JP2008205080A - Solar cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solar cell capable of efficiently utilizing light (particularly the light cast to the recessed internal surface of a converging type spherical solar cell) from a light source for a photoelectric conversion. <P>SOLUTION: The solar cell 1 has a supporter 30 with a large number of recessed sections 32 and spherical photoelectric conversion elements 10 arranged to each of these recessed sections 32 one by one. Infrared reflecting films 34 having an infrared reflecting pigment are arranged on the internal surfaces of the recessed sections 32, thus forming reflecting surfaces 34a having infrared reflecting properties. The solar cell 1 is configured so that infrared rays reflected by the reflecting surfaces 34a are projected to the photoelectric conversion elements. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a solar cell having a configuration in which a spherical photoelectric conversion element (for example, spherical silicon) is accommodated in a recess of a support.

  A spherical photoelectric conversion element is arranged one by one in each of a large number of recesses provided in the support, and the inner surface of the recess functions as a reflecting mirror to effectively use the light from the light source (increasing the light collection rate). A solar cell configured as described above is known. Patent Documents 1 to 4 are cited as conventional technical documents regarding this type of solar cell (sometimes referred to as a concentrating spherical solar cell).

JP 2002-164554 A JP 2004-063564 A JP 2006-229025 A JP 2006-245134 A

  In general, in a concentrating spherical solar cell, it is recommended that the inner surface be a mirror-finished metal surface in order to increase the reflectivity of the inner surface of the recess and improve the photoelectric conversion efficiency (for example, Patent Document 2). (See description in paragraphs 0037, 0038, etc.). Here, if light that strikes the inner surface of the recess (light incident on the inner surface of the recess) can be more efficiently reflected and introduced into the photoelectric conversion element, more light can be used for photoelectric conversion, which is beneficial. is there.

  The present invention was made for the purpose of improving conventional solar cells (typically concentrating spherical solar cells), and more efficiently photoelectrically converts light from a light source (especially light that hits the inner surface of a recess). The purpose is to provide usable solar cells.

  According to the present invention, a solar cell (typically a concentrating spherical solar cell) comprising a support having a large number of recesses and spherical photoelectric conversion elements arranged one by one in each of the recesses. There is provided a solar cell in which a reflective surface having an infrared reflective pigment is formed on the inner surface of the recess. The solar cell is configured such that infrared light reflected by the reflecting surface is incident on the element.

In general, light used as a light source for operating a solar cell (typically, sunlight or light imitating this) includes not only visible light but also infrared light. However, a metal surface (for example, a silver mirror surface) such as a concave inner surface of a conventional concentrating spherical solar cell can exhibit high reflectivity for visible light having a wavelength of approximately 780 nm or less, but is longer than that. The reflectivity of light having a wavelength (for example, near infrared rays having a wavelength of about 780 nm to 2500 nm) is poor. For this reason, in the conventional concentrating solar cell in which the concave portion inner surface is configured as a metal surface, infrared rays cannot be sufficiently utilized.
On the other hand, since the solar cell according to the present invention has a configuration in which an infrared reflecting pigment is disposed on the inner surface of the recess, the infrared light hitting the inner surface (reflection surface) of the recess is efficiently reflected and introduced into the photoelectric conversion element. be able to. Therefore, according to the solar cell concerning this invention, the light from a light source can be utilized more efficiently for photoelectric conversion by raising the utilization efficiency (condensation rate) of infrared rays.
Note that the solar cell disclosed herein is typically preferably used for photoelectric conversion using sunlight, but is not limited to this application, and is not limited to this application, and is used in photoelectric conversion using various lights that operate the battery. The solar cell (that is, the photovoltaic cell) according to the invention can be used.

  In a preferred embodiment, the reflecting surface formed on the inner surface of the recess is a reflecting surface made of an infrared reflecting film containing the infrared reflecting pigment. A solar cell having such an infrared reflecting film on the inner surface of the recess is preferable because it is easier to manufacture than a configuration in which an infrared reflecting pigment is contained in the support itself forming the recess, for example.

