JPH1041531A - Solar battery and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the effect of photoelectric conversion without impairing passivation effect and backside field effect by a method in which a metal layer is formed between the first thin film layer, with which the recombination center on the inter face between a semiconductor substrate is inactivated, and the second thin film layer on which an electric field is formed on the interface with the semiconductor substrate. SOLUTION: In a solar battery, a silicon oxide film layer 36, to be used inactivate the recombination center of the backside surface layer part of a p-type semiconductor substrate 30 by providing an aperture part 11, is formed on the backside of the p-type semiconductor substrate 30 located on the opposite side of a light entering surface, and an aluminum metal layer 10 is formed by forming the silicon oxide film layer 36. Also, a p<+> type microscopic crystal layer 37, with which the electrons are expelled as the minor carrier excited on the side of the p-type semiconductor substrate 30 on the aluminum metal layer 10 and a p<+> type microscopic crystal layer 37 with which holes are collected as a major carrier, is formed. Besides, metal backside electrode layer 38 of aluminum and silver, etc., is formed on the p<+> type microscopic crystal layer 37.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a solar cell and a method for manufacturing the same, and more particularly, to a solar cell with improved photoelectric conversion efficiency and a method for manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, there has been known a semiconductor solar cell in which the efficiency of collecting carriers (electrons or holes) generated by being excited by sunlight is improved for the purpose of improving the photoelectric conversion efficiency. This solar cell is formed by forming a silicon oxide film layer and a hydrogenated microcrystalline silicon semiconductor layer on the back side of a p-type silicon semiconductor substrate (hereinafter referred to as “p-type semiconductor substrate”). To improve the carrier collection efficiency by reducing the rate at which minority carriers (electrons) that diffuse inside the semiconductor recombine with majority carriers (holes) and disappear (hereinafter referred to as "recombination loss"). It is.

[0003] This conventional solar cell will be described with reference to FIG. Here, FIG. 5 is a cross-sectional view schematically showing the structure of a conventional solar cell. As shown in the figure, in this solar cell, phosphorus (element symbol P) is doped with an impurity (element symbol P) on the light incident surface side of a p-type semiconductor substrate 30 which has been processed into an uneven shape in order to reduce the reflection of incident sunlight. Donor) and n
It is formed by laminating a type semiconductor layer 31, a silicon oxide film layer 32, and a silicon nitride film layer 33 as an antireflection film. In addition, a grid electrode 34 made of each metal of titanium (element symbol Ti), palladium (element symbol Pd) and silver (element symbol Ag) penetrates the silicon oxide film layer 32 and the silicon nitride film layer 33 to form an n-type semiconductor. It is formed so as to be connected to the layer 31. Note that a PN junction is formed at the interface between the p-type semiconductor substrate 30 and the n-type semiconductor layer 31.

On the other hand, on the back side of the p-type semiconductor substrate 30,
The back surface structure described below is formed. That is, P
On the back surface of the p-type semiconductor substrate 30 opposite to the light incidence surface where the N junction is formed, an opening 35 is provided to form a silicon oxide film layer 36, which is laminated on the silicon oxide film layer 36. And the same conductivity type as the p-type semiconductor substrate 30,
A hydrogenated microcrystalline silicon semiconductor layer (hereinafter, referred to as “p ⁺ -type microcrystalline layer”) 37 to which a higher concentration of boron (element symbol B) is added is formed. The p ⁺ -type microcrystalline layer 37 is formed in the p-type semiconductor substrate 30 through the opening 35.
Connected to. Further, a back electrode layer 38 made of a metal such as aluminum (element symbol Al) or silver (element symbol Ag) is formed so as to be laminated on the p ⁺ -type microcrystalline layer 37.

Hereinafter, the function of each layer of the conventional solar cell formed as described above will be described focusing on the back surface structure involved in improving the photoelectric conversion efficiency. First, the p-type semiconductor substrate 3
When sunlight enters the 0 and n-type semiconductor layers 31, each of the p-type semiconductor substrate 30 and the n-type semiconductor layer 31 is excited by the sunlight to generate electron-hole pairs. The electron-hole pairs are formed by the p-type semiconductor substrate 30 and the n-type semiconductor layer 3
Under the action of the interfacial electric field in the junction region with the semiconductor device 1, electrons are collected on the n-type semiconductor layer 31 side and holes are collected on the p-type semiconductor substrate 30 side. As a result, the p-type semiconductor substrate 30 and the n-type semiconductor layer A photoelectromotive force is generated between the photovoltaic device 31 and the photovoltaic device 31.

At this time, the silicon oxide film layer 36 inactivates dangling bonds (recombination centers) of silicon atoms on the back surface portion of the p-type semiconductor substrate 30 and has a forbidden band width of the p-type semiconductor substrate 30. A potential barrier is formed between the semiconductor substrate 30 and the p-type semiconductor substrate 30 due to the larger width. As a result, minority carriers are not trapped by dangling bonds of silicon atoms on the back surface layer, and minority carriers do not flow into the silicon oxide film 36 from the back surface layer due to a potential barrier. Recombination loss at the surface layer is suppressed. Hereinafter, this function of the silicon oxide film layer 36 is referred to as a “passivation effect”.

