of the incident light 9 will be described. The antireflection film contains silica fine particles and a binder, and a void is formed between the fine particles. Due to the voids formed inside the film, the substantial refractive index of the antireflection film decreases. A decrease in the refractive index of the anti-reflection film is preferable from the viewpoint of improving the anti-reflection effect.

Examples of silica fine particles include silica fine particles synthesized by reacting silicon alkoxide with a basic catalyst such as ammonia by a sol-gel method, colloidal silica made from sodium gayate, etc., or fume synthesized in the gas phase. Dosilica or the like can be used. In order to improve the dispersibility of the raw material, the silica fine particles may contain a trace component other than silica.

The optical properties of the antireflection film depend on the particle size of the silica fine particles and the area ratio of the silica fine particles occupying the surface of the transparent substrate. The particle size of the silica fine particles is accurately determined by measurement using a transmission electron microscope. When the silica fine particles are agglomerated, the average particle size of the individual particles, that is, the average primary particle size, not the agglomerated particles (for example, secondary particles connected in a chain) is defined as the particle size.

The area ratio of the silica fine particles occupying the substrate surface can be determined by observation using a scanning electron microscope (SEM). If SEM is used, the approximate particle size can also be evaluated.

The reflectance of the anti-reflection film obtained by arranging the spherical fine particles on the substrate surface such that the center of the fine particles is arranged in a grid pattern is considered as follows, and is obtained. Assuming that the diameter of the silica fine particles is the film thickness, air occupies about half of the volume of the antireflection film. The refractive index of silica is 1.45, Since the refractive index of air is 1.00, the refractive index of such an anti-reflection film is a substance having a refractive index of n1 and a volume of V1, and a substance having a refractive index of n2 and a volume of V2. Is calculated by the following equation which gives the refractive index n of the substance obtained by mixing That is,

(n ² -l) / (n ² + 2)

= (V 1 ZV) X (n 1-1) / (n 1 ² + 2)

+ (V 2 / V) x (n 2-1) / (n 2 '+ 2)

V = V 1 + V 2

It is. From this equation, the refractive index of the antireflection film made of the fine particles of silicic acid is calculated to be 1.22. Hereinafter, the refractive index calculated based on this formula is referred to as “apparent refractive index”.

It is also known that the reflectance of the antireflection film is minimal when the following condition is satisfied between the refractive index of the antireflection film and the wavelength of the incident light.

nd = λ / 4

(η: refractive index of film, d: film thickness, λ: wavelength)

Here, “η · d” is called “optical thickness” of the antireflection film. Since the optical thickness is a component of the refractive index (apparent refractive index) of the antireflection film, its physical thickness d is smaller than the optical thickness. Therefore, in order to minimize the reflectance near the wavelength of 600 nm, at which the sensitivity of amorphous silicon becomes maximum, the thickness of the antireflection coating with the apparent refractive index of 1.2 d is about 120 nm. In addition, since the photoelectric conversion layer made of amorphous silicon or crystalline silicon has a wide absorption band from visible light to near-infrared light, the preferred particle size of the silica fine particles is 50% when calculated according to the above equation. ~ 150 mn. Thus, according to the conclusions derived from ordinary optical theory, removing the particle size of silica particles from 50 to i5O nm loses the function of the antireflection film. It is considered equivalent to Actually, the silica fine particles used in the reflection suppressing film of the photoelectric conversion device have a particle size of 50 to 15 O nm.

However, in order to increase the photoelectric conversion rate of the photoelectric conversion device, it is not only necessary to suppress the reflection of incident light to increase the amount of light introduced into the photoelectric conversion layer, but also to cause light confinement in the photoelectric conversion layer as described above. There are ways to make it easier. Conventionally, it has been recognized that this light confinement is a characteristic that should be exerted by a transparent conductive film in contact with the photoelectric conversion layer. However, from the results of many experiments on this light confinement, the present inventors have found that even an antireflection film can cause effective light scattering for light confinement. In other words, it was found that by changing the silica fine particles contained in the antireflection film to those having a relatively large particle size of 30 O nm or more, light scattering effective for confining light in the antireflection film was generated. is there. Further, since light scattering is ensured by the antireflection film, the transparent conductive film formed on the opposing surface of the transparent substrate can be smoothed, thereby solving the above-described problem of crystal growth inhibition of crystalline silicon. be able to.

