JP7068798B2 - Manufacturing method of photoelectric conversion element - Google Patents

Description

The present invention relates to a method for manufacturing a photoelectric conversion element.

A photoelectric conversion element is an element that converts light energy into electrical energy, such as a solar cell. Among them, the photoelectric conversion element using a compound semiconductor containing a group I element, a group III element, and a group VI element as the photoelectric conversion layer can be thinned and reduced in cost, and thus is a next-generation photoelectric. It is promising as a conversion element.

For example, a photoelectric conversion element that uses CuInSe ₂ as a photoelectric conversion layer is called a CIS-based photoelectric conversion element. Further, among the CIS-based photoelectric conversion elements, a photoelectric conversion element that uses In and Ga as Group III elements is called a CIGS-based photoelectric conversion element.

Of the CIS-based photoelectric conversion elements or CIGS-based photoelectric conversion elements, photoelectric conversion elements that use Se and S as Group VI elements are particularly noteworthy because they can be expected to improve characteristics such as photoelectric conversion efficiency. Here, a plurality of homologous elements A and B constituting the mixed crystal are described as (A, B), and a mixed crystal compound containing a group I element, a group III element, and a group VI element Se and S is used. , I-III- (Se, S) ₂ . A typical example of I-III- (Se, S) ₂ is Cu (In _x , Ga _1-x ) (Se _y , S _1-y ) ₂ . However, 0 ≦ x ≦ 1 and 0 <y <1. same as below.

International Publication No. 2009/017172

I-III- (Se, S) ₂ can be formed, for example, by the SAS method (Sulfurization after Selenization). In the SAS method, I-III-Se ₂ is formed by seleniumization of the precursor layer containing Group I and Group III elements, and then Se of Group VI element is replaced with S by sulfurization, and at least photoelectric is used. I-III-S ₂ or I-III- (Se, S) ₂ is formed on the surface of the conversion layer. The surface portion of the photoelectric conversion layer is a surface portion on the side opposite to the substrate side exposed to the sulfur source gas.

In the photoelectric conversion element, from the viewpoint of improving characteristics such as photoelectric conversion efficiency, the surface portion of the photoelectric conversion layer becomes I-III-S ₂ or I-III- (Se, S) ₂ after sulfurization, and I-III. -Ideally it does not contain Se ₂ . However, in reality, even after sulfurization, the crystal composed of I-III-Se ₂ is separated from the crystal composed of I-III- (Se, S) ₂ or I-III-S ₂ and is formed on the surface of the photoelectric conversion layer. Often remains. In this case, the characteristics of the photoelectric conversion element, for example, the photoelectric conversion efficiency, are worse than those of the ideal structure in which the surface portion of the photoelectric conversion layer does not contain I-III-Se ₂ .

An embodiment of the present invention proposes a production method capable of effectively replacing selenium with sulfur by sulfurization on the surface portion of a photoelectric conversion layer containing a group I element, a group III element, and selenium.

The method for manufacturing a photoelectric conversion element according to an embodiment of the present invention includes a step of forming a precursor layer containing at least a group I element and a group III element on a substrate, and the precursor in an atmosphere of a selenium source gas having selenium. In the step of seleniumizing the layer to form at least a photoelectric conversion layer containing the group I element, the group III element, and the selenium, and in an atmosphere of a sulfur source gas having sulfur and a mixed gas containing the selenium source gas. In the atmosphere of the mixed gas, the number of moles of the selenium source gas is smaller than the number of moles of the sulfur source gas, and the entire atmosphere of the mixed gas is provided. The molar ratio of the selenium source gas to the selenium source gas is 1.5% or less.

According to the embodiment of the present invention, selenium can be effectively replaced with sulfur by sulfurization on the surface portion of the photoelectric conversion layer containing the group I element, the group III element, and selenium.

