WO2015050083A1

WO2015050083A1 - Photovoltaic element

Info

Publication number: WO2015050083A1
Application number: PCT/JP2014/075889
Authority: WO
Inventors: 小林　英治; 宣孝中村
Original assignee: 長州産業株式会社
Priority date: 2013-10-01
Filing date: 2014-09-29
Publication date: 2015-04-09
Also published as: JP2015072939A; TW201526264A

Abstract

This photovoltaic element (10), of which one side is used as a light entrance surface, is provided with: an n-type crystalline semiconductor substrate (11); an n-type amorphous semiconductor thin film (13) and a first transparent conductive film (14) laminated in the given sequence to one side of the n-type crystalline semiconductor substrate (11); and a p-type amorphous semiconductor thin film (16) and a second transparent conductive film (17) laminated in the given sequence to the other side of the n-type crystalline semiconductor substrate (11). The first and/or second transparent conductive film (14, 17) is a transparent conductive film (α) formed from crystalline indium oxide doped with at least one element (x) belonging to groups 4, 5, and 6 of the periodic table, the average major-axis crystal grain size of the crystalline indium oxide being at least 10 nm and less than 300 nm.

Description

Photovoltaic element

The present invention relates to a photovoltaic device (solar cell) having a heterojunction.

Photovoltaic elements (solar cells) are attracting attention as clean power generation means that does not generate greenhouse gases such as CO _{2 and} as power generation means with high operational safety in place of nuclear power generation. As one of the photovoltaic elements, there is a photovoltaic element having a heterojunction with high power generation efficiency (heterojunction photovoltaic element). The heterojunction refers to, for example, a junction between a single crystal semiconductor and an amorphous semiconductor, and a diffusion potential is formed by this junction.

As a heterojunction photovoltaic device, an n-type amorphous semiconductor thin film and a first transparent conductive film are laminated in this order on the light incident surface side of the n-type crystal semiconductor substrate, and the n-type crystal semiconductor substrate A rear emitter type structure in which a p-type amorphous semiconductor thin film and a second transparent conductive film are laminated in this order on the side opposite to the light incident surface has been developed (see Patent Document 1). As a material for forming the transparent conductive film provided in these photovoltaic elements, indium tin oxide (ITO) having low resistance (conductivity) is widely used. Under such circumstances, in order to increase the photoelectric conversion efficiency, a crystalline silicon solar cell including a transparent conductive film whose average major axis crystal grain size (in-plane major axis average crystal grain size) is controlled to 300 to 2000 nm using ITO or the like is disclosed. It has been developed (see Patent Document 2). Here, a film made of ITO or the like is required to be formed at a relatively high temperature (for example, higher than 200 ° C.) or to be heat-treated after the film formation in order to crystallize and lower the resistance. However, in a heterojunction photovoltaic device, when a transparent conductive film is laminated or processed at a high temperature of over 200 ° C., performance tends to deteriorate due to crystallization of an amorphous semiconductor or hydrogen diffusion. .

Japanese Patent No. 5031007 JP 2012-9598 A

The present invention has been made in view of such circumstances, and an object thereof is to provide a heterojunction photovoltaic device having high power generation efficiency by forming a transparent conductive film using a material that can be crystallized even at a relatively low temperature. And

The inventors have made use of the fact that a transparent conductive film having a small crystal grain size and a high mobility is formed at a relatively low temperature by doping indium oxide with a specific dopant, and this transparent conductive film has a rear emitter structure. The present invention was found to be suitable for the heterojunction photovoltaic device.

That is, the photovoltaic device according to the present invention that meets the above object includes an n-type crystal semiconductor substrate, an n-type amorphous semiconductor thin film laminated in this order on one side of the n-type crystal semiconductor substrate, and the first transparent In a photovoltaic device comprising a conductive film, a p-type amorphous semiconductor thin film and a second transparent conductive film stacked in this order on the other side of the n-type crystal semiconductor substrate, and one side used as a light incident surface ,
Either one or both of the first and second transparent conductive films is crystalline indium oxide doped with one or more elements (x) belonging to Groups 4, 5, and 6 of the periodic table. A transparent conductive film (α) having an average major axis crystal grain size of 10 nm or more and less than 300 nm.

