JP2015164163A - Photoelectric conversion element and solar cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photoelectric conversion element capable of suppressing warpage of a substrate, and capable of improving productivity by lowering the set temperature of a heater, and to provide a solar cell having the photoelectric conversion element.SOLUTION: The photoelectric conversion element has a substrate, a back electrode formed on the substrate, and a photoelectric conversion layer formed on the back electrode and containing a CIGS-based semiconductor compound. The substrate has a base material constituted of an organic polymer, and a heat absorbing layer formed on a rear surface opposite to a front surface on which the back electrode is formed, of the base material. The average emissivity in a wavelength region of 0.4-2.5 μm of the heat absorbing layer is 0.30 or more.

Description

  The present invention relates to a photoelectric conversion element having a photoelectric conversion layer containing a CIGS semiconductor compound and a solar cell.

Currently, research on solar cells is actively conducted. The solar cell has a laminated structure in which a semiconductor photoelectric conversion layer that generates current by light absorption is sandwiched between a back electrode and a transparent electrode.
As a next-generation solar cell, chalcopyrite-based CuInSe ₂ or Cu (In, Ga) Se ₂ [hereinafter referred to as CuInSe ₂ and Cu (In, Ga) Se ₂ is simply referred to as “CIGS” in the photoelectric conversion layer. In addition, a solar cell using a CIGS film as a photoelectric conversion layer (hereinafter referred to as a “CIGS solar cell”) has high light absorption and can be thinned. It has been studied.

  At present, glass substrates are mainly used as solar cell substrates, but solar cells are also required to be flexible, and it is considered to use flexible resin substrates having flexibility. ing.

  For example, Patent Document 1 states that “a polyimide metal laminate having a polyimide film and a metal layer serving as an electrode on the polyimide film and used for manufacturing a CIS solar cell having a chalcopyrite structure semiconductor layer” A polyimide precursor solution prepared by casting a polyimide precursor solution obtained from an aromatic tetracarboxylic acid component and an aromatic diamine component on a support and heating the polyimide film. It is a polyimide film manufactured by imidizing a support film, and the metal layer to be the electrode is formed on a surface (B surface) on the side in contact with the support of the film at the time of manufacturing the self-support film. (“Claim 1”) and the surface of the polyimide film opposite to the B surface (A surface). And embodiments having a metal layer serving as a layer, a metal layer serving as the protective layer is described embodiment is a layer containing molybdenum ([Claim 5] [Claim 6]). Note that Patent Document 1 describes that warpage of a substrate can be suppressed by providing a protective layer ([0103]).

JP 2010-4029 A

  The present inventors have studied the CIGS solar cell described in Patent Document 1 and found that it is possible to suppress the warpage of the substrate. However, the CIGS is used by a non-contact heating mechanism employed in an industrial roll-to-roll method. It turns out that in order to heat the film to the temperature at which the film is formed (500 ° C. or higher), it is necessary to set the heater set temperature to a high temperature of 700 ° C. or higher. It has been clarified that there is a problem that productivity is inferior because the durability of the heater may be lowered or the life of the heater may be shortened.

  Therefore, as in Patent Document 1, the present invention provides a photoelectric conversion element capable of suppressing the warpage of the substrate, lowering the set temperature of the heater, and improving productivity, and a solar cell having the photoelectric conversion element. The issue is to provide.

As a result of intensive studies to achieve the above-mentioned problems, the present inventors have found that the surface (back surface) opposite to the surface on which the back electrode is formed on the substrate (back surface) in the wavelength range of 0.4 to 2.5 μm. By using a substrate provided with a heat absorption layer whose average emissivity is a specific value or more, it is possible to suppress the warpage of the substrate, and to lower the heater set temperature and improve productivity. The present invention has been completed by finding out what can be done.
That is, it has been found that the above object can be achieved by the following configuration.