The cross-sectional view which shows the example of the photoelectric conversion element. The cross-sectional view which shows the example of the photoelectric conversion layer. The cross-sectional view which shows one process of the manufacturing method of a photoelectric conversion element. The cross-sectional view which shows one process of the manufacturing method of a photoelectric conversion element. The cross-sectional view which shows one process of the manufacturing method of a photoelectric conversion element. The cross-sectional view which shows one process of the manufacturing method of a photoelectric conversion element. The figure which shows the relationship between the molar ratio of a selenium source gas and the photoelectric conversion efficiency. The figure which shows the relationship between the molar ratio of a selenium source gas and the photoelectric conversion efficiency. The figure which shows the XRD pattern of the surface part of a photoelectric conversion layer. The figure which shows the example of the solar cell submodule as an application example.

Hereinafter, embodiments will be described with reference to the drawings.
In the embodiment, in order to make the explanation easy to understand, the structure or the element other than the main part of the present invention will be described in a simplified or omitted manner. Further, in the drawings, the same elements are designated by the same reference numerals. In the drawings, the thickness, shape, and the like of each layer are schematically shown, and do not indicate the actual thickness, shape, and the like.

<Structure of photoelectric conversion element>
FIG. 1 shows an example of a photoelectric conversion element.
The photoelectric conversion element 10 has, for example, a substrate structure, and light 20 such as sunlight is incident on the photoelectric conversion element 10 from a side opposite to the substrate 11 side.

The substrate 11 can be selected from a glass substrate, a resin substrate, a metal substrate, and the like. The substrate 11 may contain an alkali metal such as sodium and potassium. The shape of the substrate 11 is, for example, a quadrangle, but the shape is not limited to this. Further, although the substrate 11 is assumed to be a hard substrate, a flexible flexible substrate may be used instead. The flexible substrate includes, for example, a stainless steel foil, a titanium foil, a molybdenum foil, a ceramic sheet, or a resin sheet.

The first electrode layer 12 is arranged on the substrate 11. The first electrode layer 12 is, for example, a metal electrode layer. It is desirable that the first electrode layer 12 is provided with a material that is unlikely to react with the photoelectric conversion layer 12 in the manufacturing method described later. The first electrode layer 12 can be selected from molybdenum (Mo), titanium (Ti), chromium (Cr) and the like. The first electrode layer 12 may contain the same material as that contained in the second electrode layer 15 described later. The thickness of the first electrode layer 12 is set to 200 nm to 500 nm.

The photoelectric conversion layer 13 is arranged on the first electrode layer 12. The photoelectric conversion layer 13 functions as a polycrystalline or microcrystalline p-type compound semiconductor layer. The photoelectric conversion layer 13 is a mixed crystal compound (I-III-) having a chalcopyrite structure containing a group I element, a group III element, and selenium (Se) and sulfur (S) as group VI elements (chalcogen elements). Se, S) ₂ ) is provided. Group I elements can be selected from copper (Cu), silver (Ag), gold (Au), and the like. Group III elements can be selected from indium (In), gallium (Ga), aluminum (Al) and the like. Further, the photoelectric conversion layer 13 may contain tellurium (Te) or the like in addition to selenium and sulfur as Group VI elements. The thickness of the photoelectric conversion layer 13 is set to 1.0 μm to 3.0 μm.

From the viewpoint of improving characteristics such as photoelectric conversion efficiency, it is desirable that the photoelectric conversion layer 13 includes an internal 13-1 and a surface portion 13-2, for example, as shown in FIG. The surface portion 13-2 is a portion including the surface of the photoelectric conversion layer 13 on the side opposite to the substrate 11 side and its vicinity. The internal 13-1 is a portion other than the surface portion 13-2.

In this example, the surface portion 13-2 of the photoelectric conversion layer 13 includes I-III-S ₂ or I-III- (Se, S) ₂ , and the internal 13-1 of the photoelectric conversion layer 13 is I-III. -Equipped with Se ₂ . That is, the sulfur (S) element in the photoelectric conversion layer 13 has a concentration profile having a peak value on the surface portion 13-2. Further, the concentration of the sulfur (S) element in the photoelectric conversion layer 13 gradually decreases from the portion having the peak value of the surface portion 13-2 of the photoelectric conversion layer 13-1 toward the inside 13-1.

