JP2015207707A - Solar battery and solar battery module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solar battery arranged so as to keep the electric resistance between a photoelectric conversion layer and a backside electrode low, and arranged so as to reflect light toward the photoelectric conversion layer while reducing the absorption loss by the backside electrode when reflecting the light having passed through the photoelectric conversion layer on its rear surface side, thereby achieving a high photoelectric conversion efficiency.SOLUTION: A solar battery comprises: a photoelectric conversion layer 3 made of a semiconductor material; a backside metal electrode layer 5 on the side opposite to a light-receiving surface of the photoelectric conversion layer 3; and at least three layers formed by alternately laminating a translucent conductive layer 41 made of a translucent conductive material, and a high-refraction index conductive layer 42 made of a semiconductor material or translucent conductive material and having a refraction index higher than that of the translucent conductive layer 41 between the photoelectric conversion layer 3 and the backside metal electrode layer 5, which serve to increase, of light having passed through the photoelectric conversion layer 3, light reflected toward the photoelectric conversion layer 3 before reaching the backside metal electrode layer 5.

Description

  The present invention relates to a solar cell and a solar cell module, and more particularly to a solar cell and a solar cell module having a translucent conductive layer on a surface opposite to a light receiving surface of a solar cell element.

  In recent years, solar cells capable of directly converting sunlight into electric energy have been rapidly spread as clean energy due to an increase in awareness of environmental problems. Generally, a solar cell arrange | positions an electrode on the both sides of the photoelectric converting layer which consists of a semiconductor layer, and takes out the carrier generate | occur | produced in the semiconductor layer outside. When the light absorption coefficient of the photoelectric conversion layer is low, on the side opposite to the light incident side, the light that has passed without being absorbed by the photoelectric conversion layer is reflected, led again to the photoelectric conversion layer, and the incident light utilization efficiency is increased. Yes. In particular, in a thin film solar cell, a back electrode made of a metal layer having excellent conductivity and reflectivity is used on the back surface side for both carrier extraction and back surface reflection. In addition, in the reflection by the metal surface, part of the light penetrates and is absorbed by the metal, so that the diffusion of the metal into the photoelectric conversion layer is prevented and the photoelectric conversion is performed to reflect a part of the light transmitted through the photoelectric conversion layer. In general, a transparent conductive layer is inserted between the layer and the metal layer.

  On the other hand, in a thin film solar cell, it is known that light absorption in the metal layer of the back electrode increases due to the roughened interface by forming a texture structure intended for light scattering. However, a thin film solar cell that does not use a texture structure is weak in light scattering and has a short circuit current. Accordingly, it is difficult to further enhance the light reflection at the back electrode composed of the transparent conductive layer and the metal layer, and it is difficult to increase the photoelectric conversion efficiency.

In Patent Document 1, as a structure for improving the efficiency of a thin-film silicon (Si) solar cell, the refractive index between the back electrode and the transparent conductive layer provided on the light receiving surface side of the back electrode is higher than that of the transparent conductive layer. Discloses a structure in which a refractive index adjustment layer made of a material having a small thickness is inserted. For example, when the transparent conductive layer is GZO (gallium-doped zinc oxide), SiO ₂ (silicon oxide film) is inserted between the back electrode made of Ag (silver). As a result, the light penetrating into and absorbed by the back electrode is reduced, and the light reflectance at the back electrode is improved.

  Patent Document 2 discloses a solar cell in which a conductive layer made of a semiconductor material and having a refractive index higher than that of a transparent conductive layer is inserted between a transparent conductive layer on the back side and a back metal electrode layer. Thereby, while keeping the electrical resistance between a photoelectric converting layer and a back surface electrode low, the back surface reflectance of the light of the long wavelength range which passes a photoelectric converting layer is improved, and the photoelectric conversion efficiency is raised.

  Patent Document 3 discloses a solar cell in which a back electrode is formed only of a transparent conductive layer, a translucent insulating film is formed thereon, and a back reflecting film is further laminated thereon. With this structure, since the metal reflection film can be used on a flat surface, an increase in absorption due to the metal rough surface interface can be suppressed, and an insulation failure due to a metal electrode processing failure in a cell separation process during module fabrication can be reduced. Moreover, the raw material cost of a solar cell module can also be reduced by using highly reflective insulating materials, such as a white backsheet, without using a metal for a back surface reflecting film.

JP 2006-120737 A International Publication No. 2012/001857 Japanese Patent Application Laid-Open No. 08-051229

  Patent Documents 1 and 2 each have a structure in which a film having a refractive index different from that of the transparent conductive layer is inserted between the transparent conductive layer on the back side of the photoelectric conversion layer and the back electrode. However, in such a structure, since the reflection at the interface between the semiconductor layer and the transparent conductive layer and between the transparent conductive layer and the low (high) refractive index layer is small, most of the incident light is reflected by the back electrode even if the back surface reflectance is improved. The For this reason, the absorption reduction effect by a back surface electrode was not enough. In addition, in a structure in which a low refractive index film having poor electrical conductivity is inserted between the transparent conductive film and the back electrode, there is a problem that the electrical resistance between the photoelectric conversion layer and the back electrode tends to be high.

