JP2014236123A - Solar battery module and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve module conversion efficiency of a solar battery furthermore.SOLUTION: A solar battery module including a solar battery cell between a light transmitting substrate and a rear surface protective sheet has an uneven structure in at least a non-power generation region on a surface of a light incident surface side of the light transmitting substrate. The uneven structure has a plurality of uneven portions comprising a plurality of tilted planes. When, in a cross section including an apex of one uneven portions among the plurality of uneven portions and vertical to a surface of the light transmitting substrate, the minimum angle and the maximum angle of the tilt angles formed between the tilted planes and the surface of the light transmitting substrate are denoted as θ1 and θ2, respectively, 30°<θ1<60° and 30°<θ2 are satisfied. In the rear surface protective sheet, the arithmetic average roughness Ra, the diffuse reflectance and the reflectance of the surface of a light incident surface side are 40 nm or less, 10% or less and 90% or more, respectively.

Description

  The present invention relates to a solar cell module and a manufacturing method thereof.

  In recent years, vigorous studies have been made to achieve both low cost and high efficiency of solar cells. In particular, for thin film solar cells, a method of forming a high-quality semiconductor layer on an inexpensive translucent substrate such as glass using a low-temperature process is expected as a low-cost feasible method. In addition, research on solar cell modules has been conducted energetically, and they are incident on non-power generation areas that do not contribute to solar power generation, such as areas used for collecting and sealing modules and areas used for cell separation. It has been studied to improve the module power generation efficiency by guiding the emitted light to the power generation area.

  In particular, in a solar cell module with a small area such as a building material integrated module, the ratio of the area of the non-power generation area to the area of the power generation area is high, and if light incident on the non-power generation area can be collected and effectively used, the power generation efficiency can be improved. I can expect. In order to collect the light incident on the non-power generation region, studies have been made to effectively use the light incident on the non-power generation region by the structure formed on the light incident surface.

  For example, Patent Document 1 relates to a solar battery module having a solar battery cell between a translucent substrate and a back surface protective sheet, by forming a concavo-convex structure in a non-power generation region on the light incident surface side of the translucent substrate. It describes that the collection effect of light incident on the power generation region is improved. Patent Document 2 describes that a prism structure is formed on the light incident surface side of the translucent substrate to improve the light collection efficiency.

  On the other hand, research on the back surface protection sheet has also been made, and a scattering plate having a fine concavo-convex structure is generally used as in Patent Document 3 and the like. Moreover, in patent document 4, the metal film reflective layer with an unevenness | corrugation which used an outer peripheral part and a grating | lattice part as a back surface material, and used silver, aluminum, etc. as a grating | lattice part is used.

JP 2006-411168 A JP 2000-31515 A JP2013-4948A Japanese Patent Laid-Open No. 10-284747

  In Patent Documents 1 and 2, although metal, organic resin, ceramics, a roof material such as a tile material or a slate material is used as the back surface protection sheet, no detailed study on the back surface protection sheet has been made. In addition, regarding the uneven structure of the translucent substrate, no specific structure or size has been studied, and there remains a problem in terms of the effect of collecting light incident on the non-power generation region.

  Further, according to the study by the present inventors, as described in Patent Documents 1 and 2, when a metal such as aluminum is used as the back surface protection sheet, generally, Ra ≧ 50 nm. It was found that when an uneven scattering plate or white plate as in Patent Document 3 is used, the effect of collecting light entering a non-power generation region is not necessarily sufficient because the effect of collecting light in a specific direction is low. .

  Moreover, in patent document 4, etc., the uneven | corrugated structure is attached to a part of inner side of a back surface protection sheet, and the subject remains in the point of the waterproofing ensuring at the time of a positioning precision and sealing. Patent Document 4 describes that a white reflective layer is used as a back surface protection sheet in the outer peripheral region. In the outer periphery, although the light collecting direction, that is, the direction from the non-power generation region to the power generation region is limited, a high light collection effect cannot be expected when the white reflective layer is used.

  The present invention has been made in view of such problems of the prior art. In the present invention, a predetermined concavo-convex structure is formed on the light incident surface side of the translucent substrate, and a specular reflection sheet is used as the back surface protection sheet. The light incident on the non-power generation region can be collected effectively. As a result, it aims at improving the module conversion efficiency of a solar cell more.

  That is, the present invention relates to the following.

  A solar cell module having a solar cell between a translucent substrate and a back surface protective sheet, wherein the translucent substrate has a concavo-convex structure in at least a non-power generation region on a light incident surface side surface, and the concavo-convex structure is , Having a plurality of concavo-convex portions composed of a plurality of inclined surfaces, including the apex of a certain concavo-convex portion among the plurality of concavo-convex portions, in a cross section perpendicular to the translucent substrate surface, the inclined surface is the When the minimum angle and the maximum angle of the inclination angle formed with the surface of the translucent substrate are θ1 and θ2, respectively, 30 ° <θ1 <60 ° and 30 ° <θ2 are satisfied. A solar cell module having an arithmetic average roughness Ra of 40 nm or less, a diffuse reflectance of 10% or less, and a reflectance of 90% or more.

  In the concavo-convex structure, it is preferable that the height difference of the concavo-convex portion satisfies 0.5 μm or more and 1 mm or less.

  The uneven portion preferably satisfies θ1 <θ2 when the minimum angle and the maximum angle of the inclination angle are θ1 and θ2, respectively.

  The uneven portion preferably has a maximum inclination angle of 80 ° ≦ θ2 ≦ 90 °.

  In the non-power generation region on the light incident surface side surface of the translucent substrate, the uneven portion is formed with a maximum inclined surface that satisfies the maximum angle θ2 on the power generation region side, and is farther from the power generation region than the maximum inclined surface. It is preferable that a minimum inclined surface satisfying the minimum angle θ1 is formed in the region.

  It is preferable that the uneven structure is also formed in a power generation region on the light incident surface side surface of the translucent substrate.

  It is preferable to have silver on the light incident side surface of the back surface protection sheet.

  The area of the non-power generation region is preferably 3% or more of the area of the power generation region.

  The concavo-convex structure is preferably composed of a quadrangular pyramid or a collection of inverted shapes of quadrangular pyramids.

