JP2008124381A - Solar battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solar battery capable of obtaining sufficiently high conversion efficiency by light condensing. <P>SOLUTION: The solar battery comprises: a solar battery cell 11 provided with a plurality of photoelectric conversion layers 13 formed in a plane direction on a semiconductor substrate 12 and provided with a light receiving surface side electrode 18 and a back surface electrode 19 formed on the light receiving surface side and back surface side of the photoelectric conversion layers 13; and a lens group L formed at a position corresponding to the plurality of photoelectric conversion layers 13 on the light receiving surface side of the solar battery cell 11. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a solar cell, and more particularly to a concentrating solar cell having a lens group.

Conventionally, various types of solar cells have been devised for improving the efficiency of solar cells.
Among them, it is generally known that conversion efficiency is improved by concentrating solar cells, and a concentrating solar cell system has been devised using this (see Non-Patent Document 1). .
As a concentrating solar cell, a solar cell in which a large number of small-area photoelectric conversion layers are arranged on the back surface of a lens sheet is known (see Patent Document 1).
A condensing microlens array that can be used in a solar cell array has been proposed (see Patent Document 2).
In addition, a thin film solar cell module using light condensed by a lens group has been proposed (see Patent Document 3).
Sharp Technical Report No.93 December 2005 USP 4638110 USP6804062 JP 2003-46103 A

However, in such a conventional concentrating solar cell, conversion efficiency as high as expected could not be obtained even when condensing.
The reason is that the solar cell of Patent Document 1 has a structure in which a photoelectric conversion layer is embedded in an insulator, so that a surface recombination preventing effect (passivation effect) cannot be obtained, and the light receiving surface electrode is photoelectrically converted. Since the structure is in contact with the outer peripheral surface of the layer with a narrow contact area, the series resistance is large due to the contact resistance, and the efficiency can be reduced due to the resistance. Further, in Patent Document 3, the conversion efficiency is increased by increasing the utilization efficiency of incident light. However, the conversion efficiency that can be obtained by condensing the light more than several tens of times cannot be obtained.

  This invention is made | formed in view of the said subject, and provides the solar cell from which high conversion efficiency is acquired by condensing.

According to the present invention, a solar battery cell having a plurality of photoelectric conversion layers formed in a planar direction on a semiconductor substrate and having a light receiving surface electrode and a back electrode formed on the light receiving surface side and the back surface side of the photoelectric conversion layer. And a lens group formed on the light-receiving surface side of the solar battery cell and at a position corresponding to the plurality of photoelectric conversion layers.
Moreover, according to another viewpoint of this invention, it has the photoelectric converting layer formed in multiple numbers by the plane direction on the board | substrate, and the light-receiving surface electrode and back surface electrode which were formed in the light-receiving surface side and back surface side of the said photoelectric converting layer And a lens group formed at a position corresponding to the plurality of photoelectric conversion layers on the light receiving surface side of the solar cells, and the light receiving surface electrode is a light receiving surface of each photoelectric conversion layer There is provided a solar cell (B type) formed so as to be in contact with the peripheral portion of the light receiving portion and to open the central portion of the light receiving surface.

  The A-type solar cell of the present invention can have a structure in which each photoelectric conversion layer as a light receiving portion condensed by a lens group is directly formed on a semiconductor substrate. That is, various structures (for example, a pn junction structure, a pin junction structure, a heterostructure, etc.) depending on the material (element semiconductor, compound semiconductor, etc.) and state (single crystal, polycrystal, microcrystal, amorphous, etc.) of the semiconductor substrate or photoelectric conversion layer. Can be formed with good reproducibility within the normal technical scope of solar cell production without using a special method, and the photoelectric conversion layer advantageous in conversion efficiency can be freely formed. Can be adopted. As a result, excellent conversion efficiency can be obtained by a synergistic effect of good and stable photoelectric conversion characteristics by the photoelectric conversion layer itself and improvement of conversion efficiency by light collection.

  Further, the B type solar cell of the present invention is not limited to a semiconductor substrate, and can form photoelectric conversion layers having various structures on a ceramic substrate, a glass substrate, a resin film substrate, and the like, and in particular, a thin film photoelectric conversion layer. It is suitable for. Also in this solar cell B, photoelectric conversion can be formed with good reproducibility within the normal technical range of solar cell production without using a special method, and a photoelectric conversion layer advantageous in conversion efficiency can be freely adopted. it can. As a result, excellent conversion efficiency can be obtained by a synergistic effect of good and stable photoelectric conversion characteristics by the photoelectric conversion layer itself and improvement of conversion efficiency by light collection. Furthermore, since the light receiving surface electrode is formed so as to be in contact with the periphery of the light receiving surface of each photoelectric conversion layer and to open the central portion of the light receiving surface, the series resistance of the light receiving surface electrode can be reduced, Even if a large current is generated by condensing, a decrease in efficiency due to resistance can be minimized, which is advantageous in improving conversion efficiency.

  The solar cell A and solar cell B of the present invention have a plurality of photoelectric conversion layers formed in a planar direction on a semiconductor substrate, and light receiving surface electrodes and back surfaces formed on the light receiving surface side and the back surface side of the photoelectric conversion layer. A solar battery cell having an electrode and a lens group formed on a light receiving surface side of the solar battery cell and at a position corresponding to the plurality of photoelectric conversion layers are provided.

In the solar cell A, the semiconductor substrate is not particularly limited, and either an elemental semiconductor substrate or a compound semiconductor substrate can be used, and either a single crystal or a polycrystal may be used. In this case, a back electrode can be formed on the back surface opposite to the light receiving surface of the semiconductor substrate.
In the solar cell B, the substrate is not particularly limited, and for example, the semiconductor substrate, the ceramic substrate, the glass substrate, the resin film substrate, or the like can be used. When using a substrate other than a semiconductor substrate, a configuration in which an insulating film and a back electrode are formed on the substrate and a photoelectric conversion layer is formed on the back electrode is preferable from the viewpoint of ease of manufacture.

