JP2000340813A - Optoelectronic transducer element and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a optoelectronic transducer element, in which a p-layer has satisfactory ohmic contact at interface of both n and i-layers adjacent to the p-layer with an interface characteristic small in light absorption, in a tandem photoelectric conversion element which is constituted by laminating a plurality of pin junctions, and manufacturing method thereof. SOLUTION: An optoelectronic transducer element is constituted by laminating a plurality of pin junctions 3 and 9. In this element, at least a p-layer adjacent to an n-layer is constituted by laminating an amorphous silicon layer, in which n and p-type impurities are mixed and which has a film thickness of 5 nm or smaller as a first p-layer 7, and an amorphous silicon layer, in which the impurity concentration is reduced as it comes closer to the i-layer, as a second p-layer 8.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a photoelectric conversion element and a method for manufacturing the same, and more particularly, to a photoelectric conversion element formed by stacking a plurality of pin junctions and a method for manufacturing the same.

[0002]

2. Description of the Related Art In a photoelectric conversion element having a pin junction used in a thin-film solar cell or the like, a doped layer on the light incident side has been conventionally variously developed as one of the important factors for improving the conversion efficiency. I have been. In particular, the p-layer, which is one of the doped layers on the light incident side, functions as an amorphous silicon-based window layer, but is not a photoelectric conversion layer. Therefore, various studies have been made to satisfy the conflicting performances of providing a high efficiency and good p / i interface characteristics.

For example, a method using a boron-doped a-SiC film as the p-layer is described in Japanese Patent Publication No. 3-40515 and Japanese Patent Publication No. 3-63229. In these publications, the p-layer is composed of silane or a silane derivative (for example, SiH ₄ ), a hydrocarbon (for example, C
H ₂ ) and a method of decomposing B ₂ H ₆ gas by glow discharge together with a mixed gas such as an inert gas (eg, Ar, He) to form a film. Etc. are generally known.

[0004] However, when B ₂ H ₆ gas is mixed into the source gas at the same time, B (boron) extracts hydrogen terminating the bond such as Si in the amorphous. This allows
Many dangling bonds called dangling bonds are formed in the layer. Therefore, when the boron-doped amorphous silicon-based film formed by the above method is used for the p-layer serving as the window layer, the light absorption of the p-layer increases.

[0005] In order to suppress the increase in the amount of light absorption, carbon is introduced into the film up to several tens percent. However, the increase in the amount of carbon causes deterioration of the film quality.
There is a problem that the conductivity decreases and the internal resistance of the entire device increases. As described above, if an attempt is made to obtain a desired conductivity that does not cause a series resistance in the cell characteristics, the amount of light absorption becomes so large that it cannot be ignored, and there is a problem that a sufficient photocurrent cannot be secured.

In the plasma enhanced chemical vapor deposition, boron in the plasma also increases the number of dangling bonds on the film surface, so that a large number of recombination levels are generated at the p / i interface.
Significantly affects conversion efficiency. Thus, for example, p
When a boron-doped SiC film is used as the layer, the junction with the photoelectric conversion layer is poor, and recombination of the generated photocarriers is the center, and a sufficient open voltage (Voc) and fill factor (F.F. ) Cannot be secured.

Therefore, a method is generally used in which an amorphous film or an intrinsic SiC film in which the amount of C in the film is gently changed is sandwiched as a buffer layer at the p / i interface to reduce the influence on the cell characteristics. Have been. However, these buffer layers have low conductivity and cause an increase in the internal resistance of the device. F. Can not be avoided.

On the other hand, Japanese Patent Application Laid-Open No. Hei 7-22638 discloses a method for forming a p-layer by forming an amorphous boron layer and then stacking an amorphous silicon layer to form a p-type amorphous silicon layer. A method is disclosed. Appl. Phys. 36 , 467 (1997) proposes a method of forming a p-layer by laminating amorphous carbon after forming an amorphous boron layer. However, it is still difficult to sufficiently reduce the amount of light absorbed by the amorphous boron layer.

Further, in order to efficiently utilize the spectrum of sunlight and increase the photoelectric conversion rate, a tandem type photoelectric conversion element having a structure in which a plurality of pin junctions are stacked has been widely used. In such a photoelectric conversion element, the photocurrent generated in each pin junction can be used efficiently by arbitrarily setting the optical band gap of the photoelectric conversion layer in each pin junction. However, on the other hand, there is inevitably an interface at which the intermediate p-layer and the adjacent n-layer come into contact with each other, so that the film quality is sacrificed in order to obtain a good ohmic contact, and the recombination layer has a large light absorption. At present, about 3 nm has to be inserted into this interface.