  The color of the infrared reflecting film is preferably a bright color tone from the viewpoint of enhancing the utilization efficiency of visible light, and particularly preferably white. According to such a white infrared reflective film, a high reflectance can be realized in any wavelength region of visible light and infrared light (particularly near infrared light).

  The solar cell disclosed here can further include a transparent resin filler (which means colored transparency) filled in the recess. According to the solar cell having such a configuration, the reflective surface is covered with the filler to prevent the dirt from adhering to the reflective surface, and the infrared reflectiveness (preferably, the infrared reflective property and the visible light reflective property) of the reflective surface. Can be maintained in a good state. Therefore, the light from the light source can be efficiently used for photoelectric conversion over a longer period. According to the structure having the filler, the photoelectric conversion element and the reflection surface (for example, an infrared reflection film) can be protected from damage due to external force.

  A preferred example of the resin constituting the filler is a silicone resin. Since the silicone resin is excellent in light resistance, a filler formed using the silicone resin is unlikely to be deteriorated by light (coloring, embrittlement, transparency decrease, etc.). Therefore, according to such a solar cell, photoelectric conversion can be performed efficiently over a longer period.

  In a preferred embodiment of the solar cell disclosed herein, the outer surface side of the filler is formed in a concave lens shape for each concave portion. According to the solar cell having such a configuration, since the surface area of the filling body is increased as compared with the case where the surface of the filling body is planar, more light can be taken into the concave portion (light absorption is increased). Therefore, more light can be directly or directly reflected on the inner surface of the concave portion and introduced into the photoelectric conversion element.

  The solar cell disclosed here can be configured such that an oxidation catalyst is disposed on the outer surface of the filler. By setting it as this structure, antifouling property can be provided to the outer surface of the said filler. Therefore, it is possible to prevent an event in which light from the light source is blocked by dirt adhering to the filler. According to the solar cell having such a configuration, photoelectric conversion can be efficiently performed over a longer period.

  As the catalyst to be used, a highly transparent catalyst is preferable, and in particular, a titania phosphate catalyst is preferably used. In addition, in the aspect in which the oxidation catalyst is arranged on the outer surface of the filler as described above, it is particularly preferable to employ a silicone resin as the resin constituting the filler because of excellent resistance to deterioration by the catalyst.

  Hereinafter, preferred embodiments of the present invention will be described. Note that matters other than the matters specifically mentioned in the present specification and necessary for carrying out the present invention (for example, a method for producing a support, a shape of a concave portion and a method for forming the same, and various photoelectric conversion elements are produced. The specific method and the general matters relating to the specific operation method when the photoelectric conversion elements are arranged and electrically connected, etc.) can be grasped as the design matters of those skilled in the art based on the prior art in this field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field.

  In the technique disclosed herein, spherical photoelectric conversion elements (hereinafter also referred to as “spherical elements”) are arranged one by one in each of a large number of recesses provided in a support, and the inner surface of the recess is reflected by a reflecting mirror. It can apply widely to various solar cells provided with the structure made to function as. In one typical configuration of this type of solar cell (condensing spherical solar cell), a spherical element in which an n-type semiconductor layer is formed on the surface of a spherical p-type semiconductor is used as the spherical element. The spherical element has an opening that exposes a part of the p-type semiconductor inside the part of the n-type semiconductor layer. For example, spherical particles having a diameter of, for example, about 0.5 to 2 mm (for example, about 1 mm in diameter) can be preferably used. The support has a plurality of recesses for accommodating such spherical elements one by one. A through-hole is provided at the bottom of each recess so that the exposed portion of the p-type semiconductor of the spherical element disposed in the recess faces the back side of the support. The support includes an upper conductor layer that forms the recess and is electrically connected to the n-type semiconductor layer. A lower conductor layer is disposed on the back side of the upper conductor layer, and the lower conductor layer is electrically connected to the exposed portion of the p-type semiconductor through the through hole. The upper conductor layer and the lower conductor layer are electrically insulated by an insulating layer interposed between them. Or the solar cell similarly comprised using the spherical element which formed the p-type semiconductor layer in the surface of the spherical n-type semiconductor may be sufficient.