The present inventors have investigated the relationship between the particle size of the silicic acid fine particles and light scattering in the antireflection film, and found that when the particle size exceeds 20 O nm, the photoelectric conversion rate starts to increase, and 30 O nm From the vicinity, it was found that the change became remarkable. For example, if the antireflection film has a composition ratio of silica fine particles: binder = 80: 20, the haze ratio is about 10% at a particle size of 20 O nm, and the haze ratio is 30% at a particle size of 30 O nm. Is about 20%, the haze ratio is about 55% at a particle diameter of 50 nm, and the haze rate is 70% at a particle diameter of 700 nm. Accordance particle diameter of the silica fine particles increases as this, where _n the degree physician light scattering is increased, the haze ratio is the number of fingers indicating the ratio of scattered transmitted light, larger the value Indicates that transmitted light is scattered. Photoelectric It is generally believed that the more scattered light introduced into the conversion layer, the more effective it is in confining light. Therefore, focusing on light confinement, it seems that the larger the particle size of the silica fine particles, the better. However, when the particle size exceeds 1 m, the adhesion between the silica fine particles and the transparent substrate is reduced, so that the durability of the antireflection film is reduced. Therefore, in the case where solar cells are used outdoors for a long period of time and are not easily repaired or replaced, such as solar cells, the particle size of the silica fine particles should be 200 to 100 O in consideration of light confinement and durability. nm force Considered reasonable. Further, considering the light scattering by the above-described antireflection film and the adhesiveness between the silica fine particles and the transparent substrate from the viewpoint of practicality, the particle size of the silica fine particles is from 300 to 600 nm. Seems appropriate. As described above, the optical function exerted by the anti-reflection film changes depending on the particle size of the silica fine particles. Therefore, if a plurality of types of silica fine particles having different particle sizes are mixed, the anti-reflection having various optical characteristics can be obtained. It is believed that a film is obtained. For example, when the above-described silica fine particles having a particle diameter of 300 to 60 O nm and silica fine particles having a particle diameter of 50 to 15 O nm are combined, light scattering is generated and the reflectance is too low. It is expected that not high films will be obtained. However, this antireflection film exerts more functions than the above-mentioned combination of the functions of the fine particles of each particle diameter. In other words, the combination of the two types of silica microparticles is thought to produce only an effect that compromises the respective functions, but the experimental results disappointed. When silica fine particles having a particle size of 11 O nm and a particle size of 300 nm are used in combination, the haze ratio of the antireflection film shows an intermediate value of that of only silica fine particles of each particle size. However, the photoelectric conversion rate is higher than that of only particles of each particle size. The reason why such a result is obtained is not necessarily clear, but the present inventors speculate as follows. That is, when fine particles having different particle sizes are mixed, the larger fine particles are dispersed and scattered on the transparent substrate, and a gap is formed between the fine particles. Occurs. Smaller fine particles enter this gap, and the structure is such that these fine particles partially stack or adhere to the larger fine particles and are laminated, so that the incident light is liable to cause multiple scattering in the antireflection film. Become. We believe that this multiple scattering may increase the angle of incidence on the photoelectric conversion layer, making light confinement more likely to occur.

If the photoelectric conversion rate is unambiguously increased by multiple scattering of the anti-reflection film, the same effect can be obtained by using silica fine particles with a wide particle size distribution, or by laminating the anti-reflection film with a thicker silica fine particle. It is thought to be played. However, when silica fine particles having a wide particle size distribution are used, the number of fine particles satisfying the relationship between the reflectance and the wavelength decreases, so that the reflectance of the antireflection film increases, and the amount of light incident on the photoelectric conversion layer decreases. Eventually, the photoelectric conversion rate decreases. From this, it is considered that the silica fine particles preferably have a uniform particle size as much as possible. Specifically, as long as the silica fine particles have a particle size of 30 O nm, those having a particle size distribution of about ± 10% are commercially available. On the other hand, if the thickness of the anti-reflection film is increased to deposit the fine particles, the strength of the anti-reflection film decreases, and the durability of the anti-reflection film does not reach a practical level. It is conceivable to increase the amount of binder in the anti-reflection coating to increase its strength, but this causes a new problem that the gap between fine particles becomes smaller and the apparent refractive index rises. From these facts, it is considered that the thickness of the antireflection film is preferably 1 to 2 times the particle size of the large fine particles.

When a plurality of types of silica fine particles having different particle diameters are used, the particle diameter ratio of each fine particle is preferably 3 or more. If the particle size ratio is 3 or more, small fine particles can enter the gaps between the large fine particles. On the other hand, as described above, silica fine particles of less than SO nrn induce an increase in reflectance, and silica fine particles of more than 100 O nm have poor adhesion to the transparent substrate, and the durability of the antireflection film is low. Lower. Therefore, this particle size ratio is preferably Is preferably 20 or less, that is, 3 to 20.

In addition, when silica fine particles are present in a region of 60% or more of the surface of the transparent substrate on which the antireflection film is present, various functions such as the above-described antireflection, increase in transmittance, and improvement in durability are achieved. Effectively demonstrated.