  According to the present invention, it is possible to produce a solar cell module with improved power generation efficiency by forming a predetermined concavo-convex structure on the light incident surface side surface of a translucent substrate and using a predetermined back surface protective sheet. It becomes possible.

It is a section schematic diagram of a solar cell module in one embodiment of the present invention. It is a section schematic diagram of a power generation layer in one embodiment of the present invention. It is a section schematic diagram of the concavo-convex structure of a translucent substrate in one embodiment of the present invention. FIG. 2 is a schematic diagram of a module structure of Example 1 (looking down from the light incident surface).

  Hereinafter, typical aspects of the solar cell module according to the present invention will be described.

  FIG. 1 shows a typical schematic diagram of a solar cell module according to an embodiment of the present invention. The solar cell module of this embodiment has a translucent substrate 1 on the light incident surface side of the solar cells 2 and a back surface protection sheet 4 on the back surface side.

  The translucent substrate 1 has a concavo-convex structure 5 in a non-power generation region on the light incident surface side. The solar battery cell 2 has a transparent electrode 2-2, photoelectric conversion units 2-3, 2-4, 2-5, and a back electrode 2- on the back surface side (the side opposite to the light incident surface) of the cell transparent substrate 2-1. 6. A solar battery module is manufactured by sealing the solar battery cell 2 with the sealing material 3 between the translucent substrate 1 and the back surface protective sheet 4.

  In FIG. 1, a light-transmitting substrate 1 having a concavo-convex structure 5 formed in a non-power generation region on the light incident surface side of the light-transmitting substrate 1 is used. In the present invention, as shown in FIG. 1, one main surface side (upper side) of the substrate is also referred to as a light incident side, and the back electrode side (lower side) is also referred to as a back side. In addition, a region where the power generation layer is formed is referred to as a “power generation region”, and a region where the power generation layer is not formed is referred to as a “non-power generation region”.

(Translucent substrate)
The translucent substrate 1 is not particularly limited as long as it is transparent in the ultraviolet to infrared wavelength range, but a glass substrate or the like is preferably used from the viewpoint of excellent heat resistance. Examples of the glass substrate include alkali-free glass and soda lime glass, but are not particularly limited to these types. When alkali-free glass or soda lime glass is used, a glass substrate having a refractive index of 1.50 to 1.55 is preferable from the viewpoint of cost and transmittance.

  A method for forming the concavo-convex structure 5 on the non-power generation region on the light incident surface side of the translucent substrate 1 is not particularly limited. However, a method of adhering a film having the concavo-convex structure to a substrate, And a method of forming a concavo-convex structure on the light incident surface side surface of the conductive substrate 1. As the base material, the same material as that of the translucent substrate 1 can be used. Any material can be used as the material for the film on which the concavo-convex structure is formed as long as it is a translucent material. However, cycloolefin polymer, polyethylene terephthalate (PET), and polymethacrylate (PMMA) absorb light. It is desirable from the viewpoint of fewer points and excellent workability.

  After the film material is heated to a temperature at which the film softens, a mold having the reverse pattern of the desired concavo-convex structure is pressed and cooled while maintaining the pressure, thereby transferring the concavo-convex structure of the mold to the film surface. An uneven structure can be formed. The heating temperature varies depending on the material of the film, but is preferably a temperature at which the film thickness does not change with pressure, and is preferably 150 ° C. or lower. The film thickness is a thickness obtained by dividing the volume of the film by the area of the film, and is an average thickness of the film surface unevenness. In the case of a PMMA film, it is preferable to heat to about 130 ° C. Moreover, although the pressure which presses a metal mold | die depends on the magnitude | size of the uneven structure to form and heating temperature, the pressure of 1 MPa or less is preferable and 0.5 MPa or less is more preferable. Further, in order to accurately transfer the concavo-convex structure within the above preferable temperature range, 0.1 MPa or more is preferable. Moreover, you may form an uneven | corrugated structure at the time of film preparation.

  Examples of a method for adhering a film having a concavo-convex structure to a light incident surface include a method using a UV curable adhesive or an acrylic adhesive adjusted to a refractive index close to the refractive index of the film and the substrate. Further, for the purpose of experimentally confirming the effect of the concavo-convex structure, it can also be evaluated by a method of attaching the concavo-convex structure to the light incident surface with oil whose refractive index is adjusted.

Examples of the method for forming the concavo-convex structure on the translucent substrate 1 itself include a method using a mold having a reverse pattern of a desired concavo-convex structure. Specifically, the concavo-convex structure can be formed by using a low-melting-point material such as thermoplastic resin or a high-melting-point material such as glass as the light-transmitting substrate and setting the mold temperature.
The uneven structure can be formed by a method of forming a resin material such as acrylic resin or polycarbonate by extrusion molding, a method of forming a resin material by casting, or the like.

  As a method for forming a mold, for example, a single crystal silicon substrate can be manufactured by alkali treatment to form an uneven structure on the substrate. It can also be produced by grinding nickel plated with a diamond bite. Surface treatment using a known mold release agent for the mold reduces defects during pattern formation, enables accurate transfer of uneven structures, and improves the durability of the mold when used multiple times. To do.

  In the case of producing a quadrangular pyramid mold by anisotropic etching of crystalline silicon, a method of etching a single crystal silicon wafer having a thickness of about 700 μm with an alkaline aqueous solution such as KOH can be used. The etching rate of crystalline silicon with an alkaline aqueous solution varies depending on the crystal plane, and the etching rate of the (111) plane is slow. Therefore, when a single crystal silicon substrate having a (100) plane is etched with an alkaline aqueous solution, a quadrangular pyramid composed of (111) planes is randomly formed on the substrate surface. The size of the pyramid formed can be controlled by an etching time, temperature, additives such as fine particles.

  The material of the mold is not particularly limited, but is preferably a material that is less susceptible to heat deterioration and deformation and can withstand a plurality of molding processes. For example, metal materials such as silicon, nickel, and molybdenum can be used. In the case of curing with light, it is possible to cope with the problem by using a highly transparent glass mold.

  In the present invention, the light incident surface side surface of the translucent substrate 1 has a predetermined uneven structure at least in the non-power generation region. By using such a translucent substrate 1, it is expected that the light incident on the non-power generation region is anisotropically scattered by the concavo-convex structure and further reflected by the back surface protection sheet to be effectively collected in the power generation region. it can.

