Solar cell, multi-junction solar cell, solar cell module, photovoltaic power generation system, and method for manufacturing solar cells

Abstract

To provide a solar cell, a solar cell module, and a photovoltaic power generation system with excellent conversion efficiency, as well as a method for manufacturing the solar cell. [Solution] According to the embodiment, a solar cell is provided comprising a transparent first electrode, an n-type layer, a light-absorbing layer containing an inorganic material, and a second electrode. The n-type layer is located between the first electrode and the light-absorbing layer. The light-absorbing layer is located between the n-type layer and the second electrode. The first electrode has a gap that penetrates it. The n-type layer, the light-absorbing layer, and the second electrode are each partially contained within the gap, with a portion of the n-type layer, a portion of the light-absorbing layer, and a portion of the second electrode arranged within the gap in this order.

Description

[Technical Field]

[0001] Embodiments of the present invention relate to solar cells, multi-junction solar cells, solar cell modules, photovoltaic power generation systems, and methods for manufacturing solar cells. [Background technology]

[0002] One new type of solar cell uses cuprous oxide (Cu2O) as its light-absorbing layer. Cu2O is a wide-bandgap semiconductor. Because Cu2O is a safe and inexpensive material composed of copper and oxygen, which are abundant on Earth, it is expected to enable the creation of highly efficient and low-cost solar cells.

[0003] Furthermore, multi-junction (tandem) solar cells are another type of highly efficient solar cell. Tandem solar cells can be made more efficient than single-junction cells because they can use cells with high spectral sensitivity for each wavelength band. Cu2O solar cells, which have a wide bandgap in the light-absorbing layer and high light transmittance, can be suitably used as the top cell of a tandem solar cell. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2019-57536 [Patent Document 2] International Publication No. 2019 / 146120 [Overview of the project] [Problems that the invention aims to solve]

[0005] The objective is to provide a solar cell, a solar cell module, and a photovoltaic power generation system with excellent conversion efficiency, as well as a method for manufacturing the above-mentioned solar cell. [Means for solving the problem]

[0006] According to one embodiment, a solar cell is provided comprising a transparent first electrode, an n-type layer, a light-absorbing layer containing an inorganic material, and a second electrode. The n-type layer is located between the first electrode and the light-absorbing layer. The light-absorbing layer is located between the n-type layer and the second electrode. The first electrode has a gap that penetrates it. The n-type layer, the light-absorbing layer, and the second electrode are each partially contained within the gap, with a portion of the n-type layer, a portion of the light-absorbing layer, and a portion of the second electrode arranged within the gap in this order.

[0007] In another embodiment, a multi-junction solar cell is provided, comprising a first solar cell and a second solar cell having a second light-absorbing layer having a smaller bandgap than the first light-absorbing layer of the first solar cell. The first solar cell is the solar cell according to the above embodiment. The second electrode is a transparent electrode.

[0008] According to other embodiments, a solar cell module is provided that includes the solar cell according to the above embodiment.

[0009] According to another embodiment, a photovoltaic power generation system comprising the solar cell module according to the above embodiment is provided.

[0010] Further, according to an embodiment, a method for manufacturing a solar cell including a transparent first electrode, an n-type layer, a light absorption layer containing an inorganic material, and a second electrode is provided. In the solar cell, the n-type layer is between the first electrode and the light absorption layer, and the light absorption layer is between the n-type layer and the second electrode. Also, the first electrode has a gap penetrating the first electrode. The n-type layer, the light absorption layer, and the second electrode are each partially included in the gap, and a part of the n-type layer, a part of the light absorption layer, and a part of the second electrode are arranged in this order in the gap. The manufacturing method includes forming an oxide transparent conductive film on a transparent substrate, removing a part of the oxide transparent conductive film to obtain the first electrode, forming an n-type semiconductor film on the first electrode and on the transparent substrate exposed in the gap, removing a part of the n-type semiconductor film that contacts the side surface of the first electrode located on one side of the gap and the upper surface of the first electrode adjacent to this side surface to obtain the n-type layer, forming an inorganic material film on the n-type layer, on the transparent substrate exposed in the gap, and on the exposed first electrode, removing a part of the inorganic material film that contacts the above side surface and upper surface to obtain the light absorption layer, and forming another conductive film on the light absorption layer, on the transparent substrate exposed in the gap, and on the exposed first electrode to obtain the second electrode.

Brief Description of the Drawings

[0011] [Figure 1] Cross-sectional conceptual diagram showing an example of a solar cell according to an embodiment. [Figure 2] Cross-sectional conceptual diagram showing an example of a conventional solar cell. [Figure 3] Cross-sectional conceptual diagram showing another example of a conventional solar cell. [Figure 4] Cross-sectional conceptual diagram showing an example of an array cell structure of a solar cell according to an embodiment. [Figure 5] Cross-sectional conceptual diagram showing a part of an example of manufacturing a solar cell according to an embodiment. [Figure 6] Cross-sectional conceptual diagram showing a part of an example of manufacturing a solar cell according to an embodiment. [Figure 7] Cross-sectional conceptual diagram showing a part of an example of manufacturing a solar cell according to an embodiment. [Figure 8] Cross-sectional conceptual diagram showing a part of an example of manufacturing a solar cell according to an embodiment. [Figure 9] Cross-sectional conceptual diagram showing part of an example of manufacturing a solar cell according to an embodiment. [Figure 10] Cross-sectional conceptual diagram showing part of an example of manufacturing a solar cell according to an embodiment. [Figure 11] Cross-sectional conceptual diagram showing part of an example of manufacturing a solar cell according to an embodiment. [Figure 12] Cross-sectional conceptual diagram showing part of an example of manufacturing a solar cell according to an embodiment. [Figure 13] Cross-sectional conceptual diagram showing part of the manufacturing of an example of a conventional solar cell. [Figure 14] Cross-sectional conceptual diagram showing an example of a multi-junction solar cell according to an embodiment. [Figure 15] Cross-sectional conceptual diagram showing an example of a conventional multi-junction solar cell. [Figure 16] Perspective view conceptually showing an example of a solar cell module according to an embodiment. [Figure 17] Cross-sectional conceptual diagram showing an example of a solar cell module according to an embodiment. [Figure 18] Conceptual diagram showing an example of a solar power generation system according to an embodiment.