Hereinafter, matters common to the solar cells A and B will be described.
The photoelectric conversion layer is not particularly limited, and various structures such as a pn junction structure, a pin junction structure, a heterojunction structure, and a multiple junction structure can be employed. In the case of the solar cell A, it is preferable to form the photoelectric conversion layer in a structure suitable for the type of the semiconductor substrate from the viewpoint of ease of manufacture and improvement of conversion efficiency.

In the solar cells A and B, a plurality of photoelectric conversion layers can be easily arranged on a substrate by providing a separation groove between the photoelectric conversion layers. In other words, when forming the photoelectric conversion layer, a planar photoelectric conversion layer is formed on the substrate by a conventionally known film formation technique, and separation grooves are formed in a region excluding a plurality of focused light receiving regions by the lens group. Thus, a photoelectric conversion layer that is a plurality of light receiving portions can be formed collectively. As a result, the plurality of photoelectric conversion layers are formed so as to be dispersed in the form of minute protrusions (a minute columnar shape or a prismatic shape), and separation grooves are formed between the photoelectric conversion layers.
In this case, the width in the planar direction of the photoelectric conversion layer is preferably about 100 to 2000 μm, and the width in the planar direction of the separation groove between two adjacent photoelectric conversion layers is preferably about 10 to 50 mm. Is preferably 10 to 50 mm. In addition, since each lens of a lens group will be micronized when it is smaller than the said range, it is necessary to raise the preparation accuracy of a lens group and a photovoltaic cell further, and when larger than the said range, a lens will enlarge. Does not become compact.

In addition, it is preferable that a recombination prevention layer is formed on the inner surface of the separation groove in order to efficiently use carriers generated by incident light in the photoelectric conversion layer for photoelectric conversion.
When the photoelectric conversion layer is a III-V group compound semiconductor layer and the recombination prevention layer is a III-V group compound semiconductor layer having a wider band gap than the photoelectric conversion layer, a solar cell having a relatively high conversion efficiency can be obtained.
Further, when the photoelectric conversion layer is a crystalline silicon layer and the recombination prevention layer is an insulator layer, a low-cost solar cell can be obtained.
In addition, when the photoelectric conversion layer includes an amorphous silicon germanium layer and the recombination prevention layer is an insulator layer, the use efficiency of long wavelength light is increased, and a solar cell with a high current value is obtained.
In addition, when the photoelectric conversion layer is an amorphous silicon layer or a microcrystalline silicon layer and the recombination prevention layer is an insulator layer, a thin-film silicon solar cell can be manufactured. can get.
In the case where the insulator layer is silicon oxide or silicon nitride, since the passivation effect is large for silicon, carriers generated by incident light can be efficiently used for photoelectric conversion.

  The light receiving surface electrode connects the light receiving surface side of each photoelectric conversion layer in parallel. In this case, in order not to prevent light reception by the photoelectric conversion layer, an opening having a size capable of sufficiently passing the focused light is formed in the light receiving surface electrode, the light receiving surface electrode is in contact with the peripheral portion of the light receiving surface of each photoelectric conversion layer, and It can be formed so as to open the center of the light receiving surface. In this way, the light-receiving surface electrode is in contact with the peripheral portion of the light-receiving surface of the photoelectric conversion layer with a sufficient area, so that the contact resistance is small, and the resistance of the electrode itself is also small, so the series resistance is small, Even if a large current is generated due to the light collection, a decrease in efficiency due to the resistance can be minimized.

  Although it will not specifically limit if a lens group condenses the light which injects into the several photoelectric converting layer on a board | substrate, What consists of a material with good translucency is preferable. In particular, the lens group is preferably made of an ultraviolet curable resin, since it can be easily integrated with the solar battery cell. According to the ultraviolet curable resin, since the 2P method (Photo Polymerization method) can be used using a transfer mask, the alignment of the solar battery cell and the transfer mask can be performed accurately, and the center of the plurality of lenses can be obtained. It can be easily and accurately arranged at the center of the light receiving surface of the plurality of photoelectric conversion layers. In addition, the lens group may be one in which a plurality of lenses are arranged, or may be a lens sheet having a plurality of convex lens portions.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(Embodiment 1)
FIG. 1 is a schematic cross-sectional view showing a solar cell according to Embodiment 1 of the present invention. This solar battery includes a rectangular plate-shaped solar battery cell 11 and a lens group L attached integrally to the light receiving surface of the solar battery cell 11. 2A is a plan view showing the light receiving surface of the solar cell of Embodiment 1, FIG. 2B is a front view, FIG. 2C is a side view, and FIG. 3 is an embodiment in which the lens group is omitted. 4 is a plan view showing a light receiving surface of one solar battery cell, and FIG. 4 is a bottom view showing a back surface of the solar battery of Embodiment 1. FIG.

The solar cell 11 is a compound semiconductor solar cell in which a plurality of photoelectric conversion layers 13 are dispersed in a matrix on a p-type GaAs substrate 12 that is a compound semiconductor substrate.
The photoelectric conversion layer 13 includes a p-type GaAs buffer layer 13a, a p-type InGaP-BSF layer 13b, a p-type GaAs base layer 13c, an n-type GaAs emitter layer 13d, and an n-type InGaP window layer 13e on a p-type GaAs substrate 12. The layers are stacked in this order.
Regarding the thickness of each layer, the p-type GaAs substrate 12 is 100 to 500 μm, the p-type GaAs buffer layer 13 a is 2 to 3 μm, the p-type InGaP-BSF layer 13 b is 0.05 to 0.1 μm, and the p-type GaAs base layer 13 c is The appropriate thickness is 2.5 to 3.5 μm and the n-type GaAs emitter layer 13d is 0.05 to 0.2 μm. The n-type InGaP window layer 13e becomes a direct transition material as the film thickness decreases, and the amount of light absorption decreases. Therefore, the film thickness of the n-type InGaP window layer 13e is preferably 0.01 to 0.05 μm, and more preferably 0.01 to 0.03 μm. The diameter of the photoelectric conversion layer 13 is about 100 to 2000 μm, and the pitch with the adjacent photoelectric conversion layer 13 is about 10 to 50 mm.
Further, an n-type GaAs contact layer 14 (with a film thickness of about 0.2 to 0.5 μm) is formed around the light receiving surface of each photoelectric conversion layer 13, that is, around the surface of the n-type InGaP window layer 13 e. In addition, an antireflection film 15 is formed at the center of the light receiving surface of each photoelectric conversion layer 13 where the contact layer 14 is not formed.

