JP2014183271A - Solar cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solar cell capable of securing long-term reliability even without using a special expensive sealant.SOLUTION: The solar cell has sheet resistance of a light-receiving surface diffusion layer of 40 Ω/sq or more and 80 Ω/sq or less, and volume resistivity of a sealant at 85°C of 1×10Ω cm or less.

Description

  The present invention relates to a solar cell.

Conventionally, development of clean energy has been demanded due to problems such as depletion of energy resources and global environmental problems such as an increase in CO _{2 in} the atmosphere. Solar power generation using solar cells has been developed as a new energy source. It has been put to practical use and is on the path of development.

  In particular, in recent years, a solar cell module in which a plurality of solar cells are connected in series and / or in parallel has been widely used in general homes, and a large-scale power generation facility called a mega solar using a large number of solar cell modules. Is also under construction.

  Since the above solar cell module is used outdoors for a long period of time, long-term reliability is required in all outdoor environments such as high temperature and humidity. Conventionally, since the solar cells constituting the solar cell module are mainly manufactured using crystalline silicon, it is considered that a relatively long life can be expected. The long-term reliability of the solar cell module is Improvements have been made with a focus on members other than solar cells constituting the battery module.

  However, recently, a phenomenon called PID (Potential Induced Degradation) has been observed in which the output of the solar cell module significantly decreases despite its relatively short period of use. Establishment is strongly desired.

  For example, Non-Patent Document 1 describes the cause of PID as follows. In the solar cell module, in order to prevent the failure of the solar cell module due to a lightning strike or an electric shock accident, the frame side is grounded in parallel. However, in this case, as the number of solar cells in series increases, a large potential difference is generated between the outer frame of the solar cell module and the inner solar cell. When moisture adheres to the surface of the glass substrate that protects the light receiving surface of the solar cell module, a leak current is generated between the frame and the solar cell via the moisture, and the leak current causes Electric charges accumulate on the light receiving surface of the solar battery cell. Then, carriers generated in the solar battery cell due to the incidence of sunlight are attracted to the charge accumulated on the light receiving surface of the solar battery cell and recombined with the charge, and thus are not taken out of the solar battery. Thereby, it is supposed that the output of a solar cell module will fall.

Therefore, for example, in Patent Document 1, as shown in the schematic configuration diagram of FIG. 18, a solar cell array 100 in which a plurality of solar cells 101 are connected by an interconnector 254 is referred to as a light-receiving surface side transparent protective member 251. A solar cell module having a structure in which a volume resistivity at 45 ° C. to 85 ° C. is sealed with a high-resistance sealing material 252 between the back surface protection sheet 253 on the back surface side and a resistance of 1 × 10 ¹⁶ Ω · cm or more is proposed. Has been. In Patent Document 1, it is said that a decrease in output can be suppressed by preventing a leak current from the light receiving surface side of the solar cell array 100 with a high-resistance sealing material 252.

International Publication No. 2012/145228

PV PV Media December 2012 issue, Vison Press Co., Ltd. 12-25

However, the high-resistance sealing material 252 having a volume resistivity of 1 × 10 ¹⁶ Ω · cm or more at 45 ° C. to 85 ° C. used in the solar cell module described in Patent Document 1 is very special. And since it was expensive, the manufacturing cost of the solar cell module could not be kept low.

  Moreover, since the high-resistance sealing material 252 of Patent Document 1 is extremely difficult to handle, the manufacturing efficiency of the solar cell module could not be increased.

  In view of the above circumstances, an object of the present invention is to provide a solar cell that can ensure long-term reliability without using a special and expensive sealing material.

The present invention comprises a back electrode type solar cell and a sealing material provided on the light receiving surface of the back electrode type solar cell, the back electrode type solar cell comprising a first conductivity type semiconductor substrate, A first conductive type light receiving surface diffusion layer provided on the light receiving surface side surface of the semiconductor substrate, and a first conductive type impurity diffusion layer and a second conductive type provided on the surface opposite to the light receiving surface side of the semiconductor substrate. The sheet resistance of the light-receiving surface diffusion layer is 40Ω / □ or more and 80Ω / □ or less, and the volume resistivity at 85 ° C. of the sealing material is 1 × 10 ¹⁶ Ω · cm or less. It is a solar cell. With such a configuration, long-term reliability of the solar cell can be ensured without using a special and expensive sealing material.

  ADVANTAGE OF THE INVENTION According to this invention, even if it does not use a special and expensive sealing material, the solar cell which can ensure long-term reliability can be provided.

3 is a schematic plan view of the back surface of an example of a back electrode type solar battery cell used in the solar battery of Embodiment 1. FIG. (A) is typical sectional drawing along II-II of FIG. 1, (b) is a typical expanded sectional view of a part of light-receiving surface of the n-type silicon substrate shown to (a). (A)-(i) is typical sectional drawing illustrated about an example of the manufacturing method of the back surface electrode type photovoltaic cell used for the solar cell of Embodiment 1. FIG. 4 is a schematic plan view of the surface of an example of a wiring sheet used in the solar cell of Embodiment 1. FIG. It is a typical top view illustrating the state which installed the some back electrode type photovoltaic cell on the wiring sheet shown in FIG. In Embodiment 1, it is typical sectional drawing illustrating the process of sealing the back surface electrode type photovoltaic cell installed on the wiring sheet. FIG. 3 is a schematic cross-sectional view of the solar cell in the first embodiment. 6 is a schematic cross-sectional view of a modification of the solar cell in the first embodiment. FIG. FIG. 6 is a schematic cross-sectional view of another modification of the solar cell in the first embodiment. (A) is typical sectional drawing of an example of the back electrode type photovoltaic cell used for the solar cell of Embodiment 2, (b) is a part of light-receiving surface of the n-type silicon substrate shown to (a). It is a typical expanded sectional view of. (A)-(k) is typical sectional drawing illustrated about an example of the manufacturing method of the back electrode type photovoltaic cell used for the solar cell of Embodiment 2. FIG. In Embodiment 2, it is typical sectional drawing illustrating the process of sealing the back surface electrode type photovoltaic cell installed on the wiring sheet. 6 is a schematic cross-sectional view of a solar cell according to Embodiment 2. FIG. FIG. 6 is a schematic cross-sectional view of a modification of the solar cell in the second embodiment. 6 is a schematic cross-sectional view of another modification of the solar cell of Embodiment 2. FIG. It is a typical block diagram illustrating a pseudo negative electrode ground test apparatus. It is a figure which shows the relationship between the sheet resistance of the light-receiving surface diffusion layer of the back electrode type photovoltaic cell of Examples 1-8 and Comparative Examples 1-6, and the volume resistivity at 85 degreeC of a sealing material. It is a typical block diagram illustrating the process of sealing the solar cell array of the conventional solar cell module of patent document 1 with a sealing material.

  Embodiments of the present invention will be described below. In the drawings of the present invention, the same reference numerals represent the same or corresponding parts.

[Embodiment 1]
<Back electrode type solar cell>
In FIG. 1, the typical top view of the back surface of an example of the back electrode type solar cell used for the solar cell of Embodiment 1 is shown. The back electrode type solar cell 1 has a first conductivity type on the back surface which is the surface opposite to the light receiving surface side of the back electrode type solar cell 1 of the n-type silicon substrate 4 as the first conductivity type semiconductor substrate. A strip-shaped n-electrode 2 as a working electrode and a strip-shaped p-electrode 3 as a second conductivity type electrode. The n-electrode 2 and the p-electrode 3 are alternately arranged on the back surface of the n-type silicon substrate 4. It is arranged.

  2A shows a schematic cross-sectional view along II-II in FIG. 1, and FIG. 2B schematically shows a part of the light receiving surface of the n-type silicon substrate 4 shown in FIG. 2A. An enlarged sectional view is shown. As shown in FIG. 2A, an uneven shape 5 is formed on the light receiving surface of the n-type silicon substrate 4.

  On the light receiving surface of the n-type silicon substrate 4, an n + layer 6 is formed as a light receiving surface diffusion layer which is an FSF layer. The n + layer 6 is a layer having the same n type conductivity type as the n type silicon substrate 4, and the n type impurity concentration of the n + layer 6 is higher than the n type impurity concentration of the n type silicon substrate 4. ing.