  As the spherical element, a spherical photoelectric conversion element mainly composed of silicon can be preferably used. A solar cell generally referred to as a “micro concentrating spherical silicon solar cell” is a typical example of a concentrating solar cell formed using a silicon-based spherical element. As such a spherical element, for example, spherical silicon produced by a known melt dropping method or the like, or a product obtained by appropriately processing the spherical silicon can be preferably used. In this melt dropping method, silicon is melted and dropped from a nozzle, and while the dropped droplet naturally falls, it is spheroidized using surface tension and is cooled and solidified while maintaining the spherical shape. For example, a p-type silicon sphere (spherical p-type silicon) is obtained by using p-type silicon as the molten silicon in the melt dropping method, and phosphorus is diffused from the gas phase to the p-type silicon sphere. An n-type semiconductor layer can be formed on the surface of a p-type silicon sphere (spherical p-type semiconductor). One end of the spherical silicon is removed by polishing or the like to expose the p-type semiconductor inside the n-type semiconductor layer. In this way, a photoelectric conversion element for a spherical silicon solar cell (typically, a micro concentrating spherical silicon solar cell) can be obtained.

  In the solar cell according to the present invention, a reflective surface having an infrared reflective pigment is formed on the inner surface of the recess. The infrared reflection pigment (also referred to as a heat-shielding pigment or a heat-shielding pigment) is known to have a property of reflecting infrared rays (particularly, near infrared rays having a wavelength of about 780 nm to 2500 nm). A pigment composed of a material (for example, various infrared reflective pigments marketed as having the property) can be appropriately selected and used. Specific examples of such a material exhibiting infrared reflectivity include metal oxides such as indium-doped tin oxide (ITO), antimony-doped tin oxide, and titanium oxide. Although not particularly limited, for example, a pigment exhibiting a reflectance of at least approximately 40% or more (more preferably approximately 60% or more, more preferably approximately 70% or more) in the wavelength range of 780 nm to 1500 nm is preferably employed. Can do.

  In a preferred embodiment, the reflecting surface is constituted by an infrared reflecting film containing an infrared reflecting pigment. For example, a solar cell having a configuration in which the infrared reflective film is provided on the inner surface of a recess formed by a conductive member (for example, an aluminum plate, which may be a conductive member that functions as the above-described upper conductor) is preferable. Such a reflective film is suitable, for example, by applying (typically applying) an infrared reflective film-forming composition containing an infrared reflective pigment and a suitable vehicle to the conductive member before or after the formation of the recess. Can be formed. Alternatively, the composition is formed into a film, and the infrared reflective film (infrared reflective film) is laminated on the surface of the member by, for example, thermocompression bonding the infrared reflective film to the conductive member before or after forming the recess. May be. As the infrared reflective film forming composition, various commercially available thermal barrier paints can be preferably used. Examples of such thermal barrier paints include Nagashima Special Paint Co., Ltd., product name “Miracool” series; Nippon Paint Co., Ltd. product, trade name “ATTSU-9” series; NTT Advanced Technology Corporation product, product name “AtShield” Series, etc. Or you may utilize the inner surface of the recessed part formed with the electroconductive material containing the infrared reflective pigment as said reflective surface. The color of the reflective surface (preferably an infrared reflective film) is preferably a bright color tone with the naked eye, and is particularly preferably white. The reflective surface having such a color tone can be suitably formed using, for example, a commercially available white thermal barrier paint (for example, the above-mentioned “Miracool” series white thermal barrier paint).

