JP2019083220A - Solar battery - Google Patents

Abstract

To provide a solar battery with a high photoelectric conversion efficiency by increasing an internal quantum efficiency.SOLUTION: A solar battery comprises a structure part having a superlattice structure in which a crystalline Si layer 101 as a substantially intrinsic semiconductor layer and a SiOlayer 102, alternately laminated on an insulation substrate 100 having an insulating front surface. A first side surface of the superlattice structure is a p-type superlattice structure 110p in which a p-type crystalline Si layer and the SiOlayer are alternately laminated. A second side surface opposite to the first side surface is an n-type superlattice structure 110n in which an n-type crystalline Si and the SiOlayer are alternately laminated. The p-type crystalline Si layer and the crystalline Si layer as the intrinsic semiconductor layer are pi-bonded, and the n-type crystalline Si layer and the crystalline Si layer as the intrinsic semiconductor layer are ni-bonded. Thus, loss of carriers distributed is remarkably suppressed, and a solar battery with a photoelectric conversion efficiency can be obtained by increasing an internal quantum efficiency.SELECTED DRAWING: Figure 2

Description

  The present invention relates to solar cell technology, and more particularly, to the technology of silicon solar cells with high photoelectric conversion efficiency utilizing quantum size effect.

  As social concern for environmental protection has increased in recent years, the importance of technological development of clean energy alternative to fossil fuels is becoming increasingly important. Under such a social background, solar cells have been widely used as power devices utilizing natural energy, but in order to be used as a major energy supply source, solar cells are further reduced in cost and Improvement of photoelectric conversion efficiency is required.

  Until now, various structures have been proposed as the structure of a solar cell. For example, Patent Document 1 (Japanese Patent Laid-Open No. 2014-27119) includes a light absorption layer, a semiconductor layer made of, for example, silicon, and this semiconductor A superlattice structure is disclosed in which barrier layers made of a material having a band gap larger than that of the layer (for example, silicon oxide) are alternately stacked.

JP, 2014-27119, A

FIG. 1 is a view for conceptually explaining the flow of photogenerated carriers (electrons and holes) in a solar cell provided with the above-described superlattice structure. In the example shown in this figure, a superlattice structure 210 in which a plurality of crystalline Si layers 201 and SiO ₂ layers 202 are alternately stacked is provided on the main surface of an n-type Si substrate 200. The p-type Si layer 203, the transparent conductive film layer 204, and the surface electrode 205 are sequentially formed on the top surface. When light enters this solar cell, electrons 206 and holes 207 are generated in the Si layer 201 constituting the superlattice structure 210, and the electrons 206 are directed to the n-type Si substrate 200 side, and the holes 207 are p-type Si. A current flows by diffusing in the vertical direction while crossing the SiO ₂ layer 202 to the layer 203 side.

However, such current, since carriers is caused by traversing the tunnel effect a high energy barrier with the SiO ₂ layer 202 (transmitting), a high thickness thereof by optimizing the thickness of the SiO ₂ layer 202 It is not only necessary to control with accuracy, but it is not desirable from the viewpoint of increasing the internal quantum efficiency and obtaining a solar cell with high photoelectric conversion efficiency, resulting in loss of carriers during diffusion. In addition, with annealing at a relatively high temperature performed to crystallize the Si layer 201, a dopant (in this case, P which is a donor in this case) is inevitably diffused from the n-type Si substrate, There is also a concern that contact formation can not be performed as designed.

  The present invention has been made in view of such problems, and the object of the present invention is to convert photogenerated carriers efficiently into a current to enhance internal quantum efficiency, thereby achieving high photoelectric conversion efficiency. It is an object of the present invention to provide a solar cell, and to provide a solar cell which can be easily subjected to contact formation as designed even if dopant diffusion which inevitably occurs with annealing at high temperature occurs.

In order to solve the above-mentioned subject, the solar cell concerning the present invention has a structure part which has a superlattice structure where a crystalline Si layer and a plurality of SiO ₂ layers are alternately laminated in a plurality on a substrate whose surface is insulating. The crystalline Si layer is substantially an intrinsic semiconductor layer, and the first side surface of the superlattice structure is a p-type superlattice in which a plurality of p-type crystalline Si layers and SiO ₂ layers are alternately stacked. The second side opposite to the first side has a n-type superlattice structure in which a plurality of n-type crystalline Si layers and SiO ₂ layers are alternately stacked. The crystalline Si layer and the intrinsic crystalline Si layer form a pi junction, and the n-type crystalline Si layer and the intrinsic crystalline Si layer form an ni junction.