The p ⁺ -type microcrystalline layer 37 doped with boron at a higher concentration than the p-type semiconductor substrate 30 has a forbidden band wider than that of the p-type semiconductor substrate 30. An internal electric field is formed between the substrate and the substrate 30. As a result, the minority carriers (electrons) which are about to flow to the back electrode side are pushed back into the p-type semiconductor substrate 30 by the internal electric field, and are regenerated in the p ⁺ -type microcrystalline layer 37 or the p-type semiconductor substrate 30. Coupling loss is suppressed. Less than,
This function of the p ⁺ -type microcrystalline layer 37 is referred to as “back surface field effect”.

As described above, conventionally, on the rear side of a solar cell, passivation is performed to improve the photoelectric conversion efficiency by reducing the rate at which carriers generated when excited by sunlight recombine and disappear. A back surface structure that produces an effect and a back surface field effect is formed.

Here, a method of forming the back surface structure of a conventional solar cell will be briefly described. First, the p-type semiconductor substrate 30
A silicon oxide film 36 is formed on the back surface of the substrate by using a thermal oxidation method or a chemical vapor deposition method (hereinafter, referred to as "plasma CVD method"). Subsequently, after a plurality of openings 35 are provided in the silicon oxide film 36 by photoetching, plasma CVD is performed.
A p ⁺ -type microcrystalline layer 37 is deposited by the method. Finally, the back electrode layer 38 is formed, and the back structure of the solar cell is completed.

[0010]

By the way, if the p ⁺ -type microcrystalline layer 37 is directly deposited on the silicon oxide film layer 36 to form the back surface structure, the silicon oxide film layer 3
There was a problem that a sufficient passivation effect could not be obtained at the interface between the p-type semiconductor substrate 6 and the p-type semiconductor substrate 30, and the photoelectric conversion efficiency of the solar cell was not effectively improved (first problem).

In order to identify the cause of this problem, the effective lifetime τ was evaluated by the microwave photoconductive decay method using the samples A and B described below. The effective lifetime τ is used as an index of the passivation effect, and the larger the passivation effect, the larger the effective lifetime τ tends to be.

(Sample A) A CZ single crystal p-type silicon semiconductor substrate (30) having a specific resistance of 2 Ω-cm is provided on both sides with a thickness of 30 nm.
After forming a thick silicon oxide film (36), a p ⁺ -type microcrystalline layer (37) is further formed on one side by using a plasma CVD apparatus.
Was deposited. (Sample B) After forming a silicon oxide film (36) having a thickness of 30 nm on both surfaces of a CZ single crystal p-type silicon semiconductor substrate (30) having a specific resistance of 2 Ω-cm, heat treatment and gas introduction were performed using a plasma CVD apparatus. Only done. In this case, no plasma treatment is performed, and no p ⁺ -type microcrystalline layer (37) is deposited.

Table 1 shows the evaluation results of the effective lifetime values τ of the samples A and B. As shown in the table, the plasma treatment was performed to deposit the p ⁺ -type
Decreases from 280 μs to 75 μs. On the other hand, no significant change is observed in the effective lifetime τ of the sample B not subjected to the plasma processing.
As understood from the evaluation results, the plasma treatment at the time of depositing the p ⁺ -type microcrystalline layer damages the interface between the silicon oxide film and the semiconductor substrate, and lowers the passivation effect.

[0014]

[Table 1]

That is, when a back surface structure of a conventional solar cell is formed, a high frequency electric field energy (hereinafter referred to as "RF power") is used in a process of depositing a p ⁺ -type microcrystalline layer on a silicon oxide film layer by plasma treatment. ), High-energy ions of a hydrogen gas, a silane-based gas such as monosilane, or a dopant gas such as diborane penetrate into the silicon oxide film layer, thereby causing a difference between the silicon oxide film layer and the semiconductor substrate. A defect level is generated at the interface. Then, this defect level forms a recombination center and is specified as a cause for reducing the passivation effect.

Further, in the conventional solar cell, the ratio of incident light reaching the back surface of the semiconductor substrate to be reflected back to the substrate side (hereinafter referred to as "back surface reflectance") is low, and so-called improvement in light confinement characteristics is achieved. Was sought (second problem).

The present invention has been made in view of such a problem. First, in the process of forming the back surface structure,
It is an object of the present invention to provide a solar cell having a high photoelectric conversion efficiency and a method for manufacturing the same without impairing the passivation effect and the back surface field effect. Second, the back surface reflectance of the semiconductor substrate is high and the so-called light confinement characteristics are improved. It is an object of the present invention to provide a solar cell with high photoelectric conversion efficiency and a method for manufacturing the same.