  Further, in this solar cell 11, separation grooves 16 are formed between the photoelectric conversion layers 13, and the plurality of photoelectric conversion layers 13 are separated from each other on one substrate 12 by the separation grooves 16. Has been placed. An i-type InGaP recombination prevention layer 17 (having a thickness of about 0.03 to 0.1 μm) is formed on the inner surface of the separation groove 16, that is, on the bottom surface of the substrate 12, the outer peripheral surfaces of the photoelectric conversion layers 13 and the contact layers 14. In addition, a light receiving surface electrode 18 (film thickness of about 2 to 10 μm) is formed on the recombination preventing layer 17 and the contact layer 14. At this time, the diameter of the opening of the light receiving surface electrode 18 is about 100 to 2000 μm. A back electrode 19 is formed on the back surface of the substrate 12.

  In the solar cell 11 configured as described above, the light receiving surface side of each photoelectric conversion layer 13 is connected to each other by the light receiving surface electrode 18, and the back surface side of each photoelectric conversion layer 13 is connected to the back electrode via the p-type GaAs substrate 12. The plurality of photoelectric conversion layers 13 are electrically connected in parallel to each other.

The lens group L is a group in which a plurality of lenses L1 are integrally assembled so as to be arranged at positions corresponding to the plurality of photoelectric conversion layers 13 of the solar battery cell 11, and as a whole, have substantially the same shape and size as the solar battery cell 11. It is. The lens L1 has a thickness, a refractive index, and the like so that incident light is focused on the photoelectric conversion layer 13 through the opening of the light receiving surface electrode 18. In the case of Embodiment 1, the diameter of the lens L is about 10 to 50 mm. In FIG. 1, the dotted line represents the range of the focused light.
The lens group L may include a plurality of lenses L2 having a square shape in plan view as shown in FIG. 5 in addition to a plurality of lenses L1 having a circular shape in plan view as shown in FIG. . Note that a front view and a side view of a solar cell provided with the lens group in FIG. 5 are the same as those in FIGS. 2B and 2C, and are omitted.

In this solar cell, when light is irradiated from the lens group L side, the incident light is collected by each lens L1 and incident on each photoelectric conversion layer 13, and photoelectrically converts the focused light whose light intensity is increased. Since the plurality of photoelectric conversion layers 13 are connected in parallel, current is taken out from the light receiving surface electrode 18 and the back surface electrode 19.
At this time, since the photoelectric conversion layer 13 has the n-type InGaP window layer 13e on the light receiving surface, diffusion of generated minority carriers and extinction due to surface recombination can be suppressed, and photoelectric conversion can be effectively performed. Done. Moreover, since the outer peripheral surface of the photoelectric conversion layer 13 is covered with the i-type InGaP recombination prevention layer 17, the generated carriers can be efficiently used for photoelectric conversion. Furthermore, since the light-receiving surface electrode 18 is in contact with the peripheral portion of the light-receiving surface of the photoelectric conversion layer 13 via the n-type GaAs contact layer 14, the series resistance is reduced, and a decrease in efficiency due to the series resistance is suppressed. The conversion efficiency of the battery is further increased.
In FIG. 1 and FIGS. 7 and 8 to be described later, for ease of explanation, the photoelectric conversion layer 13 of the solar battery cell 11 is depicted as projecting, but the actual projecting dimension is several microns. It is almost flat when viewed from the whole solar cell.

(Embodiment 2)
FIG. 6 is a schematic cross-sectional view showing a solar cell according to Embodiment 2 of the present invention. The solar battery of the second embodiment includes a solar battery cell 21 and a lens group L arranged on the light receiving surface side of the solar battery cell 21, and the configuration of the solar battery cell 21 is different from that of the first embodiment. The configuration of is the same. Hereinafter, the configuration of the second embodiment different from that of the first embodiment will be mainly described.

This solar battery cell 21 is a crystalline silicon solar battery cell in which a plurality of cylindrical photoelectric conversion layers 23 are formed in a matrix form on a single crystal or polycrystalline p-type Si substrate 22 that is a semiconductor substrate. .
The photoelectric conversion layer 23 includes a p layer 23a formed in a cylindrical shape on the light receiving surface side of the p-type Si substrate 22, and an n + layer 23b formed on the light receiving surface of the p layer 23a. The thickness from the BSF layer 23c to the pn junction is about 200 to 500 μm, and the thickness of the n + layer is about 0.1 to 0.3 μm. The diameter of the photoelectric conversion layer 23 and the pitch with the adjacent photoelectric conversion layer 23 are the same as those in the first embodiment. Also in this case, the p-type Si substrate 22 constitutes a part of the photoelectric conversion layer 23.

Each photoelectric conversion layer 23 is formed into a cylindrical shape by forming a separation groove (depth of about 150 to 450 μm) in a region other than the photoelectric conversion layer formation region of the p-type Si substrate 22. A SiO ₂ recombination preventing layer (passivation film) 27 having a thickness of about 0.05 to 0.3 μm is formed on the surface of the substrate 22 corresponding to the side surface and the outer peripheral surface of the photoelectric conversion layer 23. The recombination preventing layer 27 also covers the periphery of the light receiving surface (n + layer 23b) of the photoelectric conversion layer 23.
In a recess where the periphery of each photoelectric conversion layer 23 is covered with a recombination prevention layer 27, a filling layer 26 in which a filler such as a resin (for example, silicone resin) is embedded is formed. The surface is flattened.