  In Patent Document 3, since the metal electrode is not used, absorption by the metal electrode is reduced. However, since the back electrode is formed only by the transparent conductive layer, the transparent conductive layer is formed to be sufficiently thick in order to reduce the electric resistance. Therefore, the absorption when the light passing through the semiconductor layer passes through the transparent electrode layer is increased, and it is difficult to obtain a back-reflection effect equal to or higher than that using a metal electrode.

  The present invention has been made in view of the above, and keeps the electrical resistance between the photoelectric conversion layer and the back electrode low, while reducing the absorption loss of the light passing through the photoelectric conversion layer by the back electrode. The object is to obtain a solar cell and a solar cell module that reflect to the conversion layer and have high photoelectric conversion efficiency.

  In order to solve the above-described problems and achieve the object, the present invention provides a photoelectric layer composed of a semiconductor layer including a first electrode disposed on the light receiving surface side and a second electrode disposed on the opposite side of the light receiving surface. A solar cell having a conversion layer sandwiched between a second electrode and a photoelectric conversion layer, a light-transmitting conductive layer made of a light-transmitting conductive material, and a semiconductor material or a light-transmitting conductive material And a multilayer film in which three or more high refractive index conductive layers having a higher refractive index than that of the translucent conductive layer are alternately stacked.

  According to the present invention, the back reflective layer is formed of a multilayer film made of materials having different refractive indexes between the translucent conductive layer and the high refractive index conductive layer, so the optical interference effect is utilized by adjusting the film thickness. By doing so, it is possible to selectively obtain a high reflectance in the near-infrared region where incident light is easily transmitted through the photoelectric conversion layer. For this reason, the light transmitted through the photoelectric conversion layer increases the amount of light reflected to the photoelectric conversion layer before reaching the second electrode, which is the back electrode, and the back surface reflection while reducing absorption by the second electrode. The rate can be increased. Moreover, since the translucent conductive layer and the high refractive index conductive layer have conductivity, the resistance between the photoelectric conversion layer and the back electrode can be kept low. Thereby, there exists an effect that a solar cell with high photoelectric conversion efficiency is realizable.

1 is a cross-sectional view of a solar battery cell according to Embodiment 1. FIG. 2 is a perspective view of the solar cell module according to Embodiment 1. FIG. FIG. 3 is an enlarged view of the vicinity of the cell separation groove in the solar cell module according to Embodiment 1. FIG. 4 is a flowchart showing manufacturing steps of the solar cell according to Embodiment 1. FIG. 5 is a calculation result showing an example of the back surface reflectance of the solar battery cell according to Embodiment 1. FIG. 6 is a cross-sectional view of the solar battery cell according to the second embodiment. FIG. 7 is a characteristic diagram showing the wavelength dependence of the back surface reflectance of the solar battery cell according to the second embodiment. FIG. 8 is a cross-sectional view of the solar battery cell according to Embodiment 3. FIG. 9 is a cross-sectional view of the solar cell module according to Embodiment 3. FIG. 10 is a table showing the characteristics of the solar cells of Examples 1 and 2 and Comparative Examples 1 and 2.

  Embodiments of a solar cell and a solar cell module according to the present invention will be described below in detail with reference to the drawings. In addition, this invention is not limited by this embodiment, In the range which does not deviate from the summary, it can change suitably. In the drawings shown below, the relationship between the thickness and width of each layer, the ratio of the thickness of each layer, or the scale of each member may be different from the actual for easy understanding, and the same applies to the drawings. Further, even a plan view may be hatched to make the drawing easy to see. Such a solar battery cell is the minimum unit of the photoelectric conversion element, and one or a plurality of the cells are collected to constitute a photoelectric conversion element. The photoelectric conversion element of the present invention may be a single photoelectric conversion cell or a module in which a plurality of such cells are electrically connected in series or in parallel.

Embodiment 1 FIG.
The solar cell according to Embodiment 1 will be described with reference to FIG. The thin film solar cell according to the present embodiment includes a light-transmitting substrate 1, a light-receiving surface electrode layer 2 as a first electrode, a photoelectric conversion layer 3, and a light-transmitting conductive layer 41a from the light-receiving surface 10A side on which sunlight L is incident. , 41b, 41c and high-refractive-index conductive layers 42a, 42b are laminated in this order, and a back-surface reflective layer 4 made of a multilayer film and a back-surface metal electrode layer 5 as a second electrode are laminated in this order. . That is, the back surface metal electrode layer 5 is formed on the back surface 10B side.

