JP2009259926A - Solar cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solar cell capable of improving a photocurrent without being controlled by the lowest photocurrent within photocurrents generated in a photoelectric conversion layer. <P>SOLUTION: This solar cell is provided with: a plurality of cells 2 formed on the upper surface of a translucent insulation substrate 1, and each having a wide-band gap photoelectric conversion layer 12; and a plurality of tandem cells 3 formed on the lower surface of the translucent insulation substrate 1, and each having a middle-band gap photoelectric conversion layer 22 having an optical band gap different from that of the wide-band gap photoelectric conversion layer 12. The cell 2 and the tandem cell 3 facing each other interposing the translucent insulation substrate 1 constitute a unit 4. The wide-band gap photoelectric conversion layer 12 and the middle-band gap photoelectric conversion layer 22 of the unit 4 are electrically connected in parallel to each other through a through-hole 5 formed on the translucent insulation board 1. The photoelectric conversion layers 12 and the photoelectric conversion layers 22 of the units 4 adjacent to each other are electrically connected to each other. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a solar cell that generates electric power from photovoltaic power of a photoelectric conversion layer.

  In a solar cell such as a conventional thin film solar cell, a tandem cell (tandem cell) is formed on a light-transmitting insulating substrate. This tandem cell is formed by stacking a photoelectric conversion layer composed of p-layer, i-layer, and n-layer semiconductor layers between a pair of electrodes composed of a transparent conductive film and a reflective conductive film. Furthermore, in order to improve the power generation efficiency, for example, a plurality of photoelectric conversion layers such as an amorphous silicon semiconductor layer and a microcrystalline silicon semiconductor layer are stacked. The plurality of photoelectric conversion layers acting as current sources have different optical band gaps and are electrically connected in series with each other. In a tandem cell having such a configuration, for example, the short wavelength component of sunlight is absorbed by the amorphous silicon semiconductor layer and the long wavelength component is absorbed by the microcrystalline silicon semiconductor layer, respectively, thereby expanding the effective wavelength range of light and generating efficiency. Has improved.

  In addition, a structural unit (the above-mentioned tandem cell) in which a plurality of photoelectric conversion layers are stacked between a pair of electrodes composed of a transparent conductive film and a reflective conductive film is used as a unit, and the plurality of units are juxtaposed to reflect the unit. There has also been proposed a structure in which a conductive film and a transparent conductive film of an adjacent unit are connected and the photoelectric conversion layers are electrically connected to each other in series.

  In the solar cell described in Patent Document 1, cells composed of photoelectric conversion layers having optical band gaps different from each other are arranged on the upper and lower surfaces of the translucent insulating substrate, and face each other with the translucent insulating substrate interposed therebetween. A unit is constituted by the upper cell and the lower cell. The photoelectric conversion layers of the unit are electrically connected to each other through a through hole provided in the translucent insulating substrate. The difference between the structure of Patent Document 1 and the conventional structure is that, in the conventional structure, the photoelectric conversion layers are joined and directly electrically connected, whereas in the structure of Patent Document 1, the photoelectric conversion is performed. The layers are indirectly connected to each other through a through hole provided in the substrate. On the other hand, a common feature between the structure of Patent Document 1 and the conventional structure is that a plurality of photoelectric conversion layers having different optical band gaps are electrically connected in series. With this structure, the voltage generated in the solar cell is improved according to the number of photoelectric conversion layers.

Japanese Unexamined Patent Publication No. 7-79004 (page 2-4, FIG. 1-3)

  However, in the structure of Patent Document 1 and the conventional structure, since a plurality of photoelectric conversion layers serving as current generation sources are all connected in series, photocurrent generated in the entire solar cell is generated in each photoelectric conversion layer. There is a problem that the photocurrent is limited to the lowest photocurrent. For example, when two or more types of photoelectric conversion layers having different optical band gaps are connected in series in the unit, the photoelectric currents generated in the unit are different in each photoelectric conversion layer because the characteristics of the photoelectric conversion layers are different. The rate is limited to the lowest photocurrent generated.

  In addition, when the photocurrent generated in each photoelectric conversion layer changes due to changes in the sunlight spectrum due to the season or weather, the photocurrent of the entire solar cell may decrease due to the change. is there. For example, if the photocurrent increases in one photoelectric conversion layer due to a change in the spectrum of sunlight, but the photocurrent decreases in the other photoelectric conversion layer, the photocurrent of the entire solar cell may decrease. is there. In addition, the characteristics of the photoelectric conversion layer change due to a temperature change, and the photocurrent also fluctuates due to the temperature change, but in this case as well, the rate is limited to a low photocurrent.