In addition, the light receiving surface electrode 28 is formed so as to cover the surfaces of the filling layer 26 and the recombination preventing layer 27 and to be in contact with the peripheral portion of the light receiving surface of the photoelectric conversion layer 23 and to open the central portion. The film thickness of the light receiving surface electrode 28 and the diameter of the opening are approximately the same as those in the first embodiment.
An antireflection film is formed on the light receiving surface (n + layer 23 b) of the photoelectric conversion layer 23 exposed from the opening of the light receiving surface electrode 28.
A BSF layer 23c is formed on the back surface of the substrate 22, and a back electrode 29 is formed on the BSF layer 23c.

  In the solar cell of Embodiment 2 configured as described above, the light receiving surface side of each photoelectric conversion layer 23 is connected to each other by a light receiving surface electrode 28, and the back surface side of each photoelectric conversion layer 23 is a back electrode 29. Connected to each other, the plurality of photoelectric conversion layers 23 are electrically connected in parallel.

The power generation mechanism of this solar cell is the same as that of the first embodiment.
During power generation, the outer peripheral surface of the photoelectric conversion layer 23 is covered with the SiO ₂ recombination prevention layer 27, so that the generated carriers can be efficiently used for photoelectric conversion. Furthermore, since the light-receiving surface electrode 28 is in direct contact with the periphery of the light-receiving surface of the photoelectric conversion layer 23, the series resistance is reduced, the reduction in efficiency due to the series resistance is suppressed, and the conversion efficiency of the solar cell is further increased. .

(Embodiment 3)
FIG. 7 is a schematic cross-sectional view showing a solar cell according to Embodiment 3 of the present invention. The solar battery of the third embodiment includes a solar battery cell 31 and a lens group L arranged on the light receiving surface side of the solar battery cell 31, and the configuration of the solar battery cell 31 is different from those of the first and second embodiments. The configuration of the group L is the same. Hereinafter, the configuration of the third embodiment different from the first and second embodiments will be mainly described.

This solar battery cell 31 is an amorphous SiGe layer-containing solar battery cell in which a plurality of cylindrical photoelectric conversion layers 33 are formed in a matrix on a Si substrate 32 that is a semiconductor substrate.
The photoelectric conversion layer 33 is formed by forming an n-type SiC layer 33a, an amorphous i-type SiGe layer 33b, and a p-type SiC layer 33c in this order on a Si substrate 32.
The thickness of each layer is about 100 to 500 μm for the Si substrate 32, about 0.02 to 0.1 μm for the n-type SiC layer 33a, about 0.2 to 1 μm for the amorphous i-type SiGe layer 33b, and about the p-type SiC layer 33c. Is about 0.05 to 0.1 μm. The diameter of the photoelectric conversion layer 33 and the pitch with the adjacent photoelectric conversion layer 33 are the same as those in the first embodiment.
A transparent conductive film 34 made of, for example, ITO (film thickness of about 0.05 to 0.1 μm) is formed on the surface of the p-type SiC layer 33 c that is the light receiving surface of the photoelectric conversion layer 33.

Further, in the solar battery cell 31, separation grooves 36 are formed between the photoelectric conversion layers 33, and the plurality of photoelectric conversion layers 33 are separated from each other on one substrate 32 by the separation grooves 36. Has been placed. An SiO ₂ recombination prevention layer 37 having a thickness of about 0.05 to 0.3 μm is formed on the inner surface of the separation groove 36, that is, on the surface of the substrate 32 and the outer peripheral surface of each photoelectric conversion layer 33. The SiO ₂ recombination preventing layer 37 slightly covers the periphery of each transparent conductive film 34.
Further, the surface of the recombination preventing layer 37 is covered with a light receiving surface electrode 38, and the light receiving surface electrode 38 is in contact with the peripheral portion of the transparent conductive film 34 and opens at the center. The film thickness of the light-receiving surface electrode 38 and the diameter of the opening are approximately the same as those in the first embodiment.

In the solar cell 31 configured as described above, the light receiving surface side of each photoelectric conversion layer 33 is connected to each other by the light receiving surface electrode 38, and the back surface side of each photoelectric conversion layer 33 is connected to the back surface electrode 39 through the Si substrate 32. The plurality of photoelectric conversion layers 33 are connected to each other and are electrically connected to each other in parallel.
The power generation mechanism of this solar cell is the same as that of the first embodiment.
During power generation, the outer peripheral surface of the photoelectric conversion layer 33 is covered with the SiO ₂ recombination prevention layer 37, so that the generated carriers can be efficiently used for photoelectric conversion. Furthermore, since the light-receiving surface electrode 38 is in contact with the periphery of the light-receiving surface of the photoelectric conversion layer 33 via the transparent conductive film 34, the series resistance is reduced, and a decrease in efficiency due to the series resistance is suppressed. Conversion efficiency is further increased.

(Embodiment 4)
FIG. 8 is a schematic cross-sectional view showing a solar cell according to Embodiment 4 of the present invention. The solar battery of the fourth embodiment includes a solar battery cell 41 and a lens group L arranged on the light receiving surface side of the solar battery cell 41, and the configuration of the solar battery cell 41 is different from those of the first to third embodiments. The configuration of the group L is the same. Hereinafter, a configuration different from Embodiments 1 to 3 of Embodiment 4 will be mainly described.