  Here, in the present invention, the concavo-convex structure may be formed at least in the non-power generation region, but is preferably formed in 90% or more of the non-power generation region from the viewpoint of further improving the light collection effect. , More preferably 95% or more, and particularly preferably 100%, that is, the entire surface.

  In the present invention, the concavo-convex structure can be formed by a plurality of concavo-convex portions. The height difference of the uneven portion is preferably 0.5 μm or more, and more preferably 1 μm or more. By setting it as the above range, incident light can be anisotropically scattered with high efficiency. Moreover, when forming an uneven | corrugated structure in a film, 1 mm or less is preferable and 50 micrometers or less are more preferable. By setting it as said range, the cost of a film can be suppressed.

  Here, the height difference of the uneven portion means the maximum value of the height difference of the uneven portion. Here, the concavo-convex part is composed of only one surface in either the direction approaching or moving away from the translucent substrate with respect to one vertex, and the region where the direction of the surface is reversed means another concavo-convex part. . In addition, when the concavo-convex structure is composed of a plurality of concavo-convex portions having different shapes, the average height difference when the height difference is obtained for each of the concavo-convex portions selected randomly among a plurality of concavo-convex portions present in a certain region. Means. For example, by observing the surface of the substrate with an electron micrograph, randomly selecting five uneven portions, determining the height difference for each of the uneven portions, and determining the average height difference of the height differences.

  The shape of the concavo-convex structure is not particularly limited as long as it has a general concavo-convex structure, and examples thereof include a pyramid type, an inverted pyramid type, and a line & space type. The uneven structure on the light incident surface side may be a periodic structure or an aperiodic structure. That is, a structure in which the height of the concavo-convex structure is randomly distributed may be used.

  In the present invention, it is more preferable that the concavo-convex structure is also formed on the power generation region on the light incident surface side surface of the translucent substrate. In this case, the light confinement effect can be expected more in the power generation region. From the viewpoint of productivity and ease of formation of the concavo-convex structure, it is preferable to form the concavo-convex structure in the power generation region and the non-power generation region at the same time. The uneven structure on the power generation region may have the same shape as the uneven structure on the non-power generation region, or may have a different shape.

  Here, in the present invention, as shown in FIG. 3, the concavo-convex structure has a plurality of concavo-convex portions formed of a plurality of inclined surfaces. In other words, a certain uneven portion is formed by a plurality of inclined surfaces. At this time, a minimum angle and a maximum angle of inclination that the inclined surface of the uneven portion includes the apex of the uneven portion of the plurality of uneven portions, and the inclined surface of the uneven portion forms the surface of the substrate in a cross section perpendicular to the substrate surface. When the angles are θ1 and θ2, 30 ° <θ1 <60 ° and 30 ° <θ2 are satisfied.

  Here, “minimum angle θ1 of inclination angle” and “maximum angle θ2 of inclination angle” mean that the inclination angle is the most on the apex of a certain uneven part constituting the uneven structure and the inclined surface surrounding the apex. The angle formed between the side of the inclined portion and the substrate surface in the cross section passing through the side connecting the increasing directions (dotted lines in the right diagrams of FIGS. 3a and b) and perpendicular to the surface of the substrate is defined as the inclination angle θ. Sometimes, it means the smallest angle and the largest angle among the inclination angles of the plurality of inclined surfaces constituting the uneven portion. Of a plurality of inclined surfaces constituting a certain uneven portion, inclined surfaces satisfying the minimum angle θ1 and the maximum angle θ2 are referred to as a minimum inclined surface and a maximum inclined surface, respectively.

  For example, as shown in FIG. 3A, when the concavo-convex portion is a regular quadrangular pyramid, all four inclined surfaces have the same angle, so that θ1 = θ2. On the other hand, in the case of the shape as shown in FIG. 3B, θ is obtained for each of the four inclined surfaces, and the smallest angle at that time is designated as θ1, and the largest angle is designated as θ2. When the uneven portion is an n-pyramid (n ≧ 3), θ1 and θ2 can be calculated by obtaining θ for each of the n inclined surfaces.

  In addition, when the concavo-convex structure is composed of a plurality of concavo-convex portions having different shapes, an average angle when θ1 and θ2 are obtained for each of the concavo-convex portions selected randomly among a plurality of concavo-convex portions present in a certain region. (Θ1ave and θ2ave, respectively) are meant. For example, the surface of the substrate is observed with an electron micrograph, five vertices are randomly selected, the minimum angle and the maximum angle are obtained for each of the vertices, and average values of the angles (θ1ave and θ2ave, respectively) are obtained. It can be obtained as the average angle θ of the vertices.

  At this time, from the viewpoint of further improving the light confinement effect, it is more preferable that the inclined surface satisfying θ1 of one uneven portion and the inclined surface satisfying θ2 of the other uneven portion are adjacent to each other.

  Here, examples of satisfying θ1 = θ2 include a structure in which quadrangular pyramid pyramid structures are randomly distributed as shown in FIG. 3A. The quadrangular pyramid-shaped pyramid structure can be formed by fabricating a mold by anisotropic etching of crystalline silicon and using the mold from the viewpoint of reducing the cost of forming the mold and the time required for the fabrication. preferable.

  In particular, in the present invention, as shown in FIG. 3b, it is preferable to satisfy θ1 ≠ θ2 and θ1 <θ2, that is, an asymmetric shape. By using an asymmetric shape, the probability of anisotropic scattering of incident light in a desired direction is doubled at the maximum as compared with the symmetrical shape shown in FIG. 3a, which is more preferable in terms of the light collection effect. By making the cross-sectional structure of the concavo-convex structure an asymmetrical shape, more light can be anisotropically scattered in a desired direction, and light incident on the non-power generation region can be propagated to the power generation region. .

  At this time, from the viewpoint of light propagation efficiency to the power generation region, θ1 is preferably 31 ° or more, and more preferably 32 ° or more. Further, from the viewpoint of suppressing light absorption by the transparent electrode, it is desirably 58 ° or less, and more desirably 55 ° or less. θ2 is preferably 80 ° or more and 90 ° or less, and more preferably 85 ° or more and 90 ° or less from the viewpoint of light propagation efficiency.