  The present invention has been made to solve the above-described problems, and is a solar cell capable of improving the photocurrent without being limited by the lowest photocurrent generated in the photoelectric conversion layer. The purpose is to provide.

  A solar cell according to the present invention is formed on one surface of a light-transmitting insulating substrate, and includes a plurality of first cells including a first photoelectric conversion layer, and the other surface of the light-transmitting insulating substrate. And a plurality of second cells including a second photoelectric conversion layer formed and having a second optical conversion layer having an optical band gap different from that of the first photoelectric conversion layer. The first cell and the second cell that face each other with the translucent insulating substrate interposed therebetween constitute a unit. The first photoelectric conversion layer and the second photoelectric conversion layer of the unit are electrically connected in parallel to each other through a through hole provided in the light-transmitting insulating plate, and The first photoelectric conversion layers and the second photoelectric conversion layers are electrically connected in series.

  In the solar cell of the present invention, the photoelectric conversion layers having different optical band gaps are electrically connected in parallel, so that the rate is determined by the lowest photocurrent among the photocurrents generated in each photoelectric conversion layer. In addition, the photocurrent can be improved. As a result, it is possible to improve operational stability against changes in the operating ambient environment such as the sunlight spectrum and temperature due to the season and weather.

<Embodiment 1>
FIG. 1 is a cross-sectional view showing the configuration of the solar cell according to the present embodiment. As shown in FIG. 1, the solar cell according to the present embodiment includes a translucent insulating substrate 1, a cell 2, and a tandem cell 3. As the material of the translucent insulating substrate 1, for example, glass is used.

  A plurality of cells 2 that are a plurality of first cells according to the present embodiment are formed on one surface (upper surface in FIG. 1) of the light-transmitting insulating substrate 1 and are wide as a first photoelectric conversion layer. A band gap photoelectric conversion layer 12 is provided. In the present embodiment, the plurality of cells 2 further include a first transparent conductive film 11 and a second transparent conductive film 13 in addition to the wide band gap photoelectric conversion layer 12. The first transparent conductive film 11 is arranged in a predetermined pattern on the upper surface of the translucent insulating substrate 1.

  The figure which expanded the broken-line part of FIG. 1 is shown under FIG. In the wide band gap photoelectric conversion layer 12 according to the present embodiment, a p layer 15, an i layer 16, and an n layer 17 containing an i layer semiconductor material having a wide band gap are formed on the first transparent conductive film 11 so as to transmit light. The layers are sequentially stacked from the insulating substrate 1 side. The wide band gap photoelectric conversion layer 12 covers the first transparent conductive film 11. An opening 14 is provided between adjacent wide band gap photoelectric conversion layers 12. In addition, there is no restriction | limiting in particular with respect to the wide band gap photoelectric converting layer 12 contacting the transparent conductive film 11. FIG.

  The second transparent conductive film 13 is disposed on the wide band gap photoelectric conversion layer 12 on the upper side of the translucent insulating substrate 1. The second transparent conductive film 13 and the facing first transparent conductive film 11 constituting the cell 2 are spatially separated by the wide band gap photoelectric conversion layer 12 described above. On the other hand, the second transparent conductive film 13 and the first transparent conductive film 11 of the adjacent cell 2 are spatially and electrically connected at the opening 14 between the wide band gap photoelectric conversion layers 12. ing. As shown in FIG. 1, the second transparent conductive film 13 is provided with a separation portion 18 on the first transparent conductive film 11. As a result, the adjacent second transparent conductive films 13 are spatially separated from each other and electrically insulate.

  A plurality of tandem cells 3 which are a plurality of second cells according to the present embodiment are formed on the other surface (the lower surface in FIG. 1) of translucent insulating substrate 1 and are second photoelectric conversion layers. A middle band gap photoelectric conversion layer 22 is provided. In the present embodiment, in addition to the middle band gap photoelectric conversion layer 22, the plurality of tandem cells 3 include a third transparent conductive film 21, a narrow band gap photoelectric conversion layer 23 that is a third photoelectric conversion layer, and a reflective conductive film. And a layer 24. The third transparent conductive film 21 is arranged in a predetermined pattern on the lower surface of the translucent insulating substrate 1.

  In the middle band gap photoelectric conversion layer 22 according to the present embodiment, a p layer 26, an i layer 27, and an n layer 28 containing a middle band gap i-layer semiconductor material are formed on the third transparent conductive film 21. The layers are sequentially stacked from the insulating substrate 1 side. In the present embodiment, the above wide band gap photoelectric conversion layer 12 has a wider optical band gap than the middle band gap photoelectric conversion layer 22.