The type of transparent substrate is not particularly limited, and various types of transparent substrates such as a glass plate and a resin plate conventionally used as a transparent substrate of a photoelectric conversion device can be used.

The binder improves the adhesion between the silica fine particles and between the silica fine particles and the transparent substrate. The binder is preferably at least one metal oxide selected from the group consisting of silicon oxide, aluminum oxide, titanium oxide, zirconium oxide and tantalum oxide. An alkoxide containing at least one metal selected from Si, Al, Ti, Zr, and Ta is preferable as a material for the binder from the viewpoint of film strength and chemical stability. In the case of a film having a relatively large binder content, the refractive index of the binder affects the reflectance. Therefore, a silicon alkoxide having a small refractive index, particularly a silicon tetraalkoxide or an oligomer thereof is preferable as the raw material. However, a plurality of types of metal alkoxides may be used as the raw material of the binder, and even if other than metal alkoxides, M (OH) _n (M is a metal atom, n is determined based on the valence of the metal by hydrolysis) The metal compound is not particularly limited as long as it is a metal compound from which a reaction product represented by a natural number, for example, 1 to 4) is obtained. Examples of such metal compounds include metal halides and metal compounds having an isocyanate group, an acyloxy group, an aminoxy group, and the like. In addition, a compound represented by Rl ,,, M (OR2) _n — which is a kind of silicon alkoxide (M and n are the same as above, R1 is an alkyl group, amino group, epoxy group, phenyl group, methyl chloroxy R2 is an organic group that is mainly an alkyl group, m Is a natural number from 1 to (n-l). The anti-reflection film is formed, for example, by applying a coating solution containing silica fine particles and a metal compound such as a metal alkoxide to the surface of the substrate and baking the coating solution. At this time, the weight ratio between the silica fine particles and the binder is preferably in the range of 50:50 to 85:15. If the ratio of the binder is too large, the fine particles are buried in the binder, and the unevenness due to the fine particles and the porosity in the film are reduced. On the other hand, if the ratio of the binder is too small, the adhesiveness between the transparent substrate and the fine particles and between the fine particles is reduced.

The coating liquid may be prepared by mixing a hydrolyzate of a metal compound with fine particles of silica, but is preferably prepared by hydrolyzing a hydrolyzable metal compound in the presence of fine silica particles. . This is because the film strength is significantly improved. For example, when a metal alkoxide is hydrolyzed in the presence of silica fine particles, a condensation reaction between silanol groups on the surface of the silica fine particles and the metal alkoxide is promoted in the coating solution. This condensation reaction not only enhances the adhesion between the silica fine particles, but also enhances the reactivity of the surface of the silica fine particles to enhance the adhesive force between the fine particles and the glass substrate.

Hereinafter, the method for forming the antireflection film using the coating liquid will be described in more detail.

The coating liquid is prepared by mixing a hydrolyzable metal compound, a hydrolysis catalyst, water and a solvent, preferably in the presence of silica fine particles, and hydrolyzing the metal compound. The hydrolysis can be carried out, for example, by stirring the mixture at room temperature for 1 hour or more to carry out the reaction, or by stirring the mixture at a temperature higher than room temperature, for example, 40 to 80 minutes for 10 to 50 minutes. The obtained coating solution may be diluted with an appropriate solvent according to the coating method.

Hydrolysis catalysts include mineral acids such as hydrochloric acid and nitric acid and acid catalysts such as acetic acid. Is preferred. When an acid catalyst is used, the metal alkoxide reacts easily to form M (OR) n, thereby providing abundant reaction products that effectively act as a binder. With basic catalysts, hydrolysis is rate-limiting and the condensation reaction is faster. For this reason, the reaction product of the alkoxide is reduced to fine particles, or the metal alkoxide is consumed for the growth of the particle diameter of the fine particles, and the number of products acting as a binder is reduced. The amount of the catalyst to be added is preferably from 0.001 to 4 in a molar ratio to the metal compound serving as the binder.

The amount of water required for the hydrolysis is preferably from 0.1 to 100 in molar ratio to the metal compound. If the amount of water added is less than 0.1 in a molar ratio, hydrolysis of the metal compound is not sufficiently promoted. On the other hand, if the amount of water added is greater than 100 in terms of molar ratio, the stability of the liquid will be reduced.

In addition, when a compound having a black group is used as the gold compound, addition of water or a catalyst is not necessarily required. This is because the hydrolysis proceeds due to the water in the solvent or the water in the atmosphere. Hydrochloric acid is liberated in the liquid with the hydrolysis, and the hydrolysis proceeds.

