JP2010165878A - Photoelectric conversion element, and solar cell using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photoelectric conversion element stably exhibiting excellent withstand voltage properties and photoelectric conversion efficiency with a good yield. <P>SOLUTION: On a substrate 10 having an anodized film on at least one surface side of a metal base material principally consisting of Al, the photoelectric conversion element 1 includes: a photoelectric conversion layer 30, which contains a compound semiconductor consisting of group Ib elements, group IIIb elements and group VIb elements and generates current by light absorption; and electrodes 20 and 50 for taking out the current. In the metal base material, an Fe content is 0.05-1.0 mass%, a minimum diameter in the cross-section is 0.3 μm or more, and the number of Fe-containing clusters, wherein the value obtained by dividing the sum of the minimum diameter and the maximum diameter by 2 is 0.5-2.5 μm, is 1,500-40,000 pieces/mm<SP>2</SP>. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a photoelectric conversion element including a photoelectric conversion layer including a compound semiconductor composed of a group Ib element, a group IIIb element, and a group VIb element on a flexible substrate, and a solar cell using the photoelectric conversion element. .

BACKGROUND ART A photoelectric conversion element including a photoelectric conversion layer that generates current by light absorption and an electrode that extracts current generated in the photoelectric conversion layer is used for applications such as solar cells.
Conventionally, in solar cells, Si-based solar cells using bulk single-crystal Si or polycrystalline Si, or thin-film amorphous Si have been mainstream, but research and development of Si-independent compound semiconductor solar cells has been made. ing. As a compound semiconductor solar cell, CIS (Cu-In-Se) system or CIGS (Cu-In-Ga-Se) composed of a bulk system such as a GaAs system, an Ib group element, an IIIb group element, and a VIb group element is used. And other thin film systems are known. The CIS system or CIGS system has a high light absorption rate, and high energy conversion efficiency has been reported.

  At present, glass substrates are mainly used as solar cell substrates, but glass substrates lack flexibility and are easily damaged, making it difficult to reduce the thickness and weight. The resin substrate is flexible and can be thin and light, but has a lower heat resistance than the inorganic substrate and has a limited process temperature, and forms a photoelectric conversion layer with high photoelectric conversion efficiency. Is difficult.

  As a solar cell substrate, the use of a flexible metal substrate has been studied. In the case of using a metal substrate, it is essential to provide an insulating film on the surface of the substrate so as not to cause a short circuit between the substrate and the electrode and photoelectric conversion layer formed thereon. It is important that this insulating film has a high withstand voltage, that is, the dielectric breakdown of the insulating film does not occur even in a usage situation where a voltage is applied. When the dielectric breakdown occurs, a leakage current is generated, so that the photoelectric conversion efficiency is lowered. Therefore, in order to improve the yield, it is necessary to stably form an insulating film having excellent voltage resistance.

  In order to suppress warpage of the substrate due to thermal stress, it is preferable that the difference in thermal expansion coefficient between the substrate and each layer formed thereon is small. As the metal substrate, a substrate containing Al as a main component is preferable from the viewpoint of the difference in thermal expansion coefficient from the photoelectric conversion layer and the lower electrode (back electrode), cost, characteristics required for the solar cell, and the like.

In Patent Document 1, as a substrate for a solar cell, a substrate in which a porous anodic oxide film (Al ₂ O ₃ film) is formed on the surface of an Al base, or pores of the anodic oxide film are further provided on this substrate. It has been proposed to use a substrate filled with oxide. In this method, even when a large-area substrate is used, an insulating film can be easily formed on the entire surface without pinholes.

JP 2000-349320 A

  As described above, in a photoelectric conversion element substrate using a metal substrate, the insulating film formed on the surface has high insulating properties, excellent withstand voltage, and softening or deformation in a high-temperature film forming process. It is important to have heat resistance that does not occur. Although it is thought that the impurities of the substrate affect such characteristics, Patent Document 1 does not make any such studies.

  The present invention has been made in view of the above circumstances, and on a substrate having an anodized film on at least one surface side of a metal base material containing Al as a main component, a group Ib element, a group IIIb element, and a group VIb element In a photoelectric conversion element comprising a photoelectric conversion layer containing a compound semiconductor comprising: and focusing on the influence of impurities, the object is to provide a photoelectric conversion element excellent in voltage resistance and photoelectric conversion efficiency with good yield It is what.

The photoelectric conversion element of the present invention is on a substrate having an anodized film on at least one surface side of a metal base material mainly composed of Al.
In a photoelectric conversion element including a compound semiconductor composed of a group Ib element, a group IIIb element, and a group VIb element, and including a photoelectric conversion layer that generates a current by light absorption, and an electrode that extracts the current,
Fe content in the metal substrate is 0.05 to 1.0 mass%,
The number of Fe-containing clusters having a minimum diameter of 0.3 μm or more and a value obtained by dividing the sum of the minimum diameter and the maximum diameter by 2 is 0.5 to 2.5 μm in the cross section of the metal substrate. , 500 to 40,000 pieces / mm ² .

  In the present specification, the “main component of the metal substrate” is defined as a component having a content of 98% by mass. The metal substrate may be a pure Al substrate that may contain a trace element, or an alloy substrate of Al and another metal element.

  The element group descriptions in this specification are based on the short-period periodic table. In the present specification, a compound semiconductor composed of a group Ib element, a group IIIb element, and a group VIb element is abbreviated as “I-III-VI group semiconductor”. Each of the Ib group element, the IIIb group element, and the VIb group element that are constituent elements of the I-III-VI group semiconductor may be one type or two or more types. Further, the I-III-VI group semiconductor contained in the photoelectric conversion layer may be one type or two or more types.

  In the photoelectric conversion element of the present invention, the metal substrate has an Al content of 98.0% by mass or more, an Si content of 0.25% by mass or less, and a Cu content of 0.20% by mass or less. It is preferable that

  The “quantification of trace components in the metal substrate” can be performed by a plasma emission analysis method or an atomic absorption method defined in JIS H 1305 to 1307 standards. A method of performing mass spectrometry on a metal substrate sputtered can also be used in combination.

  The trace component in the metal base material dissolves almost uniformly in the entire substrate when the content is small, but the trace component exceeding the solid solution limit is unevenly distributed as fine cluster-like domains. In the present specification, a fine cluster-like domain in which Fe is unevenly distributed is referred to as “Fe-containing cluster”.

The measurement of “the number of Fe-containing clusters having a minimum diameter of 0.3 μm or more and a value obtained by dividing the sum of the minimum diameter and the maximum diameter by 2” is 0.5 to 2.5 μm. It can be carried out by observing with a surface analyzer combined with a scanning electron microscope (SEM) and an electron probe microanalyzer (EPMA). Since the appearance of the Fe-containing clusters observed can vary depending on the direction of the cross section relative to the rolling direction, the cross section is taken perpendicular to the surface of the metal substrate, and six types are provided at 30 ° intervals from any direction on the surface. Observe the cross-section in the direction. The observation visual field may be distributed so that the total area of the visual field corresponding to each direction is substantially uniform, and an area of 10 ⁻³ mm ² or more per direction may be observed. When the number of applicable clusters is large, an area where 250 or more clusters are observed in total may be used.

