JPH10326903A - Fine particle coating film and photoelectric conversion element using it and light dispersion body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the light dispersion effect and adhesion strength and to prevent a crack from occurring, by using the same material as that of a binder for one type of fine particle when forming a fine particle coating film and using a material that is different from that of the binder for another fine particle. SOLUTION: A fine particle coating film 2 is formed by applying the mixed liquid of a plurality of types of fine particles A and B and a binder C onto a glass substrate 1. SiO2 is used for one of the formation molecular constituents of the binder C, the same SiO2 as the formation molecular constituent of the binder C is used for one type of fine particle A out of the fine particles, and TiO2 is used for the other fine particle B. Therefore, incident light is scattered due to the small recesses and projections on the surface of the fine particle coating film 2 that is formed by mixing the fine particles A and B into the binder C, and the fine particle coating film 2 functions as a light diffusion layer, thus obtaining a light confinement effect by an amorphous semiconductor layer 4, improving the adhesion strength with the glass substrate 1, and forming. the fine particle coating film 2 without any cracks.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is applied to a solar cell, an optical sensor, a display element, or the like, and is formed by applying a mixture of a plurality of kinds of fine particles and a binder to a substrate to form a film. It relates to a coating film.

[0002]

2. Description of the Related Art Conventionally, in a photoelectric conversion element such as a solar cell, an optical sensor, a display element, etc., incident light is caused by unevenness formed on a substrate surface by a coating solution containing fine particles. Is prevented or the incident light is scattered so as to be confined in an amorphous semiconductor layer or the like to absorb the light and increase the conversion efficiency. As a method of forming the unevenness, there is a method of directly forming the unevenness on the base, a method of forming a film having the unevenness on the surface on the base, and the like.

As a method of forming irregularities directly on a substrate, for example, there is a method of spraying abrasive grains such as sandblast on the substrate. On the other hand, as a method for forming a film having unevenness on the surface on a substrate, there are a chemical vapor method such as a vacuum evaporation method and a sputtering method, a physical vapor method, and the like. However, conventional vacuum evaporation and sputtering methods
Equipment cost is high, such as requiring a high vacuum chamber,
Another problem is that it is difficult to increase the area of the thin film while maintaining a certain film quality.

As another method for forming a film having an uneven surface on a substrate, a method of applying a coating liquid mixed with fine particles is disclosed in, for example, Japanese Patent Application Laid-Open No. 2-18 / 1990.
No. 0081. In the method described in this publication, a raw material containing insulating fine particles having an average particle size of 0.1 to 0.9 μm is used in a coating material containing an organic silicate as a main component, and the coating material is formed of a cured silica coating. An insulating film is formed on a metal substrate.

As the insulating fine particles contained in the coating material of the insulating film, at least one of SiO ₂ , TiO ₂ , Al ₂ O ₃ , and ZrO ₂ is used. As a result, a film having irregularities formed on the surface is obtained. Thereafter, a back electrode, an amorphous semiconductor layer, a transparent conductive film, and a protective film are sequentially formed to obtain an amorphous semiconductor solar cell.

In the above method, the light incident on the solar cell is scattered by the unevenness, and the light confinement effect in the amorphous semiconductor layer can be obtained.

However, as described above, an organic silicate is used as a binder (binder), and only SiO ₂ which is the same as a molecular component forming the binder is used as fine particles, and a mixed liquid in which the binder and the fine particles are mixed is prepared. When the liquid is applied to the substrate and cured, fine particles are incorporated into the binder at the stage of baking for the purpose of curing, so that it is difficult to form irregularities on the surface.

Further, when the above-mentioned binder and fine particles are used, the effect as a stress dispersant is small.
When the film thickness is 0.2 μm or more, there is a problem that cracks (cracks) occur. Even when the film thickness is 0.2 μm or less, the average height difference of the surface irregularities is 200 nm.
However, a film having high adhesion strength cannot be formed.