Further, the surface portion 13-2 of the photoelectric conversion layer 13 is mainly composed of crystals of I-III-S ₂ or I-III- (Se, S) ₂ having a large energy band gap. That is, the surface portion 13-2 of the photoelectric conversion layer 13 contains all the crystals of I-III-Se ₂ having an energy band gap smaller than that of I-III-S ₂ or I-III- (Se, S) ₂ . It has a structure that is absent or hardly contained. However, the fact that it is hardly contained means that it is less than the amount or proportion of the crystals of I-III-Se ₂ remaining in the surface portion 13-2 by the conventional method. The conventional method is a method in which sulfurization of I-III-Se ₂ is performed in an atmosphere containing a sulfur source gas and not a selenium source gas. As a result, the energy bandgap of the surface portion 13-2 becomes larger than the energy bandgap of the inner portion 13-1. This means that the parallel resistance of the photoelectric conversion element becomes large, and the characteristics such as the photoelectric conversion efficiency are improved.

In addition, I-III-S ₂ is, for example, Cu (In _x , Ga _1-x ) S ₂ , and I-III- (Se, S) ₂ is, for example, Cu (In _x , Ga _1-x) . ) (Se _y , S _1-y ) ₂ , and I-III-Se ₂ is, for example, Cu (In _x , Ga _1-x ) Se ₂ .

Further, when the surface portion 13-2 of the photoelectric conversion layer 13 is the upper surface portion and the surface portion of the photoelectric conversion layer 13 on the substrate 11 side is the lower surface portion, the lower surface portion of the photoelectric conversion layer 13 is the surface portion 13-2. It may have a similar structure, eg, a structure containing crystals of I-III-S ₂ or I-III- (Se, S) ₂ with a large bandgap. In this case, the concentration or bandgap of the sulfur element in the photoelectric conversion layer 13 has a double graded structure in which the upper surface portion and the lower surface portion are large and the inside (middle) is small.

The buffer layer 14 is arranged on the photoelectric conversion layer 13. The buffer layer 14 is, for example, an n-type or i (intrinsic) type high resistance conductive layer. The term "high resistance" as used herein means having a resistance value higher than the resistance value of the second electrode layer 15 described later.

The buffer layer 14 can be selected from compounds containing zinc (Zn), cadmium (Cd), and indium (In). Examples of the zinc-containing compound include ZnO, ZnS, Zn (OH) ₂ , or a mixed crystal of these, Zn (O, S), Zn (O.S, OH), and ZnMgO, ZnSnO, etc. , There is. Examples of the compound containing cadmium include CdS, CdO, or a mixed crystal of these, Cd (O, S) and Cd (O, S, OH). Examples of the compound containing indium include InS, InO, or a mixed crystal of these, In (O, S), In (O, S, OH). Further, the buffer layer 14 may have a laminated structure of these compounds. The thickness of the buffer layer 14 is set to 10 nm to 100 nm.

The buffer layer 14 has an effect of improving characteristics such as photoelectric conversion efficiency, but it is also possible to omit this. When the buffer layer 14 is omitted, the second electrode layer 15 described later is arranged on the photoelectric conversion layer 13.

The second electrode layer 15 is arranged on the buffer layer 14. The second electrode layer 15 is, for example, an n-type conductive layer. It is desirable that the second electrode layer 15 is provided with, for example, a material having a wide bandgap and a sufficiently low resistance value. Further, since the second electrode layer 15 serves as a path for light such as sunlight, it is desirable that the second electrode layer 15 has a property of transmitting light having a wavelength that can be absorbed by the photoelectric conversion layer 13. In this sense, the second electrode layer 15 is called a transparent electrode layer or a window layer.

The second electrode layer 15 includes, for example, a metal oxide to which a group III element (B, Al, Ga, or In) is added as a dopant. Examples of the metal oxide include ZnO or SnO ₂ . The second electrode layer 15 is, for example, ITO (indium tin oxide), ITiO (indium tin oxide), IZO (zinc oxide zinc oxide), ZTO (zinc oxide tin), FTO (fluorine-doped tin oxide), GZO (gallium-doped). (Zinc oxide), etc. can be selected. The thickness of the second electrode layer 15 is set to 0.5 μm to 2.5 μm.

<Manufacturing method of photoelectric conversion element>
An example of a method for manufacturing the photoelectric conversion element of FIGS. 1 and 2 will be described.

