JP2008270743A - Solar cell module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solar cell module having a simple configuration and minimizing deterioration of solar cell characteristics under long-term outdoor exposure, particularly in a high temperature and high humidity environment.
SOLUTION: A through-hole solar cell module having a through-hole having a minimum cross-sectional area at the opening on the back surface. Thereby, it can suppress that the water | moisture content permeating from the back surface side permeates the light-receiving surface side through the through-hole 3.
[Selection] Figure 1

Description

  The present invention relates to a solar cell module.

  As a configuration to increase the power generation efficiency of the crystalline silicon solar cells that are currently mainstream, a configuration in which the area of the electrode formed on the light receiving surface side of the solar cell element is reduced to increase the light receiving area is being studied. . FIG. 9 is a diagram showing a configuration of the through-hole type solar cell module.

  A through-hole solar cell module is a solar cell that eliminates the electrode existing on the light-receiving surface side of the solar cell element or reduces the area occupied by the electrode by providing a through electrode from the light-receiving surface side to the back surface side. It is intended to improve the light receiving area of the battery element and increase the efficiency. For example, the first conductive type compound semiconductor layer and the second conductive type compound semiconductor layer are sequentially stacked on the surface of the first conductive type crystal substrate, and the light receiving surface side electrode is turned to the back side through the through hole. A structure is disclosed (for example, see Patent Document 1).

  Also shown is a solar cell element having a structure in which a reverse conductivity type layer is extended around the back side of the through hole (see, for example, Patent Document 2). 9A is a cross-sectional view showing the structure, FIG. 9B is a plan view seen from one main surface (light-receiving surface) side, and FIG. 9C is seen from the other main surface (back surface) side. A plan view is shown. FIG. 9A shows a cross section in the direction of the arrow X in FIGS. 9B and 9C.

  As a method for manufacturing this solar cell element, first, a number of through holes 3 are provided in a semiconductor substrate 1 having a first conductivity type (for example, P type) by a drill or the like, and then the semiconductor substrate 1 including the inner wall of the through holes 3 Second conductivity type (for example, N type) reverse conductivity type layers 2 (first reverse conductivity type layer 2a, second reverse conductivity type layer 2b, and third reverse conductivity type layer 2c) are formed on both surfaces. At this time, a region where the third reverse conductivity type layer 2c is not formed is required on the back surface side. Thereafter, the first electrode 4 (the through-hole electrode 4b and the back-side electrode 4c) is formed on the third reverse conductivity type layer 2c on the back surface side and in the through hole 3 to form the third reverse conductivity type layer 2c. The second electrode 5 is formed in a non-existing region, and the solar cell element is completed by connecting the light receiving surface side electrode 4a to the through-hole electrode 4b.

In addition, since solar cell elements cannot withstand use under harsh environments outdoors, they are generally transparent and weather-resistant light-receiving surfaces such as glass provided on the light-receiving surface side of solar cell elements. Between the side member and the back side member excellent in moisture resistance and electrical insulation, such as a film in which polyethylene terephthalate (PET) or metal foil provided on the back side of the solar cell element is sandwiched between polyvinyl fluoride resins (PVF) A solar cell element is sandwiched and laminated through a sealing resin such as polyvinyl butyral or ethylene-vinyl acetate copolymer (EVA), and used as a solar cell module.
Japanese Patent Laid-Open No. 63-211773 Special Table 2002-500825

  Solar cell modules require a high level of moisture resistance because they are used outdoors for a long period of time. However, when exposed outdoors for more than 10 years, peeling between each member is obvious due to light deterioration and thermal deterioration of the coating material. The peeling between the members may lead to corrosion of the electrodes and connection tabs made of the metal member attached to the solar cell element or the element, or yellowing of the sealing resin due to the penetration of moisture into the peeling portion, It leads to the deterioration of the solar cell characteristics. Electrode is oxidized or EVA reacts with water to generate acid, and the current collection efficiency deteriorates due to corrosion of the electrode, particularly corrosion of the interface between the electrode and the semiconductor layer.

  Compared to the light receiving surface side member such as glass, moisture easily enters from the back side member made of resin, etc., so that corrosion of the electrode on the light receiving surface side and sealing resin on the light receiving surface side have a great influence on the characteristics. However, in the case of the through-hole type solar cell module as described above, moisture that has entered from the back side has an influence on the light-receiving surface side electrode and the sealing resin through the through hole 3. Will be given.

  The present invention has been made in view of such problems, and an object of the present invention is to minimize degradation of solar cell characteristics under a simple configuration and long-term outdoor exposure, particularly in a high-temperature and high-humidity environment. It is to provide a solar cell module to limit.

  The present invention includes a light receiving surface and a back surface, a semiconductor substrate having a through hole penetrating between the light receiving surface and the back surface, the semiconductor substrate being provided in the through hole, A solar cell element having a cross-sectional area that is the smallest in the opening on the back surface side of the semiconductor substrate, a first resin that seals a light-receiving surface side of the solar cell element, and the solar cell element And a second resin that seals the back surface side. Here, `` the cross-sectional area is the smallest '' in the back opening means that the cross-sectional area of the back opening is smaller (not including the same) as the cross-sectional area in any other part in the thickness direction of the through hole. means.

  The solar cell module of the present invention includes a solar cell element having a through electrode having a minimum area in the opening on the back surface side of the semiconductor substrate, a first resin for sealing the light-receiving surface side of the solar cell element, and the solar cell element And a second resin that seals the back surface side.

  As a result, it is possible to reduce the moisture that has entered the solar cell module from the back side into the light receiving surface through the through-hole, so that corrosion of the electrode on the light receiving surface side and yellow of the sealing resin on the light receiving surface side can be reduced. The occurrence of changes can be reduced, and the deterioration of solar cell characteristics in a high temperature and high humidity environment can be reduced.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
[Solar cell element]
FIG. 1 is a cross-sectional view showing a configuration of a solar cell element 10 constituting a solar cell module according to an embodiment of the present invention.

  A case where a P-type silicon substrate is used as the semiconductor substrate 1 exhibiting the first conductivity type will be described as an example. Needless to say, an N-type silicon substrate may be used. In that case, the polarity of the electrodes may be reversed.