[0010]

When an amorphous silicon-based film doped with boron is formed, SiH _{4 is used.}
With GeH ₄ , CH ₄ , H ₂ , Ar, H
In general, B ₂ H ₆ gas is mixed into a gas obtained by mixing e and the like, and the mixture is grown by plasma enhanced chemical vapor deposition. However, if the B ₂ H ₆ gas is mixed with the above gas at the same time, the hydrogen terminating the bonds of Si and Ge in the amorphous by boron is extracted, and many dangling bonds in the film are called dangling bonds. It is formed. Due to the hydrogen extraction effect, the amount of light absorbed by the p-layer serving as the window layer increases. To suppress this increase in light absorption,
A gas such as CH ₄ described above is mixed with the source gas to mix C into the film, which causes a significant decrease in the conductivity of the p-layer. Therefore, in order to obtain a desired conductivity that does not cause series resistance in the cell characteristics,
There is a problem that the amount of light absorption becomes so large that it cannot be ignored, and that a sufficient photocurrent cannot be secured.

In addition, boron in the plasma also increases the number of dangling bonds on the film surface, so that a large amount of recombination levels are generated at the p / i interface, which has a great adverse effect on the conversion efficiency. For example, when a boron-doped SiC film is used as the p-layer, the bonding with the photoelectric conversion layer is deteriorated, and sufficient Voc or F.C. F.
Cannot be secured. For this reason, a buffer layer (intrinsic SiC film) is usually inserted at the p / i interface. This layer has a low conductivity and causes an increase in the internal resistance of the device. F. Causes a decrease.

Further, in a so-called tandem type photoelectric conversion element in which two or three or more such pin junctions are joined to form one element, an intermediate p-layer adjacent to the n-layer is connected to an adjacent lower layer. Contact layer (highly doped a-Si film) for obtaining ohmic contact with n-layer of
In general, a silicon-based alloy film having a wide gap such as C or a-SiO film is formed by lamination, but the light absorption loss of the contact layer, which is an inactive layer, is large.
The series resistance of a silicon-based alloy film having a wide gap, such as a -SiC or a-SiO film, becomes so large that it cannot be ignored. F. There is a problem that it decreases.

Thus, in the conventional method, a plurality of pi
In a tandem-type photoelectric conversion element formed by stacking n-junctions, a p-type doped layer having a small light absorption and a high conductivity,
It has been very difficult to obtain a window layer that satisfies the conflicting feature of having good interface characteristics in both the n-type amorphous silicon layer (or microcrystalline silicon layer) and the photoelectric conversion layer.

The present invention has been made in view of the above-mentioned problems, and in a tandem-type photoelectric conversion element formed by stacking a plurality of pin junctions, a p-layer is formed of an adjacent n layer.
It is an object of the present invention to provide a photoelectric conversion element having good ohmic contact at both interfaces of a layer and an i-layer and having interface characteristics with a small amount of light absorption, and a method for manufacturing the same.

[0015]

According to the present invention, there is provided a photoelectric conversion element formed by stacking a plurality of pin junctions, wherein at least a p-layer adjacent to an n-layer has n-type and p-type as a first p-layer. And an amorphous silicon layer having a thickness of 5 nm or less in which impurities are mixed and an amorphous silicon layer whose impurity concentration decreases as approaching the i-layer as a second p-layer are provided. You.

Further, according to the present invention, in a method for manufacturing a photoelectric conversion element in which a plurality of pin junctions are laminated, a p-layer adjacent to the n-layer has at least a two-layer structure, and a p-type impurity is used as the first p-layer. A doped amorphous silicon film is formed, and then a second p-layer is formed by forming and stacking an amorphous silicon layer by discharge decomposition of a source gas containing no p-type impurity. A method for manufacturing a photoelectric conversion element is provided.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION The photoelectric conversion element of the present invention is a tandem type photoelectric conversion element having at least two pin junctions, and is provided mainly in order from the light incident side.
It comprises a transparent electrode layer, a first pin junction, a second pin junction having a p-layer adjacent to the n-layer of the first pin junction, and a back electrode layer. The second pin junction includes an amorphous silicon layer (first p layer) having a thickness of 5 nm or less in which n-type and p-type impurities are mixed, and an amorphous silicon layer (first layer) whose impurity concentration decreases as approaching the i-layer. 2p layer) and an i-layer and an n-layer forming a pin junction with the p-layer. The photoelectric conversion element of the present invention further includes a stacked third, fourth,... Pin junction, and all of the plurality of pin junctions are formed of the first pin junction.
It is not necessary to include a pin junction consisting of a p-layer having a p-layer and a second p-layer. It is necessary that at least one pin junction is composed of a p-layer having a p-layer having the above-mentioned first p-layer and second p-layer. However, all the pin junctions have a first p-layer and a second p-layer. preferable. .

The photoelectric conversion device of the present invention is preferably formed on a substrate. The substrate that can be used for the photoelectric conversion element of the present invention is not particularly limited as long as it is generally used as a substrate of a solar cell, and is made of a metal such as stainless steel, aluminum, copper, and zinc. Substrate, glass substrate, polyimide, PET, PE
Various substrates such as a resin substrate of N, PES, Teflon or the like, a substrate in which a resin is applied to a metal substrate, a substrate in which a metal layer is formed on a resin substrate, and the like. Among them, a transparent substrate is preferable. The substrate may be an insulating film, another conductive film made of metal, semiconductor, or the like, a wiring layer, a buffer layer, or a combination thereof, depending on the usage of the substrate. The thickness of the substrate is not particularly limited, but may be, for example, about 0.1 to 30 mm so as to have appropriate strength and weight.
Further, the substrate surface may have irregularities.