In the photovoltaic device according to the present invention, since a specific dopant is used, crystal nuclei are likely to be formed during film formation. Therefore, the photovoltaic device is crystallized even at a relatively low temperature, and has a small crystal grain size and high mobility A conductive film is formed. Therefore, the photovoltaic device according to the present invention has high power generation efficiency.

In the photovoltaic device according to the present invention, it is preferable that the element (x) includes one or more elements (x1) selected from the group consisting of tungsten and tantalum. By using tungsten or tantalum as the element (x), low-temperature crystallinity and the like can be expressed more effectively, and power generation efficiency can be increased.

In the photovoltaic device according to the present invention, the content of the element (x1) in the transparent conductive film (α) is preferably 0.1% by mass or more and 10% by mass or less in terms of oxide. By setting the content of the element (x1) in the above range, low temperature crystallinity, crystal grain size controllability, and the like can be improved.

In the photovoltaic device according to the present invention, it is preferable that the element (x) further includes one or more elements (x2) selected from the group consisting of titanium, vanadium, and niobium. By further using these elements (x2) as the element (x), low-temperature crystallinity, low resistance, and the like can be improved.

In the photovoltaic device according to the present invention, the content of the element (x2) in the transparent conductive film (α) is preferably 0.1% by mass or more and 5% by mass or less in terms of oxide. By setting the content of the element (x2) in the above range, low-temperature crystallinity, low resistance, and the like can be further increased.

In the photovoltaic device according to the present invention, the content of the element (x) in the transparent conductive film (α) is preferably 0.1% by mass or more and 10% by mass or less in terms of oxide. By setting the total content of the element (x) within the above range, low temperature crystallinity, crystal grain size controllability, and the like can be improved.

In the photovoltaic device according to the present invention, it is preferable that the second transparent conductive film is the transparent conductive film (α). The reason for this is as follows. According to the knowledge of the inventors, in the heterojunction photovoltaic device having a rear emitter structure, the lateral direction of the second transparent conductive film laminated on the back side, that is, on the p-type amorphous semiconductor thin film The current collecting property in the (planar direction) becomes low. Therefore, it is particularly preferable to increase the low resistance of the second transparent conductive film. However, for example, simply increasing the amount of dopant and increasing the carrier density in ITO increases the absorption loss of ITO, and as a result, the light transmittance (particularly, (Transmission of light having a wavelength of 900 to 1200 nm) is lowered, and output characteristics are lowered. In a photovoltaic device, light that has not been photoelectrically converted and has passed through a pn junction is reflected and reused. For this reason, it is preferable that the 2nd transparent conductive film provided in the back side also has a high transmittance | permeability. For this reason, the power generation efficiency can be increased by providing the second transparent conductive film with the transparent conductive film (α) that can achieve crystallization at a low temperature and has low resistance without increasing the amount of dopant. .

In the photovoltaic device according to the present invention, it is preferable that the first transparent conductive film is also the transparent conductive film (α). By using the transparent conductive film (α) on both sides, productivity and the like can be further increased in addition to power generation efficiency.

In the photovoltaic device according to the present invention, the transparent conductive film (α) is preferably formed at a forming temperature of 200 ° C. or less. Thus, by forming a transparent conductive film (α) at a formation temperature of 200 ° C. or less, a heterojunction photovoltaic device having high power generation efficiency can be obtained.

Here, “amorphous” means not only amorphous but also microcrystals. “Microcrystal” means a crystal peak observed by Raman spectroscopy. The “forming temperature” refers to a substrate temperature when a sputtering method, an ion plating method, or the like is used, and a heat treatment temperature after film deposition performed as necessary.

In the photovoltaic device according to the present invention, the transparent conductive film is formed using a material that is crystallized even at a relatively low temperature, and has high power generation efficiency.

It is sectional drawing which shows the photovoltaic device which concerns on one Example of this invention. 6 is a graph showing measurement results of Comparative Examples 1 and 2 and Experimental Examples 1 to 4.

Next, embodiments of the present invention will be described with reference to the accompanying drawings.
As shown in FIG. 1, the photovoltaic device 10 which concerns on one Example of this invention is a plate-shaped multilayered structure. The photovoltaic element 10 includes an n-type crystal semiconductor substrate 11, a first intrinsic amorphous semiconductor thin film 12 stacked in this order on one side (the upper side in FIG. 1) of the n-type crystal semiconductor substrate 11, an n-type A second intrinsic amorphous semiconductor thin film laminated in this order on the other side (lower side in FIG. 1) of the amorphous semiconductor thin film 13 and the first transparent conductive film 14 and the n-type crystal semiconductor substrate 11 15, a p-type amorphous semiconductor thin film 16 and a second transparent conductive film 17. Further, the photovoltaic element 10 is a collector electrode 18 disposed on the surface (one side) of the first transparent conductive film 14 and a collector electrode disposed on the surface (other side) of the second transparent conductive film 17. And an electrode 19.