  The P-type silicon substrate 1 has a through hole 3 penetrating between one main surface (hereinafter referred to as “light receiving surface”) and another main surface (hereinafter referred to as “back surface”). In FIG. 1, the through hole 3 penetrates in the thickness direction of the silicon substrate 1. The conventional through-hole 3 has a light receiving surface side opening as described in Patent Document 2 from the viewpoint of securing a light receiving area from the viewpoint of securing a light receiving area, or having a light receiving surface side and a back surface side having the same circular shape. It is formed so that the sectional area of

  On the other hand, in the solar cell element 10 of the present embodiment, the through hole 3 is formed so that the cross-sectional area at the back surface opening is minimized. Thereby, the infiltration of moisture from the back side can be reduced.

  An N-type first reverse conductivity type layer 2a and a third reverse conductivity type layer 2c are formed on the light receiving surface and the back surface of the semiconductor substrate 1 by diffusing phosphorus or the like. An N-type second reverse conductivity type layer 2b is formed on the inner wall of the through hole 3 by diffusing phosphorus or the like. The first reverse conductivity type layer 2a, the second reverse conductivity type layer 2b, and the third reverse conductivity type layer 2c are collectively referred to as the reverse conductivity type layer 2.

  Next, the first electrode 4 is an electrode that is formed so as to fill the through hole 3 and is connected to the reverse conductivity type layer 2. The light receiving surface side electrode 4 a, the through hole internal electrode 4 b, and the back surface side electrode 4 c Consists of. The 1st electrode 4 is formed with the material which has silver, copper, etc. as a main component. In the present embodiment, the “through electrode” corresponds to the through-hole electrode 4b.

  In the present embodiment, the first electrode 4 formed in the through hole 3 is formed so that the cross-sectional area on the back surface is minimized.

  Here, it is preferable that the first electrode 4 exists so as to wrap around the light receiving surface, whereby more current can be collected.

  In addition, in order to form so that the space volume of the through-hole 3, in other words, the volume of the 1st electrode 4 may not change with the resistance value of the conventional through-electrode, it will become the volume substantially the same as the volume of the conventional through-electrode. It is formed.

  FIG. 2 is a plan view of the solar cell element 10 as seen from the light receiving surface side. For example, as shown in FIG. 2A, the light receiving surface side electrode 4a is preferably composed of a plurality of line electrodes, and each line electrode is electrically connected to at least one of the through-hole electrodes 4b. Is done. Thereby, the carriers (electrons and holes) generated in the semiconductor substrate 1 can be collected efficiently, and can be taken out from the back surface side electrode 4c through the through-hole electrode 4b. In the present embodiment, the back electrode 4c corresponds to the extraction electrode described in the claims.

  Here, the back surface side electrode 4c is preferably formed at a position so as to block the through hole 3, and this can more effectively prevent moisture from entering the through hole 3.

  Further, as shown in FIG. 2B, the light-receiving surface side electrode 4a may be a point-like (island-like) electrode formed on at least the through-hole electrode 4b. As a result, the amount of light received by the semiconductor substrate 1 can be increased.

  Further, the back side electrode 4c formed on the back side of the semiconductor substrate 1 is provided on the third reverse conductivity type layer 2c.

  In FIG. 1, the heavily doped layer 6 is a back surface of the semiconductor substrate 1 and is formed by diffusing boron or aluminum at a high concentration over substantially the entire surface other than the vicinity of the through hole 3. And a second electrode 5 described later. Here, the high concentration means that the impurity concentration is higher than the concentration of the first conductivity type impurity in the semiconductor substrate 1.

  This highly doped layer 6 is preferably formed so as to cover an area of 70% or more and 90% or less of the entire back surface region of the semiconductor substrate 1. By setting it to 70% or more, the output characteristics of the solar cell element can be effectively improved, and by setting it to 90% or less, the area of the back surface side electrode 4c which is an external extraction electrode is secured and resistance loss is reduced. It becomes possible to reduce.

  The second electrode 5 is located on the back surface of the semiconductor substrate 1 and has a polarity different from that of the first electrode 4. The second electrode 5 includes a collector electrode 5b made of a material mainly composed of aluminum or silver, and an output extraction electrode 5a connected to the collector electrode 5b and mainly composed of silver or the like. .

  Note that the collecting electrode 5b is preferably formed on the above-described heavily doped layer 6, whereby the carriers generated in the semiconductor substrate 1 can be collected efficiently. The collecting electrode 5b also has a role of increasing photocurrent by reflecting light that has not been absorbed in the semiconductor substrate 1 back into the semiconductor substrate 1. Furthermore, by using aluminum as a main component, the high-concentration doped layer 6 can be formed at the same time when the collecting electrode 5b is formed.

Hereinafter, a solar cell module according to an embodiment of the present invention will be described with reference to the drawings.
[Solar Cell Module of First Embodiment]
3A and 3B are diagrams showing the configuration of the solar cell module 20 according to the first embodiment. FIG. 3A is a cross-sectional view, and FIG. 3B is a plan view seen from the light receiving surface side.

  The solar cell module 20 of the present embodiment includes a first resin 14 that seals the light-receiving surface side of the plurality of solar cell elements 10 and a second resin 15 that seals the back surface side. In FIG. 3, the first resin 14 is provided with a light receiving surface side member 12, and the second resin 15 is provided with a back surface side member 13.

  Such a solar cell module 20 includes a sealing resin 14 made of transparent polyvinyl butyral, ethylene vinyl acetate copolymer (EVA), and the like, and a wiring member 11 on a light receiving surface side member 12 made of glass or the like. A plurality of solar cell elements 10 connected, a sealing resin 15 made of EVA or the like, and a back side member 13 such as a film in which polyethylene terephthalate (PET) or metal foil is sandwiched between polyvinyl fluoride resins (PVF); Are laminated in order and integrated by deaeration, heating and pressing in a laminator device to obtain a solar cell module 20.

  As the wiring member 11, generally, a linear copper foil having a thickness of about 0.1 to 0.2 mm and a width of about 2 mm covered with a solder material and cut into a predetermined length is preferably used. It is done. This is used by being soldered onto the electrode of the solar cell element 10 using hot air, soldering iron or the like.

