JPH10229209A - Photovolaic element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve photoelectric conversion efficiency as well as reliability, by a method wherein the region in the decreasing density of IV group element as the main component of doped layers is diffused in the forming surface of the doped layers. SOLUTION: A back electrode 102 and a transparent conductive layer 103 are formed on a substrate 101 and then an n type semiconductor layer 104 is formed on the layer 103. Next, an i type semiconductor layer 105 made of fine crystalline grains 111 and a p type semiconductor layer 106 are successively formed on the layer 104. Next, a part of the n type semiconductor layer 104 and the p type semiconductor layer 106 are doped to form doped layers so that the regions 109, 110 in decreased density of the IV group element as the main component of the doped layers may be diffused in the forming surface of the doped layers to form a transparent electrode 107 and a collector electrode 108 on the topmost part. Through these procedures, the photoelectric conversion efficiency and the reliability can be improved, thereby enabling a power supply source to be realized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a photovoltaic device having a specific doping layer. Specifically, the present invention has a semiconductor junction such as a pin junction, and the doping layer includes a plurality of group IV element low-density regions in which the density of a group IV element that is a main component of the layer is low. The present invention relates to a photovoltaic device having dispersed photovoltaic devices in a layer formation surface and exhibiting improved photovoltaic device characteristics.

[0002]

2. Description of the Related Art A photovoltaic element (solar cell) that can be used as a photoelectric conversion element for converting light such as sunlight into electric energy is widely used as a power supply source for various consumer appliances, and is used outdoors. It is also often used as a power source for power supplies. More recently, it has been used as a power supply for vehicles and as a power supply for houses. The photovoltaic element is expected as a power source that replaces fossil power generation and nuclear power generation, for which the problem of environmental pollution has been pointed out, and R & D on such power generation is being actively conducted.

As such photovoltaic elements (solar cells), typically, photovoltaic elements, polycrystalline photovoltaic elements,
There are amorphous photovoltaic devices, copper indium selenide, compound semiconductor photovoltaic devices, and the like. These photovoltaic elements use the photovoltaic power of a pn junction of a semiconductor, and the semiconductor absorbs sunlight to generate photocarriers of electrons and holes. It drifts due to the internal electric field and is taken out as electric power.

In the above-described photovoltaic device, a crystal (ie, a crystal)
The (single-crystal) silicon photovoltaic element is most excellent in terms of reliability and photoelectric conversion efficiency, but has various problems as described below.

[0005] First, the crystalline silicon photovoltaic element is usually manufactured through a semiconductor process. That is, a single crystal of silicon whose valence electrons are controlled to p-type or n-type is formed by a crystal growth method such as the CZ method, and the single crystal is sliced to form a silicon wafer having a thickness of about 300 μm. Then, a pn junction is formed by forming a layer of a different conductivity type by an appropriate means such as diffusion of a valence power control agent so that the conductivity type is opposite to the conductivity type of the wafer. As described above, the crystalline silicon photovoltaic element manufactured through the semiconductor process inevitably has a high production cost.

In addition to this problem, there are the following problems.

That is, since single crystal silicon is an indirect transition and has a small light absorption coefficient, the single crystal silicon photovoltaic element has at least 5
It must have a thickness of 0 micron, and its band gap is about 1.1 eV, which is narrower than 1.5 eV suitable for a photovoltaic device, so that short wavelength components cannot be used effectively. When polycrystalline silicon is used instead of monocrystalline silicon to make a polycrystalline silicon photovoltaic element, the production cost can be lower than that of crystalline silicon photovoltaic element, The problem is again here, and its thickness cannot be reduced. Also, when using polycrystalline silicon, there are problems associated with grain boundaries and other problems.

Further, in the case of a crystalline silicon photovoltaic device, it is difficult to obtain a large-area wafer because a crystalline material is used for the production thereof. Therefore, the photovoltaic device has a large area. It is difficult. Therefore, in order to extract a large amount of power, it is necessary to connect and integrate a number of crystalline silicon photovoltaic elements in series or in parallel via wiring. Also, expensive implementations are needed to protect the photovoltaic elements from damage caused by various weather conditions when used outdoors. Therefore, there is a problem that the production cost per unit power generation becomes higher than the existing power generation method.

As described above, the crystalline silicon photovoltaic element has a problem that the production cost is high and it is difficult to increase the area. Therefore, it is technically difficult to use it as a power supply source for outdoor installation. Problems and economic problems must be overcome. For this reason, non-single-crystal photovoltaic elements such as amorphous photovoltaic elements, which can be made to have a large area at a relatively low production cost and can be suitably used as a power supply source for outdoor installation, have been attracting attention. Is actually used as a power supply for outdoor installations, and various research and developments have been made on it.

As such a non-single-crystal photovoltaic element,
For example, amorphous silicon (a-Si), amorphous silicon germanium (a-SiGe), amorphous silicon carbide (a-Si
Amorphous (amorphous) photovoltaic elements using a tetrahedral group IV element amorphous semiconductor such as SiC) as a photovoltaic generation layer, and II-V such as CdS and Cu2S.
There is a compound semiconductor photovoltaic device using a group I or III-V compound semiconductor such as GaAs or GaAlAs as a photovoltaic generation layer. Among these, a so-called thin film amorphous photovoltaic element using an amorphous semiconductor as a photovoltaic generation layer can easily form a film having a large area as compared with a single crystal photovoltaic element. There are many advantages, such as a small thickness and the ability to deposit on any substrate material. However, although such an amorphous photovoltaic device has the above-mentioned advantages, it is necessary to further improve its photoelectric conversion efficiency and its reliability for practical use as a desirable power generation source. It has become.

Various methods have been known as means for improving the photoelectric conversion efficiency of a photovoltaic element using a non-single-crystal semiconductor. For example, in the case of a photovoltaic element using a pin-type semiconductor junction, to improve the photoelectric conversion efficiency, the p-type semiconductor layer, the i-type semiconductor layer, the n-type semiconductor layer, and the transparent There is known a method for improving the characteristics of each layer of the electrode and the back electrode.

Further, US Pat. No. 2,949,498 discloses a method of improving the photoelectric conversion efficiency of a photovoltaic element using a so-called stack cell in which a plurality of photovoltaic elements having a unit element structure are stacked. Is disclosed. This stack cell uses a pn junction crystal semiconductor. The method of improving the photoelectric conversion efficiency using the stack cell can be applied to both amorphous and crystalline photovoltaic devices. According to this method, the solar spectrum can be efficiently absorbed by photovoltaic elements having different band gaps, and the power generation efficiency can be improved by increasing Voc.

The technique using such a stack cell is to improve the photoelectric conversion efficiency by stacking elements having different band gaps and efficiently absorbing each part of the spectrum of sunlight, and improving the photoelectric conversion efficiency. Is designed so that the band gap of the so-called bottom layer located below the top layer is smaller than the band gap of the so-called top layer located at the bottom. However, even in the case of the technique using the stack cell, the same as in the case of the single-layer cell (single cell), in order to improve the photoelectric conversion efficiency, the p-type semiconductor layer and the i-type semiconductor It is necessary to improve the characteristics of each layer, the n-type semiconductor layer, the transparent electrode, and the back electrode.

For example, the i-type semiconductor layer needs to have a desired band gap depending on the use of a single cell or a stacked cell. The level in the gap (localized level) is reduced as much as possible, and the optical carrier travels. It is important to improve the performance.

There are other proposals for improving the photoelectric conversion efficiency of the photovoltaic element, other than the method of essentially improving the film quality of the i-type semiconductor layer as described above. For example, U.S. Pat. Nos. 4,254,429 and 4,37.
No. 7,723 discloses a method of using a so-called buffer layer having a bandwidth gradient at a junction interface between a p-type semiconductor and / or an n-type semiconductor and an i-type semiconductor. In the method, the purpose of the buffer layer is:
At the junction interface between the amorphous silicon p-type semiconductor or n-type semiconductor and the amorphous silicon germanium i-type semiconductor,
Since a large number of levels are generated due to the difference in lattice constant, the use of amorphous silicon at the junction interface improves the Voc by eliminating the levels to improve the junction and not to impair the mobility of carriers. It is in.

As another method, for example, amorphous silicon germanium is used as the i-type semiconductor layer, and a composition ratio is provided in the intrinsic layer by changing the composition ratio of silicon and germanium to improve the characteristics. A method for providing a gradient layer is known. For example, U.S. Pat. No. 4,816,082 discloses that the band gap of an i-type semiconductor layer in contact with a valence electron-controlled first semiconductor layer on the light incident side is widened, and the band gap increases toward the center. A method is disclosed in which the band gap is gradually narrowed, and the band gap is gradually widened toward the second semiconductor layer in which valence electrons are controlled. According to this method, carriers generated by light can be efficiently separated by the action of an internal electric field, and the photoelectric conversion efficiency is improved.

Further, as another method, when amorphous silicon or amorphous silicon germanium is used as the i-type semiconductor layer, it is often slightly n-type.
There is known a method in which a p-type valence electron controlling agent is slightly mixed in the i-layer to improve the hole mobility.

On the other hand, a photovoltaic element which has been hardly observed to undergo photodegradation by using microcrystalline silicon for the i-type semiconductor layer has recently been announced. (J. Meier et.al. 1994 IEE
E First World Conference on Photovoltaic Energy Co
nversion p409) This photovoltaic element uses plasma CVD by glow discharge, similar to the manufacturing process of a conventional amorphous photovoltaic element. There is a possibility that a large-area photovoltaic device can be manufactured by an inexpensive manufacturing process as well as the device. However, the photoelectric conversion efficiency of this photovoltaic element is still inferior to the value of a conventional amorphous silicon single cell (about 13%). As described above, an important issue of a photovoltaic element using microcrystalline silicon for an i-type semiconductor layer is improvement in photoelectric conversion efficiency.

In order to improve the photoelectric conversion efficiency of a photovoltaic device using an amorphous semiconductor or microcrystalline silicon for the i-type semiconductor layer, a p-type semiconductor layer constituting the photovoltaic device, i It is necessary to improve the characteristics of each layer of the type semiconductor layer, the n-type semiconductor layer, the transparent electrode, and the back electrode.

Of these layers, a so-called doped layer such as a p-type semiconductor layer or an n-type semiconductor layer is first required to have a high density of activated acceptors or donors and a small activation energy of the thin film. You. Thereby, the diffusion potential (built-in potential) when the pin junction is formed increases, the open-circuit voltage (Voc) of the photovoltaic element increases, and the photoelectric conversion efficiency improves.

Next, since the doping layer basically does not contribute to the generation of a photocurrent, it is required that the incidence of light on the i-type semiconductor layer for generating the photocurrent is not hindered as much as possible. Therefore, it is important for the doping layer to widen the optical band gap and reduce the film thickness.

Further, it is required that a homo or hetero pin junction is formed between the doping layer and the i-type semiconductor layer, and the interface level at the junction interface is small.

Further, as for the doping layer, in the case of a stacked cell, the following characteristics are required in addition to the above characteristics. That is, a pn junction or pin
When a plurality of junctions are stacked, a reverse junction where the p-type semiconductor layer and the n-type semiconductor layer are in contact with each other occurs. This portion is required to be a tunnel junction, have ohmic properties, and have low series resistance.

With respect to achieving a doping layer having characteristics as described above, proposals have been made regarding constituent materials and a method for forming the same.

For example, there is a proposal to use a material such as Si, SiC, SiN, or SiO as a constituent material of the doping layer and make the material in an amorphous or microcrystalline form. As a forming method, there are proposals using RF plasma CVD, ECR plasma CVD, optical CVD, or the like.

Among the constituent materials of the doping layer, amorphous silicon (a-S) is used as a doping layer on the back side of the i-type semiconductor layer with respect to the light incident direction because of its easy formation.
i) is widely used, and as a doping layer on the light incident side of the i-type semiconductor layer, amorphous silicon carbide (a-SiC) is used from the viewpoint of a small absorption coefficient, and the absorption coefficient is small and the activation energy is small. Therefore, microcrystalline silicon (μc-Si) is used.

[0027]

However, for example, amorphous silicon carbide (a-SiC) is used as a basic constituent material of the doping layer, and a material whose optical band gap is increased by adding a predetermined element thereto is used. When a doping layer is formed by adding H, C, N, O, or H, C, N, O,
Alternatively, by using an element such as a halogen element and increasing the amount of addition, the absorption coefficient of the doping layer can be reduced and the short-circuit current (Jsc) of the photovoltaic element can be increased. However, the activation energy of the doping layer tends to increase, the built-in potential of the photovoltaic element tends to decrease, and the open-circuit voltage (Voc) tends to decrease.
Further, as the difference between the composition of the doping layer and the composition of the i-type semiconductor layer increases, there is often a problem that the interface state at the interface between the doping layer and the i-type semiconductor layer increases.

In the doping layer, when the concentration of the valence electron controlling agent (dopant) is higher, the activation energy of the doping layer decreases, the built-in potential of the photovoltaic element increases, and the open-circuit voltage (Voc) increases. However, when the dopant concentration of the doping layer is high, the optical band gap of the doping layer decreases, the light absorption in the doping layer increases, and the short-circuit current (Js
c) tends to decrease.

Further, in terms of the form of the constituent material of the doping layer, microcrystals generally have a smaller absorption coefficient, a larger optical band gap, and a smaller activation energy than amorphous, so that However, there are often the following problems.

That is, it is difficult to form a desired microcrystalline material having a high activated acceptor or donor density and a small activation energy. That is, for materials other than microcrystalline Si (μc-Si), the open-circuit voltage (Vo
Published examples of high photovoltaic element of c) is greater photoelectric conversion efficiency is low, prospect of practical application is not passed. Even when microcrystalline Si is used, suitable conditions for forming microcrystalline Si are found only within a limited range, and control is difficult. Further, on the amorphous i-type semiconductor layer,
When the microcrystalline doping layer is formed, the i-type semiconductor layer may be damaged when the microcrystalline doping layer is formed because the microcrystalline doping layer forming conditions are different from the i-type semiconductor layer forming conditions. . In addition, when the i-type semiconductor layer and the doping layer form a hetero junction, the interface state increases, which may adversely affect the pin junction when the pin junction is formed.

Further, when designing the thickness of the doping layer suitable for the photovoltaic element, regardless of which material is used, the thinner the thickness of the doping layer, the larger the amount of light transmitted through the doping layer. Therefore, the short-circuit current (Jsc) of the photovoltaic element can be increased. However, when the thickness of the doping layer is reduced, the activation energy of the doping layer increases, and the built-in potential of the photovoltaic element decreases. Therefore, the open-circuit voltage (Voc) tends to decrease. Therefore, the thickness of the doping layer for maximizing the photoelectric conversion efficiency of the photovoltaic element is limited to a narrow range, and if it is outside the range, the photoelectric conversion efficiency tends to decrease.

As described above, in the prior art,
It is difficult to realize a doping layer having a large light transmittance, a large built-in potential, and a low interface state, and the development of a doping layer for a non-single-crystal type photovoltaic element has not yet been sufficiently developed. From these facts, in order to further improve the photoelectric conversion efficiency of the non-single-crystal based photovoltaic element, it is also important to further improve the i-type semiconductor layer, It is important to make the doping layer ideal.

The present invention overcomes the above-mentioned problems in the prior art, has an ideal doping layer that achieves the above-mentioned objects, has a high photoelectric conversion efficiency and high reliability, and has a large amount at a reasonable production cost. An object of the present invention is to provide a photovoltaic element which can be produced and practically used as a power source.

[0034]

Means for Solving the Problems The inventors of the present invention overcame the above-mentioned problems in the prior art, and as a result of intensive studies on the structure of a doping layer of a photovoltaic element and a method of forming the same to achieve the above object. The photovoltaic element provided with a doping layer having the following configuration has an open-circuit voltage (V
oc) was large, the photoelectric conversion efficiency was high, the reliability was high, and mass production was possible at a reasonable production cost.

That is, the basic aspect is a photovoltaic element having a semiconductor junction, in which the region where the density of the group IV element, which is the main component of the doping layer, is low (ie, the low density of the group IV element is low). Regions) are scattered in the formation surface of the doping layer.