Examples of the transparent electrode layer used in the photoelectric conversion device of the present invention include conductive oxides such as ZnO, ITO and SnO ₂ . These electrode materials can be formed as a single layer or multiple layers. The thickness of such a back electrode can be appropriately adjusted depending on the material to be used and the like, and for example, about 200 to 2000 nm. In addition, irregularities may be formed on the surface of such a transparent electrode layer. The unevenness is, for example, about the wavelength of light in the visible light region, a height of about 0.1 to 1.2 μm,
One having a pitch of 10 μm is exemplified.

The first p used in the photoelectric conversion element of the present invention
The in junction may be a pin junction according to a conventional technique, or a second junction used in a photoelectric conversion element of the present invention described later.
It may be a pin junction. One or more first pin junctions may be provided on the p-layer of the second pin junction used in the photoelectric conversion element of the present invention. The p-layer of the second pin junction of the photoelectric conversion device of the present invention includes an amorphous silicon layer (first p-layer) having a thickness of 5 nm or less in which n-type and p-type impurities are mixed, and an impurity as the i-layer approaches. An amorphous silicon layer (second p layer) having a reduced concentration is laminated, and with this configuration, hydrogen is extracted from silicon in the boron film while ensuring good ohmic contact with the underlying n layer. It is possible to form a p-layer which does not cause deterioration of the p-layer film quality due to the effect.

The p-layer includes a first p-layer and a second p-layer,
A semiconductor layer, especially an amorphous silicon layer, for example, a-
It can be formed of Si: H, a-SiGe: H, or the like. The first p-layer and the second p-layer need not necessarily be formed of the same semiconductor layer. First p layer and second p layer
Preferably, each of the layers is a-Si: H, not SiC.

In the first p-layer, a thickness of 5 nm or less means a thickness in a range where the optical absorption of the first p-layer can be neglected, and includes a film of one or more atomic layers of a semiconductor. This film preferably has a uniform thickness over the entire surface, but may be formed in an island shape on the surface of the transparent electrode layer, for example. It is preferable that a predetermined amount of impurity is added to the entire first p-layer.
That is, when the first p-layer is formed of a silicon-based layer, 10 ²² Si / cm 2 are contained in one atomic layer of the first p-layer.
² and the carrier density is sufficient if impurities are present in the layer at 10 ¹⁹ / cm ² or more. This is the Si atom 1
Since it means that only one carrier is required for every 000 carriers, the film thickness and the impurity concentration are adjusted so that such a carrier as can maintain such a carrier density, for example, an acceptor such as boron exists. be able to.

By forming the first p-layer as described above, a sufficient internal electric field can be formed in the i-layer described later.
Since a relatively large open-circuit voltage can be secured and an increase in the amount of light absorption can be suppressed, a relatively large short-circuit current can be obtained. The first p-layer may have its surface plasma-treated as described later. By performing the plasma treatment on the surface in this manner, it is possible to provide a good p / i interface characteristic together with a second p layer described later.

In the second p-layer, the p-layer composed of an amorphous silicon layer whose impurity concentration decreases as approaching the i-layer is defined by the discharge decomposition of a source gas containing no p-type impurity when this layer is formed. An i-layer is formed. Simultaneously with or after the formation of the i-layer, diffusion of impurities from the lower first p-layer and / or mixing of impurities from the film formation atmosphere cause
It means a layer that can be p-type.

Therefore, it is preferable that the impurity of the second conductivity type in the second p-layer is lower than the impurity concentration of the first p-layer and gradually decreases from the first p-layer to the i-layer described later. As described above, when the impurity concentration in the second p-layer is gradually reduced, the light absorption coefficient can be gradually increased toward the i-layer, that is, the effect of the impurity to extract hydrogen from the second p-layer. And the amount of light absorption can be gradually reduced, and the film quality of the second p-layer can be prevented from deteriorating. Note that the second p-layer is 1
It may be formed of layers, or may be formed of a plurality of layers in which film formation conditions and the like are changed. The thickness of the second p-layer is not particularly limited, but may be, for example, about 1 to 200 nm. When the second p-layer is formed of a plurality of layers, the thickness of each layer is preferably about 1 to 30 nm.

As will be described later, the surface of the second p-layer may be subjected to plasma treatment each time a predetermined thickness is formed, or a plurality of second p-layers may be formed. If such is the case, the surface of each layer may be plasma-treated. Note that all surfaces of the plurality of layers may be plasma-treated, or the surfaces of some of the layers may be plasma-treated.

In the photoelectric conversion device of the present invention, the second pi
The i-layer and the n-layer forming the n-junction are not particularly limited as long as they are the i-layer and the n-layer usually used for the pin junction in the photoelectric conversion element. For example, i-layer and n
Each of the layers may be formed of the above-described amorphous silicon layer, or may be formed of a crystalline silicon layer. The i-layer does not contain an impurity serving as a carrier, and the n-layer includes a layer into which an impurity serving as a donor, for example, phosphorus or arsenic is introduced at about 10 ¹⁸ to 10 ¹⁹ cm ⁻³ . These film thicknesses can be appropriately adjusted depending on the energy to be obtained by the photoelectric conversion element, the impurity concentration in the p layer, the n layer, and the like. For example, about 1 to 100 nm and about 1 to 200 nm, respectively. No.