  As shown in FIG. 2B, a light-receiving surface passivation film 8 is formed on the n + layer 6. The light-receiving surface passivation film 8 is made of a silicon oxide film. The thickness of the light-receiving surface passivation film 8 is preferably 30 nm or more and 200 nm or less. When the thickness of the light-receiving surface passivation film 8 is 30 nm or more and 200 nm or less, the characteristics of the back electrode type solar cell 1 tend to be improved.

  As shown in FIG. 2B, an antireflection film 12 is formed on the light receiving surface passivation film 8. Antireflection film 12 includes an n-type impurity having the same n-type conductivity as n-type silicon substrate 4, and is made of, for example, a titanium oxide film containing phosphorus as an n-type impurity. Moreover, the thickness of the antireflection film 12 can be, for example, 30 nm or more and 500 nm or less.

  Moreover, it is preferable that phosphorus in the antireflection film 12 is contained as a phosphorus oxide in an amount of 15 mass% or more and 35 mass% or less of the antireflection film 7. In addition, 15 mass% or more and 35 mass% or less of the anti-reflective film 12 is contained as a phosphorus oxide that the content of the phosphorus oxide in the anti-reflective film 12 is 15 mass% or more and 35 mass% of the whole anti-reflective film 12. It means the following.

  As shown in FIG. 2A, on the back surface of the n-type silicon substrate 4, an n ++ layer 10 which is an n-type impurity diffusion layer as a first conductivity-type impurity diffusion layer, and a second conductivity-type impurity diffusion layer are formed. P + layers 11 which are p-type impurity diffusion layers are alternately formed. Further, a back surface passivation film 15 in which a second back surface passivation film 14 and a first back surface passivation film 13 are laminated in this order from the n type silicon substrate 4 side is formed on the back surface of the n type silicon substrate 4. An n electrode 2 and a p electrode 3 are formed on the n ++ layer 10 and the p + layer 11 exposed from the back surface passivation film 15, respectively.

  Hereinafter, an example of a method for manufacturing the back electrode type solar cell 1 used in the solar cell of Embodiment 1 will be described with reference to the schematic cross-sectional views of FIGS. 3 (a) to 3 (i).

  First, as shown in FIG. 3A, after the texture mask 21 is formed on the back surface of the n-type silicon substrate 4, the uneven shape 5 is formed on the light-receiving surface of the n-type silicon substrate 4 as shown in FIG. Form.

  Next, as shown in FIG. 3C, after removing the texture mask 21 on the back surface of the n-type silicon substrate 4, a diffusion mask 22 is formed on the light receiving surface of the n-type silicon substrate 4, and a part of the back surface is formed. A diffusion mask 23 is formed, and then an n ++ layer 10 is formed on a part of the back surface of the n-type silicon substrate 4.

  Next, as shown in FIG. 3D, after removing the diffusion mask 22 on the light-receiving surface of the n-type silicon substrate 4 and the diffusion mask 23 on the back surface, the diffusion mask 24 is applied to the light-receiving surface of the n-type silicon substrate 4. At the same time, a diffusion mask 25 is formed on a part of the back surface, and then a p + layer 11 is formed on a part of the back surface of the n-type silicon substrate 4.

  Next, as shown in FIG. 3E, the solution 27 is applied to the light receiving surface of the n-type silicon substrate 4 and then dried. Here, application and drying of the solution 27 can be performed, for example, as follows.

  First, a diffusion mask 24 and a diffusion mask 25 formed on the light receiving surface and the back surface of the n-type silicon substrate 4, respectively, and a glass layer formed by diffusing p-type impurities such as boron into the diffusion masks 24 and 25, for example, It is removed by etching using hydrofluoric acid or the like. Next, a first back surface passivation film 13 that also serves as a diffusion mask such as a silicon oxide film having a thickness of 50 nm to 100 nm is formed on the back surface of the n-type silicon substrate 4. The first back surface passivation film 13 can be formed by, for example, CVD or SOG (spin-on-glass) coating and baking. Thereafter, a solution 27 containing a phosphorus-containing compound, titanium alkoxide, and alcohol is applied to the light-receiving surface of the n-type silicon substrate 4 by spin coating or the like and then dried. Here, as the compound containing phosphorus contained in the solution 27, for example, phosphorus pentoxide can be used. In addition, as the titanium alkoxide, for example, tetraisopropyl titanate can be used. Furthermore, as alcohol, isopropyl alcohol etc. can be used, for example.

  Next, as shown in FIGS. 3 (f) and 3 (i), an n + layer 6, a light-receiving surface passivation film 8 and an antireflection film 12 are formed on the light-receiving surface of the n-type silicon substrate 4, and n A second back surface passivation film 14 is formed between the back surface of the mold silicon substrate 4 and the first back surface passivation film 13.

  Here, the n + layer 6 and the antireflection film 12 can be formed by heat-treating the n-type silicon substrate 4 on which the solution 27 is applied to the light receiving surface, for example, at a temperature of 850 ° C. or more and 1000 ° C. or less. That is, by this heating, phosphorus diffuses from the solution 27 on the light receiving surface of the n-type silicon substrate 4 to form the n + layer 6 and the antireflection film 12 made of a titanium oxide film containing phosphorus.

  The light-receiving surface passivation film 8 and the second back surface passivation film 14 can be formed by performing thermal oxidation with oxygen or water vapor on the n-type silicon substrate 4 after the formation of the n + layer 6 and the antireflection film 12. it can. As a result, as shown in FIG. 3I, a light-receiving surface passivation film 8 is formed between the n + layer 6 on the light-receiving surface of the n-type silicon substrate 4 and the antireflection film 12, and an n-type silicon substrate is formed. 4, a second back surface passivation film 14 is formed between the back surface 4 and the first back surface passivation film 13. A laminated body of the first back surface passivation film 13 and the second back surface passivation film 14 is referred to as a back surface passivation film 15. The reason why the light-receiving surface passivation film 8 is formed between the n + layer 6 and the antireflection film 12 is that the film thickness of the antireflection film 12 in the concave portion of the concavo-convex shape 5 on the light receiving surface is increased and the antireflection film 12 is formed. It is considered that a silicon oxide film, which is the light-receiving surface passivation film 8, grows due to oxygen or water vapor entering from the portion where the crack is generated. In addition, since the antireflection film 12 is thin at the convex portion of the concave-convex shape 5 on the light receiving surface, it is considered that oxygen or water vapor is transmitted and a silicon oxide film that is the light receiving surface passivation film 8 grows. Furthermore, the reason why the second back surface passivation film 14 is formed between the back surface of the n-type silicon substrate 4 and the first back surface passivation film 13 is that the first back surface passivation film on the back surface of the n-type silicon substrate 4 is used. Since 13 is a film formed by a CVD method or the like, it is considered that oxygen or water vapor passes through the inside of the first back surface passivation film 13, thereby growing a silicon oxide film as the second back surface passivation film 14. . Note that the thickness of the light-receiving surface passivation film 8 is not less than 100 nm and not more than 200 nm, for example, and the thickness of the second back surface passivation film 14 is not less than 30 nm and not more than 100 nm on the n ++ layer 10, for example. On the layer 11, the thickness is 10 nm or more and 40 nm or less.

  Here, the thermal oxidation of the n-type silicon substrate 4 with oxygen or water vapor for forming the light-receiving surface passivation film 8 and the second back surface passivation film 14 is performed by placing the n-type silicon substrate 4 in an oxygen atmosphere or a water vapor atmosphere. It can carry out by heat-processing in a state.

  The sheet resistance of the n + layer 6 is 40Ω / □ or more and 80Ω / □ or less. Note that the sheet resistance of the n + layer 6 can be appropriately adjusted by changing at least one of the phosphorus content in the solution 27, the temperature during the thermal oxidation, and the time, for example.

  The light-receiving surface passivation film 8 and the second back surface passivation film 14 are n-type silicon substrates by switching the atmospheric gas to an oxygen atmosphere or a water vapor atmosphere following the heat treatment for forming the n + layer 6 and the antireflection film 12. 4 can also be formed by performing thermal oxidation.