The solvent is not particularly limited as long as it can dissolve the metal compound.Alcohols such as methanol, ethanol, propanol, and butanol, cellosolves such as ethylcellosolve, butylcellosolve, and propylcellosolve, and ethylene Glycols such as glycol and hexylene glycol can be used.

If the concentration of the metal compound dissolved in the solvent is too high, the gap between the fine particles in the film will not be formed sufficiently depending on the amount of the silica fine particles to be dispersed. Therefore, the concentration of the metal compound is preferably 20% by weight or less, and more specifically, 1 to 20% by weight.

In addition, the ratio of the fine particles of the silicon force to the metal compound in the coating solution is determined by changing the metal compound to the corresponding metal oxide (eg, SiO ^ AO ^ TiO _2, Zr0 in terms of _{_{_{2, Ta 2 0 5),}}} 0 5 at a weight ratio: 5 0-9 9: 1 is not preferred. When the coating solution is prepared by hydrolyzing a metal compound in the presence of silica fine particles, the above weight ratio is more preferably 66:34 to 95: 5, and further preferably 75: 5. 25 to 90: 10 When the metal compound is hydrolyzed in the absence of silica fine particles, the weight ratio is more preferably 50:50 to 85:15, and even more preferably 60:40 to 50:50. 7 5: 25

Preferred mixing ratios of the coating liquid are shown in the following (Table 1). table 1

The coating liquid is applied to a glass substrate and heated, whereby a dehydration-condensation reaction of a metal compound hydrolyzate, vaporization and burning of volatile components proceed, and a reflection suppressing film is formed on the glass substrate.

The method of applying the coating liquid to the glass substrate is not particularly limited, but may be a method using an apparatus such as a spin-coat, a mouth-coat, a spray-coat, a curtain-coat, or the like. Various methods such as a lifting method (dip coating method) and a flow coating method (flow coating method), and screen printing, gravure printing, and curved surface printing can be used.

Depending on the surface condition of the transparent substrate, it may not be possible to apply evenly by repelling the coating liquid. In such a case, cleaning and surface modification may be performed. Methods for cleaning and surface modification include degreasing with an organic solvent such as alcohol, acetone or hexane, cleaning with an alkali or acid, and polishing. Surface polishing with an abrasive, ultrasonic cleaning, ultraviolet irradiation treatment, ultraviolet ozone treatment or plasma treatment can be mentioned.

The heat treatment after the application is effective in improving the adhesion between the antireflection film substantially consisting of silica fine particles and the binder and the transparent substrate. The heating temperature, expressed in terms of the maximum temperature, is preferably 200 ° C or higher, more preferably 400 ° C or higher, particularly preferably 600 ° C or higher, and 180 ° C or lower. Below is preferred. In general, at 200 ° C. or higher, the solvent component of the coating liquid evaporates, and the gelation of the film proceeds to generate an adhesive force. Above 400 ° C, the organic components remaining in the film are almost completely eliminated by combustion. With a value of 600 or more, the condensation reaction of the remaining unreacted silanol groups and hydrolyzable groups of the hydrolyzate of the metal compound is almost completed, and the film strength is improved. The heating time is preferably from 5 seconds to 5 hours, more preferably from 30 seconds to 1 hour.

The photoelectric conversion rate of the photoelectric conversion device is improved by the reflection suppressing effect of the reflection suppressing film. The reflectance of the transparent substrate on which the anti-reflection film is formed is preferably not more than 3.5%, and is preferably not more than 3.5%, expressed as the reflectance not including the reflection of the opposing surface (the surface on which the transparent conductive film was formed). The following is more preferable, and the most preferable is 0.5% or less. A water-repellent film or an anti-fogging film may be further formed on the reflection suppressing film. By coating with a water-repellent film, water-repellent performance can be obtained, and dirt-removing property is also improved. When coated with a water-repellent film, excellent water-repellency can be obtained as compared with the case where the surface of a transparent substrate on which no antireflection film is formed is treated with the same water-repellent agent. This is due to an increase in surface irregularities (W enzee 1 theory). Similarly, coating with an anti-fogging film can provide improved anti-fogging performance as well as improved soil removal.

The antireflection film is formed on the main surface of the transparent substrate of the thin-film or crystal-type photoelectric conversion device, thereby realizing the above-described transmittance and high light confinement. Also, the silica fine particles are firmly fixed to the transparent substrate by the binder. Therefore, it shows high durability. Further, since the irregularities derived from the silica fine particles are formed on the surface of the antireflection film, this film has extremely high durability.

The underlayer 1 is preferably a two-layer film composed of a first underlayer 1a and a second underlayer 1b, or a single-layer film. When the base film 1 is a two-layer film, the first base layer la preferably contains tin oxide as a main component. The second underlayer 1b preferably contains at least one of silicon oxide and aluminum oxide as a main component, and is particularly preferably a silicon oxide film. In this case, for example, a film containing silicon oxide, SiOC, aluminum oxide, or the like as a main component, or a film made of a composite oxide of silicon oxide and tin oxide is preferable.