[0018]

Means for Solving the Problems The present invention has the following arrangement to achieve the above object. That is, claim 1
The solar cell according to the invention described in (1) is a solar cell formed on a semiconductor substrate, formed at least with a predetermined region opened on the back surface side of the semiconductor substrate, and a recombination center at an interface with the semiconductor substrate. A first thin film layer that inactivates the first thin film layer, and is formed on the back surface side of the semiconductor substrate so as to sandwich the first thin film layer. A second thin film layer for forming an electric field at an interface with the semiconductor substrate so as to collect the light, and a metal layer formed between the first thin film layer and the second thin film layer. ing.

A solar cell according to a second aspect of the present invention is a solar cell formed on a semiconductor substrate to which an impurity of a first conductivity type is added, wherein a predetermined region is formed on a back surface of the semiconductor substrate. A silicon oxide film layer laminated by opening; a metal layer laminated by opening the predetermined region on the silicon oxide film layer; and the semiconductor substrate in the predetermined region on the metal layer and the predetermined region. A microcrystalline semiconductor layer which is stacked so as to be connected to the semiconductor substrate and in which the impurity of the first conductivity type is added at a higher concentration than the semiconductor substrate; and a back electrode layer which is stacked on the microcrystalline semiconductor layer. Is configured.

Further, a solar cell according to a third aspect of the present invention is the solar cell according to the first or second aspect, wherein the metal layer is made of a metal containing aluminum as a main component. I have.

According to a fourth aspect of the present invention, there is provided a solar cell according to the first aspect, wherein a predetermined region where the silicon oxide film layer and the metal layer are opened is formed. In order to cover, an insulating or conductive transparent film layer having a smaller refractive index than the microcrystalline semiconductor layer and the back electrode layer is provided between the microcrystalline semiconductor layer and the back electrode layer. .

Furthermore, a method of manufacturing a solar cell according to the invention according to claim 5 is a method of manufacturing a solar cell formed on a semiconductor substrate to which impurities of a first conductivity type are added, wherein A first step of forming a silicon oxide film layer by opening a predetermined region on the back surface of the semiconductor device; a second step of forming a metal layer having the predetermined region opened on the silicon oxide film layer; And a third step of forming a microcrystalline semiconductor layer on the predetermined region to which the impurity of the first conductivity type is added at a higher concentration than the semiconductor substrate so as to be connected to the semiconductor substrate in the predetermined region. And a fourth step of forming a back electrode layer on the microcrystalline semiconductor layer.

Furthermore, the method for manufacturing a solar cell according to the invention according to claim 6 is the method for manufacturing a solar cell according to claim 5, wherein the method comprises the steps of: An insulating layer having a smaller refractive index than the microcrystalline semiconductor layer and the back electrode layer between the microcrystalline semiconductor layer and the back electrode layer so as to cover a predetermined region where the silicon oxide film layer and the metal layer are opened. A fifth step of forming a conductive or conductive transparent film layer is further provided.

The operation of the present invention constructed as described above will be described below. That is, according to the solar cell according to the first or second aspect of the present invention, the metal layer formed on the back surface side of the semiconductor substrate covers the first thin film layer (silicon oxide film layer) to form the second metal layer. In the process of forming the thin film layer (microcrystalline semiconductor layer), the first of high energy ions existing in the atmosphere
Effectively intruding into the thin film layer (silicon oxide film layer) side. As a result, damage to the interface between the semiconductor substrate and the first thin film layer (silicon oxide film layer) by the high energy ions is reduced. Therefore, the formation of recombination centers due to high-energy ions is suppressed, and the passivation effect is improved.

According to the solar cell according to the third aspect of the present invention, in the solar cell according to the first or second aspect of the present invention, the aluminum layer is used as the metal layer to further improve the passivation effect. In addition, in the infrared region of sunlight, the back surface reflectance at the interface between the metal layer and the first thin film layer (silicon oxide film layer) is improved.

According to the solar cell according to the fourth aspect of the present invention, in the solar cell according to the first aspect, the interface between the transparent film layer and the microcrystalline semiconductor layer or the transparent film. The difference in the reflectance at any of the interfaces between the layer and the back electrode layer is smaller than the difference in the reflectance at the interface when the transparent film layer is not provided (that is, the interface between the microcrystalline semiconductor layer and the back electrode layer). Also increases. Therefore, the light that has entered the predetermined region is effectively reflected at any interface and returned to the semiconductor substrate side.
Further, by making the transparent film layer conductive, the electric resistance of the transparent film layer is reduced, so that the series resistance between the semiconductor substrate and the microcrystalline semiconductor layer is reduced, and the internal resistance of the solar cell is reduced.