  Next, each member which comprises the solar cell of this Embodiment 1 is demonstrated. The translucent substrate 1 is made of an insulating material having high transparency, and is not particularly limited as long as each thin film can be deposited thereon. From the viewpoint of weather resistance and mechanical strength, glass, polycarbonate, etc. A substrate made of the above resin is preferably used.

The light-receiving surface electrode layer 2 includes a light-transmitting conductive oxide (TCO) including at least one of zinc oxide (ZnO), tin oxide (SnO ₂ ), and indium oxide (In ₂ O ₃ ). Consists of. Further, a conductive doping material may be added to these materials. For example, ZnO includes aluminum (Al), gallium (Ga), and boron (B), SnO ₂ includes fluorine (F), In ₂ O ₃ includes zinc (Zn), tin (Sn), and titanium (Ti ), Tungsten (W), molybdenum (Mo), silicon (Si), cerium (Ce), and the like. Moreover, the light-receiving surface electrode layer 2 may have a surface texture structure in which irregularities are formed on the surface. This surface texture structure has a function of scattering incident sunlight and increasing the light use efficiency in the photoelectric conversion layer 3. Such a light receiving surface electrode layer 2 is formed by sputtering, electron beam deposition, atomic layer deposition, atmospheric pressure chemical vapor deposition (CVD), low pressure CVD, metal organic chemical vapor deposition ( It can be produced by various methods such as MOCVD: Metal Organic Chemical Deposition) method, sol-gel method, printing method, spray method and the like.

The photoelectric conversion layer 3 has a pn junction or a pin junction, and is configured by laminating one or more thin film semiconductor layers that generate power by incident light. When the photoelectric conversion layer 3 is made of a Si-based thin film, an amorphous Si thin film, a microcrystalline Si thin film, or the like is used as the photoelectric conversion layer 3. An amorphous Si thin film is usually called hydrogenated amorphous Si in which dangling bonds are terminated with hydrogen, and microcrystalline Si is a thin film containing fine crystalline Si partially containing amorphous Si. It is. In addition, compound materials such as CIS (copper indium selenium: Cu—In—Se), CIGS (copper indium gallium selenium: Cu—In—Ga—Se), GaAs (gallium arsenide), CdTe (cadmium tellurium), and organic materials Materials etc. are used. When the photoelectric conversion layer 3 is configured by stacking a plurality of thin film semiconductor layers, a configuration in which a wider optical spectrum can be photoelectrically converted with high efficiency by stacking a plurality of thin film semiconductor layers having different band gaps. be able to. When a plurality of thin film semiconductor layers are stacked to constitute the photoelectric conversion layer 3, an intermediate such as TCO such as SnO ₂ , ZnO, ITO, SiO ₂ , titanium oxide (TiO ₂ ) or the like is provided between different thin film semiconductor layers. Layers may be inserted to improve electrical and optical connections between different thin film semiconductor layers.

The translucent conductive layers 41a, 41b and 41c are composed of TCO containing at least one of ZnO, SnO ₂ and In ₂ O ₃ . Moreover, you may add at least 1 or more types of doping materials selected from Al, Ga, B, etc. to these materials. Alternatively, a mixed crystal material with a low refractive material such as magnesium oxide (MgO) may be used as long as the conductivity is not impaired. The translucent conductive layers 41a, 41b, and 41c are formed by an electron beam evaporation method, a sputtering method, an atomic layer deposition method, a CVD method, a low-pressure CVD method, an MOCVD method, a sol-gel method, a printing method, a coating method, or the like.

The high-refractive-index conductive layers 42a and 42b are layers that are alternately stacked with the light-transmitting conductive layers 41a, 41b, and 41c to form the back reflective layer 4, and use light interference in the near-infrared region. Are selectively reflected and reflected to the photoelectric conversion layer 3, and the translucent conductive layers 41a, 41b, and 41c are electrically connected. The high-refractive-index conductive layers 42a and 42b have only to be higher in refractive index than the translucent conductive layers 41a, 41b, and 41c and have conductivity and translucency in the near-infrared region. TiO ₂ , zirconium oxide It can be composed of a TCO such as (ZrO) or a semiconductor thin film such as Si. Further, at least one kind of doping material selected from niobium (Nb), iron (Fe), etc. may be added to these TCOs. As the Si-based semiconductor thin film, a p-, i-, or n-type Si semiconductor or a Si-based semiconductor thin film containing Si as a main component to which at least one of carbon, germanium, oxygen, or other elements is added is used. This Si-based semiconductor thin film is not limited to a specific crystallinity such as amorphous or microcrystalline.