Here, the group IV element low-density region is:
This is a region where the density of the group IV element, which is the main component of the doping layer, is lower than that of other parts in the doping layer, and a plurality of such regions are intermittent in the surface on which the doping layer is formed. Exists. The shape of the low-density region is spherical, spheroidal, or three-dimensional polygonal,
It may be indefinite. Further, the adjacent low-density regions may be in contact with each other and may be non-uniformly continuous.

When the average height in the thickness direction of the low density region is d and the average diameter in the direction parallel to the substrate surface on which the semiconductor layer is formed is L, 3 nm ≦ d ≦ 40 nm and 3 nm ≦ L ≦
The thickness is 80 nm.

In the low-density region, the concentration of an element for expanding an optical band gap is higher than that of another portion of the doping layer.

[0039] The low-density region is characterized in that the concentration of the valence electron controlling agent is higher than the other parts of the doping layer.

At least a part of the doping layer in which the low-density region exists is made of a microcrystalline semiconductor.

The low-density region is amorphous.

The semiconductor device is characterized by having a pin junction comprising the doping layer and a substantially intrinsic semiconductor layer.

Further, the semiconductor device has a doping layer in which low-density regions in which the density of the group IV element as a main component is low are discretely present, and a substantially intrinsic semiconductor layer at least partially composed of microcrystals. A photovoltaic element characterized by the above. Further, a photovoltaic element having the following features is provided.

The average height in the film thickness direction of the low density region is
d, where L is the average diameter in the direction parallel to the semiconductor layer formation surface, 3 nm ≦ d ≦ 40 nm and 3 nm ≦ L ≦ 80 nm.

In the low-density region, the concentration of the element for expanding the optical band gap is higher than in other portions of the doping layer.

At least a part of the doping layer is made of a microcrystalline semiconductor.

The low density region is amorphous.

The volume ratio of the microcrystals of the substantially intrinsic semiconductor layer is 50% or more, the average particle size of the microcrystals is 3 nm or more, and the microcrystals are in a direction perpendicular to the surface on which the semiconductor layer is formed. Is not less than twice the average diameter in the horizontal direction.

A doping layer of the same conductivity type and at least partially made of a microcrystalline semiconductor is laminated on the amorphous doping layer, and a substantially intrinsic semiconductor layer at least partially made of microcrystal is formed thereon. Are laminated.

The semiconductor device has a plurality of pin junctions including the doping layer and the substantially intrinsic semiconductor layer.

(Function) A doped layer having a high density of activated acceptors or donors and having both low activation energy and low absorption coefficient can be formed, and the open-circuit voltage of the photovoltaic element can be increased. (Voc)
, The short circuit current (Jsc) and the fill factor (FF) increase, and the photoelectric conversion efficiency improves. Further, the stress of the doping layer is relieved, and the film at the upper and lower interfaces of the doping layer does not peel off, and the yield of manufacturing the photovoltaic element is improved.

Although the detailed mechanism of the above action has not yet been sufficiently elucidated, the following may be considered. First, the intermittent existence of the group IV element low-density region in which the density of the group IV element is small increases the optical band gap of the group IV element low-density region, and causes light absorption in the entire doping layer. And the incidence of light on the i-type semiconductor layer increases, so that the density of the group IV element is reduced. As a result, the short-circuit current (Jsc) is improved. Further, since the group IV element low-density regions are discretely present, the activation energy of the doping layer is maintained at a low value, and the built-in potential is maintained at a high value. Voc) is maintained at a high value. Also, compared to a conventional doping layer having a reduced thickness so that light absorption is reduced to the same extent as the doping layer of the present invention, the activation energy of the doping layer is lower, the built-in potential is higher, and The open-circuit voltage of the electromotive element (Vo
c) is improved. In addition, the increase in the built-in potential increases the internal electric field of the i-type semiconductor layer of the photovoltaic element, reduces the recombination of photocarriers at the interface between the doping layer and the i-type semiconductor layer, and reduces the fill factor. (FF) is improved.

When the average height of the group IV element low-density region in the thickness direction is d and the average diameter in the direction parallel to the substrate surface on which the semiconductor layer is formed is L, 3 nm ≦ d ≦ 40 nm and 3 nm By setting ≦ L ≦ 80 nm, the operation in the first aspect described above is further emphasized, and the open-circuit voltage (Voc), short-circuit current (Jsc), and fill factor (FF) of the photovoltaic element further increase, and Conversion efficiency is further improved. Although the detailed mechanism of this action has not yet been sufficiently elucidated, the following may be considered. That is, by arranging the group IV element low-density regions in a minute size as described above and discretely arranging them,
The region where the group IV element has a normal density also has a minute size similarly to the above-described size, and a quantum well effect occurs in a direction parallel to the surface where the doping layer is formed. The band gap increases, and the light absorption in the doping layer further decreases.

The effect of the first aspect described above is further emphasized by the fact that the concentration of the element for expanding the optical band gap is higher in the low density region of the group IV element than in other portions of the doping layer. In addition, the open-circuit voltage (Voc) and short-circuit current (Jsc) of the photovoltaic element further increase, and the photoelectric conversion efficiency further improves. Here, when the group IV element that is the main component is Si, examples of the element that enlarges the optical band gap include H, C, N, O, and a halogen element. In the conventional doping layer having a uniform composition, as described above, when the addition amount of these elements is increased, the light absorption of the doping layer is reduced, but the activation energy is increased and the opening of the photovoltaic element is increased. The voltage (Voc) may decrease. On the other hand, when the doping layer of the present invention is used, the region where the concentration of the element for expanding the optical band gap is high is locally and discretely arranged. Is suppressed, the donor or the acceptor is activated, and the activation energy is maintained at a low value. As a result, even when the short-circuit current (Jsc) is increased, the built-in potential is maintained at a high value. It is considered that the open circuit voltage (Voc) of the electromotive element is maintained at a high value.

Since the concentration of the valence electron controlling agent in the group IV element low-density region is higher than that of the other portion of the doping layer, the effect of the first embodiment described above is further emphasized, and The open-circuit voltage (Voc), short-circuit current (Jsc), and fill factor (FF) of the element further increase, and the photoelectric conversion efficiency further improves. Here, when the group IV element which is the main constituent is Si, as the valence electron controlling agent, a p-type valence electron controlling agent (Group III atom B, Al, Ga, In, Tl) or n Type valence electron control agents (atoms P, As, Sb, Bi in group V of the periodic table) and the like. In a conventional doping layer having a uniform composition, as described above, when the addition amount of these elements is increased, the activation energy of the doping layer is reduced, but the optical band gap is often reduced. In some cases, the light absorption of the doping layer may increase. On the other hand, when the doping layer of the present invention is used, the region where the concentration of the valence electron controlling agent is high (heavy doping region) is locally and discretely arranged. Even if the concentration of the valence electron controlling agent is increased (heavy doping) so as to suppress the disorder of the doping layer and lower the activation energy of the doping layer, the decrease in the optical band gap of the doping layer is small, and the light absorption of the doping layer is small. Is suppressed, and the short-circuit current (J
It is considered that sc) can be maintained at a high value. In addition, since the heavy doping region is locally and discretely arranged, it is conceivable that the optical band gap of this region is widened due to the quantum well effect and the light absorption of the doping layer is reduced.

Since at least a part of the doping layer in which the group IV element low-density region exists is made of a microcrystalline semiconductor, the optical band gap of the doping layer increases, light absorption decreases, and the photovoltaic element Short-circuit current (Js
c) increases. Also, the activation energy of the doping layer decreases, and the built-in potential increases,
The open voltage (Voc) of the photovoltaic element is improved.

By making the group IV element low-density region amorphous, the stress of the doping layer is reduced even when the other region of the doping layer is mainly formed of a microcrystalline semiconductor. As a result, the films at the upper and lower interfaces of the doping layer do not peel off, and the production yield of the photovoltaic element is improved. Further, the interface state at the interface between the doping layer and the i-type semiconductor layer is reduced, and the fill factor (FF) of the photovoltaic element is improved.

In a stack type photovoltaic device in which a plurality of pin junctions are stacked, the density of a group IV element as a main component is contained in at least one of the doping layers at the reverse junction where the n layer and the p layer are in contact. Is reduced, the ohmic property of the reverse junction is improved, and the series resistance is reduced.
The fill factor (FF) of the photovoltaic element is improved.
This is considered to be because the doping layer is heavily doped while suppressing light absorption to lower the activation energy of the doping layer, so that the reverse junction becomes a tunnel junction and the ohmic properties are improved. In addition, it is considered that the interface state at the interface between the n-layer and the p-layer is reduced due to the relaxation of the stress of the doping layer. Further, the light deterioration rate of the photovoltaic element is reduced. This is because the strength of the internal electric field in the i-type semiconductor layer increases due to the improvement of the built-in potential of the photovoltaic element, and the Staebler increases.
It is considered that the influence of the -Wronski effect is reduced, and that the reverse junction becomes a tunnel junction and the ohmic property is improved, so that the optical degradation of the reverse junction is reduced.

Conventionally, when the i-type semiconductor layer is microcrystalline, carrier recombination is likely to occur at the grain boundaries of the microcrystals, and especially near the interface between the doping layer and the i-type semiconductor layer, especially at the grain boundaries. The effect of recombination was significant. Then, the portion of the grain boundary of the microcrystal was considered to be a factor of an increase in leakage current. On the other hand, in the configuration of the present invention, the low-density region where the density of the group IV element is small serves as a buffer against contact between the doping layer and the crystal grain boundary of the i-type semiconductor layer, and the carrier recombination occurs. It is thought that the fill factor (FF) of the photovoltaic element and the production yield were improved by reducing the leakage current and the leak current.

In a conventional amorphous photovoltaic device including microcrystals, one of the causes of deterioration of the photovoltaic device due to heat is thermal diffusion of a valence electron controlling agent, and the fine crystal particles It was thought that heat diffusion was large in the boundary area. On the other hand, in the configuration of the present invention, the low-density region where the density of the group IV element of the photovoltaic element is small serves as a buffer for the contact between the doping layer and the grain boundary of the microcrystal of the i-type semiconductor layer. By
It is considered that the thermal diffusion of the valence electron controlling agent through the grain boundaries of the microcrystals was reduced, and the heat resistance of the photovoltaic element was improved.

The volume fraction of the microcrystals in the i-type semiconductor layer is 50% or more, the average diameter of the microcrystals is 3 nm or more, and the average diameter of the microcrystals in the direction perpendicular to the surface on which the semiconductor layer is formed. Is twice or more the average diameter in the horizontal direction, the following effects are obtained.

When the volume fraction of the microcrystal is 50% or more, particularly the absorption coefficient of infrared long-wavelength light increases, the short-circuit current (Jsc) of the photovoltaic element improves, and the photodegradation rate decreases. It decreased to less than 5%. In addition, the average particle size of the microcrystals is 3 nm or more, the runnability of the photocarrier is promoted, the fill factor (FF) of the photovoltaic element is improved, and the photodegradation rate is reduced to 5% or less. .

Further, since the average diameter in the vertical direction with respect to the surface on which the semiconductor layer of the microcrystalline grains is formed is twice or more the average diameter in the horizontal direction, a high absorption coefficient of ultraviolet light and visible light can be maintained. The traveling property of the photocarrier in the film thickness direction in the intrinsic semiconductor layer was promoted, and the fill factor (FF) of the photovoltaic device was improved.

A doping layer of the same conductivity type and at least partly made of a microcrystalline semiconductor is laminated on the amorphous doping layer, and a substantially intrinsic semiconductor layer at least partly made of microcrystal is formed thereon. Has the following effects.

The damage to the underlying layer caused by forming a doping layer at least partially composed of a microcrystalline semiconductor on a transparent conductive layer or a doping layer of a different conductivity type is eliminated, and a series of photovoltaic devices is provided. Resistance decreased and fill factor (FF) improved.

The photodegradation rate of the entire stack type photovoltaic element is reduced by having at least a part where the doping layer and a substantially intrinsic semiconductor layer made of microcrystals are joined at least in part. .

[0067]

BEST MODE FOR CARRYING OUT THE INVENTION

(Configuration of Photovoltaic Element) A configuration example of a photovoltaic element (or a photovoltaic device) of the present invention and a manufacturing example thereof will be described with reference to the drawings.

FIG. 1a is a schematic sectional view of an example of the photovoltaic device of the present invention for explaining the concept of the present invention. FIG. 1B illustrates a case where a microcrystalline semiconductor is used for the i-type semiconductor layer 105. However, the present invention is not limited to the photovoltaic element having the configuration shown in FIG.

In FIG. 1, 101 is a substrate, 102 is a back electrode, 103 is a transparent conductive layer, 104 is an n-type semiconductor layer,
105 is an i-type semiconductor layer, 106 is a p-type semiconductor layer, 107
Is a transparent electrode, and 108 is a current collecting electrode. Also, 109,
Reference numeral 110 denotes a group IV element low-density region in which the density of the group IV element, which is a main component of the doping layer, is small, which is a feature of the present invention. FIG. 1 shows a configuration in which light is incident from the p-type semiconductor layer side. In the case of a photovoltaic element having a configuration in which light is incident from the n-type semiconductor layer side, p
The type semiconductor layer 106 becomes an n-type semiconductor layer.

Further, FIG. 1 shows a configuration in which light is incident from the side opposite to the substrate. In a photovoltaic element having a configuration in which light is incident from the substrate side, the respective layers are arranged in the reverse order to FIG. 1 except for the substrate. May be laminated.

FIG. 2 is a schematic cross-sectional view of an example of a stacked photovoltaic device of the present invention for explaining the concept of the present invention in detail.

The stack type photovoltaic element shown in FIG.
It has a structure in which three pin junctions are stacked, and 215
Is the first pin junction counted from the light incident side, and 216 is the second pin junction.
217 is a third pin junction. These three pin junctions are formed on the substrate 201 on the back surface electrode 202.
And a transparent conductive layer 203 are formed and laminated thereon, and a transparent electrode 213 is formed on the top of the three pin junctions.
And a collector electrode 214 are formed to form a stack type photovoltaic element. The respective pin junctions are formed by n-type semiconductor layers 204, 207, 210, i-type semiconductor layers 205, 208, 211, and p-type semiconductor layers 206, 20.
9,212. Further, as in the case of the photovoltaic element in FIG. 1, the arrangement of the doping layers and the electrodes may be switched depending on the incident direction of light.

Hereinafter, the components of the photovoltaic element of the present invention will be described in detail.

(Substrate) Semiconductor layers 104 to 106 and 204
.About.212 have a thickness of about 1 .mu.m and are deposited on a suitable substrate. Such substrates 101, 201
May be single-crystalline or non-single-crystalline, and they may be conductive or electrically insulating. Further, they may be light-transmitting or non-light-transmitting, but preferably have little deformation and distortion and have a desired physical strength. Specifically, Fe, N
i, Cr, Al, Mo, Au, Nb, Ta, V, Ti,
Metals such as Pt and Pb or alloys thereof, for example, thin plates such as brass and stainless steel and composites thereof, and polyester, polyethylene, polycarbonate, cellulose acetate, polypropylene, polyvinyl chloride,
Films or sheets of heat-resistant synthetic resins such as polyvinylidene chloride, polystyrene, polyamide, polyimide, epoxy, or composites of these with glass fibers, carbon fibers, boron fibers, metal fibers, etc., and thin plates or resin sheets of these metals Metal thin films of different materials and / or SiO2, Si3N
Examples thereof include those obtained by subjecting an insulating thin film such as 4, Al2O3, and AlN to a surface coating treatment by a sputtering method, a vapor deposition method, a plating method, or the like, glass, ceramics, and the like.

When the substrate is an electrically conductive material such as a metal, the substrate may be directly used as an electrode for extracting current. When the substrate is an electrically insulating material such as a synthetic resin, Al, Ag,
Pt, Au, Ni, Ti, Mo, W, Fe, V, Cr,
Cu, stainless steel, brass, nichrome, SnO2, In2
So-called metal simple substance or alloy such as O3, ZnO, ITO, and transparent conductive oxide (TCO),
It is desirable to perform a surface treatment in advance by a method such as sputtering to form an electrode for extracting current.

