WO2010150358A1

WO2010150358A1 - Photoelectromotive device, and method for manufacturing the same

Info

Publication number: WO2010150358A1
Application number: PCT/JP2009/061425
Authority: WO
Inventors: 濱本　哲; 隆石原
Original assignee: 三菱電機株式会社
Priority date: 2009-06-23
Filing date: 2009-06-23
Publication date: 2010-12-29
Also published as: TW201104898A; WO2010150606A1

Abstract

Disclosed is a photoelectromotive device comprising a semiconductor substrate (1) of a first conduction type having such an impurity-diffused layer (3) on one face side as has an impurity element of a second conduction type diffused, a reflection preventing film (4) formed over the impurity-diffused layer, first electrodes (5) connected electrically with the impurity-diffused layer (3) through the reflection preventing film (4), a back insulating film (8) so formed on the other face side of the semiconductor substrate (1) as has a plurality of openings (8a) to reach the other face side of the semiconductor substrate (1), second electrodes (9) buried in at least the openings (8a) and connected electrically with the other face side of the semiconductor substrate (1), and a back reflecting film (10) either made of a metal film formed by a vapor-phase growth method or constituted to include a metal foil, and formed to cover at least the back insulating film (8).

Description

Photovoltaic device and manufacturing method thereof

The present invention relates to a photovoltaic device and a manufacturing method thereof.

In recent photovoltaic devices, materials and manufacturing processes have been improved for higher output. For this reason, in order to further increase the output, the wavelength that has not been fully utilized before can be achieved by confining light in the photovoltaic device and suppressing the recombination speed of carriers on the front and back surfaces. It is important to realize structures and manufacturing methods that contribute to the generation of light in the region. Therefore, it is very important to improve the back surface structure of the substrate that plays the role.

Therefore, with the aim of suppressing reflection on the back side of the substrate and recombination rate on the back side of the substrate, for example, there is a technique for forming a film that suppresses the recombination rate after locally printing and baking the back electrode. Has been proposed (see, for example, Patent Document 1). In addition, for example, after forming a film that suppresses the recombination rate on the back surface of the substrate, a technique is proposed in which an opening is provided in a part of the substrate, and a back electrode paste is printed and fired on the entire surface. (For example, refer to Patent Document 2).

JP-A-6-169096 JP 2002-246625 A

However, in the method of Patent Document 1, a film that suppresses the recombination rate is formed after the back electrode is printed and baked. In this case, especially during firing, the attachment and fixation of contaminants proceeds on the back surface of the substrate, and therefore it is extremely difficult to keep the carrier recombination rate on the back surface of the substrate low as intended. There is.

Further, in the method of Patent Document 2, an electrode paste is printed so as to cover almost the entire surface of the film that suppresses the recombination speed to form a back electrode that also functions as a light reflection function. This contact is partially made. However, when the back electrode is made of, for example, a paste containing aluminum (Al), which is a typical material, the light reflectivity on the back surface cannot be increased, and sufficient photovoltaic power can be introduced into the photovoltaic device. There is a problem that the optical confinement effect cannot be obtained. Further, when the back electrode is made of, for example, a paste containing silver (Ag), which is a typical material, a film that suppresses the recombination rate even in a region other than the original contact portion during the electrode firing process. Is eroded by fire-through, and there is a problem that a sufficient effect of suppressing the recombination rate of carriers cannot be obtained.

The present invention has been made in view of the above, and an object of the present invention is to obtain a photovoltaic device having a low recombination speed and a high back surface reflectance and excellent photoelectric conversion efficiency and a method for manufacturing the photovoltaic device.

In order to solve the above-described problems and achieve the object, a photovoltaic device according to the present invention includes a first conductivity type semiconductor substrate having an impurity diffusion layer in which a second conductivity type impurity element is diffused on one side. An antireflection film formed on the impurity diffusion layer, a first electrode that penetrates the antireflection film and is electrically connected to the impurity diffusion layer, and a plurality of layers reaching the other surface side of the semiconductor substrate A back surface insulating film formed on the other surface side of the semiconductor substrate with an opening; a second electrode embedded in at least the opening and electrically connected to the other surface side of the semiconductor substrate; It comprises a metal film formed by a growth method or includes a metal foil, and includes a back surface reflection film formed to cover at least the back surface insulating film.

According to the present invention, a back surface structure having both a low recombination speed and a high back surface reflectance can be realized, and a solar cell having excellent long wavelength sensitivity and high photoelectric conversion efficiency can be obtained. There is an effect that it is possible.

FIG. 1-1 is a cross-sectional view of relevant parts for explaining the cross-sectional structure of the solar battery cell according to the first embodiment of the present invention. FIG. 1-2 is a top view of the solar cell according to the first embodiment of the present invention as viewed from the light receiving surface side. FIG. 1-3 is a bottom view of the solar battery cell according to the first embodiment of the present invention as viewed from the back surface side. FIG. 2 is a characteristic diagram showing the reflectance on the back surface of the semiconductor substrate in three types of samples having different back surface structures. FIG. 3 is a characteristic diagram showing the relationship between the area ratio of the back electrode and the open circuit voltage (Voc) in the sample manufactured by simulating the solar battery cell according to the first embodiment. FIG. 4 is a characteristic diagram showing the relationship between the area ratio of the back electrode and the short-circuit current (Jsc) in the sample manufactured by simulating the solar battery cell according to the first embodiment. FIGS. 5-1 is sectional drawing for demonstrating the manufacturing process of the photovoltaic cell concerning Embodiment 1 of this invention. FIGS. FIGS. 5-2 is sectional drawing for demonstrating the manufacturing process of the photovoltaic cell concerning Embodiment 1 of this invention. FIGS. FIGS. 5-3 is sectional drawing for demonstrating the manufacturing process of the photovoltaic cell concerning Embodiment 1 of this invention. FIGS. FIGS. 5-4 is sectional drawing for demonstrating the manufacturing process of the photovoltaic cell concerning Embodiment 1 of this invention. FIGS. FIGS. 5-5 is sectional drawing for demonstrating the manufacturing process of the photovoltaic cell concerning Embodiment 1 of this invention. FIGS. FIGS. 5-6 is sectional drawing for demonstrating the manufacturing process of the photovoltaic cell concerning Embodiment 1 of this invention. FIGS. FIGS. 5-7 is sectional drawing for demonstrating the manufacturing process of the photovoltaic cell concerning Embodiment 1 of this invention. FIGS. FIGS. 5-8 is sectional drawing for demonstrating the manufacturing process of the photovoltaic cell concerning Embodiment 1 of this invention. FIGS. FIGS. 5-9 is sectional drawing for demonstrating the manufacturing process of the photovoltaic cell concerning Embodiment 1 of this invention. FIGS. FIG. 6-1 is a plan view showing an example of a printed region of the back surface side electrode material paste on the back surface insulating film of the solar battery cell according to the first embodiment of the present invention. FIG. 6-2 is a plan view showing an example of a printed region of the back surface side electrode material paste on the back surface insulating film of the solar battery cell according to the first embodiment of the present invention. FIG. 7: is principal part sectional drawing for demonstrating the cross-section of the photovoltaic cell concerning Embodiment 2 of this invention.

