JP2012212696A - Fresnel lens structure, light condensing device, fresnel lens for solar cells with cover glass, and manufacturing method of the fresnel lens for the solar cells with the cover glass - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light condensing device, such as a solar cell device, having a fresnel lens with a cover glass which is made up entirely of glass.SOLUTION: A light condensing device includes: a cover glass; a glass fresnel lens which has uneven surfaces on a first surface and a rear surface and directly contacts with one surface of the cover glass at the first surface to be integrated therewith; and a light receiving element facing the fresnel lens and disposed so as to be spaced away from the fresnel lens. The above problem is solved by including these components.

Description

  The present invention relates to a condensing device that collects light on a light receiving element using a Fresnel lens such as a solar cell device, and more specifically, a Fresnel lens structure made entirely of glass, a Fresnel lens with a cover glass made entirely of glass, The present invention also relates to a light collecting device that can be miniaturized by using this, and a method for manufacturing a Fresnel lens for a solar cell with a cover glass.

A concentrating solar cell device is known as a solar cell device for converting light energy into electric energy with high efficiency.
In this concentrating solar cell device, as disclosed in Patent Document 1 and the like, light collected by a condensing lens enters a solar cell and is converted into electric energy.

In such a concentrating solar cell device, a Fresnel lens is used as a condensing lens.
Here, as also shown in Patent Document 1, conventionally, a Fresnel lens used in a solar cell device is made of resin. The Fresnel lens has a surface on which irregularities for changing the traveling direction of incident light are formed. And the smooth surface facing the surface of the Fresnel lens and the cover glass are joined using an adhesive.

JP 2006-332535 A

  Here, the refractive index of the resin-made Fresnel lens is generally about 1.4 to 1.6 and is low. Therefore, it is necessary to sufficiently secure a position (a distance to the solar battery cell) for condensing light from the Fresnel lens. Therefore, there is a problem in that the device needs to be thick, and as a result, the solar device itself becomes large.

  The present invention has been proposed in view of the above-described conventional situation, and when used in a solar cell device or the like, the Fresnel lens structure, which can be reduced in size by reducing the thickness, and the light collecting Provided are a device, a Fresnel lens with a cover glass for a solar cell device, and a method of manufacturing the Fresnel lens.

  To achieve the above object, the Fresnel lens structure of the present invention is a Fresnel lens structure including a glass substrate having a first surface and a second surface opposite to the first surface, the glass substrate. A first Fresnel lens structure is provided in which a plurality of concentric annular lenses having a concavo-convex cross section are formed on the first surface.

  Another aspect of the Fresnel lens structure of the present invention is a Fresnel lens structure including a glass substrate and a glass Fresnel lens provided on the glass substrate, and the Fresnel lens has a cross section. A first surface on which a plurality of concentric annular lenses having a concavo-convex shape are formed and a second surface facing the first surface and smoother than the first surface, the second surface being the glass Provided is a Fresnel lens structure characterized by facing a substrate.

  The light collecting device of the present invention is provided on a cover glass having a first surface on which light is incident and a second surface on which the light is emitted, and on the second surface of the cover glass, and has a cross section. A third surface on which a plurality of concentric annular lenses having an uneven shape are formed, and a fourth surface facing the first surface and smoother than the third surface, wherein the fourth surface is the cover A condensing device comprising: a glass Fresnel lens facing the second surface of the glass; and a light receiving element disposed facing the Fresnel lens and spaced apart from the Fresnel lens. To do.

  In such a light collecting device of the present invention, the light receiving element is preferably a solar cell, and the Fresnel lens preferably has a uniform height in the optical axis direction of the convex and concave portions of the unevenness. .

According to another aspect of the light collecting apparatus of the present invention, the cover has a first surface on which a plurality of concentric annular lenses having a concavo-convex cross section are formed, and a second surface facing the first surface. Glass,
Provided is a light collecting device comprising a light receiving element that faces the first surface of the cover glass and is spaced apart from the cover glass.

  Moreover, the Fresnel lens for solar cells with a cover glass of the present invention has a first surface and an uneven surface on the back surface of the first surface, and is integrated by directly contacting the first surface with one surface of the cover glass. And a glass-made Fresnel lens, and a cover glass-attached solar cell Fresnel lens.

  Furthermore, in the method for producing a Fresnel lens for a solar cell with a cover glass of the present invention, a paste containing a glass frit having a softening point lower than the softening point of the cover glass and a binder is applied to the surface of the cover glass. A step of forming a film, and a step of pressing and releasing a mold having irregularities formed on the surface of the coating film at a first temperature at which the binder is softened, and forming irregularities on the surface of the coating film. Removing the binder in the coating film at a second temperature higher than the first temperature; and fusing the glass frit at a third temperature lower than the second temperature; The manufacturing method of the Fresnel lens for solar cells with a cover glass characterized by having.

  According to the present invention having the above-described configuration, the focal length can be greatly shortened, and a small device can be realized.