Of course, even if the substrate is made of an electrically conductive material such as a metal, the reflectance of long-wavelength light on the substrate surface can be improved or the mutual diffusion of constituent elements between the substrate material and the deposited film can be improved. A different kind of metal layer or the like may be provided on the side of the substrate on which the deposited film is formed, for the purpose of preventing the occurrence of the problem. In the case where the substrate is relatively transparent and a photovoltaic element having a layer configuration in which light is incident from the side of the substrate is used, a conductive thin film such as the transparent conductive oxide or a metal thin film may be used in advance. It is desirable to deposit and form.

The surface of the substrate may be a so-called smooth surface or a fine uneven surface. In the case of a minute uneven surface, the uneven shape is spherical, conical, pyramidal, or the like, and its maximum height (Rma
When x) is preferably 0.05 μm to 2 μm, light reflection on the surface becomes irregular reflection, and the optical path length of the light reflected on the surface is increased. The shape of the substrate is plate-like with a smooth surface or uneven surface, depending on the application of the photovoltaic element.
It can be in the form of a long belt, a cylinder, or the like, and its thickness is appropriately determined so that a desired photovoltaic element can be formed. When flexibility is required for the photovoltaic element, or when light is incident from the side of the substrate, the thickness can be made as thin as possible within a range where the function as the substrate is sufficiently exhibited. However, from the viewpoints of the production and handling of the substrate, mechanical strength, etc., it is usually 10 μm.
m or more.

(Back Electrode) The back electrodes 102 and 202 are electrodes arranged on the back surface of the semiconductor layer in the light incident direction.
Therefore, either at the position 102 in FIG.
In the case where 1 is light-transmitting and light is incident from the direction of the substrate, it is arranged at the position 107. Examples of the material of the back electrode include metals such as gold, silver, copper, aluminum, nickel, iron, chromium, molybdenum, tungsten, titanium, cobalt, tantalum, niobium, and zirconium, and alloys such as stainless steel. Among them, aluminum,
Highly reflective metals such as copper, silver, and gold are particularly preferred. In the case of using a metal having a high reflectance, the back electrode can also serve as a light reflecting layer that reflects light that could not be absorbed by the semiconductor layer again to the semiconductor layer. Further, as the back metal reflection layer, two or more kinds of materials may be stacked in two or more layers.

Although the shape of the back electrode may be flat,
It is more preferable to have an uneven shape that scatters light. By having an uneven shape that scatters light, it scatters long-wavelength light that could not be absorbed by the semiconductor layer, extends the optical path length in the semiconductor layer, improves the long-wavelength sensitivity of the photovoltaic element, and increases the short-circuit current. And the photoelectric conversion efficiency can be improved. In the uneven shape for scattering light, it is desirable that the difference between the heights of the peaks and valleys of the unevenness is 0.2 to 2.0 μm in Rmax.

However, when the substrate also serves as the back electrode,
In some cases, it is not necessary to form the back electrode.

The back electrode is formed by vapor deposition, sputtering,
It can be performed by a plating method, a printing method, or the like.

In the case of forming the back electrode into an uneven shape that scatters light, the formed metal or alloy film is formed by dry etching, wet etching, sand blasting, heating, or the like. In addition, the above-mentioned metal or alloy can be deposited while heating the substrate to form an uneven shape for scattering light.

(Transparent Conductive Layer) The transparent conductive layer 103 is disposed between the back metal reflective layer 102 and the semiconductor layer 104 mainly for the following purposes. That is, first, diffuse reflection on the back surface of the photovoltaic element is improved, light is confined in the photovoltaic element by multiple interference by the thin film, the optical path length in the semiconductor layer is extended, and the short-circuit current ( Jsc); to prevent the metal of the back metal reflective layer, which also serves as the back electrode, from diffusing or migrating into the semiconductor layer to prevent the photovoltaic element from shunting; By providing a slight resistance value, the back metal reflective layer 102
Short-circuit caused by a defect such as a pinhole in the semiconductor layer between the semiconductor device and the transparent electrode 107 is prevented.

The transparent conductive layer 103 is required to have a high transmittance in a wavelength region that can be absorbed by the semiconductor layer and to have an appropriate resistivity. Preferably, the transmittance at 650 nm or more is 80% or more, more preferably 85% or more, and most preferably 90% or more. The resistivity is preferably 1 × 10 ⁻⁴ Ωcm or more and 1 × 10 ⁶ Ωcm or less, more preferably 1 × 10 ⁻² Ωcm or more and 5 × 10 ⁴ Ωcm.
It is desirable that it be Ωcm or less.

The material of the transparent conductive layer 103 is In2
O3, SnO2, ITO (In2O3 + SnO2), Z
nO, CdO, Cd2SnO4, TiO2, Ta2O
A conductive oxide such as 5, Bi2O3, MoO3, and NaxWO3, or a mixture thereof is preferably used. Further, an element (dopant) that changes the conductivity may be added to these compounds.

As an element (dopant) for changing the conductivity, for example, when the transparent conductive layer 103 is ZnO,
Al, In, B, Ga, Si, F, etc.
3, Sn, F, Te, Ti, Sb, Pb, etc., and SnO2, F, Sb, P, As, I
n, Tl, Te, W, Cl, Br, I and the like are preferably used.

The transparent conductive layer 103 can be formed by various evaporation methods such as EB evaporation and sputter evaporation, various CVD methods, spray methods, spin-on methods, and dipping methods. (Semiconductor layer)

The material of the semiconductor layer used in the present invention may be a non-single-crystal material containing a group IV element such as Si, C, Ge, or the like, or an IGe material such as SiGe, SiC, SiSn.
A group V alloy non-single crystal material can be used.

Among the above semiconductor materials, specific examples of the semiconductor material particularly preferably used for the photovoltaic element of the present invention include, for example, a-Si: H (abbreviation for hydrogenated amorphous silicon), a -Si: F, a-Si: H: F, a-SiG
e: H, a-SiGe: F, a-SiGe: H: F, a
Group IV and Group IV alloy-based non-single-crystal semiconductor materials such as -SiC: H, a-SiC: F, and a-SiC: H: F.

The semiconductor layer can perform valence electron control and / or forbidden band width control. In this case, specifically, for example, a raw material compound containing an element serving as a valence electron controlling agent or a forbidden band width controlling agent when forming a semiconductor layer is used alone or in the raw material gas for forming a deposited film or the diluting gas. It can be performed by mixing and introducing into the film formation space.

Further, at least a part of the semiconductor layer is doped with p-type and n-type by valence electron control, so that at least one pair of pin junctions can be formed. By stacking a plurality of pin junctions, a so-called stack cell configuration is obtained.

The semiconductor layer is formed by microwave plasma C
VD method, RF plasma CVD method, optical CVD method, thermal CVD
And various CVD methods such as a MOCVD method, or various vapor deposition methods such as an EB evaporation, MBE, ion plating, and ion beam methods, a sputtering method, a spray method, a printing method, and the like. A plasma CVD method in which a raw material gas is decomposed by plasma and deposited on a substrate, which is a method industrially employed, is preferably used.
In addition, as the reaction device, a batch type device, a continuous film forming device, or the like can be used as desired.

Hereinafter, a particularly preferable group IV non-single-crystal semiconductor material or IV is used for the semiconductor layer of the photovoltaic device of the present invention.
The case of using a group alloy non-single-crystal semiconductor material will be described.

(1. i-type semiconductor layer (intrinsic semiconductor layer)) In particular, in a photovoltaic element using a group IV non-single-crystal semiconductor material or a group IV alloy non-single-crystal semiconductor material,
The i-type semiconductor layer used for bonding is an important layer that generates and transports carriers with respect to irradiation light.

Note that a slightly p-type or slightly n-type layer can be used as the i-type semiconductor layer.

As described above, the group IV non-single-crystal semiconductor material or the group IV alloy non-single-crystal semiconductor material contains a hydrogen atom (H, D) or a halogen atom (X), which plays an important role. Have.

The hydrogen atoms (H, H) contained in the i-type semiconductor layer
D) and / or a halogen atom (X) serves to compensate for dangling bonds of the i-type semiconductor layer and to improve the product of carrier mobility and lifetime in the i-type semiconductor layer. It is. Further, the hydrogen atoms and / or the halogen atoms function to compensate the interface states at the respective interfaces of the p-type semiconductor layer / i-type semiconductor layer and the n-type semiconductor layer / i-type semiconductor layer, and the light level of the photovoltaic element is reduced. This has the effect of improving electromotive force, photocurrent, and photoresponsiveness. Hydrogen atoms and / or halogen atoms contained in the i-type semiconductor layer are 1 to 4
0 at% is mentioned as the optimum content. In particular, it is preferable to adopt a distribution mode in which the content of hydrogen atoms and / or halogen atoms is large at each interface side of the p-type semiconductor layer / i-type semiconductor layer or the n-type semiconductor layer / i-type semiconductor layer. The content of hydrogen atoms and / or halogen atoms near the interface is preferably in the range of 1.1 to 2 times the content in the bulk. Further, it is preferable that the content of hydrogen atoms and / or halogen atoms is changed in accordance with the content of silicon atoms.

In the stack type photovoltaic element, the material of the pin junction i-type semiconductor layer close to the light incident side is a material having a wide band gap and a material far away from the light incident side is p-type.
As a material for the in-junction i-type semiconductor layer, a material having a narrow band gap is preferably used.

As a specific constituent material of the i-type semiconductor, amorphous silicon (a-Si), amorphous silicon germanium (a-SiGe), and the like can be given. These are a-Si: H, depending on the element that compensates for dangling bonds.
a-Si: F, a-Si: H: F, a-SiGe: H,
It is written as a-SiGe: F, a-SiGe: H: F, or the like.

Further, as the preferred i-type semiconductor layer in the photovoltaic device of the present invention, the hydrogen atom content (CH)
Is 1.0 to 25.0 atomic%; AM 1.5, 10
Photoconductivity (σp) under 0 mW / cm ² simulated sunlight irradiation
Is not less than 1.0 × 10 −7 S / cm; the dark conductivity (σd) is not more than 1.0 × 10 ⁻⁹ S / cm; and the Urbach energy by the constant photocurrent method (CPM) is 55 meV or less; preferably, the localized level density is 10 ¹⁷ / cm ³ or less.

In the case of containing microcrystals, the content of hydrogen atoms (CH) is 0.1 to 15.0%, AM 1.5, 100 mW
/ Cm ² photoelectric conductivity (σp) under simulated sunlight irradiation,
1.0 × 10 ⁻⁶ S / cm or more, dark conductivity (σd)
1.0 × 10 ⁻³ S / cm or less, Urbach Energy by Constant Photocurrent Method (CPM)
Those having 57 meV or less and a localized level density of 10 ¹⁷ / cm ³ or less are suitably used.

(2. Doping layer (p-type semiconductor layer or n-type semiconductor layer)) Doping layer (p-type semiconductor layer or n-type semiconductor layer)
Semiconductor layer) is a feature of the photovoltaic device of the present invention,
The doping layer is an important layer that affects the characteristics of the photovoltaic device.

The feature of the doping layer of the present invention is that, as described above, the main constituent component of the doping layer is I
That is, a group IV element low-density region in which the density of the group V element is small is discretely present.

When the average height in the film thickness direction of the group IV element low density region is d and the average diameter in the direction parallel to the substrate surface on which the semiconductor layer is formed is L, preferably 3 nm ≦ d
≦ 40 nm and 3 nm ≦ L ≦ 80 nm, more preferably 4 nm ≦ d ≦ 30 nm and 4 nm ≦ L ≦ 60 nm,
Optimally, 5 nm ≦ d ≦ 20 nm and 5 nm ≦ L ≦ 40
nm is desirable. If the size of the group IV element low-density region is smaller than the above range, the light absorption of the doping layer may increase. If it is larger than the above range, the group IV element low-density regions tend to be connected to each other and become continuous. In this case, the light absorption of the doping layer decreases, but the activation energy increases, and the open-circuit voltage (Voc) of the photovoltaic element tends to decrease. By reducing the size of the group IV element low-density region to the above-described range, light absorption of the doping layer is reduced while maintaining low activation energy,
Open voltage (Voc) and short-circuit current (Js) of the photovoltaic element
c) can be improved. The shape of the group IV element low-density region may be spherical, spheroidal, three-dimensional polygonal, or irregular.

The presence of the group IV element low-density region in the doping layer of the present invention can be analyzed by various methods. For example, a cross section obtained by cutting a photovoltaic element in a direction perpendicular to the substrate is a transmission electron microscope (TEM). Can be confirmed by observation.

In the doping layer of the present invention, it is desirable that the concentration of the element for expanding the optical band gap in the group IV element low-density region is higher than the other parts of the doping layer. Here, its main component, I
When the group V element is Si, examples of the element for expanding the optical band gap include H, C, N, O, and a halogen element.

The suitable concentration of the element for expanding the optical band gap varies depending on the element. In general, in the low-density region of the group IV element, it is preferably 1 to 90 atomic%, more preferably 3 to 80 atomic%
It is desirable that In the other part of the doping layer, the content is preferably 0.1 to 50 atomic%, more preferably 1 to 40 atomic%. The IV
The ratio of the concentration of the element that widens the optical band gap in the low-density group region to the concentration of the other part of the doping layer is preferably 2 to 200 times, more preferably 3 to 100 times. desirable.

In the doping layer of the present invention, it is desirable that the concentration of the valence electron controlling agent is higher in the low density region of the group IV element than in other portions of the doping layer. The suitable concentration of the valence electron controlling agent varies depending on the constituent material of the doping layer, but is generally preferably 0.5 to 90 atomic%, more preferably 1 to 90 atomic%, in the low density region of the group IV element. It is desirable that the content be set to 80 to 80 atomic%. In other portions of the doping layer, preferably, the
05 to 50 atomic%, more preferably 0.1 to 40 atomic%
Atomic% is desirable. The ratio of the concentration of the valence electron controlling agent in the group IV element low-density region to the concentration of the other part of the doping layer is preferably 2 to 500 times,
More preferably, it is 3 to 300 times.

In the doping layer of the present invention, it is preferable that at least a part of the doping layer in which the group IV element low-density region exists is made of a microcrystalline semiconductor. In the doping layer according to the present invention, it is preferable that the low-density region of the group IV element is amorphous.

The constituent materials of the doping layer of the present invention are preferably amorphous (amorphous (a-) material, microcrystalline (microcrystal (μc-)) material, and polycrystalline (polycrystal (poly-)). The material is representative.

As specific examples of the amorphous material and the microcrystalline material, for example, a-Si: H, a-Si: H
X, a-SiC: H, a-SiC: HX, a-SiG
e: H, a-SiGe: HX, a-SiGeC: H, a
-SiGeC: HX, a-SiO: H, a-SiO: H
X, a-SiN: H, a-SiN: HX, a-SiO
N: H, a-SiON: HX, a-SiOCN: H, a
—SiOCN: HX, μc-Si: H, μc-Si: H
X, μc-SiC: H, μc-SiC: HX, μc-S
iO: H, μc-SiO: HX, μc-SiN: H, μ
c-SiN: HX, μc-SiGeC: H, μc-Si
GeC: HX, μc-SiON: H, μc-SiON:
HX, μc-SiOCN: H, μc-SiOCN: HX
For example, p-type valence electron control agents (Group III atoms B, Al, Ga, In, and Tl in the periodic table) and n-type valence electron control agents (Group V atoms P, As, Sb, and Bi in the periodic table) ) At a high concentration.

Specific examples of the polycrystalline material include, for example, poly-Si: H, poly-Si: HX, poly
-SiC: H, poly-SiC: HX, poly-S
iO: H, poly-SiO: HX, poly-Si
N: H, poly-SiN: HX, poly-SiGe
C: H, poly-SiGeC: HX, poly-Si
ON: H, poly-SiON: HX, poly-Si
OCN: H, poly-SiOCN: HX, poly-
Si, poly-SiC, poly-SiO, poly
-SiN and other p-type valence electron controlling agents (Periodic Table III
Materials to which high-concentration addition of group atoms B, Al, Ga, In, and Tl and n-type valence electron control agents (group V atoms P, As, Sb, and Bi in the periodic table) are given.