  The size of each cluster is evaluated by the size of the white area in the SEM image (area where the amount of reflected electrons emitted is large), and whether or not the cluster is a cluster in which Fe is unevenly distributed is a characteristic X-ray response of EPMA. The determination is made based on whether or not the signal contains an Fe-derived component.

  When EPMA is energy dispersive (EDX), the response signal derived from Fe is observed when the energy of the X-ray photon is around 0.69 keV, 6.4 keV, and 7.1 keV. When a cross section of a metal base material containing Al as a main component is observed, the signal is rarely observed except in a region that appears white in the SEM image. Therefore, it is possible to determine whether or not a region that appears white in the SEM image is an Fe-containing cluster by the above-described method.

  Note that it is difficult to evaluate the size of the Fe-containing cluster from the spatial distribution image of the EPMA response signal because the spatial resolution of the EPMA is insufficient. Further, when the value obtained by dividing the sum of the minimum diameter and the maximum diameter of the cluster by 2 is less than 0.5 μm, the response signal derived from Fe of EPMA becomes weak and is not clearly detected. Therefore, in the present invention, the lower limit of the value obtained by dividing the sum of the minimum diameter and the maximum diameter of the Fe-containing cluster to be counted by 2 is set to 0.5 μm. In practice, it is extremely rare that an Fe-containing cluster having a value obtained by dividing the sum of the minimum diameter and the maximum diameter by 2 exceeds 2.5 μm, and the sum of the minimum diameter and the maximum diameter is divided by 2. In the present invention, the sum of the minimum diameter and the maximum diameter of the Fe-containing cluster to be counted is 2 because even if there is even one Fe-containing cluster having a value of more than 2.5 μm, dielectric breakdown of the insulating film occurs and cannot be used. The upper limit of the divided value was 2.5 μm.

In the photoelectric conversion element of the present invention,
The photoelectric conversion layer is
At least one group Ib element selected from the group consisting of Cu and Ag;
At least one group IIIb element selected from the group consisting of Al, Ga and In;
It is preferable to include a compound semiconductor composed of at least one VIb group element selected from the group consisting of S, Se, and Te.

  The solar cell of the present invention comprises the above-described photoelectric conversion element of the present invention.

  According to the present invention, an optoelectronic device comprising a compound semiconductor comprising a group Ib element, a group IIIb element, and a group VIb element on a substrate having an anodized film on at least one surface side of a metal base material mainly composed of Al. In the photoelectric conversion element including the conversion layer, it is possible to provide a photoelectric conversion element that is stable with high yield and excellent in voltage resistance and photoelectric conversion efficiency.

1 is a schematic cross-sectional view in a short direction of a photoelectric conversion element according to an embodiment of the present invention 1 is a schematic sectional view in a longitudinal direction of a photoelectric conversion element according to an embodiment of the present invention. Schematic cross-sectional view showing the configuration of the substrate The perspective view which shows the manufacturing method of a board | substrate Diagram showing the relationship between lattice constant and band gap in I-III-VI compound semiconductors Example of SEM cross-section photograph of substrate Example of EDX chart

"Photoelectric conversion element"
With reference to drawings, the structure of the photoelectric conversion element of one Embodiment which concerns on this invention is demonstrated. 1A is a schematic cross-sectional view in the short direction of the photoelectric conversion element, FIG. 1B is a schematic cross-sectional view in the longitudinal direction of the photoelectric conversion element, FIG. 2 is a schematic cross-sectional view illustrating the configuration of the substrate, and FIG. 3 illustrates a method for manufacturing the substrate. It is a perspective view. In order to facilitate visual recognition, the scale of each component in the figure is appropriately different from the actual one.

The photoelectric conversion element 1 is an element in which a lower electrode (back electrode) 20, a photoelectric conversion layer 30, a buffer layer 40, and an upper electrode 50 are sequentially stacked on a substrate 10.
The photoelectric conversion element 1 includes a first groove 61 that penetrates only the lower electrode 20, a second groove 62 that penetrates the photoelectric conversion layer 30 and the buffer layer 40, and A third groove portion 63 penetrating only the upper electrode 50 is formed, and a fourth groove portion 64 penetrating the photoelectric conversion layer 30, the buffer layer 40, and the upper electrode 50 in the longitudinal sectional view is formed. Is formed.

  With the above configuration, a structure in which the element is separated into a large number of cells C by the first to fourth groove portions 61 to 64 is obtained. Further, by filling the second groove 62 with the upper electrode 50, a structure in which the upper electrode 50 of a certain cell C is connected in series to the lower electrode 20 of the adjacent cell C is obtained.

(substrate)
In the present embodiment, the substrate 10 is a substrate obtained by anodizing at least one surface side of a metal base 11 mainly composed of Al. The substrate 10 may have an anodized film 12 formed on both sides of the metal base 11 as shown in the left diagram of FIG. 2, or the substrate 10 of the metal base 11 as shown in the right diagram of FIG. 2. One having an anodized film 12 formed on one side may be used. The anodic oxide film 12 is a film containing Al ₂ O ₃ as a main component.

In order to suppress the warpage of the substrate due to the difference in thermal expansion coefficient between Al and Al ₂ O ₃ and the film peeling due to this in the device manufacturing process, as shown in the left diagram of FIG. It is preferable that the anodic oxide film 12 is formed on both sides of the film. Examples of the anodic oxidation method on both sides include a method of applying an insulating material on one side and anodizing both sides of each side, and a method of anodizing both sides simultaneously.

  When the anodic oxide films 12 are formed on both sides of the substrate 10, the two anodic oxide films 12 have substantially the same thickness in consideration of the balance of thermal stresses on both sides of the substrate, or a surface on which no photoelectric conversion layer or the like is formed. The anodic oxide film 12 on the side is preferably slightly thicker than the other anodic oxide film 12.

  The metal substrate 11 may be Japanese Industrial Standard (JIS) 1000 series pure Al, Al—Mn alloy, Al—Mg alloy, Al—Mn—Mg alloy, Al—Zr alloy, Al— An alloy of Al and other metal elements such as an Si-based alloy and an Al—Mg—Si-based alloy may be used (see “Aluminum Handbook 4th Edition” (1990, published by Light Metal Association)). The metal substrate 11 may contain various trace metal elements such as Fe, Si, Mn, Cu, Mg, Cr, Zn, Bi, Ni, and Ti.

  Anodization can be performed by immersing the metal base material 11 that has been subjected to cleaning treatment, polishing smoothing treatment, and the like as needed as an anode together with a cathode and applying a voltage between the anode and the cathode. Carbon, aluminum, or the like is used as the cathode. The electrolyte is not limited, and an acidic electrolytic solution containing one or more acids such as sulfuric acid, phosphoric acid, chromic acid, oxalic acid, sulfamic acid, benzenesulfonic acid, and amidosulfonic acid is preferably used.