  The back surface reflection layer 4 is preferably formed so that the thickness of each layer has an optical path length of 1/4 of the designated wavelength λ desired to be reflected. Reflection occurs at the boundary between films having different refractive indexes, and when the optical film thickness (refractive index × film thickness) of each layer is λ / 4, the phases of the light reflected by each layer are aligned and strengthened. Since the light traveling in the transmission direction cancels out, a high reflectance is obtained around the wavelength λ. For example, when microcrystalline Si is used for the photoelectric conversion layer 3, since the absorption coefficient decreases at 800 nm or more, incident light is transmitted through the photoelectric conversion layer 3, while light having a wavelength of 1200 nm or more is subjected to photoelectric conversion. Does not contribute. For this reason, the designated wavelength λ is set between 800 nm and 1200 nm. The reflection wavelength may be widened by slightly changing the designated wavelength λ between the translucent conductive layers 41a, 41b, 41c and the high refractive index conductive layers 42a, 42b, or by slightly shifting λ for each layer of the multilayer film. .

Moreover, the refractive index in 950 nm of the translucent conductive layers 41a, 41b, and 41c is about 1.7 to 2.0 in any material. If a multilayer film is formed with a material having a lower refractive index than that of the light-transmitting conductive layer, a material having a refractive index of 1.4 or less is necessary to obtain a reflection effect at the boundary. Many low refraction materials have a low refractive index, and it is necessary to form a relatively thick film in order to make the optical film thickness λ / 4. The electrical connection between the photoelectric conversion layer and the back electrode is There is a risk that the series resistance of the solar cells increases. On the other hand, high refractive index materials can easily form TiO ₂ and ZrO having a refractive index of about 2.5 for translucent conductive materials, and films with a refractive index of 3 to 4.5 for Si-based semiconductor thin films. can do. These films have conductivity, and the higher the refractive index, the thinner the film thickness necessary to obtain the optical path length λ, so that the connection resistance can be kept low.

  The back surface metal electrode layer 5 has reflectivity and conductivity. Ag, Al, gold (Au), copper (Cu), nickel (Ni), rhodium (Rh), platinum (Pt), palladium (Pr), titanium ( The layer is composed of at least one element or alloy selected from Ti), chromium (Cr), molybdenum (Mo), and the like. In order to increase the reflectance, it is most preferable to be made of a metal mainly composed of Ag. In addition, the specific material as the high reflectance and conductive material of these back surface metal electrode layers 5 is not particularly limited, and may be appropriately selected from known materials.

  FIG. 2 is a perspective view showing a typical structure of the overall configuration of the solar cell module according to Embodiment 1. FIG. 3 is an enlarged view of the vicinity of the separation groove of the solar battery cell 10 in the solar battery module 100 of FIG. The solar cell module 100 shown in FIG. 2 is divided into a plurality of solar cells 10, and the solar cells 10 are connected in series on the insulating translucent substrate 1. As shown in FIG. 2, the solar battery cell 10 has an elongated rectangular shape such as a strip. Many solar cells 10 (photoelectric conversion elements) are arranged in the short side direction. FIG. 2 shows a case where the insulating translucent substrate 1 is arranged in a direction along the side. The light receiving surface electrode layer 2 is divided by forming the first groove 71 and separated between the adjacent solar cells 10. The first groove 71 is a groove reaching the translucent substrate 1 from the surface of the light-receiving surface electrode layer 2. The photoelectric conversion layer 3 is laminated on the light-receiving surface electrode layer 2 separated in this way. In the photoelectric conversion layer 3, a second groove 72 that reaches the light-receiving surface electrode layer 2 from the upper surface of the photoelectric conversion layer 3 is formed at a position slightly away from the first groove 71. A back surface metal electrode layer 5 as a second electrode is formed on the photoelectric conversion layer 3, and the back surface metal electrode layer 5 is in contact with the light receiving surface electrode layer 2 inside the second groove 72. Thereby, the back surface metal electrode layer 5 of one adjacent photovoltaic cell 10 is connected in series to the other light receiving surface electrode layer 2. Further, on the opposite side of the second groove 72 from the first groove 71, a third groove 73 that separates the back surface metal electrode layer 5 between the adjacent solar cells 10 is formed. A back reflection layer 4 is formed between the photoelectric conversion layer 3 and the back metal electrode layer 5.

  Various sizes of the solar cell module 100 are possible, but a large translucent substrate 1 having a side of 1 to 2 m or the like is generally used in a solar cell installed outdoors. The solar battery cell 10 has an elongated rectangular shape with a short side of 5 to 10 mm, for example. A large number of strip-like cells of about 5 to 10 mm are arranged in parallel on the large substrate at intervals of 5 to 10 mm with the third groove 73 interposed therebetween. Although not shown, a back surface side cover layer is bonded as a protective layer on the solar battery cell 10 so as to cover the back surface metal electrode layer 5 to form a thin film solar cell module. As the back surface side cover layer, a weather-resistant fluorine-based resin sheet sandwiching an aluminum foil so as not to transmit moisture, a polyethylene terephthalate sheet deposited with alumina or silica, and the like are preferably used.