Hereinafter, embodiments of the photovoltaic device and the manufacturing method thereof according to the present invention will be described in detail with reference to the drawings. In addition, this invention is not limited by the following description, In the range which does not deviate from the summary of this invention, it can change suitably. In the drawings shown below, the scale of each member may be different from the actual scale for easy understanding. The same applies between the drawings.

Embodiment 1 FIG.
FIGS. 1-1 to 1-3 are diagrams showing a configuration of a solar battery cell that is a photovoltaic device according to the present embodiment, and FIG. 1-1 is for explaining a cross-sectional structure of the solar battery cell. FIG. 1-2 is a top view of the solar cell viewed from the light receiving surface side, and FIG. 1-3 is a bottom view of the solar cell viewed from the side opposite to the light receiving surface (back side). FIG. 1-1 is a cross-sectional view of an essential part taken along line AA in FIG. 1-2.

As shown in FIGS. 1-1 to 1-3, the solar cell according to the present embodiment includes a solar cell substrate having a photoelectric conversion function and having a pn junction, An antireflection film 4 made of a silicon nitride film (SiN film) which is an insulating film formed on the light receiving surface side (surface) and prevents reflection of incident light on the light receiving surface, and a light receiving surface side of the semiconductor substrate 1 On the surface (front surface), the light receiving surface side electrode 5 that is the first electrode formed surrounded by the antireflection film 4 and the silicon nitride film (back surface) opposite to the light receiving surface of the semiconductor substrate 1 (back surface) A back insulating film 8 made of SiN film, a back electrode 9 as a second electrode formed on the back surface of the semiconductor substrate 1 and surrounded by the back insulating film 8, and a back insulating film 8 on the back surface of the semiconductor substrate 1. Back surface reflection film 1 provided to cover back surface side electrode 9 And, equipped with a.

The semiconductor substrate 1 includes a p-type polycrystalline silicon substrate 2 which is a first conductivity type layer, and an impurity diffusion layer (n-type impurity diffusion) which is a second conductivity type layer formed by phosphorous diffusion on the light receiving surface side of the semiconductor substrate 1. The layer) 3 constitutes a pn junction. The n-type impurity diffusion layer 3 has a surface sheet resistance of 30 to 100Ω / □.

The light-receiving surface side electrode 5 includes a grid electrode 6 and a bus electrode 7 of the solar battery cell, and is electrically connected to the n-type impurity diffusion layer 3. The grid electrode 6 is locally provided on the light receiving surface to collect electricity generated by the semiconductor substrate 1. The bus electrode 7 is provided substantially orthogonal to the grid electrode 6 in order to take out the electricity collected by the grid electrode 6.

On the other hand, a part of the back surface side electrode 9 is embedded in the back surface insulating film 8 provided over the entire back surface of the semiconductor substrate 1. That is, the back insulating film 8 is provided with a substantially circular dot-shaped opening 8 a that reaches the back surface of the semiconductor substrate 1. A back-side electrode 9 made of an electrode material containing aluminum, glass, or the like is provided so as to fill the opening 8a and to have an outer shape wider than the diameter of the opening 8a in the in-plane direction of the back insulating film 8. Yes.

The back insulating film 8 is made of a silicon nitride film (SiN film), and is formed on almost the entire back surface of the semiconductor substrate 1 by a plasma CVD (Chemical Vapor Deposition) method. By using a silicon nitride film (SiN film) formed by the plasma CVD method as the back surface insulating film 8, it is possible to obtain a favorable carrier recombination rate suppressing effect on the back surface of the semiconductor substrate 1.

The back surface reflection film 10 is provided on the back surface of the semiconductor substrate 1 so as to cover the back surface side electrode 9 and the back surface insulating film 8. By providing the back surface reflecting film 10 covering the back surface insulating film 8, the light transmitted through the semiconductor substrate 1 and the back surface insulating film 8 can be reflected and returned to the semiconductor substrate 1, and a good light confinement effect can be obtained. it can. And in this Embodiment, the back surface reflecting film 10 is comprised by the silver (Ag) film | membrane (silver sputtering film) formed by the sputtering method which is a metal film formed by a vapor phase growth method. Since the back surface reflecting film 10 is not a film formed by a printing method using an electrode paste but is formed by a sputtering film, it realizes higher light reflection than a silver (Ag) film formed by the printing method. Thus, more light transmitted through the semiconductor substrate 1 and the back surface insulating film 8 can be reflected back to the semiconductor substrate 1. Therefore, the solar battery cell according to the present embodiment can obtain an excellent light confinement effect by including the back surface reflection film 10 formed of a silver sputtering film.

As the material of the back surface reflection film 10, for example, it is preferable to use a metal material having a reflectance of 90% or more, preferably 95% or more with respect to light having a wavelength near 1100 nm. Thereby, a solar cell having high long wavelength sensitivity and excellent light confinement effect for light in the long wavelength region can be realized. That is, although depending on the thickness of the semiconductor substrate 1, light having a long wavelength of 900 nm or more, particularly about 1000 nm to 1100 nm, can be efficiently taken into the semiconductor substrate 1 and a high generated current (Jsc) can be realized. Characteristics can be improved. As such a material, for example, aluminum (Al) can be used in addition to silver (Ag).