  In one aspect, a plurality of the superlattice structures are formed apart from each other on the substrate.

  In one aspect, adjacent superlattice structures of the plurality of superlattice structures are arranged such that the p-type superlattice structures face each other and the n-type superlattice structures face each other.

  In one aspect, adjacent superlattice structures of the plurality of superlattice structures are arranged such that the p-type superlattice structure and the n-type superlattice structure face each other.

  Furthermore, in one aspect, a p-type electrode or an n-type electrode is formed in a region where the superlattice structures are separated from each other.

  In a preferred embodiment, the superlattice structure has a mesa shape having a slope on the side surface on which the p-type superlattice structure and the n-type superlattice structure are formed.

  For example, the acceptor in the p-type crystalline Si layer and the donor in the n-type crystalline Si layer are ion-implanted impurities.

  Preferably, the thickness of the crystalline Si layer is 5 nm or less.

  In addition, preferably, the substrate is a translucent substrate.

In one aspect, the thickness of the SiO ₂ layer constituting the superlattice structure is thicker toward the light receiving side.

  In one aspect, the distance between the first side surface and the second side surface of the superlattice structure is 10 μm or less.

  Furthermore, in one aspect, an opening is provided in a central region of the superlattice structure.

  In one aspect, the superlattice structure includes an electrode pattern formed by connecting in series a p-type electrode and an n-type electrode formed in an area separated from each other.

  In another aspect, the superlattice structure is provided with an electrode pattern connecting in parallel a p-type electrode and an n-type electrode formed in the mutually spaced area.

  A solar cell according to the present invention is a tandem solar cell in which a top cell provided on the light incident side and a bottom cell provided below the top cell are stacked, and the top cell includes the above-described structure. The bottom cell may be made of crystalline Si, a light receiving surface electrode may be provided on the surface of the top cell, and a back surface electrode may be provided on the back surface of the bottom cell.

In the solar cell according to the present invention, since it is not necessary to cross the high energy barrier of the SiO ₂ layer when the photogenerated carriers diffuse in the superlattice structure consisting of the crystalline Si layer / SiO ₂ layer, SiO ₂ While the restriction on the thickness of the layer is relaxed, the loss of carriers during diffusion is significantly suppressed, and the internal quantum efficiency can be enhanced to obtain a solar cell with high photoelectric conversion efficiency.

  Also, in order to form junctions (pi junctions and ni junctions) in the lateral direction, even if the dopant is inevitably diffused from the substrate along with annealing at a relatively high temperature for crystallizing the Si layer, contact formation is It is generally possible to do as designed.

In the solar cell provided with the conventional super lattice structure, it is a figure for demonstrating notionally the flow of the photogenerated carrier (electron and hole). It is a sectional view for explaining an outline of basic structure of a solar cell concerning the present invention. It is a figure for demonstrating notionally the structure of the solar cell of the aspect by which the superlattice structure employ | adopted by this invention mutually separates mutually, and is formed in multiple numbers on the board | substrate with an insulating surface. The figure for demonstrating notionally the structure of the solar cell of the aspect by which several adjacent superlattice structures are arrange | positioned with n-type superlattice structures facing each other while p-type superlattice structures face each other. is there. It is a figure for demonstrating the aspect which has a mesa shape in which the superlattice structure has a slope in the side in which a p-type superlattice structure and an n-type superlattice structure are formed. It is a figure for demonstrating the structural example in which the opening part is provided in the center area | region of a superlattice structure. It is a figure for demonstrating the structural example provided with the electrode pattern which carries out the parallel connection of the p-type electrode and the n-type electrode which were formed in the area | region where a super lattice structure mutually separates. It is a perspective view of a solar cell provided with an electrode pattern shown in Drawing 7A. It is a figure for demonstrating the structural example provided with the electrode pattern which connects in series the p-type electrode and the n-type electrode which were formed in the area | region where a super lattice structure mutually separates. It is a perspective view of a solar cell provided with an electrode pattern shown in Drawing 8A. It is a figure for demonstrating the example which applied the structure which concerns on this invention to a tandem-type solar cell.

  The structure of the solar cell according to the present invention will be described below with reference to the drawings. In the following description, the crystalline Si layer may be a single crystal Si layer or a polycrystalline Si layer.