  Next, as shown in FIG. 3G, a part of the back surface passivation film 15 is removed to expose a part of the n ++ layer 10 and a part of the p + layer 11 from the back surface passivation film 9. .

  Next, as shown in FIG. 3H, the n electrode 2 is formed on the n ++ layer 10 and the p electrode 3 is formed on the p + layer 11. By the above, the back electrode type solar cell 1 can be manufactured.

<Wiring sheet>
In FIG. 4, the typical top view of the surface of an example of the wiring sheet used for the solar cell of Embodiment 1 is shown. As shown in FIG. 4, the wiring sheet 30 includes an insulating substrate 31 and wirings 36 installed on the surface of the insulating substrate 31. The wiring 36 includes an n wiring 32, an n wiring 32 a, a p wiring 33, a p wiring 33 a, and a connection wiring 34.

  Here, the n wiring 32, the n wiring 32a, the p wiring 33, the p wiring 33a, and the connection wiring 34 are conductive. The n wiring 32 and the p wiring 33 have a comb shape including a shape in which a plurality of rectangles are arranged in a direction orthogonal to the longitudinal direction of the rectangle. Further, the n wiring 32a, the p wiring 33a, and the connection wiring 34 are strip-shaped. Further, the adjacent n wiring 32 and the p wiring 33 other than the n wiring 32 a and the p wiring 33 a located at the end of the wiring sheet 30 are electrically connected by the connection wiring 34.

  In the wiring sheet 30, the portions corresponding to the comb teeth (rectangular) of the comb-shaped n wiring 32 and the portions corresponding to the comb teeth (rectangular) of the comb-shaped p wiring 33 are alternately meshed one by one. Thus, the n wiring 32 and the p wiring 33 are arranged. As a result, a portion corresponding to the comb teeth of the comb-shaped n wiring 32 and a portion corresponding to the comb teeth of the comb-shaped p wiring 33 are alternately arranged at predetermined intervals. . Note that at least one of the portions corresponding to the comb teeth of the n wiring 32 and the p wiring 33 may be alternately arranged instead of one.

  The insulating base material 31 can be used without particular limitation as long as it is an electrically insulating material. For example, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyphenylene sulfide (PET) A material containing at least one resin selected from the group consisting of PPS (Polyphenylene sulfide), polyvinyl fluoride (PVF) and polyimide (Polyimide) can be used.

  The thickness of the insulating base material 31 is not specifically limited, For example, it can be 25 micrometers or more and 150 micrometers or less.

  The insulating substrate 31 may have a single-layer structure consisting of only one layer or a multi-layer structure consisting of two or more layers.

  The material of the wiring 36 can be used without particular limitation as long as it is a conductive material. For example, at least one selected from the group consisting of copper (Cu), aluminum (Al), and silver (Ag) is used. A metal containing, for example, can be used.

  The thickness of the wiring 36 is not particularly limited, and can be, for example, 10 μm or more and 50 μm or less.

  Needless to say, the shape of the wiring 36 is not limited to the shape described above, and can be set as appropriate.

  At least a part of the surface of the wiring 36 has, for example, nickel (Ni), gold (Au), platinum (Pt), palladium (Pd), silver (Ag), tin (Sn), SnPb solder, and ITO (Indium). A conductive material including at least one selected from the group consisting of Tin Oxide may be provided. In this case, there is a tendency that the electrical connection between the wiring 36 of the wiring sheet 30 and the electrode of the back electrode type solar battery cell to be described later can be improved, and the weather resistance of the wiring 36 can be improved.

  At least a part of the surface of the wiring 36 may be subjected to a surface treatment such as a rust prevention treatment or a blackening treatment.

  The wiring 36 may also have a single-layer structure composed of only one layer, or may have a multilayer structure composed of two or more layers.

  Below, an example of the manufacturing method of the wiring sheet 30 of the structure shown by FIG. 4 is demonstrated. First, an insulating substrate 31 such as a PET film is prepared, and a conductive material such as a metal foil or a metal plate is bonded to the entire surface of one surface of the insulating substrate 31. For example, a roll of an insulating base material cut to a predetermined width is pulled out, an adhesive is applied to one surface of the insulating base material 31, and a roll of metal foil cut slightly smaller than the width of the insulating base material 31 is applied. Can be bonded together by applying pressure and heating.

  Next, by patterning the conductive material by removing a part of the conductive material bonded to the surface of the insulating base material 31 by photoetching or the like, the surface of the insulating base material 31 is patterned. A wiring 36 including an n wiring 32, an n wiring 32a, a p wiring 33, a p wiring 33a, and a connection wiring 34 made of a conductive material is formed. As described above, the wiring sheet 30 having the configuration shown in FIG. 4 can be manufactured.

<Installation of back electrode type solar cells>
FIG. 5 is a schematic plan view illustrating a state where the back electrode type solar cell 1 is installed on the wiring sheet 30 shown in FIG. Here, the back electrode type solar cell 1 is installed on the wiring sheet 30 such that the back side of the back electrode type solar cell 1 faces the installation side of the wiring 36 of the wiring sheet 30.

  The back electrode type solar cell 1 is arranged on the wiring sheet 30 so that the n electrode 2 and the p electrode 3 of the back electrode type solar cell 1 are in contact with the n wiring 32 and the p wiring 33 of the wiring sheet 30, respectively. Installed. The n electrode 2 and the p electrode 3 may be mechanically and electrically connected to the n wiring 32 and the p wiring 33 by a conductive adhesive such as solder, for example. Moreover, the n electrode 2 and the p electrode 3 are respectively connected to the n wiring 32 and the p electrode 3 by the shrinkage force when the insulating resin composition placed between the back electrode type solar cell 1 and the wiring sheet 30 is cured. The wiring 33 may be directly connected to be electrically connected and mechanically connected.

  In addition, since the adjacent n wiring 32 and p wiring 33 of the wiring sheet 30 are electrically connected by the connection wiring 34, the back electrode type solar cells installed so as to be adjacent to each other on the wiring sheet 30. The ones are electrically connected to each other. Thereby, all the back surface electrode type photovoltaic cells 1 installed on the wiring sheet 30 are electrically connected in series.

  The current generated when light enters the light receiving surface of the back electrode type solar cell 1 is extracted from the n electrode 2 and the p electrode 3 of the back electrode type solar cell 1 to the n wiring 32 and the p wiring 33. Then, currents extracted to the n wiring 32 and the p wiring 33 of the wiring sheet 30 are extracted from the n wiring 32a and the p wiring 33a positioned at the terminal of the wiring sheet 30 to the outside of the solar cell.

<Sealing of back electrode type solar cells>
FIG. 6 is a schematic cross-sectional view illustrating the process of sealing the back electrode type solar battery cell 1 installed on the wiring sheet 30. Here, on the light-receiving surface of the back electrode type solar cell 1, from the back electrode type solar cell 1 side, the sheet-like first resin layer 40, the sheet-like second resin layer 41, and the transparent protective substrate. 42 are arranged in this order. On the insulating base 31 of the wiring sheet 30, the sheet-like first resin layer 40 and the back surface protection sheet 43 are arranged in this order from the wiring sheet 30 side.

  As the transparent protective substrate 42, any substrate that is transparent to sunlight can be used without particular limitation, and for example, a glass substrate or the like can be used.

  The first resin layer 40 was selected from the group consisting of ethylene vinyl acetate resin, epoxy resin, acrylic resin, urethane resin, olefin resin, polyester resin, silicone resin, polystyrene resin, polycarbonate resin, and rubber resin, for example. A layer made of at least one transparent resin can be used.

  As the second resin layer 41, a layer made of an olefin resin is preferably used. As the olefin resin used for the second resin layer 41, for example, at least one selected from the group consisting of a polyethylene resin, a polypropylene resin, and a polybutene resin can be used.

  The polyethylene resin is a homopolymer of ethylene or a copolymer of ethylene and one or more other monomers. The polypropylene resin is a homopolymer of propylene or a copolymer of propylene and one or more other monomers. Further, the polybutene resin is a butene homopolymer or a copolymer of butene and one or more other monomers.

  As the polyethylene resin, for example, polyethylene or an ethylene-α-olefin copolymer can be used. Examples of the polyethylene that can be used include low density polyethylene, linear low density polyethylene, and linear ultra-low density polyethylene.