Mode for Carrying Out the Invention

[0012] Hereinafter, a solar cell and a method for manufacturing the same according to an embodiment will be described with reference to the drawings. In each embodiment, substantially the same constituent parts are denoted by the same reference numerals, and the description thereof may be partially omitted. The drawings are schematic, and the relationship between the thickness and the planar dimensions, the ratio of the thicknesses of each part, etc. may be different from the actual ones. The terms indicating directions such as up and down in the description indicate the relative directions when the surface of the transparent substrate provided with the electrodes and the photoelectric conversion member described later is regarded as the upper surface, and may be different from the actual directions based on the direction of the gravitational acceleration.

[0013] (First Embodiment) According to the first embodiment, a solar cell is provided. The solar cell comprises a transparent first electrode, an n-type layer, a light-absorbing layer, and a second electrode. The first electrode has a gap that penetrates it. The n-type layer is located between the first electrode and the light-absorbing layer. The light-absorbing layer contains an inorganic material and is located between the n-type layer and the second electrode. The n-type layer, the light-absorbing layer, and the second electrode are each partially contained within the gap of the first electrode. A portion of the n-type layer, a portion of the light-absorbing layer, and a portion of the second electrode are arranged within the gap in this order.

[0014] The solar cell in question is a photoelectric element capable of exhibiting excellent power conversion efficiency (PCE). The reason for its superior conversion efficiency is explained below.

[0015] <Solar Cells> Figure 1 shows a schematic cross-sectional view representing an example of the solar cell. The illustrated solar cell 100 comprises a transparent substrate 1, a transparent n-type first electrode 2 having a layered structure sequentially stacked thereon, an n-type layer 3, a light-absorbing layer 4, and a p-type second electrode 5 having a layered structure. Although not shown in the example, an intermediate layer (buffer layer) may be provided between the first electrode 2 and the n-type layer 3. The first electrode 2 is provided with a gap 21 that penetrates the first electrode 2 in a first direction 10 which is in the thickness direction and along the stacking direction of the above-mentioned components, and the first electrode 2 is divided into a negative first electrode piece 2a and a positive first electrode piece 2b by having this gap 21.

[0016] The main portion of the n-type layer 3 is located between the first electrode 2 and the light-absorbing layer 4 along the first direction 10, and is aligned with the main surface of the first electrode 2. Another portion of the n-type layer 3 extends into the gap 21 and covers the side surface of the negative first electrode piece 2a. The portion of the n-type layer 3 extending into the gap 21 reaches the surface of the transparent substrate 1. Similarly, the main portion of the light-absorbing layer 4 is located between the n-type layer 3 and the second electrode 5 along the first direction 10, and is aligned with the main surface of the n-type layer 3. Another portion of the light-absorbing layer 4 extends into the gap 21 and covers the portion of the n-type layer 3 extending into the gap 21. In the illustrated example, the portion of the light-absorbing layer 4 extending into the gap 21 reaches the surface of the transparent substrate 1. The light-absorbing layer 4 does not necessarily have to reach the transparent substrate 1. Similarly, with respect to the second electrode 5, its main portion aligns with the main surface of the light-absorbing layer 4, while another portion extends into the gap 21, covering a portion of the n-type layer 3 and the side surface of the positive first electrode piece 2b that extends into the gap 21. Furthermore, a portion of the second electrode 5 that extends into the gap 21 reaches the surface of the transparent substrate 1. Thus, the gap 21 of the first electrode 2 is filled by portions of the n-type layer 3, light-absorbing layer 4, and second electrode 5 that extend into it. The portions of the n-type layer 3, light-absorbing layer 4, and second electrode 5 within the gap 21 are arranged in this order from the negative first electrode piece 2a to the positive first electrode piece 2b. Note that the shape of the main surface of each component is not limited to a flat surface as shown in the figure, but can be a curved surface, for example.

[0017] The illustrated solar cell 100 has a superstrate structure, with the surface on the transparent substrate 1 side being the light incident surface. Most of the light incident from the transparent substrate 1 side passes through the transparent substrate 1, as well as the main parts of the first electrode 2 and the n-type layer 3, and is at least partially absorbed by the light absorption layer 4. Specifically, light is absorbed at a position close to the pn junction region in the light absorption layer 4, that is, near the interface between the n-type layer 3 and the light absorption layer 4, generating electron-hole pairs. In other words, the n-type layer 3 and the light absorption layer 4 constitute the photoelectric conversion section, and free carriers (free electrons and free holes) are generated in the pn junction region. Next, the dissociated free electrons and free holes diffuse along the direction of the potential gradient to the negative side first electrode piece 2a of the first electrode 2, which is the n electrode, and to the second electrode 5, which is the p electrode, respectively. The negative first electrode piece 2a becomes the anode, and the positive first electrode piece 2b, which is electrically connected to the second electrode 5, becomes the cathode. By connecting the current path 25 to these electrodes, a current I flows. Therefore, power can be extracted to the outside of the solar cell 100 through the current path 25. In this way, for example, light energy from sunlight can be converted into electricity, that is, solar power generation can be achieved. The light that can be converted into electricity by photoelectric conversion is not limited to sunlight.

[0018] In the solar cell 100, a portion of the n-type layer 3, a portion of the p-type light-absorbing layer 4, and a portion of the p-type second electrode 5 are arranged in the gap from the negative first electrode piece 2a to the positive first electrode piece 2b, thereby forming a bandgap buffer structure between the negative first electrode piece 2a and the positive first electrode piece 2b. This suppresses the occurrence of electron-hole recombination before power is extracted through the current path 25. Furthermore, it avoids current leakage, which is a concern when the gap 21 is filled with only an n-type semiconductor or only a p-type semiconductor. For this reason, the solar cell 100 can exhibit excellent conversion efficiency.

[0019] In addition, for example, when such a solar cell is used as the top cell of a multi-junction solar cell, it is joined to the bottom cell on the second electrode side, which is the back electrode with respect to the light incident surface. Since there is no need to provide a sealing glass substrate on the second electrode side, the number of glass substrates etc. included in the top cell can be limited to one transparent substrate on the first electrode side. Therefore, a material-saving and lightweight solar cell can be realized.