The transparent conductive film 2 is preferably a film containing tin oxide as a main component, and more preferably a material to which a predetermined amount of an element such as fluorine is added for improving conductivity. The transparent conductive film 2 is preferably formed by a method involving a thermal decomposition oxidation reaction of a raw material.

Preferred thicknesses of the respective films shown in FIG. 1 are exemplified below.

First underlayer l a 0 to l O O nm

Second underlayer l b 10 to 4 O nm

Transparent conductive film 2400 to 1200 nm

In the case where a glass plate is used for the transparent substrate, a method of sequentially depositing each film on the glass ribbon surface using the heat of the glass ribbon in the float glass manufacturing process may be applied to each of the above films. preferable. This is because film formation can be performed at a high temperature and the heat of the glass ribbon can be used. Specifically, there are a spray method in which the raw material liquid is atomized and supplied to the glass ribbon surface, and a CVD method in which the raw material is vaporized and supplied to the glass ribbon surface. In this case, the surface on which the transparent conductive film is to be formed is float glass top. It is preferable that the surface on which the antireflection film is formed be the bottom surface of the float glass. The bottom surface of the float glass is more excellent in flatness than the top surface. For example, when a reflection suppressing film is formed by a roll coating method, it is easy to control unevenness.

FIG. 2 shows an embodiment of an apparatus for forming a transparent conductive film on the surface of the glass ribbon by the CVD method. As shown in Fig. 2, in this apparatus, a predetermined number of glass ribbons flow out of the melting furnace 11 into the tin float tank 12 and immediately above the glass ribbon 10 which is formed into a belt shape in the tin bath 15 and moves. 6 (in the illustrated form, five coaters 16a, 16a, 16c, 16c, 16d, 16e) are arranged. From these moments, the vaporized raw material adjusted according to the type of film to be formed is supplied, and each film (for example, the first surface) is applied to the glass ribbon 10 surface (top surface; tin non-contact surface). Underlayer, second underlayer, transparent conductive film) Force Continuously formed. In this case, it is preferable that the transparent conductive film formed to be thicker than both underlayers is formed using a plurality of layers. The temperature of the glass ribbon 10 is controlled by a heater and a cooler (not shown) arranged in the tin float tank 12 so that the temperature becomes a predetermined temperature immediately before the temperature 16. Here, the predetermined temperature of the glass ribbon is preferably 6 ° C. to 75 ° C., and more preferably 63 ° C. to 75 ° C. The glass ribbon 10 on which each film is formed in this way is pulled up by the roll 17 and cooled in the annealing furnace 13.

When a film containing tin oxide as a main component is formed by the CVD method, tin raw materials include monobutyltin trichloride, tin tetrachloride, dimethyltin dichloride, dibutyltin dichloride, dioctyltin dichloride, and tetra. Methyltin and the like. As a tin raw material, organotin chlorides such as monobutyltin trichloride and dimethyltin dichloride are particularly suitable. Oxygen, water vapor, dry Dry air or the like may be used as the oxidizing material. In addition, when fluorine is added to the film, examples of the fluorine raw material include hydrogen fluoride, trifluoroacetic acid, bromotrifluoromethane, and chlorodifluoromethane.

When a film containing silicon oxide as a main component is formed by the CVD method, the silicon raw materials include monosilane, disilane, trisilane, monochlorosilane, 1,2-dimethylsilane, 1,1,2-trimethyldisilane, 1, Examples include 1,2,2-tetramethyldisilane, tetramethylorthosilicate, and tetraethylorthosilicate. As an oxidizing material, oxygen, steam, dry air, carbon dioxide, carbon monoxide, nitrogen dioxide, ozone, or the like may be used. When a highly reactive raw material such as monosilane is used, the reactivity may be controlled by adding an unsaturated hydrocarbon gas such as ethylene, acetylene or toluene.

Similar to the case of gay oxide, when using a CVD method to form a film mainly containing aluminum oxide, which is suitable as the second underlayer, aluminum materials include trimethylaluminum, aluminum triisopopropoxide, and getylaluminum chloride. Aluminum acetyl acetonate, aluminum chloride and the like. In this case, examples of the oxidizing raw material include oxygen, steam, and dry air.

In order to effectively generate light confinement in the photoelectric conversion layer, the surface of the transparent conductive film may be provided with irregularities. However, as described above, when the surface irregularities of the transparent conductive film become large, crystal growth of crystalline silicon is inhibited. Therefore, the surface irregularities are preferably not more than 10% in terms of a haze ratio. Further, the surface irregularities of the transparent conductive film can also be formed by etching or the like.

