JP2013011670A - Light guide member - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light guide member that has a large sunlight receiving surface (for example, more than 1 m), can efficiently guide received sunlight, and can be manufactured by a simple method.SOLUTION: A light guide member includes: a sunlight receiving surface on which a reflective metal film is laminated; a light guide layer that guides sunlight entering from the sunlight receiving surface; and a mounting part for mounting a solar cell on the light guide layer. The sunlight receiving surface has incident ports comprising a recessed part penetrating the metal film to reach the light guide layer, and the inside surface of the recessed part is formed in a reverse conical shape.

Description

  The present invention relates to a light guide member, and more particularly to a light guide member for guiding sunlight to a solar cell (for example, a multi-junction compound solar cell).

  Among solar cells, there is a multi-junction type III-V group compound solar cell as a solar cell having the highest efficiency and suitable for a concentrating solar cell. As such a light-condensing structure for a high-efficiency solar cell, a solar cell element combined with a light-guiding structure for efficiently guiding sunlight (for example, Patent Document 1 and Non-Patent Document 1). See).

  The light guide structure of the solar cell disclosed in Patent Document 1 is shown in FIG. 9A. FIG. 9A is a schematic cross-sectional view of a light guide structure of a solar cell. The light guide structure 200 illustrated in FIG. 9A includes a light receiving layer 210, a light guide layer 220, an irregular reflection layer 230, and the solar cell element 100.

  As a conventional light guide structure, a technique of giving directionality to light with a prism array sheet has also been proposed (see Non-Patent Document 1). As shown in FIG. 9B, the light having the directionality given by the prism array sheet 300 is further condensed on the solar cell 320 by the reflector 310 having a light guide structure as another component.

JP 2010-212280 A

Japan Solar Energy Society 2009, 189, P53-60 “Optimum design of prism array sheet for condensing PV by evolutionary algorithm”

However, in the light guide structure 200 of Patent Document 1, since the light receiving layer 210 and the light guide layer 220 are configured as separate parts and bonded together, the production lead time becomes long. It has been difficult to uniformly bond a light receiving layer having a light receiving surface of a large size (for example, more than 1 m ² ) and a light guide layer due to a difference in thermal expansion coefficient. In addition, since the irregular reflection layer 230 diffuses light in various directions, the diffuse reflection layer 230 cannot efficiently guide light toward the solar cell element 100, and the light collection rate of the solar cell element 100 is reduced. There is.

Also in the light guide structure shown in Non-Patent Document 1, the prism array sheet 300 and the reflector 310 are separate components and need to be integrated while holding an appropriate gap. Therefore, the production lead time becomes long, and when a prism array sheet of a large size (for example, more than 1 m ² ) and a reflector are to be bonded together, a stable gap cannot be maintained.

Further, depending on the incident angle of sunlight to the reflector, light once incident on the reflector is emitted from the reflector again, and the light collection efficiency to the solar cell 320 is lowered. In addition, since the reflector 310 is disposed at an angle (θ _l ) with respect to the light receiving surface, the solar cell 320 becomes larger and the weight becomes heavier when the reflector 310 becomes larger, so the practicality is low.

Therefore, the present invention is a member that has a large sunlight receiving surface (for example, more than 1 m ² ) and can efficiently guide received sunlight, and can be manufactured by a simple method. An object is to provide an optical member.

1st of this invention is related with the light guide member comprised as follows.
[1] A sunlight receiving surface on which a reflective metal film is laminated, a light guide layer for guiding sunlight incident from the sunlight receiving surface, and an attachment portion for attaching a solar cell to the light guide layer A light guide member comprising:
A light guide member, wherein the light receiving surface has an incident port including a recess that penetrates the metal film and reaches the light guide layer, and an inner surface of the recess has an inverted weight shape.

According to the light guide member of [1], the production lead time is shortened, the light guide member is enlarged (for example, the light receiving surface is 1 m ² or more), and the light collection efficiency is improved. .

2nd of this invention is related with the light guide member comprised as follows.
[2] A light guide member comprising a sunlight receiving surface, a light guide layer that guides sunlight incident from the sunlight receiving surface, and an attachment portion for connecting a solar cell to the light guide layer. There,
A light guide member that faces the sunlight receiving surface is an asymmetric prism surface, and makes it easy to guide light guided through the light guide layer to the connection portion.

  According to the light guide member of [2], sunlight incident on the light guide layer can be more efficiently collected on the solar cell element.