This solar battery cell 41 is a solar battery cell in which a plurality of cylindrical photoelectric conversion layers 43 are formed in a matrix form on a ceramic substrate 42 via a SiO ₂ insulating layer 45 and a back electrode 49.
The photoelectric conversion layer 43 is an amorphous silicon layer or microcrystal in which an n-type a-Si layer 43a, an i-type a-Si layer 43b, and a p-type a-Si: C layer 43c are formed in this order on the back electrode 49. It is a silicon layer. The thickness of each layer is about 0.02 to 0.05 μm for the n-type a-Si layer 43a, about 0.2 to 1 μm for the i-type a-Si layer 43b, and 0.05 for the p-type a-Si: C layer 43c. About 0.1 μm. The diameter of the photoelectric conversion layer 43 and the pitch with the adjacent photoelectric conversion layer 43 are approximately the same as those in the first embodiment.
On the surface of the p-type a-Si: C layer 43c that is the light receiving surface of the photoelectric conversion layer 43, a transparent conductive film 44 made of, for example, ITO (film thickness of about 0.05 to 0.1 μm) is formed.

Further, in the solar battery cell 41, separation grooves 46 are formed between the photoelectric conversion layers 43, and the plurality of photoelectric conversion layers 43 are separated from each other on one substrate 42 by the separation grooves 46. Has been placed. A SiO ₂ recombination prevention layer 47 having a thickness of about 0.05 to 0.3 μm is formed on the inner surface of the separation groove 46, that is, on the surface of the back electrode 49 and the outer peripheral surface of each photoelectric conversion layer 43. The SiO ₂ recombination prevention layer 47 slightly covers the periphery of each transparent conductive film 44.
The surface of the recombination preventing layer 47 is covered with a light receiving surface electrode 48, which is in contact with the peripheral portion of the transparent conductive film 44 and has an opening at the center. The film thickness of the light-receiving surface electrode 38 and the diameter of the opening are approximately the same as those in the first embodiment.

In the solar cell 41 configured in this way, the light receiving surface side of each photoelectric conversion layer 43 is connected to each other by the light receiving surface electrode 48, and the back surface side of each photoelectric conversion layer 43 is connected to each other by the back surface electrode 49, The photoelectric conversion layers 43 are electrically connected to each other in parallel.
The power generation mechanism of this solar cell is the same as that of the first embodiment.
During power generation, the outer peripheral surface of the photoelectric conversion layer 43 is covered with the SiO ₂ recombination prevention layer 47, so that the generated carriers can be efficiently used for photoelectric conversion. Furthermore, since the light-receiving surface electrode 48 is in contact with the peripheral portion of the light-receiving surface of the photoelectric conversion layer 43 via the transparent conductive film 44, the series resistance is reduced, and a decrease in efficiency due to the series resistance is suppressed. Conversion efficiency is further increased.

(Other embodiments)
1. In Embodiment 1 (FIG. 1), Embodiment 3 (FIG. 7), and Embodiment 4 (FIG. 8), the filling layer as in Embodiment 2 is provided in the recess around each photoelectric conversion layer on the light-receiving surface electrode. It may be formed to flatten the surface.
2. The solar cell of the present invention is not limited to the structure of the photoelectric conversion layer of Embodiments 1 to 4, and can be applied to various structures having a photoelectric conversion function, and may be a tandem structure, for example.

(Example 1)
The solar cell of Example 1 shown in FIG. 1 was produced as follows.
<Production of GaAs solar cells>
(1) First, a 10 cm square p-type GaAs substrate having a thickness of 0.2 mm and doped with Zn at a concentration of 1 × 10 ¹⁹ atoms / cm ³ was prepared.
(2) A p-type GaAs buffer layer, a p-type InGaP-BSF layer, a p-type GaAs base layer, an n-type GaAs emitter layer, and an n-type InGaP window layer were sequentially laminated on the surface of the p-type GaAs substrate. Each of these layers is continuously formed by a metal organic chemical vapor deposition (MOCVD) method at a growth temperature of about 700 ° C., and the lattice constant of each layer is formed to be substantially equal to the lattice constant of the p-type GaAs substrate. It was. The p-type GaAs buffer layer has a thickness of 0.5 μm, the p-type InGaP-BSF layer has a thickness of 0.1 μm, the p-type GaAs base layer has a thickness of 3 μm, the n-type GaAs emitter layer has a thickness of 0.1 μm, Each of the n-type InGaP window layers was formed with a film thickness of 0.02 μm.

(3) An n-type GaAs contact layer was formed on the surface of the n-type InGaP window layer to a thickness of 0.3 μm by MOCVD.
(4) According to the photolithography technique, first, circular photoresist having a radius of 0.5 mm was formed at a pitch of 20 mm in a plurality of photoelectric conversion layer forming regions on the surface of the n-type GaAs contact layer. Then, the exposed n-type GaAs contact layer was removed by wet etching using a plurality of photoresists as a mask. An NH ₄ OH: H ₂ O: H ₂ O ₂ solution was used for etching.
Thereafter, the photoresist was removed with a photoresist stripping solution.

(5) Next, in accordance with the photolithography technique, a photoresist is formed on the remaining n-type GaAs contact layer in the photoelectric conversion layer formation region, and the n-type InGaP window layer, n-type GaAs emitter layer, p exposed through the photoresist as a mask. The p-type GaAs base layer, p-type InGaP-BSF layer and p-type GaAs buffer layer were removed by etching. NH ₄ OH: H ₂ O: H ₂ O ₂ solution was used for etching the GaAs layer, and HCl: H ₂ O ₂ : H ₂ O solution was used for etching the InGaP layer.
Thereafter, the photoresist was removed with a photoresist stripping solution.
(6) An i-type InGaP layer having a thickness of 0.1 μm was formed on the entire surface of the laminate formed so far at a growth temperature of about 700 ° C. by metal organic vapor phase epitaxy.