The method for manufacturing the thin film type or crystal type photoelectric conversion device is not particularly limited, and other structures may be used if the antireflection film is formed by the above-described means. W

The component can be manufactured by a known means.

Example

Hereinafter, the present invention will be described more specifically with reference to examples. However, it is not limited to the following examples.

The method of measuring the transmittance and the haze of the substrate for a photoelectric conversion device in the examples is as follows.

(Transmissivity)

Using a spectrophotometer (manufactured by Shimadzu Corporation), the transmittance at 400 to 110 _nm was measured, and the average value was determined.

[Haze rate]

Using an integrating sphere light transmittance measuring device (HGM-2DP, manufactured by Suga Test Instruments Co., Ltd.), the method for testing the optical properties of plastics (JIS (Japanese Industrial Standard) K 7105-198 1) The haze was measured by the described haze measurement method.

In each of Examples and Comparative Examples, a 1 Ocm square ordinary float glass (2.8 mm thick) was used as a transparent substrate for forming the anti-reflective film. The glass plate was washed and dried, and a silicon dioxide film and a fluorine-doped tin oxide film were deposited in this order using a belt-conveying normal pressure CVD apparatus. The silicon dioxide film was formed by heating a glass plate to 550 ° C. and supplying monosilane, oxygen and nitrogen. Its film thickness was 50 nm. For the fluorine-doped tin oxide film, the glass on which the silicon dioxide film is formed is heated to 600 ° C, and a mixed gas comprising dimethyltin dichloride, water vapor, oxygen, hydrofluoric acid, and nitrogen is supplied. Formed. Its film thickness was 45 O nm. The glass substrate with a transparent conductive film thus obtained had a transmittance T1 of 78.3% and a haze ratio H1 of 4.5%.

(Example 1) First silica fine particle dispersion (Nippon Shokubai Co., Ltd. “Siphos Yuichi KE—W10” average primary particle size 11 1 Onm solids 15%) 5 6.67 g, ethilse Mouth Solve 33.7 g Then, 1 g of concentrated hydrochloric acid and 5.2 g of tetraethoxysilane were sequentially added, and the mixture was reacted with stirring for 24 hours to prepare a first silica fine particle hydrolyzed liquid. In addition, a second silica fine particle dispersion (Nippon Shokubai Co., Ltd. “Seahoster KE-E30” average primary particle size 30 Onm, solid content 20%) 42.5 g, Etyrse mouth solve 48.7 g, IN hydrochloric acid 3.6 g and 5.2 g of tetratraethoxysilane were sequentially added and reacted with stirring for 24 hours to prepare a second hydrolyzed silica fine particle. A coating solution was prepared by mixing 12 g of the first hydrolyzed silica fine particle solution, 18 g of the second hydrolyzed silica fine particle solution, 40 g of ethylene glycol, and 30 g of ethyl ethyl solvent. This coating solution was applied to the glass surface of the glass substrate with a transparent conductive film (the surface facing the transparent conductive film) by spin coating. The number of revolutions was set to 120 Or.pm. After being left to dry in a room, it was placed in an electric furnace set at 600 for 10 minutes to form a reflection suppressing film. The maximum temperature of the glass substrate in the electric furnace was 52 Ot :.

(Example 2)

1st silica fine particle dispersion (Nippon Shokubai Co., Ltd. “Siphos Yuichi KE-W10” average primary particle size 110 nm solid content 15%) 18 g, second silica fine particle dispersion (Japan (KE-W50, manufactured by Catalyst Co., Ltd.) Average primary particle size 55 5 Onm solid content 20%) 9 g, hexylene glycol 40 g, ethyl acetate solvent 29 g, concentrated hydrochloric acid 1 g and tetraethoxysilane 3 g The solution was added sequentially, and reacted with stirring for 24 hours to prepare a coating solution. Using this coating liquid, a reflection suppressing film was formed in the same manner as in Example 1 except that the spin rotation speed was set to 150 Or.p.m.

(Example 3) Silica fine particle dispersion ("KE-W50" manufactured by Nippon Shokubai Co., Ltd., average primary particle size: 55 Onm solids: 20%) While stirring 40 g, add ethyl acetate 52.1 g, concentrated hydrochloric acid lg and tetraethoxy 6.9 g of silane was added sequentially, and reacted while stirring for 240 minutes, to prepare a hydrolyzed silica fine particle solution. 30 g of this hydrolyzed silica fine particle solution was diluted by adding 30 g of ethyl acetate solvent and 40 g of hexylene glycol to prepare a coating solution. Using this coating liquid, a reflection suppressing film was formed in the same manner as in Example 1 except that the spin speed was set to 100 rpm.