  According to the light guide member of the solar cell of the present invention, sunlight can be efficiently guided to the solar cell. In addition, sunlight irradiated to a larger area than the solar cell element size can be guided to the solar cell element to efficiently generate power.

It is a schematic cross section (FIG. 1A) which shows the whole structure of the light guide member of this invention, and the enlarged view (FIG. 1A) of the A section in FIG. 1A. In the light guide member of the present invention, a diagram (FIG. 2A) showing a state in which sunlight irradiated on the light receiving surface is incident on the light guide layer through an incident port made of a surface recess, and light incident on the light guide layer FIG. 2B is a diagram (FIG. 2B) illustrating a state of guiding light inside the light guide layer. The figure (FIG. 3A) which shows the 1st process (process which prepares a light guide material board | substrate) of the manufacturing flow of the light guide member of this invention, and the figure which shows the 2nd process (process which forms a recessed part in the back surface of a light-receiving surface). (FIG. 3B). The figure (FIG. 4A) which shows the 3rd process (process which forms a metal film on the surface of a light guide material board | substrate) of the manufacturing flow of the light guide member of this invention, and a 4th process (a recessed part is formed in a light-receiving surface). It is a figure (FIG. 4B) which shows a process. It is a figure which shows a mode that a solar cell is arrange | positioned in the light guide layer of the light guide member of this invention. It is a figure which shows a mode that a solar cell is mounted in an interposer board | substrate. It is a figure which shows the structure of a multijunction compound solar cell, and the absorption spectrum of sunlight. It is a figure which shows the detailed structure of a multijunction type compound solar cell package. It is a schematic cross section of the light guide structure of the conventional solar cell.

1. About the light guide member The first light guide member of the present invention includes 1) a sunlight receiving surface on which a reflective metal film is laminated, and 2) a light guide for guiding sunlight incident from the sunlight receiving surface. A light layer; and 3) an attachment portion for attaching a solar cell to the light guide layer. Sunlight enters the light guide layer from the sunlight receiving surface, guides the inside of the light guide layer, and is condensed on the attachment portion. The first light guide member may be characterized by an incident port disposed on the sunlight receiving surface.

  That is, the sunlight receiving surface of the first light guide agent of the present invention is provided with an incident port that is a concave portion that penetrates the metal film and reaches the light guide layer, and the concave portion has an inverted weight shape. It is a recess. Thereby, the light irradiated on the sunlight receiving surface can be efficiently incident on the light guide layer through the incident port regardless of the angle of irradiation (see FIG. 2A).

  Moreover, since the said metal film is arrange | positioned in surfaces other than the entrance of the sunlight light-receiving surface of the 1st light guide member of this invention, the light which once entered into the light guide layer is from a sunlight light-receiving surface. Leakage is suppressed (see FIG. 2B).

  The second light guide member of the present invention includes 1) a sunlight receiving surface, 2) a light guide layer for guiding sunlight incident from the sunlight receiving surface, and 3) a solar cell on the light guide layer. An attachment portion for attachment. Similarly to the first light guide member, sunlight enters the light guide layer from the sunlight receiving surface, guides the inside of the light guide layer, and is condensed on the attachment portion. The second light guide member may be characterized by a surface opposite to the sunlight receiving surface.

  That is, the surface opposite to the sunlight receiving surface of the second light guide member of the present invention is an asymmetric prism surface. By adjusting the shape of the asymmetric prism, the sunlight that enters the light guide layer and guides the light guide layer can be efficiently guided to the solar cell mounting portion (FIG. 2B). reference).

  Hereinafter, a light guide member of a solar cell according to an embodiment of the present invention will be described with reference to the accompanying drawings. In the drawings, substantially the same members are denoted by the same reference numerals, and description thereof is omitted.

<Overall configuration of light guide member>
FIG. 1A is a schematic cross-sectional view showing an overall configuration of a light guide member according to an embodiment of the present invention. As shown in FIG. 1A, the light guide member 50 is used to guide sunlight to the solar cell element 10. The shape of the light guide member 50 is not particularly limited, but may be a sheet shape, for example, an elongated sheet shape.

  The light guide member 50 includes the light guide layer 1 and the metal film 2 laminated on the surface of the light guide layer 1. In the light guide member, a plurality of incident ports made of the surface recesses 3 are formed on a surface that receives sunlight (light receiving surface). On the other hand, the surface opposite to the light receiving surface of the light guide member 50 is formed with an asymmetric prism formed of the back surface concave portion 7 and is an asymmetric prism surface.