[0020] When such a solar cell is operated independently, for example, not as a top cell in a multi-junction solar cell, but without being stacked with other solar cells, the second electrode does not need to be light-transmitting. In this case, for example, the second electrode can be formed from a metal or alloy material with excellent conductivity. This makes it possible to lower the electrical resistance of the second electrode itself, as well as the electrical resistance of the connection interface between the second electrode extending from the top to the bottom of the solar cell and the positive first electrode piece.

[0021] Next, the solar cell according to the embodiment will be compared with a conventional solar cell.

[0022] Figure 2 shows a conceptual diagram representing an example of a conventional solar cell. The illustrated solar cell 110 comprises a substrate 111, p electrodes 112 sequentially stacked thereon, a light-absorbing layer 113, an n-type layer 114, a buffer layer 145 (for example, a zinc-tin oxide (ZTO) film), a transparent n electrode 115, and a encapsulation substrate 116. The p electrode 112 is divided into a positive p electrode piece 112a and a negative p electrode piece 112b. The gap between the positive p electrode piece 112a and the negative p electrode piece 112b is filled with a portion of the light-absorbing layer 113. A portion of the n electrode 115 extends from the top to the bottom of the solar cell 110, penetrating the n-type layer 114, the buffer layer 145, and the light-absorbing layer 113, and is electrically connected to the negative p electrode piece 112b at the bottom.

[0023] The solar cell 110 has a substrate structure, and the surface on the back side of the solar cell 110 relative to the substrate 111, that is, the surface on the side of the encapsulation substrate 116, is the light incident surface. Light incident from the side of the encapsulation substrate 116 passes through the encapsulation substrate 116, the n electrode 115, the buffer layer 145, and the n-type layer 114, and is absorbed by the light absorption layer 113, generating electron-hole pairs. The dissociated free electrons and free holes diffuse to the n electrode 115 and the positive p electrode piece 112a of the p electrode 112, respectively. The positive p electrode piece 112a becomes the cathode, and the negative p electrode piece 112b, which is electrically connected to the n electrode 115, becomes the anode. By connecting the current path 25 to these electrode pieces, a current I flows, and power can be extracted to the outside of the solar cell 110.

[0024] In this conventional solar cell 110, since only a light-absorbing layer 113 is interposed between the positive p-electrode piece 112a and the negative p-electrode piece 112b, the effect of suppressing electron-hole recombination achieved by the solar cell 100 according to the above embodiment is not exhibited. Furthermore, glass substrates are typically used for both the substrate 111 located above and below the solar cell 110 and the sealing substrate 116, resulting in a total of two glass substrates. Consequently, a large amount of material is required, increasing the thickness and weight. In addition, while a transparent material is necessary for the n-electrode 115 not only when forming a multi-junction solar cell with other solar cells but also when using the solar cell 110 alone, it is not possible to replace the n-electrode 115, which penetrates the solar cell 110 in the stacking direction, with a material with excellent conductivity such as metal, making it impossible to reduce the resistive component.

[0025] Figure 3 shows a conceptual diagram representing another example of a conventional solar cell. The illustrated solar cell 120 comprises a transparent substrate 121, transparent n electrodes 122 sequentially stacked thereon, an n-type layer 123, a light-absorbing layer 124, and a p electrode 125. The n electrode 122 is divided into a negative n electrode piece 122a and a positive n electrode piece 122b. The gap between the negative n electrode piece 122a and the positive n electrode piece 122b is filled with a portion of the n-type layer 123. A portion of the p electrode 125 penetrates the light-absorbing layer 124 and the n-type layer 123, extending from the top to the bottom of the solar cell 120, and is electrically connected to the lower positive n electrode piece 122b.

[0026] The solar cell 120 has a superstraight structure, with the surface on the transparent substrate 121 side being the light incident surface. Light incident from the transparent substrate 121 side passes through the transparent substrate 121, the n electrode 122, and the n-type layer 123, and is at least partially absorbed by the light absorption layer 124. Specifically, light is absorbed near the pn junction region in the light absorption layer 124, that is, near the interface between the n-type layer 123 and the light absorption layer 124, generating electron-hole pairs. The dissociated free electrons and free holes diffuse to the negative n electrode piece 122a of the n electrode 122 and the p electrode 125, respectively. The negative n electrode piece 122a becomes the anode, and the positive n electrode piece 122b, which is electrically connected to the p electrode 125, becomes the cathode. By connecting the current path 25 to these electrode pieces, a current I flows, and power can be extracted to the outside of the solar cell 120.

[0027] In this conventional solar cell 120, since only an n-type layer 123 is interposed between the negative n-electrode piece 122a and the positive n-electrode piece 122b, the effect of suppressing electron-hole recombination achieved by the solar cell 100 according to the above embodiment is not realized.

[0028] The above shows an example of a single solar cell, but an array may be constructed by electrically connecting multiple cells in series, in parallel, or by combining series and parallel connections. Figure 4 shows an example of an array cell structure of a solar cell according to the embodiment. Specifically, an example of a two-series array of such a solar cell is shown.

[0029] The illustrated solar cell array 101 includes two solar cells 100 that are electrically connected in series. In the illustrated example, a single transparent substrate 1 is shared between the two solar cells 100, and one first electrode 2 serves as both the positive first electrode piece of the solar cell 100 on the left side of the figure and the negative first electrode piece of the solar cell 100 on the right side. Alternatively, the array may be constructed by combining individually prepared solar cells 100 without using a single common component.

[0030] The electrical connection between the two solar cells 100 is via the first electrode 2 located between them. To prevent a short circuit between the second electrode 5 of the left solar cell 100 and the n-type layer 3 of the right solar cell 100, a portion of the second electrode 5 that is on the upper surface of the first electrode 2 has been removed. However, for the second electrode 5 of the right solar cell 100, since there is no other component that could cause a short circuit, it is not necessarily required to remove the portion on the upper surface of the first electrode 2 as shown in the illustration.

[0031] The solar cell array according to this embodiment is not limited to a two-series array as shown in the illustrated example, nor is the number of individual cells connected to form an array limited to two. Furthermore, the connection configuration is not limited to a series connection.