The anodizing conditions are not particularly limited by the type of electrolyte used. As conditions, for example, an electrolyte concentration of 1 to 80% by mass, a liquid temperature of 5 to 70 ° C., a current density of 0.005 to 0.60 A / cm ² , a voltage of 1 to 200 V, and an electrolysis time of 3 to 500 minutes are appropriate. It is.

As the electrolyte, sulfuric acid, phosphoric acid, oxalic acid, or a mixture thereof is preferable. When such an electrolyte is used, an electrolyte concentration of 4 to 30% by mass, a liquid temperature of 10 to 30 ° C., a current density of 0.05 to 0.30 A / cm ² , and a voltage of 30 to 150 V are preferable.

  Immediately after the start of the anodizing treatment, the amount of current flowing through the metal substrate 11 is reduced, and then the current amount is controlled so that the current amount is gradually increased to a desired value. The number of local plaques can be reduced, which is preferable.

As shown in FIG. 3, when the metal base material 11 mainly composed of Al is anodized, an oxidation reaction proceeds in a direction substantially perpendicular to the surface from the surface 11s, and the anode mainly composed of Al ₂ O _3. An oxide film 12 is generated. The anodic oxide film 12 produced by anodic oxidation has a structure in which a number of fine columnar bodies 12a having a substantially regular hexagonal shape in plan view are arranged without gaps. A minute hole 12b extending substantially straight from the surface 11s in the depth direction is opened at a substantially central portion of each fine columnar body 12a, and the bottom surface of each fine columnar body 12a has a rounded shape. Usually, a barrier layer (usually 0.01 to 0.4 μm in thickness) having no fine holes 12b is formed at the bottom of the fine columnar body 12a. If the anodic oxidation conditions are devised, the anodic oxide film 12 without the fine holes 12b can be formed.

  The diameter of the fine hole 12b of the anodic oxide film 12 is not particularly limited. From the viewpoint of surface smoothness and insulating properties, the diameter of the fine holes 12b is preferably 200 nm or less, and more preferably 100 nm or less. The diameter of the fine hole 12b can be reduced to about 10 nm.

The hole density of the fine holes 12b of the anodic oxide film 12 is not particularly limited. From the viewpoint of insulating properties, hole density of the micropores 12b is preferably 100 to 10000 pieces / [mu] m ^2, more preferably 100 to 5,000 pieces / [mu] m ^2, particularly preferably at 100 to 1000 / [mu] m ² is there.

  The surface roughness Ra of the anodic oxide film 12 is not particularly limited. From the viewpoint of uniformly forming the upper photoelectric conversion layer 30, it is preferable that the surface smoothness of the anodic oxide film 12 is higher. The surface roughness Ra is preferably 0.3 μm or less, more preferably 0.1 μm or less.

  The thickness of the metal substrate 11 and the anodic oxide film 12 is not particularly limited. Considering the mechanical strength and reduction in thickness and weight of the substrate 10, the thickness of the metal base 11 before anodization is preferably 0.05 to 0.6 mm, for example, and more preferably 0.1 to 0.3 mm. Considering the insulating properties, mechanical strength, and reduction in thickness and weight of the substrate, the thickness of the anodic oxide film 12 is preferably 0.1 to 100 μm, for example.

  For the purpose of suppressing variations in the arrangement and diameter of the micropores 12b, anodization may be performed after forming a recess that is a starting point for generating the micropores 12b. Moreover, you may perform a well-known sealing process to the fine hole 12b of the anodic oxide film 12 as needed. The withstand voltage and the insulation characteristics can be improved by the sealing treatment. In addition, when sealing is performed using a material containing alkali metal ions, alkali metal ions, preferably Na ions, diffuse into the photoelectric conversion layer 30 during annealing of the photoelectric conversion layer 30 made of CIGS or the like, whereby photoelectric conversion is performed. The crystallinity of the layer 30 may be improved and the photoelectric conversion efficiency may be improved.

  In the substrate for photoelectric conversion elements, the insulating film formed on the surface has high insulating properties, excellent withstand voltage, and heat resistance that does not cause softening or deformation in a high-temperature film forming process. is important. Although it is considered that the amount of impurities on the substrate affects such characteristics, there has been no specific example in the past.

  In the metal substrate 11 containing Al as a main component, the heat resistance tends to be improved as the Fe content increases. However, if the Fe content becomes too high, the voltage resistance of the anodic oxide film 12 tends to decrease. The inventor paid attention not only to the Fe content but also to the form of Fe in the metal substrate 11. It is preferable that Fe is dispersed in as small particles as possible because the heat resistance of the metal substrate 11 is high. In addition, when Fe is present in the form of clusters having large grains, dielectric breakdown of the anodic oxide film 12 is likely to occur.

The inventor has a Fe content in the metal substrate 11 of 0.05 to 1.0% by mass, and a minimum diameter in the cross section of the metal substrate 11 is 0.3 μm or more. When the number of Fe-containing clusters having a value obtained by dividing the sum of the maximum diameters by 2 is 0.5 to 2.5 μm is 1,500 to 40,000 pieces / mm ² , the voltage resistance is stable with good yield. And it discovered that the photoelectric conversion element 1 excellent in the photoelectric conversion efficiency could be provided. When the metal substrate 11 satisfies such characteristics, the present inventor provides the photoelectric conversion element 1 that is stable in yield and stable in voltage resistance and photoelectric conversion efficiency even in a high-temperature process at 470 to 550 ° C. I found out that I can do it.

The Fe content in the metal substrate 11 is preferably 0.1 to 0.7% by mass. The number of Fe-containing clusters having a minimum diameter of 0.3 μm or more in the cross section of the metal substrate 11 and a value obtained by dividing the sum of the minimum diameter and the maximum diameter by 2 is preferably 0.5 to 2.5 μm. 3,000 to 24,000 pieces / mm ² .

  The Fe content and the number of Fe-containing clusters can be controlled within the above ranges by adjusting the amount of trace components and the production conditions when producing the metal substrate 11 containing Al as a main component.

  The metal substrate 11 containing Al as a main component is manufactured by casting a molten metal prepared according to the composition and subjected to a cleaning treatment as necessary, and then rolling. Examples of the cleaning process for the molten metal include a degassing process for removing unnecessary gas such as hydrogen in the molten metal, a filtering process for removing foreign substances, and a combination thereof. Examples of the casting method include a DC casting method and a continuous casting method.

  In DC casting, solidification occurs at a cooling rate of 0.5 to 30 ° C./second. The obtained ingot is subjected to face cutting for cutting 1 to 30 mm of the surface layer as necessary. Before and after that, soaking treatment is performed as necessary. When performing the soaking process, heat treatment is performed at 450 to 620 ° C. for 1 to 48 hours so that the intermetallic compound does not become coarse.