The n-type crystal semiconductor substrate 11 is not particularly limited as long as it is a crystalline substrate having n-type semiconductor characteristics, and a known substrate can be used. Examples of the crystal semiconductor constituting the n-type crystal semiconductor substrate 11 include SiC (SiGe), SiN, etc. in addition to silicon (Si), but silicon is preferable from the viewpoint of productivity. The n-type crystal semiconductor substrate 11 may be a single crystal or a polycrystal.

A texture structure is formed on one surface of the n-type crystal semiconductor substrate 11. This texture structure may also be formed on the other surface. This texture structure enables light confinement due to diffuse reflection of light. Specifically, as this texture structure, a concavo-convex structure having a large number of pyramid shapes is irregularly arranged so as to cover substantially the entire upper and lower surfaces (one side and the other side) of the n-type crystal semiconductor substrate 11. . The height (size) of the concavo-convex structure (texture structure) may be uneven, and adjacent concavo-convex portions may overlap. Moreover, a vertex and a trough part may be roundish. The height of the unevenness is about several μm to several tens of μm. Such a texture structure can be obtained, for example, by immersing the substrate material in an etching solution containing about 1 to 5% by mass of sodium hydroxide and anisotropically etching the (100) plane of the substrate material.

The first intrinsic amorphous semiconductor thin film 12 is stacked on one side of the n-type crystal semiconductor substrate 11. Examples of the semiconductor constituting the first intrinsic amorphous semiconductor thin film 12 include silicon (Si), SiC, SiGe, SiN, etc., but silicon is preferable from the viewpoint of productivity. The thickness of the intrinsic amorphous semiconductor thin film 12 is not particularly limited, but can be, for example, 1 nm or more and 10 nm or less, and preferably 8 nm or less. When the film thickness is less than 1 nm, recombination of carriers is likely to occur due to defects easily occurring. Moreover, when this film thickness exceeds 10 nm, it becomes easy to produce the fall of a short circuit current and the increase in light absorption.

The n-type amorphous semiconductor thin film 13 is laminated on one side of the first intrinsic amorphous semiconductor thin film 12. Examples of the semiconductor constituting the n-type amorphous semiconductor thin film 13 include n-type amorphous silicon, n-type amorphous SiC, SiGe, SiN, etc. From this point, n-type amorphous silicon is preferable. The thickness of the n-type amorphous semiconductor thin film 13 is not particularly limited, but is preferably 1 nm to 15 nm, for example, and more preferably 2 nm to 10 nm. By setting the film thickness within such a range, occurrence of carrier recombination and series resistance can be reduced in a balanced manner.

The first transparent conductive film 14 (transparent conductive film (α)) is stacked on one side of the n-type amorphous semiconductor thin film 13. The first transparent conductive film 14 is made of crystalline indium oxide doped with one or more elements (x) belonging to Groups 4, 5 and 6 of the periodic table.

The element (x) is not particularly limited as long as it is an element belonging to Group 4, Group 5, and Group 6 of the periodic table, but preferably includes elements of the sixth period (hafnium, tungsten, and tantalum). And one or more elements (x1) selected from the group consisting of tantalum and tantalum. The content of the element (x1) in the first transparent conductive film 14 is preferably 0.1% by mass or more and 10% by mass or less, more preferably 0.3% by mass or more in terms of oxide (WO ₃ , Ta ₂ O ₅ ). 5 mass% or less is more preferable, and 0.5 mass% or more and 3 mass% or less are still more preferable. By setting the content of the element (x1) in the above range, low temperature crystallinity, crystal grain size controllability, and the like can be improved.

The element (x) preferably contains at least one element (x2) selected from the group consisting of titanium, vanadium and niobium in addition to the element (x1). Of the elements (x2), titanium is more preferable. The content of the element (x2) in the first transparent conductive film 14 is preferably 0.1% by mass or more and 5% by mass or less in terms of oxides (TiO ₂ , V ₂ O ₅ and Nb ₂ O ₅ ), and 0 More preferably, the content is 5% by mass or more and 3% by mass or less.