The back electrode layer is not particularly limited as long as it is a conductive material usually used as an electrode. For example, metals such as gold, platinum, silver, copper, and aluminum, and the above-described conductive oxide And the like. These film thicknesses can be appropriately selected according to the usage mode of the photoelectric conversion element. Further, a buffer layer, an intermediate layer, a conductive layer, an insulating layer, and the like may optionally be further provided between the transparent electrode layer, the p layer, the i layer, the n layer, and the back electrode layer.

In the method for manufacturing a photoelectric conversion element of the present invention, preferably, first, the surface of the n-layer of the first pin junction is
An amorphous silicon film doped with a p-type impurity at a high concentration is formed as a first p-layer so as to have a thickness of 5 nm or less.
The first p-layer is formed by a known method, for example, SiH ₄ , GeH ₄ ,
It can be formed by a CVD method using a gas such as H ₂ , Ar, or He, a plasma CVD method, or the like.

A p-type impurity (boron or the like) constituting the p-layer
For example, B ₂ H ₆ gas may be mixed into the source gas and doped simultaneously with film formation, or after the semiconductor layer is formed, doping may be performed by a method such as ion implantation or thermal diffusion. Further, the first p-layer may be subjected to a plasma treatment on its surface as described above. The plasma treatment at this time is preferably performed by a gas-phase plasma containing at least one gas of H ₂ , Ar, and He.

Next, a second p-layer made of an amorphous silicon layer is formed on the first p-layer by discharge decomposition of a source gas containing no p-type impurity. The method for forming the second p-layer can be the same as the method for forming the first p-layer except that the source gas does not contain impurities.

By forming a film by such a method, p
Do not positively contain the impurities of the mold.
The diffusion of p-type impurities from the p-layer results in i
A second p-layer in which the impurity concentration decreases as approaching the layer can be formed. In the case where the first and second p-layers are formed by a film forming apparatus, for example, a plasma CVD apparatus, the second p-layer is formed in the same chamber as the first p-layer so that the second p-layer exists in the atmosphere. P when forming 1p layer
As a result, the second p-layer can be formed by mixing the type impurities.

Further, the second p-layer has its surface and / or
Alternatively, the surface of the obtained second p-layer is preferably subjected to plasma treatment every time a predetermined thickness is formed. The predetermined thickness at this time is, for example, about 1 to 30 nm. Further, when performing the plasma processing a plurality of times for each predetermined film thickness,
It is preferable to gradually reduce the plasma irradiation time and / or the power input during the processing to the second time from the first time and the third time from the second time. By such a plasma treatment, the light absorption coefficient in the second p-layer can be gradually increased as approaching the i-layer, that is, the increase in the light absorption in the first p-layer can be suppressed gradually. Voc and F.I. F. Can be suppressed. The conditions of the plasma processing described above can be set, for example, as shown in Table 1.

[0034]

[Table 1]

The formation of the second p-layer may be performed in the same chamber as that of the film forming apparatus in which the first p-layer is formed. In this case, the light absorption coefficient can be increased without designing a special doping profile,
That is, an increase in the amount of light absorption in the first and second p-layers can be suppressed, so that a reduction in manufacturing cost can be realized. The i-layer is not necessarily formed in the same chamber as the chamber of the film forming apparatus in which the first p-layer is formed, but is preferably formed in a different chamber. In this case, the second p
The second layer does not cause excessive diffusion of impurities to the layer.
It is possible to easily control the internal electric field in the p-layer.

The i-layer is formed as a silicon layer containing no p-type and n-type impurities by an i-layer deposition chamber.
The n-layer is formed as a silicon layer in which n-type impurities are diffused by an n-layer deposition chamber. Note that the first pin junction may be one using a conventional film forming method, or a pin junction having a p-layer of the present invention described below (hereinafter referred to as a second pin junction).
n-junction), and the description is omitted here.

As described above, in the tandem-type photoelectric conversion element of the present invention, the p-layer adjacent to the n-layer has a boron doped a
-Since the configuration uses only the a-Si film instead of the configuration using the SiC film, the interface characteristics at the interface of both the adjacent n-layer and i-layer are improved, thereby reducing the amount of light absorption in the p-layer. The increase can be suppressed and good ohmic contact between the layers can be obtained.

FIG. 1 shows a specific cross-sectional structure of a tandem photoelectric conversion element of the present invention. The tandem-type photoelectric conversion element includes a transparent electrode layer 2, a first pin
The junction 3, the second pin junction 9, and the back electrode layer 6 are sequentially formed. The second pin junction 9 is connected to the p-layer (1
1, 12, 13, 14), an i-layer 4, and an n-layer 5. Each of the p-layers (11 to 14) is a highly doped p-type a
A first p-layer 7 made of a -Si layer and a second p-layer 8 (a to d) made of a p-type a-Si layer.