(Example 4)

Silica fine particle dispersion (“KE_W30”, manufactured by Nippon Shokubai Co., Ltd., average primary particle size 30 Onm, solid content 20%) While stirring 35 g, add 52.1 g of ethylcellosolve, 1 g of concentrated hydrochloric acid and 10 g of tetraethoxysilane. .4 g were sequentially added and reacted while stirring for 300 minutes to prepare a hydrolyzed silica fine particle solution. To 30 g of this hydrolyzed silica fine particle was added 30 g of ethyl ethyl solvent and 40 g of hexylene glycol for dilution to prepare a coating solution. Using this coating liquid, a reflection suppressing film was formed in the same manner as in Example 1 except that the spin rotation speed was set to 100 Or.p.m. (Comparative Example 1)

Silica fine particle dispersion ("KE-W10" manufactured by Nippon Shokubai Co., Ltd., average primary particle size: 110 nm, solid content: 15%) While stirring 45 g, add 48.3 g of ethyl ethyl cellulose, 1 g of concentrated hydrochloric acid and 5.7 g of tetraethoxysilane was sequentially added, and the mixture was reacted with stirring for 4 hours to prepare a hydrolyzed silica fine particle solution. 35 g of this hydrolyzed silica fine particle solution was diluted with 30 g of diacetone alcohol and 3δ-hexylene glycol to prepare a coating solution. Using this coating liquid, a reflection suppressing film was formed in the same manner as in Example 1 except that the spin speed was set to 1200 rpm. (Comparative Example 2)

Silica fine particle dispersion ("KE-W20" manufactured by Nippon Shokubai Co., Ltd. Average primary particle size

2 3 Onm solid content 20%) While stirring 35 g, 53.6 g of ethylcellosolve, 1 g of concentrated hydrochloric acid and 10.4 g of tetraethoxysilane were sequentially added thereto, and stirred for 300 minutes. The reaction was performed to prepare a hydrolyzed silica fine particle solution. 30 g of the hydrolyzed liquid

30 g and 40 g of hexylene recall were added and diluted to prepare a coating solution. Using this coating solution, a reflection suppressing film was formed in the same manner as in Example 1 except that the spin speed was set at 100 Or.p.m. The transmittance T 2 and the haze H 2 of the transparent conductive film and the glass substrate with a reflection suppressing film manufactured in Examples 1 to 4 and Comparative Examples 1 and 2 were measured, and the change ΔT before and after the formation of the reflection suppressing film was measured. And ΔΗ were determined by the following equations. That is, the following ΔT and ΔΗ indicate the optical characteristics of the antireflection film.

Δ T = T 2 () — Τ 1 {%)

Η = Η 2%) One H I (%)

In addition, the surface on which the anti-reflection film was formed was observed with an electron microscope (magnification: 50,000), and the proportion of fine particles present on the glass surface was measured. The results are shown below (Table 2).

Table 2

Next, the influence of the above-described antireflection film on the photoelectric conversion rate of the photoelectric conversion device was measured. First, the same antireflection film as in Examples 1 to 4 and Comparative Examples 1 and 2 was formed on one surface of a borosilicate glass plate having a thickness of 0.7 mm. This glass substrate was placed so that the reflection suppressing film was on the light incident side, and the change in short-circuit current when sunlight was incident outdoors was measured. Here, an increase in the short-circuit current corresponds to an increase in the occurrence of light confinement in the photoelectric conversion layer based on light scattering in the reflection suppressing film. The measurement results are shown below (Table 3) as relative values based on the measurement values of Comparative Example 1. Table 3

By the way, as described above, if the surface roughness of the transparent conductive film surface is increased, light confinement in the photoelectric conversion layer is likely to occur, but this is mainly due to the short wavelength region of 300 to 600 nm. Fig. 3 shows an example of the relationship between the haze ratio of the transparent conductive film and the diffusion transmission spectrum _{(in the} thin-film photoelectric conversion device, the light of amorphous silicon in the photoelectric conversion layer is shown in Fig. 3). The absorption band is mainly in the short wavelength range of the visible light range of 400 to 60 orn. W

For example, when a tin oxide film is used as the transparent conductive film, light confinement in the photoelectric conversion layer can be easily generated by increasing the haze ratio of the tin oxide film. On the other hand, in the antireflection film of the present invention, when the haze ratio is increased by increasing the number of fine particles having a large particle diameter, the diffuse transmittance not only in the short wavelength region but also in the long wavelength region of 60 O nm or more is increased. Can be. Examples are Example 1 (fine particle diameter 110 nm + 300 nm), Example 2 (fine particle diameter 110 nm + 550 nm) and Example 3 (fine particle diameter 55 nm). Fig. 4 shows the diffuse transmission spectrum of the manufactured glass substrate with a reflection suppressing film and a transparent conductive film.