[Outline of basic structure]
FIG. 2 is a cross-sectional view for explaining an outline of a basic structure of a solar cell according to the present invention. In the example shown in this figure, a plurality of crystalline Si layers 101 and SiO ₂ layers 102 are alternately stacked on the main surface of a substrate 100 having an insulating surface to form a superlattice structure. Note that the crystalline Si layer 101 is substantially an intrinsic semiconductor. The first side surface (left side surface in this figure) of the superlattice structure is a p-type superlattice structure 110p in which a plurality of p-type crystalline Si layers and SiO ₂ layers are alternately stacked. Further, a second side surface (right side surface in this figure) opposite to the first side surface is an n-type superlattice structure 110n in which a plurality of n-type crystalline Si layers and SiO ₂ layers are alternately stacked. The p-type crystalline Si layer constituting the p-type superlattice structure 110p and the intrinsic crystalline Si layer constituting the superlattice structure form a pi junction, and an n-type crystalline Si layer constituting the n-type superlattice structure 110n And the intrinsic crystalline Si layer constituting the superlattice structure is a Ni junction. A p-type electrode 105p and an n-type electrode 105n are formed in each of the p-type superlattice structure 110p and the n-type superlattice structure 110n, and the one shown by reference numeral 104 in the figure is a protective film.

That is, the solar cell according to the present invention comprises a structural portion having a superlattice structure in which a plurality of crystalline Si layers and SiO ₂ layers are alternately stacked on a substrate having an insulating surface, and the crystalline Si layer Is substantially an intrinsic semiconductor layer, and the first side surface of the superlattice structure has a p-type superlattice structure in which a plurality of p-type crystalline Si layers and SiO ₂ layers are alternately stacked. The second side opposite to the first side has an n-type superlattice structure in which a plurality of n-type crystalline Si layers and SiO ₂ layers are alternately stacked, and the p-type crystalline Si layer The intrinsic crystalline Si layer has a pi junction, and the n-type crystalline Si layer and the intrinsic crystalline Si layer have an ni junction.

When light enters this solar cell, electrons 106 and holes 107 are generated in the intrinsic crystalline Si layer 101 constituting the superlattice structure, and the electrons 106 are on the n-type electrode 105 n side, and the holes 107 are p-type. By diffusing toward the electrode 105p, current flows. That is, in the solar cell of this configuration, it is not necessary to cross the high energy barrier of the SiO ₂ layer when the photogenerated carriers diffuse in the superlattice structure of the crystalline Si layer / SiO ₂ layer. In addition, in the plane of each of the intrinsic crystalline Si layers 101 forming the superlattice structure, carriers are maintained in a state of being spread over the entire plane without being localized regardless of the application of the electric field. Therefore, the restriction on the thickness of the SiO ₂ layer is alleviated, and the loss of carriers during diffusion is significantly suppressed, and it is possible to enhance the internal quantum efficiency and obtain a solar cell with high photoelectric conversion efficiency.

  Moreover, the pi junction of the p-type crystalline Si layer constituting the p-type superlattice structure 110 p and the intrinsic crystalline Si layer constituting the superlattice structure, and the n-type crystalline Si constituting the n-type superlattice structure 110 n Both the layer and the ni junction of the intrinsic crystalline Si layer constituting the superlattice structure are formed on the side surface of the superlattice structure. In the conventional structure, it was necessary to use a substrate containing a dopant impurity to form a pi junction or an ni junction between the superlattice and the substrate, but in the present invention, it is not necessary to use such a substrate. As a result, the problem of irreversible diffusion of the dopant from the unintended substrate accompanying the annealing at a relatively high temperature (for example, 1000 to 1100 ° C.) for crystallizing the Si layer formed by sputtering or the like is avoided. can do. For this reason, in the case of the present invention, contact formation can be carried out generally as designed.

The substrate 100 may have an insulating surface, and may be an insulating substrate such as a quartz substrate, for example, an n-type or p-type Si substrate provided with an insulating film such as SiO ₂ . In addition, in the case of the solar cell of the structure which makes a board | substrate side a light-incidence surface, a board | substrate needs to be a translucent board | substrate. In the case of a solar cell having a light incident surface on the substrate side, a texture layer made of a material such as ZnO is provided on the surface of the superlattice structure to increase the reflectance on the back surface (surface opposite to the substrate). You may do so.