The first pin junction 3 also forms one pin junction by laminating the p layer, the i layer and the n layer.
Second pi including the layers (11 to 14), the i-layer 4 and the n-layer 5.
a tandem photoelectric conversion element 10 integrated with the n-junction 9;
20, 30, 40 are formed. The first pin junction 3
Of the p-layer, i-layer and n-layer of the second pi
It may be configured by a manufacturing method different from the pin junction of the n-junction 9.

Hereinafter, a method for manufacturing a tandem photoelectric conversion element according to the present invention will be described with reference to four embodiments.
Here, a doped layer composed mainly of Si will be described, but a similar effect can be obtained for an amorphous silicon-based doped layer containing Ge such as an a-SiGe: H film by the same method.

Example 1 In this embodiment, as shown in FIG. 1, a tandem-type photoelectric conversion element 10 has a transparent electrode layer 2, a first pin junction 3, and a second pin junction 9 on a transparent glass substrate 1. p layer 1
1, an i layer 4, an n layer 5, and a back electrode layer 6 are sequentially formed. In this example, the p-layer 11 includes a first p-layer 7 and a second p-layer 8a. A method for manufacturing the tandem photoelectric conversion element 10 will be described below.

First, a transparent glass substrate 1 with a transparent electrode layer 2 made of uneven ZnO is placed on a substrate support in a p-layer deposition chamber in a plasma vapor deposition apparatus. A first pin junction 3 was produced. Gas of SiH ₄ : CH ₄ : B ₂ H ₆ = 1: 1: 0.02
It is supplied at a flow rate of 00 sccm, deposited at a power of 200 W, and doped with a high concentration of boron.
An SiC layer was formed. A 10 nm non-doped a-SiC film is laminated on this p-type doped a-SiC film, and a 100 nm i layer formed in an i layer film forming chamber and a 30 nm n layer formed in an n layer film forming chamber are stacked. Thus, a first pin junction 3 was manufactured. On the n layer of this pin junction 3, SiH ₄ : B
₂₀₀ sc of a source gas of ₂ H ₆ : H ₂ = 1: 0.1: 20
cm. At this time, the film formation temperature was 200 ° C.
The substrate temperature was set to 200 ° C., the input power was set to 200 W, and the film was formed for about 1 minute to form a highly doped p-type a-Si layer doped with boron at a high concentration as the first p layer 7. The thickness of the obtained highly doped p-type a-Si layer was set to a thickness that allows negligible light absorption, in this case, a thickness of about 3 nm. Here, the growth time was set to a time (approximately one minute as described above) in which boron was sufficiently mixed into the underlying n-layer and good ohmic contact with the upper layer was obtained.

Subsequently, in the same chamber, SiH ₄ : H ₂ =
An a-Si layer not doped with boron was formed to a thickness of about 10 nm using a source gas of 100: 200 sccm. At this time, the a-Si layer becomes a highly doped p-type a-Si layer underlying the a-Si layer, that is, the layer is diffused from the first p-layer 7 or mixed with boron in the atmosphere gas. The whole is turned into a p-layer to form a second p-layer 8a.

Next, on the p-layer (p-type amorphous silicon layer) 11 in which the first p-layer 7 and the second p-layer 8a are laminated,
In the i-layer film forming chamber, SiH ₄ : H ₂ = 200: 500
Using a raw material gas of sccm, the input power is set to 100 W,
An i-layer 4 having a thickness of about 200 nm is formed.
Above, in an n-layer film forming chamber, SiH ₄ : H ₂ : PH ₃ =
10: 500: 3, the input power is 100 W, and the film thickness is 30.
An n layer 5 having a thickness of about nm was formed, whereby a second pin junction 9 was formed. Next, on the n-layer 5 of the second pin junction 9, at a film forming temperature of 200 ° C. and a film thickness of 500
A backside electrode layer 6 was formed by forming an Ag film having a thickness of about nm, and a tandem-type photoelectric conversion element 10 was manufactured.

Embodiment 2 In this embodiment, as shown in FIG. 1, a tandem photoelectric conversion element 20 is formed by forming a transparent electrode layer 2, a first pin junction 3, and a second pin junction 9 on a transparent glass substrate 1. p layer 1
2, an i-layer 4, an n-layer 5, and a back electrode layer 6 are sequentially formed. In this example, the p-layer 12 includes the first p-layer 7 and the second p-layer 8b, and the second p-layer 8b forms the second p-layer every time a predetermined thickness is formed when forming the second p-layer 8b. It is formed by a manufacturing method of performing a plasma treatment on the surface of the layer 8b.