  The material of the light guide layer 1 may be a transparent material that can transmit sunlight, and may be various resins or glass. Specific examples of the transparent resin include perfluorinated polymer, polymethyl methacrylate, polycarbonate, polystyrene, acrylic (PMMA), polyamide, polyester, copolymers based on these, and mixtures thereof. Examples of glass include quartz glass.

  The thickness of the light guide layer 1 is preferably 0.5 to 10 mm, for example, about 3 mm.

  The metal film 2 is preferably a reflective metal; examples of reflective metals include Ag, Al, Au, Pt, Pd, etc., with Ag or Al being preferred. Although the thickness of the metal film 2 is not specifically limited, Usually, it is the range of 10-30 micrometers.

  FIG. 1B is an enlarged view of a portion A in FIG. 1A. The angle θ formed by the inner side surface of the surface recess 3 constituting the entrance is preferably 30 ° ≦ θ <90 °. This is because the light applied to the light receiving surface is efficiently incident on the light guide layer 1 through the entrance. That is, the inner side surface (incident reflection surface 2 </ b> X, see FIG. 2A) of the surface recess 3 constituting the incident port promotes the incidence of sunlight on the light guide layer 1.

  The width (incident aperture width 5) in the light guide layer 1 of the surface recess 3 constituting the incident aperture is preferably 1.2 μm to 2 μm. It is preferable that the depth (incident port depth 6) in the light guide layer 1 of the surface concave portion 3 constituting the incident port is 0.6 to 2 μm. The incident aperture width 5 and the incident aperture depth 6 may be set so that the sunlight can be efficiently incident on the light guide layer 1 while efficiently diffracting sunlight. The above-mentioned size is a size set to use up to a wavelength of 650 to 1200 nm of the sunlight spectrum.

  On the other hand, the back surface recess 7 of the light guide member 50 forms an asymmetric prism structure. The reflected light on the long side 7 a proceeds to the solar cell 10, and the reflected light on the short side 7 b proceeds on the opposite side to the solar cell 10. By doing in this way, the sunlight which guides the light guide layer 1 is efficiently guided to the solar cell 10. The back surface recess depth 8 is preferably 1 to 100 μm, and the angle formed by the inner surface of the back surface recess (the apex angle θ ′ of the prism) is preferably 90 ° <θ ′ ≦ 150 °.

  The light guide member of the present invention is used for concentrating sunlight on a solar cell. Specifically, the light guide member 50 has an attachment portion 30 for attaching the solar cell 10. The metal film 2 is not laminated on the attachment portion 30, and the light guide layer 1 is exposed. When the light guide member 50 is a sheet-like member, for example, the attachment portion 50 can be provided on the side surface of the sheet.

  The solar cell 10 attached to the attachment portion 30 of the light guide member 50 is disposed with its light receiving surface facing the surface of the attachment portion 50. The solar cell 10 is preferably fixed to the attachment portion 30 of the light guide member 50. Fixing may be performed with the transparent adhesive 24, for example.

<Solar cell element>
The solar cell 10 attached to the attachment part 30 of the light guide member 50 may be an element that can convert sunlight into electric energy, and various known elements can be used. Examples of known solar cell elements include silicon-based, compound-based, and organic-based solar cells. Silicon-based solar cells include single crystal or polycrystalline crystalline silicon solar cells, and thin-film silicon solar cells in which amorphous silicon is formed into a thin film. Compound solar cells include CIS solar cells using copper, indium, selenium, etc. as raw materials, GaAs solar cells using compound semiconductors such as gallium arsenide, Ge solar cells, and CdTe-CdS solar cells. and so on. Organic-based solar cells include dye-sensitized solar cells.

  In particular, a GaAs solar cell has high photoelectric conversion efficiency with respect to an increase in light energy incident on the element, and the amount of power generation is effectively increased by combining a light guide member. A multi-junction GaAs solar cell that can be suitably used in the present invention will be described later.

  The sunlight 26 irradiated to the light receiving surface of the light guide member 50 of the present invention enters the light guide layer 1 through the entrance, and is guided through the light guide layer 1 to the mounting portion 30 of the solar cell ( FIG. 2AB).

  Specifically, the sunlight 26 that has entered the entrance made of the surface recess 3 is incident on the entrance formed on the light receiving surface of the light guide layer 1 while being repeatedly reflected by the entrance reflection surface 2X. (FIG. 2A). The sunlight 26 incident on the light guide layer 1 is generated by the asymmetric prism 7 having a light guide reflection surface 2Y at the boundary between the light guide layer 1 and the metal film 2 and a back surface recess 7 formed on the surface opposite to the light receiving surface. The inside of the light guide layer 1 is guided while repeating reflection at the interface (light guide reflection surface 2Z) with the metal film 2 formed on the surface (FIG. 2B). At that time, since the shape of the asymmetric prism formed of the back surface concave portion 7 is controlled, the sunlight 26 is guided to the mounting portion 30 more efficiently. As a result, the sunlight 26 irradiated to the light receiving surface of the light guide member 50 is efficiently incident on the solar cell 10 and subjected to photoelectric conversion.