[0032] Next, we will explain the details of the materials and other aspects of each component of the solar cell in question.

[0033] <Transparent substrate> A transparent substrate is a plate-shaped substrate made of a material that has light-transmitting and insulating properties, and functions as a support substrate. Suitable materials for transparent substrates include inorganic materials such as alkali-free glass, quartz glass, white glass, chemically strengthened glass, and sapphire, as well as organic materials such as polyethylene (PE), polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyimide, polyamide-imide, acrylic, and liquid crystal polymer. It is preferable to use soda-lime glass for the transparent substrate.

[0034] <1st electrode> The first electrode is an electrode on the n-type layer side that has light transparency to visible light. It is preferable to use an oxide transparent conductive film (TCO film) for the first electrode. The oxide transparent conductive film used for the first electrode is preferably one or more transparent conductive films selected from the group consisting of indium tin oxide (ITO), aluminum-doped zinc oxide (AZO), boron-doped zinc oxide (BZO), gallium-doped zinc oxide (GZO), indium-doped zinc oxide (IZO), aluminum gallium oxide (AGO), titanium-doped indium oxide (ITiO), indium gallium zinc oxide (IGZO), and hydrogen-doped indium oxide (In2O3).

[0035] There is no particular limitation on the thickness of the first electrode, but typically it can be 1 nm or more and 2 μm or less. The thickness of the first electrode is preferably 50 nm or more and 1 μm or less.

[0036] The gap penetrating the first electrode can be, for example, a groove having a width of 10 μm or more and 100 μm or less.

[0037] <n-type layer> The n-type layer is an n-type semiconductor layer. The n-type layer is located between the first electrode and the light absorption layer. A material having electron accepting properties is used for the n-type semiconductor. As the n-type layer, a layer including an oxide layer or a sulfide layer is preferable. More specifically, as the oxide layer used for the n-type layer, Zn (1-x) A x O y (A = Si, Ge, Sn; 0 ≤ x ≤ 1, 0 < y ≤ 4), Cu (2-x) M x O (M = Mn, Mg, Ca, Zn, Sr, Ba; 0 ≤ x ≤ 2), Al (2-x)Ga x A layer selected from the group consisting of O3 (0 ≤ x ≤ 2) is preferred. As the sulfide layer used for the n-type layer, Zn x In (2-2x) S (3-2x) (0 ≤ x ≤ 1), ZnS, In x Ga (1-x) S (0 ≤ x ≤ 1) is preferably a layer composed of one or more sulfides selected from the group consisting of. Zn (1-x) A x O y When used for the n-type layer, the Zn / A composition ratio is preferably in the range of 1 to 3, more preferably 1.5 to 2.5.

[0038] The thickness of the n-type layer is preferably 5 nm or more and 100 nm or less. The thickness of the n-type is more preferably 10 nm or more and 50 nm or less. If the thickness of the n-type layer is 5 nm or more, leakage current is unlikely to occur even when the coverage of the n-type layer is poor. If the thickness of the n-type layer is 100 nm or less, the transmittance is good and it does not interfere with the current.

[0039] <Light absorption layer> The light-absorbing layer is a p-type semiconductor layer mainly composed of inorganic materials. The light-absorbing layer is located between the n-type semiconductor layer and the second electrode. Examples of inorganic materials that are p-type semiconductors include metal oxides mainly composed of copper (Cu). Examples of metal oxides mainly composed of Cu include cuprous oxide (Cu2O) and composite oxides of cuprous oxide. Metal oxides mainly composed of Cu contain 60.0 atom% to 67.0 atom% of copper (Cu) and 32.5 atom% to 34.0 atom% of oxygen (O). Composite oxides of cuprous oxide also contain metals other than Cu. The metals contained in composite oxides of cuprous oxide are, in addition to Cu, one or more metals selected from the group consisting of, for example, Sn, Sb, Ag, Li, Na, K, Cs, Rb, Al, Ga, In, Zn, Mg, and Ca. The band gap of the light absorption layer can be adjusted by including one or more metals selected from the group consisting of Ag, Li, Na, K, Cs, Rb, Al, Ga, In, Zn, Mg, and Ca, in addition to Cu. An example of another material is Cu(In,Ga)(S,Se)2. Specific examples include CuInSn2, CuInSe2, CuGaS2, CuGaSev, and mixed crystals thereof. There are also examples where some of the Cu is replaced with Al.

[0040] The band gap of the light-absorbing layer is preferably 2.0 eV to 2.2 eV. With a band gap in this range, in a multi-junction solar cell using a solar cell with Si as the light-absorbing layer as the bottom cell and the solar cell of the embodiment as the top cell, sunlight can be efficiently utilized in both the top and bottom cells. The light-absorbing layer may further contain Sn or Sb. The Sn and Sb in the light-absorbing layer may be added to the light-absorbing layer or may originate from the second electrode, which is the p-electrode. Note that if the concentration of Sn and Sb in the p-type light-absorbing layer is high, defects will increase and carrier recombination will increase. Therefore, the total volume concentration of Sb and Sn in the light-absorbing layer is 1.5 x 10⁻⁶. 19 atoms / cm 3 The following are preferable.

[0041] The light-absorbing layer is, for example, Cu a M b Oc This is an oxide layer represented by . M is one or more metals selected from the group consisting of Ag, Li, Na, K, Cs, Rb, Al, Ga, In, Zn, Mg, and Ca. a, b, and c preferably satisfy 1.80 ≤ a ≤ 2.01, 0.00 ≤ b ≤ 0.20, and 0.98 ≤ c ≤ 1.02. The composition ratio of the light-absorbing layer in the above example is the overall composition ratio of the light-absorbing layer. Furthermore, the compound composition ratio of the light-absorbing layer in the above example is preferably satisfied throughout the light-absorbing layer.

[0042] The thickness of the light-absorbing layer is, for example, between 1000 nm and 10000 nm. Preferably, the thickness of the light-absorbing layer is 6000 nm or less.

[0043] <Second electrode> The second electrode may be, for example, a transparent conductive film, a metal film, or a laminated film of a transparent conductive film and a metal film.