  After DC casting, hot rolling and cold rolling are performed to obtain a rolled sheet. An appropriate starting temperature for hot rolling is 350 to 500 ° C. An intermediate annealing treatment may be performed before or after hot rolling or in the middle thereof. The conditions for the intermediate annealing treatment are heating at 280 to 600 ° C. for 2 to 20 hours using a batch annealing furnace or heating at 400 to 600 ° C. for 6 minutes or less using a continuous annealing furnace. The crystal structure can be made finer by heating at a heating rate of 10 to 200 ° C./second using a continuous annealing furnace.

  As a continuous casting method, a method using a cooling roll represented by the twin roll method (Hunter method) and the 3C method, or a cooling belt or a cooling block represented by the twin belt method (Hasley method) and the Al Swiss Caster II type The method using is industrially performed. When the continuous casting method is used, it solidifies at a cooling rate of 100 to 1000 ° C./second.

  When continuous casting is performed, for example, if a method using a cooling roll such as a Hunter method is used, a cast plate having a thickness of 1 to 10 mm can be directly continuously cast, and the hot rolling step can be omitted. it can. When using a method using a cooling belt such as the Husley method, a cast plate having a thickness of 10 to 50 mm can be cast. Generally, a hot rolling roll is arranged immediately after casting and continuously rolled. A continuous cast and rolled plate having a thickness of 1 to 10 mm is obtained. In either method, cold rolling is subsequently performed to obtain a rolled sheet. Also in the case of continuous casting, intermediate annealing treatment may be performed.

  In either case of performing the DC casting method or the continuous casting method, the obtained rolled plate is subjected to a post-treatment such as a surface smoothing treatment as necessary.

  By appropriately selecting the amount of trace components, conditions for casting, rolling, intermediate annealing, etc., the composition and crystal structure state in the metal substrate 11 can be controlled, and the Fe content and the number of Fe-containing clusters can be controlled. It can be controlled within the specified range of the invention.

  Qualitatively, the average volume of the Fe-containing cluster increases as the time during which the temperature is high and the rate of temperature decrease are slow in the casting, rolling, and annealing processes. At this time, the total number of Fe-containing clusters decreases in a manner that is inversely proportional to the average volume. In the casting and rolling process, the DC casting → hot rolling → cold rolling is longer than the continuous casting → cold rolling and the temperature lowering rate is longer and the average volume of the Fe-containing cluster is larger. The number tends to decrease. Further, when an intermediate annealing step is added, the average volume of Fe-containing clusters is large, and the number is reduced. Therefore, this property can be used to adjust the number of Fe-containing clusters in a specific size range even with the same Fe content.

  The amount of trace components other than Fe in the metal substrate 11 is not particularly limited. The metal substrate 11 preferably has an Al content of 98.0% by mass or more, an Si content of 0.25% by mass or less, and a Cu content of 0.20% by mass or less. The Al content is more preferably 99.0% by mass or more. The Si content is more preferably 0.15% by mass or less, and particularly preferably 0.03 to 0.15% by mass. The Cu content is more preferably 0.15% by mass or less, and particularly preferably 0.02 to 0.15% by mass. If the amount of trace components other than Fe is within such a range, the substrate 10 for photoelectric conversion elements having high voltage resistance can be obtained, and the photoelectric conversion element 1 having high yield and high photoelectric conversion efficiency can be stably obtained.

(Photoelectric conversion layer)
The photoelectric conversion layer 30 is composed of one or more compound semiconductors (I-III-VI group semiconductors) composed of at least one type Ib element, at least one type IIIb element, and at least one type VIb element. And a layer that generates current by light absorption.

The photoelectric conversion layer 30 is
At least one group Ib element selected from the group consisting of Cu and Ag;
At least one group IIIb element selected from the group consisting of B, Al, Ga, and In;
A layer containing at least one compound semiconductor composed of at least one VIb group element selected from the group consisting of O, S, Se, and Te is preferable.

Because the light absorption rate is high and high photoelectric conversion efficiency is obtained,
The photoelectric conversion layer 30 is
At least one group Ib element selected from the group consisting of Cu and Ag;
At least one group IIIb element selected from the group consisting of Al, Ga and In;
It is preferable to include one or more compound semiconductors composed of at least one VIb group element selected from the group consisting of S, Se, and Te.

As the compound semiconductor,
CuAlS ₂ , CuGaS ₂ , CuInS ₂ ,
CuAlSe ₂ , CuGaSe ₂ , CuInSe ₂ (CIS),
AgAlS ₂ , AgGaS ₂ , AgInS ₂ ,
AgAlSe ₂ , AgGaSe ₂ , AgInSe ₂ ,
AgAlTe ₂ , AgGaTe ₂ , AgInTe ₂ ,
_{Cu (In 1-x Ga x} ) Se 2 (CIGS), Cu (In 1-x Al x) Se 2, Cu (In 1-x Ga x) (S, Se) 2,
_{Ag (In 1-x Ga x} ) Se 2, and _{Ag (In 1-x Ga x} ) (S, Se) 2 , and the like.

The photoelectric conversion layer 30 particularly preferably includes CuInSe ₂ (CIS) and / or Cu (In, Ga) Se ₂ (CIGS) in which Ga is dissolved. CIS and CIGS are semiconductors having a chalcopyrite crystal structure, have high light absorption, and high energy conversion efficiency has been reported. Moreover, there is little degradation of efficiency by light irradiation etc. and it is excellent in durability.

  The photoelectric conversion layer 30 contains impurities for obtaining a desired semiconductor conductivity type. Impurities can be contained in the photoelectric conversion layer 30 by diffusion from adjacent layers and / or active doping.

  In the photoelectric conversion layer 30, the constituent elements and / or impurities of the I-III-VI group semiconductor may have a concentration distribution, and a plurality of layer regions having different semiconductor properties such as n-type, p-type, and i-type May be included. For example, in the CIGS system, when the Ga amount in the photoelectric conversion layer 30 has a distribution in the thickness direction, the band gap width / carrier mobility and the like can be controlled, and the photoelectric conversion efficiency can be designed high.

  The photoelectric conversion layer 30 may include one or more semiconductors other than the I-III-VI group semiconductor. As a semiconductor other than the I-III-VI group semiconductor, a semiconductor composed of a group IVb element such as Si (group IV semiconductor), a semiconductor composed of a group IIIb element such as GaAs and a group Vb element (group III-V semiconductor), and Examples thereof include semiconductors (II-VI group semiconductors) composed of IIb group elements such as CdTe and VIb group elements.

  The photoelectric conversion layer 30 may contain an optional component other than a semiconductor and impurities for obtaining a desired conductivity type as long as the characteristics are not hindered. Content in particular of the I-III-VI group semiconductor in the photoelectric converting layer 30 is not restrict | limited, 75 mass% or more is preferable, 95 mass% or more is more preferable, 99 mass% or more is especially preferable.

  As CIGS layer deposition methods, 1) multi-source co-evaporation, 2) selenization, 3) sputtering, 4) hybrid sputtering, and 5) mechanochemical process are known.