[1] A photoelectric conversion element having a substrate, a back electrode formed on the substrate, and a photoelectric conversion layer containing a CIGS semiconductor compound formed on the back electrode,
The substrate has a base material composed of an organic polymer, and a heat absorption layer formed on the back surface opposite to the surface on which the back electrode of the base material is formed,
The photoelectric conversion element whose average emissivity in the 0.4-2.5 micrometer wavelength range of a heat absorption layer is 0.30 or more.
[2] The photoelectric conversion element according to [1], wherein the heat absorption layer is made of ceramics.
[3] The photoelectric conversion element according to [1] or [2], wherein the heat absorption layer is made of a nonmetallic material having a melting point of 1000 ° C. or higher.
[4] The photoelectric conversion according to any one of [1] to [3], wherein the heat absorption layer is composed of at least one selected from the group consisting of molybdenum oxide (MoOx) and molybdenum nitride (MoNx). element.
[5] The photoelectric conversion element according to any one of [1] to [4], wherein the heat absorption layer is made of molybdenum containing oxygen or nitrogen at 5 atom% or more and 50 atom% or less.
[6] The photoelectric conversion element according to any one of [1] to [5], wherein the heat absorption layer is made of molybdenum containing oxygen or nitrogen in an amount of 10 atomic% to 30 atomic%.
[7] A solar cell comprising the photoelectric conversion element according to any one of [1] to [6].
[8] The solar cell according to [7], wherein the curvature radius is 30 mm or more.

  ADVANTAGE OF THE INVENTION According to this invention, the photoelectric conversion element which can suppress the curvature of a board | substrate, can make the preset temperature of a heater low, and can improve productivity, and a solar cell which has it can be provided.

FIG. 1 is a schematic cross-sectional view showing an example of an embodiment of the photoelectric conversion element of the present invention. FIG. 2A is a schematic cross-sectional view showing an example of an embodiment of a substrate used in the photoelectric conversion element of the present invention, and FIG. 2B shows a substrate used in the photoelectric conversion element of the present invention. It is a typical sectional view showing other examples of an embodiment. FIG. 3 is a schematic cross-sectional view showing an example of an embodiment of the solar cell of the present invention.

Hereinafter, the present invention will be described in detail.
The description of the constituent elements described below may be made based on typical embodiments of the present invention, but the present invention is not limited to such embodiments.
In the present specification, a numerical range expressed using “to” means a range including numerical values described before and after “to” as a lower limit value and an upper limit value.

[Photoelectric conversion element]
The photoelectric conversion element of the present invention is a photoelectric conversion element having a substrate, a back electrode formed on the substrate, and a photoelectric conversion layer containing a CIGS semiconductor compound formed on the back electrode, It has the base material comprised with the organic polymer, and the heat absorption layer formed in the back surface on the opposite side to the surface in which the back surface electrode of a base material is formed, 0.4-2.5 micrometers of a heat absorption layer. It is a photoelectric conversion element whose average emissivity in a wavelength region is 0.30 or more.

The photoelectric conversion element of the present invention having such a configuration and the solar cell of the present invention to be described later can suppress the warpage of the substrate, and lower the set temperature of the heater at the time of manufacturing to improve productivity. be able to.
This is not clear in detail, but is estimated to be as follows.
First, as shown in Comparative Example 3 to be described later, when a metal layer made of molybdenum (Mo) is provided on the back surface of the substrate, when the substrate temperature is heated to 550 ° C., the heater set temperature is set. It is necessary to make it 850 ° C. This is considered to be because heat transfer from the heater cannot be used efficiently because infrared rays, which are the heat source of the heater, are reflected by the metal layer.
On the other hand, as shown in each example described later, it is composed of molybdenum oxide (MoOx), molybdenum nitride (MoNx), etc., and has an average emissivity in the wavelength range of 0.4 to 2.5 μm (hereinafter simply referred to as “average emissivity”). It was also found that when the heat absorption layer having a temperature of 0.30 or more is provided, the temperature of the substrate can be heated to 550 ° C. even if the heater set temperature is less than 700 ° C.
That is, in the present invention, it is considered that the heat absorption layer provided on the back surface of the substrate absorbs heat transfer from the heater and can be used efficiently. This can also be inferred from the fact that the set temperature of the heater can be lowered as the average emissivity of the heat absorption layer is higher.
On the other hand, as shown in each Example described later, it was found that the higher the average emissivity, the larger the radius of curvature unexpectedly, and the more the substrate warpage tends to be suppressed.

  Next, after describing the entire configuration of the photoelectric conversion element of the present invention with reference to FIG.