  The narrow band gap photoelectric conversion layer 23 is formed by sequentially stacking a p layer 29, an i layer 30, and an n layer 31 containing a narrow band gap i layer semiconductor material on the middle band gap photoelectric conversion layer 22 from the translucent insulating substrate 1 side. It becomes. Thus, in this embodiment, the narrow band gap photoelectric conversion layer 23 is stacked on the middle band gap photoelectric conversion layer 22 on the side opposite to the translucent insulating substrate 1, and is electrically connected to the middle band gap photoelectric conversion layer 22. Connected in series. In the present embodiment, the middle band gap photoelectric conversion layer 22 described above has a wider optical band gap than the narrow band gap photoelectric conversion layer 23.

  In the following description, when the wide band gap photoelectric conversion layer 12, the middle band gap photoelectric conversion layer 22, and the narrow band gap photoelectric conversion layer 23 are not distinguished, they may be simply referred to as photoelectric conversion layers 12, 22, and 23. . Further, when the middle band gap photoelectric conversion layer 22 and the narrow band gap photoelectric conversion layer 23 are not distinguished from each other, they are simply referred to as lower photoelectric conversion layers 22 and 23, and the wide band gap photoelectric conversion layer 12 is referred to as the lower band gap photoelectric conversion layer 12. It may be described as the upper photoelectric conversion layer 12.

  The lower photoelectric conversion layers 22 and 23 cover the third transparent conductive film 21. An opening 25 is provided between the adjacent lower photoelectric conversion layers 22 and 23. There are no particular restrictions on the lower photoelectric conversion layers 22 and 23 coming into contact with the third transparent conductive film 21.

  The reflective conductive layer 24 is disposed on the narrow band gap photoelectric conversion layer 23 on the lower side of the translucent insulating substrate 1. The reflective conductive layer 24 and the facing third transparent conductive film 21 constituting the tandem cell 3 are spatially separated by the lower photoelectric conversion layers 22 and 23. On the other hand, the reflective conductive layer 24 and the third transparent conductive film 21 of the adjacent tandem cell 3 are spatially and electrically connected in the opening 25 between the lower photoelectric conversion layers 22 and 23. ing. As shown in FIG. 1, the reflective conductive layer 24 is provided with a separation portion 32 on the third transparent conductive film 21. As a result, the adjacent reflective conductive layers 24 are spatially separated from each other and electrically insulate.

  The cell 2 and the tandem cell 3 that face each other with the translucent insulating substrate 1 in between constitute a unit 4. The translucent insulating substrate 1 is provided with a through hole 5, and a conductive member provided continuously in the thickness direction of the translucent insulating substrate 1 is provided on at least a part of the inner wall of the through hole 5. . Thereby, the first transparent conductive film 11 and the third transparent conductive film 21 are electrically connected through the through hole 5 provided in the translucent insulating substrate 1. As the translucent insulating substrate 1, for example, a substrate having a thickness of 1.1 mm is used, and the through hole 5 is formed in a cylindrical shape having a radius of 0.5 mm, for example.

  Inside the through-hole 5, for example, a silver brazing material is filled or a sputter transparent conductive film is formed. FIG. 2 is a cross-sectional view showing a structure at an intermediate stage in which the first transparent conductive film 11 and the third transparent conductive film 21 are formed on the translucent insulating substrate 1 in which the through holes 5 according to the present embodiment are formed. It is a figure (Fig.2 (a)) and a top view (FIG.2 (b)). As shown in FIG.2 (b), the through-hole 5 is arrange | positioned on the line at the fixed space | interval defined based on the electrical resistance. With this structure, the cell 2 and the tandem cell 3 are connected in parallel.

  The middle band gap photoelectric conversion layer 22 and the narrow band gap photoelectric conversion layer 23 have the same stacking direction of the p layers 26 and 29, the i layers 27 and 30, and the n layers 28 and 31, and are electrically connected in series. The The p layer 26 of the middle band gap photoelectric conversion layer 22 and the p layer 15 of the wide band gap photoelectric conversion layer 12 are electrically connected to each other through the first and third transparent conductive films 11 and 21 and the through hole 5. Connected. Thereby, the wide band gap photoelectric conversion layer 12 and the middle band gap photoelectric conversion layer 22 of the unit 4 are electrically connected in parallel to each other through the through hole 5 provided in the translucent insulating substrate 1.