[0044] Examples of transparent conductive films include indium tin oxide (ITO), aluminum-doped zinc oxide (AZO), boron-doped zinc oxide (BZO), gallium-doped zinc oxide, fluorine-doped tin oxide (FTO), antimony-doped tin oxide (ATO), titanium-doped indium oxide (ITiO), indium zinc oxide (IZO), and indium gallium zinc oxide (IGZO). The transparent conductive films that can be used for the second electrode are not limited to these. The transparent conductive film may be a multilayer film, and other films such as tin oxide may be included in the multilayer film in addition to the above oxides.

[0045] Examples of metal films include films of Mo, Au, and W. However, the metal films that can be used for the second electrode are not limited to these.

[0046] Furthermore, the second electrode may be an electrode in which dot-shaped, line-shaped, or mesh-shaped metal is provided on the surface of the transparent conductive film. In this case, the dot-shaped, line-shaped, or mesh-shaped metal is placed between the transparent conductive film and the light-absorbing layer. Preferably, the aperture ratio of the dot-shaped, line-shaped, or mesh-shaped metal is 50% or more relative to the transparent conductive film. The dot-shaped, line-shaped, or mesh-shaped metal can include, for example, Mo, Au, or W, and is not particularly limited.

[0047] The thickness of the second electrode may be, for example, between 1 nm and 1 μm. Preferably, the thickness of the second electrode is between 5 nm and 100 nm.

[0048] <Manufacturing method> The solar cell can be manufactured as follows. The method for manufacturing the solar cell includes obtaining a first electrode, obtaining an n-type layer, obtaining a light-absorbing layer, and obtaining a second electrode. A transparent first electrode with a gap can be obtained by depositing an oxide transparent conductive film on a transparent substrate and partially removing the oxide transparent conductive film. An n-type semiconductor film can be deposited on the first electrode and on the transparent substrate exposed in the gap, and an n-type layer can be obtained by removing a portion of the n-type semiconductor film that is in contact with the side surface of the first electrode located on one side of the gap and a portion that is in contact with the upper surface of the first electrode adjacent to this side. A light-absorbing layer can be obtained by depositing an inorganic material film on the n-type layer, on the transparent substrate exposed in the gap, and on the exposed first electrode, and removing the portions of the inorganic material film that are in contact with the aforementioned side surface and upper surface, respectively. A second electrode can be obtained by depositing other conductive films on the light-absorbing layer, on the transparent substrate exposed in the gap, and on the exposed first electrode. In obtaining the second electrode, it may be necessary to remove a portion of the other conductive film that is located on the first electrode.

[0049] A specific example of the manufacturing method will be explained with reference to Figures 5 through 12. Here, we will illustrate the method for manufacturing the two-series array shown in Figure 4.

[0050] First, a transparent substrate 1 is prepared (Figure 5). An oxide transparent conductive film 20 is deposited on the transparent substrate 1 (Figure 6). The oxide transparent conductive film 20 can be deposited, for example, by sputtering using the material of the first electrode described above. Then, a portion of the oxide transparent conductive film 20 is removed to obtain a first electrode 2 having a gap 21 (Figure 7). To remove a portion of the oxide transparent conductive film 20, for example, patterning can be performed by chemical etching or laser etching. The gap 21 penetrates the first electrode 2 in the first direction, assuming the thickness direction of the oxide transparent conductive film 20 is the first direction 10. For example, a groove with a width of several tens of micrometers that penetrates the oxide transparent conductive film 20 is provided as the gap 21.

[0051] Next, an n-type semiconductor film 30 is deposited on the first electrode 2 and on the transparent substrate 1 exposed in the gap 21 (Figure 8). For example, the n-type semiconductor material is deposited by chemical vapor deposition (CVD) at a temperature of 500°C or higher. However, since the thickness of the n-type semiconductor film 30 is only about several tens of nanometers, and at most 100 nm, it is not practical to fill the gap 21, which has a width of several tens of micrometers, with the n-type semiconductor film 30 alone. Subsequently, the portion of the n-type semiconductor film 30 that is in contact with the side surface 22 of the first electrode 2 located on one side of the gap 21, and a portion of the portion that is in contact with the upper surface of the first electrode 2 adjacent to this side surface 22, is removed to obtain an n-type layer 3 (Figure 9). For removal, for example, patterning by chemical etching or laser etching is performed.

[0052] Next, an inorganic material film 40 is formed on the n-type layer 3, on the transparent substrate 1 exposed in the gap 21, and on the exposed first electrode 2 (Figure 10). For example, the inorganic material film constituting the light-absorbing layer described above is formed by electrodeposition, CVD, or sputtering. After that, the portion of the inorganic material film 40 that is in contact with the side surface 22 of the first electrode 2 and the portion that is in contact with the upper surface of the first electrode 2 adjacent to this side surface 22 is removed to obtain the light-absorbing layer 4 (Figure 11). For removal, for example, patterning by chemical etching or laser etching is performed.

[0053] Next, other conductive films are deposited on the light-absorbing layer 4, the transparent substrate 1 exposed in the gap 21, and the exposed first electrode 2 to obtain the second electrode 5 (Figure 12). The other conductive films can be deposited, for example, by CVD using the material of the second electrode described above. When manufacturing an array as illustrated, in order to eliminate the short circuit between the second electrode 5 and the n-type layer 3, the portion of the second electrode 5 enclosed by the dashed line 50 is removed by patterning, for example, chemical etching or laser etching. Of the two portions enclosed by the dashed line 50, only the left portion may be removed. If both portions enclosed by the dashed line 50 are removed, a two-series array having a structure similar to the solar cell array 101 shown in Figure 4 can be obtained.

[0054] In the method described above, when patterning is performed at each stage, the areas to be removed by etching are the wide gaps 21 and the areas adjacent to them. Because there is spatial clearance for the materials that are not to be removed, for example, a wider clearance can be provided for the laser irradiation area when laser etching is performed. In the manufacturing of conventional solar cell arrays, for example, a laser may be irradiated to remove the film in recessed areas between materials that are not to be removed, but in this case, the area adjacent to the irradiated laser of the light absorption layer may be heated and defects may be formed. Defect formation can reduce the current that can flow through the light absorption layer, which can reduce the conversion efficiency.