  As shown in FIG. 3, in the solar cell module 20 of the present embodiment, the wiring member 11 is connected to a plurality of electrodes provided on the back surface of the plurality of solar cell elements 10. For this reason, it is not necessary to bend and arrange the wiring member 11 on the light receiving surface side, and the peeling between the wiring member 11 and the electrode can be reduced.

  A frame 18 such as aluminum can be fitted to the outer periphery of the solar cell module 20 via an elastic insulating member made of butyl rubber or the like. Furthermore, among the plurality of solar cell elements 10 connected in series, one end of each electrode of the solar cell element 10 at the endmost portion is connected to a terminal box 17 which is an output extraction portion by an output extraction wiring 16.

  The solar cell module 20 having the above-described configuration uses the solar cell element 10 having the through hole 3 that penetrates the semiconductor substrate 1 and has the smallest cross-sectional area at the back surface opening, thereby allowing the back surface of the solar cell module 20 to be used. Moisture that has entered the module from the side member 13 does not easily enter the light-receiving surface through the through hole 3.

  Thereby, the corrosion of the light receiving surface side electrode 4a formed on the light receiving surface side can be reduced, and the ohmic contact property between the light receiving surface side electrode 4a and the first reverse conductivity type layer 2a can be maintained in a good state. Therefore, it is possible to reduce deterioration of the solar cell characteristics under a high temperature and high humidity environment.

  The light-receiving surface side electrode 4a makes sufficient contact with the semiconductor substrate 1 so that light is incident on the solar cell element 10 and efficiently generates photogenerated carriers (electron carriers or hole carriers) generated by absorption and photoelectric conversion. Can be collected well. Therefore, the light receiving surface side electrode 4a needs to be designed in consideration of ohmic contact with the first reverse conductivity type layer 2a.

  In particular, after the antireflection film 7 is formed on the first reverse conductivity type layer 2a, a conductive paste is directly applied to the antireflection film 7 and baked to thereby form the light receiving surface side electrode 4a and the first reverse conductivity type layer 2a. When making contact with the glass frit, it is necessary to use a glass frit that contributes to fire-through for the light-receiving surface side electrode 4a. Therefore, the light receiving surface side electrode 4a has a problem that a conductive paste containing glass frit having high moisture resistance cannot be used, and an electrode having both ohmic contact property and moisture resistance can be formed. Not necessarily.

  On the other hand, the through-hole inner electrode 4b and the back surface side electrode 4c do not need to consider ohmic contact properties with the second reverse conductivity type layer 2b and the third reverse conductivity type layer 2c, and thus have high moisture resistance. It is preferable to perform electrode formation using glass frit.

  Further, as shown in the sectional view of FIG. 4, in the solar cell element 11 as another embodiment, the third reverse conductivity type layer 2 c is eliminated, and the insulating material layer 8 is formed on the back surface of the semiconductor substrate 1. It doesn't matter. By forming the back surface side electrode 4c on the semiconductor substrate 1 through the insulating material layer 8, the semiconductor substrate 1 and the back surface side electrode 4c are not in direct contact with each other, so that the occurrence of leakage can be reduced. In addition, when an oxide film or a nitride film is used as the insulating material layer 8, it is possible to improve the output characteristics of the solar cell element by reducing the surface recombination rate of the back surface of the semiconductor substrate 1 by the passivation effect.

  Furthermore, if the insulating material layer 8 contains hydrogen, the passivation effect can be further improved. As the hydrogen-containing insulating material layer 8, for example, a hydrogenated amorphous silicon film having another conductivity type may be used. Further, a non-doped (i-type) hydrogenated amorphous silicon film may be provided between a semiconductor substrate and a hydrogenated amorphous silicon film having another conductivity type.

  The light receiving surface of the semiconductor substrate 1 preferably has a texture structure in which a number of fine protrusions having a width and height of 2 μm or less and an aspect ratio of 0.1 to 2 are formed. By doing so, the reflectance at the light receiving surface is reduced, and sunlight is absorbed much into the semiconductor substrate 1, so that the characteristics of the solar cell element 10 can be improved.

Moreover, it is preferable that the sheet resistance of a light-receiving surface is 60-300 ohm / square (sq.), And setting it as this range can suppress the increase in the surface recombination in a light-receiving surface, and the increase in surface resistance. In particular, by combining with fine protrusions having a texture structure as described above, the short-circuit current when a solar cell module is formed can be greatly increased. The sheet resistance value of the light receiving surface can be measured by a four-probe method. Four metal needles arranged in a straight line are brought into contact with the surface of the semiconductor element while being pressed, and the two outer needles are contacted. The voltage generated between the two inner needles when a current is passed through is measured, and the resistance value is obtained from this voltage and the passed current by Ohm's law.
[Method for producing solar cell element]
The manufacturing method of the solar cell element 10 of this invention is demonstrated using the process drawing of FIG.
<Preparation process of semiconductor substrate>
First, a P-type silicon substrate is prepared as the semiconductor substrate 1 having the first conductivity type (FIG. 5A).

  If the silicon substrate is a single crystal silicon substrate, it can be obtained by cutting it from a single crystal silicon ingot produced by a manufacturing method such as FZ or CZ.

  In addition, a polycrystalline silicon substrate can be obtained by cutting out from a polycrystalline silicon ingot produced by a manufacturing method such as a casting method or an in-mold solidification method. In addition, when using plate-like silicon obtained by a pulling-up method such as a ribbon method, the desired silicon substrate is obtained by cutting the plate-like silicon into a predetermined size and performing surface polishing treatment or the like as necessary. Obtainable.

  Control of the conductivity type of the silicon substrate can be realized by dissolving an appropriate amount of the dopant element itself or a dopant material containing an appropriate amount of the dopant element in the silicon melt in the silicon ingot manufacturing process.

Hereinafter, a case where a P-type crystalline silicon substrate doped with B (boron) or Ga (gallium) at a concentration of about 1 × 10 ¹⁵ to 1 × 10 ¹⁷ atoms / cm ³ will be described. Here, if Ga is used, it is possible to avoid the photodegradation phenomenon caused by the relationship between O (oxygen) and B in the substrate, which is suitable for high efficiency. The thickness of the silicon substrate is preferably 300 μm or less, more preferably 250 μm or less, and even more preferably 150 μm or less. An N-type crystalline silicon substrate doped with P (phosphorus) or the like can also be used.