The total content of the element (x) in the first transparent conductive film 14 is preferably 0.1% by mass or more and 10% by mass or less, and 0.5% by mass or more and 5% by mass or less in terms of oxide. More preferred is 3% by mass or less. By setting the total content of the element (x) within the above range, low temperature crystallinity, crystal grain size controllability, and the like can be improved. Note that the first transparent conductive film 14 may further contain other elements (for example, tin or the like) as long as the effects of the present invention are not impaired. Moreover, as content of indium oxide in the 1st transparent conductive film 14, 90 mass% or more is preferable, 95 mass% or more is more preferable, 97 mass% or more and 99.9 mass% or less are further more preferable.

The average major axis crystal grain size of crystalline indium oxide in the first transparent conductive film 14 is 10 nm or more and less than 300 nm, and preferably 40 nm or more and 250 nm or less. The average long-axis crystal grain size (in-plane long-axis average crystal grain size) is measured by measuring the longest diameter of each crystal grain existing in the plane in an image obtained from a scanning electron microscope (SEM). The average value of the measured values of the top 20 particles with the largest value. Since the first transparent conductive film 14 is mainly composed of crystalline indium oxide having such a small particle diameter, even if the formation temperature is 200 ° C. or less, the film has high crystallinity and high mobility. It becomes. In addition, it is thought that the formation of a crystal having such a small particle diameter is derived from the element (x) to be doped.

Although it does not specifically limit as a film thickness of the 1st transparent conductive film 14, 40 nm or more and 100 nm or less are preferable from the point of being able to make translucency and current collection compatible. Further, the specific resistance value of the first transparent conductive film 14 is preferably 5 × 10 ⁻⁵ Ω · cm to 1 × 10 ⁻³ Ω · cm, and more preferably 5 × 10 ⁻⁴ Ω · cm. Further, in order to achieve both the light transmitting property and the current collecting property, it is preferable that the carrier density has an upper limit of 3 × 10 ²⁰ cm ⁻³ and the mobility has a lower limit of 40 cm ² V ⁻¹ s ^−1. .

The second intrinsic amorphous semiconductor thin film 15 is stacked on the other side of the n-type crystal semiconductor substrate 11. The semiconductor constituting the second intrinsic amorphous semiconductor thin film 15 can be the same as the first intrinsic amorphous semiconductor thin film 12. The film thickness of the second intrinsic amorphous semiconductor thin film 15 can be, for example, 1 nm or more and 10 nm or less.

The p-type amorphous semiconductor thin film 16 is laminated on the other side of the second intrinsic amorphous semiconductor thin film 15. Examples of the semiconductor composing the p-type amorphous semiconductor thin film 16 include p-type amorphous silicon, p-type amorphous SiC, SiGe, SiN and the like. From this point, p-type amorphous silicon is preferable. The thickness of the p-type amorphous semiconductor thin film 16 is not particularly limited, but is preferably 1 nm or more and less than 6 nm, for example, and more preferably 2 nm or more and 5 nm or less. By setting the film thickness within such a range, occurrence of carrier recombination and series resistance can be reduced in a balanced manner.

The second transparent conductive film 17 (transparent conductive film (α)) is laminated on the other side of the p-type amorphous semiconductor thin film 16. The material (composition), characteristics, crystal grain size, film thickness, and the like that form the second transparent conductive film 17 are the same as those of the first transparent conductive film 14. However, the first transparent conductive film 14 and the second transparent conductive film 17 may be different in composition, film thickness, specific resistance, and the like. For example, according to the knowledge of the inventors, in the heterojunction photovoltaic device 10 having a rear emitter structure, the second transparent conductive layer laminated on the back side, that is, on the p-type amorphous semiconductor thin film 16. Since the current collecting property in the lateral direction (planar direction) of the film 17 becomes low, it is preferable that the second transparent conductive film 17 has a lower resistance than the first transparent conductive film 14. As the carrier density increases, the absorption in the near-infrared wavelength region of 900 nm or more in the transparent conductive film increases remarkably. However, when the n-type crystal semiconductor substrate 11 is silicon (Si), the wavelength is 900 nm to 1200 nm. Since the light absorptance is low, light with a wavelength of 900 nm to 1200 nm tends to reach the second transparent conductive film 17 laminated on the back side. Therefore, in order to effectively use light with a wavelength of 900 nm to 1200 nm, it is necessary to increase the mobility while lowering the carrier density of the second transparent conductive film 17. Specifically, it is preferable that the upper limit of the carrier density in the second transparent conductive film 17 is 3 × 10 ²⁰ cm ⁻³ and the lower limit of the mobility is 40 cm ² V ⁻¹ s ⁻¹ .