  When light is absorbed by the photoelectric conversion layers 12, 22, and 23, photocurrent flows from the n layer to the p layer of the photoelectric conversion layers 12, 22, and 23. Therefore, in the upper photoelectric conversion layer 12, a photocurrent is generated from the upper surface in FIG. 1 to the translucent insulating substrate 1 side, and in the lower photoelectric conversion layers 22 and 23, the transparent surface from the lower surface in FIG. A photocurrent is generated on the photoconductive substrate 1 side. These photocurrents are generated independently in each of the photoelectric conversion layers 12, 22, and 23. Therefore, the photocurrent generated in the unit 4, that is, the photocurrent generated in the entire solar cell is the sum of the photocurrents generated above and below the translucent insulating substrate 1.

  In addition, one unit 4 formed over the entire surface of the light-transmitting insulating substrate 1 and composed of the upper cell 2 and the lower tandem cell 3 facing each other with the light-transmitting insulating substrate 1 interposed therebetween is an adjacent unit. 4 and the first and third transparent conductive films 11 and 21 are electrically connected in series. Thereby, the wide band gap photoelectric conversion layers 12 and the middle band gap photoelectric conversion layers 22 of the adjacent units 4 are electrically connected in series.

  With this structure, the photocurrent generated in the upper photoelectric conversion layer 12 is delivered to the upper photoelectric conversion layer 12 of the adjacent unit 4. On the other hand, the photocurrent generated in the lower photoelectric conversion layers 22 and 23 is delivered to the lower photoelectric conversion layers 22 and 23 of the adjacent unit 4. As a result, the voltage generated in the entire solar cell is the sum of the voltages generated in the units 4 connected in series.

  Next, the operation in which the solar cell according to the present embodiment absorbs light serving as the generation source of the above-described photocurrent and voltage will be described. In the configuration of the solar cell according to the present embodiment, the upper surface of the translucent insulating substrate 1 is a light receiving surface that receives sunlight. Sunlight incident from the upper surface passes through the second transparent conductive film 13, and light of a short wavelength component is mainly absorbed by the wide band gap photoelectric conversion layer 12. The remaining light passes through the first transparent conductive film 11, the translucent insulating substrate 1 and the third transparent conductive film 21, and in each of the middle band gap photoelectric conversion layer 22 and the narrow band gap photoelectric conversion layer 23, the medium wavelength component. And light having a long wavelength component are absorbed.

  The remaining light is reflected by the reflective conductive layer 24, travels in the direction opposite to the traveling direction of the light, and is absorbed by the photoelectric conversion layers 12, 22, and 23. Although the main light progress is as described above, reflection, refraction, and interference occur at the interface of each film, so the actual light progress is more complicated. In addition, in order that sunlight can permeate | transmit also in the through-hole 5 of the translucent insulated substrate 1, it is desirable that the film | membrane formed in the through-hole 5 is a transparent conductive film.

  In addition, although there is no restriction | limiting in particular about the surface structure of each film | membrane, For example, the texture structure which provides uneven | corrugated shape in the surface of either one of the 1st transparent conductive film 11 and the 3rd transparent conductive film 21, or both It is desirable to form. If the structure is formed, the traveling direction of sunlight is changed by refraction, and the action length of light on the photoelectric conversion layers 12, 22, and 23 is increased, and light is projected to the outside by regular reflection. It is possible to suppress and provide an optical action to confine light as much as possible inside.

  For example, when the first transparent conductive film 11 has the above-described texture structure, the underlying texture structure is provided to the surface of the wide band gap photoelectric conversion layer 12 and the second transparent conductive film 13 to be formed later on the surface. A reflected surface shape is formed. In this case, since the sunlight that has reached the second transparent conductive film 13 is refracted according to the surface shape thereof, the second transparent conductive film 13 can contribute to the internal confinement of light. In addition to the air layer or the upper filling layer (not shown) and the photoelectric conversion layer, the internal confinement of light is not limited to the interface between the second transparent conductive film 13 and the wide band gap photoelectric conversion layer 12 and the wide band gap photoelectric. This also occurs at the interface between the conversion layer 12 and the first transparent conductive film 11. Further, when the third transparent conductive film 21 has the texture structure described above, not only in the cell 2 above the translucent insulating substrate 1 but also in the tandem cell 3 below the translucent insulating substrate 1. In addition, it becomes possible to confine light by refraction or the like.

  In addition, in FIG. 1, although the photoelectric converting layers 12, 22, and 23 were shown with the simple structure, the structure which inserts a component other than this may be sufficient. For example, a structure in which a transparent conductive film such as ZnO is inserted between the reflective conductive layer 24 and the narrow band gap photoelectric conversion layer 23 may be used in order to improve the light reflectivity by wave optics. Further, for example, in order to improve the internal confinement efficiency of light and the electrical connectivity between the middle band gap photoelectric conversion layer 22 and the narrow band gap photoelectric conversion layer 23, between these photoelectric conversion layers 22 and 23, A structure in which a semiconductor film or a conductive film is inserted may be used.