1) As a multi-source simultaneous vapor deposition method,
A three-step method (JRTuttle et.al, Mat. Res. Soc. Symp. Proc., Vol. 426 (1996) p. 143, etc.);
The EC group co-evaporation method (L. Stolt et al .: Proc. 13th ECPVSEC (1995, Nice) 1451. etc.) is known.
In the former three-stage method, In, Ga, and Se are first co-deposited at a substrate temperature of 300 ° C. in a high vacuum, and then heated to 500 to 560 ° C., and Cu and Se are co-evaporated. In this method, Ga and Se are further vapor-deposited. The latter EC group simultaneous vapor deposition method is a method in which Cu-excess CIGS is vapor-deposited in the early stage of vapor deposition and In-rich CIGS is vapor-deposited in the latter half.

In order to improve the crystallinity of the CIGS film, as a method of improving the above method,
a) a method using ionized Ga (H. Miyazaki, et.al, phys.stat.sol. (a), Vol.203 (2006) p.2603, etc.),
b) Method of using cracked Se (68th Japan Society of Applied Physics Academic Lecture Proceedings (Autumn 2007, Hokkaido Institute of Technology) 7P-L-6 etc.),
c) Method using radicalized Se (Proceedings of the 54th Japan Society of Applied Physics (Aoyama Gakuin University) 29P-ZW-10 etc.)
d) A method using a photoexcitation process (the 54th Japan Society of Applied Physics Academic Lecture Proceedings (Spring 2007 Aoyama Gakuin University) 29P-ZW-14 etc.) is known.

2) The selenization method is also called a two-step method. First, a metal precursor of a laminated film such as a Cu layer / In layer or a (Cu—Ga) layer / In layer is formed by sputtering, vapor deposition, or electrodeposition. This is a method of forming a selenium compound such as Cu (In _1-x Ga _x ) Se ₂ by a thermal diffusion reaction by forming a film and heating it in selenium vapor or hydrogen selenide to about 450 to 550 ° C. . This method is called a vapor phase selenization method. In addition, there is a solid-phase selenization method in which solid-phase selenium is deposited on a metal precursor film and selenized by a solid-phase diffusion reaction using the solid-phase selenium as a selenium source.

  In the selenization method, in order to avoid the rapid volume expansion that occurs during selenization, a method of previously mixing selenium in a metal precursor film at a certain ratio (T. Nakada et.al, Solar Energy Materials and Solar Cells 35 (1994) 204-214, etc.), and a multilayered precursor film with selenium sandwiched between thin metal layers (for example, a Cu layer / In layer / Se layer ... stacked with a Cu layer / In layer / Se layer) The forming method (T. Nakada et.al, Proc. Of 10th European Photovoltaic Solar Energy Conference (1991) 887-890. Etc.) is known.

  In addition, as a method for forming a graded band gap CIGS film, a Cu—Ga alloy film is first deposited, an In film is deposited thereon, and when this is selenized, natural thermal diffusion is used to form Ga. There is a method in which the concentration is inclined in the film thickness direction (K. Kushiya et.al, Tech.Digest 9th Photovoltaic Science and Engineering Conf. Miyazaki, 1996 (Intn. PVSEC-9, Tokyo, 1996) p.149.).

3) As a sputtering method,
A method targeting CuInSe ₂ polycrystal,
Two-source sputtering method using Cu ₂ Se and In ₂ Se ₃ as targets and using H ₂ Se / Ar mixed gas as sputtering gas (JHErmer, et.al, Proc. 18th IEEE Photovoltaic Specialists Conf. (1985) 1655-1658. etc),
Three-source sputtering method (T. Nakada, et.al, Jpn. J. Appl. Phys. 32 (1993) L1169-L1172. Etc.) in which a Cu target, an In target, and a Se or CuSe target are sputtered in Ar gas. )It has been known.

  4) As the hybrid sputtering method, in the sputtering method described above, Cu and In metal are DC sputtering, and only Se is vapor deposition (T. Nakada, et.al., Jpn.Appl.Phys.34 ( 1995) 4715-4721.

  5) In the mechanochemical process method, raw materials corresponding to the CIGS composition are put into a planetary ball mill container, and the raw materials are mixed by mechanical energy to obtain CIGS powder, which is then applied onto the substrate by screen printing and annealed. To obtain a CIGS film (T. Wada et.al, Phys.stat.sol. (A), Vol.203 (2006) p2593, etc.).

  6) Other CIGS film forming methods include screen printing, proximity sublimation, MOCVD, and spraying. For example, a fine particle film containing an Ib group element, an IIIb group element, and a VIb group element is formed on a substrate by a screen printing method or a spray method, and a thermal decomposition process (in this case, a thermal decomposition process in an VIb group element atmosphere). For example, Japanese Patent Application Laid-Open No. 9-74065 and Japanese Patent Application Laid-Open No. 9-74213).

  FIG. 4 is a diagram showing the relationship between the lattice constant and the band gap in main I-III-VI compound semiconductors. Various forbidden band widths (band gaps) can be obtained by changing the composition ratio. When a photon having energy larger than the band gap is incident on the semiconductor, the energy exceeding the band gap becomes a heat loss. It is known from theoretical calculation that the conversion efficiency is about 1.4 to 1.5 eV at the combination of the spectrum of sunlight and the band gap.

In order to increase the photoelectric conversion efficiency, for example, the Ga concentration of Cu (In, Ga) Se ₂ (CIGS) is increased, the Al concentration of Cu (In, Al) Se ₂ is increased, or Cu (In, Ga) (S , Se) By increasing the S concentration of ₂ or increasing the band gap, a band gap with high conversion efficiency can be obtained. In the case of CIGS, it can be adjusted in the range of 1.04 to 1.68 eV.

  The band structure can be inclined by changing the composition ratio in the film thickness direction. The tilted band structure is a single graded band gap that increases the band gap from the light incident window side to the opposite electrode direction, or the band gap decreases from the light incident window toward the PN junction, and the PN junction is There are two types of double graded band gaps that become larger after passing (T. Dullweber et.al, Solar Energy Materials & Solar Cells, Vol. 67, p.145-150 (2001), etc.). In both cases, the electric field generated inside due to the inclination of the band structure accelerates the carriers induced in the light to easily reach the electrode, and lowers the probability of coupling with the recombination center, thereby improving the power generation efficiency (WO2004 / 090995 pamphlet).

  When a plurality of semiconductors having different band gaps are used for each spectrum range, heat loss due to the difference between photon energy and band gap can be reduced, and power generation efficiency can be improved. Such a layer using a plurality of photoelectric conversion layers is called a tandem type. In the case of a two-layer tandem, for example, the power generation efficiency can be improved by using a combination of 1.1 eV and 1.7 eV.

(Electrode, buffer layer)
Both the lower electrode 20 and the upper electrode 50 are made of a conductive material. The upper electrode 50 on the light incident side needs to have translucency. In consideration of effective use of light, the lower electrode 20 on the substrate side preferably has light reflectivity.