It is a figure which shows notionally an example of the solar cell apparatus concerning the condensing apparatus of this invention. It is a figure which shows notionally an example of the Fresnel lens structure used for the solar cell apparatus shown in FIG. 1, (A) is a top view, (B) is sectional drawing of the AA in (A). It is a figure which shows notionally another example of a Fresnel lens structure. (A)-(E) are the conceptual diagrams for demonstrating an example of the manufacturing method of this invention. It is a flowchart of the manufacturing method shown in FIG.

  Hereinafter, the condensing device of the present invention, a Fresnel lens for a solar cell with a cover glass, and a method for manufacturing the Fresnel lens will be described in detail with reference to the accompanying drawings.

In FIG. 1, an example which utilized the condensing apparatus of this invention for the solar cell apparatus is shown notionally.
A solar cell device 10 shown in FIG. 1 is a concentrating solar cell device that condenses light and enters a solar cell 12, and basically includes a solar cell 12, a housing 14, and a Fresnel. And a lens structure 16. In addition, it goes without saying that the solar cell device 10 of the present invention may include various members of other known solar cell devices.
Such a solar cell device 10 is, for example, arranged one-dimensionally or two-dimensionally and used as a power generation device (power generation facility).

The solar battery cell 12 receives light and converts light energy into electric energy.
In the present invention, the solar battery cell 12 is not particularly limited, and various known solar battery cells such as Si, GaAs, CuInGaSe, CdTe, AlGaAs, InGaP, InGaAsP, AlInGaP, AlInGaAsP, and Ge can be used. . The structure can be applied in various forms such as a single-junction cell, a monolithic multi-junction cell, and a mechanical stack type in which various solar cells having different wavelength sensitivity regions are connected.

  In the present invention, the light receiving element is not limited to a solar battery cell. For example, various elements that receive light and convert light energy into some energy, such as a photothermal conversion element, can be used.

The housing 14 is a housing that constitutes an outer frame of the solar cell device 10.
In the illustrated example, the housing 14 is a regular quadrangular prism-shaped housing whose upper surface is open, the solar battery cell 12 is fixed at the center of the bottom surface, and the Fresnel lens structure 16 is incorporated into the upper surface, which is an open surface. / Fixed.
In the present invention, the housing 14 may be composed of various plate materials having sufficient heat resistance and strength, as in a normal solar cell device. If the solar battery cell 12 and the Fresnel lens structure 16 can be held at predetermined positions, the housing 14 may not be a plate material but may be a frame shape made of a rod-like material, and the plate material and the rod-like material. And may be used in combination.

As described above, the Fresnel lens structure 16 is fixed to the open top surface of the regular quadrangular prism-shaped housing 14. Then, the incident light is collected and incident on the solar battery cell 12 fixed at the center of the bottom surface of the housing 14. Here, the Fresnel lens structure 16 includes a square cover glass 18 and a circular Fresnel lens 20 as conceptually shown in FIG.
FIG. 2A is a top view (viewed from the light incident surface side of the Fresnel lens 20 in the optical axis direction). 2B is a cross-sectional view taken along the line AA of FIG. 2A as viewed from the same direction as FIG.

In the present invention, the cover glass 18 and the Fresnel lens 20 are both made of glass, and both are formed in direct contact without using an adhesive layer or the like (without using an adhesive or the like). Has been. Here, joining the cover glass 18 and the Fresnel lens 20 without using a resin adhesive is referred to as “integrated”.
That is, this Fresnel lens structure 16 is a Fresnel lens for solar cells with a cover glass of the present invention.

  The cover glass 18 is arranged so as to cover the light incident surface of the Fresnel lens 20, thereby preventing the Fresnel lens 20 from coming into direct contact with rain, dust and dirt in the air, and the Fresnel lens. It also acts as a substrate that supports the substrate 20.

In the illustrated example, the cover glass 18 is a flat plate glass.
In the present invention, the material for forming the cover glass 18 is not particularly limited, and various glass materials can be used. Examples include soda lime silicate glass, aluminosilicate glass, borate glass, lithium aluminosilicate glass, quartz glass, borosilicate glass substrate, alkali-free glass substrate, and the like.
The cover glass 18 constitutes the Fresnel lens structure 16 that is an optical component (optical element). Therefore, the cover glass 18 is preferably formed of glass having high transparency and excellent optical characteristics. In particular, considering high light transmittance, soda lime silicate glass, so-called highly transmissive glass or the like with a reduced iron content in soda lime silicate glass is preferably used.

  Moreover, the cover glass 18 may be strengthened as necessary. Further, after the Fresnel lens 20 is formed, the entire glassy structure 10 may be strengthened.

In the present invention, the thickness of the cover glass 18 is not particularly limited, and may be appropriately selected according to the strength required for the Fresnel lens structure 16, but is 1.5 to 4.5 mm. Is preferred.
By setting the thickness of the cover glass 18 within the above range, it is preferable in that both strength and lightness can be achieved.

  The Fresnel lens 20 is a lens composed of several concentric ring-shaped lenses in order to reduce the thickness, and has a concave-convex cross section. The illustrated example is a so-called circular Fresnel lens. As shown in FIG. 2B, the Fresnel lens is composed of a semicircular central protrusion at the center and a plurality of sawtooth peripheral protrusions located on both sides of the central protrusion. The Here, the peripheral protrusion has a right triangle shape, and the slope of the slope becomes steeper as the distance from the central protrusion increases.