In the solar battery cell according to the present embodiment, as described above, the fine back surface side electrode 9 is formed on the back surface of the semiconductor substrate 1, and the back surface reflection film 10 is formed thereon. For this reason, although the back surface reflecting film 10 shown in FIG. 1C actually has fine unevenness due to the back side electrode 9, the description of the fine unevenness is omitted in FIG. ing.

In addition, an aluminum-silicon (Al—Si) alloy portion 11 is formed in a region on the back surface side of the semiconductor substrate 1 and in the vicinity of the region in contact with the back electrode 9. Further, on the outer periphery thereof, the BSF (Back
Surface Filed layer) 12 is formed.

In the solar cell configured as described above, sunlight is applied from the light receiving surface side of the solar cell to the pn junction surface of the semiconductor substrate 1 (the junction surface between the p-type polycrystalline silicon substrate 2 and the n-type impurity diffusion layer 3). When irradiated, holes and electrons are generated. Due to the electric field at the pn junction, the generated electrons move toward the n-type impurity diffusion layer 3, and the holes move toward the p-type polycrystalline silicon substrate 2. As a result, the number of electrons in the n-type impurity diffusion layer 3 becomes excessive, and the number of holes in the p-type polycrystalline silicon substrate 2 becomes excessive. As a result, a photovoltaic force is generated. This photovoltaic power is generated in the direction of biasing the pn junction in the forward direction, the light receiving surface side electrode 5 connected to the n-type impurity diffusion layer 3 becomes a negative electrode, and the back surface side electrode 9 connected to the p-type polycrystalline silicon substrate 2. Becomes a positive pole, and current flows in an external circuit (not shown).

FIG. 2 is a characteristic diagram showing the reflectance on the back surface of the semiconductor substrate in three types of samples having different back surface structures. FIG. 2 shows the relationship between the wavelength of light incident on the sample and the reflectance. Each sample is produced by imitating a solar battery cell, and the basic structure other than the back surface structure is the same as that of the solar battery cell according to this embodiment. The details of the back surface structure of each sample are as follows.

(Sample A)
An aluminum (Al) paste electrode formed from an electrode paste containing aluminum (Al) is provided over the entire back surface of the semiconductor substrate (corresponding to a conventional general structure).
(Sample B)
A back insulating film made of a silicon nitride film (SiN) is formed over the entire back surface of the semiconductor substrate, and an aluminum (Al) paste electrode formed from an electrode paste containing aluminum (Al) is provided over the entire back insulating film (preceding) Technology (equivalent to Patent Document 2)).
(Sample C)
A back insulating film made of a silicon nitride film (SiN) is formed over the entire back surface of the semiconductor substrate, and an aluminum (Al) paste electrode formed from an electrode paste containing aluminum (Al) is locally provided on the back surface of the semiconductor substrate. Further, a high reflection film made of a silver sputtering film is provided on the entire surface of the back insulating film (corresponding to the solar battery cell according to the present embodiment).

Since each sample is different only in the back surface structure and the other structure is the same, the difference in reflectance between “silicon (semiconductor substrate) -back surface structure” can be confirmed from FIG. In order to see the state of back surface reflection, it is preferable to compare the vicinity of a wavelength of 1200 nm where there is almost no absorption in silicon. This is because the wavelength of 1100 nm or less is absorbed in silicon and has already contributed to power generation, and is not suitable for comparison of back surface reflection. Note that the reflectance shown in FIG. 2 is a component that leaks to the surface of the semiconductor substrate again as a result of multiple reflection on the back surface.

As can be seen from FIG. 2, the sample B corresponding to the prior art (Patent Document 2) has a slight improvement in reflectance as compared with the sample A corresponding to the conventional general structure, but the effect of improving the reflectance is sufficient. It can not be said. On the other hand, Sample C corresponding to the solar battery cell according to the present embodiment has a higher reflectance than Sample A and Sample B, and a high reflectance between “silicon (semiconductor substrate) and back surface structure” is recognized. Thus, it can be seen that it is suitable for high efficiency based on the light confinement action on the back surface.

FIG. 3 shows the area ratio of the back electrode (ratio occupied by the back electrode on the back surface of the semiconductor substrate) and the open-circuit voltage (Voc) in the sample manufactured by simulating the solar battery cell according to the present embodiment in the same manner as the sample C described above. FIG. Further, FIG. 4 shows the area ratio of the back electrode (ratio occupied by the back electrode on the back surface of the semiconductor substrate) and the short-circuit current in the sample manufactured by imitating the solar battery cell according to the present embodiment in the same manner as the sample C described above. It is the characteristic view which showed the relationship with (Jsc).

As can be seen from FIGS. 3 and 4, the open circuit voltage (Voc) increases as the area ratio of the aluminum (Al) paste electrode as the back electrode decreases, that is, as the area ratio of the highly reflective film according to the present embodiment increases. ) And the short-circuit current (Jsc) are improved, and it is recognized that a good effect of suppressing the recombination rate of carriers is obtained on the back surface of the semiconductor substrate. Thereby, by the structure of the solar cell according to the present embodiment, it is possible to achieve both the back surface reflection improvement and the suppression of the carrier recombination rate on the back surface of the semiconductor substrate, and the area ratio of the highly reflective film according to the present embodiment. It can be seen that the above effect can be obtained more remarkably as the value is increased.

In the solar cell according to the first embodiment configured as described above, by providing a silicon nitride film (SiN film) formed by plasma CVD on the back surface of the semiconductor substrate 1 as the back surface insulating film 8, A good effect of suppressing the recombination rate of carriers on the back surface of the semiconductor substrate 1 can be obtained. Thereby, in the photovoltaic cell concerning this Embodiment, the improvement of an output characteristic is achieved and the high photoelectric conversion efficiency is implement | achieved.

In the solar cell according to the first embodiment, the back surface reflection film 10 made of a silver sputtering film is provided so as to cover the back surface insulating film 8, thereby making it more than a silver (Ag) film formed by a conventional printing method. High light reflection can be realized, and more light transmitted through the semiconductor substrate 1 and the back surface insulating film 8 can be reflected back to the semiconductor substrate 1. Therefore, in the solar cell according to the present embodiment, an excellent light confinement effect can be obtained, the output characteristics can be improved, and high photoelectric conversion efficiency is realized.