FIG. 1 is a schematic cross-sectional view showing an example of an embodiment of the photoelectric conversion element of the present invention.
The photoelectric conversion element 30 shown in FIG. 1 includes a substrate 10, a back electrode 32 formed on the surface of the substrate 10 (the surface 12a of the base material 12), and a photoelectric including a CIGS semiconductor compound formed on the back electrode 32. A conversion layer 34.
As shown in FIG. 1, the photoelectric conversion element of the present invention includes a buffer layer 36 formed on the photoelectric conversion layer 34, a transparent electrode 38 formed on the buffer layer 36, a back electrode 32, and a transparent layer. It is preferable to have an upper electrode 40 formed on the electrode 38.
The curvature radius R of the photoelectric conversion element 30 is the curvature radius at the back surface 14 s of the heat absorption layer 14 of the substrate 10.

〔substrate〕
FIG. 2A is a schematic cross-sectional view showing an example of an embodiment of a substrate used in the photoelectric conversion element of the present invention, and FIG. 2B shows a substrate used in the photoelectric conversion element of the present invention. It is a typical sectional view showing other examples of an embodiment.
A substrate 10 illustrated in FIGS. 2A and 2B is a substrate used for a photoelectric conversion element, and includes a base material 12 and a heat absorption layer 14 provided on a back surface 12 b of the base material 12. In addition, the surface 12a of the base material 12 is the surface of the board | substrate 10, and functional layers, such as a photoelectric conversion element, the electrode of a solar cell, and a photoelectric conversion layer, are formed in the surface 12a of the base material 12. FIG.
If the average emissivity of the entire layer is 0.30 or more, the heat absorption layer 14 is formed by laminating the first heat absorption layer 14a and the second heat absorption layer 14b as shown in FIG. Although not shown in FIG. 1, the aspect which laminated | stacked the heat absorption layer of three or more layers may be sufficient.

<Base material>
The base material 12 functions as a core material of the substrate 10.
This base material 12 is composed of an organic polymer and has flexibility.
As a material which comprises the base material 12, a polyimide-type resin is mentioned, for example, Among these, it is preferable that it is a polyimide-type resin.

The thickness of the substrate 12 is preferably selected from the viewpoints of flexibility, lightness, and handling properties, preferably 5 μm to 200 μm, and more preferably 7 μm to 100 μm.
When the thickness of the base material 12 is 5 μm or more, handling when transporting while heating the substrate by a roll-to-roll method is good, and when the thickness of the base material 12 is 200 μm or less, flexibility and lightness are good. It becomes.

<Heat absorption layer>
The heat absorption layer 14 is a layer having an average emissivity of 0.30 or more in a wavelength range of 0.4 to 2.5 μm.
In the present invention, as described above, by providing a heat absorption layer satisfying such an average emissivity, warpage of the substrate can be suppressed, and the heater set temperature is reduced during production, Can be improved.
Here, “average emissivity in the wavelength range of 0.4 to 2.5 μm” refers to an average value of emissivity calculated by the following formula (I). For example, UV-visible using an integrating sphere It can be measured using a near-infrared spectrophotometer.
Emissivity (εn) = 1−spectral reflectance (ρn) (I)
(Spectral reflectance ρn: reflectance measured every 1 nm in the wavelength range (0.4 to 2.5 μm) of thermal radiation of the lamp heater (2500 K))

  Since the heat absorption layer 14 can further suppress the warpage of the substrate and lower the set temperature of the heater, the average emissivity in the wavelength range of 0.4 to 2.5 μm is 0.40 or more. Is more preferable and 0.50 or more is more preferable.

The heat absorption layer 14 is not particularly limited as long as the average emissivity in the wavelength range of 0.4 to 2.5 μm is 0.30 or more. Examples of the metal material include molybdenum oxide (MoOx), molybdenum nitride (MoNx), and silicon (Si).
Of these, MoOx and MoNx are preferable because the heat resistance of the substrate, in particular, the tensile resistance (hereinafter also referred to as “tensile resistance”) when the substrate is at a high temperature is high. Is more preferable.

The heat absorption layer 14 has a high average emissivity, a high heat resistance (particularly tensile resistance), and further a compressive stress, so that oxygen or nitrogen is contained at 5 atomic% or more and 50 atomic% or less. It is preferably composed of molybdenum (Mo), and is preferably composed of Mo contained in an amount of 10 atomic% to 30 atomic%.
Moreover, it is comprised with the molybdenum (Mo) which contains oxygen or nitrogen at 10 atomic% or more and 50 atomic% or less from the reason which the curvature of a board | substrate is suppressed more and the setting temperature of a heater can be made lower. preferable.
Here, the “atomic%” of oxygen or nitrogen is obtained by measuring the surface 14 s of the heat absorption layer 14 on the side opposite to the substrate 12 by X-ray photoelectron spectroscopy (XPS). Refers to oxygen or nitrogen content.