  Next, a manufacturing process example of the solar cell according to the present embodiment will be described with reference to FIG. As shown in FIG. 3A, for example, a translucent insulating substrate 1 made of glass is prepared. The through hole 5 is formed in the translucent insulating substrate 1 by using, for example, an electroforming drill provided with diamond abrasive grains. For example, a sputtered film of Cr and Ti is formed on the inner wall of the through hole 5. The hollow portion inside the through hole 5 is filled with, for example, a silver brazing material or a transparent conductive material, and the metal portion and the conductive material on the surface of the translucent insulating substrate 1 other than the through hole 5 are removed by pad polishing.

  The translucent insulating substrate 1 is not limited to a glass substrate, and may be a plastic substrate, for example. When a plastic substrate is used for the translucent insulating substrate 1, the through hole 5 may be formed by processing with a laser or a mold including a punch and a die. In addition, formation of the through-hole 5 shown here is only an example, and does not restrict | limit this invention in particular. Further, a film such as SiOx or SiNx as a barrier layer may be provided in advance on the surface of the light-transmitting insulating substrate 1 in order to suppress impurity diffusion from the light-transmitting insulating substrate 1 to a film to be formed in a later step.

As shown in FIG. 3B, a transparent conductive film made of SnO ₂ and having a thickness of 1.0 μm is formed on one surface of the translucent insulating substrate 1 by, eg, thermal CVD (Chemical Vapor Deposition). As film formation conditions, for example, the temperature of the translucent insulating substrate 1 is set to 500 ° C., 2.0 mol% SnCl ₄ as a source gas, 10 mol% H ₂ 0 and 1.0 mol% O ₂ as an oxidizing gas. If necessary, a gas of 1.0 mol% F dopant is added to the carrier gas using N ₂ and these gases are supplied under normal pressure. A transparent conductive film formed on one surface of the translucent insulating substrate 1 is irradiated with pulsed light of a fundamental wave of an Nd: YVO ₄ laser. By this irradiation, the transparent conductive film between the cells is scribed and removed in a line to divide the transparent conductive film. On the other surface of the translucent insulating substrate 1, formation of a transparent conductive film and laser scribing removal are performed in the same manner as described above.

Thus, the first transparent conductive film 11 is formed on the upper surface of the translucent insulating substrate 1, and the third transparent conductive film 21 is formed on the lower surface of the translucent insulating substrate 1. Here, the case where the material of the first and third transparent conductive films 11 and 21 is SnO ₂ has been described, but it may be ITO (Indium Tin Oxide), IZO (Indiumu Zinc Oxide), or ZnO. Good. In addition, the transparent conductive film is formed on both surfaces of the light-transmitting insulating substrate 1 by plasma CVD by using reaction chambers separated on each surface of the light-transmitting insulating substrate 1. You may form into a film simultaneously. In addition, the transparent conductive film formed on both surfaces of the translucent insulating substrate 1 may be simultaneously divided by laser scribing.

  As shown in FIG. 3C, on the first transparent conductive film 11, for example, a 10 nm thick p layer 15 made of boron-doped a-SiC, an 200 nm thick i layer 16 made of a-SiC, and phosphorus doped A 15 nm thick n layer 17 made of a-Si is sequentially formed to form a wide band gap photoelectric conversion layer 12. On the third transparent conductive film 21, for example, a 10 nm thick p layer 26 made of boron-doped a-SiC, a 250 nm thick i layer 27 made of a-Si, and a 15 nm thick n layer made of phosphorus doped a-Si. The layer 28 is sequentially formed to form the middle band gap photoelectric conversion layer 22. Then, on the middle band gap photoelectric conversion layer 22, for example, a 10 nm thick p layer 29 made of boron-doped microcrystalline silicon (μc-Si) including an amorphous portion, a 2 μm thick i layer 30 made of μc-Si, An n layer 31 made of μc-Si having a thickness of 15 nm is sequentially formed to form a narrow band gap photoelectric conversion layer 23.

For these film formations, for example, parallel plate type RF plasma CVD is used. As the film formation conditions, the temperature of the translucent insulating substrate 1 is set to 200 ° C., and the raw material gases for film formation are SiH ₄ , CH ₄ , and H ₂ for a-SiC and SiH for a-Si. ₄ and H ₂ are used, and SiH ₄ and H ₂ are used for μc-Si. For a-Si, the gas concentration ratio [H ₂ ] / [SiH ₄ ] = 15, and for μc-Si, the gas concentration ratio [H ₂ ] / [SiH ₄ ] = 50. Other film deposition conditions by plasma CVD are set to be optimum.