Generally, the unevenness can provide the light confinement effect as described above.
Irregularities of about 500 nm can exhibit the light diffusion effect of increasing the diffusion of incident light and improving the energy conversion efficiency of the solar cell. However, when a mixed solution in which only the fine particles made of the same raw material as the forming molecular component of the binder are mixed with the binder is applied, it is possible to obtain a coating film having no crack and having a height difference of about 100 to 500 nm. There was a problem that can not be.

On the other hand, an organic silicate is used as a binder, and only one of TiO ₂ , Al ₂ O ₃ , and ZrO ₂ which is different from a molecular component forming the binder is used as fine particles, and the fine particles and the binder are mixed to form a coating film. When formed, since the effect as a stress dispersant is obtained,
It is possible to suppress the generation of cracks up to about μm. However, in this coating film, there is a problem that the fine particles aggregate on the film surface, and the adhesion strength to the substrate is reduced.

At this time, the fine particles having a particle size of 10
When a particle having a thickness of 0 nm or more is used, fine particles are aggregated in a drying and baking process for curing the film, so that unevenness with a height difference of about several hundred nm cannot be obtained, or the size of the unevenness is not sufficient. There has been a problem of uniformity.

By the way, many studies have been made on a film having a function of preventing reflection and antistatic by applying a coating film mixed with fine particles. In particular, a film (anti-reflection film) for reducing the reflectance of the surface of a transparent plate by forming fine irregularities on the outer surface of a fine particle film has been studied for a long time. (Visual Display Terminal)
It is also used for anti-reflection filters and the like.

A method for obtaining the above antireflection film is disclosed in, for example, Japanese Patent Application Laid-Open No. 3-150501. According to this publication, a composite granular material composed of two or more types of inorganic oxides, wherein two or more types of oxides are mixed with each other or one of the inorganic oxides is Fine particles having an average particle size of 0.1 μm or less that form a granular structure included in the object are used.

In the fine particles, at least one kind of inorganic oxide has an antireflection function, and another inorganic oxide has a conductive function. After a thin film mainly composed of such fine particles is formed on a substrate, an etching process is performed to form fine irregularities on the surface of the thin film. In this case, the unevenness of the formed surface is set to 0.1 μm or less.

In the method of forming fine irregularities on the surface of a thin film by forming a thin film mainly composed of fine particles on a substrate as described above and then performing etching, not only the number of processes of etching increases, There was a problem that the substrate used was limited to those that were not affected by etching. Further, in this case, the unevenness of the thin film surface is 1
When the thickness is less than 00 nm, there is a problem that even if an antireflection effect as an antiglare film can be obtained, a sufficient light diffusion effect cannot be obtained.

In view of the above problems, an object of the present invention is to provide a fine particle coating film which has a sufficient light diffusion effect, has high adhesion strength to a substrate, and does not generate cracks.

[0017]

The object of the present invention is to form a film by applying a mixed solution obtained by mixing a plurality of kinds of fine particles and a binder on a substrate, and forming irregularities due to the fine particles on the surface. In the fine particle coating film, at least one type of fine particles is composed of the same raw material as the molecular component of the binder, and the other fine particles are composed of a raw material different from the molecular component of the binder.

[0018] to be specific, SiO ₂ is used for one of the forming molecule component of the binder, SiO ₂ is used in the microparticles. TiO ₂ , Al ₂ O ₃ , Zr
One of O ₂ , ITO, SnO _{2 and} MgF ₂ is used. With such a configuration, a sufficient light diffusion effect can be obtained, and a fine particle coating film having high adhesion strength to the substrate and free from cracks can be obtained.

Further, in this case, the height difference between the irregularities is 100 to 100.
500 nm or fine particles having a particle size of 10 to 90 nm
Or a mass ratio of the binder to all the fine particles of 1: 1 to 1:10 is desirable for obtaining the light diffusion effect.

Further, the fine particle coating film is formed as a light diffusion layer for confining incident light, in particular, between a transparent substrate such as a glass substrate and a plastic substrate and a transparent conductive film, and is used as in a solar cell. It may be applied to a simple photoelectric conversion element.
Or you may apply to the light diffuser which apply | coated the fine particle application film to the translucent substrate.