When the sensitivity of the photoelectric conversion layer is in the visible light range, it is sufficient to express the surface roughness of the transparent conductive film, that is, its haze ratio, as a standard for measuring the degree of light confinement in the photoelectric conversion layer. In other words, the higher the haze ratio, the greater the light confinement effect. On the other hand, thin-film photoelectric conversion devices with microcrystalline or polycrystalline silicon in the photoelectric conversion layer, crystalline photoelectric conversion devices, or solar cells, such as IS, in which the sensitivity of the photoelectric conversion layer includes a wavelength range longer than visible light. It is necessary to judge the degree of light confinement in the photoelectric conversion layer not by the haze ratio but by the diffusion transmission spectrum.

3 and 4, it can be seen that the antireflection film of the present invention not only achieves a high haze ratio but also exhibits a high diffuse transmittance in a wide wavelength range. That is, the antireflection film can realize high light confinement there regardless of the material of the photoelectric conversion layer.

In each of the above Examples and Comparative Examples, even when the glass substrate was heated to a temperature equal to or higher than the softening point, the glass was hardly warped due to the shrinkage of the reflection suppressing film. This is presumably because the main material of the antireflection film is silica fine particles, and the silicon fine particles do not substantially shrink. In addition, in particular, in a reflection suppressing film which is hydrolyzed in the presence of silica fine particles, a binder It is considered that this is because the binder does not exist in the form of a film and the contraction force of the binder hardly acts on the glass. From these facts, it is considered that if this antireflection film is used, it is possible to obtain a glass substrate for a photoelectric conversion device whose strength is improved by strengthening the air cooling or the like.

The present invention has the following effects because it is configured as described above.

By forming a reflection suppressing film containing silica fine particles having a particle size of 30 O nm or more on the main surface of the transparent substrate, the photoelectric conversion rate of the photoelectric conversion device can be increased. By setting the particle size of the silica fine particles to 300 to 600 runs, a substrate for a photoelectric conversion device having excellent physical durability such as abrasion resistance can be obtained.

Effective light confinement in the photoelectric conversion layer is achieved by forming a reflection suppression film containing silica fine particles with a particle size of 30 O nm or more and silica fine particles with different particle sizes on the main surface of the transparent substrate. And the photoelectric conversion rate can be further increased. Further, by setting the particle size of the silica fine particles having different particle sizes to 50 to 15 O nm, the reflectance of the reflection suppressing film from visible light to near-infrared light can be effectively reduced.

In particular, if silica fine particles are present in a region of 60% or more of the main surface of the transparent substrate, a substrate for a photoelectric conversion device that effectively exhibits various functions such as suppression of reflection, increase in transmittance, and improvement in durability can be obtained. Can be

Further, when a transparent conductive film having a haze ratio of 10% or less is formed on the surface of the transparent substrate facing the key surface, a substrate suitable for a photoelectric conversion device having a photoelectric conversion layer made of crystalline silicon can be obtained.

Thus, a photoelectric conversion device having a high photoelectric conversion rate can be obtained according to the present invention. The present invention may include other specific forms without departing from the spirit and essential characteristics thereof. The form disclosed in this specification However, the description is not restrictive, and the scope of the present invention is indicated not by the above description but by the appended claims, and all modifications within the scope equivalent to the invention described in the claims are to be made. Shall also be included here.

Claims

The scope of the claims

1. A substrate for a photoelectric conversion device in which a reflection suppression film containing fine particles mainly composed of silica having a particle diameter of 30 O nm or more is formed on a main surface of a transparent substrate.

δ

2. The substrate for a photoelectric conversion device according to claim 1, wherein the particle size of the fine particles is from 300 to 600 _nm .

3. The antireflection film further comprises fine particles mainly composed of silica having a particle diameter different from that of fine particles mainly composed of silica having a particle diameter of 30 O nm or more.

2. The substrate for a photoelectric conversion device according to 1.

4. The substrate for a photoelectric conversion device according to claim 3, wherein the fine particles mainly composed of silica having different particle diameters have a particle diameter of 50 to 15 O nm.

Five

5. The substrate for a photoelectric conversion device according to any one of claims 1 to 4, wherein fine particles are present in a region of 60% or more on the main surface of the transparent substrate.

6. The substrate for a photoelectric conversion device according to any one of claims 1 to 5, wherein a transparent conductive film having a haze ratio of 10% or less is formed on a surface facing the main surface of the transparent substrate.

7. A photoelectric conversion device comprising the substrate according to any one of claims 1 to 6.