In particular, the doping layer (p-type semiconductor layer or n-type semiconductor layer) on the light incident side is preferably a crystalline semiconductor layer with little light absorption or an amorphous semiconductor layer with a wide band gap.

A hydrogen atom (H, D) contained in a p-type semiconductor layer or an n-type semiconductor layer as a doping layer and / or
The halogen atom (X) serves to compensate for dangling bonds of the p-type semiconductor layer or the n-type semiconductor layer, and improves the doping efficiency of the p-type semiconductor layer or the n-type semiconductor layer. Suitable amounts of hydrogen atoms and / or halogen atoms added to the p-type semiconductor layer or the n-type semiconductor layer are as described above. However, when the p-type semiconductor layer or the n-type semiconductor layer is crystalline, hydrogen atoms or / And the halogen atom is 0.1 to
10 atomic% is mentioned as the optimum amount. The electrical characteristics of the p-type semiconductor layer and the n-type semiconductor layer of the photovoltaic element include:
It is desirable that the activation energy is preferably 0.2 eV or less, and most preferably 0.1 eV or less. The specific resistance is preferably 100 Ωcm or less, and most preferably 1 Ωcm.
It is desirable to do the following. Further, a p-type semiconductor layer and n
The thickness of the semiconductor layer is preferably 1 to 50 n.
m, optimally 3 to 10 nm.

(3. Method for Forming Semiconductor Layer) Forming a Semiconductor Layer Consisting of a Suitable Group IV Non-Single Crystal Material or Group IV Alloy Non-Single Crystal Material as a Semiconductor Layer in the Photovoltaic Device of the Present Invention Can be performed by a known film forming method. As a preferable film forming method, an RF plasma CVD method,
A plasma CVD method using an alternating current or a high frequency such as a microwave plasma CVD method may be used.

In the microwave plasma CVD method,
A material gas such as a source gas or a diluent gas is introduced into a deposition chamber (vacuum chamber) that can be decompressed, and the inside of the deposition chamber is evacuated by a vacuum pump while the inside pressure of the deposition chamber is kept constant. Microwave
Guided by a waveguide, introduced into the deposition chamber through a dielectric window (such as alumina ceramics) to generate a plasma to decompose the material gas and deposit a desired deposition on a substrate disposed in the deposition chamber. Form a film. In the microwave plasma CVD method, a deposited film applicable to a photovoltaic element can be formed under a wide range of deposition conditions.

When the semiconductor layer for a photovoltaic device of the present invention is formed by microwave plasma CVD, preferable film forming conditions include a substrate temperature of 100 to 450 ° C., an internal pressure of 0.5 to 30 mTorr, and the like. Microwave power is 0.0
1-1 W / cm ³ , microwave frequency is 0.1-10
GHz, the deposition rate is 0.05 to 20 nm / sec.

The formation of the semiconductor layer by the RF plasma CVD method can be performed in the same manner as the above-described film formation method by the microwave plasma CVD method except that RF power is used instead of microwave power. When forming the semiconductor layer by RF plasma CVD, preferable film forming conditions include a substrate temperature of 100 to 350 ° C., an inner pressure of 0.1 to 10 Torr, and an RF power of 0.001 to 0.001.
0.5 W / cm ³ , the deposition rate is 0.01 to ³ nm / sec
c.

In the case of forming an i-type semiconductor layer containing microcrystals, it is preferable to use an RF high frequency of 0.1 to 100 MHz superimposed on a microwave plasma of 0.1 to 10 GHz by a microwave CVD method. It is desirable to apply a negative bias voltage to the electrode (RF electrode) to which RF high frequency is applied.
In addition, a DC bias voltage may be superimposed.
Further, a microwave of 0.1 to 10 GHz may be applied from the same electrode as the electrode to which the RF high frequency is applied. It is desirable to apply a bias voltage of preferably -100 V or less, more preferably -200 V or less to the RF electrode. Thus, damage to the surface of the deposited film due to positive ions is reduced, and an i-type semiconductor layer including microcrystals having desirable characteristics as described above can be formed.

The hydrogen dilution ratio (the ratio of the flow rate of the hydrogen gas to the flow rate of the source gas containing the constituent elements of the deposited film) is preferably 10 times or more, and more preferably 20 times or more. Also greater than microwave power
It is desirable to apply RF power.

The volume fraction of microcrystals in the i-type semiconductor layer of the present invention is preferably at least 50%, more preferably at least 60%, and most preferably at least 70%. The average particle size of the microcrystals is
Preferably 3 nm or more, more preferably 4 nm or more, optimally
5 nm or more is desirable. In addition, the average diameter in the vertical direction with respect to the formation surface of the semiconductor layer of the microcrystalline grains is preferably twice or more, more preferably three or more times, and most preferably five times or more the average diameter in the horizontal direction.
It is desirable that the number be twice or more. The volume fraction of the microcrystal is measured by observing the cross section with a transmission electron microscope (TEM) or analyzing the ratio of peaks by Raman spectroscopy. The average particle diameter of the microcrystal is calculated from the half width of the peak in X-ray diffraction. When the i-type semiconductor layer has microcrystals in the above range, ultraviolet light,
The absorption coefficients of visible light and infrared light were increased, the traveling property of the photocarrier was improved, and the photodegradation of the photovoltaic element was reduced to 5% or less.
For example, when silicon is used as a semiconductor material of the i-type semiconductor layer, the band gap estimated from a graph of light absorption coefficient and light energy is single crystal silicon (1.1e
It was estimated to be 1.0 eV, smaller than V). Further, the preferred film thickness of the i-type semiconductor layer at least partially composed of microcrystals varies depending on the material.For example, in the case of silicon, preferably 0.2 μm or more and 10 μm or less, more preferably 0.4 μm or more 5 μm
μm or less is desirable.

The above-mentioned group IV non-single-crystal material or IV
As a material gas for film formation used when a semiconductor layer composed of a group III alloy non-single crystal material is formed by a plasma CVD method, a silicon atom-containing compound which is in a gaseous state at room temperature or which can be easily gasified. Examples thereof include a germanium atom-containing compound which is in a gaseous state at room temperature or can be easily gasified, a carbon atom-containing compound which is in a gaseous state at room temperature or can be easily gasified, and a mixture of these compounds.

Examples of the silicon atom-containing compound include a linear or cyclic silane compound which is in a gaseous state at room temperature or can be easily gasified. As a specific example, for example, SiH4, Si2H6, SiF4
SiFH3, SiF2H2, SiF3H, Si3H8,
SiD4, SiHD3, SiH2D2, SiH3D, S
iFD3, SiF2D2, Si2D3H3, (SiF
2) 5, (SiF2) 6, (SiF2) 4, Si2F
6, Si3F8, Si2H2F4, Si2H3F3, S
iCl4, (SiCl2) 5, SiBr4, (SiBr
2) 5, Si2Cl6, SiHCl3, SiH2Br
2, compounds such as SiH2Cl2, Si2Cl3F3, which are in a gaseous state at room temperature or can be easily gasified.

Specific examples of the germanium atom-containing compound include, for example, GeH4, GeD4, GeF4, G
eFH3, GeF2H2, GeF3H, GeHD3, G
Compounds that are in a gaseous state at room temperature or can be easily gasified at room temperature, such as eH2D2, GeH3D, Ge2H6, and Ge2D6.

Specific examples of the carbon atom-containing compound include, for example, CH4, CD4, CnH2n + 2 (n is an integer), CnH2n (n is an integer), C2H2, C6H6,
Compounds that are in a gaseous state at ordinary temperature or that can be easily gasified, such as CO2 and CO, are mentioned.

In addition to these source gases for film formation, gaseous nitrogen atom-containing compounds and gaseous oxygen atom-containing compounds can be used, if necessary.

Specific examples of such a nitrogen atom-containing compound include, for example, N2, NH3, ND3, NO, NO2, and N2.
2O.

As specific examples of the oxygen atom-containing compound,
For example, O2, CO, CO2, NO, NO2, N2O,
CH3CH2OH, CH3OH, H2O and the like.

Examples of the substance introduced into the p-type semiconductor layer or the n-type semiconductor layer for controlling valence electrons include Group III atoms and Group V atoms.

Examples of useful starting materials for introducing group III atoms include, for example, B2H6, B4H10, B5H9, and B5H1 for introducing boron atoms.
Boron hydride which is in a gas state at room temperature or can be easily gasified, such as 1, B6H10, B6H12, B6H14, and boron halide which can be easily gasified at room temperature, such as BF3, BCl3, etc. Can be mentioned. In addition, AlCl3, GaCl3,
Compounds that are in a gaseous state at room temperature or can be easily gasified, such as InCl3 and TlCl3, can also be used. Among them, B2H6 and BF3 are particularly suitable.

Examples of a substance effectively used as a starting material for introducing a group V atom include those for introducing a phosphorus atom,
Phosphorous hydride, such as H3, P2H4, which is in a gaseous state at room temperature or can be easily gasified, PH4I, PF3, PF
5, PCl3, PCl5, PBr3, PBr5, PI3
Phosphorus halides which are in a gaseous state at ordinary temperature or can be easily gasified. In addition, AsH3, As
F3, AsCl3, AsBr3, AsF5, SbH3
SbF3, SbF5, SbCl3, SbCl5, BiH
Compounds that are in a gaseous state at room temperature or can be easily gasified, such as 3, BiCl3 and BiBr3, can be used. Of these, PH3 and PF3 are particularly suitable.

In any case, the source gas used may be appropriately diluted with a gas such as H2, He, Ne, Ar, Xe, or Kr and introduced into the deposition chamber. In particular, when a layer made of a microcrystalline or polycrystalline semiconductor material or a semiconductor material having low light absorption or a wide band gap such as a-SiC: H is formed by a microwave plasma CVD method or an RF plasma CVD method, It is preferable to dilute the source gas with hydrogen gas and to introduce relatively high power for microwave power or RF power.

(4. Method of Forming Doping Layer)
A method for forming a doping layer which is a feature of the present invention will be described.

In order to form the doping layer of the present invention in which low-density regions of the group IV element in which the density of the group IV element which is the main component is small are discretely formed, the above-described semiconductor layer is basically formed. Can be used, but it is necessary to suitably adjust at least the following forming conditions. That is, the first is a bias voltage applied to an electrode to which a high frequency is applied to the substrate, and the second is a dilution rate when a film forming source gas is diluted with a hydrogen gas.

The preferable range of these forming conditions differs depending on the method of forming the semiconductor layer and cannot be unconditionally determined. Here, for example, an RF having a frequency of 13.56 MHz
When the plasma CVD method is used, the frequency is 2.45 GHz.
This will be described below by taking as an example the case where microwave CVD of z is used.

Regarding the first condition, that is, the bias voltage of the high-frequency electrode with respect to the substrate, it is important that a positive bias voltage be applied. Thereby, positive ions are incident on the substrate to form the doping layer of the present invention. The self-bias voltage of the high-frequency electrode is
Generally, a negative voltage appears. This is probably because the electrode surface area of the high-frequency electrode (cathode) is generally small, and electrons having high mobility and capable of following high-frequency frequencies are charged up to the high-frequency electrode. However, in the present invention, for example, on the electrode surface of the high-frequency electrode (cathode), the area in which the sheath is formed in contact with the plasma is more in contact with the plasma in the grounded portion such as the inner wall of the film formation chamber. By making it larger than the area to be formed,
A positive self-bias voltage is applied to the cathode. Therefore, when the substrate is grounded (grounded), a positive bias voltage is applied to the cathode with respect to the substrate. In the present invention, the cathode positive bias voltage for such a substrate is set to, for example, a frequency of 13.5.
When a 6 MHz RF plasma CVD method is used, the voltage is preferably set to 100 V or more, more preferably 130 V or more. Here, the value of the positive bias voltage of the cathode with respect to the substrate largely depends on the applied RF power and the deposition pressure, in addition to the ratio of the electrode surface area. Further, since it varies depending on the type and the mixing ratio of the film forming raw material gas, it is necessary to appropriately adjust the bias voltage in the above-described range. Further, there is the following method for setting the cathode to a positive bias voltage with respect to the substrate. One method is to superimpose a positive DC voltage on the cathode, and the other is to float the substrate and superimpose a negative DC voltage on the substrate side.

When the frequency of the high frequency is high, for example, when microwave CVD at a frequency of 2.45 GHz is used, the microwave is injected into the film forming space from the dielectric introduction window, rather than using the high frequency electrode. It is desirable to float the substrate and superimpose a negative DC voltage on the substrate side, or
Or install an electrode that can apply RF bias,
The electrode may be adjusted so that a positive bias voltage is applied to the substrate with respect to the substrate.

The hydrogen dilution ratio, which is the second condition, is a ratio of the flow rate of the hydrogen gas to the flow rate of the source gas containing the constituent elements of the deposited film, and the preferable range varies depending on the type of the deposited film to be formed. , For example, a frequency of 13.56 MHz
When using the RF plasma CVD method of
It is desirable to make it 0 times or more, more preferably 200 times or more. In that case, the deposited film may include microcrystals.
Since the upper limit of the hydrogen dilution rate varies depending on the type of the source gas, it cannot be unconditionally determined. For example, in the case of forming a silicon film containing boron, it is desirable to set a higher dilution ratio than in the case of forming a silicon film containing phosphorus.

When microwave CVD at a frequency of 2.45 GHz is used, the preferable range of the hydrogen dilution ratio varies depending on the type of the deposited film to be formed. More preferably, it is desired to be 30 times or more. In that case, the deposited film may include microcrystals.

As described above, by adjusting the bias voltage and the hydrogen dilution ratio with respect to the substrate to appropriate values, the low-density region of the group IV element, in which the density of the group IV element, which is the main component, is reduced, becomes discrete. It is possible to form the doping layer of the present invention which is present in a natural state.

Although the details of this mechanism are not clear, the bias voltage of the cathode with respect to the substrate is made positive or the bias voltage of the substrate is made relatively negative,
By adjusting to the above-mentioned preferable value, and by adjusting the hydrogen dilution rate to the above-mentioned preferable value, the positive ions of hydrogen, the positive ions of the element for expanding the band gap, and the positive ions of the valence electron controlling agent. It is considered that, by accelerating at least one of the substrates with moderate energy, a group IV element low-density region in which the density of the group IV element, which is the main component, is reduced is discretely formed. .

(Transparent Electrode) The transparent electrode 107 is a light incident side electrode that transmits light, and also functions as an anti-reflection film by optimizing the film thickness. The transparent electrode 107 is required to have a high transmittance in a wavelength region where the semiconductor layer can absorb light and to have a low resistivity. Preferably, the transmittance at 550 nm is at least 80%, more preferably at least 85%.
The resistivity is preferably 5 × 10 ⁻³ Ωcm or less, more preferably 1 × 10 ⁻³ Ωcm or less.

As a constituent material of the transparent electrode, In2O
3, SnO2, ITO (In2O3 + SnO2), Zn
O, CdO, Cd2SnO4, TiO2, Ta2O5
Conductive oxides such as Bi2O3, MoO3, and NaxWO3 or mixtures thereof are preferably used.
Further, an element (dopant) that changes the conductivity may be added to these materials.

As the element (dopant) for changing the conductivity, for example, when the transparent electrode 107 is ZnO,
1, In, B, Ga, Si, F, etc., and In2O3
In the case of Sn, F, Te, Ti, Sb, Pb, etc., and in the case of SnO2, F, Sb, P, As, I
n, Tl, Te, W, Cl, Br, I and the like are preferably used.

The formation of the transparent electrode 107 is performed by a vapor deposition method, a CVD method, or the like.
Method, a spray method, a spin-on method, a dipping method, or the like.

(Current Collecting Electrode) The current collecting electrode 108 is formed on the transparent electrode 107 as necessary when the resistivity of the transparent electrode 107 cannot be sufficiently reduced, and reduces the resistivity of the transparent electrode 107 to form a photovoltaic element. Works to reduce series resistance. As a constituent material of the current collecting electrode 108, a metal such as gold, silver, copper, aluminum, nickel, iron, chromium, molybdenum, tungsten, titanium, cobalt, tantalum, niobium, zirconium, or an alloy such as stainless steel, or a powdery material A conductive paste using a metal may be used. The collecting electrode 108 is formed in a branch shape as shown in FIG. 5, for example, so as not to block incident light on the semiconductor layer as much as possible.