  As the ethylene-α-olefin copolymer, it is preferable to use a copolymer consisting of ethylene and at least one selected from α-olefins having 3 to 20 carbon atoms. It is more preferable to use a copolymer composed of at least one selected from α-olefins. Examples of the α-olefin include propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 4-methyl-1-pentene, 3-methyl-1-pentene, 1-decene and 1-dodecene. , 1-tetradecene, 1-hexadecene, 1-octadecene, and 1-eicosane can be used.

  As the polypropylene resin, for example, a propylene-α-olefin copolymer or a terpolymer of propylene, ethylene, and α-olefin can be used.

  The propylene-α-olefin copolymer is a copolymer composed of at least one selected from propylene and α-olefin. As the propylene-α-olefin copolymer, it is preferable to use a copolymer composed of at least one selected from ethylene and an α-olefin having 3 to 20 carbon atoms and propylene, and ethylene and 4 to 4 carbon atoms. It is more preferable to use a copolymer composed of at least one selected from 8 α-olefins and propylene. Examples of the α-olefin having 3 to 20 carbon atoms include propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 4-methyl-1-pentene, 3-methyl-1-pentene, 1 At least one selected from the group consisting of -decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene and 1-eicosane can be used.

  As the polybutene resin, for example, a crystalline copolymer comprising at least one selected from ethylene, propylene, and an olefin compound having 5 to 8 carbon atoms and butene can be used.

  The first resin layer 40 and the second resin layer 41 may contain additives such as conventionally known crosslinking agents in addition to the above resin components. Further, the first resin layer 40 and the second resin layer 41 are formed into a sheet shape by, for example, mixing a conventionally known additive such as a crosslinking agent into the above resin component and molding the mixture into a predetermined shape. can do.

  As the back surface protection sheet 43, any material can be used without particular limitation as long as it can protect the back surface of the first resin layer 40. For example, a weathering film such as PET that has been conventionally used may be used. it can.

  Further, from the viewpoint of sufficiently suppressing the permeation of water vapor and oxygen into the first resin layer 40 to ensure long-term reliability, the back surface protection sheet 43 includes a metal film such as aluminum, for example. Also good.

  Moreover, it is also possible to completely adhere the back surface protection sheet 43 such as the end face of the solar cell module to a part where it is difficult to adhere using a moisture permeation prevention tape such as a butyl rubber tape.

  Next, pressure is applied between the transparent protective substrate 42 and the back surface protective sheet 43 to press the first resin layer 40 against the light receiving surface of the back electrode type solar cell 1 and the first resin layer 40 and the first back surface sheet 43. By heating the second resin layer 41, the first resin layer 40 and the second resin layer 41 are integrated and cured. Accordingly, as shown in the schematic cross-sectional view of FIG. 7, the back electrode type connected by the wiring sheet 30 in the sealing material 50 in which the first resin layer 40 and the second resin layer 41 are integrated. The solar battery cell 1 is sealed. Thereafter, the frame 61 made of, for example, an aluminum alloy is attached to the entire circumference of the outer periphery of the sealing material 50 that seals the back electrode type solar battery cell 1 to manufacture the solar battery of the first embodiment. In addition, in the solar cell of Embodiment 1, the back electrode type solar cell 1 sealed in the sealing material 50 is not limited to plural, and may be single.

<Effect>
In the solar cell of the first embodiment, the sheet resistance of the n + layer 6 as the light-receiving surface diffusion layer of the back electrode type solar cell 1 is set to 40Ω / □ or more and 80Ω / □ or less, and the back electrode type solar cell 1 The volume resistivity at 85 ° C. of the sealing material (second resin layer 41) provided on the light receiving surface is set to 1 × 10 ¹⁶ Ω · cm or less. As a result of intensive studies by the inventor, the sheet resistance of the n + layer 6 as the light-receiving surface diffusion layer is set to 40Ω / □ or more and 80Ω / □ or less, so that the light-receiving surface of the back electrode type solar cell 1 is obtained. Even when a sealing material having a volume resistivity at 85 ° C. of 1 × 10 ¹⁶ Ω · cm or less is used as the sealing material (second resin layer 41) provided in the back electrode type solar cell 1 itself, This is because it has been found that the output can be made high and the decrease in the output of the solar battery including the back electrode type solar battery cell 1 can be stably and sufficiently suppressed.

  That is, when the sheet resistance of the n + layer 6 as the light-receiving surface diffusion layer of the back electrode type solar cell 1 is less than 40 Ω / □, recombination in the n + layer 6 increases, so that the back electrode type The output of the solar battery cell 1 itself decreases. Further, when the sheet resistance of the n + layer 6 is higher than 80Ω / □, a large potential difference is generated between the back electrode type solar cell 1 and the frame 61, and moisture or the like is present on the surface of the transparent protective substrate 42. If accumulated, charge accumulates in the light-receiving surface passivation film 8 of the back electrode type solar cell 1, and the function of the n + layer 6 as an FSF (Front Surface Field) is deteriorated.

Thereby, in the solar cell of Embodiment 1, like the conventional solar cell module described in Patent Document 1, the volume resistivity at 45 ° C. to 85 ° C. is as high as 1 × 10 ¹⁶ Ω · cm or more. Since it is possible to suppress a decrease in output due to PID or the like without using a special sealing material, the choice of sealing material provided on the light-receiving surface of the back electrode type solar cell 1 is more than conventional. It can be expanded and long-term reliability can be ensured.

Further, in the solar cell of the first embodiment, as in the conventional solar cell module described in Patent Document 1, a special high resistance such that the volume resistivity at 45 ° C. to 85 ° C. is 1 × 10 ¹⁶ Ω · cm or more. In addition, since it is not necessary to use an expensive sealing material, the manufacturing cost of the solar cell module can be kept low.

Furthermore, in the solar cell of Embodiment 1, the volume resistivity at 45 ° C. to 85 ° C. is as high as 1 × 10 ¹⁶ Ω · cm or more as in the conventional solar cell module described in Patent Document 1, Since it is not necessary to use a sealing material that is very difficult to handle, the manufacturing efficiency of the solar cell module can be improved.

In addition, the volume resistivity at 85 ° C. of the sealing material (second resin layer 41) provided on the light receiving surface of the back electrode type solar cell 1 is 1 × 10 ¹² Ω · cm or more and 1 × 10 ¹⁶ Ω · cm or ^{less, 1 × 10 15 Ω · 1} × more preferably not more than 10 ¹⁶ Omega · cm or more ^{cm, 2.8 × 10 15 Ω ·} cm or more 5.1 × 10 ¹⁵ Ω · cm More preferably, it is as follows. In these cases, the long-term reliability of the solar cell of Embodiment 1 can be further improved without using a special and expensive sealing material.

<Modification>
FIG. 8 shows a schematic cross-sectional view of a modification of the solar cell of the first embodiment. In the modification of the solar cell of Embodiment 1 shown in FIG. 8, the sealing material 50 that seals the back electrode type solar cell 1 is the second resin on the light receiving surface of the back electrode type solar cell 1. It consists of the laminated body of the layer 41 and the 1st resin layer 40 on the wiring sheet 30, It is characterized by the above-mentioned.

Also in the modification of the solar cell of Embodiment 1 shown in FIG. 8, the sheet resistance of n + layer 6 as the light-receiving surface diffusion layer of back electrode type solar cell 1 is set to 40Ω / □ or more and 80Ω / □ or less. Therefore, a sealing material having a volume resistivity of 1 × 10 ¹⁶ Ω · cm or less at 85 ° C. is used as the sealing material (second resin layer 41) provided on the light receiving surface of the back electrode type solar battery cell 1. be able to. Thereby, the modification of the solar cell of Embodiment 1 shown in FIG. 8 can also be set as the solar cell which can ensure long-term reliability, without using a special and expensive sealing material.

<Other variations>
FIG. 9 shows a schematic cross-sectional view of another modification of the solar cell of the first embodiment. In another modification of the solar cell of Embodiment 1 shown in FIG. 9, the sealing material for sealing the back electrode type solar cell 1 is composed of a sealing material 52 made of a single layer of olefin resin. It is characterized by that.