Therefore, in the solar cell according to the first embodiment, by having the structure of the back surface having both the low recombination speed and the high back surface reflectance, the long-wavelength sensitivity is excellent and the photoelectric conversion efficiency is improved. The obtained solar battery cell is realized.

Next, an example of a method for manufacturing such a solar battery cell will be described with reference to FIGS. 5-1 to 5-9. FIGS. 5-1 to 5-9 are cross-sectional views for explaining the manufacturing process of the solar battery cell according to the present embodiment.

First, as the semiconductor substrate 1, for example, a p-type polycrystalline silicon substrate that is most frequently used for consumer solar cells is prepared (hereinafter referred to as a p-type polycrystalline silicon substrate 1a) (FIG. 5-1). As the p-type polycrystalline silicon substrate 1a, for example, a polycrystalline silicon substrate having an electrical resistance of about 0.5 to 3 Ωcm containing a group III element such as boron (B) is used.

Since the p-type polycrystalline silicon substrate 1a is manufactured by slicing an ingot formed by cooling and solidifying molten silicon with a wire saw, damage at the time of slicing remains on the surface. Therefore, the p-type polycrystalline silicon substrate 1a is first removed by immersing the surface of the p-type polycrystalline silicon substrate 1a in an acid or a heated alkaline solution, for example, in an aqueous solution of sodium hydroxide so as to remove the damaged layer. Thus, the damaged region existing near the surface of the p-type polycrystalline silicon substrate 1a is removed. The thickness of the p-type polycrystalline silicon substrate 1a after the damage removal is, for example, 200 μm, and the dimension is, for example, 150 mm × 150 mm.

Also, at the same time as the removal of damage or subsequent to the removal of damage, fine irregularities may be formed as a texture structure on the surface of the p-type polycrystalline silicon substrate 1a on the light receiving surface side. By forming such a texture structure on the light receiving surface side of the semiconductor substrate 1, multiple reflection of light is caused on the surface of the solar battery cell, and light incident on the solar battery cell is efficiently transmitted to the p-type polycrystalline silicon substrate. 1a can be absorbed, and the reflectance can be effectively reduced and the conversion efficiency can be improved.

In addition, since this invention is invention concerning the back surface structure of a photovoltaic apparatus, it does not restrict | limit in particular about the formation method and shape of a texture structure. For example, an alkaline aqueous solution containing isopropyl alcohol, a method using acid etching mainly composed of a mixed solution of hydrofluoric acid and nitric acid, or a mask material partially provided with an opening is formed on the surface of the p-type polycrystalline silicon substrate 1a. A method of obtaining a honeycomb structure or an inverted pyramid structure on the surface of the p-type polycrystalline silicon substrate 1a by etching through the mask material, or reactive gas etching (RIE)
Any method such as a method using Ion Etching may be used.

Next, this p-type polycrystalline silicon substrate 1a is put into a thermal oxidation furnace and heated in an atmosphere of phosphorus (P) which is an n-type impurity. Through this step, phosphorus (P) is diffused on the surface of the p-type polycrystalline silicon substrate 1a to form an n-type impurity diffusion layer 3 to form a semiconductor pn junction (FIG. 5-2). In the present embodiment, the n-type impurity diffusion layer 3 is formed by heating the p-type polycrystalline silicon substrate 1a in a phosphorus oxychloride (POCl ₃ ) gas atmosphere at a temperature of, for example, 800 ° C. to 850 ° C. Here, the heat treatment is controlled so that the surface sheet resistance of the n-type impurity diffusion layer 3 is, for example, 30 to 80Ω / □, preferably 40 to 60Ω / □.

Here, since a phosphorus glass layer mainly composed of glass is formed on the surface immediately after the formation of the n-type impurity diffusion layer 3, it is removed using a hydrofluoric acid solution or the like.

Next, a silicon nitride film (SiN film) is formed as the antireflection film 4 on the light receiving surface side of the p-type polycrystalline silicon substrate 1a on which the n-type impurity diffusion layer 3 is formed in order to improve the photoelectric conversion efficiency (FIG. 5-3). For the formation of the antireflection film 4, for example, a plasma CVD method is used, and a silicon nitride film is formed as the antireflection film 4 using a mixed gas of silane and ammonia. The film thickness and refractive index of the antireflection film 4 are set to values that most suppress light reflection. Note that two or more films having different refractive indexes may be laminated as the antireflection film 4. Further, a different film forming method such as a sputtering method may be used for forming the antireflection film 4. Further, a silicon oxide film may be formed as the antireflection film 4.

Next, the n-type impurity diffusion layer 3 formed on the back surface of the p-type polycrystalline silicon substrate 1a is removed by diffusion of phosphorus (P). Thus, the p-type polycrystalline silicon substrate 2 as the first conductivity type layer, the impurity diffusion layer (n-type impurity diffusion layer) 3 as the second conductivity type layer formed on the light receiving surface side of the semiconductor substrate 1, Thus, the semiconductor substrate 1 having a pn junction is obtained (FIG. 5-4).

The removal of the n-type impurity diffusion layer 3 formed on the back surface of the p-type polycrystalline silicon substrate 1a is performed using, for example, a single-sided etching apparatus. Alternatively, a method of using the antireflection film 4 as a mask material and immersing the entire p-type polycrystalline silicon substrate 1a in an etching solution may be used. As the etching solution, an alkaline aqueous solution such as sodium hydroxide or potassium hydroxide heated to room temperature to 95 ° C., preferably 50 ° C. to 70 ° C. is used. Alternatively, a mixed aqueous solution of nitric acid and hydrofluoric acid may be used as the etching solution.

After the etching for removing the n-type impurity diffusion layer 3, the silicon surface exposed on the back surface of the semiconductor substrate 1 is washed in order to keep the recombination rate low in film formation described later. The cleaning is performed using, for example, RCA cleaning or a 1% to 20% hydrofluoric acid aqueous solution.