  Next, the manufacturing method of the solar cell of this Embodiment is demonstrated. FIG. 4 is a flowchart showing manufacturing steps of the solar cell according to Embodiment 1. In the present embodiment, first, a light-transmitting conductive film as a light-receiving surface electrode layer 2 (first electrode), a photoelectric conversion layer having at least one pair of pin structures on the surface of a light-transmitting substrate 1 made of a glass substrate. 3, the back surface reflective layer 4 and the back surface metal electrode layer 5 as a 2nd electrode are laminated | stacked in order. The back surface reflection layer 4 is formed of a five-layer structure of a light-transmitting conductive layer 41a, a high refractive index conductive layer 42a, a light transmitting conductive layer 41b, a high refractive index conductive layer 42b, and a light transmitting conductive layer 41c.

  First, a glass substrate is prepared as the translucent substrate 1. Then, the light-receiving surface electrode layer 2 as a first electrode made of a light-transmitting conductive film is formed on the light-transmitting substrate 1 (step S1).

  Here, in the step of forming a light-transmitting conductive film as the light-receiving surface electrode layer 2, a light-transmitting conductive film made of ZnO: Al (0.5 wt%) is formed on the entire surface of the light-transmitting substrate 1 by sputtering. The first groove 71 is formed by laser drawing, and the translucent conductive film is pattern-separated to form an array structure in which a plurality of light-receiving surface electrode layers 2 are arrayed in parallel (step S2).

  Thereafter, the photoelectric conversion layer 3 having a pair of pin structures is stacked by a CVD method (step S3).

  And the back surface reflection layer 4 is formed (step S4). Here, the step of forming the back reflective layer 4 is to form the translucent conductive layer 41a, and then the high refractive index conductive layer 42a, the translucent conductive layer 41b, the high refractive index conductive layer 42b, and the translucent conductive layer. 41c is sequentially stacked (steps S41 to S45). Here, the translucent conductive layer 41a, the translucent conductive layer 41b, and the translucent conductive layer 41c are ZnO: Al (0.5 wt%) formed by sputtering, the high refractive index conductive layer 42a, and the high refractive index. The rate conductive layer 42b is an n-type amorphous silicon layer formed by a CVD method.

  Then, the second groove 72 is formed by laser drawing, and the back surface reflection layer 4 and the photoelectric conversion layer 3 are pattern-separated (step S5).

  And the back surface metal electrode layer 5 as a 2nd electrode is laminated | stacked by sputtering (step S6).

  Finally, the third groove 73 is formed by laser drawing, and the back surface metal electrode layer 5 is pattern-separated (step S7).

  In the present embodiment, it is possible to obtain high reflection characteristics at a desired wavelength by equalizing the optical film thickness of each translucent conductive layer so as to align the phase of reflected light at each translucent conductive layer interface.

  FIG. 5 is a characteristic diagram showing the wavelength dependence of the back surface reflectance of the solar cell of the present embodiment. In this figure, the translucent conductive layers 41a, 41b and 41c constituting the back reflective layer 3 are layers containing ZnO as a main component, and the high refractive index conductive layers 42a and 42b are made of n-type amorphous Si. It is the result of having calculated the reflectance reflected in the photoelectric conversion layer 3 side by the back surface reflection layer 4 and the back surface metal electrode layer 5 when light is incident toward the back surface metal electrode layer 5 side from the 3 side. The vertical axis in the figure is the reflectance, the total reflection is 100%, and the horizontal axis is the wavelength (nm). In the calculation, the back metal electrode layer 5 was Ag, and the photoelectric conversion layer 3 was microcrystalline silicon. The film thicknesses of the translucent conductive layers 41a, 41b, 41c and the high refractive index conductive layers 42a, 42b constituting the back reflective layer 4 were set such that the specified wavelength λ was 950 nm. The back reflective layer 4 is laminated in the order of ZnO / Si / ZnO... From the photoelectric conversion layer 3 side, and shows the reflection characteristics when the total number of layers is 1, 3, and 5 (curves a, b, c). Yes. When the number of layers is 1, that is, when only ZnO is inserted between the photoelectric conversion layer 3 and the back surface metal electrode layer 5, the reflection characteristics of the solar cell are shown as a comparative example. By increasing the number of back surface reflection layers 4 to 3, the reflectance of 650 to 1300 nm increases from the solar cell of the comparative example. When further increased, the reflection characteristic approaches a rectangle and the selective reflectivity is further increased, and a higher reflectance is exhibited at 700 to 1300 nm. The photoelectric conversion efficiency can be increased by increasing the reflectance in the wavelength range of 800 to 1200 nm that is easily transmitted through the photoelectric conversion layer 3. In addition, since a texture structure is formed in an actual solar cell as described above, absorption at the time of reflection by the back surface metal electrode layer 5 increases. For this reason, the back surface reflectance in the solar cell of the comparative example with a large amount of light reaching the back surface metal electrode layer 5 is lower than the calculation, and when the number of back surface reflection layers 4 is increased, the amount of light reaching the back surface metal electrode layer 5 is increased. Since it decreases, the difference from the calculated value is expected to be small.