According to the method of manufacturing a solar cell according to the fifth aspect of the present invention, in the first step, the silicon oxide film layer is formed by opening a predetermined region on the back surface opposite to the main surface of the semiconductor substrate. Is formed, and in the second step, a metal layer having an opening in the predetermined region is formed on the silicon oxide film layer. A third step of forming a microcrystalline semiconductor layer having a higher impurity concentration than the semiconductor substrate so as to be stacked on the metal layer and connected to the back surface of the semiconductor substrate through the predetermined region; Thereby, a back surface electrode layer is formed by being stacked on the microcrystalline semiconductor layer. As described above, a solar cell having a back surface structure formed by stacking an oxide film layer, a metal layer, a microcrystalline semiconductor layer, and a back electrode layer is obtained. here,
In the step of forming the microcrystalline semiconductor layer in the third step, the silicon oxide film layer is covered with the metal layer, so that high-energy ions existing in the atmosphere for forming the microcrystalline semiconductor layer Cannot easily enter the film layer side. As a result, damage caused by the high-energy ions to the interface between the semiconductor substrate and the silicon oxide film layer can be reduced, and a solar cell with an improved passivation effect can be obtained.

According to the method for manufacturing a solar cell according to the present invention, the fifth step covers the microcrystalline semiconductor layer so as to cover a predetermined region where the silicon oxide film layer and the metal layer are opened. A solar cell having a back surface structure in which an insulating or conductive transparent film layer having a smaller refractive index than the microcrystalline semiconductor layer and the back electrode layer is formed between the back electrode layer and the microcrystalline semiconductor layer.

[0029]

BEST MODE FOR CARRYING OUT THE INVENTION

(First Embodiment) Hereinafter, a first embodiment according to the present invention will be described.
The solar cell according to the embodiment will be described with reference to FIGS. 1 and 2. Here, FIG. 1 is a cross-sectional view of the solar cell of the present embodiment, and FIG. 2 is a manufacturing process diagram of the solar cell of the present embodiment. Note that the structure of the solar cell according to the present embodiment on the light incident surface side is the same as that of the conventional solar cell shown in FIG. 5. A detailed description of the structure on the light incident surface side will be omitted.

As shown in FIG. 1, the solar cell of this embodiment has the same structure as the conventional one on the light incident surface side of the p-type semiconductor substrate 30. Further, as will be described in detail below, the back side has a back side structure provided with an aluminum metal layer 10 so as to cover the silicon oxide film layer 36.
Thereby, high energy ions are prevented from entering the substrate 30 side.

That is, in the solar cell of this embodiment, the p-type semiconductor substrate 30 (semiconductor substrate) on the side opposite to the light incident surface
An opening 11 is provided on the back surface of the p-type semiconductor substrate 30.
A silicon oxide film layer 36 (first thin film layer) for inactivating the recombination centers in the back surface layer portion of the aluminum metal layer 10 is formed on the silicon oxide film layer 36.
(Metal layer) is formed. The aluminum metal layer 10 has the same opening 11 as the opening of the silicon oxide film layer 36.

The p ⁺ -type layer, which is stacked on the aluminum metal layer 10, rejects electrons as minority carriers excited on the p-type semiconductor substrate 30 side to the substrate 30 side and collects holes as majority carriers. A microcrystalline layer 37 (second thin film layer) is formed. This p ⁺ type microcrystalline layer 37
Are connected to the p-type semiconductor substrate 30 through the opening 11 described above. Furthermore, by laminating on this p ⁺ type microcrystalline layer 37,
A back electrode layer 38 (back electrode layer) made of a metal such as aluminum (element symbol Al) or silver (element symbol Ag) is formed.

Next, an example of a method of manufacturing the solar cell according to the present embodiment will be described with reference to FIG. 1 and along a manufacturing process diagram shown in FIG. First, a single crystal p-type semiconductor substrate 3
0 (100 mm diameter, 300 μm thickness, specific resistance 2Ω-cm)
Is cleaned (step S01), and anisotropic etching is performed so that the surface becomes uneven (step S02). Here, instead of the single-crystal p-type semiconductor substrate 30, polycrystalline (amorphous)
A silicon p-type semiconductor substrate may be used. in this case,
The formation of the surface irregularities is performed by a method of mechanically (physically) digging a groove using a laser or the like.

Next, an n-type semiconductor layer 31 is formed on the surface of the p-type semiconductor substrate 30 by vapor phase diffusion of phosphorus (element symbol P) using phosphorus oxychloride (POCl ₃ ) (step S0).
3). Subsequently, the back surface of the p-type semiconductor substrate 30 is etched using a mixed solution of nitric acid and hydrofluoric acid to form the n-type semiconductor layer 3.
The n-type semiconductor layer formed on the rear surface side is removed simultaneously with the formation of 1 (step S04), and the silicon oxide film layer 32 on the light incident surface side and the silicon oxide film layer 36 on the rear surface side are simultaneously formed by a thermal oxidation method. (Step S05). Next, a silicon nitride film layer 33 as an anti-reflection film
Formed by Method D (Step S06).