The solar cell disclosed here can be preferably implemented, for example, in a mode in which the concave portion is filled with a transparent resin filler. The resin filler may be colored transparent or colorless and transparent. Usually, a colorless and transparent resin filler is more preferable. It is preferable to use a resin filler having high transparency for both visible light and infrared light (particularly near infrared light). In addition, from the viewpoint of followability to bending deformation and the like of the support (and thus the solar cell), a resin filler made of a flexible (easily elastically deformable) material can be preferably employed.
Examples of resins that can be preferably used as the constituent material of the resin filler include silicone resins, ethylene-vinyl acetate copolymers, acrylic resins (for example, (meth) acrylic ester polymers), and the like. Among these, the use of a silicone resin (a polymer having a siloxane bond as a main skeleton) is preferable. For example, a concave portion is filled with a curable silicone resin composition (composition for forming a resin filler) mainly comprising a partially hydrolyzed condensate of dialkoxysilane or trialkoxysilane (silicone resin precursor) and cured. By doing so, a silicone resin filler can be formed.

  In addition to the resin component, the above resin filler is an appropriate optional component (various additives commonly used in the field of resin moldings) as required, as long as the transparency of the filler is not significantly impaired. May be included. Similarly, the composition for forming a resin filler used for the preparation of the filler includes, as necessary, appropriate optional components (additives, additives) as long as the transparency of the resin obtained from the composition is not significantly impaired. Solvent and the like). Examples of the composition for forming a resin filler include, for example, a composition mainly composed of a precursor of a resin (a concept including a monomer, an oligomer, a prepolymer, etc.) constituting the resin filler, and the resin. A composition or the like dissolved or dispersed in an appropriate solvent can be preferably used.

  Such a resin filler is provided, for example, so as to fill a gap between the inner surface of the recess and the spherical element, and preferably so that the upper end of the spherical element is buried in the resin filler. The filler may have two or more structural parts having different compositions and / or properties (such as hardness). For example, a resin filler having a structure in which a relatively hard first resin layer disposed on the bottom side of the recess and a relatively soft second resin layer laminated on the molded body is laminated. Can do. According to such a resin filler, the spherical element can be reliably protected by the relatively hard first resin layer, and the entrance side (upper part) of the recess is formed by the relatively soft second resin layer. Therefore, it is possible to realize good followability with respect to bending deformation of the support (and thus the solar cell).

  In a preferred embodiment of the solar cell disclosed herein, the outer surface side of the resin filler is formed in a concave lens shape for each concave portion. That is, the upper end of the filling body is a concave surface that is recessed from the peripheral edge of each recess toward the center. Such a concave lens shape is obtained by using, for example, a composition containing a small amount of a solvent as the above-described resin filler forming composition, filling the concave portion with the composition, and then removing the solvent from the filled composition. It can be easily formed by removing (typically evaporating). The shape (dentation) of the concave lens can be adjusted, for example, by the ratio of the solvent contained in the composition used when forming the resin filler (preferably the silicone resin filler). However, if the content ratio of the solvent is too large, bubbles may be easily generated when the solvent is removed from the composition filled in the recesses. When such bubbles remain in the filling body, the transparency (light transmission) of the filling body may be hindered. Accordingly, it is usually appropriate that the content of the solvent in the composition is 15% by mass or less (typically 0.1 to 15% by mass), and 10% by mass or less (typically 0.1% or less). To 10 mass%). For example, the content ratio can be about 4 to 6% by mass.

  As a preferred embodiment, the solar cell disclosed herein can be configured such that a photocatalyst or other oxidation catalyst is disposed on the outer surface of the resin filler. As this catalyst, for example, various conventionally known photocatalysts can be appropriately selected and used. It is preferable to use a catalyst exhibiting high transparency for both visible light and infrared light (particularly near infrared light). From the viewpoint of transparency, a titania phosphate catalyst can be particularly preferably used. Commercially available products of the titania phosphate catalyst include a trade name “Titania Home” series available from Daiko Co., Ltd., a trade name “Ecoprif” series available from Aisei Environmental System Co., Ltd., and the like. By applying such a titania phosphate catalyst to the surface of the resin filler, for example, in the form of a solution, the titania phosphate catalyst can be disposed on the surface of the filler.