As shown in FIG. 3 (d), the photoelectric conversion layers 12, 22, and 23 between the cells are scribed and removed in a line shape when viewed from the top to form openings 14 and 25, and the photoelectric conversion layers 12, 22, and 23 is divided into patterns. This division is performed by irradiating the photoelectric conversion layers 12, 22, and 23 formed on both surfaces of the translucent insulating substrate 1 with the second harmonic (2ω) of the Nd: YVO ₄ laser. In this scribing removal, the first and third transparent conductive films 11 and 21 and the translucent insulating substrate 1 are also irradiated with laser, but are not scribed because they transmit light of the laser wavelength. The shape is maintained.

As shown in FIG. 3E, on the wide band gap photoelectric conversion layer 12 patterned on the upper surface side of the translucent insulating substrate 1, a thickness made of an Al: 2 wt% doped ZnO film is formed by, for example, DC magnetron sputtering. A second transparent conductive film 13 having a thickness of 500 nm is formed. On the other hand, an Al: 2 wt% doped ZnO film having a thickness of 100 nm is formed on the narrow band gap photoelectric conversion layer 23 patterned on the lower surface side of the translucent insulating substrate 1 by, for example, DC magnetron sputtering. Then, a reflective electrode layer 24 made of, for example, Ag, Al, Au, Pt, or an alloy thereof is formed on the ZnO film. Here, as an example, the reflective conductive layer 24 made of an Ag film and having a thickness of 300 nm is stacked on the ZnO film. Here, although the ZnO film is formed on the narrow band gap photoelectric conversion layer 23, the present invention is not limited to this. For example, an ITO film, an IZO film, or a SnO ₂ film may be formed.

  As shown in FIG. 3 (f), for example, a clearance is set with reference to the interface between the translucent insulating substrate 1 and the first transparent conductive film 11, and mechanical scribing is performed between the cells 2 by using a processing needle. The second transparent conductive film 13 is removed, and a separation portion 18 is formed. The position where the second transparent conductive film 13 is removed is the edge of the wide band gap photoelectric conversion layer 12, and a part (a small amount) of the wide band gap photoelectric conversion layer 12 and a part of the first transparent conductive film 11. The second transparent conductive film 13 between the cells 2 is removed together with the (trace amount) surface layer. Thereby, the second transparent conductive films 13 of the adjacent cells 2 are separated from each other. The reflective conductive layer 24 between the tandem cells 3 on the lower surface side of the translucent insulating substrate 1 is scribed and removed in a line by the above-mentioned 2ω laser, and the reflective conductive layers 24 of the adjacent tandem cells 3 are separated from each other.

  FIG. 4 is a cross-sectional view showing the structure of another aspect of the solar cell according to the present embodiment. The structure of the solar cell according to FIG. 4 is different from the structure of the solar cell according to FIG. 1 in that the positions of the through holes 5 connecting the first transparent conductive film 11 and the third transparent conductive film 21 are different. Is a point. The through hole 5 of the translucent insulating substrate 1 of the solar cell according to FIG. 1 was provided between the wide band gap photoelectric conversion layer 12 and the middle band gap photoelectric conversion layer 22.

  On the other hand, the through-hole 5 of the translucent insulating substrate 1 of the solar cell according to FIG. 4 includes a connection portion between the first transparent conductive film 11 and the third transparent conductive film 13 and a second transparent conductive film. 21 and a connection portion between the reflective conductive layer 24 and the connection portion. That is, the through hole 5 of the translucent insulating substrate 1 of the solar cell according to FIG. 4 is provided avoiding the gap between the wide band gap photoelectric conversion layer 12 and the middle band gap photoelectric conversion layer 22. According to the solar cell according to FIG. 4, compared with the solar cell according to FIG. 1, it is possible to eliminate the harmful effect that sunlight transmitted from the upper surface to the lower surface of the translucent insulating substrate 1 is shielded by the through hole 5. .

Next, a manufacturing process example of the solar cell according to FIG. 4 will be described with reference to FIG. Here, only the steps different from FIG. 3 will be described, except for the parts common to FIG. As shown in FIG. 5A, for example, a translucent insulating substrate 1 made of glass is prepared. The through hole 5 is formed in the translucent insulating substrate 1 by using, for example, an electroforming drill provided with diamond abrasive grains. For example, a sputtered film of ITO, IZO or SnO ₂ or ZnO is formed on the inner wall of the through hole 5. The cavity inside the through hole 5 is filled with, for example, polyaniline, and the polymer film on the surface of the translucent insulating substrate 1 other than the through hole 5 is removed by pad polishing.