The

collector electrodes

18 and 19 have a plurality of bus bar electrodes formed in parallel with each other at equal intervals, and a plurality of finger electrodes orthogonal to these bus bar electrodes and formed in parallel with each other at equal intervals.

The bus bar electrode and the finger electrode each have a linear shape or a strip shape, and are formed of a conductive material. As this conductive material, a conductive adhesive such as a silver paste or a metal conductive wire such as a copper wire can be used. The width of each bus bar electrode is, for example, about 0.5 mm to 2 mm, and the width of each finger electrode is, for example, about 10 μm to 300 μm. Moreover, as a space | interval between each finger electrode, it is about 0.5 mm or more and 4 mm or less, for example.

In addition, the collector electrode 19 on the other side (opposite to the light incident surface) may be a structure in which a conductive material is laminated on the entire surface, instead of a structure including a bus bar electrode and a finger electrode. The collector electrode having such a structure can be formed by plating, metal foil lamination, or the like. By making the collector electrode 19 on the other side in such a structure, the current collection efficiency on the other side can be increased. In addition, among incident light from one side, incident light transmitted through the pn junction portion is reflected by the entire surface of the collector electrode laminated on the entire surface, so that power generation efficiency can be improved.

The photovoltaic elements 10 having such a structure are usually used by connecting a plurality of photovoltaic elements 10 in series. By using a plurality of photovoltaic power generation devices 10 connected in series, the generated voltage can be increased.

The light incident surface of the photovoltaic element 10 is on one side (the upper side in FIG. 1). That is, the photovoltaic device 10 has a rear emitter structure in which a p-type amorphous semiconductor thin film 16 is provided on the side opposite to the light incident surface with respect to the n-type crystal semiconductor substrate 11. In the photovoltaic element 10, the transparent

conductive films

14 and 17 made of crystals with a small particle diameter are formed of indium oxide doped with a specific dopant (element (x)). Low resistance and excellent power generation efficiency. In particular, in the photovoltaic device 10, the second transparent conductive film 17 on the back side that can reduce the lateral current collecting property usually has the specific dopant and crystallinity. For this reason, since low resistance can be achieved by increasing mobility without increasing the carrier density of the second transparent conductive film 17, it is light transmissive (especially, light transmissive with a wavelength of 900 nm to 1200 nm). Low resistance can be achieved while suppressing the decrease.

Next, a method for manufacturing the photovoltaic element 10 will be described. The photovoltaic element 10 includes a step of laminating a first intrinsic amorphous semiconductor thin film 12 on one side of an n-type crystal semiconductor substrate 11, a step of laminating an n-type amorphous semiconductor thin film 13, and a first step. A step of laminating the transparent conductive film 14, a step of laminating the second intrinsic amorphous semiconductor thin film 15 on the other side of the n-type crystal semiconductor substrate 11, and a step of laminating the p-type amorphous semiconductor thin film 16. Further, a step of laminating the second transparent conductive film 17 and a step of disposing the

collector electrodes

18 and 19 on the one side surface of the first transparent conductive film 14 and the other side surface of the second transparent conductive film 17. Have. In addition, the order of each process will not be specifically limited as long as it is the order which can obtain the layer structure of the photovoltaic device 10. FIG.

As a method of laminating the first and second intrinsic amorphous semiconductor

thin films

12 and 15, for example, chemical vapor deposition (for example, plasma CVD method or catalytic CVD method (also called hot wire CVD method)) or the like is used. A well-known method is mentioned. In the case of the plasma CVD method, for example, a mixed gas of SiH ₄ and H ₂ can be used as the source gas.

As a method of laminating the n-type amorphous semiconductor thin film 13 and the p-type amorphous semiconductor thin film 16, for example, a chemical vapor deposition method (for example, a plasma CVD method or a catalytic CVD method (also called hot wire CVD method)) The film can be formed by a known method such as If by plasma CVD method, a mixed gas of SiH _4, _{H _2,} and PH ₃ for example in the n-type amorphous-based semiconductor 13 as a source gas, the p-type amorphous-based semiconductor thin film 16 is for example a SiH ₄ A mixed gas of H ₂ and B ₂ H ₆ can be used.