Next, an aluminum metal layer is deposited to a thickness of 500 nm by a vacuum deposition method so as to cover the silicon oxide film layer 36 (step S07). This aluminum metal layer 1
0, as described later, the p ⁺ type since it serves to prevent penetration of plasma-like high energy ions during the microcrystalline layer 37 deposition (during plasma treatment), deposition conditions of the p ⁺ -type microcrystalline layer 37 Set an appropriate thickness according to.

Next, heat treatment is performed at 400 ° C. for one hour in an atmosphere of hydrogen (H ₂ ) gas or a mixed gas of hydrogen gas and nitrogen gas (N ₂ ) or argon gas (Ar) (step S08). The conditions (temperature and time) of this heat treatment vary depending on the type of the atmosphere gas,
Heat treatment at 50 to 480 ° C. for several minutes to about 2 hours is required. The conditions of this heat treatment are set appropriately according to the type of the atmospheric gas.

Next, the aluminum metal layer 10 and the silicon oxide film layer 36 are patterned by using a photo-etching method, and an opening for connecting a p ⁺ -type microcrystalline layer 37 described later to the p-type semiconductor substrate 30 is formed. 11 is formed (Step S09). Next, the p ⁺ -type microcrystalline layer 37 is formed to a thickness of 200 nm by a plasma CVD method.
(Step S10). This plasma C
As the deposition conditions for the p ⁺ -type microcrystalline layer 37 by the VD method, the type of reaction gas is H ₂ -diluted monosilane (SiH ₄ ) or a mixed gas of disilane Si ₂ H ₆ and diborane B ₂ H ₆ ,
The reaction gas flow rate ratio _{H 2 / SiH 4 = 150,} B 2 H 6 / Si
H ₄ = 0.01, the reaction gas pressure was 20 Pa, the substrate temperature was 150 ° C., and the RF power was 100 W (13.
56 MHz). Note that the deposition conditions are merely examples, and a film can be formed under general plasma CVD conditions without being limited to these conditions.

Next, aluminum is vapor-deposited on the entire rear surface by a vacuum vapor deposition method to form a rear electrode layer 38.
1). Next, an opening is made to penetrate the silicon oxide film layer 32 and the antireflection film 33 on the light incident side using a photoetching method, and titanium (element symbol Ti), palladium (element symbol Pd), and silver (element symbol) Ag) in order in the order of Ag), and a grid electrode 34 is deposited by a lift-off method.
Is formed (Step S12).

Finally, heat treatment is performed at 300 ° C. for several minutes in an atmosphere of nitrogen gas (N ₂ ) (step S13).
The solar cell is completed. Incidentally, nitrogen gas (N ₂ ), argon gas (Ar) or a mixed gas thereof was used as this atmosphere, and the atmosphere temperature was set to 200 ° C. to 400 ° C.
The processing time was set from several minutes to one hour. However, the condition of this heat treatment is an example, and is not limited to this condition.

Table 2 shows FIG. 1 prepared by the above manufacturing method.
(Hereinafter referred to as "solar cell I") and a solar cell shown in FIG. 1 (hereinafter referred to as "solar cell II") produced by using silver instead of aluminum for the metal layer 10 in the above manufacturing method. 5) and the conventional solar cell shown in FIG. 5 (hereinafter, referred to as “solar cell III”) in which the p ⁺ -type microcrystalline layer 37 is formed directly on the silicon oxide film layer 36. Are shown in comparison. In addition, these solar cells I to III were manufactured under the same conditions except for the place where the back surface structure was different. The photoelectric conversion characteristics were measured using a solar simulator having a light intensity similar to that of 100 mW / cm ² sunlight in the AM1.5 global spectrum.

[0041]

[Table 2]

As can be understood from Table 2, the solar cells I and II on which the metal layer 10 is formed have a larger interface at the interface between the silicon oxide layer film 36 and the p-type semiconductor substrate 30 than the conventional solar cell III. As a result of improving the passivation effect, the short-circuit current density and the release voltage are greatly improved, and the conversion efficiency is improved. Further, the solar cell I using aluminum as the metal layer 10 has a further improved passivation effect and a higher photoelectric conversion efficiency than the solar cell II using silver.

As described above, the reason why the passivation effect is improved is that the p ⁺ type microcrystalline layer 37 is formed by the plasma treatment.
This is because during the process of forming the high-energy ions, the high-energy ions generated by the plasma treatment are eliminated by the metal layer 10 and the high-energy ions that enter the inside of the silicon oxide film layer 36 are reduced. As a result, at the interface with the p-type semiconductor substrate, the formation of recombination centers due to the high energy ions penetrating the silicon oxide film layer 36 is suppressed, and the passivation effect is improved.