  When the main layer excluding the region near the buffer layer 40 of the photoelectric conversion layer 30 is a p-type semiconductor, the lower electrode 20 is a positive electrode and the upper electrode 50 is a negative electrode. When the main layer of the photoelectric conversion layer 30 is an n-type semiconductor, ± of the lower electrode 20 and the upper electrode 50 is reversed.

As the main component of the lower electrode 20, Mo, Cr, W, and combinations thereof are preferable. As the main component of the upper electrode 50, ZnO, ITO (indium tin oxide), SnO ₂ , and combinations thereof are preferable. The lower electrode 20 and / or the upper electrode 50 may have a single layer structure or a laminated structure such as a two-layer structure. The buffer layer 40 is preferably CdS, ZnS, ZnO, ZnMgO, ZnS (O, OH), or a combination thereof. The main component of the electrode and the buffer layer is defined as a component of 50% by mass or more.
As a combination of preferable compositions, for example, Mo lower electrode / CdS buffer layer / CIGS photoelectric conversion layer / ZnO upper electrode may be mentioned.

In a photoelectric conversion element using a soda lime glass substrate, it has been reported that the alkali metal element (Na element) in the substrate diffuses into the CIGS film, resulting in high energy conversion efficiency. Also in this embodiment, it is preferable to diffuse the alkali metal into the CIGS film. As a method for diffusing the alkali metal element, a method of forming a layer containing an alkali metal element on the Mo lower electrode by vapor deposition or sputtering (JP-A-8-222750, etc.), or an immersion method on the Mo lower electrode. A method of forming an alkali layer made of Na ₂ S or the like (WO03 / 0669684 pamphlet, etc.), a precursor containing In, Cu, and Ga metal elements as components on the Mo lower electrode is formed on the precursor. Examples include a method of attaching an aqueous solution containing sodium molybdate.

Further, the lower electrode 20 has a laminated structure, and one or more alkali metal compounds such as Na ₂ S, Na ₂ Se, NaCl, NaF, and sodium molybdate are placed between the laminated structures of the lower electrode 20. A structure in which a layer including the same is provided is also preferable. This layer may contain a material not containing an alkali metal such as aluminum oxide.

  The conductivity type of the photoelectric conversion layer 30 to the upper electrode 50 is not particularly limited. Usually, the photoelectric conversion layer 30 is a p-layer, the buffer layer 40 is an n-layer (n-CdS, etc.), and the upper electrode 50 is an n-layer (n-ZnO layer, etc.) or a laminated structure of i-layer and n-layer (i-ZnO). Layer and n-ZnO layer). With this conductivity type, it is considered that a pn junction or a pin junction is formed between the photoelectric conversion layer 30 and the upper electrode 50. Further, when the buffer layer 40 made of CdS is provided on the photoelectric conversion layer 30, Cd diffuses to form an n layer on the surface layer of the photoelectric conversion layer 30, and a pn junction is formed in the photoelectric conversion layer 30. it is conceivable that. It is considered that an i layer may be provided below the n layer in the photoelectric conversion layer 30 to form a pin junction in the photoelectric conversion layer 30.

(Other layers)
The photoelectric conversion element 1 can be provided with arbitrary layers other than what was demonstrated above as needed. For example, an adhesion layer (buffer layer) is provided between the substrate 10 and the lower electrode 20 and / or between the lower electrode 20 and the photoelectric conversion layer 30 as necessary to enhance the adhesion between the layers. be able to. Moreover, an alkali barrier layer that suppresses diffusion of alkali ions can be provided between the substrate 10 and the lower electrode 20 as necessary. For the alkali barrier layer, see JP-A-8-222750.

The photoelectric conversion element 1 of this embodiment is configured as described above.
The photoelectric conversion element 1 according to the present embodiment includes a group Ib element, a group IIIb element, and a group VIb element on a substrate 10 having an anodized film 12 on at least one surface side of a metal base material 11 mainly composed of Al. An element including a photoelectric conversion layer 30 including a compound semiconductor comprising:
The Fe content in the metal substrate 11 is 0.05 to 1.0% by mass, and the minimum diameter in the cross section of the metal substrate 11 is 0.3 μm or more, and the sum of the minimum diameter and the maximum diameter is The number of Fe-containing clusters whose value divided by 2 is 0.5 to 2.5 μm is 1,500 to 40,000 pieces / mm ² .
According to the present embodiment, it is possible to provide the photoelectric conversion element 1 that is stable with high yield and excellent in voltage resistance and photoelectric conversion efficiency.
The photoelectric conversion element 1 can be preferably used for a solar cell or the like. If necessary, a cover glass, a protective film, or the like can be attached to the photoelectric conversion element 1 to obtain a solar cell.

(Design changes)
The present invention is not limited to the above-described embodiment, and the design can be changed as appropriate without departing from the spirit of the present invention.
The present invention can be applied to any process of a CIGS photoelectric conversion element. For example, a CIGS photoelectric conversion element using a resin substrate such as polyimide has been studied. In the case of using a resin substrate, it is necessary to form a photoelectric conversion layer at a temperature lower than the heat resistant temperature of the resin, and a process of about 400 ° C. is the limit. Since it is difficult to form a high-performance photoelectric conversion layer at this temperature, a device such as an energy assist layer has been devised. The present invention is also applicable to such a low-temperature process photoelectric conversion element. However, the present invention is effective in a high temperature process that requires higher heat resistance to the substrate, specifically, a process at 470 ° C. or higher.

  Examples and comparative examples according to the present invention will be described.

(Manufacture of substrates for photoelectric conversion elements SUB1 to SUB15)
<Manufacture of metal substrate>
A total of 15 types of Al rolled plates (all with an Al purity of 98.0% by mass or more) were obtained by changing the amount of trace components and the conditions of casting, rolling, and intermediate annealing. After removing the adhering rolling oil and applying a desmut treatment in a 30% by mass H ₂ SO ₄ aqueous solution to each of the obtained Al substrates, the surface was polished in the following three stages. The Al substrate was a 5 cm square sample, which was adhered to a mirror-finished metal block with a double-sided tape and subjected to polishing.

1) Mechanical polishing with abrasive paper Polishing machine Marumoto Struers Co., Ltd. Trade name: Labopol-5,
Abrasive paper: Trade name Marumoto Struers Co., Ltd.
Abrasive paper was mounted on a polishing board and rotated, and each Al substrate (5 cm square sample) was brought into contact therewith to perform surface polishing. # 80 → # 240 → # 500 → # 1000 → # 1200 → # 1500 In this order, the count of the polishing paper was increased, and polishing was performed until the irregularities on the surface of the Al substrate could not be visually confirmed.