A method for manufacturing the tandem photoelectric conversion element 20 will be described below. First, uneven ZnO is deposited on a substrate support in a p-layer deposition chamber in a plasma vapor deposition apparatus.
A transparent glass substrate 1 having a transparent electrode layer 2 made of was placed, and an a-Si pin junction 3 was formed on the substrate 1. On the n layer of the pin junction 3, SiH ₄ : B ₂ H ₆ :
A source gas of H ₂ = 1: 0.1: 20 was supplied at a flow rate of 200 sccm. At this time, a film formation temperature is set to 200 ° C., a substrate temperature is set to 200 ° C., and an input power is set to 200 W, and a film is formed for about 1 minute. Was prepared. Highly doped p obtained
The thickness of the mold a-Si layer was set to a thickness where the amount of light absorption was negligible, and here a thickness of about 3 nm.

Subsequently, in the same chamber, SiH ₄ : H ₂ =
Using a 100: 200 sccm source material, an a-Si layer not doped with boron was formed to a thickness of about 10 nm.
At this time, the a-Si layer is formed as a p-layer by diffusing boron from the highly doped p-type a-Si layer underlying the a-Si layer, or by mixing the entire layer with boron in an ambient gas. This becomes the 2p layer 8b.

In this example, when a second p-layer having a thickness of about 10 nm is formed, a-Si layer is formed on the first p-layer 7 to reduce light absorption loss of the second p-layer 8b. H ₂ plasma treatment was performed every time a layer was formed to a thickness of 3 nm. Next, the i-layer 4 and the n-layer 5 were stacked on the formed p-layer 12 in the same manner as in the case of the photoelectric conversion element 10 described above to form the second pin junction 9. Then, the second pin junction 9
The back electrode layer 6 was formed on the n-layer 5 of the above, and a tandem-type photoelectric conversion element 20 was manufactured.

Embodiment 3 In this embodiment, as shown in FIG. 1, a tandem-type photoelectric conversion element 30 is formed on a transparent glass substrate 1 by forming a transparent electrode layer 2, a first pin junction 3, and a second pin junction 9. p layer 1
3, an i layer 4, an n layer 5, and a back electrode layer 6 are sequentially formed. In this example, the p-layer 13 includes the first p-layer 7 and the second p-layer 8c, and when the second p-layer 8c forms the second p-layer 8c, a predetermined thickness is formed on the surface of the second p-layer 8c. Each time a film is formed, it is formed by a manufacturing method in which plasma treatment is performed with a reduced plasma irradiation time and / or processing power.

A method for manufacturing the tandem photoelectric conversion element 30 will be described below. First, uneven ZnO is deposited on a substrate support in a p-layer deposition chamber in a plasma vapor deposition apparatus.
A transparent glass substrate 1 having a transparent electrode layer 2 made of was placed, and an a-Si pin junction 3 was formed on the substrate 1. On the n layer of the pin junction 3, SiH ₄ : B ₂ H ₆ :
A source gas of H ₂ = 1: 0.1: 20 was supplied at a flow rate of 200 sccm. At this time, the film formation temperature was set to 200 ° C., the substrate temperature was set to 200 ° C., and the input power was set to 200 W. The film was formed for 1 minute, and a highly doped p-type a-Si layer doped with boron at a high concentration was used as the first p layer 7. Produced. Highly doped p obtained
The thickness of the mold a-Si layer was set to a thickness where the amount of light absorption was negligible, and here a thickness of about 3 nm.

Subsequently, in the same chamber, SiH ₄ : H ₂ =
Using a 100: 200 sccm source material, an a-Si layer not doped with boron was formed to a thickness of about 10 nm.
At this time, the a-Si layer is formed as a p-layer by diffusing boron from the highly doped p-type a-Si layer underlying the a-Si layer, or by mixing the entire layer with boron in an ambient gas. This becomes the 2p layer 8c.

In this example, when a second p-layer having a thickness of about 10 nm is formed, a-Si layer is formed on the first p-layer 7 to reduce light absorption loss of the second p-layer 8c. Each time the layer was formed to have a thickness of 3 nm, the input power of the H ₂ plasma treatment was reduced for 5 minutes. That is, a-Si is formed to a thickness of about 3 nm on the first p-layer 7 and H ₂ plasma treatment is performed for 5 minutes at an applied power of 300 W,
Then formed into a film having a thickness of about 3nm and a-Si, performs irradiation for 5 minutes with H ₂ plasma treatment applied power as 200 W, and then formed into a film having a thickness of about 3nm and a-Si, H ₂ plasma The irradiation was performed for 5 minutes with the input power set to 100 W. As a result, the second p having a thickness of about 10 nm is formed.
The layer 8c was formed.

The second pin junction 9 was formed on the formed p layer 13 by laminating the i layer 4 and the n layer 5 in the same manner as described above. Next, the back electrode layer 6 was formed on the n-layer 5 of the second pin junction 9, and a tandem-type photoelectric conversion element 30 was manufactured. In this example, the plasma processing was performed with the plasma irradiation time kept constant and the processing power gradually reduced. However, the plasma irradiation time may be gradually reduced with the processing power kept constant, or the plasma irradiation time and the processing may be reduced. The power may be gradually reduced together.