Also in another modification of the solar cell of the first embodiment shown in FIG. 9, the sheet resistance of the n + layer 6 as the light-receiving surface diffusion layer of the back electrode type solar cell 1 is 40Ω / □ or more and 80Ω / □ or less. Therefore, as the sealing material provided on the light receiving surface of the back electrode type solar cell 1, the sealing material 52 made of a single layer of olefin resin having a volume resistivity at 85 ° C. of 1 × 10 ¹⁶ Ω · cm or less. Can be used. Thereby, the other modification of the solar cell of Embodiment 1 shown in FIG. 9 can also be made into a solar cell which can ensure long-term reliability, without using a special and expensive sealing material.

<Others>
In the above description, the first conductivity type is n-type and the second conductivity type is p-type. However, the present invention is not limited to this, and the first conductivity type is p-type. The second conductivity type may be n-type. When the first conductivity type is p-type and the second conductivity type is n-type, the n-type silicon substrate is a p-type silicon substrate, and the light-receiving surface diffusion layer is a p + layer in which p-type impurities are diffused. Thus, the antireflection film is made of a titanium oxide film containing p-type impurities.

  Moreover, the concept of the back electrode type solar cell which is one embodiment of the present invention includes a back electrode type solar cell having a configuration in which both an n electrode and a p electrode are formed only on one surface (back surface) of a semiconductor substrate. In addition to the cell, a solar cell having a configuration such as an MWT (Metal Wrap Through) type (a solar cell in which a part of an electrode is disposed in a through hole provided in a semiconductor substrate) is also included.

[Embodiment 2]
<Back electrode type solar cell>
FIG. 10 (a) shows a schematic cross-sectional view of an example of a back electrode type solar battery cell used in the solar battery of Embodiment 2, and FIG. 10 (b) shows an n-type silicon substrate shown in FIG. 10 (a). 4 is a schematic enlarged cross-sectional view of a part of the light receiving surface 4. As shown in FIG. 10A, an uneven shape 5 is formed on the light receiving surface of the n-type silicon substrate 4.

  On the light receiving surface of the n-type silicon substrate 4, an n + layer 6 is formed as a light receiving surface diffusion layer which is an FSF layer. The n + layer 6 is a layer having the same n type conductivity type as the n type silicon substrate 4, and the n type impurity concentration of the n + layer 6 is higher than the n type impurity concentration of the n type silicon substrate 4. ing.

  As shown in FIG. 10B, a light-receiving surface passivation film 8 is formed on the n + layer 6. The light-receiving surface passivation film 8 is made of a silicon oxide film. The thickness of the light-receiving surface passivation film 8 is preferably 30 nm or more and 200 nm or less. When the thickness of the light-receiving surface passivation film 8 is 30 nm or more and 200 nm or less, the characteristics of the back electrode type solar battery cell 16 tend to be improved.

  As shown in FIG. 10B, an antireflection film 7 is formed on the light receiving surface passivation film 8. The antireflection film 7 includes an n-type impurity having the same n-type conductivity as that of the n-type silicon substrate 4 and is made of, for example, a titanium oxide film containing phosphorus as an n-type impurity. Moreover, the thickness of the antireflection film 7 can be set to, for example, 0 nm or more and 500 nm or less. In addition, the location where the thickness of the antireflection film 7 is 0 nm means that the portion of the antireflection film 7 is not formed.

  Moreover, it is preferable that phosphorus in the antireflection film 7 is contained as a phosphorus oxide in an amount of 15 mass% or more and 35 mass% or less of the antireflection film 7. In addition, 15 mass% or more and 35 mass% or less of the anti-reflective film 7 are contained as phosphorous oxide, when the content of the phosphorus oxide in the anti-reflective film 7 is 15 mass% or more and 35 mass% of the whole anti-reflective film 7. It means the following.

  As shown in FIG. 10A, on the back surface of the n-type silicon substrate 4, an n ++ layer 10 which is an n-type impurity diffusion layer as a first conductivity-type impurity diffusion layer, and a second conductivity-type impurity diffusion layer are formed. P + layers 11 which are p-type impurity diffusion layers are alternately formed. Further, a back surface passivation film 9 made of a silicon oxide film is formed on a part of the back surface of the n-type silicon substrate 4. An n electrode 2 and a p electrode 3 are formed on the n ++ layer 10 and the p + layer 11 exposed from the back surface passivation film 9, respectively.

  Hereinafter, with reference to the schematic cross-sectional views of FIGS. 11A to 11K, an example of a method for manufacturing the back electrode type solar battery cell 16 used in the solar battery of Embodiment 2 will be described.

  First, as shown in FIG. 11A, a texture mask 21 is formed on the back surface of the n-type silicon substrate 4. Here, as the texture mask 21, for example, a silicon nitride film or the like can be used. The texture mask 21 can be formed by, for example, a CVD (Chemical Vapor Deposition) method or a sputtering method.

  Next, as shown in FIG. 11B, the uneven shape 5 is formed on the light receiving surface of the n-type silicon substrate 4. The uneven shape 5 can have a texture structure, for example. The uneven shape 5 is formed by etching the light-receiving surface of the n-type silicon substrate 4 with a solution in which isopropyl alcohol is added to an alkaline aqueous solution such as a sodium hydroxide aqueous solution or a potassium hydroxide aqueous solution and heated to 70 ° C. or higher and 80 ° C. or lower. Can be formed.

  Next, as shown in FIG. 11C, an n ++ layer 10 is formed on a part of the back surface of the n-type silicon substrate 4. Here, the n ++ layer 10 can be formed as follows, for example.

First, the texture mask 21 on the back surface of the n-type silicon substrate 4 is removed. Next, a diffusion mask 22 such as a silicon oxide film is formed on the light receiving surface of the n-type silicon substrate 4. Next, a diffusion mask 23 is formed by applying a masking paste to a region other than the region where the n ++ layer 10 is formed on the back surface of the n-type silicon substrate 4 and then heat-treating the masking paste. Thereafter, the n ++ layer 10 is formed by diffusing phosphorus from the diffusion mask 23 to the portion where the back surface of the n-type silicon substrate 4 is exposed by vapor phase diffusion using POCl ₃ .

  In addition, as a masking paste, the thing containing a solvent, a thickener, and a silicon oxide precursor etc. can be used, for example. Further, as a method for applying the masking paste, for example, an ink jet printing method or a screen printing method can be used.

  Next, as shown in FIG. 11D, a p + layer 11 is formed on a part of the back surface of the n-type silicon substrate 4. Here, the p + layer 11 can be formed, for example, as follows.

  First, a diffusion mask 22 and a diffusion mask 23 formed on the light-receiving surface and the back surface of the n-type silicon substrate 4, respectively, and a glass layer formed by diffusing phosphorus into the diffusion masks 22 and 23, for example, using hydrofluoric acid or the like. Removed by etching. Next, a diffusion mask 24 such as a silicon oxide film is formed on the light receiving surface of the n-type silicon substrate 4. Next, a diffusion mask 25 is formed by applying a masking paste to a region other than the region where the p + layer 11 is formed on the back surface of the n-type silicon substrate 4 and then heat-treating the masking paste. Thereafter, a solution obtained by dissolving a polymer obtained by reacting a boron compound with an organic polymer in an alcohol aqueous solution is applied to the back surface of the n-type silicon substrate 4, dried, and then subjected to heat treatment. A p + layer 11 is formed by diffusing boron in the portion where the back surface of the mold silicon substrate 4 is exposed.

  Next, as shown in FIG. 11E, the solution 27 is applied to the light receiving surface of the n-type silicon substrate 4 and then dried. Here, application and drying of the solution 27 can be performed, for example, as follows.

  First, a diffusion mask 24 and a diffusion mask 25 formed on the light receiving surface and the back surface of the n-type silicon substrate 4, respectively, and a glass layer formed by diffusing p-type impurities such as boron into the diffusion masks 24 and 25, for example, It is removed by etching using hydrofluoric acid or the like. Next, a diffusion mask 26 such as a silicon oxide film is formed on the back surface of the n-type silicon substrate 4. Thereafter, a solution 27 containing, for example, a compound containing phosphorus as a compound containing impurities of the first conductivity type, titanium alkoxide, and alcohol is applied to the light receiving surface of the n-type silicon substrate 4 by a spin coating method or the like. Later dry. Here, as the compound containing phosphorus contained in the solution 27, for example, phosphorus pentoxide can be used. In addition, as the titanium alkoxide, for example, tetraisopropyl titanate can be used. Furthermore, as alcohol, isopropyl alcohol etc. can be used, for example.