In the present invention, not only the cover glass 18 but also the Fresnel lens 20 are made of glass. The lower surface (surface on the solar battery cell 12 side) of the cover glass 18 and the plane side of the Fresnel lens 20 are directly joined to form the Fresnel lens structure 16.
By having such a configuration, the present invention has various advantages as compared with a conventional Fresnel lens formed by resin.

Since the refractive index of the resin-made Fresnel lens used in the conventional solar cell device is generally about 1.4 to 1.6, the resin-made Fresnel lens has a long focal length. Therefore, in order to collect light efficiently, it is necessary to increase the distance from the Fresnel lens to the solar battery cell. Therefore, the thickness (light incident direction) of the solar cell device is increased, and as a result, the solar cell device is increased in size. In general, the solar cell device is installed in a place where the distance from the ground is high. Therefore, if the solar cell device is large, an increase in installation man-hours and an increase in cost are inevitable in order to prevent falling.
However, according to the solar cell device of the present invention, by using a glass Fresnel lens having a refractive index higher than that of the resin, the distance to the solar cell can be shortened as compared with the conventional solar cell device. . Therefore, compared with the conventional solar cell device, the solar cell device of the present invention can be thinned and reduced in size. Further, since the solar cell device is downsized, the number of installation steps can be reduced as compared with the conventional solar cell device, and as a result, the cost can be reduced.
Moreover, the resin-made Fresnel lens used for the conventional solar cell apparatus is colored with time, and, thereby, a condensing capability falls.
However, according to the solar cell device of the present invention, by using a glass Fresnel lens, it is less likely to be colored with time than a conventional solar cell device. Therefore, it is possible to maintain a high light collecting ability as compared with the conventional solar cell device.
In addition, a resin-made Fresnel lens used in a conventional solar cell device is joined to a cover glass via a resin adhesive. Therefore, an optical loss is caused by the resin adhesive itself, and as a result, the light collection efficiency is lowered. In addition, since the resin has a large coefficient of thermal expansion, it is heated and expanded by sunlight during the day. That is, the resin-made Fresnel lens has poor dimensional stability, the focal position fluctuates due to thermal expansion and contraction, and the light collection efficiency decreases. In addition, the resin is easy to absorb moisture, and the light collection efficiency also decreases due to deformation due to moisture absorption or a change in refractive index. In addition, the glass cover glass and the resin Fresnel lens have a significantly different coefficient of thermal expansion. When heated / expanded by sunlight during the day, the difference between the coefficient of thermal expansion and the Fresnel lens The cover glass may peel off.
However, according to the solar cell device of the present invention, since no resin adhesive is used for joining the cover glass and the glass Fresnel lens, there is no optical loss and high light collection efficiency. Furthermore, according to the solar cell device of the present invention, since there may be almost no difference in thermal expansion coefficient between the cover glass and the Fresnel lens, there is no problem of peeling, and thus the reliability in long-term use is high.

In the present invention, the material for forming the Fresnel lens 20 is not particularly limited, and various glass materials can be used.
For example, SiO ₂ —B ₂ O ₃ —Al ₂ O ₃ system, SiO ₂ —B ₂ O ₃ —Bi ₂ O ₃ system, B ₂ O ₃ —ZnO—Bi ₂ O ₃ system, SiO ₂ —B ₂ O _3— ZnO system, SiO ₂ —BaO—B ₂ O ₃ system, B ₂ O ₃ —BaO—ZnO system, SnO—ZnO—P ₂ O ₅ system, B ₂ O ₃ —ZnO—La ₂ O ₃ system, P ₂ O ₅ —B ₂ O ₃ —R ′ ₂ O—R ″ O—TiO ₂ —Nb ₂ O ₅ —WO ₃ —Bi ₂ O ₃ , TeO ₂ —ZnO, B ₂ O ₃ —Bi ₂ O ₃ Type, SiO ₂ —Bi ₂ O ₃ type, SiO ₂ —ZnO type, B ₂ O ₃ —ZnO type, P ₂ O ₅ —ZnO type, ZnO—B ₂ O ₃ —SiO ₂ —Al ₂ O ₃ type, Bi ₂ O ₃ —B ₂ O ₃ —SiO ₂ —Al ₂ O ₃ , Bi ₂ O ₃ —ZnO—B ₂ O ₃ —SiO ₂ , Bi ₂ O ₃ —ZnO—B ₂ O ₃ —SiO ₂ —Al ₂ O ₃ type, P ₂ O ₅ —Nb ₂ O ₅ —T iO ₂ —R ′ ₂ O, SiO ₂ —TiO ₂ —R ′ ₂ O—R ″ O, SiO ₂ —B ₂ O ₃ —Nb ₂ O ₅ —R ′ ₂ O, P ₂ O ₅ —R _'2 O-R _{"O-based, SiO 2 -Bi 2 O 3 -R} ' 2 O -based, SiO ₂ -Bi ₂ O _{3 -BaO-based, SiO 2 -Bi 2 O 3 -La} 2 O 3 -R" O Various types of glass such as a system are preferably exemplified. In the above formula, R ′ represents an alkali metal element, and R ″ represents an alkaline earth metal element.