Further, in the entire area of the photovoltaic element,
The area occupied by the collecting electrode is preferably 15% or less, more preferably 10% or less, and most preferably 5% or less.

The pattern of the current collecting electrode 108 is formed by using a mask, and as a forming method, a vapor deposition method, a sputtering method, a plating method, a printing method, or the like is used. Alternatively, the metal wire may be fixed with a conductive paste.

[0149]

EXAMPLE When a photovoltaic device (module or panel) having a desired output voltage and output current is manufactured using the photovoltaic device of the present invention, a plurality of photovoltaic devices of the present invention are prepared. Then, they are connected in series or in parallel, a protective layer is formed on the front and back surfaces, and an output extraction electrode and the like are attached. When a plurality of photovoltaic elements of the present invention are connected in series, a diode for preventing backflow may be incorporated. The photovoltaic element of the present invention can be manufactured using, for example, a film forming apparatus having a structure shown in FIG. 4 or FIG.

The film forming apparatus shown in FIG. 4 is suitable for manufacturing a photovoltaic element of the present invention having a relatively small area. The film forming apparatus shown in FIG. 4 basically includes a plurality of connected transfer chambers 401, 402, 403, 404, and 405, and semiconductor layer deposition chambers 417, 418, and 4 installed below the transfer chamber.
19 and heaters 410, 411, 412 for heating the substrate
, RF high-frequency electrodes 420 and 421, a microwave introduction window 425, gas supply pipes 429, 449 and 469,
It comprises an exhaust port (not shown) and an exhaust device (not shown). The semiconductor layer deposition chambers 417, 418, and 419 are classified according to the type of the semiconductor layer to be deposited. The n-type semiconductor layer is deposited in the deposition chamber 417 by RF plasma CVD, and the microwave (MW) is deposited in the deposition chamber 418. I) The i-type semiconductor layer is deposited by plasma CVD,
Each p-type semiconductor layer is deposited by the F plasma CVD method. 4 is an enlarged view of the inside of the deposition chamber 418. In addition to the microwave introduced from the microwave introduction window 425, bias power of RF and / or DC is applied from the bias electrode 428. Is done. Also, R
The F high-frequency electrodes 420 and 421 have a surface area in contact with plasma larger than that of the conventional RF high-frequency electrode, so as to be suitable for the above-described method for forming the doping layer of the photovoltaic device of the present invention.

The film forming apparatus shown in FIG. 6 is an apparatus suitable for continuously manufacturing the photovoltaic element of the present invention. A method of continuously laminating and forming a plurality of semiconductor layers on a substrate while transporting and passing the substrate in the longitudinal direction (so-called roll-
Two-roll method). The roll-to-roll method has an effect of reducing the manufacturing cost and improving the uniformity, and is particularly preferably used.

FIG. 6A is a schematic view of a continuous film forming apparatus using a roll-to-roll method. This apparatus includes a substrate delivery chamber 601, a plurality of deposition chambers 602 to 614,
The substrate take-up chambers 615 are sequentially arranged, and connected between them by a separation passage 616. Each of the deposition chambers has an exhaust port, and the inside can be evacuated.

The strip-shaped substrate 617 is wound up from the substrate delivery chamber to the substrate winding chamber through these deposition chambers and separation passages. At the same time, gas can be introduced from the gas inlets of the respective deposition chambers and separation passages, and the gas can be exhausted from the respective exhaust ports to form respective layers. In each deposition chamber, a halogen lamp heater 618 for heating the substrate is installed inside, whereby the substrate 617 is heated to a predetermined temperature in each deposition chamber.

FIG. 6B is a top view of the deposition chamber of the apparatus shown in FIG. 6A. Each deposition chamber has a source gas inlet 619 and an exhaust port 620, and an RF electrode 621 or a microwave introduction part 622 is attached. A source gas supply device (not shown) is connected to the source gas inlet 619. . Vacuum pumps (not shown) such as oil diffusion pumps and mechanical booster pumps are provided at the exhaust ports of each deposition chamber.
Is connected, and a separation passage 616 connected to the deposition chamber has an inlet 624 through which scavenging gas flows.

An i-type layer (MW-
An RF bias electrode 631 is disposed in the deposition chambers 604 and 609, which are deposition chambers for the i-layer), and an RF power supply (not shown) is connected as a power supply. The substrate feeding chamber has a feeding roll 625 and a guide roller 626 for applying an appropriate tension to the substrate and always keeping the substrate horizontal. The substrate winding chamber has a winding roll 627 and a guide roller 62.
There are eight.

Example 1 A photovoltaic element having the structure shown in FIG. 1 was manufactured using the apparatus shown in FIG. The photovoltaic element was manufactured by sequentially performing the following steps. (1) The substrate 101 is washed, (2) a back electrode 102 is formed, (3) a transparent conductive layer 103 is formed, and (4) an n-type hydrogenated amorphous silicon layer (abbreviated as an layer).
And (5) forming an n-type microcrystalline silicon layer (abbreviated as μc-n layer), and (6) forming an an layer again.
(7) An intrinsic semiconductor layer (abbreviated as i layer) 105 made of hydrogenated amorphous silicon (a-Si: H) is formed, and (8) a p-type microcrystalline silicon layer (abbreviated as μcp layer). 106 was formed, (9) a transparent electrode 107 was formed, and (10) a current collecting electrode 108 was formed to obtain the photovoltaic element.

At this time, by changing the formation conditions of μc-n in (5), the silicon element low-density regions having various sizes and having a small silicon density are discretely present in the n-layer. Could be formed. Although not shown, the n-type semiconductor layer 104 of the present embodiment has a configuration including the three layers (4) to (6) described above.

Hereinafter, the above-described manufacturing process will be described in detail.

<Step (1)> First, a substrate was manufactured. The support 101 made of stainless steel (SUS430BA) having a thickness of 0.5 mm and a size of 50 × 50 mm 2 was ultrasonically washed with acetone and isopropanol, and dried with hot air.

<Step (2)> Next, the stainless steel support 10 was formed at room temperature by DC magnetron sputtering.
A back electrode 102 of Ag having a thickness of 0.3 μm was formed on one surface.

<Step (3)> A transparent conductive layer 103 of ZnO having a layer thickness of 1.0 μm was formed thereon at a substrate temperature of 350 ° C. by DC magnetron sputtering.

<Step (4)> The product obtained in the step (3) was introduced into the apparatus shown in FIG. 4 to form an a-n layer having a thickness of 20 nm on the ZnO transparent conductive layer 103.

In FIG. 4, a deposition apparatus 400 includes a carry-in chamber 401 and a carry-out chamber 405, and transports a substrate between a plurality of film forming chambers under reduced pressure to stack a plurality of semiconductor layers. In the apparatus, microwave plasma CVD
Both the method and the RF plasma CVD method can be performed. Using this, each semiconductor layer is formed on the substrate.

A raw material gas cylinder (not shown) is connected to the deposition apparatus via a gas introduction pipe. The raw material gas cylinders were all purified to ultra-high purity, and they were made of SiH
₄ gas cylinder, SiF ₄ gas cylinder, CH ₄ gas cylinder,
GeH ₄ gas cylinder, GeF ₄ gas cylinder, Si ₂ H ₆ gas cylinder, PH ₃ / H ₂ (PH ₃ gas diluted with H ₂ , concentration:
2%) gas cylinder, BF ₃ / H ₂ (concentration: 2%) gas cylinder, H ₂ gas cylinder, He gas cylinder, SiH ₄ / H
₂ (concentration: 10%) Gas cylinder.

Next, the substrate 490 is placed on the substrate transfer rail 413 in the loading chamber 401, and the pressure in the loading chamber 401 is increased to about 1 × 10 ⁻⁵ Torr by a vacuum exhaust pump (not shown).
The chamber was evacuated until.

Next, the gate valve 406 was opened and the substrate 490 was transferred into the transfer chamber 402 and the deposition chamber 417 that were previously evacuated by a vacuum pump (not shown). The back surface of the substrate 490 is heated by bringing the back surface of the substrate 490 into close contact with the heater 410 for substrate heating.
7 has a pressure of about 1 × 10 by a vacuum pump (not shown).
The chamber was evacuated to -5 Torr. Preparation for film formation was completed as described above.

Then, by the RF plasma CVD method,
An an layer was formed by the following method. First, H2 gas was introduced into the deposition chamber 417 via a gas introduction pipe 429, a valve (not shown) was opened so that the H2 gas became 50 sccm, and adjustment was performed by a mass flow controller (not shown). The conductance valve (not shown) was adjusted so that the pressure in the deposition chamber 417 became 1.2 Torr.
The substrate heating heater 410 is set so that the temperature of the substrate 490 becomes 350 ° C., and when the substrate temperature is stabilized,
SiH ₄ gas and PH ₃ / H ₂ gas are deposited in a deposition chamber 417.
The gas was introduced through a gas introduction pipe 429 by operating a valve (not shown). At this time, the SiH4 gas is 2 sccm and H
2 gas is 50 sccm, PH ₃ / H ₂ gas is 0.5 scc
m, and the pressure in the deposition chamber 417 was adjusted to 1.2 Torr. The power of a 13.56 MHz RF high frequency (hereinafter abbreviated as “RF”) power supply 422 is set to 5 mW / cm.
³ and the plasma forming cup 42 as the RF electrode
0, RF power is introduced, a glow discharge is generated, the formation of an an-layer on the substrate is started, and when the an-layer having a thickness of 20 nm is formed, the RF power is turned off to stop the glow discharge. The formation of the an layer was completed. At this time, the substrate was grounded, and a self-bias of +13 V was applied to the RF electrode 420.

<Step (5)> Next, a 30 nm-thick μc-n layer was formed using the same deposition apparatus. The μc−
The method of forming the n-layer is the same as the method of forming the an-layer in the above step (4), but by changing the formation conditions as shown in the following table, various sizes of discretely existing sizes can be obtained. Thus, a silicon element low-density region in which the silicon density was reduced could be formed in the n-layer.

After the formation of the photovoltaic element, the photovoltaic element was cut perpendicularly to the substrate and observed by a cross-sectional TEM. As a result, the average height in the thickness direction of the low-density region was d, Assuming that the average diameter in the direction parallel to the formed substrate surface is L, the values of d and L under each forming condition are as shown in Table 1. Further, the inside of the silicon element low density region was amorphous.

[0170] However, this time the SiH ₄ gas by using the SiH ₄ / H ₂ gas to a concentration of 10% was diluted with H _2, and controls the flow rate by the mass flow. In addition, PH ₃ / H ₂
The gas was controlled at a flow rate of １ ／ of the SiH ₄ / H ₂ gas. The substrate temperature is 350 ° C. and the gas pressure is 1.0 T
orr.

<Step (6)> Next, an an-layer having a thickness of 10 nm was formed in the same manner as in the step (4).

Thereafter, the Si in the deposition chamber 417 is
The flow of H ₄ gas and PH ₃ / H ₂ was stopped, and the H ₂ gas was kept flowing into the deposition chamber for 5 minutes. Then, the flow of H ₂ was also stopped, and the deposition chamber and the gas pipe were evacuated to 1 × 10 ⁻⁵ Torr. Exhausted.

<Step (7)> Next, in the following steps, an i-layer 105 made of a-Si: H was formed to a thickness of 400 nm by microwave plasma CVD.

First, the gate valve 407 was opened and the substrate 490 was transferred into the transfer chamber 403 and the i-layer deposition chamber 418 evacuated by a vacuum pump (not shown). The back surface of the substrate 490 was heated by bringing the back surface of the substrate 490 into close contact with a heater 411 for heating the substrate, and the inside of the i-layer deposition chamber 418 was evacuated by a vacuum exhaust pump (not shown) until the pressure became about 1 × 10 ⁻⁵ Torr.

The formation of 105 was performed as follows.
The substrate heating heater 411 is set so that the temperature of the substrate 490 becomes 350 ° C., and when the substrate is sufficiently heated, the valve (not shown) is gradually opened, and the SiH ₄ gas and the H ₂ gas are introduced into the gas introduction pipe 449. I-layer deposition chamber 418
Allowed to flow in. At this time, the SiH ₄ gas is 50 scc.
The mass flow controllers (not shown) were adjusted so that m and H2 gas became 100 sccm. The opening of the conductance valve (not shown) was adjusted so that the pressure in the i-layer deposition chamber 418 became 5 mTorr. Next, RF power of 0.5 W / cm ³ was applied to the bias bar 428 from the RF power supply 424.

Thereafter, a microwave of 0.2 W / cm ³ is applied from the power of a microwave power supply (not shown) to the i-layer deposition chamber 418 via the microwave introduction waveguide 426 and the microwave introduction window 425. To generate a glow discharge and open the shutter 427, thereby forming i on the n layer.
When the formation of the layer was started and the i-layer having a thickness of 400 nm was formed, the microwave glow discharge was stopped, the output of the RF power supply 424 was turned off, and the formation of the i-layer 105 was completed. The valve (not shown) is closed, and the SiH4
After stopping the inflow of the gas and continuing to flow the H ₂ gas into the i-layer deposition chamber 418 for 2 minutes, the valve (not shown) is closed,
1 × 1 inside i-layer deposition chamber 418 and gas pipe
The chamber was evacuated to 0 ^-5 Torr.

<Step (8)> Next, a p-layer made of microcrystalline silicon was formed to a thickness of 10 nm by the following procedure. First, the gate valve 408 is opened into the transfer chamber 404 and the p-layer deposition chamber 419 that have been previously evacuated by a vacuum exhaust pump (not shown) to open the substrate 490.
Was transported. The back surface of the substrate 490 is heated with the heater 4 for heating the substrate.
12 and heated, and the pressure in the p-layer deposition chamber 419 is about 1 × 10 ⁻⁵ To by a vacuum exhaust pump (not shown).
The system was evacuated to rr. When the temperature of the substrate 490 is 23
The substrate heating heater 412 is set to be 0 ° C.
When the substrate temperature was stabilized, H ₂ gas and BF ₃ / H ₂ gas were introduced into the deposition chamber 419 through a gas introduction pipe 469 by operating a valve (not shown). At this time, H2
35 sccm of gas, 0.2 sccm of SiH ₄ gas,
The opening of a conductance valve (not shown) was adjusted so that the BF ₃ / H ₂ gas became 0.5 sccm by a mass flow controller and the pressure in the layer deposition chamber 419 became 2.0 Torr. The power of the RF power source 423 is
Set to 5 mW / cm ³ , plasma forming cup 421
RF power is introduced into the device to generate glow discharge, and μcp
When the layer was formed to a thickness of 10 nm, the RF power was turned off to stop glow discharge, and the formation of the μcp layer 106 was completed. At this time, the substrate is grounded, and the RF electrode 423
Had a self bias of + 72V. Next, the valve (not shown) is closed to stop the flow of the SiH4 / H2 gas and the BF3 / H2 gas into the p-layer deposition chamber 419.
After continuing the flow of the H2 gas into the p-layer deposition chamber 419 for 3 minutes, the valve (not shown) is closed to stop the inflow of H2, and the inside of the p-layer deposition chamber 419 and the inside of the gas pipe are set to 1
The chamber was evacuated to ^10-5 Torr. Next, the gate valve 409 was opened into the unloading chamber 405 that was previously evacuated by an unillustrated evacuation pump, the substrate 490 was transported, and the unloading leak valve was opened to leak the unloading chamber 405.

As a result of observation by a cross-sectional TEM, a low-density silicon element region in which the density of silicon was reduced to about 2 nm for both d and L was discretely observed in the p layer.

<Step (9)> Next, a mask having 25 holes (area of 0.25 cm ² ) was placed on the p-layer, and ITO (In ₂₎ having a thickness of 70 nm was formed as the transparent conductive layer 107.
O ₃ + SnO ₂ ) was formed by resistance heating vacuum evaporation.

<Step (10)> Next, a mask having a comb-shaped hole is placed on the transparent conductive layer 107, and Cr (40 nm) /
A comb-shaped current collecting electrode 113 made of Ag (1000 nm) / Cr (40 nm) was formed by electron beam vacuum evaporation.