  The thickness of the heat absorption layer 14 is preferably 5 nm or more and 10 μm or less, and more preferably 5 nm or more and 1 μm or less, because the warpage of the substrate is further suppressed and the set temperature of the heater can be further lowered. .

Although the formation method of the heat absorption layer 14 is not specifically limited, For example, it can form on a base material by a sputtering method, an ion plating method, CVD method etc.
Here, the adjustment of the emissivity in the heat absorption layer 14 is basically not caused by the fact that it is caused by the constituent material. For example, when molybdenum oxide (MoOx) or molybdenum nitride (MoNx) is used. Can be adjusted by adjusting the composition ratio of the sputtering gas and the sputtering pressure and changing the content (atomic%) of oxygen or nitrogen, as shown in the examples described later.

[Back electrode]
The back electrode 32 is an electrode formed on the surface of the substrate 10 (the surface 12a of the base material 12), and a back electrode of a conventionally known optical element can be appropriately employed and may have a single layer structure. A laminated structure such as a two-layer structure may be used.
The back electrode 32 is preferably composed of, for example, Mo, chromium (Cr), tungsten (W), and a combination thereof. Of these, the back electrode made of Mo is more preferable.
The thickness of the back electrode 32 is preferably about 100 to 1000 nm.

  The method for forming the back electrode 32 is not particularly limited. For example, the back electrode 32 can be formed by a vapor deposition method such as an electron beam evaporation method or a sputtering method.

[Photoelectric conversion layer]
The photoelectric conversion layer 34 is a photoelectric conversion layer formed on the back electrode 32 and includes a CIGS semiconductor compound having a chalcopyrite crystal structure. That is, the photoelectric conversion layer 34 is composed of a CIGS film. The photoelectric conversion layer 34 is made of a known material used for CIGS films such as CuInSe ₂ and Cu (In, Ga) Se ₂ .
The thickness of the photoelectric conversion layer 34 is preferably 1.0 to 3.0 μm, and more preferably 1.5 to 2.5 μm.

Here, it is generally known that when an alkali metal, particularly Na, is diffused into the photoelectric conversion layer 34 made of CIGS, the photoelectric conversion efficiency is increased.
The alkali supply method is not particularly limited, and a method of adding the photoelectric conversion layer 34 (CIGS film) before, during or after the formation of the photoelectric conversion layer 34 can be used. As the alkali supply material, various materials mainly containing a compound containing an alkali metal (a composition containing an alkali metal compound) such as NaO ₂ , Na ₂ S, Na ₂ Se, NaCl, NaF, and sodium molybdate are used. Is possible.

  A method for forming the photoelectric conversion layer 34 (a method for forming a CIGS film) is not particularly limited. For example, 1) a multi-source deposition method, 2) a selenization method, 3) a sputtering method, 4) a hybrid sputtering method, and 5) It can be formed by a method such as a mechanochemical process method. Examples of other CIGS film deposition methods include screen printing, proximity sublimation, MOCVD, and spray (wet deposition).

[Buffer layer]
The buffer layer 36 preferably includes, for example, a metal sulfide containing at least one metal element selected from the group consisting of Cd, Zn, Sn, and In.
Specific examples of the metal sulfide include CdS; ZnS, Zn (S, O), Zn (S, O, OH); SnS, Sn (S, O), Sn (S, O, OH). InS, In (S, O), In (S, O, OH); and the like.
Further, the thickness of the buffer layer 36 is preferably 10 nm to 2 μm, and more preferably 15 to 200 nm.

[Transparent electrode]
The transparent electrode 38 captures light into the photoelectric conversion layer 34 and functions as an electrode through which a current generated in the photoelectric conversion layer 34 flows in a pair with the back electrode 32. The transparent electrode 38 can be composed of a known composition, but is preferably composed of ZnO doped with aluminum or the like.
The thickness of the transparent electrode 38 is, for example, 50 nm to 2 μm.

[Upper electrode]
The upper electrode 40 is an electrode for taking out the current generated in the photoelectric conversion layer 34 from the transparent electrode 38 when the photoelectric conversion element 30 is a cell, and is also referred to as a grid electrode. For this reason, the upper electrode 40 may not be provided in the form of the solar cell module.
The upper electrode 40 is made of aluminum, for example.
The upper electrode 40 is formed by, for example, a sputtering method, a vapor deposition method, a CVD method, or the like.