  The solar cell of this embodiment is characterized in that it is composed of a multilayer film composed of a light-transmitting conductive layer and a conductive high refractive index layer. Reflection by a conventional general optical multilayer film generally uses a dielectric and does not have conductivity. Also, in Patent Documents 1 and 3 in which reflection due to a difference in refractive index with a light-transmitting conductive layer is increased, a film having low conductivity is used for the low refractive index layer. Expected to get worse. In contrast, in the solar cell of the present embodiment, a semiconductor having a certain degree of conductivity and a light-transmitting conductive material can be used by forming a high refractive index layer, and the higher the refractive index, the more optical interference effect in the multilayer film. Since the film thickness required for using the film becomes thin, it is possible to obtain a structure that does not impair the electrical characteristics even when stacked.

  As described above, according to the present embodiment, the multi-layer film of the translucent conductive layer and the high refractive index conductive layer is formed on the back surface side of the photoelectric conversion layer, thereby increasing the reflection before reaching the back electrode. Can do. Moreover, since both the translucent conductive layer and the high refractive index conductive layer have conductivity, the connection resistance between the semiconductor layer and the back electrode can be kept low. Therefore, it is possible to increase the back surface reflectance in the near-infrared region where incident light passes through the photoelectric conversion layer while keeping the connection resistance between the photoelectric conversion layer and the back electrode layer low, thereby providing a solar cell with high photoelectric conversion efficiency. it can.

  In addition, by adjusting the film thickness and the number of layers of the light-transmitting conductive layer and the high-refractive index conductive layer so as to selectively reflect light in the near-infrared region, a photoelectric conversion layer is obtained by an optical interference effect. The reflectance of light in the near-infrared region that easily transmits light can be increased, and the photoelectric conversion efficiency can be improved.

  In addition, by making the optical film thickness of all the layers of the translucent conductive layer and the high refractive index conductive layer 1/4 of the specified wavelength in the near infrared region, the optical interference effect can be obtained more effectively, and the efficiency The back surface reflectance can be improved well.

  Furthermore, according to Embodiment 1, the back surface reflectance in the near infrared region can be improved by providing a metal electrode made of a metal material as the back surface electrode having high conductivity and reflectance.

Embodiment 2. FIG.
The solar cell according to the second embodiment is different from the first embodiment in that a back surface translucent electrode layer 6 is used for a back surface electrode as a second electrode as shown in FIG. The back surface transparent electrode layer 6 is made of TCO containing at least one of ZnO, SnO ₂ , and In ₂ O ₃ . Further, the light-transmitting conductive oxide film may be formed of a light-transmitting film such as a film in which at least one element selected from Al, Ga, B, or the like is added. The back surface transparent electrode layer 6 is formed by an electron beam evaporation method, a sputtering method, an atomic layer deposition method, a CVD method, a low pressure CVD method, an MOCVD method, a sol-gel method, a printing method, a coating method, or the like.

  In the present embodiment, the side closest to the photoelectric conversion layer 3 of the back reflective layer 4 is defined as the translucent conductive layers 41a, 41b, and 41c, and the far side is defined as the high refractive index conductive layers 42a, 42b, and 42c. It is formed in the same manner as Embodiment Mode 1.

  FIG. 7 is a characteristic diagram showing the wavelength dependence of the back surface reflectance of the photoelectric conversion device of this embodiment. This figure shows that when the high refractive index conductive layers 42a, 42b, and 42c are made of n-type amorphous Si and light is incident from the photoelectric conversion layer 3 side to the back surface transparent electrode layer 6 side, back surface reflection is performed. It is the result of having calculated the reflectance reflected by the photoelectric converting layer 3 side by the layer 4 and back surface translucent electrode layer 6 interface. In the figure, the vertical axis represents the reflectance, the total reflection is 100%, and the horizontal axis is the wavelength (nm). In the calculation, the back transparent electrode layer 6 was ZnO, and the photoelectric conversion layer 3 was microcrystalline silicon. The film thickness of the translucent conductive layers 41a, 41b, 41c and the high refractive index conductive layers 42a, 42b, 42c is set so that the specified wavelength λ is 950 nm, and the number of back reflective layers 4 is six. did. A high reflectance of 90% or more at 750 to 1250 nm and 95% or more at 800 to 1150 nm is shown. Since this reflectance is a reflection up to the interface between the back surface transparent electrode layer 6 and the back surface reflective layer 4, there is no absorption due to passing through the back surface transparent electrode layer 6. Further, the translucent conductive layers 41a, 41b and 41c used for the back reflective layer 4 are thinner than the back translucent electrode layer 6 and have a low absorption because the conductivity of a single film may not be high. The membrane can be used. Thereby, the absorption which became a subject when absorbing a back surface electrode only with a translucent conductive layer can be suppressed, and the utilization efficiency of incident light can be improved.