By the above-described method, five types of photovoltaic elements belonging to the present invention were produced. That is, five photovoltaic element samples (actual 1-1) were formed in accordance with the above-described method, except that the conditions for forming the n-type semiconductor layer 104 were changed as shown in columns 1-1 to 1-5 in Table 1. 1 to 1-5) were produced. These photovoltaic elements were converted to AM 1.5, 100 mW
/ Cm ² , and the VI characteristics were measured at 25 ° C., and the photoelectric conversion efficiency (η), open-circuit voltage (Voc), short-circuit current (Jsc), and fill factor (F) were measured.
F) was determined.

In this way, by changing the manufacturing conditions, devices having various sizes of d (average height of the low-density region) were obtained, and the device characteristics (conversion efficiency, open-circuit voltage, short-circuit current, fi
llfactor). The measurement results are defined assuming that the value of the sample of the ratio 1-1 obtained in Comparative Example 1 described later is 1.
FIG. 3A collectively shows them.

[0183]

[Table 1]

Comparative Example 1 Three photovoltaics were formed in the same manner as in Example 1 except that the formation conditions were changed as shown in Table 2 in the formation of the μc-n layer in step (5) of Example 1. Device samples (ratio 1-1 to ratio 1-3) were prepared. Note that the entire n layers of the sample ratios 1-1 and 1-2 were amorphous. Further, in the sample ratio 1-1, a silicon element low-density region where the silicon density was low was not observed.
These photovoltaic elements were converted to AM 1.5, 100 mW / c
The device was placed under irradiation with light of m ² , and V-1 characteristics were measured at 25 ° C., and photoelectric conversion efficiency (η), open-circuit voltage (Voc), short-circuit current (Jsc), and fill factor (FF) were obtained. The measurement results are shown in FIG.
(A) summarizes.

[0185]

[Table 2]

Example 2 In the method of fabricating the photovoltaic element sample 1-3 in Example 1 (that is, Example 1-3), the conditions for forming the μcp layer 106 were changed as shown in Table 3. . Deposition gas at this time, to increase the hydrogen dilution ratio, instead of the SiH ₄ gas, SiH ₄ was a 10% concentration was diluted with H ₂
/ H ₂ gas was used. Table 3 shows that SiH ₄ and BF ₃
Is a calculated value obtained by multiplying the flow rates of SiH ₄ / H ₂ and BF ₃ / H ₂ by their respective concentrations of 10% and 2%.

[0187]

[Table 3]

As a result of increasing the hydrogen dilution ratio, decreasing the pressure, increasing the RF power, and increasing the bias value as shown in Table 3, the size of the silicon element low-density region where the silicon density is reduced becomes smaller. It becomes moderately large, and the open-circuit voltage (Voc), short-circuit current (Jsc) and fill factor (FF) of the photovoltaic element are further improved as compared with Example 1-3.
The photoelectric conversion efficiency was further improved. Yield also improved. Here, the value of the photovoltaic element is set to 1 in Comparative Example 1-1.

Further, comparing Example 2-1 with Example 2-2, it was found that secondary ion mass spectrometry (SIMS) was performed despite the difference only in the size of the silicon element low-density region where the silicon density was low. )), The composition of the μcp layer 106 was analyzed. As a result, the intensity of hydrogen, boron, and fluorine increased with a slight decrease in the Si detection intensity.
It is considered that the density of hydrogen, boron, and fluorine in the silicon element low-density region is higher than in other parts. The ratios were estimated to be about 5 times the hydrogen, about 4 times the boron, and about 4 times the fluorine.

Example 3 In Example 1, the n-type semiconductor layer 104 was formed with hydrogenated amorphous silicon to have a thickness of 20 nm, and the p-type semiconductor layer 106 was formed.
With amorphous silicon carbide (abbreviated as a-SiC)
A photovoltaic element having a difference of 5 nm was manufactured in the same manner as in Example 1.

Here, by changing the conditions for forming the p-layer of a-SiC, the a-SiC
Two types of photovoltaic devices (Examples 3-1 and 3-2) having different sizes of silicon element low-density regions in which the density of silicon in the p-layer was small were manufactured.

For the formation of the a-SiC p layer, a CH4 gas was used in addition to the film forming gas described in the first embodiment. Also,
The conditions for forming the a-SiC p-layer were as shown in Table 4, and the substrate temperature was controlled at 200 ° C. In Table 4, BF
The flow rate of ₃ is a calculated value obtained by multiplying the flow rate of BF ₃ / H _{2 by} the concentration.

[0193]

[Table 4]

As is clear from Table 4, as a result of increasing the hydrogen dilution ratio, increasing the RF power and increasing the bias value as shown in Table 4, the silicon element low-density region where the silicon density is reduced is obtained. Is moderately large, and the open-circuit voltage (Voc) and short-circuit current (Jsc) of the photovoltaic element are increased.
And the fill factor (FF) were improved, and the photoelectric conversion efficiency was improved. Yield also improved. Here, as for the characteristics of the photovoltaic element, the value of the photovoltaic element sample (Comparative Example 2-1) obtained in Comparative Example 2 described later is set to 1.

Comparative Example 2 Table 5 shows the conditions for forming the a-SiC p layer in Example 3.
In the same manner as in Example 3, except that
A photovoltaic element sample (Comparative Example 2-1) was produced. This photovoltaic element was placed under AM1.5, 100 mW / cm ² light irradiation, and the VI characteristics were measured at 25 ° C., and the photoelectric conversion efficiency (η), open-circuit voltage (Voc), short-circuit current (J
sc) and the fill factor (FF) were determined. The measurement result of the photovoltaic element sample is understood from the results shown in Table 4 since the value of the sample is set to 1 in Table 4.

[0196]

[Table 5]

Example 4 A photovoltaic element different from Example 3 in that the p-type semiconductor layer 106 was formed of amorphous silicon nitride (abbreviated as a-SiN) in a thickness of 15 nm was produced in the same manner as in Example 1. .

Here, by changing the conditions for forming the p-layer of a-SiN, as shown in Table 6, the p-layer of a-SiN was
Two types of photovoltaic elements (Examples 4-1 and 4-2) having different sizes of silicon element low-density regions in which the density of silicon in the layer was low were produced.

[0199] To form the p layer of a-SiN, in addition to the film forming gas described in Example 1, using NH ₃ / H ₂ gas diluted to 10% concentration in H _2. The conditions for forming the p-layer of a-SiN were as shown in Table 6, and the substrate temperature was controlled at 250 ° C. In Table 6, the flow rates of NH ₃ and BF ₃ are calculated values obtained by multiplying the flow rates of NH ₃ / H ₂ and BF ₃ / H _{2 by} the concentration.

[0200]

[Table 6]

As is clear from Table 6, the hydrogen dilution ratio was increased, the RF power was increased, and the bias value was increased as shown in Table 6, and as a result, the silicon element low-density region where the silicon density was reduced was reduced. The size became moderately large, the open-circuit voltage (Voc), short-circuit current (Jsc), and fill factor (FF) of the photovoltaic element were improved, and the photoelectric conversion efficiency was improved. Yield also improved. Here, as for the characteristics of the photovoltaic element, the value of the photovoltaic element sample (Comparative Example 3-1) obtained in Comparative Example 3 described later is set to 1.

Comparative Example 3 Table 7 shows the conditions for forming the p-layer of a-SiN in Example 4.
Except for having been changed as shown in
A photovoltaic element sample (Comparative Example 3-1) was produced. This photovoltaic element was placed under AM1.5, 100 mW / cm ² light irradiation, and the VI characteristics were measured at 25 ° C., and the photoelectric conversion efficiency (η), open-circuit voltage (Voc), short-circuit current (J
sc) and the fill factor (FF) were determined. The measurement results of the photovoltaic element sample are understood from the results shown in Table 6, since the value of the sample is set to 1 in Table 6.

[0203]

[Table 7]

Embodiment 5 In Embodiment 3, light is different in that 15 nm of microcrystalline silicon oxide (abbreviated as μc-SiO) is formed as a p-type semiconductor layer 106 by a microwave CVD method in a deposition chamber 418. An electromotive element was manufactured in the same manner as in Example 1. At this time, at the same time as applying the RF power to the bias rod 428, a positive DC voltage from a DC power supply (not shown) was superimposed on the bias rod 428.

Here, by changing the conditions for forming the p-layer of μc-SiO, as shown in Table 8, the μc-SiO
Two types of photovoltaic elements (Examples 5-1 and 5-2) having different sizes of silicon element low-density regions in which the density of silicon in the p-layer was small were manufactured.

The formation of the p-layer of μc-SiO was performed in the same manner as in Example 1.
In addition to the film formation gas described in the above section, gasified H ₂ O was used. The conditions for forming the μc-SiO p layer were as shown in Table 8, and the substrate temperature was controlled at 250 ° C. Also,
The flow rate of BF ₃ in Table 8, describing the calculated value obtained by multiplying the concentration on the flow rate of BF ₃ / H _2.

[0207]

[Table 8]

As is clear from Table 8, as a result of increasing the hydrogen dilution ratio, increasing the RF power, and increasing the DC voltage, the size of the silicon element low-density region where the silicon density is reduced becomes moderately large. , The open-circuit voltage (V
oc), short circuit current (Jsc) and fill factor (F)
F) was improved, and the photoelectric conversion efficiency was improved. Yield also improved. Here, the characteristics of the photovoltaic element are the same as those of the photovoltaic element sample obtained in Comparative Example 4 described later (Comparative Example 4).
The value of -1) is set to 1.

Comparative Example 4 A photovoltaic device sample (Comparative Example 4) was prepared in the same manner as in Example 5 except that the conditions for forming the μc-SiO p layer were changed as shown in Table 9. 1) was produced. This photovoltaic element was manufactured using AM1.5, 100 mW / c.
The sample was placed under light irradiation of m ² , and the VI characteristics were measured at 25 ° C., and the photoelectric conversion efficiency (η), open-circuit voltage (Voc), short-circuit current (Jsc), and fill factor (FF) were determined. The measurement result of the photovoltaic element sample is shown in Table 8 because the value of the sample is 1 in Table 8.
It is understood from the results shown in FIG.

[0210]

[Table 9]

Example 6 A photovoltaic element having a triple cell (Si / SiGe / SiGe) configuration shown in FIG. 2 was produced in the same steps as in Example 1 except for the semiconductor layer. The photovoltaic element having the triple cell configuration is formed by the i-type semiconductor layer 211 of the first pin junction 215.
Is made of amorphous silicon, and the i-type semiconductor layer 208 of the second pin junction 216 and the third pin junction 217
Is a stack type photovoltaic element made of amorphous silicon germanium (a-SiGe) (see Table 10).

[0212]

[Table 10]

This triple cell was manufactured by the following method using a film forming apparatus using the roll-to-roll method shown in FIG.

The substrate is a belt-shaped stainless steel (SUS430BA) having a length of 100 m, a width of 30 cm and a thickness of 0.15 mm.
Sheets were used. The SUS430BA sheet is wound around a feed bobbin (not shown) in a vacuum container (not shown), and a winding bobbin connected to one end is rotated to make the SUS430BA sheet.
RF plasma etching with Ar plasma was performed while feeding the sheet. Thereafter, an AlSi reflective layer and a ZnO transparent conductive layer were formed under the conditions shown in Table 10 by DC magnetron sputtering of a roll-to-roll method. The obtained product was introduced into the film forming apparatus shown in FIG. 6, and a triple cell was formed under the conditions shown in Tables 10 and 11 by the method described below.

First, the SUS430BA sheet is wound around a delivery roll 625 (with an average radius of curvature of 30c).
m) After being set in the substrate sending chamber 601 and passing through each deposition chamber, the end of the substrate is wound around the substrate take-up roll 627. The entire device is evacuated with a vacuum pump,
The lamp heater in each deposition chamber is turned on to set the substrate temperature in each deposition chamber to a predetermined temperature. When the pressure of the entire apparatus becomes 1 mTorr or less, the inlet 6 of the scavenging gas
A scavenging gas flows in from 19, and the substrate is taken up by a take-up roll while moving the substrate in the direction of the arrow in the figure. Each source gas flows into each deposition chamber. At this time, the flow rate of the scavenging gas flowing into each separation passage or the pressure of each deposition chamber is adjusted so that the source gas flowing into each deposition chamber does not diffuse into other deposition chambers. Next, RF power or microwave power and RF bias power are introduced to generate plasma, and the first pi is generated under the conditions shown in Tables 10 and 11.
n1 layer in the deposition chamber 602 as an n-junction;
05, an i-layer (RF-i1 layer) by RFCVD, 60
4, i-layer (MW-i1 layer) by microwave CVD,
The p1 layer is deposited in the deposition chamber 606, the n2 layer is deposited in the deposition chamber 607 as a second pin junction, and the RF is deposited in the deposition chambers 608 and 610.
-I2 layer, 609 at MW-i2 layer, p2 at deposition chamber 611
The layer is deposited and n is deposited in deposition chamber 612 as a third pin junction.
Three layers, an i3 layer is deposited in the deposition chamber 613, and a p3 layer is deposited in the deposition chamber 614 to form a triple cell composed of three pin junctions. In this manner, a triple cell was formed on the transparent electrode layer 203. The GeH ₄ gas was introduced into one deposition chamber from a plurality of gas inlets 629 at different flow rates as indicated by 630.

When the winding of the substrate was completed, the supply of power from all the microwave power supply and the RF power supply was stopped, the plasma was extinguished, and the flow of the source gas and the scavenging gas was stopped. The entire device was leaked, and the take-up roll was taken out.

Next, a transparent electrode 213 was formed on the p3 layer 212 of the top cell 215 under the conditions shown in Table 10 using a reactive sputtering apparatus.

Next, a carbon paste having a layer thickness of 5 μm and a line width of 0.5 mm was printed by a screen printing method, and a silver paste having a layer thickness of 10 μm and a line width of 0.5 mm was printed thereon to form a current collecting electrode. . The band-like solar cell thus obtained is
Cut into a size of 50mm x 100mm, nipnip
A plurality of nip type photovoltaic elements (solar cells) were produced.

The conditions for forming the above-mentioned layers are as shown in Table 11.

[0220]

[Table 11]

Here, the conditions for forming the p1, p2, and p3 layers are as shown in Table 12, so that the silicon element low-density region where the silicon density is reduced in the p-layer made of microcrystalline silicon. Thus, photovoltaic elements having different sizes were obtained. Here, the cathode electrode of each p-layer has a large surface area so that a positive self-bias is applied.

[0222]

[Table 12]

As is clear from Table 12, as a result of increasing the hydrogen dilution ratio, increasing the RF power, and increasing the bias voltage, the size of the silicon element low-density region where the silicon density is reduced becomes moderately large. The open-circuit voltage (Voc), short-circuit current (Jsc), and fill factor (FF) of the photovoltaic element were improved, and the photoelectric conversion efficiency was improved. Yield also improved. Also, the light deterioration rate was reduced. Here, the characteristics and the photodegradation rate of the photovoltaic element were measured using a photovoltaic element sample (Comparative Example 5-
The value of 1) is set to 1.

Comparative Example 5 A photovoltaic element sample (Comparative Example 5) was prepared in the same manner as in Example 6 except that the conditions for forming the p1, p2, and p3 layers were changed as shown in Table 13. 5-1) was produced. This photovoltaic element was converted to AM 1.5, 100 mW /
The sample was placed under irradiation with light of cm ² , and VI characteristics were measured at 25 ° C., and the photoelectric conversion efficiency (η), open-circuit voltage (Voc), short-circuit current (Jsc), and fill factor (FF) were determined.
The produced photovoltaic element was kept at 50 ° C.
5, the photoelectric conversion efficiency after irradiation with light of 100 mW / cm ² for 1000 hours was measured at 25 ° C., and the light deterioration rate was calculated. The measurement result of the photovoltaic element sample is
Since the value of the sample is set to 1 in Table 12, it can be understood from the results shown in Table 12.

[0225]

[Table 13]

Example 7 The photovoltaic element shown in FIG. 1B was manufactured using the deposition apparatus shown in FIG.