Embodiment 4 In this embodiment, as shown in FIG. 1, a tandem-type photoelectric conversion element 40 is formed by forming a transparent electrode layer 2, a first pin junction 3, and a second pin junction 9 on a transparent glass substrate 1. p layer 1
4, an i-layer 4, an n-layer 5, and a back electrode layer 6 are sequentially formed. In this example, the p-layer 14 is composed of a first p-layer 7 and a second p-layer 8d, and is formed by a manufacturing method in which after the first p-layer 7 is formed, the surface of the first p-layer 7 is subjected to plasma processing. .

A method for manufacturing the tandem photoelectric conversion element 40 will be described below. First, uneven ZnO is deposited on a substrate support in a p-layer deposition chamber in a plasma vapor deposition apparatus.
A transparent glass substrate 1 having a transparent electrode layer 2 made of was placed, and an a-Si pin junction 3 was formed on the substrate 1. On the n layer of the pin junction 3, SiH ₄ : B ₂ H ₆ :
A source gas of H ₂ = 1: 0.1: 20 was supplied at a flow rate of 200 sccm. At this time, the film formation temperature was set to 200 ° C., the substrate temperature was set to 200 ° C., and the input power was set to 200 W. The film was formed for 1 minute, and a highly doped p-type a-Si layer doped with boron at a high concentration was used as the first p layer 7. Produced. Highly doped p obtained
The thickness of the mold a-Si layer was set to a thickness where the amount of light absorption was negligible, and here a thickness of about 3 nm.

Subsequently, in the same chamber, the surface of the first p layer 7 was subjected to a plasma treatment using H ₂ gas under the conditions shown in Table 1. Then, in the same chamber, SiH ₄ :
Using a source gas of H ₂ = 100: 200 sccm, an a-Si layer not doped with boron was formed to a thickness of about 10 nm. At this time, the whole of the a-Si layer is p-typed by diffusion of boron from the highly doped p-type a-Si layer underlying the a-Si layer, or by mixing of boron in the atmosphere gas.
Layering becomes the second p-layer 8d. The second pin junction 9 was formed by laminating the i-layer 4 and the n-layer 5 on the formed p-layer 14. Next, the back electrode layer 6 was formed on the n-layer 5 of the second pin junction 9, and a tandem-type photoelectric conversion element 40 was manufactured.

Comparative Test Each of these tandem photoelectric conversion elements 10, 20, 3
Apart from 0 and 40, on a transparent glass substrate for comparison,
Conventional contact layer (highly doped p-type a-Si layer and p-type
A conventional tandem-type photoelectric conversion element formed by laminating a second pin junction including a p-layer having a -SiC layer) was fabricated. First, SiH ₄ : CH ₄ : B ₂ H ₆ = 1: 1: 0.02
Is supplied at a flow rate of 200 sccm, and the input power 20
A film was formed at 0 W, and a high boron-doped a-SiC layer doped with boron at a high concentration was produced. This p-type doped a-S
A 10 nm non-doped a-SiC film is stacked on the iC film, and an 80 nm i layer formed in the i layer film forming chamber and a 30 nm n layer formed in the n layer forming chamber are stacked to form a first pin junction 3.
Was prepared. On top of this, a highly doped p-layer serving as a recombination layer is 3
nm, and then SiH ₄ : CH ₄ : B ₂ H ₆ = 1: 1:
A gas of 0.02 was supplied at a flow rate of 200 sccm, a film was formed at an input power of 200 W, and a high boron-doped a-SiC layer doped with boron at a high concentration was produced. On this p-type doped a-SiC film, a non-doped a-SiC film is
m-layer, and a 300 nm i-layer and n
A 30 nm n-layer formed in a layer forming chamber is laminated to form a second pi
An n-junction 3 was produced. Thereafter, a backside metal electrode layer 6 was formed by sputtering to manufacture a tandem-type photoelectric conversion element (pin junction cell 100).

The conventional tandem type photoelectric conversion element and the tandem type photoelectric conversion element 10 according to the present invention,
The spectral sensitivity characteristics of 20 and 30, that is, the wavelength (Wavelengt)
h) The spectral response to () was measured. The results are shown in FIG. It should be noted that reference numeral 110 in the figure indicates the characteristics of the upper pin junction. Regarding the photoelectric conversion element 30, although the alloy film is not used for the p-layer, the spectral sensitivity characteristics of the photoelectric conversion element 30 are similar to those of the conventional p-type a-SiC layer using the p-type a-SiC layer.
The sensitivity was equivalent to that of the in-junction cell 100. In addition, as the plasma processing conditions are relaxed as approaching the i-layer, p
/ I, the adverse effect of the interface was suppressed and recombination at the interface was reduced. F. Is F. F. > 0.74.

Further, the IV characteristics of the conventional tandem photoelectric conversion device and the tandem photoelectric conversion device 30 according to the present invention, that is, the current with respect to the voltage were measured. The results are shown in FIG. As is clear from FIG.
In the tandem-type photoelectric conversion element 30 according to the third embodiment, p
Due to the small light absorption of the layer, the conventional p-type a-SiC
A large short-circuit current value equivalent to or slightly exceeding that of the pin junction cell 100 using the layer was obtained. Also,
As is clear from Voc (open circuit voltage), it is understood that the carrier density as the p-layer is also sufficient.