As shown in FIG. 5B, the positional relationship between the through-hole 5, the first transparent conductive film 11, and the third transparent conductive film 13 is a later process as viewed from the upper surface of the translucent insulating substrate 1. The first and third transparent conductive films 11 and 13 are formed so that they do not overlap with the photoelectric conversion layers 12, 22 and 23 to be formed. As shown in FIG. 5D, the photoelectric conversion layers 12, 22, and 23 are irradiated with pulsed Nd: YVO ₄ −2ω laser to be positioned between adjacent cells, that is, above and below the through hole 5. The photoelectric conversion layers 12, 22, and 23 are scribed to remove the photoelectric conversion layers 12, 22, and 23. At this time, the first transparent conductive film 11, the third transparent conductive film 13, and the through-hole 5 hold the shape because they transmit light of the laser wavelength.

  According to the solar cell according to the present embodiment as described above, since the photoelectric conversion layers 12, 22, and 23 have different optical band gaps, they generate photocurrents by absorbing light in different wavelength ranges. . Since the upper photoelectric conversion layer 12 and the lower photoelectric conversion layers 22 and 23 are electrically connected in parallel, the photocurrent generated in the entire solar cell is generated in the upper photoelectric conversion layer 12. And the photocurrent generated in the lower photoelectric conversion layers 22 and 23. Thereby, since it is not rate-limited to the low photocurrent among the photocurrents generated in the upper photoelectric conversion layer 12 and the lower photoelectric conversion layers 22 and 23, the photocurrent generated in the entire solar cell can be improved. Of the upper photoelectric conversion layer 12 and the lower photoelectric conversion layers 22 and 23, one photoelectric conversion layer increases the photocurrent, and the other photoelectric conversion layer decreases the photocurrent. Even if there is a change in the operating ambient environment such as the sunlight spectrum and temperature, the photocurrent of the entire solar cell is not rate-limited to a low photocurrent. Therefore, it is possible to improve the operation stability against changes in the operating environment. Moreover, since the voltage generated in the entire solar cell is the sum of the voltages generated in the units 4 connected in series, the operating voltage can be improved.

  Further, according to the solar cell according to the present embodiment, since the narrow band gap photoelectric conversion layer 23 having a wide optical band gap is provided, photoelectric conversion can be performed more efficiently.

  In general, the photovoltaic power generated in the wide band gap photoelectric conversion layer 12 is the same as the photovoltaic power generated in the middle band gap photoelectric conversion layer 22 or the photovoltaic power generated in the narrow band gap photoelectric conversion layer 23. It is larger than that. On the other hand, in the solar cell according to the present embodiment described above, the upper photoelectric conversion layer 12 having the largest photovoltaic power and the lower photoelectric conversion layers 22 and 23 connected in series with each other and having the smallest photovoltaic power are provided. It will be connected in parallel. Therefore, even when the photocurrent generated by the upper photoelectric conversion layer 12 having a large photovoltaic power and the lower photoelectric conversion layers 22 and 23 having a small photovoltaic power are different, the current can be efficiently extracted.

  In addition, when the photovoltaic power generated by the cell 2 and the photovoltaic power generated by the tandem cell 3 are different, there is a problem that the difference is reversely applied to the lower photovoltaic power side. Therefore, the photovoltaic power of the wide band gap photoelectric conversion layer 12 is substantially equal to the sum of the photovoltaic power of the middle band gap photoelectric conversion layer 22 and the photovoltaic power of the narrow band gap photoelectric conversion layer 23. Also good. In order to configure in this way, for example, the combination selection of the semiconductor materials of the photoelectric conversion layers 12, 22, 23, the doping concentration of the p layers 15, 26, 29 and the n layers 17, 28, 31 and the film quality of each layer, etc. Adjust it.

  Hereinafter, a configuration in which the photovoltaic power of the upper photoelectric conversion layer 12 and the photovoltaic power of the lower photoelectric conversion layers 22 and 23 are substantially equal will be described in detail. For example, amorphous silicon is added to the wide band gap photoelectric conversion layer 12, microcrystalline silicon is added to the middle band gap photoelectric conversion layer 22, and germanium is added to the narrow band gap photoelectric conversion layer 23, for example. Silicon is used. The open-circuit voltage of the photoelectric conversion layer formed of amorphous silicon is 0.8 to 0.8 by adjusting the dopant concentration of the p layer and the n layer, the hydrogen concentration contained in the p layer, the i layer, and the n layer, and the film thickness. It can be adjusted to about 0.95V. The open-circuit voltage of the photoelectric conversion layer formed of microcrystalline silicon is 0.4 to 0.5 V by adjusting the dopant concentration of the p layer and the n layer, the ratio of microcrystalline silicon to amorphous silicon, and the film formation conditions. It can be adjusted to the extent. Furthermore, it can adjust to about 0.3-0.45V by adding germanium to this microcrystalline silicon.