  The incident angle of the sunlight 26 irradiated to the light receiving surface of the light guide member 50 is constantly changed by the movement of the sun during the day. It is ideal from the incident light rate that the sunlight 26 is irradiated from a direction perpendicular to the light receiving surface. In order to always irradiate the light receiving surface with sunlight whose incident angle constantly changes from the vertical direction, the surface angle of the light receiving surface of the light guide member 50 must always be adjusted using a sun tracking device (tracker). However, the tracker also has installation errors and tracking errors, and the surface angle of the light receiving surface cannot always be optimized. In addition, trackers are complex and expensive. For this reason, it is required that the light guide member be fixed and installed to be tracker-less.

  The sunlight 26 irradiated from an oblique direction with respect to the light receiving surface of the light guide member 50 of the present invention is repeatedly subjected to total reflection once or a plurality of times on the incident reflection surface 2X formed on the light receiving surface, and finally. The light is guided to the recess formed in the light guide layer 1 and enters the light guide layer 1 (FIG. 2A). Thus, the sunlight 26 incident on the light receiving surface obliquely can be condensed on the surface recess 3 and incident on the light guide layer 1. Therefore, even if the light guide member 50 of the present invention is fixedly installed, the sunlight 26 can be efficiently incident on the light guide layer 1.

  The sunlight 26 incident on the light guide layer 1 is guided through the inside of the light guide layer 1 to the mounting portion 30 of the solar cell 10 (FIG. 2B). Specifically, the light guide layer 1 is guided to the mounting portion 30 of the solar cell 10 while repeatedly reflecting on the inner wall surface (interface with the metal film 2). Sunlight 26 incident on the light guide layer 1 is totally reflected at the interface (light guide reflection surface 2Z) with the metal film 2 formed on the surface of the asymmetric prism 7 formed of the back surface concave portion 7 formed on the back surface of the light receiving surface. In addition, the light is totally reflected by the light guide reflection surface 2Y formed on the inner surface of the light guide layer on the light receiving surface side. The sunlight 26 repeats this total reflection, is guided to the mounting portion 30 without the metal film 2, and enters the solar cell 10.

  A small part of the sunlight 26 that is guided is emitted from an incident port that is formed by a concave surface on the light receiving surface, so that an outgoing light loss occurs. However, since the entrance width 5 is as very fine as 1.2 to 2 μm, the emission light loss is extremely small.

  Thus, the sunlight 26 irradiated to the light-receiving surface of the light guide member 50 of the present invention is efficiently condensed and irradiated on the solar cell 10. Therefore, the solar cell connected to the light guide member of the present invention exhibits a sufficient amount of power generation.

2. About the manufacturing method of a light guide member Although the light guide member of this invention can be manufactured by arbitrary methods as long as the effect of this invention is acquired, the example is demonstrated below.

<Preparation of light guide material substrate>
First, a light guide material substrate 1 ′ to be the light guide layer 1 is prepared (FIG. 3A). The light guide material substrate 1 ′ is usually a plate-like member. As described above, the light guide material substrate 1 ′ may be made of a transparent material that transmits sunlight. In this embodiment, PMMA (polymethyl methacrylate) is used, and its refractive index is about 1.49.

  The size (area) of the light guide material substrate 1 ′ is not particularly limited, but may be 1 m × 1 m, and may be larger. Moreover, it is preferable that the thickness of the light guide layer 1 is in the range of 0.5 mm to 10 mm.

<Asymmetric prism surface formation process>
One surface of the light guide material substrate 1 ′ is an asymmetric prism surface (FIG. 3B). One surface of the light guide material substrate 1 ′ is made into an asymmetric prism surface by forming the back surface concave portion 7 by a grinding method using a diamond cutting tool 25. The asymmetric prism surface is formed on the back surface of the sunlight receiving surface. A load corresponding to the depth 8 of the back surface recess 7 is applied to the diamond tool 25 brought into contact with one surface of the light guide material substrate 1 ′, and the diamond tool 25 is scanned while one of the light guide material substrates 1 ′ is scanned. A recess is formed on the surface. The scan speed of the diamond cutting tool 25 may be about 10 to 100 mm / s depending on the grinding depth.