  Moreover, the back surface reflection layer 4 of the present embodiment has low reflectance and transmits incident light in the visible light region of 400 to 700 nm other than the near infrared region, and in the infrared region of 1500 nm or more. The light of 1200 nm or more does not contribute to photoelectric conversion, but if it is absorbed by the photoelectric conversion layer 3 or the backside transparent electrode layer 6, it is converted into thermal energy, leading to a rise in the temperature of the solar cell, and the power generation efficiency of the solar cell Incurs a decline. In the solar cell of the present embodiment, infrared light having a wavelength of 1500 nm or more is transmitted to the back side of the solar cell, so that the temperature increase of the solar cell due to such infrared light can be suppressed. Thereby, even when it is used outdoors for a long time, a high power generation amount can be stably obtained.

  As described above, in this embodiment, even when the back electrode is made of a metal electrode and a light-transmitting conductive layer made of a light-transmitting conductive material, high photoelectric conversion efficiency is maintained because a high back-surface reflectance can be obtained in the near infrared region. can do. Since no metal electrode is used, it is possible to realize a solar cell with reduced processing defects and reduced raw material costs during processing of the metal electrode. Moreover, since the back surface reflection layer and the back surface electrode transmit infrared rays, a temperature rise due to infrared rays can be suppressed, and a high power generation amount can be stably obtained even outdoors.

Embodiment 3 FIG.
In the above-described second embodiment, the scattering reflection layer 9 may be provided on the side opposite to the light receiving surface 10A of the back surface transparent electrode layer 6. FIG. 8 is a cross-sectional view showing a typical solar battery cell according to the present embodiment. FIG. 9 is a cross-sectional view showing a solar battery module using this solar battery cell. A light-transmitting insulating layer 8 made of a moisture-permeable resin sheet or the like is formed on the back light-transmitting electrode layer 6, and a scattering reflection layer 9 made of a white back sheet or a white paint is further laminated thereon. The scattering reflection layer 9 is formed so as to cover the upper surface and the side surface of the back surface transparent electrode layer 6 that is the second electrode. The second electrode is made of a translucent conductive film, and in the solar cell module according to the present embodiment, the scattering reflection layer 9 covers the second electrode via the translucent insulating layer 8. The second electrode is formed so as to integrally cover the second electrode. Others are the same as those of the solar cell of the second embodiment, and although the description is omitted here, the same parts are denoted by the same reference numerals.

  As a result, the light that has not been reflected by the back surface reflection layer 4 is reflected, and the light that has entered the separation grooves as the second and third grooves 72 and 73 is reflected by the scattering reflection layer 9, to the photoelectric conversion layer 3. It can be made incident. At this time, since the back surface reflection layer 4 has high transmittance in the visible light region where the photoelectric conversion layer 3 has a high absorption coefficient, the reflected light can be efficiently guided to the photoelectric conversion layer 3, and the solar cell having high light utilization efficiency. Cells and solar cell modules can be provided.

  Although the reflectance in the solar cell of Embodiment 2 is shown in FIG. 7, a very high reflectance is obtained in the peak region of the reflectance in the vicinity of 900 to 1100 nm, but in other wavelength regions, the silver electrode and the like In comparison, the reflectance is lowered, and the conversion efficiency is expected to be lowered. Also, this calculated value is the reflectivity when light is ideally stacked on a flat surface, and the reflectivity may actually be lower than the calculated value due to changes in the texture structure and the angle of the incident light. . Therefore, higher efficiency can be obtained when the reflective layer (here, the scattering reflective layer 9) is further provided on the back surface 10B side as in the solar cell of the third embodiment.

Hereinafter, the effects of the solar cells of Embodiments 1 to 3 will be described in detail by way of examples.
Example 1.
ZnO: Al (0.5 wt%) was formed as the light-receiving surface electrode layer 2 on the glass substrate as the translucent substrate 1. On the light-receiving surface electrode layer 2, a pin layer made of an amorphous Si-based thin film is sequentially stacked as a first photoelectric conversion layer, and a pin layer made of a microcrystalline Si-based thin film is sequentially stacked as a second photoelectric conversion layer. Layer 3 was formed. The thickness of the i layer was 300 nm and 2000 nm, respectively. On the photoelectric conversion layer 3, ZnO is used as the translucent conductive layers 41a and 41b, and n-type amorphous Si is used as the high refractive index conductive layer 42a so that the film thicknesses become 125 nm / 60 nm / 125 nm alternately. Three layers were laminated to form the back reflective layer 4. 300 nm of Ag was formed as the back surface metal electrode layer 5 on the back surface reflection layer 4, and the photovoltaic cell was produced.