Next, a back surface insulating film 8 made of a silicon nitride film (SiN film) is formed on the back surface side of the semiconductor substrate 1 (FIG. 5-5). A back insulating film 8 made of a silicon nitride film (SiN film) having a refractive index of 1.9 to 2.2 and a thickness of 60 nm to 300 nm is formed on the silicon surface exposed on the back side of the semiconductor substrate 1 by plasma CVD. Film. By using plasma CVD, the back surface insulating film 8 made of a silicon nitride film can be reliably formed on the back surface side of the semiconductor substrate 1. By forming such a back surface insulating film 8, the recombination rate of carriers on the back surface of the semiconductor substrate 1 can be suppressed, and silicon (Si) and silicon nitride film (SiN film) on the back surface of the semiconductor substrate 1 can be suppressed. ), A recombination velocity of 100 cm / sec or less is obtained. Thereby, it is possible to realize a sufficient back surface interface for high output.

If the refractive index of the back surface insulating film 8 deviates from 1.9 to 2.2, it is difficult to stabilize the deposition environment of the silicon nitride film (SiN film), and the film quality of the silicon nitride film (SiN film) deteriorates. As a result, the recombination rate at the interface with silicon (Si) also deteriorates. On the other hand, when the thickness of the back insulating film 8 is smaller than 60 nm, the interface with silicon (Si) is not stable, and the carrier recombination rate is deteriorated. When the thickness of the back insulating film 8 is larger than 300 nm, there is no functional inconvenience, but it takes time to form a film and increases costs, which is not preferable from the viewpoint of productivity.

The back insulating film 8 may have a two-layer structure in which a silicon oxide film (silicon thermal oxide film: SiO ₂ film) formed by thermal oxidation and a silicon nitride film (SiN film) are stacked, for example. The silicon oxide film (SiO ₂ film) here is not a natural oxide film formed on the back side of the semiconductor substrate 1 during the process, but a silicon oxide film (SiO ₂ film) intentionally formed by thermal oxidation, for example. To do. By using such a silicon oxide film (SiO ₂ film), the effect of suppressing the recombination rate of carriers on the back surface of the semiconductor substrate 1 can be obtained more stably than the silicon nitride film (SiN film).

The thickness of the silicon oxide film (SiO ₂ film) intentionally formed by thermal oxidation is preferably about 10 nm to 50 nm. When the thickness of the silicon oxide film (SiO ₂ film) formed by thermal oxidation is less than 10 nm, the interface with silicon (Si) is not stable, and the recombination rate of carriers deteriorates. When the thickness of the silicon oxide film (SiO ₂ film) formed by thermal oxidation is larger than 50 nm, there is no functional inconvenience, but the film formation takes time and the cost increases. It is not preferable from the viewpoint. In addition, when the film formation process is performed at a high temperature in order to shorten the time, the quality of the crystalline silicon itself is lowered, leading to a reduction in lifetime.

Thereafter, in order to make contact with the back surface side of the semiconductor substrate 1, dot-shaped openings 8a having a predetermined interval are formed on a part or the entire surface of the back insulating film 8 (FIGS. 5-6). The opening 8a is formed by performing direct patterning, for example, by laser irradiation on the back surface insulating film 8.

In order to form a good contact with the back side of the semiconductor substrate 1, the cross-sectional area of the opening 8 a in the in-plane direction of the back insulating film 8 is increased, and the opening of the opening 8 a in the plane of the back insulating film 8. It is preferable to increase the density. However, in order to obtain a high light reflectance (back surface reflectance) on the back surface side of the semiconductor substrate 1, it is preferable that the cross-sectional area of the opening 8a is small and the opening density of the opening 8a is low. Therefore, it is preferable that the shape and density of the opening 8a be kept to a minimum level necessary for realizing a good contact.

Specifically, the shape of the opening 8a has a diameter or width of 20 μm to 200 μm, and a substantially circular dot shape or a substantially rectangular shape with an interval between adjacent opening portions 8a of 0.5 mm to 2 mm. Is mentioned. As other shapes of the opening 8a, a stripe shape having a width of 20 μm to 200 μm and a distance between adjacent openings 8a of 0.5 mm to 3 mm can be cited. In the present embodiment, dot-shaped openings 8 a are formed by laser irradiation on the back surface insulating film 8.

Next, a back-side electrode material paste 9a containing aluminum, glass, or the like, which is an electrode material for the back-side electrode 9, fills the opening 8a and is slightly larger than the diameter of the opening 8a in the in-plane direction of the back-side insulating film 8. It is applied in a limited manner by screen printing so as not to come into contact with the back-side electrode material paste 9a covering a wide area and filling the adjacent opening 8a (FIGS. 5-7). The application shape, application amount, and the like of the back-side electrode material paste 9a can be changed according to various conditions such as the diffusion concentration of aluminum in the Al—Si alloy part 11 and the BSF 12 in the firing step described later.

It is necessary to secure a sufficient amount of paste in the opening 8a and to surely form the Al—Si alloy part 11 and the BSF layer 12 in the firing step. On the other hand, the light reflectance (back surface reflectance) by the back surface side electrode 9 in the region where the back surface insulating film 8 (silicon nitride film) and the back surface side electrode 9 are laminated on the back surface of the semiconductor substrate 1 is not sufficient. For this reason, when the formation area of the back surface side electrode 9 on the back surface insulating film 8 becomes wide, the light confinement effect in the photovoltaic device is lowered. Therefore, the area where the back side electrode material paste 9a is printed is limited to the minimum necessary after balancing the formation conditions of the Al—Si alloy part 11 and the BSF 12 and the light confinement effect in the photovoltaic device. There is a need.

In this embodiment, printing is performed with a thickness of 20 μm in such a manner that aluminum (Al) -containing back-side electrode material paste 9a is overlapped on the back-side insulating film 8 by a width of 20 μm from the end of the opening 8a. In this case, by overlapping the back surface insulating film 8, there is an effect that the back surface electrode 9 to be formed is prevented from peeling off at the opening 8 a portion of the back surface insulating film 8. FIGS. 6A and 6B are plan views showing an example of the printing region of the back surface side electrode material paste 9a on the back surface insulating film 8. FIGS. FIG. 6A shows an example in which the opening 8a has a substantially circular dot shape, and FIG. 6B shows an example in which the opening 8a has a substantially rectangular shape.