The thermal expansion coefficient of the Fresnel lens 20 is preferably close to that of the cover glass 18 in order to more reliably prevent stress due to thermal expansion, peeling due to the stress, and the like.
For example, when soda lime glass (thermal expansion coefficient 80 to 90 × 10 ⁻⁷ / ° C.) is used as the cover glass 18, a Fresnel lens made of glass having a thermal expansion coefficient of 50 to 100 × 10 ⁻⁷ / ° C. is preferable. .

In the present invention, the Fresnel lens 20 is a so-called circular Fresnel lens. However, the present invention is not limited to this, and various types of Fresnel lenses used for a light collecting device such as a solar cell device can be used. .
In addition, the configuration and shape of the Fresnel lens, such as the shape and width of the irregularities of the Fresnel lens (width (pitch) in the direction orthogonal to the optical axis direction), are not particularly limited, and according to the required light collection characteristics, etc. All of the various Fresnel lens configurations are available.

Here, there are two types of Fresnel lenses. In one type, the height of the unevenness constituting the lens (height in the optical axis direction) indicated by an arrow h in FIG. 2B is constant, and the width of the unevenness is directed outward from the center. It is the structure which changes sequentially. The other type is a configuration in which the width of the unevenness constituting the lens is constant, and the height of the unevenness is sequentially changed from the center toward the outside.
Here, in the case of the former configuration, if the prism pitch in the horizontal direction is constant, the height increases toward the periphery, and in the manufacturing method of the present invention described later, it is necessary to increase the thickness of the coating film by the paste. As a result, there is a drawback that the material cost of the paste becomes high. On the other hand, if the latter height is made constant, the film thickness of the coating film by the paste can be suppressed, and the material cost of the paste can be reduced. However, it is conceivable that the prism pitch becomes fine, and the effective surface shape error at the time of processing each prism is integrated by the number of prisms, resulting in a total light collection loss.
The present invention can use any configuration, but can be easily manufactured, has good moldability, and can produce a highly accurate Fresnel lens. The material cost can be reduced by reducing the thickness of the lens layer. A configuration is adopted in which the height of the unevenness is made constant and the width is sequentially changed in terms of reduction.

Further, the Fresnel lens structure 16 of the present invention can be suitably manufactured by the manufacturing method of the present invention described later.
Here, according to this manufacturing method, the large Fresnel lens structure 16 can be easily manufactured. That is, the present invention can easily cope with an increase in the size of a light collecting device such as a solar cell device. Further, according to the present invention, since the thermal expansion of the Fresnel lens 20 is small, it is possible to easily cope with an increase in size in this respect.
Considering the above points, in the present invention, the size of the Fresnel lens structure 16 (the length in the direction perpendicular to the optical axis) is 10 cm or more in that the effects of the present invention can be suitably expressed. It is preferable to do this.

The Fresnel lens structure 16 in the illustrated example is obtained by integrating the cover glass 18 and the Fresnel lens 20 in direct contact with each other. However, the present invention is conceptually illustrated in FIG. The Fresnel lens structure 24 in which a Fresnel lens is formed on the surface of the cover glass may be used.
That is, in this structure, the surface of the cover glass on the solar battery cell 14 side is in a state in which unevenness to be a Fresnel lens is formed. In other words, in this configuration, the cover glass also serves as a Fresnel lens.

  In such a Fresnel lens structure 24, when the refractive index of the cover glass and the Fresnel lens is the same, loss due to light reflection at the interface does not occur, and stress due to the difference in the thermal expansion coefficient between the cover glass and the Fresnel lens occurs. This is preferable in that it does not occur. Note that when there is a difference in refractive index between the cover glass and the Fresnel lens, an interface reflection loss is generated correspondingly, but this is preferable because it is much smaller than the difference in reflectance between air and material.

Hereinafter, an example of a method for manufacturing the Fresnel lens structure 16 will be described with reference to FIGS. 4A to 4E and the flowchart of FIG.
In the method for producing a Fresnel lens structure of the present invention, a paste containing a glass frit having a softening point lower than that of the cover glass 18 and a binder is applied to the cover glass 18. In addition, you may dry the coating film obtained by application | coating as needed. Next, the mold is pressed onto the coating film at a first temperature to transfer the shape of the mold. Next, the transferred coating film is debindered at a second temperature higher than the first temperature. Next, the glass frit is fused by firing at a third temperature higher than the second temperature and lower than the softening point of the cover glass 18. Therefore, the Fresnel lens structure 16 is manufactured by the above process.

Hereinafter, the manufacturing method of the Fresnel lens structure of the present invention will be specifically described.
First, as shown in FIG. 4A, a cover glass 18 is prepared.

  On the other hand, a glass frit paste (hereinafter referred to as a paste) to be the Fresnel lens 20 is prepared. This paste is a paste formed by mixing (kneading) at least glass frit (glass fine particles) and a binder, and dispersing the glass frit in the binder.