  Next, as shown in FIGS. 11 (f) and 11 (j), an n + layer 6 and an antireflection film 7 are formed on the light receiving surface of the n-type silicon substrate 4. Here, the n + layer 6 and the antireflection film 7 can be formed by heat-treating the n-type silicon substrate 4 on which the solution 27 is applied to the light receiving surface, for example, at a temperature of 850 ° C. or more and 1000 ° C. or less. That is, by this heating, phosphorus is diffused from the solution 27 on the light receiving surface of the n-type silicon substrate 4 to form the n + layer 6 and the antireflection film 7 made of a titanium oxide film containing phosphorus is formed.

  Next, as shown in FIGS. 11 (g) and 11 (k), a light-receiving surface passivation film 8 is formed on the light-receiving surface of the n-type silicon substrate 4. Here, the light-receiving surface passivation film 8 can be formed, for example, as follows.

  First, the diffusion mask 26 on the back surface of the n-type silicon substrate 4 is removed by etching using hydrofluoric acid. At this time, a part of the antireflection film 7 is also etched by hydrofluoric acid, and a part of the light receiving surface of the n-type silicon substrate 4 is exposed. Here, since the antireflection film 7 is made of a titanium oxide film containing phosphorus, it has high hydrofluoric acid resistance. As a result, as shown in FIG. 11 (k), only the convex portions of the concave-convex shape 5 on the light receiving surface of the n-type silicon substrate 4 where the antireflection film 7 is thin are exposed.

  Next, thermal oxidation of the n-type silicon substrate 4 with oxygen or water vapor is performed. As a result, a back surface passivation film 9 made of a silicon oxide film is formed on the back surface of the n-type silicon substrate 4, and a light receiving surface passivation film 8 made of a silicon oxide film is also formed on the light receiving surface of the n type silicon substrate 4. . At this time, as shown in FIG. 11 (k), the n + layer 6 and the antireflection film 7 on the light-receiving surface of the n-type silicon substrate 4 together with the convex portions of the uneven shape 5 on the light-receiving surface where the n-type silicon substrate 4 is exposed. The light-receiving surface passivation film 8 is also formed between the two. The reason why the light-receiving surface passivation film 8 is formed between the n + layer 6 and the antireflection film 7 is that the film thickness of the antireflection film 7 in the concave portion of the concavo-convex shape 5 on the light receiving surface is increased and the antireflection film 7 is formed. It is considered that a silicon oxide film, which is the light-receiving surface passivation film 8, grows due to oxygen or water vapor entering from the portion where the crack is generated. The thickness of the light-receiving surface passivation film 8 is, for example, 100 nm or more and 200 nm or less, and the thickness of the back surface passivation film 9 is, for example, 30 nm or more and 100 nm or less on the n ++ layer 10, and on the p + layer 11. Is 10 nm or less.

  Here, thermal oxidation of the n-type silicon substrate 4 with oxygen or water vapor can be performed by heat treatment in a state where the n-type silicon substrate 4 is placed in an oxygen atmosphere or a water vapor atmosphere.

  The sheet resistance of the n + layer 6 is 40Ω / □ or more and 80Ω / □ or less. Note that the sheet resistance of the n + layer 6 can be appropriately adjusted by changing at least one of the phosphorus content in the solution 27, the temperature during the thermal oxidation, and the time, for example.

  Next, as shown in FIG. 11 (h), a part of the back surface passivation film 9 is removed to expose a part of the n ++ layer 10 and a part of the p + layer 11 from the back surface passivation film 9, respectively. . Here, a part of the back surface passivation film 9 can be removed, for example, by applying the etching paste to a part of the back surface passivation film 9 by a screen printing method or the like and then heating the etching paste. Thereafter, the etching paste can be removed, for example, by performing an acid treatment after ultrasonic cleaning. The etching paste includes, for example, at least one selected from the group consisting of phosphoric acid, hydrogen fluoride, ammonium fluoride, and ammonium hydrogen fluoride as an etching component, and also includes water, an organic solvent, and a thickener. Things can be used.

  Next, as shown in FIG. 11 (i), the n electrode 2 is formed on the n + + layer 10 and the p electrode 3 is formed on the p + layer 11. Here, for example, the n electrode 2 and the p electrode 3 are dried by applying a silver paste to a predetermined position of the back surface passivation film 9 on the back surface of the n-type silicon substrate 4 by screen printing, and then firing the silver paste. Can be formed. By the above, the back surface electrode type solar cell 16 used for the solar cell of Embodiment 2 can be manufactured.

<Sealing of back electrode type solar cells>
FIG. 12 is a schematic cross-sectional view illustrating the process of sealing the back electrode type solar cells 16 installed on the wiring sheet 30. Here, on the light-receiving surface of the back electrode type solar cell 16, from the back electrode type solar cell 16 side, the sheet-like first resin layer 40, the sheet-like second resin layer 41, and the transparent protective substrate 42 are arranged in this order. On the insulating base 31 of the wiring sheet 30, the sheet-like first resin layer 40 and the back surface protection sheet 43 are arranged in this order from the wiring sheet 30 side.

  Next, pressure is applied between the transparent protective substrate 42 and the back surface protective sheet 43 to press the first resin layer 40 against the light receiving surface of the back electrode type solar cell 16 and the first resin layer 40 and the first back surface sheet 43. By heating the second resin layer 41, the first resin layer 40 and the second resin layer 41 are integrated and cured. Thus, as shown in the schematic cross-sectional view of FIG. 13, the back electrode type connected by the wiring sheet 30 in the sealing material 50 in which the first resin layer 40 and the second resin layer 41 are integrated. The solar battery cell 16 is sealed. Thereafter, a frame 61 made of, for example, an aluminum alloy is attached to the entire circumference of the outer periphery of the sealing material 50 that seals the back electrode type solar cell 16 to produce the solar battery of the second embodiment. In addition, in the solar cell of Embodiment 2, the back surface electrode type solar cell 16 sealed in the sealing material 50 is not limited to plural, and may be single.

<Effect>
Also in the solar cell of the second embodiment, the sheet resistance of the n + layer 6 as the light-receiving surface diffusion layer of the back electrode type solar cell 16 is set to 40Ω / □ or more and 80Ω / □ or less, and the back electrode type solar cell 16 The volume resistivity at 85 ° C. of the sealing material (second resin layer 41) provided on the light receiving surface is set to 1 × 10 ¹⁶ Ω · cm or less. Thus, even when a sealing material (second resin layer 41) having a volume resistivity at 85 ° C. of 1 × 10 ¹⁶ Ω · cm or less is used, the output of the back electrode solar cell 16 itself is set to a high output. In addition, the decrease in the output of the solar battery including the back electrode type solar battery cell 16 can be stably and sufficiently suppressed.

  That is, when the sheet resistance of the n + layer 6 as the light-receiving surface diffusion layer of the back electrode type solar cell 16 is less than 40 Ω / □, recombination in the n + layer 6 increases, so that the back electrode type The output of the solar battery cell 16 itself decreases. Further, when the sheet resistance of the n + layer 6 is higher than 80Ω / □, a large potential difference is generated between the back electrode type solar cell 16 and the frame 61, and moisture or the like is present on the surface of the transparent protective substrate 42. If accumulated, charge accumulates in the light-receiving surface passivation film 8 of the back electrode type solar cell 16, and the function of the n + layer 6 as an FSF (Front Surface Field) is deteriorated.

Thereby, also in the solar cell of Embodiment 2, as in the conventional solar cell module described in Patent Document 1, the volume resistivity at 45 ° C. to 85 ° C. is as high as 1 × 10 ¹⁶ Ω · cm or more. Since it is possible to suppress a decrease in output due to PID or the like without using a special sealing material, the choice of the sealing material provided on the light-receiving surface of the back electrode type solar cell 16 as compared with the prior art It can be expanded and long-term reliability can be ensured.