Example 2
On the photoelectric conversion layer 3, ZnO is used as the translucent conductive layers 41a, 41b, and 41c, and n-type amorphous Si is used as the high refractive index conductive layers 42a, 42b, and 42c, and the film thicknesses are 125 nm / 60 nm / 125 nm, respectively. Six back layers were alternately laminated so as to be / 60 nm / 125 nm / 60 nm to form the back surface reflection layer 4. A ZnO: Al (0.5 wt%) layer having a thickness of 1000 nm is formed on the back surface reflective layer 4 as the back surface light transmissive electrode layer 6, and titanium oxide is used as the scattering reflective layer 9 on the back surface light transmissive electrode layer 6. A solar cell was produced in the same manner as in Example 1 except that the resin was mixed.

Comparative Example 1
Between the photoelectric conversion layer 3 and the back surface metal electrode layer 5, only one light-transmitting conductive layer made of ZnO having a thickness of 90 nm was formed, and a solar cell was manufactured in the same manner as in Example 1.

Comparative Example 2
On the photoelectric conversion layer 3, without forming the back surface reflection layer 4, ZnO: Al (0.5 wt%) is formed as the back surface light-transmitting electrode layer 6 at 1000 nm, and otherwise the solar cell is formed in the same manner as in Example 2. A battery cell was produced.

  Table 1 in FIG. 10 shows the characteristics of the solar cells of the examples and comparative examples. As shown in Table 1, the solar cell provided with the back surface reflection layer 4 shown in Example 1 had a high short circuit current. Moreover, since the back surface reflection layer 4 has electroconductivity, the electrical property comparable as the comparative example 1 was maintained. In Example 2, by providing the back surface reflective layer 4, a high short-circuit current was obtained while maintaining the same electrical characteristics as in Comparative Example 2 in which a transparent electrode was similarly used on the back surface. The short circuit current value at this time was higher than that of Comparative Example 1 in which a metal electrode was used on the back surface.

  From the above results, it is possible to increase the back surface reflectance while reducing absorption by the back surface electrode by providing a back surface reflective layer in which a light-transmitting conductive layer and a high refractive index conductive layer are laminated. Was able to improve. Furthermore, since the resistance between the photoelectric conversion layer and the back electrode can be kept low, the solar cell has a higher photoelectric conversion efficiency than the case where the back surface reflection layer in which the light-transmitting conductive layer and the high refractive index conductive layer are laminated is not provided. It was found that can be realized.

  Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 1 Translucent board | substrate, 2 Light-receiving surface electrode layer, 3 Photoelectric conversion layer, 4 Back surface reflection layer, 41a, 41b, 41c Translucent conductive layer, 42a, 42b, 42c High refractive index conductive layer, 5 Back surface metal electrode layer, 6 Back surface translucent electrode layer, 71 1st groove | channel, 72 2nd groove | channel, 73 3rd groove | channel, 8 Translucent insulating layer, 9 Scattering reflection layer, 10 Solar cell, 10A Light-receiving surface, 10B Back surface, 100 Solar cell Module, L Sunlight.

Claims (10)

A solar cell in which a photoelectric conversion layer made of a semiconductor layer is sandwiched between a first electrode disposed on the light receiving surface side and a second electrode disposed on the opposite side of the light receiving surface,
Between the second electrode and the photoelectric conversion layer,
Three layers of light-transmitting conductive layers made of a light-transmitting conductive material and high-refractive-index conductive layers made of a semiconductor material or a light-transmitting conductive material and having a higher refractive index than the light-transmitting conductive layer A solar cell having a multilayer film laminated as described above.   The solar cell according to claim 1, wherein the multilayer film selectively reflects light in a near infrared region.   3. The film thickness and the number of layers of the translucent conductive layer and the high refractive index conductive layer are adjusted so that the multilayer film selectively reflects light in a near infrared region. Solar cells.   The optical film thickness of all the layers of the translucent conductive layer and the high refractive index conductive layer is ¼ of the specified wavelength in the near-infrared region, 4. The solar cell as described in.   The solar cell according to any one of claims 1 to 4, wherein the second electrode includes a metal electrode made of a metal material.   The solar cell according to claim 1, wherein the second electrode is a translucent electrode made of a translucent conductive material.   The solar cell of Claim 6 which has a scattering reflection layer on the opposite side to the said light-receiving surface of a said 2nd electrode. A plurality of solar cells in which a first electrode made of a light-transmitting conductive material, a photoelectric conversion layer made of a semiconductor layer, and a second electrode are sequentially stacked are disposed on the light-transmitting insulating substrate. A solar cell module in which the adjacent solar cells are electrically connected in series,
Between the photoelectric conversion layer and the second electrode, a light-transmitting conductive layer made of a light-transmitting conductive material, and a semiconductor material or a light-transmitting conductive material, from the light-transmitting conductive layer A solar cell module having a multilayer film in which three or more high refractive index conductive layers having a high refractive index are alternately laminated.   The solar cell module according to claim 8, wherein the second electrode is a translucent electrode made of a translucent conductive material.   The solar cell module of Claim 9 which has a scattering reflection layer in the opposite side to the light-receiving surface of a said 2nd electrode.

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