The interface between aluminum and silicon oxide has a higher reflectance in the infrared region of sunlight than the interface between p ⁺ -type microcrystalline layer and silicon oxide. For this reason, by forming the metal layer 10 using aluminum, the reflectance at the interface between the metal layer 10 and the silicon oxide film layer 36 is improved, and the back surface reflectance is further improved.
Therefore, when the metal layer 10 is made of aluminum,
The passivation effect and the back surface reflectivity can be further improved.

(Second Embodiment) Next, a solar cell according to a second embodiment of the present invention will be described with reference to FIGS. Here, FIG. 3 is a cross-sectional view of the solar cell of the present embodiment, and FIG. 4 is a manufacturing process diagram of the solar cell of the present embodiment. The structure of the solar cell of the present embodiment on the light incident surface side is such that the transparent film layer 20 having a small refractive index is formed between the p ⁺ -type microcrystalline layer 37 and the back electrode layer 38 as described later. Except for the solar cell shown in FIG. 1, the same components as those of the conventional solar cell shown in FIG. 1 are denoted by the same reference numerals, and the detailed description thereof is omitted. I do.

As shown in FIG. 3, the solar cell according to this embodiment is different from the first solar cell shown in FIG. 1 in that the p ⁺ -type microcrystalline layer 37 and the back electrode layer 38 are formed so as to cover the opening 11. And a transparent film layer 20 is formed between the layers. The refractive index of this transparent film layer depends on the p ⁺ type microcrystalline layer 37 and the back electrode layer 38.
Are set to be smaller than any of the above. The solar cell according to the present embodiment having such a configuration improves the back surface reflectance by returning the sunlight reaching the back surface electrode side through the opening 11 to the p-type semiconductor substrate 30 side, thereby improving the so-called light confinement characteristics. It is intended to improve the photoelectric conversion efficiency.

That is, the transparent film layer 20 having a small refractive index is formed by p ⁺
By providing between the type microcrystalline layer 37 and the back electrode layer 38, the reflectance at the interface between the transparent film layer 20 and the p ⁺ type microcrystalline layer 37 or the interface between the transparent film layer 20 and the back electrode layer 38 is increased. Therefore, the light incident on the predetermined region is effectively reflected at this interface and returned to the p-type semiconductor substrate 30 side. Here, if the transparent film layer is made conductive, the electric resistance of the transparent film layer 20 is reduced, and the p-type semiconductor substrate 30 and the p ⁺ -type microcrystalline layer 37 are formed.
Is reduced. As a result, the internal resistance of the solar cell is reduced, and the photoelectric conversion efficiency is further improved.

On the other hand, light incident on the area other than the opening 11 is reflected by the metal layer 10 and returned to the p-type semiconductor substrate 30 side. Therefore, by providing the transparent film layer 20, most of the sunlight passing through the p-type semiconductor substrate 30 can be removed from the p-type semiconductor substrate 3.
The value is returned to the 0 side, and the back surface reflectance is improved. As described above, the interface between aluminum and silicon oxide has a higher reflectance in the infrared region of sunlight than the interface between p ⁺ -type microcrystalline layer and silicon oxide. Is formed using aluminum, the back surface reflectance can be further improved.

Next, an example of a method for manufacturing a solar cell according to the present embodiment will be described with reference to the process chart shown in FIG. The back surface structure of the solar cell according to this embodiment is the same as that of the solar cell according to the first embodiment except that the transparent film layer 20 is formed. Since the steps are the same except for the step of forming the transparent film layer 20, the following description of the manufacturing method focuses on the step of forming the transparent film layer 20.

First, similarly to the solar cell of the first embodiment, an opening 1 is formed on the back side of a single crystal p-type semiconductor substrate 30.
1, the silicon oxide film layer 36 and the metal layer 10 are formed, and then the p ⁺ -type microcrystalline layer 37 is laminated on the metal layer 10 so as to be in contact with the p-type semiconductor substrate 30 through the opening 11 (steps S01 to S01). S10). Here, the refractive indexes of the aluminum metal layer and the p ⁺ -type microcrystalline layer in the infrared region of sunlight are both formed to be larger than 3.0.

Next, an insulating transparent film layer 20 made of silicon nitride having a refractive index of 2.0 is deposited to a thickness of 300 nm so as to cover the p ⁺ -type microcrystalline layer 37 by a plasma CVD method (step S10A). ). As the deposition conditions for silicon nitride, the types of reaction gas are SiH ₄ and ammonia (NH ₃ ),
A mixed gas of N ₂ and a reactant gas flow ratio of SiH ₄ : N
H ₃ : N ₂ = 3: 4: 10 and the reaction gas pressure was 20 Pa
And the substrate temperature is 150 ° C. and the RF power is 100 W
(13.56 MHz). However, the deposition conditions are merely an example, and the film formation can be performed under general plasma CVD conditions without being limited to these conditions.