2) Mechanical polishing with diamond slurry.
Abrasive cloth: Marumoto Struers Co., Ltd. Polished cloth No773 (Abrasive particle size of 10 μm or more), No751 (Abrasive particle size of less than 10 μm),
Abrasive: Brand name Diamond abrasive DP-spray P manufactured by Marumoto Struers Co., Ltd.
A polishing cloth was mounted on a polishing board, and an abrasive was supplied thereto and rotated. The Al substrate (5 cm square sample) that had been mechanically polished with abrasive paper was brought into contact therewith to carry out surface polishing. Sequentially, the polishing agent was changed as follows, and polishing was performed until the uneven portions on the surface of the Al substrate could not be visually confirmed. The polishing cloth was changed every time the abrasive was changed.
SPRI (particle size 45 μm) → SPRAM (particle size 25 μm) → SPRUF (particle size 15 μm) → SPRAC (particle size 9 μm) → SPRIX (particle size 6 μm) → SPRET (particle size 3 μm) → SPRON (particle size 1 μm) → SPRYT (Particle size 0.25 μm).

3) Electropolishing Electrolyte: Phosphoric acid, sulfuric acid, ethylene glycol, monoethyl ether, water mixture,
Temperature: 50 ° C
Time: 5 minutes
Energizing condition: DC 15V.

By the above three-step polishing, the surface of the Al substrate was finished in a state of residual density of blisters: 0 / dm ² , surface roughness Ra: 0.1 μm, and average glossiness: 75%. In the course of the polishing process, the surface roughness Ra was evaluated appropriately by the following means.

First, after measurement with a stylus type roughness meter according to JIS-B601-1994, Ra was measured with AFM when the surface roughness Ra was 0.1 μm or less.
The conditions for measuring Ra with a roughness meter are as follows.
Model: Surfcom 575A manufactured by Tokyo Seimitsu Co., Ltd.
Measurement conditions: Cut-off 0.8 mm, tilt correction FLAT-ML, measurement length 2.5 mm, T-speed 0.3 mm / s, Polarity positive,
Measuring needle: A sapphire needle with a tip diameter of 10 μm.
Ra is a value (μm) obtained by folding the roughness curve obtained by the measurement from the center line and dividing the area obtained by the roughness curve and the center line by the length L.

Ra measurement by AFM was performed in the DFM cyclic contact mode under the following conditions.
Scanning area 3000nm,
Scan frequency 0.5Hz,
Amplitude decay rate -0.16,
I gain 0.0749 / P gain 0.0488,
Q curve gain 2.00,
Excitation voltage 0.044V,
Resonance frequency 318.5kHz,
Measurement frequency 318.2kHz,
Vibration amplitude 0.995V,
Q value near 460,
Measuring needle A Si needle having a tip diameter of 10 nm (product name: cantilever SI DF40P, manufactured by Seiko Instruments Inc.).

  Substrate manufacturing conditions, Al purity, trace component content, and substrate cross section minimum diameter is 0.3 μm or more, and the sum of minimum diameter and maximum diameter divided by 2 is 0.5 to 2.5 μm Table 1 shows the number of Fe-containing clusters. In the table, “%” indicates mass%. In the table, “x” is added to the numerical values of the Fe content and the number of Fe-containing clusters that are not defined in the invention.

  The content of the trace component was measured by emission spectroscopic analysis by photoelectric photometry according to JIS H 1305. The number of Fe-containing clusters was determined under the condition of an accelerating voltage of 15 kV using an analysis apparatus in which SEM / EDX was integrated. 5A and 5B show measurement examples of SEM cross-sectional photographs and EDX charts. The EDX chart is data of the Fe rich portion 004 and the Fe poor portion 007 in the SEM cross-sectional photograph.

<Anodic oxidation>
Anodizing film was formed on both sides of each Al substrate (thickness 0.30 mm) obtained as described above by direct current anodic oxidation in an electrolytic solution of 10% by mass sulfuric acid at 23 ° C. Immediately after the start of the anodizing treatment, the amount of current flowing through the Al substrate is set to 0.02 A / cm ^2, and then the amount of current flowing through the Al substrate is set so as to gradually increase the amount of current to 0.20 A / cm ^2. Controlled. An anodic oxide film having an anodized film thickness of 9.0 μm (of which the barrier layer thickness is 0.38 μm) and a fine pore diameter of about 100 nm was formed. Thus, photoelectric conversion element substrates SUB1 to SUB15 were obtained.

<Evaluation of voltage resistance of substrate for photoelectric conversion element>
For each photoelectric conversion element substrate SUB1 to SUB15, the terminal of the transformer is connected to one place of the test piece, and mercury particles are placed on the film surface of the insulator film (anodized film). The end of the copper wire connected to was inserted, the voltage was raised to cause break conduction, and the withstand voltage was measured. The results are shown in Table 1.

(Examples 1-1 to 1-8, Comparative Examples 1-1 to 1-8)
In each example, the photoelectric conversion element was manufactured on the same conditions except changing the kind of substrate for photoelectric conversion elements. Table 2 shows the substrates used in each example. As the substrate, in addition to the SUB1 to SUB15 created above, a soda lime glass substrate having a thickness of 0.50 mm generally used as a substrate for solar cells was also used.

  On the photoelectric conversion element substrate, a Mo layer, a NaF layer, and a Mo layer were sequentially formed by RF sputtering (high frequency sputtering) to form a lower electrode having a laminated structure thereof. The total thickness of the lower electrode was about 1.0 μm. When the substrate was soda lime glass, NaF was not formed because the substrate contained Na. After forming the lower electrode, scribing was performed to form a first groove.

Then, on the lower electrode, at a multi-source coevaporation, the two-layer structure as the photoelectric conversion layer _{Cu (In 1-x Ga x} ) was deposited Se ₂ thin film. _{Cu (In 1-x Ga x} ) Se 2 deposition of the thin film deposition source of vacuum inside the container Cu, In evaporation source, Ga evaporation source, and providing a Se deposition source, the vacuum degree of about ^10-4 The test was carried out under Pa (10 ⁻⁷ Torr). At that time, the temperature of the vapor deposition crucible was appropriately adjusted.

  The first layer forms a film so that the atomic composition of Cu is excessive with respect to the total atomic composition of In and Ga, and the second layer is the total atomic composition of In and Ga with respect to the atomic composition of Cu. A film was formed so as to be excessive. The substrate temperature was constant at 530 ° C. The thickness of the first layer was about 2 μm. The composition ratio (molar ratio) of the first layer was Cu / (In + Ga) = about 1.0 to 1.2. Next, the second layer was evaporated by about 1 μm, and the final atomic composition ratio (molar ratio) was Cu / (In + Ga) = 0.8 to 0.9.

  Next, a semiconductor film having a stacked structure was formed as a buffer layer. First, a CdS film having a thickness of about 50 nm was deposited by chemical precipitation. The chemical precipitation method was performed by warming an aqueous solution containing Cd nitrate, thiourea and ammonia to about 80 ° C. and immersing the photoelectric conversion layer in this aqueous solution. Further, a ZnO film having a thickness of about 80 nm was formed on the CdS film by MOCVD. After the formation of the buffer layer, scribing was performed on the stacked layer of the photoelectric conversion layer and the buffer layer to form a second groove portion.

  Next, an Al-added ZnO film having a thickness of about 500 nm was deposited as an upper electrode by MOCVD. After forming the upper electrode, scribing was performed on the upper electrode to form a third groove portion. Further, a scribe process was performed on the stack of the photoelectric conversion layer, the buffer layer, and the upper electrode to form a fourth groove portion.