  In another example of the method in which one surface of the light guide material substrate 1 ′ is an asymmetric prism surface (FIG. 3B), a back surface recess is formed on the cavity surface of a mold for forming the light guide material substrate 1 ′. An uneven portion corresponding to 7 may be provided. According to this method, the light guide material substrate 1 'to which the uneven portions of the cavity surface are transferred is obtained in the same process as the formation of the light guide material substrate 1', and the asymmetric prism surface is more easily formed. Thus, it is preferable to use a compression molding technique to transfer the concavo-convex portion of the cavity surface to the light guide material substrate 1 ′; in order to perform more accurate transfer, the load application profile of the mold is multi-staged. It is preferable to do.

<Metal film formation process>
A metal film 2 is formed on the entire surface of the light guide material substrate 1 ′ on which the back surface recess 7 is formed (FIG. 4A). The thickness of the metal film 2 is, for example, 10 to 30 μm and can be an Ag film. Various known methods can be used for forming the metal film 2. An example of a preferable method is an electroless plating method using a silver mirror reaction. This technique is referred to as “plastic mirror” in Japanese Patent Application Laid-Open No. 2010-107854. Silver mirror reaction is one of the chemical reactions used in mirror manufacturing. When ammoniacal nitric acid solution is reduced, silver (99.9%) is deposited and adheres to the target substance. It is a reaction that becomes like this.

  Among the plating techniques using the silver mirror reaction, there are various plating methods such as a coating method, a plating method, and spray coating. The optimum method may be selected according to the size and film thickness of the light guide layer 1.

  For the formation of the metal film 2, a metal vapor deposition method by a metal sputtering method may be employed. The film thickness of the metal film 2 by metal sputtering is usually 0.1 μm to 0.3 μm. Examples of the metal to be deposited include Ag, Al, Au, Pt, and Pd.

<Recess formation process of light receiving surface>
A surface recess 3 is formed on the light receiving surface of the light guide material substrate 1 ′ on which the metal film 2 is formed (FIG. 4B). The light receiving surface is a surface on the opposite side to the asymmetric prism surface including the above-described back surface concave portion 7. The surface recesses 3 are formed by grinding the metal film 2 on the light receiving surface and the surface layer of the light guide layer 1 with a diamond tool 25.

  Other examples of the method of forming the surface recess 3 on the light receiving surface of the light guide material substrate 1 ′ (FIG. 4B) include removing the metal film 2 and the light guide layer 1 partially by laser cutting, or using a resist film There is a method in which the metal film 2 and the light guide layer 1 are partially wet etched to form a recess.

  In still another example of the method of forming the surface recess 3 on the light receiving surface of the light guide material substrate 1 ′ (FIG. 4B), the surface is formed on the cavity surface of the mold for molding the light guide material substrate 1 ′. An uneven portion corresponding to the recess 3 is provided; a metal film 2 is formed on the entire surface of the molded light guide material substrate 1 ′ (where the surface recess 3 is formed); The entrance is formed by cutting or wet etching. According to this method, the light guide material substrate 1 ′ on which the concave and convex portions of the cavity surface are transferred is obtained in the same process as the formation of the light guide material substrate 1 ′. Thus, it is preferable to use a compression molding technique in order to transfer the concave and convex portions of the cavity surface to the light guide material substrate 1 ′, and in order to perform more accurate transfer, the load application profile of the mold is multi-staged. It is preferable to do.

<Positioning process of light guide member and solar cell>
Of the metal film 2 formed on the surface of the light guide material substrate 1 ′, the metal film 2 on the attachment portion 30 is mirror-polished to expose the light guide layer 1 (FIG. 5A). In this way, the light guide member 50 is obtained.

  The mounting portion 30 of the light guide member 50 is aligned with the packaged solar cell 10 (described later) (FIG. 5A). Next, a transparent adhesive 24 is applied to the light receiving surface of the solar cell 10. The light receiving surface of the solar cell 10 is brought into contact with the attachment portion 30 of the light guide member 50 through the transparent adhesive 24.

<Solar cell mounting process>
The solar cell 10 is mounted by curing the transparent adhesive 24 of the solar cell 10 brought into contact with the mounting portion 30 of the light guide member 50 (FIG. 5B). The transparent adhesive 24 is irradiated with UV light 27 to cure the transparent adhesive 24 and mechanically fix the solar cell 10 and the attachment portion 30. As a result, the solar cell 10 has a structure in which sunlight that guides the light guide layer 1 can enter.