[0055] Figure 13 shows an example of the manufacturing process for a conventional solar cell. This shows an example of manufacturing a two-series array of solar cells having a structure similar to the conventional solar cell shown in Figure 2. After repeatedly depositing films and patterning on the substrate 111 to sequentially stack the p-electrode 112, light-absorbing layer 113, n-type layer 114, and n-electrode 115, the connections between solar cells other than the series connection by the lower p-electrode 112 are severed to separate the individual cells. Specifically, for example, etching with a laser L is performed to remove the material above the p-electrode 112, leaving the p-electrode 112 and carving a narrow groove. Here, since the p-electrode 112 is located in the recessed part of the narrow groove, the distance between the side of the groove and the laser L tends to decrease, and for example, the surface temperature of the side of the light-absorbing layer 113 may become high. Due to the heat, a defect region 117 is formed on the side of the light-absorbing layer 113, and the current that can flow decreases.

[0056] (Second Embodiment) According to the second embodiment, a multi-junction solar cell is provided. This multi-junction solar cell comprises a first solar cell and a second solar cell having a second light-absorbing layer having a smaller bandgap than the first light-absorbing layer of the first solar cell. The first solar cell is a solar cell according to the first embodiment. The second electrode is a transparent electrode.

[0057] Figure 14 shows a cross-sectional conceptual diagram of an example of the multi-junction solar cell 200. The illustrated multi-junction solar cell 200 has a first solar cell 201 and a second solar cell 202. The first solar cell 201 is a solar cell according to the first embodiment. The first solar cell 201 is located on the light incident side of the multi-junction solar cell 200 and is in contact with the second solar cell 202 on the side of the second electrode 5 (p electrode). In the multi-junction solar cell 200, transparent electrodes are used not only for the first electrode 2 (n electrode) of the first solar cell 201 but also for the second electrode 5. As a result, light that is not absorbed by the light absorption layer 4 from the light incident from the first electrode side can be transmitted through the second electrode 5 and incident on the second solar cell 202. Therefore, electricity can be generated in the second solar cell 202 using incident light that cannot be fully utilized by the first solar cell 201. The first solar cell 201 and the second solar cell 202 can be joined together, for example, via an intermediate adhesive layer 203.

[0058] The second solar cell 202 could be, for example, a silicon solar cell.

[0059] The band gap of the light-absorbing layer of the second solar cell 202 is smaller than that of the light-absorbing layer 4 of the first solar cell 201. Note that the multi-junction solar cell of this embodiment also includes solar cells formed by joining three or more solar cells. When the first solar cell 201, equipped with a wide-bandgap light-absorbing layer, is used as the top cell, and the second solar cell 202, equipped with a narrow-bandgap light-absorbing layer, is used as the bottom cell, the top cell has higher transmittance of wavelengths that contribute to power generation on the bottom cell side, resulting in higher power generation on the bottom cell side. Therefore, excellent conversion efficiency can be achieved.

[0060] Since the second solar cell 202 does not contain a glass substrate, the multi-junction solar cell 200 contains only one glass substrate (the transparent substrate 1 of the first solar cell 201). Furthermore, because the only intermediate layer between the first solar cell 201 and the second solar cell 202 is the intermediate adhesive layer 203, a large amount of light reaches the second solar cell 202 via the first solar cell 201. Therefore, the multi-junction solar cell 200 is lightweight and has excellent conversion efficiency because it uses the solar cell of the first embodiment.

[0061] Figure 15 shows a conceptual cross-sectional view of an example of a multi-junction solar cell using a conventional substrate-type solar cell as the top cell. The multi-junction solar cell 210 shown has a first solar cell 211 and a second solar cell 202. The first solar cell 211 has the same structure as the conventional solar cell 110 shown in Figure 2. Therefore, the first solar cell 211 includes a total of two glass substrates: the substrate 111 on the p electrode 112 side and the sealing substrate on the n electrode 115 side. As a result, although the second solar cell 202 does not contain a glass substrate, the multi-junction solar cell 210 contains two glass substrates, requiring more material and increasing its thickness and weight.

[0062] The band gap of the light-absorbing layer of the second solar cell 202 may be, for example, 1.0 eV to 1.6 eV. Specific examples of the light-absorbing layer of the second solar cell 202 include one or more compound semiconductor layers from among CIGS, CIT, and CdTe systems with a high In content, or crystalline silicon.

[0063] (Third embodiment) According to the third embodiment, a solar cell module is provided. This solar cell module comprises a solar cell according to the first embodiment. Therefore, the solar cell module has excellent conversion efficiency.

[0064] Figure 16 shows a perspective conceptual diagram of an example of the solar cell module 300. The illustrated solar cell module 300 is a solar cell module in which a first solar cell module 301 and a second solar cell module 302 are stacked. The first solar cell module 301 is located on the light incident side and is equipped with the solar cell of the first embodiment. It is preferable to use the second solar cell 202 in the second solar cell module 302.

[0065] Figure 17 shows a cross-sectional conceptual diagram of an example of a solar cell module 300. This figure shows the structure of the first solar cell module 301 in detail, while the details of the structure of the second solar cell module 302 are omitted from the illustration. For the second solar cell module 302, the structure of the solar cell module is appropriately selected according to the light absorption layer of the solar cell used. The first solar cell module 301 and the second solar cell module 302 are laminated with a sealing layer 303 that also serves as an intermediate adhesive layer. The sealing layer 303 fills the gap between the first solar cell module 301 and the second solar cell module 302.

[0066] The illustrated example solar cell module 300 includes multiple submodules 304, each containing multiple solar cells 100 (solar cells) arranged horizontally and electrically connected in series, as indicated by the dashed lines. These multiple submodules 304 are electrically connected in parallel or in series. Adjacent submodules 304 can also be electrically connected by busbars 305. For example, in the illustrated example, a group of submodules 304 connected in series horizontally in the drawing is connected in parallel to another group of adjacent submodules (not shown) in the depth direction of the drawing via busbars 305.