The glass frit (that is, the glass that becomes the Fresnel lens 20) is preferably a glass having a softening point lower than that of the cover glass 18, and in particular, a glass frit made of glass that is 50 ° C. lower than the softening point of the cover glass 18. Preferably there is. That is, in the present invention, the Fresnel lens 20 is preferably formed of a material having a softening point lower than the softening point of the cover glass 18.
If the softening point of the glass frit is lower than the softening point of the cover glass 18, particularly 50 ° C. or more, it is preferable to prevent the cover glass 18 from being thermally deformed in the firing step described later, The glass frit can be fused. For example, when the cover glass 18 is soda lime glass, since the softening point is around 730 ° C., the softening point of the glass frit is preferably 680 ° C. or less.

The glass frit may be the same glass as the cover glass forming material.
Thereby, the Fresnel lens structure 24 in which the Fresnel lens is formed on the cover glass as shown in FIG. 3 can be obtained.

On the other hand, the softening point of the glass frit is preferably higher than the decomposition temperature of the binder contained in the paste. Although it varies depending on the type of the binder, the softening point of the glass frit is particularly preferably 350 ° C. or higher.
By using the glass frit having such a softening point, it is possible to suitably prevent simultaneous debinding and glass fusing in the debinding step at the second temperature described later.

The glass frit preferably has a smaller viscosity change with respect to a temperature change in a temperature region near the softening point.
When this change in viscosity is small, it is possible to reduce the collapse of the shape in the glass frit sintering step due to the third temperature described later, and it is possible to produce a glass structure having a fine shape with higher accuracy. it can.

The average particle size of the glass frit is preferably 10 μm or less.
By setting the average particle size of the glass frit to 10 μm or less, it is possible to prevent the surface roughness of the coating film formed by applying / drying the glass frit paste from increasing, and the shape of the mold in the press process described later Can be transferred more reliably, and further, damage to the mold can be prevented more reliably.
The lower limit of the particle diameter is not particularly limited, but is preferably about 0.5 μm or more in consideration of the cost of pulverizing the glass when producing the glass frit.

As described above, the (glass frit) paste is a paste formed by mixing at least glass frit and a binder.
In the present invention, the binder holds the paste on the cover glass 18, and plays a role of developing adhesiveness with the glass so that the glass frit is not peeled off from the cover glass 18 in the press process described later. It plays the role of adjusting the hardness of the coating film formed by coating and improving the shape transferability of the mold.

The binder (binder resin) is not particularly limited, and various resins can be used.
Examples include cellulose polymers such as nitrocellulose, acetylcellulose, ethylcellulose, carboxymethylcellulose, and methylcellulose, natural polymers such as natural rubber, polybutadiene rubber, chloroprene rubber, acrylic rubber, isoprene synthetic rubber, and cyclized rubber, and polyethylene. And synthetic polymers such as polypropylene, polymethyl acrylate, polymethyl methacrylate, polystyrene, polyvinyl alcohol, polyvinyl butyral, polyvinyl acetate, polyester, polycarbonate, polyacrylonitrile, polyvinyl chloride, polyamide, polyurethane, etc. .
These resins may be used alone, or may be used as a mixture or a copolymer.

In this production method, the content of glass frit in the paste is not particularly limited, but is preferably 20 to 90 wt%.
By setting the glass frit content in the paste to 20 wt% or more, a sufficient film thickness can be ensured by a single application of the paste, and a plurality of applications are performed to obtain a desired film thickness. The cost increase by this can be suppressed. On the other hand, by setting the content of glass frit in the paste to 90 wt% or less, it is possible to prevent the viscosity of the paste from becoming too high, and to apply the paste to the paste suitably. Further, by setting the glass frit content to 90 wt% or less, the amount of the binder in the paste can be sufficiently secured, and thereby sufficient adhesion between the cover glass 18 and the coating film can be obtained.
Considering the above points, the glass frit content in the paste is more preferably 50 to 80 wt%.

On the other hand, the content of the binder in the paste used in this production method is not particularly limited, but the binder is preferably 1 to 50 parts by weight with respect to 100 parts by weight of the frit.
By setting the binder to 1 part by weight or more with respect to 100 parts by weight of the frit, sufficient adhesion between the cover glass 18 and the coating film can be secured. Further, by setting the binder to 50 parts by weight or less with respect to 100 parts by weight of the frit, it is possible to sufficiently obtain the rigidity of the coating film in the press process described later, and to prevent the coating film from adhering to the mold. Further, by setting the binder to 50 parts by weight or less, voids generated by the binder removal step can be reduced, and the shape change in the subsequent glass frit firing step can be reduced to control the shape of the Fresnel lens 20 with higher accuracy. Can be done.
Considering the above points, the amount of the binder in the paste is more preferably 5 to 30 parts by weight with respect to 100 parts by weight of the glass frit.

In addition to such components, the paste may contain a solvent as necessary in order to adjust the viscosity of the paste and improve the coating property to glass. Solvents include hydrocarbons such as toluene and xylenetetralin, alcohols such as methanol and ethanol, ketones such as acetone and methyl ethyl ketone, esters such as methyl acetate and ethyl acetate, ethylene glycol and diethylene glycol solvents. Can be used.
Furthermore, you may add surfactant for improving applicability | paintability, the plasticizer for adjusting the hardness of a coating film, etc. to a paste as needed.