[0021]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 is a diagram showing a schematic cross section of a thin film solar cell to which a fine particle coating film according to one embodiment of the present invention is applied. In this thin-film solar cell, a glass substrate 1, a fine particle coating film 2, a transparent conductive film 3, an amorphous semiconductor layer 4, a p-layer 5, an i-layer 6, an n-layer 7, a back electrode 8, and a metal thin-film back electrode 9 are formed. It is configured to be laminated.

The fine particle coating film 2 has a plurality of types (2 in FIG. 1).
The mixture is formed by applying a mixed solution obtained by mixing fine particles A and B of the above type) and a binder C onto the glass substrate 1. SiO ₂ (silicon oxide) using silicon alkoxide as a raw material is used as one of the molecular components forming the binder C, and one type of fine particles A among a plurality of types of fine particles is formed of the same raw material as the molecular component forming the binder C. Certain SiO ₂ is used. Thus, by using SiO ₂ for the fine particles A, it is possible to form a thin film at a low cost and at a relatively low temperature. Here, the composition of the binder is shown in Table 1.

[0024]

[Table 1] In the fine particle coating film 2, TiO ₂ (titanium oxide) is used for the other fine particles B. The other fine particles B are made of Al ₂ O ₃ (aluminum oxide), Zr instead of TiO _2.
Any one or more of O ₂ (zirconium oxide), ITO (indium tin oxide), SnO ₂ (tin oxide), MgF ₂ (magnesium fluoride) and the like may be used. By using the other fine particles B,
The finely-coated fine particle coating film 2 can be obtained.

As described above, the fine particles A and B are combined with the binder C
, Fine irregularities are formed on the surface of the fine particle coating film 2. Due to the unevenness, for example, light incident on the solar cell is scattered, and the fine particle coating film 2 functions as a so-called light diffusion layer. Therefore, a light confinement effect in the amorphous semiconductor layer 4 can be obtained. Further, the height difference of the unevenness is preferably 100 to 500 nm. If such unevenness is formed, a light diffusion effect can be obtained, and the energy conversion efficiency of the solar cell can be improved.
Further, due to the unevenness, the fine particle coating film 2 having high adhesion strength to the glass substrate 1 and free from cracks can be formed.

The particle size of the fine particles A is more preferably from 10 to 90 nm. This is because, if a particle having a particle diameter smaller than 10 nm or larger than 90 nm is used, the height difference of the irregularities becomes larger than 500 nm due to the aggregation of the fine particles A, and the whole becomes non-uniform.

Next, a method for forming the fine particle coating film 2 will be described. Here, first, fine particles A and B are dispersed in a dispersion medium to prepare a fine particle dispersion. In this case, after preparing two kinds of fine particles A and B in each dispersion liquid, the respective dispersion liquids may be mixed, or two kinds of fine particles A and B may be dispersed in one dispersion liquid. May be.

Here, the solvent necessary for dispersion is water,
Use organic solvents such as alcohols or ethanols. As a method of dispersing the fine particles A and B in the dispersion, a ball mill, a bead mill, ultrasonic vibration, a stirrer, or the like is used.

Further, a coupling agent may be used to prevent the fine particles A and B from aggregating in the dispersion and increasing the particle diameter of the secondary particles, or preventing the particles from becoming large and sedimenting. As the coupling agent, a silane-based, titanium-based, aluminum-based, zirconium-based, or magnesium-based coupling agent can be used. Alternatively, a surfactant or the like may be used.

Next, the fine particle dispersion of SiO ₂ (average particle diameter of fine particles: 20 nm, solid content: 10 mass%, dispersion medium ethyl alcohol) and the fine particle dispersion of TiO ₂ (average particle of fine particles) (A diameter of 15 nm, a solid content of 10% by mass, a dispersion medium ethyl alcohol) and a binder C are mixed.