  Further, as shown in FIG. 1 (a), on the light incident surface side surface of the translucent substrate, the uneven portion in the non-power generation region is formed with a maximum inclined surface that satisfies the maximum angle θ2 on the solar cell side, It is preferable that a minimum inclined surface satisfying the minimum angle θ1 is formed in a region farther from the solar cell than the maximum inclined surface.

  In this case, the light collection effect can be expected more. In particular, when a solar cell as shown in FIG. 4 is used, as shown in FIG. 1 (c), the uneven portions in the non-power generation region on both sides of the power generation region both have a maximum inclined surface on the solar cell side, the maximum It is preferable to have the minimum inclined surface in a region farther than the inclined surface. That is, it is preferable that L1> L2 is satisfied when the distances between the maximum slope and the minimum slope and the power generation region are L2 and L1, respectively.

  Here, as shown in FIG. 3C, the distance between the inclined surface in a certain uneven portion and the power generation region is parallel to the side of the inclined surface and the substrate surface in a cross section perpendicular to the substrate surface of the inclined surface where θ is measured. It means the closest distance between the intersection with the correct direction and the power generation area. That is, when a plurality of uneven portions are randomly formed, the average value can be calculated as described above. That is, for example, the surface of the substrate is observed with an electron micrograph, and five vertices are selected at random, and the distance (L2 and L1) between the maximum inclined surface and the minimum inclined surface and the power generation region for each of the apexes. ) And the average value of the distances (L2ave and L1ave, respectively) can be obtained as the average distance.

  In the present invention, a specular reflection sheet is used as the back surface protection sheet, and the surface unevenness of the light-transmitting substrate on the light incident side has the above-described structure, so that a non-power generation region compared with the case where a conventional diffusion plate is used. The light collection effect from can be expected more.

  The refractive index of the concavo-convex structure 5 is preferably 1.47 to 1.57, more preferably 1.50 to 1.55 as a value measured at a wavelength of 500 nm, from the viewpoint of suppressing light reflection. . By using the above refractive index, particularly when a substrate having a concavo-convex structure formed thereon is used, a decrease in power generation efficiency due to reflection at the interface between the concavo-convex structure and the substrate can be suppressed. At this time, it is more preferable to use a material having a small difference in refractive index between the substrate and the concavo-convex structure.

(Solar cell)
Although the case where a thin film silicon-type solar cell is used as the photovoltaic cell 2 is demonstrated based on FIGS. 1-2 below, it is not limited to the following.

  As the cell transparent substrate 2-1, the same material as that of the translucent substrate 1 can be used as described above. At this time, the cell transparent substrate 2-1 may also serve as the translucent substrate 1. That is, you may form the below-mentioned photoelectric conversion unit etc. in a part of translucent board | substrate 1. FIG.

  In the present embodiment, a transparent electrode 2-2 is formed on one main surface of the cell transparent substrate 2-1. The transparent electrode is highly transparent in the wavelength range of 350 to 1500 nm and can be used without limitation as long as it is conductive, but an oxide is used from the viewpoint of the thermal history applied when manufacturing the photoelectric conversion device. In particular, a transparent conductive oxide mainly composed of zinc oxide, indium oxide, indium-tin composite oxide, indium-molybdenum composite oxide, indium-titanium composite oxide, or the like can be used. Here, “main component” means that a certain component is contained in an amount of more than 50%, preferably 70% or more, more preferably 90% or more.

  The transparent electrode 2-2 preferably has a film thickness of 150 to 2000 nm. By setting it as the film thickness of this range, the transparent conductive layer excellent in electroconductivity and transparency can be formed. Among these, 700 nm or more is more preferable from the viewpoint of suppressing resistance loss in the transparent electrode layer, and 1500 nm or less is preferable from the viewpoint of further suppressing light absorption in the transparent electrode layer.

  Here, like this embodiment, when using a thin film silicon-type solar cell, it is preferable to form from two or more different photoelectric conversion units. “Two or more different photoelectric conversion units” means two or more photoelectric conversion units having different band gaps, and usually means a band gap of an i-type semiconductor layer. This makes it possible to absorb light in a wide wavelength region.

  Specifically, as the photoelectric conversion units 2-3, 2-4, and 2-5, a silicon semiconductor laminated structure including a pin junction is used, and two or more such photoelectric conversion units are connected in series. It is preferable to arrange and configure the connection.

  Each semiconductor layer can be suitably manufactured by a plasma CVD method. The plasma CVD method is a method in which silane gas is used as a silicon material and silicon is formed using plasma energy. A proper amount of gas such as diborane or phosphine is added to the p-type layer and n-type layer, respectively. This is possible.

  When two or more photoelectric conversion units are connected in series as described above, a wide band gap light incident side photoelectric conversion unit 2-3 is arranged on the light incident side, and a narrow band gap back surface photoelectric conversion is formed thereon. It is preferable to arrange the units 2-5. As the photoelectric conversion unit 2, it is preferable to use non-single crystal silicon, and among them, polycrystalline silicon and amorphous silicon can be preferably used. At this time, the crystal structure may be different depending on p / i / n. Note that the amorphous or crystalline silicon-based material is not only a case where only silicon is used as a main element constituting a semiconductor, but also an alloy material including elements such as carbon, oxygen, nitrogen, and germanium. Good.

  In this case, for example, a photoelectric conversion unit made of amorphous silicon can be arranged as the light incident side photoelectric conversion unit 2-3, and a photoelectric conversion unit made of microcrystalline silicon can be arranged as the back surface side photoelectric conversion unit 2-5. In addition to the light incident side photoelectric conversion unit 2-3 and the back surface side photoelectric conversion unit 2-5, for example, one or more photoelectric conversion units 2-4 between the light incident side photoelectric conversion unit and the back surface side photoelectric conversion unit. May be arranged.

  A transparent intermediate layer can be formed between the plurality of photoelectric conversion units, and a layer that selectively reflects and transmits light can be provided. Thereby, in said example, more light can be taken in into the light-incidence side photoelectric conversion unit 2-3, and the light which permeate | transmitted can contribute to the electric power generation of the back surface side photoelectric conversion unit 2-5. The “crystalline” in the present invention includes polycrystals and microcrystals. In addition, the terms “crystalline” and “microcrystal” are intended to mean those partially containing an amorphous material.