In addition, in order to remove the mechanical damage layer and the contamination layer of the substrate surface layer part due to the cutting (slicing) of the substrate, the surface layer portions on the light receiving surface side and the back surface side of the cut substrate are NaOH, KOH, or hydrofluoric acid and nitric acid. Etching with a mixed solution of about 10 to 20 μm, respectively, and then cleaning with pure water or the like.
<Through-hole formation process>
Next, a through-hole 3 that penetrates the semiconductor substrate 1 in the thickness direction is formed (FIG. 5B).

  By forming the through hole 3 from the light receiving surface side to the back surface side of the semiconductor substrate 1 using a mechanical drill, a water jet, or a laser device, the cross-sectional area at the back surface opening can be minimized. It becomes. The plurality of through holes 3 are preferably formed at a constant pitch over the entire light receiving surface. Moreover, it is preferable that the diameter of the circular opening part of the through-hole 3 is 50 micrometers or more and 300 micrometers or less. Specifically, the ratio (S2 / S1) of the cross-sectional area S2 in the back surface opening to the cross-sectional area S1 in the light-receiving surface opening is 0.5 ≦ (S2 / S1) ≦ 0.9. Is preferable, and more preferably, 0.6 ≦ (S2 / S1) ≦ 0.8.

  If (S2 / S1) is smaller than 0.5, the resistance value of the first electrode 4 on the back surface side is increased, and if it is larger than 0.9, the intrusion of moisture cannot be sufficiently prevented.

Further, when there is a damaged layer in the through-hole 3, it is preferable to perform etching. For example, mirror etching may be performed with a solution in which hydrofluoric acid and nitric acid are mixed at 2: 7.
<Texture structure forming process of light receiving surface>
Next, a texture structure 1a having fine protrusions (convex portions) for effectively reducing the light reflectance is formed on the light receiving surface side of the semiconductor substrate 1 (FIG. 5C).

  As a method for forming the texture structure 1a, a wet etching method using an alkali solution such as NaOH or KOH, or a dry etching method using an etching gas having a property of etching Si can be used.

  The former can also be carried out continuously with the process for removing the damage layer on the substrate surface layer described above, so that a texture structure is also formed on the back side unless the back side is masked with an etching inhibitor. preferable.

  In the latter, a fine texture structure 1a is basically formed only on the processed surface (light receiving surface side). There are a variety of dry etching methods. Particularly, when the RIE method (Reactive Ion Etching method) is used, a fine texture structure 1a that can be suppressed to a very low light reflectance over a wide wavelength range is obtained over a wide range. Since it can be formed in a short time, it is extremely effective for high efficiency. In addition, when the RIE method is used, the texture structure 1a can be formed without being greatly affected by the crystal plane orientation. Therefore, even when a polycrystalline silicon substrate is used as the crystalline silicon substrate, each crystal in the polycrystalline silicon substrate is used. A fine texture structure having a low reflectivity can be formed uniformly over the entire substrate without depending on the plane orientation of the grains.

In addition, since the cross-sectional area of the light receiving surface opening of the through hole 3 is relatively large, a fine texture structure is easily formed inside the through hole 3, particularly on the light receiving surface side. The strength of the electrode can be improved.
<Reverse conductivity type layer formation process>
Next, the first reverse conductivity type layer 2a is formed on the light receiving surface, the second reverse conductivity type layer 2b having the reverse conductivity type is formed on the inner wall of the through hole 3, and the third reverse conductivity type layer 2c is formed on the back surface. Is formed (FIG. 5D).

P (phosphorus) is preferably used as an N-type doping element for forming the reverse conductivity type 2, and an N ⁺ type having a sheet resistance of about 60 to 300 Ω / □ is used. As a result, a PN junction is formed between the P-type bulk region.

The reverse conductivity type layer 2 is a coating thermal diffusion method in which P ₂ O ₅ in a paste state is applied to the surface of the semiconductor substrate 1 for thermal diffusion, and gas using POCl ₃ (phosphorus oxychloride) in a gas state as a diffusion source. It is formed by a phase thermal diffusion method or an ion implantation method for directly diffusing P ⁺ ions, but if a vapor phase diffusion method is used, the opposite conductivity type layer 2 is simultaneously formed on both surfaces of the semiconductor substrate 1 and the inner walls of the through holes. This is preferable because it can be performed.

  The first reverse conductivity type layer 2a is preferably formed to a depth of about 0.2 to 0.5 μm from the surface. In addition, since the 2nd reverse conductivity type layer 2b is formed in the inside of the through-hole 3, compared with the 1st reverse conductivity type layer 2a, dopant concentration is low and thickness tends to become thin.

  Also, under conditions where a diffusion region is formed in addition to the region to be processed, diffusion can be partially reduced by forming an insulating material layer in that portion in advance, and when an insulating material layer is not formed Alternatively, a portion formed outside the processing target region may be removed by etching later.

  As will be described later, when the high-concentration doped layer 6 on the back surface is formed of an aluminum paste, aluminum that is a P-type dopant can be diffused to a sufficient depth at a sufficient concentration, so that it has already diffused. The influence of the shallow reverse conductivity type layer can be ignored, and the reverse conductivity type layer existing at the position where the heavily doped layer 6 is formed does not need to be removed.

The method of forming the reverse conductivity type layer 2 is not limited to the above method. For example, a thin film technology is used to form a hydrogenated amorphous silicon film, a crystalline silicon film including a microcrystalline silicon film, or the like. Also good. Here, when the reverse conductivity type layer 2 is formed using a hydrogenated amorphous silicon film, the thickness is 50 nm or less, preferably 20 nm or less, and when it is formed using a crystalline silicon film, the thickness is It is 500 nm or less, preferably 200 nm or less. Furthermore, an i-type silicon region may be formed with a thickness of 20 nm or less between the semiconductor substrate 1 and the reverse conductivity type layer 2.
<Antireflection film formation process>
Next, the antireflection film 7 is formed on the first reverse conductivity type layer 2a (FIG. 5E).