As described above, in the solar cell according to the present invention, the p-type crystalline Si layer constituting the p-type superlattice structure 110p and the intrinsic crystalline Si layer constituting the superlattice structure form a pi junction, and an n-type superlattice structure The n-type crystalline Si layer constituting 110 n and the intrinsic crystalline Si layer constituting the superlattice structure are in an n-junction. That is, this solar cell has a structure of p-type superlattice / i-type superlattice / n-type superlattice, and pi junction and ni junction are constituted only by superlattices in which a plurality of Si layers / SiO ₂ layers are stacked. ing. This is to provide a wide band gap (that is, the band gap of the superlattice structure) of about 1.7 eV in the pi junction region and the ni junction region, and to prevent the decrease in open circuit voltage due to the formation of the junction. .

Assuming that p-type and n-type polysilicon electrodes having no superlattice structure are formed on opposing sides of a superlattice structure in which a plurality of crystalline Si layers and SiO ₂ layers are alternately stacked. The band gap of these junction regions is that of the polysilicon electrode (about 1.1 eV), and the open circuit voltage of the solar cell is limited by this value, which may lead to a drop in the open circuit voltage at the junction regions.

  Such pi junctions and ni junctions are formed, for example, by ion implantation of p-type impurity (acceptor) or n-type impurity (donor) on the side surface after forming the superlattice structure.

In order to secure the effect of widening the band gap and increasing the open circuit voltage by the quantum size effect, it is preferable to design the thickness of the crystalline Si layer constituting the superlattice structure to 5 nm or less. In addition, the refractive index of the superlattice structure can be changed by controlling the thickness of the SiO ₂ layer constituting the superlattice structure. It is also possible to design the thickness of the SiO ₂ layer constituting the superlattice structure to be thicker toward the light receiving side (light incident surface side) by using this principle, and to enhance the photoelectric conversion efficiency.

[Outline of a structure having a plurality of superlattice structures]
Although only one superlattice structure described above is illustrated in FIG. 2, it goes without saying that a plurality of such superlattice structures may be provided adjacent to each other when configured as a solar cell. is there.

  FIG. 3 is a view for conceptually explaining the structure of the solar cell in a mode in which a plurality of the superlattice structures 110 described above are formed separately from each other on the substrate 100 having an insulating surface.

  In the embodiment shown in this figure, the superlattice structures adjacent to each other are arranged such that the p-type superlattice structure 110p and the n-type superlattice structure 110n face each other, and the superlattice structures are separated from each other. A p-type electrode or an n-type electrode is formed, but as shown in FIG. 4, the adjacent superlattice structures 110 are n-type superlattices while the p-type superlattice structures 110p face each other. The structures 110 n may be arranged to face each other.

  In addition, as shown in FIG. 5, the superlattice structure 110 may have a mesa shape having a slope on the side on which the p-type superlattice structure 110 p and the n-type superlattice structure 110 n are formed. Good. In the case of such a mesa-shaped superlattice structure 110, distribution control of implanted ions becomes easy when forming the p-type superlattice structure 110p and the n-type superlattice structure 110n by ion implantation. There is an advantage.

  Furthermore, as shown in FIG. 6, an opening 108 may be provided in the central region of the superlattice structure. When such an opening 108 is provided, if a relatively large number of defects are contained in the crystalline Si layer 101 constituting the superlattice structure, the defects are not removed by hydrogen treatment. It has the advantage of being easy to activate. The distance between the first side surface (p-type super lattice structure 110 p-forming surface) and the second side surface (n-type super lattice structure 110 n-forming surface) of the superlattice structure is preferably 10 μm or less. The diameter of 108 is, for example, about 2 μm.

[Design example of electrode pattern]
In a solar cell having a plurality of adjacent superlattice structures, a special method of interconnecting the p-type electrode and the n-type electrode provided in each structure having the superlattice structure is provided. There is no limit.

  For example, as shown in an example shown in FIG. 7A, the super lattice structure may be configured to include an electrode pattern 109 connecting in parallel a p-type electrode and an n-type electrode formed in the mutually separated region. A perspective view of the solar cell 10 in this case is shown in FIG. 8A. In addition, the code | symbol 103 in a figure is a wall formation part.

  For example, as in the example illustrated in FIG. 8A, an electrode pattern 109 may be provided in which a p-type electrode and an n-type electrode formed in a region where the superlattice structures are separated from each other are connected in series. A perspective view of the solar cell 10 in this case is shown in FIG. 8B.

[Application to tandem solar cells]
The solar cell having the above-described structure can also be a tandem solar cell.