  The paste preparation method is not particularly limited. For example, a predetermined amount of glass frit and binder, or other necessary components such as a solvent, is added to a mixing device or a kneading device to uniformly disperse the glass frit. Thus, it is sufficient to mix (knead) sufficiently.

After the paste is prepared in this way, the paste is applied to the surface of the cover glass 18 as shown in FIG.
In the production method of the present invention, the paste coating method is not particularly limited, and various known coating methods can be used.
For example, roller coating, hand coating, brush coating, spin coating, dip coating, screen printing, curtain flow, bar coating, die coating, gravure coating, micro gravure coating, reverse coating, roll coating, flow coating, spray coating, etc. A method is illustrated.
Of these, die coating and screen printing are preferably used because large-area coating is easy and a sufficiently thick film can be obtained by a single coating.

  In addition, what is necessary is just to set the application | coating thickness of a paste suitably according to the shape height of the Fresnel lens 20 to form, the shape of the unevenness | corrugation of the Fresnel lens 20 formed with the shaping | molding die mentioned later.

Further, as shown in FIG. 4B, after applying the paste to the surface of the cover glass 18, the coating film (that is, paste) is dried to form the coating film 30 as necessary.
The method for drying the paste is not particularly limited, and for example, a method of heating the cover glass 18 coated with the paste in an oven, a method of UV irradiation, or the like can be used.
In addition, when drying the coating film of a paste by heating, it is preferable to heat at the temperature which does not change a binder. Specifically, the heating is preferably performed at a temperature of 80 to 200 ° C. in the atmosphere for 5 to 60 minutes.

  In addition, when the coating film is dried, the layer thickness of the coating film 30 becomes thinner than the coating thickness of the paste. In this case, considering the layer thickness of the coating film 30 obtained after drying, It is preferable to set the coating thickness of the paste.

When the coating film 30 is thus formed on the surface of the cover glass 18, the coating film 30 is then heated to a first temperature.
The method for heating the coating film 30 is not particularly limited, and various known methods can be used. In this regard, the following heating to the second temperature and the third temperature is the same.

The first temperature is not particularly limited, and the temperature at which the binder of the coating film 30 is softened and can be press-molded by the mold 32 may be appropriately set according to the type of the binder. 100 to 200 ° C. is preferable.
As will be described later, in the present invention, the coating film 30 is formed in a predetermined shape by pressing the coating film 30 with the molding die 32 at the first temperature. Here, by setting the first temperature to 100 ° C. or higher, the paste layer can be sufficiently softened with many pastes, and accurate molding can be performed. Further, by setting the first temperature to 200 ° C. or lower, it is possible to suppress excessive softening of the binder due to the temperature being too high, and adhesion of the binder due to this to the mold or excessive heating of the binder. Decomposition and alteration can be suitably prevented.

When the coating film 30 is set to the first temperature, as shown in FIGS. 4C to 4D, molding having a pressing surface on which irregularities corresponding to the shape of the irregular surface of the Fresnel lens 20 to be formed are formed. The coating film 30 is pressed (pressed) by the mold 32, and then the forming mold 32 is removed from the coating film 30, as shown in FIGS. 4 (D) to 4 (E).
Thereby, the shape of the shaping | molding die 32 can be transcribe | transferred to the coating film 30, and it can shape | mold to the predetermined | prescribed shape according to the uneven surface of the Fresnel lens 20. FIG.

Here, in the present invention, the cover glass 18 is not used, and the coating film 30 having a thickness in consideration of the thickness of the cover glass is formed on a flat molding table, and not only the Fresnel lens but also the cover glass. The coating film 30 is pressed using the molding die 32 having a shape including the shape, and the shape of the molding die 32 is transferred to the coating film 30 as shown in FIG. And may be formed into a predetermined shape.
Thereby, the Fresnel lens structure 24 in which the Fresnel lens is formed on the cover glass as shown in FIG. 3 can be obtained.

In the manufacturing method of the present invention, the bulk glass is not directly molded, but the softer coating film 30 is press-molded to keep the press temperature and pressure low and to make the press conditions mild. Therefore, the wear of the expensive press mold can be almost eliminated and the life can be extended, and the glass structure can be manufactured at low cost. Moreover, since the soft coating film 30 is press-molded at a relatively low temperature and low pressure, very fine molding can be performed, and optical members such as Fresnel lenses and lenticular lenses having fine irregularities can be manufactured. It is preferable.
Further, the moldability of the coating film 30 and the releasability (peelability) between the coating film 30 and the mold 32 can be controlled by the binder contained in the paste, and does not depend on the material characteristics of the glass frit. Wide selection of glass frit materials.

The forming material of the mold 32 is not particularly limited, and can provide desired dimensional accuracy, can maintain the required accuracy with little deformation of the coating film 30 by pressing, and the temperature during pressing. Various materials can be used as long as they do not soften or change quality.
For example, metal, ceramics, etc. can be used. Specifically, examples of the material of the metal mold include nickel, hardened steel, and various other materials used for press-molding ceramic fired products. Further, as the ceramic type material, there are silicon nitride, alumina, zirconia and the like.