Examples of the material for the antireflection film 7 include a SiNx film (composition ratio (x) having a width centered on Si ₃ N ₄ stoichiometry), a TiO ₂ film, a SiO ₂ film, a MgO film, an ITO film, and a SnO film. _Two films, a ZnO film, or the like can be used. The refractive index and thickness may be appropriately selected depending on the material so that non-reflection conditions can be realized with respect to appropriate incident light. For example, when the semiconductor substrate 1 is a silicon substrate, the refractive index is 1.8 to About 2.3 and the thickness may be about 500 to 1200 mm.

  As a method for forming the antireflection film 7, a PECVD method (plasma chemical vapor deposition method), a vapor deposition method, a sputtering method, or the like can be used.

  The antireflection film 7 may be patterned in a predetermined pattern in order to form the light receiving surface side electrode 4a. As a patterning method, an etching method using a mask such as a resist (wet or dry) or a method of forming a mask in advance when forming the antireflection film 7 and removing the mask after forming the antireflection film 7 is used. Can do.

  A so-called fire-through method in which the light receiving surface side electrode 4a and the first reverse conductivity type layer 2a are electrically contacted by directly applying and baking the conductive paste of the light receiving surface side electrode 4a on the antireflection film 7 is performed. When using, the above patterning is not necessary.

Further, the antireflection film 7 may be formed after the formation of the light receiving surface side electrode 4a. By doing so, it is not necessary to perform patterning and it is not necessary to use the fire-through method. The formation conditions can be widened, and for example, it is not necessary to perform high-temperature baking at about 800 ° C.
<High-concentration dope layer forming step on the back surface>
Next, a heavily doped layer 6 in which impurities of the first conductivity type semiconductor are diffused at a high concentration is formed on the back surface of the semiconductor substrate 1 (FIG. 5F).

  The heavily doped layer 6 means a layer having a higher doping ratio of the first conductivity type impurity than the semiconductor substrate 1, and an internal electric field is applied in order to reduce efficiency reduction due to carrier recombination near the back surface of the semiconductor substrate 1. To form.

B (boron) or Al (aluminum) can be used as the impurity element, and the impurity element concentration is set to a high concentration of about 1 × 10 ^{18 to} 5 × 10 ²¹ atoms / cm ³ , and the P ⁺ type is obtained. An ohmic contact can be obtained between the collector electrode 5b described later.

The heavily doped layer 6 can be formed at a temperature of about 800 to 1100 ° C. using a thermal diffusion method using BBr ₃ (boron tribromide) as a diffusion source. When performing this step, it is desirable to form a diffusion barrier such as an oxide film in the reverse conductivity type layer 2 already formed.

  When aluminum is used as the impurity element, an aluminum paste made of aluminum powder and an organic vehicle is applied by a printing method, and then heat-treated (fired) at a temperature of about 700 to 850 ° C. to direct the aluminum toward the semiconductor substrate 1. A diffusion method can be used. In this method, a desired diffusion region can be formed only on the printing surface of the paste, and the baked aluminum can be used as it is as the collecting electrode 5b without being removed.

Further, the present invention is not limited to the above methods, and for example, a hydrogenated amorphous silicon film or a crystalline silicon film containing a microcrystalline Si phase may be formed by using a thin film technique. In particular, when the pn junction is formed using thin film technology, the high concentration doped layer 6 is also formed using thin film technology. At this time, the film thickness is about 10 to 200 nm. Furthermore, if an i-type silicon region is formed with a thickness of 20 nm or less between the semiconductor substrate 1 and the heavily doped layer 6, it is effective for improving the characteristics.
<Method for forming first electrode and second electrode>
Next, the light receiving surface side electrode 4a and the through hole inner electrode 4b are formed on the semiconductor substrate 1 (FIG. 5G).

  For these electrodes, a conductive paste may be applied to the light receiving surface of the semiconductor substrate 1 by using a coating method. For example, a conductive paste made of silver, copper, gold, platinum or the like is generally used. From the viewpoint of both characteristics, silver paste is preferably used.

  In the method for manufacturing solar cell element 10 of the present embodiment, a conductive paste containing metal powder, organic vehicle, and glass frit is received so as to have a predetermined electrode shape as shown in FIG. It is applied to the surface, and the conductive paste is also filled in the through holes 3.

  Since the through-hole 3 is formed so that the cross-sectional area at the back surface opening is smaller than the cross-sectional area at the light-receiving surface opening, for example, the conductive paste can be printed and filled from the light-receiving surface side. By doing so, the number of times that the light receiving surface side comes into contact with the printing stage can be reduced, so that damage to the texture structure due to contact with the printing stage can be reduced.

  The conductive paste applied to the light receiving surface and the conductive paste filled in the through holes may be the same or different, but the conductive paste applied to the light receiving surface is the same as that of the first reverse conductivity type layer 2a. It is preferable to use a paste that places importance on contactability and uses a paste that places importance on moisture resistance as the conductive paste that fills the through holes. The order of application may be before or after the light receiving surface side. And the light-receiving surface side electrode 4a and the through-hole inner electrode 4b are formed by baking for several dozen seconds to several tens of minutes at the maximum temperature of 500-850 degreeC.

  In addition, after application | coating, it is more preferable to evaporate and dry a solvent at predetermined temperature. In addition, after applying the paste in the light receiving surface and the through hole, it is preferable to fire the paste on the light receiving surface and the paste in the through hole at the same time from the viewpoint of productivity. Firing may be performed.

  In particular, after forming the antireflection film 7, it is preferable to apply a conductive paste directly to the antireflection film 7 and fill the through holes 3 with the conductive paste, followed by baking. By the above method, the fire-through and light-receiving-surface-side electrode 4a and the through-hole electrode 4b are fired simultaneously, so that productivity can be improved.

  As a conductive paste used for the light-receiving surface side electrode 4a, the main component is silver powder, for example, 10 to 30 parts by weight of an organic vehicle and 0.1 to 10 parts by weight of glass frit are added to 100 parts by weight of silver. The conductive paste used for the through-hole electrode 4b is composed of 10 to 30 parts by weight of an organic vehicle added to 100 parts by weight of silver.