The order of manufacturing the photovoltaic element is as follows: (1) washing the substrate 101, (2) forming the back electrode 102,
(3) forming a transparent conductive layer 103, (4) forming an n-type hydrogenated amorphous silicon layer (abbreviated as an layer), and (5) forming an n-type microcrystalline silicon layer (μc-n layer). Abbreviated.) To form (6)
An intrinsic semiconductor layer (abbreviated as μc-i layer) 105 made of microcrystalline silicon (μc-Si) is formed, and (7) a p-type microcrystalline silicon layer
(abbreviated as μc-p layer). 106 was formed, (8) a transparent electrode 107 was formed, and (9) a current collecting electrode 108 was formed. Thus, a photovoltaic element according to an example of the present invention was completed.

At this time, by changing the conditions for forming μc-n in (5), discretely varying regions having a reduced silicon density can be formed in the n-layer. Was completed. Although not shown, n in the present embodiment is not shown.
The mold semiconductor layer 104 has a configuration including the two layers (4) and (5) described above. Hereinafter, the manufacturing process will be described in detail.

<Step (1)> First, a substrate was manufactured. A support 101 made of stainless steel (SUS430BA) having a thickness of 0.5 mm and 50 × 50 mm 2 was subjected to ultrasonic cleaning with acetone and isopropanol, and dried with hot air.

<Step (2)> Next, a 0.3 μm-thick Ag back electrode 102 was formed on the surface of the stainless steel support 101 at room temperature by DC magnetron sputtering.

<Step (3)> A ZnO layer having a thickness of 1.0 μm and a substrate temperature of 350 ° C. was formed thereon by DC magnetron sputtering.
Of the transparent conductive layer 103 was formed.

<Step (4)> An an layer having a thickness of 20 nm was formed thereon by the deposition apparatus shown in FIG. Deposition equipment 400
Is an apparatus that includes a carry-in chamber 401 and a carry-out chamber 405, transports a substrate between a plurality of film formation chambers under reduced pressure, and stacks a plurality of semiconductor layers. Microwave plasma CVD and RF plasma C
Both VD methods can be performed. Using this, each semiconductor layer is formed on the substrate.

[0233] A raw material gas cylinder (not shown) is connected to the deposition apparatus through a gas introduction pipe. The raw material gas cylinders are all purified to ultra-high purity, and include SiH ₄ gas cylinders,
SiF ₄ gas cylinder, CH ₄ gas cylinder, GeH ₄ gas cylinder, GeF
₄ gas cylinder, Si ₂ H ₆ gas cylinder, PH ₃ / H ₂ (diluted with H ₂
PH ₃ gas, concentration: 2%) Gas cylinder, BF ₃ / H ₂ (concentration: 2%)
Gas cylinder, H ₂ gas cylinder, He gas cylinder, SiH ₄ / H
₂ (Concentration: 10%) A gas cylinder was connected.

Next, the substrate 490 formed up to ZnO is placed on the substrate transfer rail 413 in the loading chamber 401, and the pressure in the loading chamber 401 is reduced to 1 × 10 ⁻⁵ Torr by a vacuum pump (not shown).
The chamber was evacuated until the pressure became below.

Next, the substrate was transported by opening the gate valve 406 into the transport chamber 402 and the deposition chamber 417 evacuated by a vacuum pump (not shown) in advance.
The back surface of the substrate 490 was heated while being closely attached to a substrate heating heater 410, and the inside of the deposition chamber 417 was evacuated by a vacuum evacuation pump (not shown) until the pressure became 1 × 10 ⁻⁵ Torr or less. Preparation for film formation was completed as described above.

Then, an layer was formed by the following steps by RF plasma CVD.

First, H2 gas was introduced into the deposition chamber 417 through the gas introduction pipe 429, and a valve (not shown) was opened so that the H2 gas became 50 sccm, and adjustment was performed by a mass controller (not shown). The pressure inside the deposition chamber 417 is 1.2 To
rr was adjusted by a conductance valve (not shown). The substrate heating heater 410 was set so that the temperature of the substrate 490 became 350 ° C, and when the substrate temperature was stabilized, the SiH
_Four gases, PH ₃ / H ₂ gas, were introduced into the deposition chamber 417 through a gas introduction pipe 429 by operating a valve (not shown). At this time, the mass flow controller was adjusted so that the SiH ₄ gas was ₂ sccm, the H ₂ gas was 50 sccm, and the PH ₃ / H ₂ gas was 0.5 sccm, and the pressure in the deposition chamber 417 was adjusted to 1.2 Torr. The power of a 13.56 MHz RF high frequency (hereinafter abbreviated as “RF”) power supply 422 is set to 8 mW / cm ³ , RF power is introduced into the plasma forming cup 420 which is an RF electrode, and a glow discharge is generated. The formation of the an layer was started on the substrate, and when the an layer having a thickness of 20 nm was formed, the RF power was turned off, the glow discharge was stopped, and the formation of the an layer was completed. At this time, the substrate was grounded, and a self-bias of +13 V was applied to the RF electrode 420.

<Step (5)> Next, a 30 nm-thick μc-n layer was formed using the same deposition apparatus. The formation process is (4)
Similar to the an layer, but by changing the forming conditions as shown in Table 14 below, regions having various sizes that are discretely present and having a reduced silicon density are formed in the n layer. I was able to. After the formation of the photovoltaic element, the photovoltaic element was cut perpendicular to the substrate and observed by a cross-sectional TEM.As a result, the average height in the film thickness direction of the region was d, and the average height in the direction parallel to the semiconductor layer formation surface was d. When the diameter is L, the values of d and L under each forming condition are as shown in Table 14 below. Further, the inside of the region was amorphous.

In this case, however, the SiH4 gas is diluted with H2
The flow rate was controlled by mass flow using SiH4 / H2 gas at a concentration of 10%. PH ₃ / H ₂ gas is SiH ₄ / H ₂
The flow was controlled to 1/4 of the gas flow. The substrate temperature is 3
00 ° C and the gas pressure were controlled at 1.0 Torr. Also,
In the following table, the n layers having the ratios 6-1 and 6-2 were entirely amorphous. (The ratio is a comparative example, actually an example.) In the sample of the ratio 6-1, a region where the silicon density was low was not observed.

[0240]

[Table 14]

[0241] Thereafter, SiH ₄ gas into the deposition chamber 417, stopping the flow of PH ₃ / H _2, 5 minutes, after which continued to flow H ₂ gas into the deposition chamber, stopping the inflow of H _2, the depositing chamber The inside of the gas pipe was evacuated to 1 × 10 ⁻⁵ Torr or less.

<Step (6)> Next, in the following steps, an i-type semiconductor layer 105 made of μc-Si was formed to a thickness of 2 μm by microwave plasma CVD.

First, the gate valve 407 was opened and the substrate 490 was transferred into the transfer chamber 403 and the i-layer deposition chamber 418, which were previously evacuated by a vacuum exhaust pump (not shown). The back surface of the substrate 490 was heated by being brought into close contact with a substrate heating heater 411, and the inside of the i-layer deposition chamber 418 was evacuated by a vacuum exhaust pump (not shown) until the pressure became 1 × 10 ⁻⁵ Torr or less.

To form an i-layer, the temperature of the substrate 490 is set to 350
The substrate heating heater 411 was set so that the temperature became ℃. When the substrate was sufficiently heated, a valve (not shown) was gradually opened to deposit an i-layer of SiH ₄ gas and H ₂ gas through a gas introduction pipe 449. Flowed into the chamber 418. At this time, the SiH ₄ gas
0 sccm, H ₂ gas was adjusted by the mass controllers each not shown so that the 1300 sccm. i-layer deposition chamber 41
The pressure in the conductance valve (not shown) was adjusted so that the pressure in 8 became 25 mTorr. Next, at a frequency of 13.56 MHz
RF power of 65 mW / cm ³ was applied to bias bar 428 from RF power supply 424. Thereafter, a microwave of 50 mW / cm ³ is supplied from a microwave power supply having a frequency of 2.45 GHz (not shown) through a microwave introduction waveguide 426 and a microwave introduction window 425.
Introduced into the i-layer deposition chamber 418 to generate a glow discharge, and by opening the shutter 427, the formation of the i-layer on the n-layer was started. Off, turn off the output of RF power supply 424,
Finished. Here, bias rod 42 for applying RF power
8 was floating with respect to the grounded deposition chamber and the grounded substrate, resulting in a self-bias of -420V. Close the valve (not shown), stop the flow of SiH ₄ gas into the i-layer deposition chamber 418, and
After continuing the flow of the H2 gas into the layer deposition chamber 418, the valve (not shown) was closed, and the inside of the i-layer deposition chamber 418 and the gas pipe were evacuated to 1 × 10 ⁻⁵ Torr or less.

After the formation of the photovoltaic element, the photovoltaic element was cut perpendicular to the substrate and observed by a cross-sectional TEM. As a result, the i-type semiconductor layer was microcrystalline silicon, and the volume fraction of the microcrystal was:
At 85%, the average length in the vertical direction with respect to the formation surface of the semiconductor layer having the diameter of the fine crystal grains was 5 times the average length in the horizontal direction. Also, from the X-ray diffraction measurement, the average particle size of the microcrystal was 1
It was estimated to be 2nm.

<Step (7)> Next, a p-layer made of microcrystalline silicon was formed to a thickness of 10 nm by the following procedure.

First, the gate valve 408 is opened into the transfer chamber 404 and the p-layer deposition chamber 419 that have been evacuated by a vacuum pump (not shown).
490 was conveyed. The back of the substrate 490 is heated with a heater for substrate heating.
The inside of the p-layer deposition chamber 419 was evacuated by a vacuum evacuation pump (not shown) until the pressure became 1 × 10 ⁻⁵ Torr or less. The substrate heating heater 412 is set so that the temperature of the substrate 490 becomes 230 ° C. When the substrate temperature is stabilized, H ₂ gas and BF ₃ / H ₂ gas are supplied into the deposition chamber 419 by a valve (not shown). Was operated to introduce gas through the gas introduction pipe 469. At this time, H ₂ gas is 40 sccm, 10% concentration of SiH ₄ / H ₂ gas is 0.2 sccm, and 2% concentration of BF ₃ / H ₂ gas is
The opening of a conductance valve (not shown) was adjusted so that the pressure in the layer deposition chamber 419 was adjusted to 2.0 Torr by adjusting with a mass flow controller so as to be 0.5 sccm. The power of the RF power supply 423 was set to 170 mW / cm ³ , and RF power was introduced into the plasma forming cup 421 to cause a glow discharge.
When the -p layer was formed to a film thickness of 10 nm, the RF power was turned off, glow discharge was stopped, and the formation of the μc-p layer 106 was completed. At this time, the substrate was grounded, and a self-bias of +140 V was applied to the RF electrode 423. Next, the valve (not shown) is closed to stop the flow of the SiH ₄ / H ₂ gas and the BF ₃ / H ₂ gas into the p-layer deposition chamber 419, and the H ₂ gas is introduced into the p-layer deposition chamber 419 for 3 minutes.
After the gas continued to flow, the valve (not shown) was closed to stop the inflow of H ₂ , and the inside of the p-layer deposition chamber 419 and the gas piping were 1x.
The chamber was evacuated to 10 ^-5 Torr or less. Next, the unloading chamber 4 was previously evacuated by a vacuum pump (not shown).
The gate valve 409 was opened into the substrate 05, the substrate 490 was transported, the leak valve (not shown) was opened, and the discharge chamber 405 was leaked.

As a result of observation by a cross-sectional TEM, it was found that d
Are 8 nm on average and L is 10 nm on average, and regions where the density of silicon is small were discretely observed.

<Step (8)> Next, a mask having 25 holes (area of 0.25 cm ² ) is placed on the p-layer to form a transparent conductive layer 107.
In this example, ITO (In ₂ O ₃ + SnO ₂ ) having a layer thickness of 70 nm was formed by resistance heating vacuum evaporation.

<Step (9)> Next, a mask having a cross-shaped hole is placed on the transparent conductive layer 107, and Cr (40 nm) / Ag (1000 nm) /
A cross-shaped current collecting electrode 113 made of Cr (40 nm) was formed by electron beam vacuum evaporation.

Through the above steps, the fabrication of a photovoltaic element as an example of the present invention was completed. Depending on the conditions for forming the n-type semiconductor layer 104, samples of the examples (Examples 7-1 to 7-5) and the comparative examples (Comparative Examples 6-1 to 6-3) were produced. AM1.
5, Installed under light irradiation of 100 mW / cm2, measure VI characteristics at 25 ° C, photoelectric conversion efficiency (η), open circuit voltage (Voc), short circuit current
(Jsc) and the average value of the fill factor (FF) were determined.

FIG. 3B is a graph summarizing the results with the average height d in the film thickness direction of the region where the silicon density is low as the horizontal axis. Here, in the comparative example, the value of the ratio 6-1 is 1
And As is clear from the graph, the photovoltaic power is generated by the junction between the n-type semiconductor layer of the present invention and the microcrystalline i-type semiconductor layer in which the region where the density of the main group IV element is small discretely exists. Open-circuit voltage (Voc), short-circuit current (Jsc),
Fill factor (FF) was improved, and photoelectric conversion efficiency was improved. Further, when the average height in the film thickness direction of the region is d and the average diameter in the direction parallel to the substrate surface on which the semiconductor layer is formed is L, it is in the range of 3 nm ≦ d ≦ 40 nm and 3 nm ≦ L ≦ 80 nm. At times, the photoelectric conversion efficiency was significantly improved. Further, as shown in Table 14, the production yield of the photovoltaic element was improved. Here, the production yield was such that 100 photovoltaic elements each having a size of 0.25 cm2 were manufactured and the shunt resistance was 5 × 10E4Ω / cm2 or more. Further, when the photovoltaic element was subjected to a heat resistance test for 24 hours in the air at 180 ° C., as shown in Table 14, the thermal degradation rate of the photovoltaic element (the initial value of the photoelectric conversion efficiency after 24 hours of thermal degradation) (Decrease rate) was reduced, and the heat resistance was improved.

The p-layer portions of Examples 7-3 to 7-5 and Comparative Example 6-3 were analyzed by secondary ion mass spectrometry (SIMS) to determine the concentrations of silicon, hydrogen, fluorine, and boron. As a result,
As the size of the region where the density of silicon is reduced becomes larger, the intensity of hydrogen and fluorine is increased with a slight decrease in the detection intensity of Si. It is thought that it is higher than the part. The ratio is that hydrogen is about 5%
Fluorine was estimated to be about four times that of the other parts.

Example 8 In Example 7-3, when depositing the i-type semiconductor layer 105,
Using a high frequency of 500 MHz instead of a microwave of 2.45 GHz and changing the forming conditions variously as shown in Table 15, i
A photovoltaic element in which the type semiconductor layer was made of amorphous and a photovoltaic element in which the type semiconductor layer was made of microcrystals having various grain sizes were produced. Here, a high frequency of 500 MHz applied a power of 45 mW / cm ² not from the dielectric window but from the metal electrode. 13.56MHz RF
The power was applied only to Comparative Example 7-1 with the electrodes grounded, and the other photovoltaic elements were applied in a floating state. As a result, except for Comparative Example 7-1, a negative self-bias was applied to the RF electrode. The volume fraction of the crystallite was 520 cm as a result of Raman spectroscopy.
The integrated intensity of the peak of the 480 cm ^{-2 -2} was determined by comparison. The average particle size of the fine crystals was calculated from the half width of the X-ray diffraction peak. Further, by observing the photovoltaic element by cross-sectional TEM, the average diameter of the microcrystals in the direction perpendicular to the surface on which the semiconductor layer is formed is H, and the average diameter of the microcrystals in the direction horizontal to the surface on which the semiconductor layer is formed is H As W, the ratio of H / W was calculated.

The manufactured photovoltaic element was kept at 50 ° C.
5, the photoelectric conversion efficiency after irradiation with light of 100 mW / cm ² for 1000 hours was measured at 25 ° C. The characteristics of the photovoltaic element are shown in Comparative Example 7-
The value of 1 was set to 1.