  A layer intended to improve electrical contact can be provided between the transparent electrode 2-2 and the photoelectric conversion unit 2-3. When a semiconductor layer having a wider band gap than the photoelectric conversion unit is used as this layer, electron-hole recombination in the vicinity of the interface between the transparent electrode layer and the photoelectric conversion layer can be suppressed. As a result, the electron-hole generated in the photoelectric conversion layer can be efficiently taken out to the electrode, and as a result, the conversion efficiency can be improved, which is preferable. An example of such a semiconductor is p-type silicon carbide.

  A back electrode 2-6 is formed on the photoelectric conversion units 2-3, 2-4, and 2-5 thus provided. The back electrode 2-6 can be provided with two layers of a transparent conductive oxide layer and a back metal electrode layer, but it can also be formed of two or more layers by providing other layers.

  The transparent conductive oxide layer is used to suppress mutual diffusion of silicon forming the photoelectric conversion units 2-3, 2-4, and 2-5 and metal atoms forming the back surface metal electrode layer 2-6. . Further, it is used for enhancing the photoelectric conversion characteristics by intensifying light of an arbitrary wavelength by causing light interference. As the transparent conductive oxide layer, for example, a layer containing indium oxide, zinc oxide, titanium oxide or the like can be used.

  The transparent conductive oxide layer is preferably provided in a thickness range of 25 to 120 nm. Furthermore, the range of 30 to 85 nm is optically preferable. By setting the film thickness within this range, not only is it preferable in terms of optical effects, conductivity and cost, but also metal atoms used for the back surface metal electrode layer and photoelectric conversion units 2-3, 2-4, 2 Since it can play the role of the barrier layer which suppresses atomic diffusion with the silicon atom which forms -5, it is preferable.

  The back surface metal electrode layer 2-6 has sufficiently high conductivity, reflects light that has passed through the photoelectric conversion units 2-3, 2-4, and 2-5, and again photoelectric conversion units 2-3, 2 and 2 In order to be included in -4 and 2-5, those having a high reflectance are preferable. Examples of such a material include silver and aluminum.

  The film thickness of the back surface metal electrode layer is preferably 150 nm or more, and more preferably 200 nm or more, from the viewpoint of effectively functioning the effect of reflecting the light reaching the back surface and sending it back to the photoelectric conversion unit again. Moreover, 300 nm or less is preferable from a viewpoint of suppressing the metal cost used for a back surface metal electrode layer.

  In addition, since the light collection effect in this invention is based on the uneven structure and back surface protection sheet which were formed in the light-incidence surface of a board | substrate, a photovoltaic cell is not specifically limited, A thin film silicon solar cell, a crystalline silicon solar cell, a compound It may be a solar cell.

  The photoelectric conversion units thus produced are electrically connected in series or in parallel to produce a solar cell module composed of a plurality of thin film solar cell elements. In the solar cell module, for the purpose of protecting the electrode layer and the semiconductor layer from moisture, oxygen, etc., and electrically insulating from the outside, the entire solar cell element is formed with a sealing resin 3 as a filling material. The structure is sealed with the back surface protective sheet 4.

  As the resin used as the sealing resin 3, EVA (ethylene / vinyl acetate copolymer) is mainly used, but PVB (polyvinyl butyral), PIB (polyisobutylene), silicone resin, and the like can also be used. At this time, as shown in FIG. 1, the sealing resin 3 may be disposed only between the solar battery cell and the back surface protection sheet 4 (that is, the back surface side of the solar battery cell). May also be disposed between the conductive substrates (that is, the light incident side of the solar battery cell).

(Back protection sheet)
Generally as said back surface protection sheet, it is the surface layer (white resin film) / base material layer (PET film etc.) / Back surface layer (the waterproof layer which formed the metal in the resin film, Teflon (in order from a cell side), (Registered trademark) film) or a black backsheet having a black resin film as a cell-side surface layer.

  However, since the white backsheet diffusely reflects the light incident on the backsheet, when the light that is anisotropically scattered by the concavo-convex structure reaches the backsheet, it cannot reflect the light in a desired direction at a high rate. . Further, when the back surface protection sheet is a black back sheet, reflection is minimized and light incident on the back sheet is lost. In addition, when a metal plate is used, an aluminum foil of about Ra = 50 nm is usually used, but in this case, the reflection angle of light is widened, and the proportion of light reflected in a desired direction is reduced. There is a problem.

  On the other hand, in the present invention, a specular reflective sheet is used as the back surface protection sheet 4 and a translucent substrate having a predetermined concavo-convex structure on the light incident surface side is used. It can be expected that the reflected light is reflected with high reflectivity in a desired direction and the light is effectively propagated to the power generation region. The back surface protective sheet 4 preferably has a high reflectance, and the reflectance is preferably 90% or more.

  In this invention, arithmetic mean roughness Ra of the light-incident surface side surface of the said back surface protection sheet is 40 nm or less. If the arithmetic average roughness is 40 nm or less, the diffuse reflectance can be easily reduced to 10% or less. Here, the diffuse reflectance is the ratio of the incident light to the incident light that is reflected in a direction in which the angle of the incident angle and the angle of the reflection angle are separated by ± 2.5 degrees or more. When the arithmetic average roughness of the back surface protective sheet is 40 nm or less and has a high reflectance, the light incident on the back surface protective sheet is specularly reflected.

  The back protective sheet is preferably a mirror-finished metal sheet, and as the metal single-layer sheet, a mirror-finished aluminum reflective sheet is particularly preferred because of its low price and high reflectance. Moreover, the surface which formed the metal into the metal lamination sheet, the film with small surface roughness, etc. is preferable, and the surface which formed silver into the film is especially preferable from the high reflectance. Further, a metal-plated surface and a dielectric mirror can also be used. When the back surface protection sheet is specularly reflected, the light that is anisotropically scattered by the uneven structure on the light incident surface side can be efficiently propagated to the power generation region.

  The distance from the light incident surface of the translucent substrate 1 to the back surface protective sheet is preferably 1 mm or more, and more preferably 3 mm or more from the viewpoint of light collection efficiency. Moreover, 10 mm or less is preferable and 7 mm or less is more preferable from the viewpoint of suppressing weight and reducing light absorption. Here, “the light incident surface side surface of the translucent substrate 1” means the surface farthest from the back surface protective sheet among the vertices of the convex portions of the concavo-convex structure.