Here, in the example shown in FIG. 4, a flat mold (stamp mold) is illustrated as the mold 32, but in the present invention, a roll mold that can be continuously molded is also suitable. Is available.
In the case of the roll type, the load of the forming die is concentrated in a line shape, so that the shape can be transferred satisfactorily with a small load and the mold release is easy. On the other hand, in the case of a roll mold, the mold is difficult to perform complex two-dimensional processing such as a circular Fresnel lens.
On the other hand, in the case of a flat mold, it is necessary to apply a load to the entire surface, a larger load is required depending on the press area, and it is difficult to release compared to a roll mold. On the other hand, two-dimensional mold processing is easy.
Therefore, as the mold 32, a roll mold or a plane mold may be appropriately selected and used according to the shape of the intended Fresnel lens 20.

In the production method of the present invention, the binder is removed from the coating film 30 formed in the binder removal step at the second temperature described later, and further, the coating film 30 exists in the baking step at the third temperature. The frit is fused so as to fill the voids generated and the voids generated by debinding.
Therefore, volume shrinkage is unavoidable in the entire coating film 30 formed by the mold 32. Therefore, the mold 32 for press-molding the coating film 30 needs to design the shape of the mold by incorporating the shrinkage.

Although the press pressure by the shaping | molding die 32 changes with paste materials, it is preferable that it is 10-80 Mpa.
By setting the pressing pressure to 10 MPa, the shape of the mold 32 can be reliably transferred to the paste layer, that is, sufficient transferability of the mold shape can be obtained. Further, by setting the pressing pressure to 80 MPa or less, it is possible to suitably prevent the cover glass 18 and the mold 32 from being damaged due to the pressure being too high. Considering the above points, the press pressure by the mold 32 is more preferably 10 to 50 MPa.
The press time of the coating film 30 by the mold 32 is not particularly limited, but is preferably 10 to 120 seconds.

  After the coating film 30 is pressed and molded by the molding die 32 in this way, the paste layer is then brought to a second temperature higher than the first temperature to remove the binder from the coating film 30. Do the binder.

The second temperature, that is, the binder removal temperature may be appropriately set according to the type of the binder, but is preferably 300 ° C to 500 ° C. The binder removal time (time for keeping the coating film 30 at the second temperature) varies depending on the type of binder and the amount of binder in the paste, but is preferably 5 to 60 minutes.
Note that the binder removal at the second temperature is preferably performed in an air atmosphere in order to promote oxidative decomposition of the binder.

  After the binder is removed in this way, firing is then performed at a third temperature higher than the second temperature and lower than the softening point of the cover glass 18 to fuse the glass frit. Thus, the Fresnel lens 20 is completed, and the cover glass 18 and the Fresnel lens 20 are fused together to complete the Fresnel lens structure 16.

The third temperature, that is, the firing temperature, may be appropriately set according to the glass frit to be used, but it is preferably performed at 350 to 650 ° C.
The firing atmosphere may be in the air, but it is more preferred to fire under reduced pressure in order to positively discharge bubbles present in the frit film out of the film.
As a result, no bubbles are present in the Fresnel lens 20, and a more transparent film can be obtained.

In the production method of the present invention, the coating film 30 is heated to a second temperature at which the binder decomposes, and is held for a certain period of time to perform a debinding process, and then a third fusing of the glass frit occurs. It is preferable that the glass frit be fused by heating to a temperature and holding for a certain period of time for firing.
However, the present invention is not limited to this. For example, in the case where the binder is easily decomposed, after the molding of the coating film 30 at the first temperature, from the first temperature to the third temperature. A method of terminating the binder removal while heating the glass frit to the third temperature at which the frit of the glass frit occurs gradually (or stepwise) can be suitably used. is there. That is, in this case, the second temperature is not a constant temperature, and the temperature that is higher than the first temperature and that is lower than the third temperature is the second temperature.

  Such a manufacturing method of the present invention does not directly press-mold bulk glass but presses a softer (glass frit) coating film 30 to perform molding, so that the selection of materials and shapes can be performed at low cost. The degree of freedom is high, the area can be easily increased, and fine irregularities can be formed.

  As described above, the Fresnel lens structure, the light collecting device, the Fresnel lens for solar cell with cover glass, and the manufacturing method thereof have been described in detail. However, the present invention is not limited to the above-described examples, and the present invention. It goes without saying that various improvements and changes may be made without departing from the gist of the invention.

  Hereinafter, the present invention will be described in more detail with reference to specific examples of the present invention. The present invention is not limited to these.

[Example 1]
<1. Formation of coating film>
First, butyral resin (Sekisui Chemical Co., Ltd. ESREC BL-1H) as a binder was dissolved in 15 parts by weight and 85 parts by weight of butyl carbitol acetate to prepare a binder solution.
Subsequently, 100 parts by weight of the binder solution, glass frit (SiO ₂ —B ₂ O ₃ —ZnO glass, thermal expansion coefficient 85 ± 5 × 10 ⁻⁷ / ° C., softening point 650 ° C., refractive index 1.72 ) 100 parts by weight were mixed and stirred to prepare a (glass frit) paste.