  FIG. 9 is a view for explaining an example in which the structure according to the present invention is applied to a tandem solar cell, in which reference numeral 10 is a top cell and reference numeral 20 is crystalline Si. It is a bottom cell. In the example shown in this figure, the structure shown in FIG. 5 is used as the top cell. It is needless to say that the substrate in this case needs to be translucent.

  That is, this solar cell is a tandem solar cell in which a top cell provided on the light incident side and a bottom cell provided below the top cell are stacked, and the top cell includes the above-described structure, The bottom cell is made of crystalline Si, a light receiving surface electrode is provided on the surface of the top cell 10, and a back surface electrode is provided on the back surface of the bottom cell 20.

Thus, in the solar cell according to the present invention, it is not necessary to cross the high energy barrier of the SiO ₂ layer when the photogenerated carriers diffuse through the crystalline Si layer / SiO ₂ layer superlattice structure. Therefore, the restriction on the thickness of the SiO ₂ layer is relaxed, and the loss of carriers during diffusion is significantly suppressed, and it is possible to increase the internal quantum efficiency and obtain a solar cell with high photoelectric conversion efficiency.

Reference Signs List 100 substrate 101 crystalline Si layer 102 SiO ₂ layer 103 wall portion 104 protective film 105 p p-type electrode 105 n n-type electrode 106 electron 107 hole 108 opening 109 electrode pattern 110 p p-type superlattice structure 110n n-type superlattice structure

Claims (15)

A structure portion having a superlattice structure in which a plurality of crystalline Si layers and SiO ₂ layers are alternately stacked in a plurality on a substrate having an insulating surface;
The crystalline Si layer is substantially an intrinsic semiconductor layer,
The first side surface of the superlattice structure has a p-type superlattice structure in which a plurality of p-type crystalline Si layers and SiO ₂ layers are alternately stacked, and a second side facing the first side surface is formed. The side surface has an n-type superlattice structure in which a plurality of n-type crystalline Si layers and SiO ₂ layers are alternately stacked,
The p-type crystalline Si layer and the intrinsic crystalline Si layer form a pi junction, and the n-type crystalline Si layer and the intrinsic crystalline Si layer form an ni junction.
A solar cell characterized by   The solar cell according to claim 1, wherein a plurality of the superlattice structures are formed apart from each other on the substrate.   The adjacent superlattice structures of the plurality of superlattice structures are arranged such that the p-type superlattice structures face each other and the n-type superlattice structures face each other. Solar cell.   The solar cell according to claim 2, wherein adjacent superlattice structures of the plurality of superlattice structures are arranged such that the p-type superlattice structure and the n-type superlattice structure face each other.   The solar cell according to claim 2, wherein a p-type electrode or an n-type electrode is formed in a region where the superlattice structures are separated from each other.   The superlattice structure according to any one of claims 1 to 5, wherein the superlattice structure has a mesa shape having a slope on a side surface on which the p-type superlattice structure and the n-type superlattice structure are formed. Solar cells.   The solar cell according to any one of claims 1 to 6, wherein the acceptor in the p-type crystalline Si layer and the donor in the n-type crystalline Si layer are ion-implanted impurities.   The solar cell according to any one of claims 1 to 7, wherein the thickness of the crystalline Si layer is 5 nm or less.   The solar cell according to any one of claims 1 to 8, wherein the substrate is a translucent substrate. The solar cell according to any one of claims 1 to 9, wherein the thickness of the SiO ₂ layer constituting the superlattice structure is thicker toward the light receiving side.   The solar cell according to any one of claims 1 to 10, wherein a distance between the first side surface and the second side surface of the super lattice structure is 10 μm or less.   The solar cell according to any one of claims 1 to 11, wherein an opening is provided in a central region of the super lattice structure.   The solar cell according to any one of claims 5 to 12, further comprising an electrode pattern in which p-type electrodes and n-type electrodes formed in mutually spaced areas of the superlattice structure are connected in series.   The solar cell according to any one of claims 5 to 12, further comprising an electrode pattern connecting in parallel a p-type electrode and an n-type electrode formed in mutually spaced regions of the superlattice structure. It is a tandem solar cell in which a top cell provided on the light incident side and a bottom cell provided below the top cell are stacked,
The top cell comprises the structure according to any one of claims 1-14,
The bottom cell is made of crystalline Si,
A light receiving surface electrode is provided on the surface of the top cell, and a back surface electrode is provided on the back surface of the bottom cell.
A solar cell characterized by

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