The mass ratio of each fine particle dispersion in the mixed solution to the binder C is as follows: the fine particle dispersion of SiO ₂ : TiO ₂
Fine particle dispersion: Binder C = 1: 1: 2. That is, the ratio between the total mass of the two types of fine particles A and B in the mixed solution and the mass of the binder C is constant at a ratio of solid content in the fine particle dispersion: binder C = 1: 1.
The ratio between the total mass of the fine particles A and B and the mass of the binder C is more preferably about 1: 1 to 10: 1. This is because if the mass ratio of the solid content in the fine particle dispersion is less than 1: 1, unevenness on the surface of the coating film is not easily formed, and if the mass ratio is more than 10: 1, the mixed solution does not easily adhere to the glass substrate 1. .

When the two types of fine particles A and B are mixed with the binder C, the two types of fine particles A and B are directly mixed instead of preparing and mixing the respective dispersions with the fine particles A and B. A method of dispersing in the binder C may be used. After mixing, the particles A and B are uniformly dispersed throughout the mixture by stirring using a stirrer or the like.

Next, the mixed solution is applied onto the glass substrate 1 by a known method, for example, a spin coating method, a dip coating method, a spray coating method, a roll coating method, a screen printing method,
It is applied by a curtain coating method or a wire bar coating method.

The shape of the glass substrate 1 may be any shape regardless of whether it is flat or curved. In addition, as a material of the base, a film having transparency, metal, or the like can be used in addition to glass.

After coating on the glass substrate 1, drying,
Perform curing. As this method, a heating method is used. Specifically, the mixed solution is applied onto the glass substrate 1 at room temperature and in the air at a rotation speed of 1000 rpm by a spin coating method, for example.
Coating for 0 seconds, then 100 ° C, 15
After heating for one minute, the temperature is further raised, and heating is performed at 300 ° C. for 20 minutes. The heating atmosphere may be an inert atmosphere (for example, an N ₂ atmosphere), a reducing atmosphere (for example, an N ₂ atmosphere containing H ₂ ), or a vacuum, instead of the air.

The characteristics of the obtained fine particle coated film 2 were about 0.5 μm in thickness, 85 to 90% in light transmittance in the visible light region, and 12.5% in haze. Here, the haze ratio is a degree of haze, and is a value (unit:%) indicating a ratio of diffuse transmitted light to straight transmitted light.

Then, the surface shape of the fine particle coating film 2 is changed to ST.
When measured using an M (Scanning Tunneling Microscope), the height difference between the irregularities of the fine particle coating film 2 is about 100 to 50.
A 0 nm transparent film could be observed. FIG. 2 shows a state of the surface of the fine particle coating film 2.

[0038] FIG. 3 is a diagram showing the ratio of the mass TiO ₂ to the total mass of SiO ₂ and TiO _2, the relationship between the height difference of the irregularities formed on the fine particle coating film 2 surface. Here, the film thickness is about 600 nm.

According to the experiment, as the mass ratio of TiO ₂ becomes smaller, that is, as the mass ratio of SiO ₂ becomes larger,
The adhesion between the glass substrate 1 and the fine particle coating film 2 was improved.
Further, as the mass ratio of SiO ₂ is large, the height difference of the unevenness is reduced, if the fine particles becomes only SiO _2, generation of crack is observed in the fine particle coating film 2. Conversely, it is observed that as the mass ratio of TiO ₂ increases, the shape of the irregularities tends to increase. When the fine particles are only TiO ₂ , the fine particle coating film 2 is not separated from the glass substrate 1. Was observed.

When a film was formed by the above-described method using a plastic substrate instead of the glass substrate 1, the haze ratio was 13.1% when the height difference between the surface irregularities was 100 to 500 nm. A fine particle coating film was obtained. The film thickness in this case was about 600 nm. Thus, even a fine particle coating film formed on a plastic substrate can be used as a light diffusion layer.

Next, a procedure for manufacturing a thin-film solar cell to which the fine particle coating film 2 shown in FIG. 1 is applied will be described. A fine particle coating film 2 having irregularities is formed on a glass substrate 1, and then a transparent conductive film 3 is formed by, for example, a sputtering method. Evaporation method or CVD instead of the above sputtering method
Method may be used. In addition, as a raw material of the transparent conductive film 3, ITO, SnO _2, ZnO (zinc oxide), or the like can be used.