Overlap amount is, 1000 .mu.m ² from 200 [mu] m ² in sectional area from the end of the opening 8a, preferably it is desirable to control in the range of 400 [mu] m ² of 1000 .mu.m ^2. In the present embodiment, since the paste thickness of the back side electrode material paste 9a containing aluminum (Al) is 20 μm, in terms of the width of the overlap, 10 μm to 50 μm, preferably 20 μm from the end of the opening 8a. It corresponds to the range of 50 μm. If the overlap width is less than 10 μm, the effect of preventing the peeling of the back surface insulating film 8 will not be exhibited, but the supply of aluminum (Al) will not be successful at the time of firing, that is, when the alloy is formed, and the BSF structure will not be formed well. Part occurs. On the other hand, if the overlap width is larger than 50 μm, the area ratio occupied by the paste printing portion increases, that is, the area ratio of the high reflection film decreases, and the deviation from the intention of the present invention becomes large.

As shown in FIG. 6A, when the opening 8a has a substantially circular dot shape, the outer periphery of the opening 8a on the back insulating film 8 includes a ring-shaped overlap region 9b having a width of 20 μm. The back electrode material paste 9a is applied in a circular shape on the back insulating film 8 in a limited manner by screen printing. For example, when the diameter d of the opening 8a is 200 μm, the back surface side electrode material paste 9a is printed in a substantially circular shape having a diameter of “200 μm + 20 μm + 20 μm = 240 μm”.

Further, when the opening 8a has a substantially rectangular shape as shown in FIG. 6B, a frame-shaped overlap region 9b having a width of 20 μm is provided on the outer periphery of the opening 8a on the back surface insulating film 8, The back surface side electrode material paste 9a is limitedly applied on the back surface insulating film 8 by screen printing. For example, when the width w of the opening 8a is 100 μm, the back surface side electrode material paste 9a is printed in a substantially rectangular shape having a width of “100 μm + 20 μm + 20 μm = 140 μm”.

Next, on the antireflection film 4 of the semiconductor substrate 1, a light receiving surface electrode material paste 5 a which is an electrode material of the light receiving surface side electrode 5 and contains silver (Ag), glass or the like is formed into the shape of the light receiving surface side electrode 5. Selectively apply by screen printing and dry (Figure 5-7). The light-receiving surface electrode material paste 5a is, for example, a pattern of elongated grid electrodes 6 having a width of 80 μm to 150 μm and a spacing of 2 mm to 3 mm, and a strip shape having a width of 1 mm to 3 mm and a spacing of 5 mm to 10 mm in a direction substantially perpendicular to the pattern. The pattern of the bus electrode 7 is printed. However, since the shape of the light receiving surface side electrode 5 is not directly related to the present invention, it may be freely set while balancing between the electrode resistance and the printing light shielding rate.

Thereafter, firing is performed at a peak temperature of 760 ° C. to 900 ° C. using, for example, an infrared furnace heater. Thus, the light receiving surface side electrode 5 and the back surface side electrode 9 are formed, and the Al—Si alloy portion 11 is formed in the region on the back surface side of the semiconductor substrate 1 and in contact with the back surface side electrode 9 and its vicinity. Is done. Further, a BSF 12 that is a p + region in which aluminum is diffused in a high concentration from the back surface side electrode 9 is formed on the outer periphery of the Al—Si alloy portion 11, and the BSF layer 12 and the back surface side electrode 9 are electrically connected to each other. Connection (Figure 5-8). Note that the recombination speed at the interface deteriorates at this connection point, but the BSF layer 12 can negate this effect. Further, the silver in the light receiving surface side electrode 5 penetrates the antireflection film 4, and the n-type impurity diffusion layer 3 and the light receiving surface side electrode 5 are electrically connected.

At this time, since the region where the back surface side electrode material paste 9a is not applied on the back surface of the semiconductor substrate 1 is protected by the back surface insulating film 8 made of a silicon nitride film (SiN film), the semiconductor substrate 1 is also subjected to heating by baking. The adherence and fixation of contaminants do not proceed with respect to the back surface, and a good state is maintained without degrading the recombination speed.

Next, a highly reflective structure is formed on the back side of the semiconductor substrate 1. That is, a silver (Ag) film (silver sputtering film) is formed on the entire back surface of the semiconductor substrate 1 by a sputtering method so as to cover the back electrode 9 and the back insulating film 8 (FIG. 5-9). ). By forming the back surface reflection film 10 by a sputtering method, a dense back surface reflection film 10 can be formed, and the back surface reflection film 10 that realizes higher light reflection than a silver (Ag) film formed by a printing method is formed. can do. In addition, you may form the back surface reflecting film 10 by a vapor deposition method. Here, although the back surface reflection film 10 is formed on the entire back surface of the semiconductor substrate 1, the back surface reflection film 10 may be formed so as to cover at least the back surface insulating film 8 on the back surface side of the semiconductor substrate 1. .

Thus, the solar battery cell according to Embodiment 1 shown in FIGS. 1-1 to 1-3 is manufactured. Note that the order of application of the paste as the electrode material may be switched between the light receiving surface side and the back surface side.

As described above, in the method for manufacturing the solar cell according to the first embodiment, after forming the back surface insulating film 8 having the opening 8a on the back surface of the semiconductor substrate 1, the back surface side electrode material paste 9a is applied and fired. Therefore, the region where the back surface side electrode material paste 9a is not applied is protected by the back surface insulating film 8. Thereby, even in the heating by baking, adherence and fixation of the contaminant do not proceed to the back surface of the semiconductor substrate 1, and a good state is maintained without deteriorating the recombination speed, and the photoelectric conversion efficiency is improved.

Further, in the method for manufacturing the solar cell according to the first embodiment, the back surface reflecting film 10 is formed on the back surface of the semiconductor substrate 1 so as to cover at least the back surface insulating film 8. Thereby, the light transmitted through the semiconductor substrate 1 and the back surface insulating film 8 can be reflected by the back surface reflective film 10 and returned to the semiconductor substrate 1, and a good light confinement effect can be obtained. Thus, high photoelectric conversion efficiency can be realized.

Further, in the method for manufacturing the solar battery cell according to the first embodiment, the back surface reflecting film 10 is formed by a sputtering method. A dense back surface reflecting film 10 can be formed by forming the back surface reflecting film 10 by a sputtering film, not by a printing method using an electrode paste, and realizes higher light reflection than a film formed by the printing method. The back reflective film 10 can be formed, and an excellent light confinement effect can be obtained.