Examples of the method of laminating the first and second transparent

conductive films

14 and 17 include a sputtering method, a vacuum deposition method, and an ion plating method (reactive plasma deposition method). It is preferable to use a plating method. The sputtering method is excellent in film thickness controllability and the like, and can be performed at a lower cost than the ion plating method. On the other hand, according to the ion plating method, it is possible to perform film formation while suppressing generation of defects.

As a vapor deposition material used when the first and second transparent

conductive films

14 and 17 are formed by a sputtering method or an ion plating method, a main component is indium oxide, and an oxide of the element (x) is included. Is used. The component ratio of each component in the vapor deposition material can be appropriately adjusted according to the desired component ratio of the first and second transparent

conductive films

14 and 17. The vapor deposition material may further contain other components (for example, tin oxide). In addition, when the 1st or 2nd transparent

conductive films

14 and 17 are formed by sputtering method or ion plating method, content (content ratio) of the metal component in each transparent

conductive films

14 and 17 is the vapor deposition material used. Are considered to be substantially the same.

As the vapor deposition material, when the element (x) is tungsten or the like (in the case of so-called IWO), a known vapor deposition material can be used. Further, when the element (x) is tantalum, the vapor deposition material is prepared, for example, by a step (a) of preparing a solution containing a precursor of indium oxide and a precursor of tantalum oxide, and an alkali compound in the solution. To obtain a metal hydroxide precipitate (b), washing and drying the obtained metal hydroxide precipitate to obtain a metal oxide powder (c), and The metal oxide powder can be obtained by a method including a step (d) of sintering after pulverization. Examples of the indium oxide precursor include indium nitrate and indium chloride, and examples of the tantalum oxide precursor include tantalum chloride. The pH of the solution obtained in step (a) is preferably 1 to 4. Moreover, you may add other components (For example, metal components other than element (x), a pH adjuster, etc.) to this solution. The pH of the solution after adding the alkali compound in the step (b) is preferably 7 to 10. The sintering temperature in step (d) can be about 1250 to 1600 ° C., and the sintering time can be about 10 to 20 hours.

The sputtering method can be performed using a known sputtering apparatus. The initial degree of vacuum in the chamber of the sputtering apparatus can be about 1 × 10 ⁻⁷ to 1 × 10 ⁻⁵ Torr. The ion plating method can also be performed using a commonly used known apparatus. The substrate temperature during lamination (vapor deposition) by sputtering or ion plating is not particularly limited, but is preferably 200 ° C. or lower, more preferably 0 ° C. or higher and 80 ° C. or lower, and may be room temperature. The formation pressure can be about 7.5 × 10 ⁻⁴ to 7.5 × 10 ⁻³ Torr, and preferably 2 × 10 ⁻³ Torr to 7 × 10 ⁻³ Torr.

After the films are stacked by a sputtering method, an ion plating method, or the like, heat treatment can be performed as necessary. As this heat processing temperature, 50 to 200 degreeC is preferable and 180 degreeC or less is more preferable. Here, in the formation of the transparent

conductive films

14 and 17, the formation temperature (the substrate temperature during sputtering and ion plating, and the heat treatment temperature performed thereafter if necessary) is 200 ° C. or less (more preferably 150 ° C. or less). As the lower limit, for example, 20 ° C.), the transparent

conductive films

14 and 17 have the above-described composition, so that the formation of fine crystal grains proceeds even in the formation at such a relatively low temperature, A low resistance film can be obtained. In addition, since the formation temperature is 200 ° C. or lower, the influence on other amorphous semiconductor thin films and the like can be suppressed, and a heterojunction photovoltaic device having high power generation efficiency can be obtained.

The

collector electrodes

18 and 19 can be disposed by a known method. When a conductive adhesive is used as a material for the

collector electrodes

18 and 19, it can be formed by a printing method such as screen printing or gravure offset printing. Moreover, when using a metal conducting wire for the

collector electrodes

18 and 19, it can fix on the transparent

conductive films

14 and 17 with a conductive adhesive or a low melting point metal (solder etc.).