  In addition, the metal powder can be a spherical, flaky or indeterminate powder, and in the conductive paste used for the through-hole electrode 4b, the electrode shrinks when fired by using a spherical powder. Since it can suppress, it is preferable.

  Further, as the organic vehicle, at least one resin selected from cellulose resins such as methylcellulose, ethylcellulose, nitrocellulose and acrylic resins such as methyl methacrylate and butyral resin is selected from butyl carbitol, butyl carbitol acetate, and butyl cellosolve. , Butyl cellosolve acetate, terpineol, hydrogenated terpineol, hydrogenated terpineol acetate, methyl ethyl ketone, isobornyl acetate, nopyrulacetate or the like dissolved in an organic solvent can be used.

As the glass frit, a PbO—SiO ₂ —B ₂ O ₃ system, a Bi ₂ O ₃ —PbO—SiO ₂ —B ₂ O ₃ system, a leadless ZnO—SiO ₂ —B ₂ O ₃ system, or the like is used. Can do.

The paste used to form the light-receiving surface side electrode 4a that places importance on the contact property with the first reverse conductivity type layer 2a preferably contains PbO—SiO ₂ —B ₂ O ₃ glass frit as the glass frit. . Moreover, it is preferable that the paste used for the through-hole inner electrode 4b that places importance on moisture resistance contains lead-free Bi ₂ O ₃ —SiO ₂ —B ₂ O ₃ glass frit as the glass frit.

  Various methods such as a screen printing method, a roll coater method, and a dispenser method can be used as the coating and filling method.

  The through-hole electrode 4b is preferably formed by printing using a paste and a filling method. However, the light-receiving surface side electrode 4a is not limited to this, and after filling the through-hole electrode 4b, for example, a CVD method, You may form by a vapor deposition method etc.

  Next, the current collection electrode 5b of the 2nd electrode 5 is formed on the back surface of the semiconductor substrate 1 (FIG.5 (h)).

  A conductive paste may be applied to the back surface of the semiconductor substrate 1 using the same coating method as described above. For example, a metal powder made of aluminum or silver, an organic vehicle, and a glass frit are added to 100 parts by weight of the metal powder. A conductive paste formed by adding 10 to 30 parts by weight and 0.1 to 10 parts by weight, respectively, is used.

  FIG. 6 is a plan view of the semiconductor element 10 as seen from the back side. The current collecting electrode 5b is formed by applying to a predetermined striped electrode shape as shown in the figure and baking at a maximum temperature of 500 to 850 ° C. for several tens of seconds to several tens of minutes. As described above, when aluminum paste is used, the heavily doped layer 6 and the current collecting electrode 5b can be formed at the same time, and in particular, the area of 70% or more and 90% or less of the entire back surface region of the semiconductor substrate 1. It is preferable to be formed so as to cover.

  Next, the back side electrode 4c of the first electrode 4 and the output extraction electrode 5a of the second electrode 5 are formed on the back side of the semiconductor substrate 1 (FIG. 5 (i)).

  A conductive paste may be applied to the back surface of the semiconductor substrate 1 using the same coating method as described above. For example, the conductive paste is applied in a predetermined striped electrode shape as shown in FIG. The back electrode 4c and the output extraction electrode 5a are formed by baking for several tens of seconds to several tens of minutes.

  In addition, you may form the back surface side electrode 4c and the output extraction electrode 5a separately, or may form it using another conductive paste. Further, the conductive paste may be the same as that of the light-receiving surface side electrode 4a, and any of silver particle size, shape, organic vehicle component, glass frit component, silver or organic vehicle or glass frit content Different conductive pastes may be used.

  In the case where the collecting electrode 5b is formed, it is preferable that a part of the output extraction electrode 5a overlaps with a part of the collecting electrode 5b.

As described above, the solar cell element 10 of the present embodiment is completed.
[Method for manufacturing solar cell module]
Next, a manufacturing process for forming the solar cell module 20 using the solar cell element 10 as described above will be described.

  On the light-receiving surface side member 12 made of glass or the like, a sealing resin 14 made of transparent polyvinyl butyral, ethylene vinyl acetate copolymer (EVA) or the like, and the wiring member 11 make the first electrode 4 of the adjacent solar cell element. A plurality of solar cell elements 10 in which the first electrode 5 and the second electrode 5 are alternately connected, a sealing resin 15 made of EVA or the like, and, for example, polyethylene terephthalate (PET) or metal foil is sandwiched between polyvinyl fluoride resins (PVF) The back surface side member 13 such as a dent film is laminated in order and integrated by deaeration, heating and pressing in a laminator.

  In addition, as the wiring member 11 for connecting these solar cell elements 10 to each other, a copper foil having a thickness of about 0.1 to 0.2 mm and a width of about 2 mm covered with a solder material is usually used. Cut into lengths and soldered onto the electrodes of the solar cell element 10 for use. In consideration of environmental problems, it is desirable to use lead-free solder as the solder material. Moreover, you may connect an electrode and the wiring member 11 using a conductive adhesive.

  Since the solar cell element 10 used in the solar cell module 20 of the present invention is provided with the first electrode 4 and the second electrode 5 on the back surface side, the light receiving surface side of the solar cell element 10 is disposed during the manufacturing process. It is only necessary to place the wiring member 11 in contact with the wiring member 11 from above and connect it to the electrode using hot air or soldering iron. In order to connect the wiring member 11, the front and back of the solar cell element 10 are reversed. Productivity can be improved since no work such as making it necessary is required.

  Next, one end of the electrode of the first element and the last element of the plurality of elements connected in series is connected to the terminal box 17 which is an output extraction portion via the output extraction wiring 16. As shown in FIG. 3B, a frame 18 made of aluminum or the like is fitted around the semiconductor element 10 via an elastic insulating member made of butyl rubber or the like as necessary. The solar cell module 20 is completed by the above.

  In addition, you may form a solder area | region in the 1st electrode 4 and the 2nd electrode 5 which were formed in the back surface side by the solder dip process as needed.

  In the above description, the third reverse conductivity type layer 2c is formed. However, the present invention is not limited to this, and the insulating material layer 8 may be formed on the back surface side as shown in FIG.