As described above, the solar cell module according to the present invention can be manufactured. The solar cell module of the present invention is particularly preferably used as a building material integrated solar cell module. Solar cell modules featuring functions other than power generation, such as building material integrated solar cell modules, generally have a smaller area than solar cell modules specialized for power generation, and the area of the non-power generation region relative to the power generation region growing. By applying the present invention to such a solar cell module, it is possible to effectively use light incident on a non-power generation region that has not contributed to power generation so far, and further increase in power generation efficiency can be expected.
From the viewpoint of effectively increasing the module efficiency by the light collection effect according to the present invention, the ratio of the non-power generation area to the power generation area is preferably 3% or more, and more preferably 10% or more.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

(Simulation 1)
In order to examine the relationship between the shape of the concavo-convex structure formed on the glass surface and the light collection efficiency, a three-dimensional light simulation by the ray tracing method was performed. The simulated structure was a structure in which concave and convex structures having the same shape with a right-angled cross section (fixed at θ2 = 90 °) were arranged in the same direction on a glass plate. The glass plate thickness is 3 mm. The case where the back surface protective sheet was completely diffusely reflected and the case where the back surface protective sheet was specularly reflected were performed, and the inclination angle of the uneven structure was changed by 8 levels. It is assumed that light is incident on the above structure vertically from the upper side of the glass surface, and the light reaching the side surface of the glass plate having a width of 10 mm is collected. The simulation results are shown in Table 1 below. The table shows the relative ratio of the calculation result under other conditions to the simulation result when the back surface is specularly reflected at an inclination angle of 34 °, which has the highest light collection efficiency.

  From the simulation results, it can be seen that when the back surface is specularly reflected, the light collection rate varies greatly depending on the tilt angle, and shows a high value when the tilt angle is 32 ° to 55 °. Among them, 32 ° to 40 ° showed a higher value. At an inclination angle of 34 ° where the light collection rate is the highest, the light collection rate is more than twice that when the back surface is completely diffusely reflected.

(Simulation 2)
In order to examine the relationship between the glass plate thickness and the light collection efficiency of the glass having a concavo-convex structure formed on the surface, a three-dimensional light simulation by the ray tracing method was performed. The simulated structure is a structure in which the back surface is specularly reflected at an inclination angle of 34 ° in the simulation 1 and only the thickness of the glass is different. The results of the simulation are shown in Table 2 below. The table shows the relative ratio of the calculation result under other conditions to the simulation result when the glass thickness is 3 mm, which has the highest light collection efficiency.

  From the simulation results, it can be seen that the thicker the glass, the higher the light collection efficiency.

Example 1
First, the solar battery cell 2 in Example 1 was produced as follows.

  The haze of a translucent substrate (refractive index 1.52) made of white glass having a thickness of 3.2 mm was measured with a spectrophotometer (Lambda 950 manufactured by PerkinElmer) and found to be 1%. In this embodiment, the translucent substrate 1 and the cell transparent substrate 2-1 coincide.

  On one main surface of the cell transparent substrate 2-1, a transparent conductive film made of SnO2 having a thickness of 0.9 μm was formed by a thermal CVD method. After forming the transparent conductive film, by irradiating YVO4 fundamental wave laser (wavelength 1064 nm) from the glass surface side with a laser processing machine (Shibaura Mechatronics 2-wavelength laser device), and removing a part of the transparent conductive film, A transparent electrode 2-2 was formed.

  On the transparent electrode 2-2, an amorphous silicon thin film photoelectric conversion unit 2-3 as a first photoelectric conversion unit, an amorphous silicon thin film photoelectric conversion unit 2-4 as a second photoelectric conversion unit, a third A microcrystalline silicon thin film photoelectric conversion unit 2-5 was formed in this order as a photoelectric conversion unit. For each of these photoelectric conversion units 2-3, 2-4, and 2-5, a p-type layer, a non-doped photoelectric conversion layer, and an n-type layer corresponding to each of the photoelectric conversion units 2-3, 2-4, and 2-5 were formed in this order by the plasma CVD method.

  The non-doped amorphous silicon photoelectric conversion layer included in the first photoelectric conversion unit 2-3 was deposited by an RF plasma CVD method at a base temperature of 200 ° C., and the film thickness was 250 nm. The non-doped amorphous SiGe photoelectric conversion layer included in the second photoelectric conversion unit 2-4 was deposited by RF plasma CVD under a base temperature of 200 ° C., and the film thickness was 150 nm. The non-doped microcrystalline silicon photoelectric conversion layer included in the third photoelectric conversion unit 2-5 was deposited by an RF plasma CVD method at a base temperature of 180 ° C., and the film thickness was set to 2.0 μm.

  After forming the photoelectric conversion units 2-3, 2-4, and 2-5, a 90 nm ZnO layer is formed as a transparent conductive oxide layer by sputtering, and then YVO4 is formed by a laser processing machine (two-wavelength laser device manufactured by Shibaura Mechatronics). A second harmonic laser (wavelength 532 nm) was irradiated from the glass surface side, and a part of the transparent conductive film was exposed by removing a part of the photoelectric conversion unit. Next, 250 nm of a silver layer, which is a metal electrode film, was formed as the back electrode layer 2-6 by sputtering, and a back electrode 2-6 including the metal electrode film was formed.

  After film formation of the back electrode 2-6, a second harmonic laser (wavelength of 532 nm) of YVO4 is irradiated from the glass surface side by a laser processing machine (two-wavelength laser device manufactured by Shibaura Mechatronics), and one of the photoelectric conversion unit and the back electrode An integrated three-junction thin film silicon solar cell in which a separation groove was formed by removing the portion and a plurality of solar cells were electrically connected in series was produced.

  Next, the power generation layer formed in the non-power generation region existing in the peripheral portion of the fabricated cell was removed by irradiating the fundamental wave laser (wavelength 1064 nm) of YVO4 from the glass surface side. The removed regions are two non-power generation regions as shown in FIG. When the cell was confirmed after removal, the non-power generation area was transparent.

  On the back side of the produced solar cell, EVA as the sealing resin 3 and an aluminum specular reflection sheet (alanod MIRO-2 Silver) coated on one side with silver, which is a highly reflective metal, are stacked as the back surface protection sheet 4. Then, a three-junction thin film silicon solar cell module was manufactured by sealing with a vacuum laminator. At this time, the silver side of the specular reflection sheet was used as the light incident surface side. The back surface protective sheet used had a reflectance of 94% and a diffuse reflectance of 4%.