The refractive index of the transparent film layer 20 made of silicon nitride can be obtained in the range of 1.8 to 2.2 by adjusting the deposition conditions. The material of the transparent film layer 20 is not limited to silicon nitride, but may be a silicon oxide film formed by a plasma CVD method, a titanium oxide film formed by a normal pressure CVD method, an aluminum oxide film formed by a vacuum deposition method, or the like. Can be used.

Next, leaving a region covering the opening 11 where the p ⁺ -type microcrystalline layer 37 and the p-type semiconductor substrate 30 are connected,
A part of the transparent film layer 20 is removed by a photo etching method, and the transparent film layer 20 is patterned (step S10).
B). In the patterned transparent film layer 20, a mask made of metal or resin having an opening in the region where the transparent film layer 20 is to be left is placed on the p ⁺ -type microcrystalline layer 37, and the p ⁺ -type microcrystalline layer 37 can be formed by depositing the transparent film layer 20, and this transparent film layer 20 may be formed by any method. After the transparent film layer 20 is formed by patterning, the back electrode layer 38 and the grid electrode 34 are formed in the same manner as in the solar cell of the first embodiment.
(Steps S10 to S1) through a series of steps for forming
3), the solar cell of the present embodiment is completed.

In the solar cell of the present embodiment in which the transparent film layer 20 is thus formed, the interface between the p ⁺ -type microcrystalline layer 37 and the transparent film layer 20 or the interface between the transparent film layer 20 and the back electrode layer 38 is formed. The difference in the refractive index at any one of the interfaces is larger than the difference in the refractive index at the interface between the p ⁺ -type microcrystalline layer 37 and the back electrode layer 38, which is the reflection surface when the transparent film layer 20 is not formed. . As a result, the rear surface reflectance is improved, and sunlight incident on the opening 11 is effectively reflected at any interface having a larger difference in refractive index, so that so-called light confinement characteristics can be improved.

(Third Embodiment) The third embodiment of the present invention
In the solar cell according to the embodiment, instead of the transparent film layer 20 made of insulating silicon nitride of the solar cell according to the second embodiment, a conductive transparent film layer made of a tin oxide film is formed by a sputtering method. It has a configuration formed with a thickness of 400 nm (not shown), and is intended to further improve the photoelectric conversion efficiency by reducing the internal resistance of the solar cell by making the transparent film layer 20 conductive. 1.8 to 2.0 was obtained as the refractive index of the conductive transparent film layer made of the tin oxide film,
It can be formed under general evaporation conditions. Also,
As this conductive transparent film layer, a zinc oxide film (Z7nO)
Film) and tin-doped indium oxide film (ITO film)
Or the like may be used.

Table 3 shows the solar cell according to the second embodiment described above (hereinafter referred to as "solar cell IV") and the solar cell IV of the present embodiment in which the transparent film layer is replaced with a conductive transparent film. The photoelectric conversion characteristics of a solar cell (hereinafter, referred to as “solar cell V”) and the solar cell (solar cell I) of the above-described first embodiment are compared and shown. Note that these solar cells were manufactured under the same conditions except that the back surface structure was different, and the photoelectric conversion characteristics were the same as those of 100 mW / cm ^{2 in} the AM1.5 global spectrum. It was measured using a solar simulator having.

[0057]

[Table 3]

As can be understood from Table 3, the solar cells IV and V provided with the transparent film layers are the same as the solar cells I and V provided with no transparent film layer.
As a result, the short-circuit current and the like are improved. In addition, the solar cell V of the present embodiment using the conductive tin oxide film as the transparent film layer has a higher series resistance than the solar cell IV using the insulating silicon nitride film as the transparent film layer. The fill factor is obtained, and shows the highest conversion efficiency.

In the above description of the embodiment of the present invention, an example in which a solar cell is formed using a p-type silicon semiconductor substrate 30 has been described. However, the present invention is also applicable to a case where an n-type silicon semiconductor substrate is used. It is. In this case, the impurity of the p-type semiconductor layer laminated on the light incident surface side of the n-type silicon semiconductor substrate is an acceptor such as boron (element symbol B), and phosphorus (element symbol P) is used as a hydrogenated microcrystalline silicon semiconductor layer. A donor to which a high concentration is added is used.

In the description of the method of manufacturing the solar cell according to the above-described embodiment, the conditions such as the thickness of each layer, temperature, and time are merely examples, and do not limit the essence of the present invention. , May be set appropriately according to the implementation situation.

[0061]

As described above, according to the present invention, the following effects can be obtained. That is, according to the first or second aspect of the present invention, the back surface structure of the solar cell is formed between the first thin film layer (silicon oxide film layer) and the second thin film layer (p ⁺ type microcrystalline layer). Since the metal layer is provided on the first thin film layer, the second thin film layer (p ⁺ type microcrystalline layer) can be formed without damaging the interface between the semiconductor substrate (p-type semiconductor substrate) and the first thin film layer (silicon oxide film layer). In addition, both the passivation effect and the back surface field effect can be enhanced.