  The structure having the “light guide structure of the solar cell” in this example is completed through the above steps.

  As described above, an arbitrary solar cell is connected to the light guide member of the present invention, but the solar cell 10 may be packaged using an interposer. FIG. 6A shows a step of aligning the multi-junction compound solar cell 10 with the interposer substrate 11. The interposer substrate 11 is formed of silicon, ceramic, glass epoxy substrate, glass, or the like. The interposer substrate 11 has a through electrode 15 inside. An element side electrode 14 is formed on the surface of the interposer substrate 11 to which the solar cell 10 is bonded; an external extraction electrode 16 is formed on the opposite surface. Both the element-side electrode 14 and the external extraction electrode 16 have an outermost layer formed of an Au film. The Au film is formed using flash Au plating or electrolytic Au plating, and has a maximum thickness of 0.5 μm.

  Next, an ACF (Anisotropic Conductive Film) 13 is attached to the surface of the interposer substrate 11 to which the solar cells are bonded (FIG. 6A). For example, the ACF 13 may be pressed against the bonding surface and held at 80 ° C. for 1 second. Thereafter, the solar cell electrode 12 and the element side electrode 14 in the back contact type solar cell 10 are aligned.

  FIG. 6B shows a process of mounting the multi-junction compound solar cell 10 on the interposer substrate 11 and packaging it. The solar cell 10 is pressed against the interposer substrate 11 with a pressure overheating head 17 heated to 150 to 250 ° C. for about 5 to 20 seconds. The epoxy resin that is the base material of the ACF 13 is heated and cured. Since the ACF 13 contains conductive particles, the solar cell electrode 12 and the element side electrode 14 are electrically connected. In this way, the solar cell 10 can be packaged without damaging the solar cell 10.

  When the solar cell 10 to be mounted is not a back contact type but a double-sided electrode type, the lower electrode (electrode facing the interposer substrate 11) of the solar cell 10 is attached to the interposer substrate 11 with solder, ACF or the like. Mounting: The upper electrode of the solar cell 10 may be mounted on the interposer substrate 11 by wire bonding, ribbon bonding, or soldering a metal lead frame, and packaged.

<Structure of multi-junction compound solar cell>
As described above, an arbitrary solar cell 10 is connected to the light guide member of the present invention. The solar cell 10 is preferably a compound solar cell, and more preferably a multi-junction compound solar cell.

  FIG. 7 shows the structure of a three-junction compound solar cell 10 as a typical example of a multi-junction compound solar cell. The three-junction compound solar cell 10 can be manufactured by forming each compound layer on a GaAs substrate. The compound layer is formed by putting it in a vertical MOCVD (Metal Organic Chemical Vapor Deposition) apparatus and laminating it by an epitaxial growth method.

Epitaxial growth is preferably performed in an environment at a temperature of about 700 ° C. TMG (trimethylgallium) and AsH ₃ (arsine) are used as raw materials for growing the GaAs layer. As materials for growing the InGaP layer, TMI (trimethylindium), TMG, and PH ₃ (phosphine) are used. SiH ₄ (monosilane) is used as an impurity for forming the n-type GaAs layer, InGaP layer, and InGaAs layer. On the other hand, DEZn (diethyl zinc) is used as an impurity for forming the p-type GaAs layer, InGaP layer, and InGaAs layer.

  First, an AlAs layer having a thickness of about 100 nm is grown on a GaAs substrate. Next, an n-type InGaP layer having a thickness of about 0.1 μm is grown as the contact layer C.

  Next, the top cell T is stacked. An n-type InAlP layer having a thickness of about 25 nm as a window, an n-type InGaP layer having a thickness of about 0.1 μm as an emitter, a p-type InGaP layer having a thickness of about 0.9 μm as a base, and about 0.1 μm as a BSF. A p-type InGaP layer having a thickness is formed by an epitaxial growth method, and a top cell T having a thickness of about 1 μm is stacked.

  Next, a tunnel layer is stacked. A p-type AlGaAs layer having a thickness of about 12 nm and an n-type GaAs layer having a thickness of about 20 nm are grown, and a tunnel layer having a thickness of about 30 μm is laminated.

  Next, the middle cell M is stacked. About 0.1 μm thick n-type InGaP layer as window, about 0.1 μm thick n-type GaAs layer as emitter, about 2.5 μm thick p-type GaAs layer as base, and about 50 nm as BSF A p-type InGaP layer having a thickness is formed by an epitaxial growth method, and a middle cell M having a thickness of about 3 μm is stacked.