Thereafter, the p-layer 5, the i-layer 6, and the n-layer 7 of the amorphous semiconductor layer 4 are formed by a plasma CVD apparatus or the like. In this case, the p layer 5 is 150 nm, the i layer 6 is 500 nm, and the n layer 7
Is formed to a thickness of 350 nm. Table 2 shows an example of the conditions for forming each layer.

[0043]

[Table 2] Next, Zn was formed as the back electrode 8 by sputtering.
O is about 50 nm in film thickness, and Ag
(Silver) was formed to a thickness of about 500 nm.

As described above, a thin-film solar cell was formed, and characteristics at an area of 1 cm ² and AM 1.5 were measured. Specifically, the short-circuit current Isc = 16.8 mA
/ Cm ² , open circuit voltage Voc = 0.94 V, fill factor F.F. F = 0.75, output voltage Pmax = 11.8 mW
/ Cm ² and photoelectric conversion efficiency η = 11.8%.

The short-circuit current was increased by 30% as compared with a thin-film solar cell in which surface irregularities were not formed. In a thin-film solar cell having a height difference of 100 to 500 nm, the short-circuit current is 16.2 to 16.98 mA / c.
m ² was obtained, and the conversion efficiency was improved. When 100 thin film solar cells were manufactured under the same conditions, a high yield of 97% could be obtained.

For comparison with these thin-film solar cells, a fine particle coating film produced by changing the mass ratio of SiO ₂ and TiO ₂ while keeping the total mass ratio of the binder and the two kinds of fine particles constant was used. A thin-film solar cell was manufactured. And
Characteristics in an area of 1 cm ² and AM 1.5 were measured.

When the mass ratio between SiO ₂ and TiO ₂ is 50%, the fine particle coating film 2 is not formed,
The value of the short circuit current increased by 30%. However, when the proportion of TiO ₂ was 20%, the value of the short-circuit current increased only about 5%. This is because the height difference of the unevenness of the fine particle coating film 2 is 50
This is because the light diffusion effect could not be obtained because it was as small as about nm. When the fine particles were only SiO ₂ , cracks occurred in the fine particle coating film 2, the transmittance of the glass substrate 1 in the visible light region was reduced to about 50 to 60%, and the value of the short-circuit current was reduced by 25%.

[0048] Conversely, if the proportion of TiO ₂ mass of 80%, the height difference of the unevenness becomes large as about 600 nm, the light diffusion effect is but also cause a leak at the same time, the open circuit voltage of about 17 to 20% Diminished. When 100 thin-film solar cells were manufactured under the same conditions, the yield was 63%.
I could only get it.

The present invention is not limited to the above embodiment, and many modifications and changes can be made to the above embodiment within the scope of the present invention. For example, in the above embodiment, the description has been made by applying the fine particle coating film to a thin film solar cell.

The formation position of the fine particle coating film 2 applied to the above-mentioned thin film solar cell is not limited to the above, and is formed between the amorphous semiconductor layer 4 and the back electrode 8 as shown in FIG. You may. Also in this configuration, a light diffusion effect similar to that of the above-described thin film solar cell can be obtained. In the figure, 10
Is a protective layer.

The fine particle coating film 2 can be used as a light diffuser as shown in FIG. 5 by coating it on a light transmitting substrate 1 such as a glass substrate or a plastic substrate. This can be used, for example, for the surface of a cathode ray tube, a lens of a camera or glasses, or an antireflection filter of a VDT.

In the binder, TiO ₂ , Al ₂ O ₃ , ZrO ₂ , ITO, SnO ₂ or MgF ₂ may be used as one of the molecular components forming the binder.

[0053]

As described above, according to the present invention, when a mixed solution in which a plurality of types of fine particles and a binder are mixed is coated on a substrate to form a fine particle coating film, at least one type of fine particles is formed. Since the same raw material as the molecular component of the binder is used, and the raw material different from the molecular component of the binder is used for the other fine particles, irregularities having a light diffusion effect are formed on the surface, and the adhesiveness to the substrate is high due to the irregularities. A fine particle coating film free from cracks can be provided.