The present invention is not limited to the above-described embodiments, and the configuration thereof can be changed without changing the gist of the present invention. For example, the first intrinsic amorphous semiconductor thin film 12 and the second intrinsic amorphous semiconductor thin film 15 included in the photovoltaic device 10 are not essential components. In particular, the maximum output can be further increased in order to improve translucency by adopting a configuration in which the first intrinsic amorphous semiconductor thin film 12 on the light incident side is not laminated. The first transparent conductive film 14 or the second transparent conductive film 17 may be formed by another transparent conductive material or a different film formation method, and the crystallinity is not particularly limited. Examples of other transparent conductive materials include ITO.

Specifically, the first transparent conductive film 14 is a film formed by ion plating using, for example, IWO, and the second transparent conductive film 17 is formed by sputtering using indium oxide doped with at least tantalum. Film. By forming the first transparent conductive film 14 positioned on the light incident surface side by an ion plating method, deterioration of the n-type amorphous semiconductor thin film 13 is suppressed, and power generation efficiency can be increased.

Experimental example

Hereinafter, the contents of the present invention will be described more specifically with reference to experimental examples and comparative examples. Note that the present invention is not limited to the following experimental examples.

<Production Example 1>
A hydroxide precipitate was obtained by adding an alkali to an aqueous solution in which indium nitrate (In (NO ₃ ) ₃ ), tantalum chloride and tetraisopropyl orthotitanate were dissolved. The hydroxide precipitate was dried and pulverized and then sintered to obtain a sintered body (sputtering target). The amounts of tantalum chloride and tetraisopropyl orthotitanate were adjusted so that the contents of tantalum oxide and titanium oxide in the sputtering target were 0.5% by mass, respectively. The obtained sputtering target was attached to a DC magnetron sputter, an initial vacuum degree in the chamber was set to 1 × 10 ⁻⁶ Torr or less, and an In—Ta—Ti—O-based thin film was deposited on a glass substrate with a thickness of 100 nm at room temperature. It was. Thereafter, the In—Ta—Ti—O-based thin film was heat-treated at 150 ° C. for 2 hours in an air atmosphere to obtain a transparent conductive film. The surface of the obtained transparent conductive film was confirmed to have crystallinity by SEM observation, and the specific resistance was 3.78 × 10 ⁻⁴ Ω · cm. The average major axis crystal grain size based on the SEM image was 100 nm. Moreover, as a result of measuring the resistance change after storing the obtained transparent conductive film at 80 ° C. under a room temperature of 85% for 5 days, the resistance change was within 3.2%.

<Production Example 2>
A film was formed by an ion plating method using an IWO vapor deposition material (W = 1 mass%). Specifically, an In—W—O-based thin film was deposited on a glass substrate with a thickness of 100 nm at room temperature. Thereafter, the In—W—O-based thin film was heat-treated at 200 ° C. for 30 minutes in an air atmosphere to obtain a transparent conductive film. The crystallinity of the surface of the obtained transparent conductive film could be confirmed by SEM observation. The average major axis crystal grain size based on the SEM image was 200 nm.

<Comparative Production Example 1>
A transparent conductive film was obtained in the same manner as in Production Example 1 using an indium tin oxide sputtering target having an indium oxide content of 90% by mass and a tin oxide content of 10% by mass. The surface of the obtained transparent conductive film could not be confirmed by SEM observation, and the specific resistance was 7.19 × 10 ⁻⁴ Ω · cm. Moreover, as a result of measuring the resistance change after storing the obtained transparent conductive film at 80 ° C. under a room temperature of 85% for 5 days, the resistance change was within 12.9%.

<Comparative Examples 1 and 2, Experimental Examples 1 and 2>
On one side of the n-type single crystal silicon substrate, a first intrinsic amorphous silicon thin film (film thickness 6 nm), an n-type amorphous silicon thin film (film thickness 8 nm), and a first transparent conductive film (film thickness) 65 nm) was laminated in this order. In addition, the n-type single crystal silicon substrate used what formed the fine uneven structure (texture structure) which has innumerable pyramid shape on both surfaces. This concavo-convex structure was formed by immersing the substrate material in an etching solution containing about 3% by mass of sodium hydroxide and anisotropically etching the (100) plane of the substrate material.
Next, on the other side of the n-type single crystal silicon substrate, a second intrinsic amorphous silicon thin film (film thickness 6 nm), a p-type amorphous silicon thin film (film thickness 4 nm), and a second transparent conductive film ( A film thickness of 65 nm) was laminated in this order. Each silicon thin film was laminated by a plasma CVD method.