  The surface roughness of the light incident surface side surface of this specular reflection sheet was 2.2 nm in terms of arithmetic average roughness (Ra). The arithmetic average roughness was measured based on JIS B 0601: 2001 by using AFM (Nano-R manufactured by Pacific Nanotech). The observed range is 1 μm square.

  A PMMA sheet having a sheet thickness of 150 μm (refractive index: 1.50) was pressed against a mold while being heated to 130 ° to form a concavo-convex structure on the surface of the PMMA sheet. The mold used for forming was prepared by grinding a metal plate plated with nickel phosphorus with a diamond tool.

  The concavo-convex structure is a structure in which the same shape whose cross section is a right triangle is arranged in the same direction as shown in the schematic cross-sectional view of FIG. 1C, and seven types of concavo-convex structure-attached sheets having different inclination angles (θ1) were produced. . All θ2 are 90 °. As shown in FIG. 1C, the concavo-convex structure was formed so that θ2 is arranged on the power generation region side and θ1 is arranged in a region away from the power generation region. When the PMMA sheet with a concavo-convex structure was cut with a roll cutter and the cross section was observed with an SEM, the height difference of the concavo-convex structure was 40 μm. The refractive index of the sheet was 1.52, and a sheet almost equal to the glass substrate (base material) of the solar cell module was selected.

  The produced PMMA sheet with a concavo-convex structure was affixed on the light incident surface side glass (base material) of the solar cell module with oil adjusted to a refractive index of 1.52, and a translucent substrate having the concavo-convex structure 5 was produced. The position where the sheet was affixed was only the non-power generation area shown in FIG. 4 and was not affixed to the power generation area.

  The non-power generation area is 25% in area ratio with respect to the power generation area. The results of the photoelectric conversion characteristic evaluation with the sheet attached are shown below. In Table 3, the relative ratio of the measured value in other conditions with respect to the photoelectric conversion characteristic in the case without the PMMA sheet with the uneven structure (Comparative Example 1-1) is shown.

  As a result of experiments, it was found that the short-circuit current (Jsc) is improved when the minimum inclination angle θ1 of the concavo-convex structure is larger than 30 ° and smaller than 60 °. While the short circuit current was improved, the open circuit voltage (Voc) and the fill factor (FF) were not substantially changed. As a result, the power generation efficiency (Eff) was also improved.

(Example 2)
Using the solar cell module produced by the same method as in Example 1, Comparative Example 2-1 and Example 2-1 were made in the same manner as Comparative Example 1-1 and Example 1-1, respectively.

  A solar cell module that differs from Example 2-1 only in that the back surface protection sheet is composed of a white backsheet was produced as Comparative Example 2-2. The white backsheet used had 80% reflectance and diffuse reflectance. After measuring the photoelectric conversion characteristics of Comparative Example 2-2, a PMMA sheet with a concavo-convex structure was attached to the non-power generation region with oil to obtain Comparative Example 2-3.

  A solar cell module that differs from Example 2-1 only in that the back surface protection sheet is formed of a rolled aluminum sheet was produced as Comparative Example 2-4. The rolled aluminum sheet was a sheet obtained by stretching a thin aluminum plate with a roller. The arithmetic average roughness of the used rolled aluminum sheet was 50 nm, the reflectance was 88%, and the diffuse reflectance was 14%. After measuring the photoelectric conversion characteristics of Comparative Example 2-4, a PMMA sheet with a concavo-convex structure was attached to the non-power generation region with oil to obtain Comparative Example 2-5.

  Table 4 shows the relative ratios of measured values under other conditions with respect to the photoelectric conversion characteristics when the photoelectric conversion characteristics are evaluated and the PMMA sheet with the uneven structure is not provided (Comparative Example 2-1).

  When Comparative Example 2-1 and Example 2-1 and Comparative Example 2-2 and Comparative Example 2-3 are compared, Example 2-1 in which the back surface protection sheet is a specular reflection sheet is a white back sheet. Compared with comparative example 2-3, the increase rate of the short circuit current became high. Further, when Example 2-1 and Comparative Example 2-3 were compared, the conversion efficiency of Example 2-1 using a specular reflection sheet and having a concavo-convex structure of θ1 = 40 ° was higher by about 3%. .

Comparing Comparative Example 2-1 with Example 2-1 and Comparative Example 2-4 with Comparative Example 2-5,
In Example 2-1 in which the back surface protection sheet was a specular reflection sheet, the increase rate of the short circuit current was higher than that in Comparative Example 2-5 in which the rolled aluminum sheet was used. In addition, when Example 2-1 and Comparative Example 2-5 were compared, Example 2-1 using a specular reflection sheet and having a concavo-convex structure of θ1 = 40 ° increased the conversion efficiency by about 1%. .

  From the above, it can be seen that the conversion efficiency is further improved as compared with the conventional one by using a specular reflection sheet as the back surface protection sheet and using a substrate having a predetermined uneven structure as in the present invention.

Example 3
As described above, in Examples 1 and 2, the concavo-convex structure was formed only in the non-power generation region, but in Example 3 below, the concavo-convex structure was formed on the entire light incident surface of the solar cell module. That is, an uneven structure was also formed on the power generation region. In Example 3-2, Comparative Example 3-1 and Comparative Example 3-3, no concavo-convex structure was formed on the power generation region.
As shown in FIG. 1B, the concavo-convex structure was formed so that θ2 is arranged on one end side of the power generation region and θ1 is arranged on the other end side.

  The module before the formation of the concavo-convex structure of the solar cell module manufactured by a method that differs only in the comparative example 1-1 and the point that the back surface protective sheet is formed of a black backsheet was defined as a comparative example 3-1. The black backsheet used in the module of Comparative Example 3-1 had a reflectance of 5% and a diffuse reflectance of 2%.

  After measuring the photoelectric conversion characteristics of Comparative Example 3-1, a PMMA sheet with a concavo-convex structure having a random pyramid shape was adhered with an adhesive to obtain Comparative Example 3-2. The PMMA sheet with a concavo-convex structure in a random pyramid shape was produced by the same method as the PMMA sheet with a concavo-convex structure in Example 1, but a substrate obtained by etching a single crystal silicon substrate with an alkali was used as a mold. When the formed random pyramid-shaped PMMA sheet with an uneven structure was cut with a roll cutter and the cross section was observed with an SEM, the height difference of the uneven part was 10 μm.