  Next, a tunnel layer is stacked. A p-type AlGaAs layer having a thickness of about 12 nm and an n-type GaAs layer having a thickness of about 20 nm are grown, and a tunnel layer having a thickness of about 30 μm is laminated.

  Next, a grid layer is laminated. Eight n-type InGaP layers having a thickness of about 0.25 μm are stacked to form a grid layer having a thickness of about 2 μm. The grid layer suppresses the occurrence of dislocations, defects, and the like due to lattice constant mismatch.

  Next, an n-type InGaP layer having a thickness of about 1 μm is grown as a buffer layer.

  Next, the bottom cell B is stacked. About 50 nm thick n-type InGaP layer as a passivation film, about 0.1 μm thick n-type InGaAs layer as an emitter, about 2.9 μm thick p-type InGaAs layer as a base, and about 50 nm as a passivation film A p-type InGaP layer having a thickness is formed by an epitaxial growth method, and a bottom cell B having a thickness of about 3 μm is stacked.

  Next, a p-type InGaAs layer having a thickness of about 0.1 μm as the contact layer C is grown.

  As shown in the graph of FIG. 7, the forbidden band width of the top cell T is 1.87 eV, and the wavelength that can be absorbed in the solar spectrum is 650 nm or less; the forbidden band width of the middle cell M is 1.41 eV, solar The wavelength that can be absorbed in the optical spectrum is in the region of 650 nm to 900 nm; the forbidden bandwidth of the bottom cell B is 1.0 eV, and the wavelength that can be absorbed in the solar spectrum is in the region of 900 nm to 1200 nm. By adopting a three-layer structure in this manner, a highly efficient solar cell that can effectively use the sunlight spectrum can be realized.

<Detailed structure of multi-junction compound solar cell package>
FIG. 8 shows a structure in which a multi-junction (three-junction) compound solar cell 10 is mounted on an interposer substrate 11 and packaged. The three-junction compound solar cell 10 includes a ZnO layer, which is a transparent electrode 18, a contact layer C, a top cell T, a middle cell M, a bottom cell B, a contact layer C, a lower electrode 19, and Au plating on the lower electrode from the sunlight incident side. The thick film portion 19b is used. The thickness of the Au plating thick film portion 19b is 10 to 50 μm. An upper electrode 20 connected to the transparent electrode 18 and having the potential of the top cell T is disposed.

  Next, the SiN film that is the insulating film 21 is formed on the side surfaces of the top cell T, the middle cell M, and the bottom cell B, and the side electrode 22 is formed on the outer peripheral surface of the insulating film 21. The side electrode 22 is connected to the upper electrode 22 and is drawn to the position of the broken line L. In this way, the electrode having the potential of the top cell and the electrode having the potential of the bottom cell are both arranged at the position of the broken line L, so that the solar cell 10 is of the back contact type.

<Stress absorption during mounting on interposer board>
In the package structure illustrated in FIG. 8, the protruding electrode 23 includes a cylindrical portion 23b and a stress absorbing layer 23a. The cross section of the stress absorption layer 23a (the cross section perpendicular to the vertical direction in FIG. 8) has a smaller area than the cross section of the cylindrical portion 23b. Specifically, the cylindrical portion 23b has a cylindrical shape, the stress absorption layer 23a has a conical shape, and a side surface thereof has a tapered structure. For example, the side surface of the stress absorbing layer 23a has a taper structure inclined by 30 ° to 60 ° with respect to the conduction direction (vertical direction in FIG. 8). As an example of the embodiment, the diameter of the cylindrical part 23b is 20 to 50 μm, the thickness of the cylindrical part 23b is 6 to 10 μm, and the thickness of the stress absorbing layer 23a is 20 μm or more.

  When the three-junction compound solar cell 10 is mounted, the conical tip of the stress absorption layer 23a is crushed flat. As described above, the cylindrical portion 23b and the stress absorbing layer 23a of the protruding electrode 23 have different shapes, and the sectional area of the stress absorbing layer 23a is smaller than the sectional area of the cylindrical portion 23b. The stress applied during mounting is absorbed by deformation of the stress absorption layer 23a. Therefore, by providing the stress absorption layer 23a, the solar cell 10 is not easily damaged when the solar cell 10 is mounted on the interposer substrate 11.

  The material of the protruding electrode 23 can be a single material or a composite material of metal materials such as Au, Ti, Cu, Al, Sn, Ag, Pd, Cu, Bi, Pb, Ni, and Cr. is there. The protruding electrode 23 can be formed by a method such as a stud bump method using a wire bonding method.