According to the third aspect of the present invention, in the first or second aspect of the present invention, the metal layer is made of aluminum, so that the passivation effect of the oxide film layer can be further enhanced. It is possible to improve the back surface reflectance of sunlight transmitted through the semiconductor substrate and improve so-called light confinement characteristics.

Further, according to the fourth aspect of the present invention,
In the invention according to any one of claims 1 to 3, the second thin film layer (p ⁺ -type microcrystalline layer) so as to cover the opening for connection to a semiconductor substrate, a second thin film layer (p ⁺ (A microcrystalline layer) and a transparent film layer having a smaller refractive index than the back electrode layer, so that the back reflectance of light transmitted through the semiconductor substrate and incident on the opening can be improved, so-called light confinement characteristics Can be improved. In addition, by making the transparent film layer conductive, the electric resistance of the transparent film layer is reduced, so that the internal resistance of the solar cell can be reduced.

According to the fifth and sixth aspects of the present invention, the solar cells according to the second and fourth aspects can be obtained.

Therefore, according to the first to sixth aspects of the present invention, as a result of improving the passivation effect, the back surface field effect, the back surface reflectivity, the so-called light confinement characteristics and the internal resistance of the solar cell, the photoelectric conversion efficiency is greatly improved. An improved solar cell can be obtained, and a solar cell improved in this way can be manufactured.

[Brief description of the drawings]

FIG. 1 is a sectional view of a solar cell according to a first embodiment of the present invention.

FIG. 2 is a manufacturing process diagram of the solar cell according to the first embodiment of the present invention.

FIG. 3 is a sectional view of a solar cell according to a second embodiment of the present invention.

FIG. 4 is a manufacturing process diagram of a solar cell according to a second embodiment of the present invention.

FIG. 5 is a cross-sectional view of a conventional solar cell.

[Explanation of symbols]

REFERENCE SIGNS LIST 10 metal layer 11, 35 opening 20 transparent film layer 30 p-type semiconductor substrate 31 n-type semiconductor layer 32 silicon oxide film layer 33 silicon nitride film layer 34 grid electrode 36 silicon oxide film layer 37 P ⁺ type microcrystalline layer 38 back electrode layer

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tasuke Shindo 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka

Claims (6)

[Claims] 1. A solar cell formed on a semiconductor substrate, wherein at least a predetermined region is opened on the back surface side of the semiconductor substrate to inactivate a recombination center at an interface with the semiconductor substrate. A first thin film layer, formed on the back surface side of the semiconductor substrate so as to sandwich the first thin film layer, and excluding minority carriers on the semiconductor substrate side and collecting majority carriers in the predetermined region. A solar cell, comprising: a second thin film layer that forms an electric field at an interface with a semiconductor substrate; and a metal layer formed between the first thin film layer and the second thin film layer. 2. A solar cell formed on a semiconductor substrate to which impurities of a first conductivity type are added, wherein the silicon oxide film layer is formed by opening a predetermined region on a back surface of the semiconductor substrate; A metal layer laminated on the silicon oxide film layer with the predetermined region opened; and a first conductive layer laminated on the metal layer and the predetermined region so as to be connected to the semiconductor substrate in the predetermined region. A solar cell, comprising: a microcrystalline semiconductor layer to which a type impurity is added at a higher concentration than the semiconductor substrate; and a back electrode layer laminated on the microcrystalline semiconductor layer. 3. The solar cell according to claim 1, wherein the metal layer is made of a metal containing aluminum as a main component. 4. A lower refractive index than the microcrystalline semiconductor layer and the back electrode layer between the microcrystalline semiconductor layer and the back electrode layer so as to cover a predetermined region where the silicon oxide film layer and the metal layer are opened. The solar cell according to any one of claims 1 to 3, further comprising an insulating or conductive transparent film layer having the following. 5. A method of manufacturing a solar cell formed on a semiconductor substrate to which impurities of a first conductivity type are added, wherein a silicon oxide film layer is formed by opening a predetermined region on a back surface of the semiconductor substrate. A first step, a second step of forming a metal layer having an opening in the predetermined region on the silicon oxide film layer, and connecting to the semiconductor substrate in the predetermined region on the metal layer and the predetermined region Thus, a third step of forming a microcrystalline semiconductor layer to which the first conductivity type impurity is added at a higher concentration than the semiconductor substrate, and a fourth step of forming a back electrode layer on the microcrystalline semiconductor layer And a method for manufacturing a solar cell. 6. A method according to claim 6, wherein the third step and the fourth step cover the predetermined region where the silicon oxide film layer and the metal layer are opened, so that the interlayer between the microcrystalline semiconductor layer and the back electrode layer is formed. The solar cell according to claim 5, further comprising a fifth step of forming an insulating or conductive transparent film layer having a smaller refractive index than the microcrystalline semiconductor layer and the back electrode layer. Production method.