  A solar cell module that differs from Comparative Example 3-1 only in that the back surface protective sheet is a specular reflection sheet was produced and referred to as Comparative Example 3-3. After measuring the photoelectric conversion characteristics of Comparative Example 3-3, the PMMA sheet with a concavo-convex structure whose cross section was a right triangle made in the same process as Example 1 was cut into half the size of the substrate, Adhere with an adhesive (refractive index 1.49) so that the maximum inclined surface satisfying θ2 is arranged on the power generation region side shown in FIG. 4 and the minimum inclined surface satisfying θ1 is arranged in a region farther from the power generation region than the maximum inclined surface. Example 3-1.

  After measuring the photoelectric conversion characteristics of Example 3-1, the PMMA sheet with uneven structure was peeled together with the adhesive, and the PMMA sheet with uneven structure was applied only to the non-power generation region in the same manner as Example 1-1 and Example 2-1. It adhered with the adhesive and it was set as Example 3-2. After measuring the photoelectric conversion characteristics of Example 3-2, the PMMA sheet with a concavo-convex structure was peeled together with the adhesive, and the PMMA sheet with a concavo-convex structure having a random pyramid shape was adhered with the adhesive to obtain Example 3-3.

  A solar cell module different from Comparative Example 3-3 only in that the uneven structure is an antireflection fine particle layer was produced, and was designated as Comparative Example 3-4. The antireflection fine particle layer is prepared by previously mixing silica fine particles (average particle diameter of 100 nm) on the light incident surface of the translucent substrate 1 after mixing with orthokeisan tetraethyl (TEOS) by a bar coating method at 450 ° C. It was formed by firing.

  The photoelectric conversion characteristics of the solar cell module produced above are the following relative ratios of measured values under other conditions with respect to the photoelectric conversion characteristics when the back surface protective sheet is a black back sheet without the PMMA sheet with the uneven structure (Comparative Example 3-1). It shows in Table 5.

  From the comparison between Comparative Example 3-2 and Example 3-3, when the concavo-convex structure is formed on the entire surface of the light incident surface, a high short-circuit current improvement effect can be obtained even if it is a random pyramid if the back surface is a specular reflection sheet. I understand that. Moreover, it turns out from the comparison with Example 3-1 and Example 3-2 that the direction where a concavo-convex structure is formed not only in the non-power generation region but also in the power generation region provides a higher short-circuit current improvement effect. This short-circuit current improvement effect is considered to be a combination of the light collection effect from the non-power generation region and the antireflection effect in the power generation region.

  Moreover, in the comparison between Example 3-1 and Example 3-3, the uneven structure with θ1 <θ2 as in Example 3-1 is formed on the power generation region side as compared with Example 3-3 which is a random pyramid. It can be seen that a high light collection effect from the non-power generation region appears by forming the maximum inclined surface satisfying θ2 to face. From the comparison between Example 3-3 and Comparative Example 3-4, the improvement effect of the short circuit current by the random pyramid greatly exceeded the improvement effect by the simple antireflection effect. It is considered that not only the antireflection effect but also light collection was performed by the random pyramid structure, and as a result, a high short-circuit current improvement effect was obtained.

  As described above, it was found that a solar cell module having a high light collection effect and a high antireflection effect can be produced by using a light-transmitting substrate and a back surface protective sheet as in the present invention.

DESCRIPTION OF SYMBOLS 1 Translucent board | substrate 2 Solar cell 2-1 Cell transparent substrate 2-2 Transparent electrode layer 2-3 Photoelectric conversion unit 1
2-4 Photoelectric conversion unit 2
2-5 Photoelectric conversion unit 3
2-6 Back surface electrode 3 Sealing resin 4 Back surface protection sheet 5 Concave and convex structure 6 Sun ray 7 Reflected light 10 Solar cell module

Claims (9)

A solar cell module having a solar cell between a translucent substrate and a back surface protective sheet,
Having a concavo-convex structure in at least the non-power generation region on the light incident surface side surface of the translucent substrate,
The concavo-convex structure has a plurality of concavo-convex parts composed of a plurality of inclined surfaces,
Among the plurality of concavo-convex portions, the minimum inclination angle formed by the inclined surface of the concavo-convex portion with the surface of the translucent substrate in a cross section including the apex of the concavo-convex portion and perpendicular to the translucent substrate surface. When the angle and the maximum angle are θ1 and θ2, respectively, 30 ° <θ1 <60 ° and 30 ° <θ2 are satisfied,
The back surface protection sheet is a solar cell module having an arithmetic average roughness Ra of the light incident surface side surface of 40 nm or less, a diffuse reflectance of 10% or less, and a reflectance of 90% or more.   2. The solar cell module according to claim 1, wherein the uneven structure satisfies a height difference of the uneven portion of 0.5 μm to 1 mm.   The solar cell module according to any one of claims 1 to 2, wherein the uneven portion has a minimum angle and a maximum angle of the inclination angle satisfying θ1 <θ2.   The said uneven | corrugated | grooved part is a solar cell module as described in any one of Claims 1-3 in which the maximum angle of the said inclination | tilt angle satisfy | fills 80 degrees <= theta2 <= 90 degrees.   In the non-power generation region on the light incident surface side surface of the translucent substrate, the uneven portion is formed with a maximum inclined surface that satisfies the maximum angle θ2 on the power generation region side, and is farther from the power generation region than the maximum inclined surface. The solar cell module as described in any one of Claims 1-4 in which the minimum inclined surface which satisfy | fills the minimum angle (theta) 1 is formed in the area | region.   The solar cell module according to any one of claims 1 to 5, wherein the concavo-convex structure is also formed in a power generation region on a light incident surface side surface of the translucent substrate.   The solar cell module as described in any one of Claims 1-6 which has silver on the surface of the light-incidence side of a back surface protection sheet.   The solar cell module according to any one of claims 1 to 7, wherein an area of the non-power generation region is 3% or more of an area of the power generation region.   The solar cell module according to any one of claims 1 to 8, wherein the concavo-convex structure is composed of a quadrangular pyramid or a collection of inverted shapes of quadrangular pyramids.