As shown in Table 15, the hydrogen dilution rate was increased, the RF power was increased, and the electrode was floated so that a negative bias voltage was applied to the electrode. As a result, the volume fraction of the microcrystal was increased. The average particle size was increased, and the H / W ratio was increased. In particular, the volume fraction of microcrystals is 50% or more, the average particle size is 3 nm or more,
The photovoltaic element having an H / W of 2 or more showed little photodegradation, and the photovoltaic conversion efficiency after the degradation was remarkably improved. The photodegradation rates of the photovoltaic elements of Example 8-2 and Example 8-3 were 5% or less.

[0257]

[Table 15]

Example 9 In Example 7, the microwave C was used as the p-type semiconductor layer 106.
The microcrystalline silicon oxide is deposited in the deposition chamber 418 using the VD method.
A photovoltaic element different in that 15 μm (abbreviated as μc-SiO) was formed in the same manner as in Example 1. At this time RF
At the same time as applying power to the bias rod 428, a DC
A positive DC voltage from the power supply was superimposed on the bias bar 428.

Here, the size (d and L) of the region where the density of silicon in the μc-SiO p layer is low as shown in Table 16 is changed by changing the formation conditions of the μc-SiO p layer. However, different photovoltaic devices (Examples 9-1 and 9-2) were obtained.

For the formation of the p layer of μc-SiO, gasified H 2 O was used in addition to the film forming gas described in Example 7. Also,
The conditions for forming the μc-SiO p layer were as shown in Table 16, and the substrate temperature was controlled at 250 ° C. The flow rate of BF ₃ in Table 16, describing the calculated value obtained by multiplying the concentration on the flow rate of BF ₃ / H _2.

As is clear from Table 16, as the hydrogen dilution rate was increased, the RF power was increased, and the DC voltage was increased, the size of the region where the silicon density was reduced was appropriately increased, and the photovoltaic voltage was increased. The open-circuit voltage (Voc), short-circuit current (Jsc), and fill factor (FF) of the device were improved, and the photoelectric conversion efficiency was improved. Also, the yield was improved, and the thermal degradation rate after 24 hours at 180 ° C. was reduced. Here, the value of the photovoltaic element is set to 1 in Comparative Example 8-1.

When the composition of the p-layer of these photovoltaic devices was measured by Auger electron spectroscopy (AES), the oxygen concentration in the film increased as the size of the region increased. Therefore, it is considered that the concentration of oxygen in the region is higher than that in other portions. The ratio is
It was estimated to be about four times the other parts.

[0263]

[Table 16]

Example 10 A photovoltaic element different from Example 7 in that the μc-n layer, μc-i layer and μc-p layer were formed of microcrystalline silicon carbide (abbreviated as μc-SiC) was implemented. It was produced in the same manner as in Example 7.

[0265] [mu] c-n layer is the formation conditions of the p-layer of Example 9-2, BF ₃ / H ₂ gas PH ₃ / H ₂ and the conditions of replacing the gas film thickness 15nm is formed. By cross-sectional TEM, in the μc-n layer, a region in which the density of silicon was 12 nm in average and L was 15 nm in average was low in the μc-n layer.

The μc-i layer was formed to a thickness of 500 nm under the conditions for forming the i-layer in Example 8-3, with the addition of 5 sccm of CH ₄ gas. Raman spectroscopy results, volume fraction of microcrystals 80%, X-ray diffraction results, average diameter of microcrystals 9nm, cross-sectional TEM results, H / W
Was 5 times.

Here, by changing the formation conditions of the μc-SiC p-layer, the photovoltaic powers differing in the size of the region where the silicon density in the μc-SiC p-layer is reduced as shown in Table 4. The devices (Examples 10-1 and 10-2) were completed.

The p-layer of μc-SiC was formed to a thickness of 15 nm using CH ₄ / H ₂ gas in addition to the film-forming gas described in Example 7 and forming conditions as shown in Table 17. The substrate temperature was controlled at 200 ° C. in each case. In Table 17, each gas of SiH ₄ , CH ₄ , and BF ₃ is a gas diluted with H ₂ to a concentration of 10%, 10%, and 2%, respectively, and each flow rate is calculated by multiplying the concentration. The values are noted.

As is clear from Table 17, the hydrogen dilution ratio was increased, the RF power was increased, and the bias value was increased as shown in Table 17, and as a result, the size of the region where the silicon density was reduced was moderate. And the open-circuit voltage (Vo
c), the short-circuit current (Jsc) and the fill factor (FF) were improved, and the photoelectric conversion efficiency was improved. In addition, the yield has improved,
The rate of thermal deterioration after 24 hours at 180 ° C was reduced. here,
The value of the photovoltaic element is set to 1 in Comparative Example 9-1.
Also, these photovoltaic elements hardly deteriorated.

[0270]

[Table 17]

Example 11 An a-Si / μc-Si / a-SiGe triple photovoltaic device as shown in FIG. 2 was prepared. a-Si / μc-Si / a-SiGe triple is
The i-type semiconductor layer 211 of the first pin junction 215 is made of amorphous silicon, and the i-type semiconductor layer 208 of the second pin junction 216 is
Made of microcrystalline silicon, the i-type semiconductor layer 205 of the third pin junction 217 is made of amorphous silicon germanium (a-SiGe)
It is a stack type photovoltaic element made of (See Table 18.)

[0272]

[Table 18]

This triple cell was formed in the same manner as in Example 6 using the deposition apparatus using the roll-to-roll method shown in FIG. The conditions for forming each layer are as shown in Table 19. Here, the surface area of the cathode electrode of each p layer is set large so that a positive self-bias is applied.

[0274]

[Table 19]

Here, as shown in Table 20, p1 layer, p2 layer, p3 layer,
A photovoltaic device (Example 11-1) was obtained in which the size of the region where the density of silicon was low in the p-layer made of microcrystalline silicon was different depending on the formation conditions of (1). Also, in Comparative Example 10-1, instead of forming the n22 layer, an RF-i2 layer made of a-Si was formed to 10 nm, and the MW-i2 layer was replaced with μc-Si,
a-SiGe formed 65nm, RF-i instead of H2 plasma treatment
Two layers were formed to a thickness of 25 nm. That is, Comparative Example 10-1 shows that a-Si / a-
A SiGe / a-SiGe triple cell was formed. Comparative Example 10-2 and Example 11-1 differ only in the p-layer formation conditions.

The photovoltaic device was kept at 50 ° C.
5, the photoelectric conversion efficiency after irradiation with light of 100 mW / cm ² for 1000 hours was measured at 25 ° C. The value of Comparative Example 10-1 was set to 1 for the characteristics and the photodegradation rate of the photovoltaic element.

First, as is apparent from Comparative Example 10-1 and Example 11-1, the use of the i-type semiconductor layer made of microcrystalline silicon reduced the light degradation rate of the entire triple cell. Further, as is clear from Comparative Example 10-2 and Example 11-1, as a result of increasing the hydrogen dilution ratio, increasing the RF power, and increasing the bias voltage, the density of silicon was reduced as a result of the formation of the p-layer. The size of the region is appropriately increased, and by joining such a p-layer and an i-type semiconductor layer of microcrystalline silicon, the open-circuit voltage (Voc) after photodegradation of the photovoltaic element is obtained.
And short circuit current (Jsc) and fill factor (FF) are improved,
The stabilized photoelectric conversion efficiency after light degradation was improved. Also, the production yield has improved.

[0278]

[Table 20]

[0279]

As is apparent from the above description, according to the present invention, at least one semiconductor layer composed of a plurality of non-single-crystal group IV elements as main components is stacked on a substrate. In a photovoltaic element in which a pin junction is formed, at least one doping layer (referring to a p-type semiconductor layer or an n-type semiconductor layer) includes a main component I
The discrete effects of group IV element low-density regions in which the density of group V elements is small have the following effects.

That is, it is possible to form a doping layer in which the density of the activated acceptor or donor is high, the activation energy is low and the absorption coefficient is both low, and the open-circuit voltage ( Vo
c), short-circuit current (Jsc) and fill factor (FF)
And the photoelectric conversion efficiency is improved. Further, the stress of the doping layer is relieved, and the film at the upper and lower interfaces of the doping layer does not peel off, and the yield of manufacturing the photovoltaic element is improved.

When the average height of the group IV element low-density region in the film thickness direction is d and the average diameter in the direction parallel to the substrate surface on which the semiconductor layer is formed is L, 3 nm ≦ d ≦ 40 nm and 3 nm When ≦ L ≦ 80 nm, the above-mentioned effect is further emphasized, and the open-circuit voltage (Vo
c), short-circuit current (Jsc) and fill factor (FF)
Is further increased, and the photoelectric conversion efficiency is further improved.

In the low-density region of the group IV element, the above-mentioned effect is further emphasized by the fact that the concentration of the element for expanding the optical band gap is higher than that of the other part of the doping layer. Open voltage of power element (V
oc) and the short-circuit current (Jsc) are further increased, and the photoelectric conversion efficiency is further improved.

In the low density region of the group IV element, the above effect is further emphasized by the fact that the concentration of the valence electron controlling agent is higher than that of the other portion of the doping layer.
Open voltage (Voc) and short-circuit current (Js) of the photovoltaic element
c) and the fill factor (FF) are further increased, and the photoelectric conversion efficiency is further improved.

In addition, since at least a part of the doping layer in which the group IV element low-density region exists is made of a microcrystalline semiconductor, the optical band gap of the doping layer increases, light absorption increases, and The short circuit current (Jsc) of the power element increases. Further, the activation energy of the doping layer is reduced, the built-in potential is increased, and the open voltage (Voc) of the photovoltaic element is improved.

Further, since the group IV element low-density region is amorphous, the stress of the doping layer is reduced even when the other region of the doping layer is mainly formed of a microcrystalline semiconductor. As a result, the films at the upper and lower interfaces of the doping layer do not peel off, and the production yield of the photovoltaic element is improved. Further, the interface state at the interface between the doping layer and the i-type semiconductor layer is reduced, and the fill factor (FF) of the photovoltaic element is improved.

In a stack type photovoltaic device in which a plurality of pin junctions are stacked, at least one of the doping layers in the reverse junction where the n-layer and the p-layer are in contact with each other includes a group IV element as a main component. IV with reduced density
The discrete existence of the group-element low-density region improves the ohmic property of the reverse junction, reduces the series resistance, and improves the fill factor (FF) of the photovoltaic device. Further, the light deterioration rate of the photovoltaic element is reduced.

Also, the leakage current, which has been increased due to at least part of the i-type semiconductor layer being made of microcrystals, is reduced, the shunt resistance of the photovoltaic element is increased, and the production yield of the photovoltaic element is increased. Improved. Further, the heat resistance of the photovoltaic element was improved.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of an example of a photovoltaic device of the present invention.

FIG. 2 is a schematic sectional view of an example of a stacked photovoltaic device of the present invention.

FIG. 3 shows the photoelectric conversion efficiency and open-circuit voltage (Vo) of the photovoltaic element, with the average height d of the group IV element low-density region on the horizontal axis
c), short-circuit current (Jsc) and fill factor (FF)
It is a graph of.

FIG. 4 is a diagram schematically illustrating an example of a film forming apparatus for manufacturing a semiconductor layer of a photovoltaic element of the present invention.

FIG. 5 is a schematic view of one example of the photovoltaic device of the present invention as viewed from above.

FIG. 6 is a diagram schematically illustrating an example of a continuous film forming apparatus used when a photovoltaic element of the present invention is manufactured by a roll-to-roll method.

[Explanation of symbols]

101 substrate 102 back electrode 103 transparent conductive layer 104 n-type semiconductor layer 105 i-type semiconductor layer 106 p-type semiconductor layer 107 transparent electrode 108 current collecting electrode 109, 110 IV which is a main component of the doping layer
Group IV element low-density region in which group element density is reduced 111 Microcrystal grains 201 Substrate 202 Back electrode 203 Transparent conductive layer 204, 207, 210 N-type semiconductor layer 205, 208, 211 i-type semiconductor layer 206, 209, 212 p-type semiconductor layer 213 transparent electrode 214 collector electrode 215 first pin junction 216 second pin junction 217 third pin junction 251 252 261 262 RF-i layer 400 multi-chamber separation type deposition apparatus 401 Substrate loading chamber 402 N-type layer transport chamber 403 MW-i or RF-i layer transport chamber 404 P-type layer transport chamber 405 Substrate transport chamber 406, 407, 408, 409 Gate valve 410, 411, 412 Substrate heating heater 413 Substrate Transfer rail 417 n-type layer deposition chamber 418 MW-i or RF-i layer deposition chamber 419 p-type layer deposition chamber 420, 421 RF introduction cup type electrode 422, 423 RF power supply 424 bias application power supply 425 MW introduction window 426 MW introduction waveguide 427 MW-i layer deposition shutter 428 bias electrode 429, 449 , 469 Gas supply pipe 501 Light incident surface of photovoltaic element 502 Extraction electrode 601 Substrate delivery chamber 602 to 614 Deposition chamber 615 Substrate winding chamber 616 Separation passage 617 Substrate 618 Lamp heater 619 Source gas inlet 620 Exhaust port 621 RF electrode 622 Microwave introduction section 624 Scavenging gas inlet 625 Delivery roll 626 Guide roll 627 Take-up roll 628 Guide roll 629 Plural gas introduction ports 630 GeH4 gas flow rate 631 RF bias electrode

Claims (15)

[Claims] In a photovoltaic device having a semiconductor junction, a low-density group IV element region in which the density of a group IV element, which is a main component of the doping layer, is low is scattered in the surface where the doping layer is formed. A photovoltaic element characterized by the above-mentioned. 2. When the average height of the low-density region in the thickness direction is d and the average diameter in the direction parallel to the substrate surface on which the semiconductor layer is formed is L, 3 nm ≦ d ≦ 40 nm and 3 nm ≦ L ≦
The photovoltaic device according to claim 1, wherein the thickness is 80 nm. 3. The element according to claim 1, wherein the concentration of the element for expanding the optical band gap in the low-density region is higher than that of another part of the doping layer.
3. The photovoltaic device according to claim 1. 4. The photovoltaic device according to claim 1, wherein the concentration of the valence electron controlling agent is higher in the low density region than in other portions of the doping layer. . 5. The photovoltaic device according to claim 1, wherein at least a part of the doping layer in which the low-density region exists is made of a microcrystalline semiconductor. 6. The photovoltaic device according to claim 5, wherein the low-density region is amorphous. 7. The photovoltaic device according to claim 1, further comprising a pin junction comprising said doping layer and a substantially intrinsic semiconductor layer. 8. A doping layer in which low-density regions in which the density of a group IV element as a main component is low are discretely present, and a substantially intrinsic semiconductor layer at least partially composed of microcrystals A photovoltaic element characterized by the above-mentioned. 9. An average height of the low-density region in a film thickness direction.
9. The photovoltaic device according to claim 8, wherein d is 3 nm ≦ d ≦ 40 nm and 3 nm ≦ L ≦ 80 nm, where L is the average diameter in the direction parallel to the surface on which the semiconductor layer is formed. 10. The photovoltaic device according to claim 8, wherein in the low-density region, the concentration of an element for expanding an optical band gap is higher than that of another portion of the doping layer. element. 11. The semiconductor device according to claim 8, wherein at least a part of the doping layer is made of a microcrystalline semiconductor.
0. The photovoltaic element according to any one of 0. 12. The photovoltaic device according to claim 11, wherein the low density region is amorphous. 13. The volume ratio of microcrystals in the substantially intrinsic semiconductor layer is 50% or more, and the average particle size of the microcrystals is 3 nm.
The light according to any one of claims 8 to 12, wherein the average diameter in the vertical direction with respect to the formation surface of the semiconductor layer of microcrystal grains is twice or more the average diameter in the horizontal direction. Electromotive element. 14. A doping layer of the same conductivity type and at least partly made of a microcrystalline semiconductor is laminated on the amorphous doping layer, and a substantially intrinsic layer of at least partly made of microcrystal is formed thereon. 14. The photovoltaic device according to claim 8, wherein semiconductor layers are stacked. 15. The photovoltaic device according to claim 8, comprising a plurality of pin junctions comprising said doping layer and a substantially intrinsic semiconductor layer.