As the cover glass 18, soda lime glass having a plate thickness of 250 mm square was prepared.
The prepared paste was applied to the cover glass 18 by a screen printing method using a metal mask having a mask thickness of 200 μm. Thereafter, the substrate glass to which the paste was applied was put into a drier and dried at 180 ° C. for 40 minutes to obtain a cover glass 18 on which a coating film 30 having a thickness of 150 μm was formed.

<2. Press>
The cover glass 18 on which the coating film 30 is formed is set in a press machine in which a surface plate is heated to 200 ° C., and a flat molding die in which irregularities corresponding to a circular Fresnel lens are formed on the coating film ( Nickel, size 250 mm square, lens height 100 μm) was placed thereon and pressed for 60 seconds so that the pressure applied to the substrate glass was 35 MPa.
Thereafter, the mold was released to obtain a coating film 30 onto which the shape of the mold (that is, Fresnel lens 20) was transferred. When the shape height of the coating film 30 was measured, it was 100 μm, and the shape of the mold was accurately transferred. The height of the shape was measured by SEM observation of the cross section of the coating film.

<3. Firing>
The cover glass 18 on which the coating film 30 to which the shape of the mold has been transferred is formed is placed in a firing furnace, heated to 450 ° C. at a temperature increase rate of 10 ° C./min in the air atmosphere, and 90 minutes at 450 ° C. The binder was removed.
Thereafter, the inside of the firing furnace was depressurized to 1 Pa, heated to 600 ° C. at a heating rate of 10 ° C./min, and held at 600 ° C. for 30 minutes to perform firing, and the glass frit was fused, as shown in FIG. Thus, the Fresnel lens structure 16 in which the cover glass 18 and the Fresnel lens 20 were directly joined was obtained.

<4. Evaluation>
The focal length of the obtained Fresnel lens structure 16 was measured by the following method. That is, an illuminometer was installed on the extended line at the center of the Fresnel lens, and the illuminance of the collected light was measured by irradiating parallel light from the non-lens surface of the Fresnel lens. The distance between the Fresnel lens and the illuminometer was changed, and the distance between the two when the illuminance was highest was used as the focal length.
As a result, the focal length was about 245 mm.
The focal length was simulated for a Fresnel lens structure having exactly the same configuration and having a Fresnel lens made of PMMA (polymethyl methacrylate refractive index 1.5) adhered to the same cover glass 18.
As a result, the focal length was about 360 mm. That is, the Fresnel lens structure 16 of the present invention can have a focal length of about 70% compared to a structure having the same configuration using a PMMA Fresnel lens.
From the above results, the effect of the present invention is clear.

  The present invention is particularly applicable to a concentrating solar cell device.

DESCRIPTION OF SYMBOLS 10 Solar cell apparatus 12 Solar cell 14 Housing 16, 24 Fresnel lens structure 18 Cover glass 20 Fresnel lens 30 Coating film 32 Mold

Claims (8)

A Fresnel lens structure including a glass substrate having a first surface and a second surface facing the first surface,
A Fresnel lens structure, wherein a plurality of concentric annular lenses having a concavo-convex cross section are formed on the first surface of the glass substrate. A Fresnel lens structure comprising a glass substrate and a glass Fresnel lens provided on the glass substrate,
The Fresnel lens has a first surface on which a plurality of concentric ring-shaped lenses having a concavo-convex shape are formed, and a second surface that faces the first surface and is smoother than the first surface, The Fresnel lens structure, wherein the second surface faces the glass substrate. A cover glass having a first surface on which light is incident and a second surface from which the light is emitted;
A third surface provided on the second surface of the cover glass and formed with a plurality of concentric ring-shaped lenses having a concavo-convex shape is opposed to the first surface and smoother than the third surface. A glass-made Fresnel lens facing the second surface of the cover glass;
A light collecting device comprising: a light receiving element that faces the Fresnel lens and is spaced apart from the Fresnel lens.   The light collecting device according to claim 3, wherein the light receiving element is a solar battery cell.   5. The light collecting device according to claim 3, wherein the Fresnel lens has a uniform height in the optical axis direction of the projections of the irregularities. A cover glass having a first surface on which a plurality of concentric ring-shaped lenses having a concavo-convex cross section are formed, and a second surface facing the first surface;
A light collecting device, comprising: a light receiving element that faces the first surface of the cover glass and is spaced apart from the cover glass. A cover glass,
And a glass Fresnel lens that has a first surface and an uneven surface on the back surface of the first surface and is integrated by directly contacting the first surface with one surface of the cover glass. Fresnel lens for solar cells with cover glass. Applying a paste containing a glass frit and a binder having a softening point lower than the softening point of the cover glass on the surface of the cover glass to form a coating film;
At a first temperature at which the binder is softened, pressing and releasing a mold having irregularities formed on the surface of the coating film, and forming irregularities on the surface of the coating film;
Removing the binder in the coating film at a second temperature higher than the first temperature;
And a step of fusing the glass frit at a third temperature lower than the second temperature. A method for producing a Fresnel lens for a solar cell with a cover glass.

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