[Method for producing photoelectric conversion element]
The configuration of the photoelectric conversion element 30 is the same as that of a known photoelectric conversion element except for the configuration of the substrate 10. For this reason, also about the manufacturing method, except the board | substrate 10, it can manufacture with the manufacturing method of a well-known photoelectric conversion element.

In the present invention, by using the substrate 10 having the heat absorption layer 14, the set temperature of the heater can be lowered at the time of production, and the productivity can be improved.
In addition, the produced photoelectric conversion element 30 can suppress warping of the substrate.
Furthermore, by optimizing the film forming conditions for forming the heat absorption layer 14 and applying a film stress in the compression direction, it can be offset with the film stress of the photoelectric conversion layer 34 of the CIGS film, and the curl amount can be reduced. it can. As a result, handling in the manufacturing process of the photoelectric conversion element 30 does not become impossible, and the occurrence of physical defects such as cracks during handling can be greatly reduced, and productivity can be greatly improved.
Furthermore, when the space application is assumed, since the emissivity of the surface not provided with the photoelectric conversion layer 34 is increased, radiation cooling can be promoted, and the temperature rise due to sunlight can be reduced.

[Solar cell]
The solar cell of the present invention is a solar cell having the above-described photoelectric conversion element of the present invention.
FIG. 3 is a schematic cross-sectional view showing an example of an embodiment of the solar cell of the present invention.
In addition, although the board | substrate 10 shown to FIG. 2 (A) is used in the solar cell 50 of this embodiment shown in FIG. 3, it is not limited to this, The board | substrate 10 shown to FIG. 2 (B) is used. Needless to say, you can.

A solar cell 50 shown in FIG. 3 is obtained by integrating the photoelectric conversion elements 30 shown in FIG.
In the solar cell 50, the same components as those of the photoelectric conversion element 30 shown in FIG. 1 are denoted by the same reference numerals, and detailed description thereof is omitted.
Similarly to the photoelectric conversion element 30, the solar cell 50 may be warped so that the back surface 14 s of the heat absorption layer 14 is convex.
In this case, it is preferable that the radius of curvature R of the solar cell 50 is 30 mm or more for the reason that peeling of each layer hardly occurs and handling becomes easy, and the most preferable is a substantially flat surface without curling. .
In addition, the curvature radius R of the solar cell 50 is set to the curvature radius in the back surface 14s of the heat absorption layer 14 like the photoelectric conversion element 30 in FIG.

  In the solar cell 50, the back electrode 32, the photoelectric conversion layer 34, the buffer layer 36, and the transparent electrode 38 are laminated, and the first groove P 1 that penetrates only the back electrode 32, the photoelectric conversion layer 34, and the buffer layer. And a third groove P3 that penetrates the photoelectric conversion layer 34, the buffer layer 36, and the transparent electrode 38 is formed.

In the solar cell 50, it is separated into a plurality of photoelectric conversion elements 52 by the first groove portion P1 to the third groove portion P3. By filling the second open groove 62 with the transparent electrode 38, a structure in which the transparent electrode 38 of a certain photoelectric conversion element 52 is connected in series to the back electrode 32 of the adjacent photoelectric conversion element 52 is obtained. Electrically connected in series so that the voltage generated in each photoelectric conversion element 52 is added. At this time, the effective portion of the photoelectric conversion function is the region 54.
The solar cell 50 is configured such that electrons flow in the direction D shown in FIG. 3, the back electrode 32 is a positive electrode, and the transparent electrode 38 is a negative electrode.
Note that FIG. 3 illustrates the repeated series connection structure of the photoelectric conversion elements 52 in an easy-to-understand manner, and the connection of the minus lead electrode may be the transparent electrode 38 as illustrated, or the second opening P2 The back electrode 32 located below may be used.

  The solar cell 50 has the same configuration as a known solar cell or solar cell module except for the configuration of the substrate 10. For this reason, also about the manufacturing method, it can manufacture with the manufacturing method of a well-known solar cell or a solar cell module.