  Then, Al was vapor-deposited as a taking-out external electrode, and the photoelectric conversion element was obtained. Finally, a sealing transparent resin was laminated to obtain a solar cell module. A total of 20 solar cell modules were manufactured under the same conditions. Each module has a structure in which three rows of cell units in which 24 cells are connected in series are connected in parallel.

<Evaluation of photoelectric conversion efficiency and yield rate>
The produced solar cell module evaluated the photoelectric conversion efficiency using the artificial sunlight of Air Mass (AM) = 1.5 and 100 mW / cm ² . The photoelectric conversion efficiency was measured for 20 samples, and a sample having a photoelectric conversion efficiency of 80% or more with respect to the maximum value among the samples was regarded as an acceptable product, and the other samples were regarded as unacceptable products. The average value of the photoelectric conversion efficiencies of the accepted products was obtained as the photoelectric conversion efficiency. Moreover, the yield rate was calculated | required by the following formula.
Yield rate = number of accepted products / total number of evaluation samples (%)

(Examples 2-1 to 2-8, Comparative Examples 2-1 to 2-8)
A photoelectric conversion element was produced and evaluated in the same manner as in Examples 1-1 to 1-8 and Comparative Examples 1-1 to 1-8, except that a photoelectric conversion layer was formed by a selenization method. Table 3 shows the substrates used and the evaluation results.
For the formation of the photoelectric conversion layer, first, a (Cu—Ga) layer / In layer laminated film is formed by sputtering so that the total Cu / (In + Ga) composition ratio (molar ratio) is about 0.9. Then, under an atmosphere in which selenium vapor is introduced, the substrate temperature is heated so as to be in the range of 470 ° C. to 480 ° C., so that the substantial composition becomes Cu (In _1-x Ga _x ) Se by a thermal diffusion reaction. _A photoelectric conversion layer 2 was produced.

(result)
As is clear from the results in Table 1, a substrate for a photoelectric conversion element using an Al substrate having a high purity and a small amount of trace components has a high withstand voltage, and the withstand voltage tends to decrease as the amount of trace components increases. It was. From the standpoint of withstand voltage alone, the purity of the Al substrate should be as high as possible. However, as shown in Tables 2 and 3, when using an Al substrate manufactured with an emphasis only on high purity, high photoelectric conversion occurs when heated to a high temperature during device formation of the photoelectric conversion element. An efficient photoelectric conversion element could not be manufactured, and a photoelectric conversion element with poor yield and stable quality could not be manufactured. Specifically, Comparative Examples 1-1 to 1-3 and 2-1 to 2-3 using photoelectric conversion element substrates SUB1 to SUB3 using an Al substrate having an Al purity of 99.99% by mass are photoelectric conversions. The efficiency was low and the yield was bad.

  Moreover, also in Comparative Examples 1-4 to 1-7 and 2-4 to 2-7 using photoelectric conversion element substrates SUB12 to SUB15 using an Al substrate with an excessive Fe content or Fe-containing cluster number, photoelectric conversion The efficiency was low and the yield was bad.

The Fe content in the Al substrate is 0.05 to 1.0 mass%, and the minimum diameter in the cross section of the Al substrate is 0.3 μm or more, and the sum of the minimum diameter and the maximum diameter is divided by 2. The photoelectric conversion element substrates SUB4 to SUB11 using Al substrates having a value of 0.5 to 2.5 μm and Fe-containing clusters of 1,500 to 40,000 pieces / mm ² are relatively high withstand voltage. Had. In Examples 1-1 to 1-8 and 2-1 to 2-8 in which photoelectric conversion elements were manufactured using SUB4 to SUB11, even when heated to a high temperature during device formation of the photoelectric conversion elements, A photoelectric conversion element having high photoelectric conversion efficiency could be stably produced. In Examples 1-1 to 1-8 and 2-1 to 2-8, a high photoelectric conversion efficiency of 12 to 16% was obtained.

  In Examples 1-1 to 1-8 in which the photoelectric conversion layer was formed by the multi-source simultaneous vapor deposition method, a high photoelectric conversion efficiency of 14% or more was obtained. This result is a result when the substrate temperature is 530 ° C., but when the substrate temperature is 550 ° C., the superiority of the present invention over the comparative example becomes more remarkable. Also in Examples 2-1 to 2-8 in which the photoelectric conversion layer was formed by the selenization method, a high photoelectric conversion efficiency of 12% or more was obtained. This result is the result when the substrate temperature when heating in the presence of the VIb group element is in the range of 470 ° C. to 480 ° C. When the substrate temperature is changed to 500 to 510 ° C., the comparative example The superiority of the present invention over From these results, it is presumed that the high photoelectric conversion efficiency and yield rate of the present invention are the effects obtained by improving the stability of the used substrate in a high temperature environment.

Comparing the weight of the photoelectric conversion element cell between the photoelectric conversion element of the example and the photoelectric conversion element using soda lime glass as a substrate, the former is 390 g / m ² whereas the latter is 1. It was 3 kg / m ² , and it was found that the photoelectric conversion element of the example can achieve significant weight reduction compared to the photoelectric conversion element of a general glass substrate. Furthermore, since the photoelectric conversion element of the example is a solar cell using an Al substrate with a thickness of about 300 μm or more, it is superior to a general glass substrate solar cell in that it is excellent in flexibility and hard to break. .

  The photoelectric conversion element of this invention can be preferably utilized for uses, such as a solar cell and an infrared sensor.

1 Photoelectric conversion element (solar cell)
DESCRIPTION OF SYMBOLS 10 Substrate 11 Metal base material 12 Anodized film 20 Lower electrode 30 Buffer layer 40 Photoelectric conversion layer 50 Upper electrode

Claims (4)

On a substrate having an anodized film on at least one surface side of a metal base material mainly composed of Al,
In a photoelectric conversion element including a compound semiconductor composed of a group Ib element, a group IIIb element, and a group VIb element, and including a photoelectric conversion layer that generates a current by light absorption, and an electrode that extracts the current,
Fe content in the metal substrate is 0.05 to 1.0 mass%,
The number of Fe-containing clusters having a minimum diameter of 0.3 μm or more and a value obtained by dividing the sum of the minimum diameter and the maximum diameter by 2 is 0.5 to 2.5 μm in the cross section of the metal substrate. 500 to 40,000 pieces / mm ² .   The metal substrate has an Al content of 98.0% by mass or more, an Si content of 0.25% by mass or less, and a Cu content of 0.20% by mass or less. Item 2. The photoelectric conversion element according to Item 1. The photoelectric conversion layer is
At least one group Ib element selected from the group consisting of Cu and Ag;
At least one group IIIb element selected from the group consisting of Al, Ga and In;
3. The photoelectric conversion device according to claim 1, comprising a compound semiconductor comprising at least one VIb group element selected from the group consisting of S, Se, and Te.   A solar cell comprising the photoelectric conversion element according to claim 1.