  Therefore, by combining these to adjust the photovoltaic power generated in each of the photoelectric conversion layers 12, 22, and 23, the voltage generated by the cell 2 composed of the wide band gap photoelectric conversion layer 12 and the middle band gap photoelectric conversion layer 22 and the voltage generated by the tandem cell 3 composed of the narrow band gap photoelectric conversion layer 23 can be made substantially the same.

  As described above, if the photovoltaic power generated by the cell 2 and the photovoltaic power generated by the tandem cell 3 are configured to be the same, the voltage is not reversely applied on the low photovoltaic power side. , Power can be taken out efficiently.

  Even when the voltages generated by both the cell 2 and the tandem cell 3 are not completely the same, if the difference is small to some extent, the effect of eliminating the limitation of the photocurrent generated by each of the cell 2 and the tandem cell 3 can be obtained. Therefore, the effect of taking out electric power efficiently is acquired.

  In addition, the structure which makes the photovoltaic power of the upper photoelectric converting layer 12 the same as the sum of the photovoltaic power of the lower photoelectric converting layers 22 and 23 is not restricted to the above-mentioned structure. For example, amorphous silicon is added to the wide band gap photoelectric conversion layer 12, amorphous silicon to which germanium is added to the middle band gap photoelectric conversion layer 22, and microcrystalline silicon to which germanium is added to the narrow band gap photoelectric conversion layer 23. May be used. Here, the open circuit voltage of the photoelectric conversion layer of amorphous silicon to which germanium is added can be adjusted to about 0.6 to 0.8 V by adjusting the amount of germanium added and the hydrogen-containing concentration.

3 is a cross-sectional view showing a configuration of a solar cell according to Embodiment 1. FIG. 4 is a top view showing the configuration of the solar cell according to Embodiment 1. FIG. 5 is a cross-sectional view showing the method for manufacturing the solar cell according to Embodiment 1. FIG. 3 is a cross-sectional view showing a configuration of a solar cell according to Embodiment 1. FIG. 5 is a cross-sectional view showing the method for manufacturing the solar cell according to Embodiment 1. FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Translucent insulating substrate, 2 cell, 3 tandem cell, 4 unit, 5 through-hole, 11 1st transparent conductive film, 12 Wide band gap photoelectric conversion layer, 13 2nd transparent conductive film, 14, 25 Opening 15, 26, 29 p layer, 16, 27, 30 i layer, 17, 28, 31 n layer, 18, 32 separator, 21 third transparent conductive film, 22 middle band gap photoelectric conversion layer, 23 narrow band gap Photoelectric conversion layer, 24 reflective conductive layer.

Claims (3)

A plurality of first cells formed on one surface of the translucent insulating substrate and provided with a first photoelectric conversion layer;
A plurality of second cells including a second photoelectric conversion layer formed on the other surface of the translucent insulating substrate and having a different optical band gap from the first photoelectric conversion layer;
The first cell and the second cell facing each other with the translucent insulating substrate interposed therebetween constitute a unit,
The first photoelectric conversion layer and the second photoelectric conversion layer of the unit are electrically connected in parallel to each other through a through-hole provided in the translucent insulating plate,
The first photoelectric conversion layers and the second photoelectric conversion layers of the adjacent units are electrically connected in series.
Solar cell. The second cell is
A third photoelectric conversion layer stacked on the second photoelectric conversion layer on the side opposite to the translucent insulating substrate and electrically connected in series with the second photoelectric conversion layer;
The first photoelectric conversion layer has a wider optical band gap than the second photoelectric conversion layer,
The second photoelectric conversion layer has an optical band gap wider than that of the third photoelectric conversion layer.
The solar cell according to claim 1. The second cell is
A third photoelectric conversion layer stacked on the second photoelectric conversion layer on the side opposite to the translucent insulating substrate and electrically connected in series with the second photoelectric conversion layer;
The photovoltaic power of the first photoelectric conversion layer is substantially equal to the sum of the photovoltaic power of the second photoelectric conversion layer and the photovoltaic power of the third photoelectric conversion layer.
The solar cell according to claim 1.

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