Also in the solar cell 50, the above-described effects similar to those of the photoelectric conversion element 30 can be obtained. For this reason, the solar cell 50 can also lower the preset temperature of the heater at the time of manufacture and improve productivity.
Moreover, the produced solar cell 50 can suppress warping of the substrate.
Furthermore, by optimizing the film forming conditions for forming the heat absorption layer 14 and applying a film stress in the compression direction, it can be offset with the film stress of the photoelectric conversion layer 34 of the CIGS film, and the curl amount can be reduced. it can. Thereby, it becomes impossible to handle in the manufacturing process of the solar cell 50, and furthermore, the occurrence of physical defects such as cracks at the time of handling can be greatly reduced, and the productivity can be greatly improved.
Furthermore, when the space application is assumed, since the emissivity of the surface not provided with the photoelectric conversion layer 34 is increased, radiation cooling can be promoted, and the temperature rise due to sunlight can be reduced.

  The present invention is basically configured as described above. As mentioned above, although the photoelectric conversion element and solar cell of this invention were demonstrated in detail, this invention is not limited to the said embodiment, In the range which does not deviate from the main point of this invention, you may make various improvement or change. Of course.

  Hereinafter, the present invention will be described in more detail based on examples. The materials, amounts used, ratios, processing details, processing procedures, and the like shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the following examples.

<Example 1>
Example 1 has the same configuration as the photoelectric conversion element 30 shown in FIG.
In Example 1, a 0.025 mm-thick polyimide base material (Ube Industries Upilex (registered trademark) -S) was used as the base material. Since a roll-to-roll film forming apparatus is used for forming the CIGS film, a long polyimide film having a length that can be formed by the roll-to-roll film forming apparatus was used.
Next, a MoOx film having a thickness of 500 nm was formed as a heat absorption layer on the base material by a sputtering method, thereby manufacturing a substrate. Here, the type, thickness, oxygen content and emissivity of the formed heat absorption layer are as shown in Table 1 below. Note that oxygen was introduced into the Mo film in the vacuum apparatus by flowing argon gas through the vacuum apparatus and setting the gas pressure during film formation to 5 Pa. The oxygen content is measured using an X-ray photoelectron spectrometer (XPS), and the average emissivity in the wavelength range of 0.4 to 2.5 μm is measured by ultraviolet-visible-near infrared spectroscopy using an integrating sphere. Measurement was performed using a photometer.

Next, using a roll-to-roll film forming apparatus, a soda lime glass (SLG) layer is formed as a Na supply layer on the surface of the produced substrate, that is, the surface of the polyimide substrate. A Mo film was formed as a back electrode.
Next, a CIGS film having a thickness of 2 μm was formed as a photoelectric conversion layer by a three-stage method using a roll-to-roll film forming apparatus.
Regarding the formation of the CIGS film, first, the substrate temperature is set to 350 ° C. in the first stage with respect to the substrate on which the back electrode (Mo film) sent from the unwinding part of the roll-to-roll film forming apparatus is formed. (In, Ga) ₂ Se ₃ film is formed by evaporating In, Ga, Se in a heated state. Thereafter, Cu and Se are vapor-deposited in a state where the substrate temperature is heated to 550 ° C. in the second stage.
Here, when Cu: (In + Ga): Se = 1: 1: 2, a Cu (In, Ga) Se ₂ crystal having a chalcopyrite structure is formed. Further, by continuing the Cu and Se vapor deposition, a CuxSe layer is generated on the outermost surface, and the Cu excess composition is obtained. By depositing controlled In, Ga, and Se in a state where the substrate temperature is heated to 550 ° C. in the third stage, a CIGS film having a slightly Cu-deficient composition can be formed from the Cu-excess composition.

Next, a CdS layer having a thickness of 50 nm was formed on the CIGS film as a buffer layer by the CBD method. Then, after forming the buffer layer, a ZnO layer having a thickness of 10 nm is formed as a window layer on the buffer layer (CdS layer) by a sputtering method, and the thickness is continuously formed as a transparent electrode on the window layer (ZnO layer). A 300 nm ZnO: Al film (aluminum-doped ZnO film) was formed.
Next, a current collecting electrode made of aluminum was formed on the surface of the transparent electrode by sputtering to produce a photoelectric conversion element.

<Example 2>
The gas pressure was changed to 0.3 Pa when forming the heat absorption layer, and the MoOx film shown in Table 1 below (thickness: 500 nm, oxygen content: 5.2 atomic%, emissivity: 0.30) on the base material A photoelectric conversion element was produced in the same manner as in Example 1 except that was formed.