<Experimental Examples 3 and 4>
An n-type amorphous silicon thin film (film thickness: 8 nm) and a first transparent conductive film (film thickness: 65 nm) were laminated in this order on one side of an n-type single crystal silicon substrate (first intrinsic amorphous system) Except that the silicon thin film was not laminated), it was performed in the same manner as in Experimental Example 1 and the like.

The first and second transparent conductive films in each experimental example and comparative example were laminated by the following materials and methods.
Comparative example 1: ITO (Sn = 10 mass%), sputtering method comparative example 2: ITO (Sn = 5 mass%), ion plating method experimental example 1, experimental example 3: IWO (W = 1 mass%), ion Plating method (conditions of production example 2)
Experimental Example 2 and Experimental Example 4: In—Ta—Ti—O material (sputtering target of Production Example 1), sputtering method (deposition conditions of Production Example 1)

Next, a plurality of parallel bus bar electrodes and a plurality of finger electrodes respectively orthogonal to the bus bar electrodes were formed as collector electrodes on the surfaces (outer surfaces) of the first and second transparent conductive films. This collector electrode was formed by screen printing using a silver paste. Thus, the photovoltaic elements of Comparative Examples 1 and 2 and Experimental Examples 1 to 4 were obtained.

The maximum output (Pmax) of each obtained photovoltaic device was measured. As measurement results, values based on Comparative Example 1 are shown in FIG. In addition, each was measured by using one side as a light incident surface, that is, a heterojunction structure (Rear emitter) in which the p layer was laminated on the opposite side to the light incident side.

As shown in FIG. 2, the photovoltaic elements of Experimental Examples 1 to 4 have a maximum output that is higher than those of Comparative Examples 1 and 2 in which a transparent conductive film is formed of ITO and crystallization is not sufficiently advanced. .

A transparent conductive film is formed using a material that can be crystallized even at a relatively low temperature, so that high power generation efficiency can be obtained, and a photovoltaic device that has attracted attention in recent years can be provided.

10: photovoltaic device, 11: n-type crystal semiconductor substrate, 12: first intrinsic amorphous semiconductor thin film, 13: n-type amorphous semiconductor thin film, 14: first transparent conductive film, 15: first 2 intrinsic amorphous semiconductor thin film, 16: p-type amorphous semiconductor thin film, 17: second transparent conductive film, 18, 19: collector electrode

Claims

An n-type crystal semiconductor substrate, an n-type amorphous semiconductor thin film and a first transparent conductive film stacked in this order on one side of the n-type crystal semiconductor substrate, and this on the other side of the n-type crystal semiconductor substrate In a photovoltaic device comprising a p-type amorphous semiconductor thin film and a second transparent conductive film, which are sequentially stacked, and one side used as a light incident surface,
Either one or both of the first and second transparent conductive films is crystalline indium oxide doped with one or more elements (x) belonging to Groups 4, 5, and 6 of the periodic table. A photovoltaic device, wherein the crystalline indium oxide is a transparent conductive film (α) having an average major axis crystal grain size of 10 nm or more and less than 300 nm.
2. The photovoltaic device according to claim 1, wherein the element (x) includes one or more elements (x1) selected from the group consisting of tungsten and tantalum.
The photovoltaic device according to claim 2, wherein the content of the element (x1) in the transparent conductive film (α) is 0.1% by mass or more and 10% by mass or less in terms of oxide. element.
4. The photovoltaic element according to claim 2, wherein the element (x) further includes one or more elements (x2) selected from the group consisting of titanium, vanadium and niobium.
5. The photovoltaic device according to claim 4, wherein the content of the element (x2) in the transparent conductive film (α) is 0.1% by mass or more and 5% by mass or less in terms of oxide. element.
6. The photovoltaic device according to claim 1, wherein the content of the element (x) in the transparent conductive film (α) is 0.1% by mass or more and 10% by mass or less in terms of oxide. A photovoltaic device characterized by being.
The photovoltaic element according to any one of claims 1 to 6, wherein the second transparent conductive film is the transparent conductive film (α).
The photovoltaic device according to claim 7, wherein the first transparent conductive film is also the transparent conductive film (α).
The photovoltaic element according to any one of claims 1 to 8, wherein the transparent conductive film (α) is formed at a formation temperature of 200 ° C or lower.