[0060]

According to the present invention, in a tandem photoelectric conversion element in which a plurality of pin junctions are stacked, an optical layer having an optical band gap of 5 nm or less, in which n-type and p-type impurities are mixed on an n-layer, is formed. 1.85 eV or higher amorphous p-type a-
With the photoelectric conversion element formed by stacking Si layers, n
It is possible to achieve a p-layer without deteriorating the film quality due to the effect of extracting hydrogen from silicon in the film by boron while securing good ohmic characteristics with the layer. This element has sufficient film properties as a window layer without changing the material a-Si. Therefore, boron doped S
To solve the problem in the case of using an iC film, that is, the problem that the bonding with the photoelectric conversion layer is poor, and the recombination of generated photocarriers is the main cause, making it impossible to secure a sufficient open voltage and fill factor. Can be.

The p-layer adjacent to the n-layer is formed such that the p-type impurity concentration is high on the n-layer side and low on the i-layer side, and the optical band gap is wide on the n-layer side and narrow on the i-layer side. Thereby, good ohmic characteristics can be secured at the n / p interface, and the amount of light absorption in the p layer can be reduced. A p-layer adjacent to the n-layer has at least a two-layer structure, an amorphous silicon film doped with a p-type impurity is formed as a first p-layer, and then a discharge decomposition of a source gas containing no p-type impurity is formed as a second p-layer. If a photoelectric conversion element is formed by forming and laminating an amorphous silicon layer by p-layering, the p-layer has sufficient film properties as a window layer that does not cause a film quality deterioration due to an effect of extracting hydrogen from silicon in the film by boron. , The sensitivity of the second pin junction can be ensured.

If the first p-layer and the second p-layer are formed in the same chamber of the film forming apparatus, the p-layer can be formed without designing a special doping profile, and the manufacturing cost can be greatly reduced and simplified. Becomes Furthermore, if the first p-layer, the second p-layer, and the i-layer are formed in different chambers of the film forming apparatus, excess boron is not diffused into the i-layer, so that the internal electric field of the i-layer can be easily controlled. Can be done. This leads to suppression of the space charge in the i-layer, so that the collection efficiency of the photocurrent is improved. F. Leads to the suppression of the decrease.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a main part showing an embodiment of a tandem photoelectric conversion element of the present invention.

FIG. 2 is a graph illustrating a comparison of spectral sensitivity characteristics between a photoelectric conversion element of the present invention and a conventional photoelectric conversion element.

FIG. 3 is a graph showing IV characteristics of the photoelectric conversion device of the embodiment of FIG. 1 and a photoelectric conversion device of a conventional example.

DESCRIPTION OF SYMBOLS 1 Glass substrate 2 Transparent electrode layer 3 First pin junction 4 i layer of second pin junction 5 n layer of second pin junction 6 Back electrode layer 7 1st p layer (a-Si highly doped layer) 8 2nd p layer (P-type a-SiC layer) 9 2nd pin junction 10, 20, 30, 40 Tandem type photoelectric conversion element 11, 12, 13, 14 p layer of 2nd pin junction

Claims (9)

[Claims] 1. A photoelectric conversion element formed by stacking a plurality of pin junctions, wherein at least a p-layer adjacent to an n-layer has a thickness of 5 nm or less in which n-type and p-type impurities are mixed as a first p-layer. A photoelectric conversion element comprising: an amorphous silicon layer having the following structure: and an amorphous silicon layer whose impurity concentration decreases as approaching the i-layer as the second p-layer. 2. The p-layer adjacent to the n-layer is formed such that the p-type impurity concentration is higher on the n-layer side and lower on the i-layer side, and the optical band gap is wider on the n-layer side and narrower on the i-layer side. The photoelectric conversion element according to claim 1, wherein the photoelectric conversion element is formed. 3. A method for manufacturing a photoelectric conversion element comprising a plurality of pin junctions stacked, wherein a p-layer adjacent to the n-layer has at least a two-layer structure, and amorphous silicon doped with a p-type impurity as a first p-layer. A method for manufacturing a photoelectric conversion element, comprising forming a film, and then forming and laminating an amorphous silicon layer as a second p-layer by discharge decomposition of a source gas containing no p-type impurity. . 4. The method according to claim 3, wherein a plasma treatment is performed on the surface of the first p-layer after forming the first p-layer. 5. The method according to claim 3, wherein when forming the second p-layer, the surface of the second p-layer is subjected to plasma treatment every time a predetermined thickness is formed. 6. The method for manufacturing a photoelectric conversion element according to claim 4, wherein the plasma treatment is performed with a gas phase plasma containing at least one gas of H ₂ , Ar, and He. 7. The method for manufacturing a photoelectric conversion element according to claim 5, wherein the plasma treatment is performed with a reduced plasma irradiation time and / or processing power every time a predetermined film thickness is formed. 8. The method for manufacturing a photoelectric conversion element according to claim 3, wherein the first p-layer and the second p-layer are formed in the same chamber of a film forming apparatus. 9. The method according to claim 3, wherein the first and second p-layers and the i-layer are formed in different chambers of a film forming apparatus.