First, as shown in FIG. 3, for example, the first electrode layer 12 is formed on the substrate 11 by a sputtering method. The sputtering method may be a direct current (DC) sputtering method or a radio frequency (RF) sputtering method. Further, instead of the sputtering method, the first electrode layer 12 may be formed by using a CVD (chemical vapor deposition) method, an ALD (atomic layer deposition) method, or the like.

Further, for example, a precursor layer 13-p containing a group I element and a group III element is formed on the first electrode layer 12 by a sputtering method. After this, the precursor layer 13-p is seleniumized. As shown in FIG. 4, seleniumization is performed, for example, by a vapor phase seleniumization method. That is, selenium formation is performed by heating the precursor layer 13-p in the atmosphere of a selenium source gas having selenium (for example, hydrogen selenide or selenium vapor) 16. As a result, the precursor layer 13-p is converted into a compound (photoelectric conversion layer) containing a group I element, a group III element, and selenium.

Selenium formation is preferably performed at a temperature within the range of, for example, 300 ° C. or higher and 600 ° C. or lower. Further, if hydrogen selenide (H ₂ Se) is used as the selenium source gas 16, the handling of the selenium source gas 16 at room temperature is facilitated. Further, seleniumization is preferably carried out in a heating furnace. In this case, the selenium source gas is introduced into the heating furnace from a selenium supply source (for example, a cylinder in the case of hydrogen selenide and an evaporation source in the case of selenium steam). At this time, the molar ratio of the selenium source gas 16 to the entire atmosphere in the heating furnace is controlled by the mixing ratio with the inert gas (for example, nitrogen gas, argon gas, etc.).

The compound (photoelectric conversion layer) containing a group I element, a group III element, and selenium may be formed by a method other than the vapor phase selenium method. For example, such a compound can also be formed by a solid phase selenium method, a vapor deposition method, an ink coating method, an electrodeposition method, or the like.

Next, as shown in FIG. 5, the photoelectric conversion layer 13 containing the group I element, the group III element, and selenium is sulfurized. Sulfurization is carried out in the atmosphere of a mixed gas of a sulfur source gas having sulfur (eg, hydrogen sulfide or sulfur steam) 17-1 and a selenium source gas having selenium (eg, hydrogen selenium or selenium steam) 17-2. This is done by heating the photoelectric conversion layer 13. As a result, the photoelectric conversion layer 13 is converted into a compound containing a group I element, a group III element, and selenium and sulfur as group VI elements.

Here, the sulfur source gas 17-1 sulfurizes a crystal composed of a group I element, a group III element, and selenium, for example, selenium in a chalcopyrite crystal, on the surface portion 13-2 of the photoelectric conversion layer 13. Has the role of replacing with. Further, the selenium source gas 17-2 has a role of promoting the substitution of selenium with sulfur by the sulfur source gas 17-1. However, the effect of promoting this substitution is conditional on the number of moles of the selenium source gas 17-2 being smaller than the number of moles of the sulfur source gas 17-1 in the atmosphere of the mixed gas used for sulfurization.

As a result, after sulfide, the surface portion 13-2 of the photoelectric conversion layer 13 is a crystal (for example, I-III-S ₂ ) composed of a group I element, a group III element, and sulfur, and a group I element. A crystal composed of a group III element, sulfur and selenium as a group VI element (for example, I-III- (Se, S) ₂ ), and a group I element, a group III element, and selenium. It has a structure containing no or almost no crystals (for example, I-III-Se ₂ ) consisting of. Therefore, the parallel resistance of the photoelectric conversion element is increased, and characteristics such as photoelectric conversion efficiency are improved.

After sulfurization, the sulfur element in the photoelectric conversion layer 13 has a concentration profile having a peak value on the surface portion 13-2. Further, after sulfurization, the concentration of the sulfur element in the photoelectric conversion layer 13 may have a double graded structure.