(7) According to the photolithographic technique, first, a photoresist film having an opening in the photoelectric conversion layer formation region on the surface of the i-type InGaP window layer is formed, and the i-type InGaP layer exposed by using this is formed as an HCl: H ₂ O layer. ₂ : Removed by etching using H ₂ O solution.
Thereafter, the photoresist was removed with a photoresist stripping solution.
(8) Next, according to the photolithography technique, a photoresist film having an opening at the center of the photoelectric conversion layer forming region on the n-type GaAs contact layer is formed, and the n-type GaAs contact layer exposed by using this is removed by etching. did. An NH ₄ OH: H ₂ O: H ₂ O ₂ solution was used for etching.
Thereafter, the photoresist was removed with a photoresist stripping solution.

(9) The back surface of the p-type GaAs substrate was covered with a resist film, and a back electrode was formed on the back surface of the p-type GaAs substrate with a thickness of 5 μm by Au plating.
Thereafter, the resist film was removed with a photoresist stripping solution.
(10) According to the lift-off technique, a photoresist film is first formed on the surface of the n-type InGaP window layer, and this is used as a mask to form an Au—Ge / Ni / Au layer with a film thickness of 0.1 / 0.02 / 0.07 μm. After vapor deposition and removal of the photoresist with a photoresist stripper, heat treatment was performed at about 350 ° C. for several seconds.
Subsequently, a region where the light receiving surface electrode is not formed on the surface of the Au—Ge / Ni / Au layer is covered with a resist film, and Au plating is performed on the surface of the Au—Ge / Ni / Au layer with a film thickness of 5 μm. The light receiving surface electrode was formed. Thereafter, the resist film was removed with a photoresist stripping solution.
(11) Thereafter, an antireflection layer was formed on the exposed surface of the n-type InGaP window layer. The antireflection layer was formed by depositing ZnS / MgF ₂ with a film thickness of 0.055 / 0.09 μm through a mask opened in the window layer.
A GaAs solar cell was completed by performing a series of these steps.

<Production of lens group>
(12) A transparent glass stamper having a depression corresponding to the lens group is filled with an uncured ultraviolet curable resin, the center position of the opening of the depression corresponding to each lens, and the photoelectric conversion layer (light receiving portion of the GaAs solar cell) ) Were aligned so that the center positions coincided. At this time, since the alignment mark was previously provided in each of the transparent glass stamper (transfer mask) and the solar battery cell, highly accurate alignment was achieved. Then, the GaAs solar cell was brought into close contact with the uncured resin in the transparent glass stamper, irradiated with ultraviolet light through the transparent glass stamper to cure the ultraviolet curable resin, and then the transparent glass stamper was peeled off.
Thereby, the solar cell of Example 1 was completed.

The lens group of the solar cell of Example 1 produced here is one in which the lenses are regularly arranged at a pitch of 20 mm vertically and horizontally (see FIG. 2). The diameter of the lens is 20 mm, and the lens surface has a spherical shape with the center position of the light receiving portion as the center.
According to this solar cell, sunlight having a diameter of 20 mm is condensed on the light receiving portion having a diameter of 1 mm which is the same as the opening of the light receiving surface electrode, so that the light collecting magnification is 400 times.

In the first embodiment, the condensing magnification is set to 400 times, but a high condensing magnification of 1000 times or more is also possible. The higher the concentration factor, the higher the conversion efficiency of the solar cell. Further, when the lens is configured in a quadrangular shape, the light collection magnification is about 500 times (see FIG. 5). It is also possible to use a Fresnel lens.
Similar solar cells can be fabricated for InGaP / InGaAs / Ge cells in the same process, and according to the data of Sharp technique (Non-Patent Document 1), the electrode is around the light-receiving part in this structure, and resistance loss is taken into account. Therefore, it is possible to achieve an efficiency of slightly over 40% at 1000 times condensing and 45% efficiency at 10,000 times condensing.

(Example 2)
A solar cell of Example 2 shown in FIG. 6 was produced as follows.
<Production of Si solar cells>
(1) First, a single crystal p-type Si substrate having a thickness of 0.6 mm, a 10 cm square, and 2 Ω · cm was prepared.
(2) A SiO ₂ film for preventing diffusion was formed with a thickness of 0.3 μm on one surface serving as the light receiving surface of the Si substrate by atmospheric pressure CVD. Thereafter, boron diffusion was performed at 1000 ° C. for 60 minutes in a BBr ₃ gas atmosphere on the other surface serving as the back surface to form a BSF layer having a thickness of 1 μm.
Thereafter, the SiO ₂ film was removed with hydrofluoric acid.
Next, after similarly forming a SiO ₂ film on the back side, phosphorus diffusion is performed at 800 ° C. for 20 minutes in a POCl ₃ gas atmosphere on the light receiving side to form an n + layer having a thickness of 0.2 μm. Thereby forming a pn junction.

(3) An oxide film is formed on the light-receiving surface, and then the oxide films other than the plurality of photoelectric conversion layer formation regions and the substrate peripheral portion are selectively removed by photolithography and etching processes to form the photoelectric conversion layer formation region. A circular mask having a radius of 0.5 mm was formed at a pitch of 20 mm. The circle was 0.5 mmφ and formed at a pitch of 20 mm. Thereafter, using this oxide film as a mask, etching was performed at a depth of 300 μm by RIE, thereby forming a photoelectric conversion layer in the mask portion.
(4) Thermal oxidation was performed at 800 ° C. for 10 minutes, and subsequently, a SiO ₂ film was formed to a thickness of 0.1 μm on the light receiving surface and side surfaces of the photoelectric conversion layer by an atmospheric pressure CVD method. Next, the oxide film on the top of the photoelectric conversion layer was selectively removed by photolithography and etching processes.