[0067] Each submodule 304 contains multiple solar cells 100 that share a single transparent substrate 1. The transparent substrate 1 can also be shared among multiple submodules. Two adjacent solar cells 100 can be connected in series, for example, by electrically connecting the first electrode 2 (n electrode) of one solar cell 100 on the transparent substrate 1 side to the second electrode 5 (p electrode) on the opposite side of the adjacent solar cell 100, similar to the two-series array shown in Figure 4. Each of these solar cells 100 may have a structure similar to the solar cell according to the first embodiment. However, similar to the multi-junction solar cell according to the second embodiment, the second electrode 5 is a transparent electrode. The sealing layer 303 is also light-transmitting. Therefore, the first solar cell module 301 can take in incident light from the transparent substrate 1 side, and the light that was not absorbed by the first solar cell module 301 can be taken in by the second solar cell module 302.

[0068] In the first solar cell module 301, the electrical connection between the submodules 304 by the busbar 305 is preferably configured appropriately, taking into consideration the adjustment of the output voltage between the first solar cell module 301 and the second solar cell module 302.

[0069] (Fourth Embodiment) According to the fourth embodiment, a photovoltaic power generation system is provided. This photovoltaic power generation system comprises a solar cell module according to the third embodiment. Therefore, the photovoltaic power generation system has excellent conversion efficiency.

[0070] The solar cell module according to the third embodiment can be used as a generator in the photovoltaic power generation system of the fourth embodiment. The photovoltaic power generation system of the embodiment generates electricity using a solar cell module, and specifically includes a solar cell module that generates electricity, means for converting the generated electricity into power, and energy storage means for storing the generated electricity or a load for consuming the generated electricity.

[0071] Figure 18 shows a conceptual diagram of an example of the configuration of the photovoltaic power generation system 400. The illustrated photovoltaic power generation system includes a solar cell module 401, a converter 402, a storage battery 403, and a load 404. Either the storage battery 403 or the load 404 may be omitted. The load 404 may also be configured to utilize the electrical energy stored in the storage battery 403. The converter 402 is a device that includes circuits or elements that perform power conversion such as voltage transformation and DC-AC conversion, such as a DC-DC converter, DC-AC converter, or AC-AC converter. The configuration of the converter 402 should be suitable depending on the generated voltage and the configuration of the storage battery 403 and the load 404.

[0072] The solar cells contained in the solar cell module 401 generate electricity, and this electrical energy is converted by the converter 402 and stored in the battery 403 or consumed by the load 404. It is preferable to add a solar cell module 401 with a solar tracking drive device to keep the solar cell module 401 facing the sun, a light concentrator to concentrate sunlight, and devices to improve power generation efficiency.

[0073] The solar power generation system 400 is preferably used in real estate such as residences, commercial facilities, and factories, or in movable property such as vehicles, aircraft, and electronic equipment. By using the solar cell module according to the third embodiment, which has excellent conversion efficiency, in the solar cell module 401, an increase in power generation can be expected. [Examples]

[0074] The present invention will be described more specifically below based on examples, but the present invention is not limited to the following examples.

[0075] <Manufacturing of solar cells> (Example 1) A solar cell having the structure shown in Figure 1 was fabricated as follows. This solar cell is an example of a light-transmitting thin-film Cu2O solar cell.

[0076] An AZO transparent conductive film was deposited on a glass substrate to form an oxide transparent conductive film. A portion of this film was then removed by patterning to create a gap that penetrated the film. Patterning was performed by resist coating and wet etching. In this way, an n-electrode (first electrode) was obtained, divided into two electrode pieces. The gap was provided along a position close to one side of the conductive film, thereby making one n-electrode piece significantly larger in area than the other n-electrode piece.

[0077] Next, an n-type semiconductor film was formed by depositing Ga2O3 at 560°C using chemical vapor deposition (CVD). Subsequently, the portion above the smaller n-electrode piece and the adjacent portions within the gap were removed from the n-type semiconductor film by patterning. Patterning was performed by resist coating and wet etching. In this way, an n-type layer was obtained.

[0078] Next, a Cu2O film was deposited by heating at 500°C using CVD and sputtering in an argon gas atmosphere. Subsequently, the upper portion of the smaller n-electrode piece and the adjacent portions within the gap were removed from the Cu2O film by patterning. Patterning was performed by laser scribing. In this way, a light absorption layer was obtained.

[0079] Next, a second electrode was obtained by sequentially depositing an ATO (Antimony-doped Tin Oxide) transparent conductive film and an ITO (Indium-doped Tin Oxide) transparent conductive film as the p-electrode.

[0080] Electrode leads were connected to each n electrode piece to serve as a current supply path for extracting power.

[0081] (Comparative Example 1) A solar cell having the structure shown in Figure 2 was fabricated as follows.

[0082] A transparent conductive oxide film was formed by depositing an ITO transparent conductive film on a glass substrate, and then a gap was created through the film by removing a portion of it. Patterning was performed by resist coating and wet etching. In this way, a p-electrode divided into two electrode pieces was obtained. The gap was provided along a position close to one side of the conductive film, thereby making one p-electrode piece significantly larger in area than the other.

[0083] Next, a Cu2O film was deposited by heating at 500°C using CVD and sputtering in an argon gas atmosphere. This resulted in the acquisition of a light-absorbing layer.

[0084] Next, an n-type semiconductor film was deposited by CVD using Ga2O3 at 560°C. Subsequently, a buffer layer was deposited by depositing ZTO. In this way, the n-type layer and the buffer layer were obtained.

[0085] Next, grooves were created through the film by removing a portion of the buffer layer, n-type layer, and light absorption layer through patterning. Laser etching was used for patterning. The grooves were made to run along one side of the laminate.

[0086] Subsequently, an AZO transparent conductive film was deposited to obtain the n electrode.

[0087] Finally, a glass substrate was laminated on the n-electrode to serve as a encapsulation substrate.

[0088] Electrode leads were connected to each p-electrode piece to serve as a current supply path for extracting power.

[0089] (Comparative Example 2) A solar cell having the structure shown in Figure 3 was fabricated as follows.

[0090] A transparent conductive AZO film was deposited on a glass substrate to form an oxide transparent conductive film. After that, a portion of the film was removed by patterning to create grooves that penetrated the film. Patterning was performed by resist coating and wet etching. In this way, an n-electrode divided into two electrode pieces was obtained. The gap between them was provided along a position close to one side of the conductive film, thereby making one n-electrode piece significantly larger in area than the other n-electrode piece.