  The protruding electrode 23 is formed by applying or printing a conductive paste containing a resin such as an epoxy resin or a silicone resin and a conductive metal such as Ag, Pd, Au, Cu, Al, Ni, Cr, or Ti. It may be formed. In this case, it is not necessary to provide a tapered portion on the protruding electrode 23. Since the molten conductive paste comes into contact with the electrode of the solar cell 10 and is cured, the solar cell 10 is hardly stressed.

  A concentrating solar cell is configured by mounting the transparent electrode 18 in the solar cell package shown in FIG. 8 so as to face the mounting portion 30 of the light guide member 50 of the present invention, as shown in FIG. 1A. .

  The light guide member of the solar cell of the present invention can guide the sunlight received by the light receiving surface to the solar cell while collecting the sunlight. Therefore, it can be applied as a light guide member for condensing light on the concentrating solar cell. The light guide member of the solar cell of the present invention is a multi-junction compound solar cell (conversion efficiency) having only a light receiving surface of about 3 mm × 3 mm as well as a conventional polycrystalline silicon solar cell (conversion efficiency is about 20%). (Approx. 40%). Even if the area of the light receiving surface is the same, if the conversion efficiency is doubled, the power generation amount is doubled. Therefore, the light guide member of the solar cell of the present invention is a large-scale solar in an area with a large amount of sunlight. Ideal for power generation systems.

DESCRIPTION OF SYMBOLS 1 Light guide layer 1 'Light guide material board | substrate 2 Metal film 2X Incident reflective surface
2Y, 2Z Light guiding reflective surface
3 Surface recessed portion θ Angle formed by the inner surface of the surface recessed portion 5 Incident port width 6 Incident port depth 7 Back surface recessed portion 7a Long side 7b Short side 8 Back surface recessed portion depth θ 'apex angle 10 of solar prism 11 interposer substrate,
12 Solar cell electrode 13 ACF
14 Element side electrode 15 Through electrode 16 External extraction electrode 17 Pressure heating head 18 Transparent electrode 19 Lower electrode 19b Au plating thick film part 20 Upper electrode 21 Insulating film 22 Side electrode 23 Projection electrode
23a Stress absorption layer 23b Column 24 Transparent adhesive
25 Diamond bit 26 Sunlight 27 UV light 30 Mounting portion 50 Light guide member C Contact layer T Top cell M Middle cell B Bottom cell
100 solar cell element 200 light guide structure 210 light receiving layer 220 light guide layer 230 diffuse reflection layer 300 prism array sheet 310 reflector 320 solar cell

Claims (9)

A solar light receiving surface on which a reflective metal film is laminated; a light guide layer for guiding sunlight incident from the solar light receiving surface; and an attachment portion for attaching a solar cell to the light guide layer. A light guide member,
A light guide member, wherein the light receiving surface has an incident port including a recess that penetrates the metal film and reaches the light guide layer, and an inner surface of the recess has an inverted weight shape.   The light guide member according to claim 1, wherein the reflective metal film has a thickness of 10 to 30 μm.   The light guide member according to claim 1, wherein the reflective metal film is an Ag film or an Al film, and the light guide layer is a transparent acrylic resin (PMMA) layer. The angle θ formed by the inner surface of the concave portion constituting the entrance is 30 ° ≦ θ <90 °,
The width of the light guide layer of the concave portion constituting the entrance is 1.2 to 2 μm,
The light guide member according to claim 1, wherein a depth of the light guide layer of the concave portion constituting the incident port is 0.6 to 2 μm.   The reflective metal film includes an incident reflection surface that guides sunlight irradiated to the sunlight receiving surface to a light guide layer, and a light guide reflection surface that suppresses leakage of light from the light guide layer. The light guide member according to claim 1. A light guide member comprising a sunlight receiving surface, a light guide layer for guiding sunlight incident from the sunlight receiving surface, and an attachment portion for connecting a solar cell to the light guide layer,
A light guide member, wherein a surface opposite to the sunlight receiving surface is an asymmetric prism surface, and makes it easy to guide light guided through the light guide layer to the connection portion.   The light guide member according to claim 6, wherein a reflective metal film is laminated on the asymmetric prism surface.   The light guide member according to claim 6, wherein a prism apex angle θ ′ of the asymmetric prism surface is 90 ° <θ <150 °, and an uneven height of the prism is 1 to 100 μm. The light guide member according to claim 1 and claim 6, wherein the solar cell is a multi-junction compound solar cell.