(5) Silicone resin was filled in the recesses around the photoelectric conversion layer to flatten the whole.
(6) According to the lift-off technique, first, a photoresist film is formed at the center of the light receiving surface of the photoelectric conversion layer, and using this as a mask, a Ti / Pd / Ag layer is deposited by 0.05 / 0.02 / 5 μm to remove the photoresist. The photoresist and the electrode layer adhering thereto were removed with a liquid to form a light-receiving surface electrode having a thickness of about 5 μm. Thereafter, an Al / Ti / Pd / Ag layer was deposited on the back surface by 0.15 / 0.05 / 0.02 / 5 μm to form a back electrode having a thickness of about 5 μm.
(7) Then, TiO ₂ was deposited as an antireflection film to a thickness of 0.05 μm on the light receiving surface through a mask opened on the light receiving surface where the photoelectric conversion layer was exposed.
By performing these series of steps, a Si solar battery cell was completed.
Next, a lens group was formed on the surface of the Si solar battery cell in the same manner as in Example 1 to complete the solar battery of Example 2.

The lens group of the solar cell of Example 2 produced here is the one in which the lenses are regularly arranged at a pitch of 20 mm vertically and horizontally as in Example 1 (see FIG. 2). The diameter of the lens is 20 mm, and the lens surface has a spherical shape with the center position of the light receiving portion as the center.
According to this solar cell, sunlight having a diameter of 20 mm is condensed on the light receiving portion having a diameter of 1 mm which is the same as the opening of the light receiving surface electrode, so that the light collecting magnification is 400 times.

(Example 3)
A solar cell of Example 3 shown in FIG. 7 was produced as follows.
<Preparation of SiGe thin film solar cell>
(1) First, a single crystal n-type Si substrate having a thickness of 0.6 mm, 10 cm square, and 2 Ω · cm was prepared.
(2) An amorphous silicon carbide n-layer formed by introducing SiH ₄ gas, H ₂ gas, CH ₄ gas and PH ₃ gas in a glow discharge plasma reaction chamber by a method using a mask similar to that in Example 3. 400 liters of was deposited. After the gas supply was stopped, the reaction chamber was evacuated and SiH ₄ gas, H ₂ gas and GeH ₄ gas were introduced to deposit 4000 nm of amorphous silicon germanium i layer. After the gas supply was stopped, the reaction chamber was evacuated and SiH ₄ gas, B ₂ H ₆ gas and CH ₄ gas were introduced to deposit 0.07 μm of amorphous silicon carbon p layer.
Thereafter, the substrate was taken out of the glow discharge plasma reaction chamber, ITO was deposited as a transparent conductive film by sputtering to 0.08 μm, and then the stainless steel mask was removed.

(3) Next, by a photolithography process, a photoresist film is formed on the central portion and a part of the peripheral portion on the transparent conductive film, and an SiO ₂ film is usually formed on the back electrode, on the side surface and the outermost peripheral portion of the photoelectric conversion layer. A thickness of 0.1 μm was formed by pressure CVD. Thereafter, the photoresist film was removed together with the SiO ₂ film thereon using a resist stripping solution.
(4) Next, a photolithography process is performed to form a photoresist film (with a gap between the SiO ₂ film) in the central portion which is a light receiving portion on the transparent conductive film, and an Al film is deposited by sputtering to a thickness of 1 μm. The light receiving surface electrode was formed by the above. Thereafter, the photoresist was removed together with the Al film on the upper portion thereof with a resist stripping solution to expose the light receiving portion.
By performing these series of steps, the SiGe thin film solar cell of Example 3 was completed.
Next, as in Example 1, a lens group was formed on the surface of the SiGe thin film solar cell, and the solar cell of Example 3 was completed.

The lens group of the solar cell of Example 3 produced here is one in which lenses are regularly arranged at a pitch of 20 mm vertically and horizontally as in Example 1 (see FIG. 2). The diameter of the lens is 20 mm, and the lens surface has a spherical shape with the center position of the light receiving portion as the center.
According to this solar cell, sunlight having a diameter of 20 mm is condensed on the light receiving portion having a diameter of 1 mm which is the same as the opening of the light receiving surface electrode, so that the light collecting magnification is 400 times.

Example 4
A solar cell of Example 4 shown in FIG. 8 was produced as follows.
<Preparation of Si thin film solar cell>
(1) An SiO ₂ film of 0.3 μm was deposited on a 1 mm thick, 15 cm square ceramic substrate having a polished surface by an atmospheric pressure CVD method to flatten the surface. Thereafter, 1 μm of silver was deposited on the SiO ₂ film by sputtering to form a back electrode.
(2) The back electrode was covered with a stainless steel mask opening in a circular shape in the photoelectric conversion layer formation region. This mask has an opening radius of 0.5 mm and a plurality of openings formed at a pitch of 20 mm. Next, the substrate on which the mask was set was placed in a glow discharge plasma reaction chamber, and SiH ₄ gas, H ₂ gas and PH ₃ gas were introduced to deposit 400 nm of amorphous silicon n layer. After the gas supply was stopped, the reaction chamber was evacuated, SiH ₄ gas and H ₂ gas were introduced, and an amorphous silicon i layer was deposited by 0.4 μm. After the gas supply was stopped, the reaction chamber was evacuated and SiH ₄ gas, B ₂ H ₆ gas and CH ₄ gas were introduced to deposit 0.07 μm of amorphous silicon carbon p layer. Thereafter, the substrate was taken out from the glow discharge plasma reaction chamber, ITO was deposited by sputtering to 0.08 μm to form a transparent conductive film, and the stainless steel mask was removed.

(3) Next, by a photolithography process, a photoresist film is formed on the central portion and a part of the peripheral portion on the transparent conductive film, and an SiO ₂ film is usually formed on the back electrode, on the side surface and the outermost peripheral portion of the photoelectric conversion layer. A thickness of 0.1 μm was formed by pressure CVD. Thereafter, the photoresist film was removed together with the SiO ₂ film thereon using a resist stripping solution.
(4) Next, a photolithography process is performed to form a photoresist film (with a gap between the SiO ₂ film) in the central portion which is a light receiving portion on the transparent conductive film, and an Al film is deposited by sputtering to a thickness of 1 μm. The light receiving surface electrode was formed by the above. Thereafter, the photoresist was removed together with the Al film on the upper portion thereof with a resist stripping solution to expose the light receiving portion.
By performing these series of steps, the Si thin-film solar battery of Example 4 was completed.
Next, as in Example 1, a lens group was formed on the surface of the Si thin-film solar cell, and the solar cell of Example 4 was completed.