Also in the solar cell of the second embodiment, as in the conventional solar cell module described in Patent Document 1, a high resistivity special such that the volume resistivity at 45 ° C. to 85 ° C. is 1 × 10 ¹⁶ Ω · cm or more. In addition, since it is not necessary to use an expensive sealing material, the manufacturing cost of the solar cell module can be kept low.

Furthermore, also in the solar cell of Embodiment 2, as in the conventional solar cell module described in Patent Document 1, the volume resistivity at 45 ° C. to 85 ° C. is as high as 1 × 10 ¹⁶ Ω · cm or more, Since it is not necessary to use a sealing material that is very difficult to handle, the manufacturing efficiency of the solar cell module can be improved.

<Modification>
FIG. 14 shows a schematic cross-sectional view of a modification of the solar cell of the second embodiment. In the modification of the solar cell of Embodiment 2 shown in FIG. 14, the sealing material 50 that seals the back electrode type solar cell 16 is the second resin on the light receiving surface of the back electrode type solar cell 16. It consists of the laminated body of the layer 41 and the 1st resin layer 40 on the wiring sheet 30, It is characterized by the above-mentioned.

Also in the modification of the solar cell of the second embodiment shown in FIG. 14, the sheet resistance of n + layer 6 as the light-receiving surface diffusion layer of back electrode type solar cell 16 is set to 40Ω / □ or more and 80Ω / □ or less. Therefore, a sealing material (second resin layer 41) having a volume resistivity at 85 ° C. of 1 × 10 ¹⁶ Ω · cm or less is used as the sealing material provided on the light receiving surface of the back electrode type solar cell 16. be able to. Thereby, the modification of the solar cell of Embodiment 2 shown in FIG. 14 can also be made into a solar cell which can ensure long-term reliability, without using a special and expensive sealing material.

<Other variations>
FIG. 15 is a schematic cross-sectional view of another modification of the solar cell of the second embodiment. In another modification of the solar cell of Embodiment 2 shown in FIG. 15, the sealing material for sealing back electrode type solar battery cell 16 is formed of sealing material 52 made of a single layer of olefin resin. It is characterized by that.

Also in another modification of the solar cell of Embodiment 2 shown in FIG. 15, the sheet resistance of the n + layer 6 as the light-receiving surface diffusion layer of the back electrode type solar cell 16 is 40Ω / □ or more and 80Ω / □ or less. Therefore, as the sealing material provided on the light-receiving surface of the back electrode type solar cell 16, the sealing material 52 made of a single layer of olefin resin having a volume resistivity at 85 ° C. of 1 × 10 ¹⁶ Ω · cm or less. Can be used. Thereby, the other modification of the solar cell of Embodiment 1 shown in FIG. 15 can also be set as the solar cell which can ensure long-term reliability, without using a special and expensive sealing material.

<Others>
Since the description other than the above in Embodiment 2 is the same as that in Embodiment 1, the description thereof is omitted.

<Experiment method>
First, the back electrodes of Examples 1 to 5 and Comparative Examples 1 to 3 are manufactured by the same method as the method for manufacturing the back electrode type solar battery cell of Embodiment 1 shown in FIGS. 3 (a) to 3 (i). Type solar cell 1 was produced. Moreover, the back electrode of Examples 6-8 and Comparative Examples 4-6 is the same method as the manufacturing method of the back electrode type solar battery cell of Embodiment 2 shown by Fig.11 (a)-FIG.11 (k). Type solar cell 16 was produced.

  Here, the back electrode type solar cells 1 of Examples 1 to 5 and Comparative Examples 1 to 3 are phosphorous pentoxide, tetraisopropyl titanate, and isopropyl alcohol used for forming the n + layer 6 that is the light receiving surface diffusion layer. As shown in Table 1, by adjusting the phosphorous concentration in the solution 27 containing N, the sheet resistance of the n + layer 6 was changed, and the same conditions and the same method were used.

  In addition, the back electrode type solar cells 16 of Examples 6 to 8 and Comparative Examples 4 to 6 also contain phosphorus pentoxide, tetraisopropyl titanate, and isopropyl alcohol used for forming the n + layer 6 that is the light receiving surface diffusion layer. As shown in Table 1, by adjusting the phosphorous concentration in the solution 27 to be contained, it was produced under the same conditions and the same method except that the sheet resistance of the n + layer 6 was changed.

  In addition, in the value of sheet resistance of the light-receiving surface diffusion layer of the back electrode type solar cells of Examples 1 to 8 and Comparative Examples 1 to 6 shown in Table 1, Examples 1 to 8 and The sample was formed up to the n + layer 6 under the same conditions and the same method as the back electrode type solar cells of Comparative Examples 1 to 6, and then the surface of the n + layer 6 was exposed. The value measured by the four-probe method at room temperature (25 ° C.) was used.

  Next, as shown in FIG. 16, the back electrode type solar cells 1 of Examples 1 to 8 and Comparative Examples 1 to 6 are respectively installed on the wiring sheet 30, and a transparent protective substrate 42 made of glass, The volume resistivity at 85 ° C. was adjusted to be different as shown in Table 1 by changing the content of the additive between the back protective sheet 43 made of a PET film on which an aluminum film was deposited. It sealed in the sealing material 52 which consists of a single layer of an olefin resin.

  In addition, the value of the volume resistivity in 85 degreeC of the sealing material used for sealing of the back electrode type photovoltaic cell of Examples 1-8 shown in Table 1 and Comparative Examples 1-6 is as follows. Asked.

  On a Teflon (registered trademark) sheet, a copper foil having a diameter of 5 cm, a sealing material having a length of about 10 cm × width of about 10 cm × thickness of about 0.04 cm, a copper foil having a diameter of 5 cm, and a Teflon (registered trademark) sheet The encapsulating material was cured by applying the pressure under the same conditions as when the back electrode type solar cells were sealed, and then heating.

  Next, remove the Teflon (registered trademark) sheet from the sealing material, take it out to the copper foil, attach the electrode with Ag paste or the like, place the sealing material with the electrode in a thermostatic bath, and when the temperature reaches a predetermined temperature, A voltage of 100 V was applied between them and the current value was measured. Table 1 shows the volume resistivity of the sealing material calculated from the measured current value.

  In FIG. 17, the relationship between the sheet resistance of the light-receiving surface diffused layer of the back electrode type photovoltaic cell of Examples 1-8 and Comparative Examples 1-6 and the volume resistivity at 85 degreeC of a sealing material is shown.

And with respect to the back electrode type solar cells 1 of Examples 1 to 8 and Comparative Examples 1 to 6 sealed in the sealing material 52, using a solar simulator, a spectral distribution AM1.5, an energy density of 100 mW. / Cm ² 1SUN simulated sunlight was irradiated to create a current-voltage curve, and the cell output before the simulated negative electrode grounding test was calculated from the result. The results are shown in Table 1.

  Next, as shown in FIG. 16, after forming the pseudo negative electrode 51 made of copper foil on the surface of the transparent protective substrate 42, the pseudo negative electrode 51 is grounded, and the back electrode type solar cell in an environment of 85 ° C. A pseudo negative electrode ground test was performed in which a voltage of 600 V was applied between 1 and the pseudo negative electrode 51 and left for 20 hours.

And after the said pseudo negative electrode grounding test, again using the solar simulator with respect to the back electrode type photovoltaic cell 1 of Examples 1-8 and Comparative Examples 1-6 sealed in the sealing material 52 Then, 1 SUN pseudo-sunlight having a spectral distribution AM1.5 and an energy density of 100 mW / cm ² was irradiated to create a current-voltage curve. And from the result, while calculating the cell output after a pseudo negative electrode grounding test, the change rate of the cell output was computed from the following formula | equation (I) based on the cell output before and behind a pseudo negative electrode grounding test. The results are shown in Table 1.

Cell output change rate [%] = 100 × {(cell output after pseudo negative grounding test) − (cell output before pseudo negative grounding test)} / (cell output before pseudo negative grounding test) (I)
In addition, the sheet resistance of the light-receiving surface diffusion layer shown in Table 1, the volume resistivity of the sealing material at 85 ° C., the cell output before and after the pseudo negative electrode grounding test, and the output change rate are average values of n number of 5, respectively. is there.