  Several embodiments relating to the present invention will be described below with reference to the drawings. However, the present invention is not intended to be limited to those shown in the embodiments. Further, in the following description, members / parts having the same function are denoted by the same reference numerals, and redundant description is omitted.

<First Example>
The structure of the solar cell according to this example is shown in FIGS. This solar cell 1 is roughly composed of a support 30 having a large number of recesses 32 and spherical elements 10 housed one by one in each recess 32.
The spherical element 10 is mainly composed of silicon and has a diameter of about 1 mm. As shown in FIG. 2, the spherical element 10 includes a spherical p-type semiconductor 14 and an n-type semiconductor layer 12 provided so as to cover most of the surface thereof. An opening 16 where the n-type semiconductor layer 12 is not provided is formed at one end of the spherical element 10, and the p-type semiconductor 14 is exposed to the outside through the opening 16. As the spherical element 10, for example, a spherical silicon produced by a known melt dropping method or the like as described above can be used.

  As shown in FIGS. 1 and 2, the support 30 includes an upper conductor layer 31 made of a conductive metal (for example, aluminum) and having a thin plate shape as a whole. On the surface of the upper conductor layer 31, a white infrared reflecting film 34 containing an infrared reflecting pigment is formed. For the formation of the infrared reflecting film 34, a coating composition containing an infrared reflecting pigment and a vehicle (for example, a thermal barrier paint manufactured by Nagashima Special Paint Co., Ltd., trade name “Miracool (white)”) can be used. The upper conductor layer 31 having the infrared reflection film 34 is formed with a large number of recesses 32 adjacent to each other with an upper end opened in a regular hexagon. Therefore, a reflection surface (a surface of the infrared reflection film) 34 a made of the infrared reflection film 34 is formed on the inner surface of the recess 32. However, the infrared reflective film 34 is not formed around the substantially circular through-hole 33 provided at the bottom of each recess 32, and the upper conductor layer 31 is exposed. An insulating layer 36 made of resin is formed on the back side of the upper conductor layer 31, and a lower conductor layer 38 made of a conductive metal (for example, aluminum foil) is further provided. The upper conductor layer 31, the infrared reflecting film 34, the insulating layer 36, and the lower conductor layer 38 constitute a support 30.

  The spherical elements 10 are arranged one by one in each recess 32 so that the openings 16 face the back surface side of the upper conductor layer 31 from the through hole 33 of the recess 32. The portion where the upper conductor layer 31 is exposed around the through hole 33 and the n-type semiconductor layer 12 around the opening 16 are electrically connected via the conductive member 22. In addition, a hole is provided in the insulating layer 36 at a portion facing the opening 16 (p-type semiconductor 14) viewed from the through hole 33, and the p-type semiconductor 14 and the lower conductor layer 38 are connected to the conductive member 24 through the hole. It is electrically connected via.

  The shape of the concave portion 32 is similar to that of a conventional micro-concentrating spherical silicon solar cell. Light hitting the inner surface (light hitting the inner surface of the concave portion directly from the light source and reflected by the outer surface of the spherical element and hitting the inner surface of the concave portion) It is formed so that it can be reflected and made incident on the spherical element 10. Here, in the solar cell 1 of the present embodiment, a white infrared reflecting film 34 containing an infrared reflecting pigment is provided on the inner surface of the recess 32. Therefore, light (typically sunlight) supplied from above the support 30 (upper side in FIG. 2) and hitting the inner surface of the recess 32 (that is, the surface 34a of the infrared reflecting film 34) is converted into visible light and infrared light. Any of these can be efficiently reflected (with high reflectivity) and introduced into the spherical element 10.