[0091] Next, an n-type semiconductor film was formed by depositing Ga2O3 at 560°C using the CVD method. Thus, an n-type layer was obtained.

[0092] Next, a Cu2O film was deposited by heating at 500°C using CVD and sputtering in an argon gas atmosphere. This resulted in the acquisition of a light-absorbing layer.

[0093] Next, grooves were created through the film by removing a portion of the light-absorbing layer and the n-type layer through patterning. Laser etching was used for patterning. The grooves were made to run along one side of the laminate.

[0094] Subsequently, a second electrode was obtained by sequentially depositing an ATO (Antimony-doped Tin Oxide) transparent conductive film and an ITO (Indium-doped Tin Oxide) transparent conductive film as the p-electrode.

[0095] Electrode leads were connected to each n electrode piece to serve as a current supply path for extracting power.

[0096] <Performance Evaluation> The conversion efficiency of each solar cell fabricated in Example 1, Comparative Example 1, and Comparative Example 2 was measured as follows.

[0097] First, the power supply, ammeter, and simulated sunlight (1kW / m 2A power supply, ammeter, and solar cell were prepared. The power supply, ammeter, and solar cell were electrically connected in series. With simulated sunlight shining on the solar cell, the voltage (V) of the power supply was changed, and the current density (mA / cm²) at that time was measured. 2 The change in ) was obtained. From the obtained current-voltage characteristics, the voltage-power (mW / cm²) was obtained. 2 )Calculate the curve and the maximum power (mW / cm²) on that curve. 2 This was recorded as the conversion efficiency (%).

[0098] The above measurements revealed that the solar cell fabricated in Example 1 achieved a higher conversion efficiency compared to the solar cells fabricated in Comparative Examples 1 and 2, respectively.

[0099] A solar cell is provided according to one or more embodiments and examples described above. The solar cell comprises a transparent first electrode having a through-gap, an n-type layer, a light-absorbing layer containing an inorganic material, and a second electrode. The n-type layer is located between the first electrode and the light-absorbing layer. The light-absorbing layer is located between the n-type layer and the second electrode. The n-type layer, the light-absorbing layer, and the second electrode are each partially contained within the gap, with a portion of the n-type layer, a portion of the light-absorbing layer, and a portion of the second electrode arranged in this order within the gap. The solar cell can exhibit an excellent conversion rate.

[0100] While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These novel embodiments can be carried out in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims and their equivalents. [Explanation of Symbols]

[0101] 1...Transparent substrate, 2...First electrode, 2a...Negative side first electrode piece, 2b...Positive side first electrode piece, 3...N type layer, 4...Light absorption layer, 5...Second electrode, 100...Solar cell, 101...Solar cell array, 110...Solar cell, 111...Substrate, 112...P electrode, 112a...Positive side p electrode Pole piece, 112b... Negative p-electrode piece, 113... Light absorption layer, 114... N-type layer, 115... N-electrode, 116... Sealing substrate, 120... Solar cell, 121... Transparent substrate, 122... N-electrode, 122a... Negative-side n-electrode piece, 122b... Positive-side n-electrode piece, 123... N-type layer, 124 ...light absorption layer, 125...p electrode, 145...buffer layer, 200...multi-junction solar cell, 201...first solar cell, 202...second solar cell, 203...intermediate adhesive layer, 210...multi-junction solar cell, 211...first solar cell, 300...solar cell module, 301...first solar cell module, 302...second solar cell module, 303...encapsulation layer, 304...submodule, 305...busbar, 400...photovoltaic power generation system, 401...solar cell module, 402...converter, 403...storage battery, 404...load.

Claims

1. A transparent first electrode, n-type layer and A light-absorbing layer containing inorganic materials, It comprises a second electrode, The n-type layer is located between the first electrode and the light-absorbing layer, and the light-absorbing layer is located between the n-type layer and the second electrode. The first electrode has a gap that penetrates the first electrode, A solar cell in which the n-type layer, the light-absorbing layer, and the second electrode are each partially contained within the gap, and a portion of the n-type layer, a portion of the light-absorbing layer, and a portion of the second electrode are arranged within the gap in this order.

2. The solar cell according to claim 1, wherein the light-absorbing layer contains cuprous oxide.

3. The solar cell according to claim 1 or 2, wherein the second electrode comprises a metallic material or an alloy material.

4. The first solar cell and The system comprises a second solar cell having a second light-absorbing layer having a smaller band gap than the first light-absorbing layer of the first solar cell, A multi-junction solar cell, wherein the first solar cell is the solar cell described in claim 1 or 2, and the second electrode is a transparent electrode.

5. The multi-junction solar cell according to claim 4, wherein the first solar cell is joined to the second solar cell on the surface facing the second electrode.

6. A solar cell module comprising the solar cell described in claim 1 or 2.

7. A photovoltaic power generation system comprising the solar cell module described in claim 6.

8. A transparent first electrode, n-type layer and A light-absorbing layer containing inorganic materials, It comprises a second electrode, The n-type layer is located between the first electrode and the light-absorbing layer, and the light-absorbing layer is located between the n-type layer and the second electrode. The first electrode has a gap that penetrates the first electrode, A method for manufacturing a solar cell, wherein the n-type layer, the light-absorbing layer, and the second electrode are each partially contained within the gap, and a portion of the n-type layer, a portion of the light-absorbing layer, and a portion of the second electrode are arranged in the gap in this order. Deposition of an oxide transparent conductive film on a transparent substrate, The first electrode is obtained by partially removing the oxide transparent conductive film, The process involves forming an n-type semiconductor film on the first electrode and on the transparent substrate exposed in the gap, The n-type layer is obtained by removing a portion of the n-type semiconductor film that is in contact with the side surface of the first electrode located on one side of the gap and the upper surface of the first electrode adjacent to the side surface. The inorganic material film is formed on the n-type layer, on the transparent substrate exposed in the gap, and on the exposed first electrode. The light-absorbing layer is obtained by removing the portions of the inorganic material film that are in contact with the side surface and the top surface, A manufacturing method comprising forming another conductive film on the light-absorbing layer, on the transparent substrate exposed in the gap, and on the exposed first electrode to obtain the second electrode.

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