Specifically, a silicon oxide film (SiO ₂ film), a titanium oxide film (TiO ₂ ), a silicon nitride film (SiNx), or the like is formed using a sputtering method, a vapor deposition method, a CVD method, or the like to a thickness of about 10 nm to 50 μm. Then, the insulating material layer 8 is formed. In addition, by subjecting the semiconductor substrate 1 to heat treatment in a thermal oxidation furnace in an oxygen atmosphere or an air atmosphere, and applying and baking the oxide film material using a coating method such as a spin coating method, a spray method, or a screen printing method, The insulating material layer 8 may be formed. Note that the insulating material layer 8 may be a single layer film or a plurality of layers having a two-layer structure of a silicon oxide film and a silicon nitride film.

The silicon nitride film formed by plasma CVD, hydrogen (H ₂₎ includes a by heating after film forming and film forming, to diffuse hydrogen (H ₂₎ in the semiconductor substrate 1. By doing so, hydrogen (H ₂ ) is bonded to dangling bonds (unbonded hands) existing in the semiconductor substrate 1 and the probability that carriers are trapped in the dangling bonds can be reduced, thereby providing a passivation effect. can do. Therefore, a highly efficient solar cell element 10 can be formed by forming a silicon nitride film on substantially the entire back surface.

  Further, by forming the insulating material layer 8 on substantially the entire back surface, it is possible to reduce the formation of the reverse conductivity type layer on the back surface side of the semiconductor substrate 1 when forming the reverse conductivity type layer (diffusion layer). In particular, it is preferable to use a CVD method, a coating method, or the like because only the insulating material layer 8 can be formed only on the back surface of the semiconductor substrate 1.

  Moreover, when the 1st electrode 4 (back surface side electrode 4c) is formed on the insulating material layer 8, when the thickness of the insulating material layer 8 is thin by baking at about 500-700 degreeC as baking temperature. In FIG. 2, the problem that the component of the first electrode 4 due to fire-through penetrates the insulating material layer and the first electrode 4 contacts the semiconductor substrate 1 and leaks can be reduced.

  In addition, this invention is not limited to the said embodiment, Many corrections and changes can be added within the scope of the present invention.

  For example, the coating / firing of the first electrode 4 (light-receiving surface side electrode 4a, through-hole electrode 4b, and back surface side electrode 4c) and the second electrode 5 (output extraction electrode 5a and current collecting electrode 5b) is performed as described above. It is not necessary to form the electrodes in the order described in the embodiment. Instead, for example, all the electrodes are formed by applying the conductive pastes to be the electrodes and then baking them together, or collecting the currents. The electrode 5b, the output extraction electrode 5a, the back surface side electrode 4c, and the through-hole electrode 4b may be formed by coating and firing, and then the light receiving surface side electrode 4a may be coated and fired. May be formed.

  Moreover, the electrode shape of the back surface side electrode 4c is not limited to the stripe shape (strip shape) as shown in FIG. 6. Instead of this, for example, in the solar cell element 12 of another embodiment, As shown in FIG. 7A, the back-side electrode 4c may be formed in a point shape (island shape) formed on the through-hole electrode 4b. In this case, as shown in FIG. 7B, an insulating material layer 8 is preferably formed between the point-shaped backside electrodes 4c, and a passivation effect is obtained to obtain the output characteristics of the solar cell element. Can be improved. Moreover, you may form the high concentration doped layer 6 between each point-shaped back surface side electrode 4c.

  Furthermore, hydrogenation treatment may be performed after the insulating material layer 8 is formed. By hydrogenation treatment, hydrogen can be diffused to the grain boundary of the silicon substrate, and passivation can be exhibited at the grain boundary of the substrate. As the hydrogenation treatment, plasma treatment may be performed in a hydrogen atmosphere. Further, an inert gas such as helium or argon may be mixed in a hydrogen atmosphere. The frequency of the power source for generating hydrogen plasma may be radio frequency (RF) or microwave.

Further, as another embodiment, as shown in FIG. 8, the solar cell element 13 includes a high concentration doped layer 6 provided up to the vicinity of the third reverse conductivity type layer 2c, and then a glass paste and a high concentration doped layer 6. The pn separation may be performed by coating and baking at the boundary portion with the third reverse conductivity type layer 2c. Alternatively, the first electrode 4 may be formed on the insulating material layer 8 made of glass as it is.
[Solar Cell Module of Second Embodiment]
A second embodiment of the solar cell module of the present invention will be described. This solar cell module is different from that shown in the first embodiment in that an acid acceptor is contained in the first sealing resin 14 or the second sealing resin 16 that seals the solar cell element 10. Is different. Such an acid acceptor has a role of absorbing or neutralizing an acid. Other configurations are the same as those of the first embodiment.

  In the solar cell module of the present embodiment, EVA is hydrolyzed by moisture that has entered the inside of the solar cell module because the first sealing resin 14 or the second sealing resin 15 contains an acid acceptor. Then, when acetic acid or the like is generated, the acid acceptor can absorb or neutralize acetic acid. For this reason, the output of a solar cell module can be hard to fall, for example also in a high-temperature, high-humidity environment.

  When the first sealing resin 14 that seals the light receiving surface side of the solar cell element contains an acid acceptor, the solar cell characteristics can be improved. That is, in the solar cell element 10 of the present embodiment, the light receiving surface side electrode 4a is formed as thin as possible in order to increase the light receiving area, and the contact area with the semiconductor substrate 1 is small. On the other hand, the light-receiving surface side electrode 4a efficiently collects photogenerated carriers (electron carriers or hole carriers) generated in the solar cell element 10 by making sufficient contact with the first reverse conductivity type layer 2a. be able to. Therefore, in order to improve the reliability of the through-hole solar cell module, it is important to maintain ohmic contact with the first reverse conductivity type layer 2a of the light receiving surface side electrode 4a.