<Evaluation>
The solar cell of Examples 1-8 and Comparative Examples 1-6 in which the back electrode type solar cell of Examples 1-8 and Comparative Examples 1-6 was sealed by the sealing material 52 which consists of a single layer of an olefin resin. The evaluation of the pseudo negative electrode ground test was performed based on the following criteria from the viewpoint of the cell output before the pseudo negative electrode ground test and the rate of change of the cell output before and after the pseudo negative electrode ground test.

(A) Cell output before pseudo negative grounding test About the cell output before pseudo negative grounding test, 4.5W or more was considered acceptable and less than 4.5W was rejected.

(B) Change rate of cell output before and after the pseudo negative electrode ground test About change rate of the cell output before and after the pseudo negative electrode ground test, less than 10% was accepted and 10% or more was rejected.

(C) Evaluation When both the cell output before the pseudo negative electrode grounding test or the rate of change of the cell output before and after the pseudo negative electrode grounding test are acceptable, the evaluation is A, and when at least one is unacceptable, the B evaluation is did. The results are shown in Table 1.

As shown in Table 1, the sheet resistance of the light-receiving surface diffusion layer is 40Ω / □ or more and 80Ω / □ or less, and the volume resistivity at 85 ° C. of the sealing material is 1 × 10 ¹⁶ Ω · cm or less All of the solar cells of -8 were rated as A, and the solar cells of Comparative Examples 1-6 were all rated as B.

Therefore, the solar cells of Examples 1 to 8 can make the output of the back electrode type solar cell 1 itself higher than the solar cells of Comparative Examples 1 to 6, and the back electrode type solar cell. It was confirmed that a decrease in the output of the solar cell including 1 can be stably and sufficiently suppressed. In particular, in the solar cells of Examples 1 to 5 in which the volume resistivity at 85 ° C. of the encapsulant is 2.8 × 10 ¹⁵ Ω · cm or more and 5.1 × 10 ¹⁵ Ω · cm or less, the back electrode type solar cell It was confirmed that the decrease in the output of the solar battery including the battery cell 1 can be more stably and sufficiently suppressed.

  Based on the above results, long-term reliability can be secured without using a special and expensive sealing material for the solar cells of Examples 1 to 8, particularly the solar cells of Examples 1 to 5.

<Summary>
The present invention comprises a back electrode type solar cell and a sealing material provided on the light receiving surface of the back electrode type solar cell, the back electrode type solar cell comprising a first conductivity type semiconductor substrate, A first conductive type light receiving surface diffusion layer provided on the light receiving surface side surface of the semiconductor substrate, and a first conductive type impurity diffusion layer and a second conductive type provided on the surface opposite to the light receiving surface side of the semiconductor substrate. The sheet resistance of the light-receiving surface diffusion layer is 40Ω / □ or more and 80Ω / □ or less, and the volume resistivity at 85 ° C. of the sealing material is 1 × 10 ¹⁶ Ω · cm or less. It is a solar cell. With such a configuration, long-term reliability of the solar cell can be ensured without using a special and expensive sealing material.

  Here, in the solar cell of the present invention, the light-receiving surface diffusion layer may be formed by applying a heat treatment after applying a solution containing a compound containing a first conductivity type impurity, titanium alkoxide, and alcohol. preferable. With such a configuration, the long-term reliability of the solar cell can be ensured without using a special and expensive sealing material.

  Moreover, in the solar cell of the present invention, the sealing material is preferably composed of a single layer of olefin resin. Even if it is set as such a structure, long-term reliability of a solar cell can be ensured, without using a special and expensive sealing material.

  In the solar cell of the present invention, the sealing material includes a first resin layer on the light receiving surface of the back electrode type solar cell and a second resin layer on the first resin layer, and the second resin layer. The resin layer is preferably made of an olefin resin. Even if it is set as such a structure, long-term reliability of a solar cell can be ensured, without using a special and expensive sealing material.

In the solar cell of the present invention, the volume resistivity of the encapsulant at 85 ° C. is preferably 1 × 10 ¹² Ω · cm or more and 1 × 10 ¹⁶ Ω · cm or less. With such a configuration, the long-term reliability of the solar cell can be further improved without using a special and expensive sealing material.

In the solar cell of the present invention, the volume resistivity of the sealing material is preferably 1 × 10 ¹⁵ Ω · cm or more and 1 × 10 ¹⁶ Ω · cm or less. With such a configuration, the long-term reliability of the solar cell can be further improved without using a special and expensive sealing material.

In the solar cell of the present invention, the volume resistivity of the sealing material is preferably 2.8 × 10 ¹⁵ Ω · cm or more and 5.1 × 10 ¹⁵ Ω · cm or less. With such a configuration, the long-term reliability of the solar cell can be further improved without using a special and expensive sealing material.

  Furthermore, the present invention is a method for producing the solar cell according to any one of the above, wherein a compound containing an impurity of the first conductivity type, titanium alkoxide, alcohol on the light receiving surface side surface of the semiconductor substrate, And a step of forming a light-receiving surface diffusion layer and an antireflection film by applying a heat treatment after applying a solution containing, and a step of sealing the back electrode type solar cell with a sealing material. It is a manufacturing method. With such a configuration, long-term reliability of the solar cell can be ensured without using a special and expensive sealing material.

  Although the embodiments and examples of the present invention have been described above, it is also planned from the beginning to appropriately combine the configurations of the above-described embodiments and examples.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  INDUSTRIAL APPLICABILITY The present invention can be used for a solar cell, and in particular, a back electrode type solar cell with a wiring sheet in which a plurality of back electrode type solar cells are connected in series and / or in parallel by wiring of a wiring sheet. It can use suitably for the solar cell module sealed in.

  DESCRIPTION OF SYMBOLS 1 Back electrode type solar cell, 2 n electrode, 3 p electrode, 4 n type silicon substrate, 5 uneven | corrugated shape, 6 n + layer, 7 Antireflection film, 8 Light-receiving surface passivation film, 9 Back surface passivation film, 10 n + + Layer, 11 p + layer, 12 antireflection film, 13 first back surface passivation film, 14 second back surface passivation film, 15 back surface passivation film, 16 back electrode type solar cell, 21 texture mask, 22, 23, 24, 25, 26 Diffusion mask, 27 Solution, 30 Wiring sheet, 31 Insulating substrate, 32, 32an wiring, 33, 33ap wiring, 34 Connecting wiring, 36 wiring, 40 First resin layer, 41st 2 resin layer, 42 transparent protective substrate, 43 back surface protective sheet, 50 sealing material, 51 pseudo negative electrode, 52 sealing material, 61 frame, 100 thick Cell array, 101 a solar cell, 251 a transparent protective member, 252 sealing material, 253 back protective sheet, 254 interconnector.

Claims (5)

A back electrode type solar cell,
A sealing material provided on the light-receiving surface of the back electrode type solar cell,
The back electrode type solar cell is
A first conductivity type semiconductor substrate;
A light-receiving surface diffusion layer of a first conductivity type provided on the surface of the semiconductor substrate on the light-receiving surface side;
A first conductivity type impurity diffusion layer and a second conductivity type impurity diffusion layer provided on a surface opposite to the light receiving surface side of the semiconductor substrate;
The sheet resistance of the light-receiving surface diffusion layer is 40Ω / □ or more and 80Ω / □ or less,
A volume resistivity of the sealing material at 85 ° C. is 1 × 10 ¹⁶ Ω · cm or less.   2. The solar cell according to claim 1, wherein the light-receiving surface diffusion layer is formed by applying a heat treatment after applying a solution containing a compound containing a first conductivity type impurity, titanium alkoxide, and alcohol.   The solar cell according to claim 1, wherein the sealing material is made of a single layer of an olefin resin. The sealing material includes a first resin layer on the light receiving surface of the back electrode type solar cell, and a second resin layer on the first resin layer,
The solar cell according to claim 1, wherein the second resin layer is made of an olefin resin. 5. The solar cell according to claim 1, wherein the sealing material has a volume resistivity at 85 ° C. of 1 × 10 ¹² Ω · cm to 1 × 10 ¹⁶ Ω · cm.

Images