Further, by using SiO ₂ as one of the molecular components of the binder and forming a fine particle coating film using the same SiO ₂ as the fine particles, a thin film can be formed at low cost and at a relatively low temperature. . In addition, TiO ₂ , A
_{l 2 O 3, ZrO 2,} ITO, by using one of SnO _2, MgF _2, can be translucent to obtain a high fine particle coating film, using the required conditions of the translucent be able to.

Further, the height difference between the irregularities is 100 to 500 nm.
A sufficient light diffusion effect can be obtained by forming a fine particle coating film as follows.

Further, fine particles having a particle size of 10 to 90 nm may be used, or the mass ratio of the fine particles to the binder may be 1: 1.
By setting the ratio to 〜１０10: 1, the height difference is 100〜500.
It is possible to provide a fine particle coating film having small irregularities in nm.

When the above-mentioned fine particle coating film is applied to a photoelectric conversion element such as a solar cell, for example, a sufficient light diffusion effect can be obtained as a light diffusion layer for confining incident light, and a photoelectric conversion with a good yield can be obtained. A conversion element or the like can be manufactured. In particular, when a fine particle coating film is formed between a transparent substrate and a light-transmitting substrate such as a glass or plastic substrate, the conversion efficiency of the photoelectric conversion element can be improved.

Further, a light diffuser having a large light diffusion effect can be provided by applying the above-mentioned fine particle coating film to a light transmitting substrate.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic cross section of a thin film solar cell to which a fine particle coating film according to an embodiment of the present invention is applied.

FIG. 2 is a diagram showing a state of a surface of a fine particle coating film.

FIG. 3: TiO ₂ with respect to the total mass of SiO ₂ and TiO ₂
Figure showing the relationship between the mass ratio of and the height difference of the irregularities formed on the surface of the fine particle coating film.

FIG. 4 is a diagram showing a schematic cross section of a thin-film solar cell according to another embodiment.

FIG. 5 is a view showing a light diffuser in which a fine particle coating film of the present invention is coated on a light transmitting substrate.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Glass base 2 Fine particle coating film 3 Transparent conductive film 4 Amorphous semiconductor layer A, B Fine particle C Binder

Continued on the front page (51) Int.Cl. ⁶ Identification code FI G02B 5/02 G09F 9/00 318A G09F 9/00 318 G02B 1/10 A

Claims (9)

[Claims] 1. A film is formed by applying a mixture of a plurality of types of fine particles and a binder to a substrate,
In the fine particle coating film on the surface of which the irregularities are formed by the fine particles, at least one type of fine particles is made of the same raw material as the molecular component of the binder, and the other fine particles are made of a raw material different from the molecular component of the binder. Characterized fine particle coating film. Wherein SiO ₂ is used for one of the forming molecule component of the binder, fine particle coating film according to claim 1, wherein the SiO ₂ is used in the fine particles. 3. The method according to claim 1, wherein the other fine particles include TiO ₂ , Al ₂ O ₃ ,
_3. The fine particle coating film according to claim 2, wherein any one of ZrO ₂ , ITO, SnO _{2 and} MgF ₂ is used. 4. The height difference between the irregularities is 100 to 500 nm.
The fine particle coating film according to any one of claims 1 to 3, wherein 5. The fine particle coating film according to claim 1, wherein the fine particles have a particle size of 10 to 90 nm. 6. The mass ratio of the binder to all fine particles is from 1: 1 to 1:10.
6. The fine particle-coated film according to any one of items 1 to 5. 7. A photoelectric conversion element, wherein the fine particle coating film according to claim 1 is provided as a light diffusion layer for confining incident light. 8. The photoelectric conversion device according to claim 7, wherein said fine particle coating film is formed between a light transmitting substrate and a transparent conductive film. 9. A light diffuser formed by applying the fine particle coating film according to claim 1 to a light transmitting substrate.