Therefore, according to the manufacturing method of the solar cell according to the first embodiment, it is possible to obtain a back surface structure having both a low recombination speed and a high back surface reflectance, an excellent long wavelength sensitivity, and a photoelectric conversion efficiency. Solar cells with high efficiency can be manufactured. Further, since the photoelectric conversion efficiency of the solar battery cell can be increased, the semiconductor substrate 1 can be thinned, the manufacturing cost can be reduced, and the high-quality solar battery cell excellent in battery cell characteristics can be achieved. Can be manufactured at low cost.

Embodiment 2. FIG.
Embodiment 2 demonstrates the case where the back surface reflecting film 10 is comprised with metal foil as another form of the back surface reflecting film 10. FIG. FIG. 7 is a main part sectional view for explaining a sectional structure of the solar battery cell according to the present embodiment, and corresponds to FIG. 1-1. The difference between the solar battery cell according to the second embodiment and the solar battery cell according to the first embodiment is that the back surface reflection film is formed of an aluminum foil (aluminum foil) instead of a silver sputtering film. Since the structure of those other than this is the same as that of the photovoltaic cell concerning Embodiment 1, detailed description is abbreviate | omitted.

As shown in FIG. 7, in the solar battery cell according to the present embodiment, the back surface reflecting film 22 made of aluminum foil is formed by the conductive adhesive 21 disposed on the back surface side electrode 9 on the back surface of the semiconductor substrate 1. The backside electrode 9 and the backside insulating film 8 are attached so as to be covered, and are electrically connected to the backside electrode 9 through the conductive adhesive 21. Even in such a configuration, the light transmitted through the semiconductor substrate 1 and the back surface insulating film 8 can be reflected back to the semiconductor substrate 1 as in the case of the first embodiment, and good light confinement can be achieved with an inexpensive configuration. An effect can be obtained.

And in this Embodiment, the back surface reflecting film 22 is comprised with the aluminum foil which is a metal stay. Since the back surface reflection film 22 is not a film formed by a printing method using an electrode paste, but is made of a metal stay, it can realize a higher light reflection than a metal film formed by a printing method, More light transmitted through the semiconductor substrate 1 and the back surface insulating film 8 can be reflected back to the semiconductor substrate 1. Therefore, the solar battery cell according to the present embodiment can obtain an excellent light confinement effect as in the case of the first embodiment by including the back surface reflection film 22 composed of the aluminum foil that is a metal stay. it can.

As the material of the back surface reflection film 22, a metal material that can be processed into a foil can be used. As in the case of the back surface reflection film 10, for example, the reflectance with respect to light having a wavelength near 1100 nm is 90% or more, preferably 95%. It is preferable to use the above metal materials. Thereby, a solar cell having high long wavelength sensitivity and excellent light confinement effect for light in the long wavelength region can be realized. That is, although depending on the thickness of the semiconductor substrate 1, light having a long wavelength of 900 nm or more, particularly about 1000 nm to 1100 nm, can be efficiently taken into the semiconductor substrate 1 and a high generated current (Jsc) can be realized. Characteristics can be improved. As such a material, for example, silver (Ag) can be used in addition to aluminum (Al).

The solar battery cell according to the present embodiment configured as described above has a conductive adhesive on the back-side electrode 9 after the steps described in Embodiment 1 with reference to FIGS. 5-1 to 5-8. 21 is applied, and the back surface side electrode 9 and the back surface insulating film 8 are covered with the conductive adhesive 21 and the back surface reflecting film 22 is attached. In this case as well, the back surface reflection film 22 may be formed so as to cover at least the back surface insulating film 8 on the back surface side of the semiconductor substrate 1.

In the solar cell according to the second embodiment configured as described above, by providing a silicon nitride film (SiN film) formed by plasma CVD on the back surface of the semiconductor substrate 1 as the back surface insulating film 8, A good effect of suppressing the recombination rate of carriers on the back surface of the semiconductor substrate 1 can be obtained. Thereby, in the photovoltaic cell concerning this Embodiment, the improvement of an output characteristic is achieved and the high photoelectric conversion efficiency is implement | achieved.

Further, in the solar cell according to the second embodiment, the back surface insulating film 8 is provided so as to cover the back surface insulating film 8 and include a back surface reflecting film 22 made of aluminum foil that is a metal stay. High light reflection can be realized, and more light transmitted through the semiconductor substrate 1 and the back surface insulating film 8 can be reflected back to the semiconductor substrate 1. Therefore, in the solar cell according to the present embodiment, an excellent light confinement effect can be obtained, the output characteristics can be improved, and high photoelectric conversion efficiency is realized.

Therefore, in the solar cell according to the second embodiment, by having the structure of the back surface having both the low recombination speed and the high back surface reflectivity, the long wavelength sensitivity is excellent, and the photoelectric conversion efficiency is improved. The obtained solar battery cell is realized.

Moreover, in the method for manufacturing a solar battery cell according to the second embodiment, after the back surface insulating film 8 having the opening 8a is formed on the back surface of the semiconductor substrate 1, the back side electrode material paste 9a is applied and fired. The region where the back side electrode material paste 9a is not applied is protected by the back side insulating film 8. By this. Even in the heating by firing, the adherence and fixation of contaminants do not proceed to the back surface of the semiconductor substrate 1, and a good state is maintained without degrading the recombination speed, and the photoelectric conversion efficiency is improved.

In the method for manufacturing a solar battery cell according to the second embodiment, the back surface reflection film 22 is formed on the back surface of the semiconductor substrate 1 so as to cover at least the back surface insulating film 8. As a result, the light transmitted through the semiconductor substrate 1 and the back surface insulating film 8 can be reflected by the back surface reflective film 22 and returned to the semiconductor substrate 1, and a good light confinement effect can be obtained. Thus, high photoelectric conversion efficiency can be realized.

Further, in the method for manufacturing a solar battery cell according to the second embodiment, the back surface reflecting film 22 is formed by attaching an aluminum foil that is a metal stay on the back surface side electrode 9. A dense back surface reflection film 22 can be formed by forming the back surface reflection film 22 using an aluminum foil as a back surface reflection film 22 instead of a printing method using an electrode paste. The back surface reflection film 22 that realizes light reflection higher than that of the formed film can be formed, and an excellent light confinement effect can be obtained.