On the other hand, as shown in FIG. 5, in the solar cell 100 having the structure substantially the same as that of the solar cell 1 according to the present embodiment but having no infrared reflecting film on the inner surface 131 a of the recess 32, the inner surface 131 a is the upper portion. The metal surface is formed by the conductor layer 31. Even when the inner surface 131a is mirror-finished or when a metal (such as silver) is deposited on the inner surface 131a, the inner surface 131a is still a metal surface. Such a metal surface is inferior in infrared reflection performance as compared with the infrared reflective film 34 containing an infrared reflective pigment. Therefore, in the configuration shown in FIG. 5, the infrared component of the light impinging on the inner surface 131a of the recess 32 cannot be sufficiently utilized for photoelectric conversion.
According to the solar cell 1 of the present embodiment shown in FIGS. 1 and 2, by increasing the utilization rate of infrared rays (particularly near infrared rays) that has not been sufficiently utilized in the past, the light from the light source can be more efficiently photoelectricized. Can be used for conversion.

<Second Example>
Another example of a solar cell to which the present invention is applied is shown in FIG.
The solar cell 2 shown in FIG. 3 further includes a resin filler 40 filled in the recess 32 in addition to the configuration of the solar cell 1 shown in FIGS. The filler 40 is made of a transparent silicone resin, and is provided in a range that covers the spherical element 10 and the upper ends of the recesses 32 from the bottom of the recesses 32. A concave surface 42 is formed on the outer surface of the filling body 40 so as to be recessed from the upper end (peripheral portion) of the concave portion 32 toward the central portion. That is, the portion on the outer surface side of the filling body 40 is formed in a concave lens shape for each concave portion 32. According to the solar cell 2 of the present embodiment having such a configuration, more light can be taken into the recess 32 than when the surface of the filling body 40 is planar. Therefore, more light can be introduced into the spherical element 10 directly or after being reflected by the inner surface of the recess 32.

<Third embodiment>
Still another example of the solar cell to which the present invention is applied is shown in FIG.
The solar cell 3 shown in FIG. 4 further includes a phosphate titania catalyst 44 disposed on the outer surface of the filler 40 in addition to the configuration of the solar cell 2 shown in FIG. According to the solar cell 3 having such a configuration, dirt attached to the filler 40 can be decomposed using the function of the catalyst 44. Therefore, the phenomenon that the light from the light source is blocked by the dirt can be prevented, and more light can be directly or directly reflected on the inner surface of the recess 32 and introduced into the spherical element 10.

  As mentioned above, although this invention was demonstrated in detail, the said embodiment and Example are only illustrations and what changed and changed the above-mentioned specific example is contained in the invention disclosed here.

It is a top view which shows typically the solar cell which concerns on one Embodiment. It is the II-II sectional view taken on the line of FIG. It is sectional drawing which shows typically the solar cell which concerns on other one Embodiment. It is sectional drawing which shows typically the solar cell which concerns on another one Embodiment. It is sectional drawing which shows the conventional solar cell typically.

Explanation of symbols

1, 2, 3: Solar cell 10: Spherical element (photoelectric conversion element)
12: n-type semiconductor layer 14: p-type semiconductor 16: opening 30: support 31: upper conductor layer 32: concave portion 34: infrared reflecting film 34a: reflecting surface 36: insulating layer 38: lower conductor layer 40: resin filler 42: Concave surface 44: Catalyst

Claims (8)

A solar cell comprising a support having a large number of recesses and spherical photoelectric conversion elements arranged one by one in each of the recesses,
A solar cell, wherein a reflective surface having an infrared reflective pigment is formed on the inner surface of the recess, and the infrared light reflected by the reflective surface is incident on the element.   The solar cell according to claim 1, wherein the reflecting surface is made of an infrared reflecting film containing the infrared reflecting pigment.   The solar cell according to claim 2, wherein the color of the infrared reflecting film is white.   The solar cell according to any one of claims 1 to 3, further comprising a transparent resin filler filled in the recess.   The solar cell according to claim 4, wherein the resin constituting the filler is a silicone resin.   The solar cell according to claim 4 or 5, wherein the outer surface side of the filler is formed in a concave lens shape for each concave portion.   The solar cell according to any one of claims 4 to 6, wherein an oxidation catalyst is disposed on an outer surface of the filler.   The solar cell according to claim 7, wherein the catalyst is a titania phosphate catalyst.

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