<Example 3-1>
At the time of forming the heat absorption layer, a gas in which 10% oxygen was mixed into argon was used, the gas pressure was changed to 10 Pa, and the MoOx film (thickness: 500 nm, oxygen content: 30 shown in Table 1 below) was formed on the substrate. 0.0 atomic%, emissivity: 0.50) was formed, and a photoelectric conversion element was produced in the same manner as in Example 1.

<Example 3-2>
A photoelectric conversion element was produced in the same manner as in Example 3-1, except that the set temperature of the heater was changed to the temperature (650 ° C.) shown in Table 1 below.
Here, Example 3-2 is an example in which the set temperature of the heater was intentionally increased to the same temperature as in Example 1 in order to investigate the relationship between the emissivity of the heat absorption layer and the radius of curvature.

<Example 4>
At the time of forming the heat absorption layer, a gas in which 20% oxygen was mixed into argon was used, the gas pressure was changed to 20 Pa, and a MoOx film (thickness: 500 nm, oxygen content: 48 shown in Table 1 below) was formed on the substrate. A photoelectric conversion element was produced in the same manner as in Example 1 except that 0.0 atomic% and emissivity: 0.55) were formed.

<Example 5>
At the time of forming the heat absorption layer, a gas in which 10% nitrogen is mixed into argon is used, the gas pressure is changed to 5 Pa, and a MoNx film (thickness: 500 nm, nitrogen content: 15 shown in Table 1 below) is formed on the substrate. A photoelectric conversion element was produced in the same manner as in Example 1 except that 0.0 atomic% and emissivity: 0.36) were formed.

<Example 6>
At the time of forming the heat absorption layer, argon gas is used, the gas pressure is changed to 0.5 Pa, the target material is changed to Si, and the Si film (thickness shown in Table 1 below) is formed on the substrate using an RF magnetron sputtering apparatus. A photoelectric conversion element was produced in the same manner as in Example 1 except that 500 nm and emissivity: 0.65) were formed.

<Comparative Example 1>
A photoelectric conversion element was produced in the same manner as in Example 1 except that the heat absorption layer was not provided.
In Comparative Example 1, when the substrate temperature was heated to 550 ° C. in the second stage during the production of the photoelectric conversion element, the substrate was broken and the photoelectric conversion element could not be produced.

<Comparative Example 2>
Argon gas was used when forming the heat absorption layer, the gas pressure was changed to 0.1 Pa, and a MoOx film (thickness: 500 nm, oxygen content: 4.6 atomic%, emissivity) shown in Table 1 below on the substrate : 0.25) was formed in the same manner as in Example 1 except that a photoelectric conversion element was produced.

<Comparative Example 3>
Argon gas was used when forming the heat absorption layer, the gas pressure was changed to 0.01 Pa, and the Mo film (thickness: 500 nm, oxygen content: 2.9 atomic%, emissivity) shown in Table 1 below on the base material : 0.20), a photoelectric conversion element was produced in the same manner as in Example 1.

<Comparative Example 4>
Using a gas in which 1% nitrogen is mixed into argon gas when forming the heat absorption layer, the gas pressure is changed to 0.1 Pa, and the MoNx film (thickness: 500 nm, nitrogen content: A photoelectric conversion element was produced in the same manner as in Example 5 except that 4.0 atomic% and emissivity: 0.36) were formed.

  About each produced photoelectric conversion element, heat resistance, the lifetime of a heater, the curvature radius, and conversion efficiency were evaluated by the method shown below. The results are shown in Table 1 below. The “set temperature of the heater” shown in Table 1 below represents the minimum temperature required for heating to the substrate temperature (550 ° C.) required when forming the CIGS film, except in Example 3-2.

(Heat-resistant)
About heat resistance, after forming the CIGS film | membrane as a photoelectric converting layer, the presence or absence of the fracture | rupture in a CIGS film | membrane and a heat absorption layer was confirmed visually.

(Life of heater)
The time (monthly unit) until the heater failed when the production of the solar cell element was continued at the set temperature of the heater set at the time of production of each photoelectric conversion element was examined.

(curvature radius)
After the produced photoelectric conversion element was cut out to a size of 3 cm square, it was placed on a horizontal surface (surface plate surface) in an unconstrained state so that the CIGS film was on the upper side, and the substrate portion was observed from the horizontal direction.
The height value of the highest part in the vertical direction of the substrate with respect to the horizontal plane was measured, and the radius of curvature was determined using the value and the distance between the sides.