  However, even if a small amount of acetic acid is generated from EVA used for the light-receiving surface side sealing resin 14, the contact area with the first reverse conductivity type layer 2a is small as described above. The ohmic contact property is greatly affected, and the output of each solar cell element 10 is reduced. On the other hand, by containing an acid acceptor in the first sealing resin 14 that seals the light receiving surface side of the solar cell element, the generated acetic acid can be absorbed or neutralized by the action of the acid acceptor. . Accordingly, the ohmic contact property between the light receiving surface side electrode 4a and the first reverse conductivity type layer 2a can be maintained for a long period of time, so that the deterioration of the solar cell characteristics in a high temperature and high humidity environment can be reduced. It is particularly effective to add an acid acceptor to EVA used for the light-receiving surface side sealing resin 14.

  In addition, when the second sealing resin 16 that seals the back surface side of the solar cell element contains an acid acceptor, the acid acceptor is contained on the back surface side where moisture easily enters from the outside of the solar cell module. The characteristic deterioration of the solar cell module can be reduced.

The first resin is made of EVA, for example. In this embodiment, the acid acceptor is, for example, magnesium oxide, calcium oxide, calcium hydroxide, magnesium hydroxide, barium hydroxide, calcium carbonate, barium carbonate, calcium carbonate, calcium borate, zinc oxide, calcium silicate, It consists of basic phosphite. Such an acid acceptor absorbs or neutralizes acetic acid generated by the hydrolysis of EVA. In particular, when magnesium hydroxide (Mg (OH) ₂ ) is used as the acid acceptor, rusting and high resistance of the wiring member 11 inside the solar cell module and the electrode of the solar cell element 10 can be particularly reduced.

  The average particle size of the particles constituting such an acid acceptor is preferably 0.1 μm to 4.0 μm. When the average particle diameter is 0.1 μm or more, the particles are not uniformly dispersed in the EVA, and aggregation of particles forming a cluster can be reduced. In addition, when the average particle size is 4.0 μm or less, it is possible to absorb and neutralize the generated acid, and to disperse the particles uniformly in EVA, and to ensure high transparency. . Therefore, it is difficult to reduce the photoelectric conversion efficiency of the solar cell module without reducing the amount of light reaching the solar cell element 10.

  The particles constituting the acid acceptor are preferably contained in an amount of 0.01 to 0.15 parts by mass with respect to 100 parts by mass of the first sealing resin 14. By making it 0.01 parts by mass or more, the acid generated is easily absorbed or neutralized, and by making it 0.15 parts by mass or less, the transparency is hardly lowered.

  Moreover, in the solar cell module of this embodiment, the through-hole electrode of the solar cell element 10 has a structure in which the area in the opening on the back surface side of the semiconductor substrate is the smallest. In such a structure, when the acid acceptor contained in the first resin 14 is less than the acid acceptor contained in the second resin 16, the characteristics of the solar cell module can be improved. That is, the amount of the acid acceptor contained in the first sealing resin 14 disposed on the light receiving surface side from the solar cell element 10 is greater than that of the second sealing resin 16 disposed on the side where moisture easily enters. The amount of solar light that has advanced into the solar cell module is efficiently incident on the solar cell element, and the solar cell characteristics are less likely to deteriorate due to the ingress of moisture from the back side of the solar module. be able to. In the present embodiment, since the through-hole electrode has a structure in which the area of the opening on the back surface side of the semiconductor substrate is minimum, the solar cell element receives light when no acid acceptor is added to the first sealing resin 14. It is possible to improve efficiency and improve power generation efficiency.

It is sectional drawing which shows the structure of the solar cell element 10 which comprises the solar cell module which is one Embodiment of this invention. It is the top view which looked at the solar cell element 10 from the light-receiving surface side. It is a figure which shows the structure of the solar cell module 20 of this invention. 4 is a cross-sectional view showing another configuration of the solar cell element 11. FIG. FIG. 3 is a process diagram illustrating a method for manufacturing the solar cell element 10. FIG. 3 is a plan view of the semiconductor element 10 as viewed from the back side. It is a figure which shows the electrode shape of the back surface side electrode 4c. It is a fragmentary sectional view which shows the structure of the solar cell element 13 of this invention. It is a figure which shows the structure of the conventional through-hole type solar cell element.

Explanation of symbols

1 Semiconductor substrate 1a Texture structure 2 Reverse conductivity type layer (diffusion layer)
2a 1st reverse conductivity type layer 2b 2nd reverse conductivity type layer 2c 3rd reverse conductivity type layer 3 Through-hole 4 1st electrode 4a Light-receiving surface side electrode 4b Through-hole internal electrode 4c Back surface side electrode 5 2nd electrode 5a Output extraction electrode 5b Current collecting electrode 6 Highly doped layer 7 Antireflection film 8 Insulating material layer 10, 11, 12, 13 Solar cell element 20 Solar cell module

Claims (9)

A semiconductor substrate including a light receiving surface and a back surface, the semiconductor substrate having a through hole penetrating between the light receiving surface and the back surface, and the cross-sectional area of the through hole is provided in the through hole of the semiconductor substrate A solar cell element having a through electrode that is the smallest in the opening on the back side of the semiconductor substrate
A first resin that seals the light receiving surface of the solar cell element;
A second resin that seals the back surface of the solar cell element;
A solar cell module. The ratio (S2 / S1) of the cross-sectional area S2 in the back surface opening portion to the cross-sectional area S1 in the light receiving surface opening portion of the through hole is 0.5 ≦ (S2 / S1) ≦ 0.9. The solar cell module according to claim 1. The solar cell module according to claim 1, wherein the first resin includes an acid acceptor. The solar cell module according to claim 3, wherein the first resin is an ethylene-vinyl acetate copolymer, and the acid acceptor is magnesium hydroxide. The solar cell module according to claim 1, wherein the second resin includes an acid acceptor. The solar cell module according to claim 5, wherein the second resin is an ethylene-vinyl acetate copolymer, and the acid acceptor is magnesium hydroxide. The first resin and the second resin contain an acid acceptor, and the amount of the acid acceptor contained in the first resin is less than the acid acceptor contained in the second resin. The solar cell module according to claim 1 or 2, characterized by the above. The said back surface side of the said solar cell element has an extraction electrode which is electrically connected to the said penetration electrode and takes out the electric power which the said solar cell element generate | occur | produced, Solar cell module. Electrically connected to the through electrode, and having a back electrode formed on the back side of the solar cell element;
The solar cell module according to claim 8, wherein the extraction electrode is partially connected to the back electrode.

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