Therefore, according to the method for manufacturing a solar battery cell according to the second embodiment, it is possible to obtain a back surface structure having both a low recombination speed and a high back surface reflectance, an excellent long wavelength sensitivity, and a photoelectric conversion efficiency. Solar cells with high efficiency can be manufactured. Further, since the photoelectric conversion efficiency of the solar battery cell can be increased, the semiconductor substrate 1 can be thinned, the manufacturing cost can be reduced, and the high-quality solar battery cell excellent in battery cell characteristics can be achieved. Can be manufactured at low cost.

In the above embodiment, the case where a p-type silicon substrate is used as the semiconductor substrate has been described. However, as a reverse conductivity type solar cell in which a p-type diffusion layer is formed using an n-type silicon substrate. Also good. Further, although a polycrystalline silicon substrate is used as the semiconductor substrate, a single crystal silicon substrate may be used. In the above description, the substrate thickness of the semiconductor substrate is 200 μm. However, a semiconductor substrate that can be self-held, for example, thinned to about 50 μm, can be used. Furthermore, in the above description, the size of the semiconductor substrate is 150 mm × 150 mm, but the size of the semiconductor substrate is not limited to this.

As described above, the photovoltaic device according to the present invention is useful for realizing a highly efficient photovoltaic device with a low recombination speed and a high back surface reflectance.

DESCRIPTION OF SYMBOLS 1 Semiconductor substrate 1a p-type polycrystalline silicon substrate 2 p-type polycrystalline silicon substrate 3 n-type impurity diffusion layer 4 Antireflection film 5 Light-receiving surface side electrode 5a Light-receiving surface electrode material paste 6 Grid electrode 7 Bus electrode 8 Back surface insulating film 8a Opening Part 9 Back side electrode 9a Back side electrode material paste 9b Overlapping region 10 Back side reflection film 11 Aluminum-silicon (Al-Si) alloy part 12 BSF layer 21 Conductive adhesive 22 Back side reflection film

Claims

A first conductivity type semiconductor substrate having an impurity diffusion layer in which an impurity element of the second conductivity type is diffused on one side;
An antireflection film formed on the impurity diffusion layer;
A first electrode penetrating the antireflection film and electrically connected to the impurity diffusion layer;
A back surface insulating film formed on the other surface side of the semiconductor substrate with a plurality of openings reaching the other surface side of the semiconductor substrate;
A second electrode embedded in at least the opening and electrically connected to the other side of the semiconductor substrate;
A back surface reflecting film formed of a metal film formed by a vapor deposition method or including a metal foil, and formed to cover at least the back surface insulating film;
A photovoltaic device comprising:
The back insulating film is a silicon nitride film formed by a plasma CVD method;
The photovoltaic device according to claim 1.
The back insulating film is a laminated film in which a silicon oxide film formed by thermal oxidation and a silicon nitride film formed by a plasma CVD method are laminated from the other surface side of the semiconductor substrate;
The photovoltaic device according to claim 1.
The silicon oxide film has a thickness of 10 nm to 50 nm,
The photovoltaic device according to claim 3.
The silicon nitride film has a refractive index of 1.9 to 2.2 and a thickness of 60 nm to 300 nm.
The photovoltaic device according to claim 2, wherein:
The opening has a diameter or width of 20 μm to 200 μm, and has a substantially circular dot shape or a substantially rectangular shape with an interval between adjacent opening portions of 0.5 mm to 2 mm.
The photovoltaic device according to claim 1.
The opening has a stripe shape with a width of 20 μm to 200 μm, and an interval between adjacent openings of 0.5 mm to 3 mm.
The photovoltaic device according to claim 1.
The photovoltaic device according to claim 6 or 7, wherein the second electrode is embedded in the opening and formed to overlap the back insulating film.
The second electrode has a width of 10 μm to 50 μm from the end of the opening, and is formed to overlap the back insulating film;
The photovoltaic device according to claim 8.
The metal foil is an aluminum foil;
The photovoltaic device according to claim 1.
The metal foil is attached to the second electrode by a conductive adhesive and is electrically connected to the second electrode via the conductive adhesive;
The photovoltaic device according to claim 1.
The metal film formed by the vapor deposition method is a metal sputtering film or a vapor deposition film,
The photovoltaic device according to claim 1.
A first step of forming an impurity diffusion layer in which an impurity element of the second conductivity type is diffused on one surface side of the first conductivity type semiconductor substrate;
A second step of forming an antireflection film on the impurity diffusion layer;
A third step of forming a back surface insulating film on the other surface side of the semiconductor substrate;
A fourth step of forming a plurality of openings reaching the other surface side of the semiconductor substrate in at least a part of the back surface insulating film;
A fifth step of applying a first electrode material on the antireflection film;
A sixth step of applying a second electrode material so as to fill at least the plurality of openings;
The first electrode material and the second electrode material are baked, and the first electrode that penetrates the antireflection film and is electrically connected to the impurity diffusion layer is electrically connected to the other surface side of the semiconductor substrate. A seventh step of forming a second electrode to be connected;
An eighth step of forming a back reflecting film made of a metal film formed by vapor deposition or including a metal foil so as to cover at least the back insulating film;
A method for manufacturing a photovoltaic device, comprising:
In the third step, a silicon nitride film is formed by plasma CVD as the back surface insulating film,
The method for manufacturing a photovoltaic device according to claim 13.
In the third step, a silicon oxide film is formed by thermal oxidation on the other surface side of the semiconductor substrate as the back surface insulating film, and a silicon nitride film is further formed on the silicon oxide film by a plasma CVD method,
The method for manufacturing a photovoltaic device according to claim 13.
In the sixth step, the second electrode material is applied to fill the opening and overlap the back insulating film with a width of 10 μm to 50 μm from the end of the opening;
The method for manufacturing a photovoltaic device according to claim 13.
The metal foil is an aluminum foil;
The method for manufacturing a photovoltaic device according to claim 13.
The metal film formed by the vapor deposition method is a metal sputtering film or a vapor deposition film,
The method for manufacturing a photovoltaic device according to claim 13.