The lens group of the solar cell of Example 4 produced here is the one in which the lenses are regularly arranged at a pitch of 20 mm vertically and horizontally as in Example 1 (see FIG. 2). The diameter of the lens is 20 mm, and the lens surface has a spherical shape with the center position of the light receiving portion as the center.
According to this solar cell, sunlight having a diameter of 20 mm is condensed on the light receiving portion having a diameter of 1 mm which is the same as the opening of the light receiving surface electrode, so that the light collecting magnification is 400 times.

It is a schematic sectional drawing which shows the solar cell of Embodiment 1 of this invention. (A) is a top view which shows the light-receiving surface of the solar cell of Embodiment 1, (b) is a front view, (c) is a side view. It is a top view which shows the light-receiving surface of the photovoltaic cell of Embodiment 1 which abbreviate | omitted the lens group. 4 is a bottom view showing the back surface of the solar cell of Embodiment 1. FIG. It is a top view which shows another lens group in this invention. It is a schematic sectional drawing which shows the solar cell of Embodiment 2 of this invention. It is a schematic sectional drawing which shows the solar cell of Embodiment 3 of this invention. It is a schematic sectional drawing which shows the solar cell of Embodiment 4 of this invention.

Explanation of symbols

11 Solar cell (compound semiconductor solar cell)
12 Semiconductor substrate (p-type GaAs substrate)
13, 23, 33, 43 Photoelectric conversion layer 13a p-type GaAs buffer layer 13b p-type InGaP-BSF layer 13c p-type GaAs base layer 13d n-type GaAs emitter layer 13e n-type InGaP window layer 14 n-type GaAs contact layer 15, 25 Antireflection film 16 Separation groove 17 Recombination prevention layer (i-type InGaP layer)
18, 28, 38, 48 Light-receiving surface electrode 19, 29, 39, 49 Back electrode 21 Solar cell (crystalline silicon solar cell)
22 Semiconductor substrate (p-type Si substrate)
23a p layer 23b n + layer 23c BSF layer 26 Filling layer (silicone resin)
27, 37, 47 Recombination prevention layer (SiO ₂ layer)
31 Solar cell (Amorphous SiGe layer-containing solar cell)
32 Semiconductor substrate (Si substrate)
33a n-type SiC layer 33b i-type SiGe layer 33c p-type SiC layer 34, 44 Transparent conductive film (ITO film)
41 Solar cell 42 Substrate (ceramic substrate)
43a n-type a-Si layer 43b i-type a-Si layer 43c p-type a-Si: C layer 45 SiO ₂ layer

Claims (11)

  A solar cell having a plurality of photoelectric conversion layers formed in a planar direction on a semiconductor substrate and having a light receiving surface electrode and a back electrode formed on a light receiving surface side and a back surface side of the photoelectric conversion layer, and the solar cell And a lens group formed at a position corresponding to the plurality of photoelectric conversion layers. A photovoltaic cell having a plurality of photoelectric conversion layers formed in a planar direction on a substrate, and having a light receiving surface electrode and a back electrode formed on a light receiving surface side and a back surface side of the photoelectric conversion layer; and A lens group formed on a light receiving surface side and at a position corresponding to the plurality of photoelectric conversion layers,
The solar cell, wherein the light receiving surface electrode is formed so as to contact a peripheral portion of the light receiving surface of each photoelectric conversion layer and to open a central portion of the light receiving surface.   The solar cell according to claim 1 or 2, wherein the plurality of photoelectric conversion layers are formed to be dispersed in the form of minute protrusions, and separation grooves are formed between the photoelectric conversion layers.   4. The solar cell according to claim 3, wherein a width of the photoelectric conversion layer in a planar direction is 100 to 2000 μm, and a width of the separation groove in a planar direction between two adjacent photoelectric conversion layers is 10 to 50 mm.   The solar cell according to claim 3 or 4, wherein a recombination prevention layer is formed on an inner surface of the separation groove.   The plurality of photoelectric conversion layers are formed to be dispersed in the form of minute protrusions, separation grooves are formed between the photoelectric conversion layers, a recombination prevention layer is formed on the inner surface of the separation grooves, and the photoelectric conversion layer is III- 2. The solar cell according to claim 1, wherein the solar cell is a group V compound semiconductor layer, and the recombination preventing layer is a group III-V compound semiconductor layer having a wider band gap than the semiconductor layer.   The plurality of photoelectric conversion layers are formed by being dispersed in the form of minute protrusions, separation grooves are formed between the photoelectric conversion layers, a recombination prevention layer is formed on the inner surface of the separation grooves, and the photoelectric conversion layer is made of crystalline silicon. The solar cell according to claim 1, wherein the recombination preventing layer is an insulating layer.   The plurality of photoelectric conversion layers are formed to be dispersed in the form of minute protrusions, separation grooves are formed between the photoelectric conversion layers, a recombination prevention layer is formed on the inner surface of the separation grooves, and the photoelectric conversion layers are amorphous. The solar cell according to claim 1, further comprising a porous silicon germane layer, wherein the recombination prevention layer is an insulator layer.   The plurality of photoelectric conversion layers are formed to be dispersed in the form of minute protrusions, separation grooves are formed between the photoelectric conversion layers, a recombination prevention layer is formed on the inner surface of the separation grooves, and the photoelectric conversion layer is non-coated. The solar cell according to claim 1, wherein the solar cell is a crystalline silicon layer or a microcrystalline silicon layer, and the recombination prevention layer is an insulator layer.   The solar cell according to claim 7, wherein the insulator layer is silicon oxide or silicon nitride.   The solar cell according to claim 1, wherein the lens group is made of an ultraviolet curable resin.

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