(Conversion efficiency)
The photoelectric conversion element produced by 3 cm square size was divided | segmented into 8 cells (1 cell: 0.5cm < ² >), and the photovoltaic cell was produced. Next, the current-voltage characteristic (IV characteristic) under a pseudo sun of AM (Air mass) 1.5 and 100 mW / cm ² is measured, and the conversion efficiency η (%) is calculated using the measurement result. It was measured.

As shown in Table 1 above, for a photoelectric conversion element using a layer having an average emissivity in the wavelength range of 0.4 to 2.5 μm of less than 0.30, the heater set temperature is set to 700 ° C. or more. It was found that the heater life was short and the productivity was poor (Comparative Examples 2 to 4). In Comparative Example 1, as described above, when the substrate temperature was heated to 550 ° C. in the second stage in the process of manufacturing the photoelectric conversion element, the photoelectric conversion element could be manufactured. There wasn't.
On the other hand, the photoelectric conversion element having the heat absorption layer having an average emissivity in the wavelength range of 0.4 to 2.5 μm of 0.30 or more suppresses the warpage of the substrate to be equal to or higher than those of Comparative Examples 2 to 4. Moreover, it turned out that the preset temperature of a heater can be set as low as 10% or more (Examples 1-6).
Further, from comparison between Examples 1 to 5 and Example 6, it is found that when a MoOx film or a MoNx film is used as the heat absorption layer, the heat resistance tends to be good, and in particular, oxygen or nitrogen is 10 atoms. When using a MoOx film or a MoNx film containing not less than 30% and not more than 30 atomic% (Example 1, Example 3-1, Example 3-2 and Example 5), the set temperature of the heater can be further lowered, And it turned out that heat resistance becomes more favorable.
Further, from the results of Examples 1 to 5, when a MoOx film or a MoNx film containing oxygen or nitrogen of 10 atomic% to 50 atomic% is used (Example 1, Example 3-1, Example 3). 2, Example 4 and Example 5), it can be seen that the set temperature of the heater can be lowered, and in particular, from the results of Example 1, Example 3-1, and Example 3-2, the emissivity of the heat absorption layer is It was found that the higher the temperature, the larger the radius of curvature of the substrate, regardless of the heater set temperature, and the emissivity of the heat absorption layer unexpectedly contributed to the suppression of the warp of the substrate.

DESCRIPTION OF SYMBOLS 10 Board | substrate 12 Base material 14 Heat absorption layer 14a 1st heat absorption layer 14b 2nd heat absorption layer 30,52 Photoelectric conversion element 32 Back surface electrode 34 Photoelectric conversion layer 36 Buffer layer 38 Transparent electrode 40 Upper electrode 50 Solar cell 54 Area | region

Claims (8)

A photoelectric conversion element having a substrate, a back electrode formed on the substrate, and a photoelectric conversion layer containing a CIGS semiconductor compound formed on the back electrode,
The substrate has a base material composed of an organic polymer, and a heat absorption layer formed on the back surface opposite to the surface on which the back electrode of the base material is formed,
The photoelectric conversion element whose average emissivity in the 0.4-2.5 micrometer wavelength range of the said heat absorption layer is 0.30 or more.   The photoelectric conversion element according to claim 1, wherein the heat absorption layer is made of ceramics.   The photoelectric conversion element of Claim 1 or 2 with which the said heat absorption layer is comprised with the nonmetallic material whose melting | fusing point is 1000 degreeC or more.   The photoelectric conversion element of any one of Claims 1-3 comprised by the at least 1 sort (s) selected from the group which the said heat absorption layer consists of molybdenum oxide (MoOx) and molybdenum nitride (MoNx).   The photoelectric conversion element of any one of Claims 1-4 with which the said heat absorption layer is comprised with the molybdenum which contains oxygen or nitrogen at 5 atomic% or more and 50 atomic% or less.   The photoelectric conversion element of any one of Claims 1-5 by which the said heat absorption layer is comprised with the molybdenum which contains oxygen or nitrogen at 10 atomic% or more and 30 atomic% or less.   It has a photoelectric conversion element of any one of Claims 1-6, The solar cell characterized by the above-mentioned.   The solar cell according to claim 7, wherein the curvature radius is 30 mm or more.