For example, sulfurization is preferably performed at a temperature within the range of 450 ° C. or higher and 650 ° C. or lower. Further, if hydrogen sulfide (H ₂ S) is used as the sulfur source gas 17-1, the handling of the sulfur source gas 17-1 at room temperature is facilitated. When the sulfur source gas 17-1 is hydrogen sulfide (H ₂ S), the sulfurization temperature is preferably 500 ° C. or higher in order to promote the decomposition of hydrogen sulfide. The selenium source gas 17-2 used during sulfurization is preferably hydrogen selenide (H ₂ Se). This is because hydrogen selenide, like hydrogen sulfide, is easy to handle at room temperature.

Sulfurization is preferably performed in a heating furnace. In this case, first, the selenium source gas 16 of FIG. 4 used for seleniumization is discharged from the heating furnace. However, this is the case when seleniumization is performed by the vapor phase seleniumization method. After that, a mixed gas containing the sulfur source gas 17-1 and the selenium source gas 17-2 used for sulfurization is introduced into the heating furnace. The sulfur source gas 17-1 and the selenium source gas 17-2 are a sulfur source (for example, a bomb in the case of hydrogen sulfide, an evaporation source in the case of sulfur steam) and a selenium source (for example, in the case of hydrogen selenium), respectively. Is introduced into the heating furnace from the bomb (evaporation source in the case of selenium steam). At this time, the molar ratio of the sulfur source gas 17-1 and the selenium source gas 17-2 to the entire atmosphere in the heating furnace is controlled by the mixing ratio with the inert gas (for example, nitrogen gas, argon gas, etc.).

What is important here is the molar ratio of the selenium source gas 17-2 to the entire atmosphere and the molar ratio of the selenium source gas 17-2 to the sulfur source gas 17-1 in the atmosphere. In principle, if the number of moles of the selenium source gas 17-2 is smaller than the number of moles of the sulfur source gas 17-1 in the atmosphere, the effect of replacing selenium with sulfur is promoted, and the surface portion 13-2 , Group I elements, Group III elements, and selenium (for example, I-III-Se ₂ ) are less likely to remain, that is, it is considered that characteristics such as photoelectric conversion efficiency can be improved. .. However, in order to obtain a more remarkable effect, it may be desirable to limit the molar ratio of the selenium source gas 17-2 to a predetermined range. This will be described in an experimental example.

Finally, as shown in FIG. 6, the buffer layer 14 is formed on the photoelectric conversion layer 13 by a method such as a CBD (chemical bath deposition) method or a sputtering method. Further, the second electrode layer 15 is formed on the buffer layer 14 by a method such as a sputtering method, a CVD method, or an ALD method. The buffer layer 14 can be omitted.

Through the above steps, the photoelectric conversion elements of FIGS. 1 and 2 are completed.

<Modification example>
The above-mentioned manufacturing method can be variously modified. Hereinafter, some modification examples will be described.

-Gas introduction timing In the sulfurization step, the introduction timing of the sulfur source gas and the selenium source gas into the heating furnace may be the same or different. In the latter case, the selenium source gas may be introduced into the heating furnace after the sulfur source gas has been introduced into the heating furnace, or the sulfur source gas may be heated after the selenium source gas has been introduced into the heating furnace. It may be introduced into the furnace. Further, the sulfur source gas and the selenium source gas may be mixed outside the heating furnace and then introduced into the heating furnace as a mixed gas.

In the sulfurization step, the sulfur source gas may be introduced into the heating furnace only once, or may be divided into a plurality of times. Similarly, in the sulfurization step, the selenium source gas may be introduced into the heating furnace only once, or may be divided into a plurality of times.

-Heating timing In the sulfurization step, the heating by the heating furnace may be performed before the sulfur source gas and the selenium source gas are introduced into the heating furnace, or after being introduced into the heating furnace. Further, heating by the heating furnace may be started after a part of the sulfur source gas and the selenium source gas is introduced into the heating furnace. Further, the sulfur source gas and the selenium source gas may be introduced into the heating furnace during the temperature rise by the heating furnace or after the inside of the heating furnace reaches a predetermined temperature.

-Relationship with the sulfurization reaction In the sulfurization step, the timing of introducing the selenium source gas into the heating furnace may be at the start of the sulfurization reaction, before the start of the sulfurization reaction, or after the start of the sulfurization reaction. .. For example, when the sulfur source gas is introduced into the heating furnace and the temperature in the heating furnace reaches a predetermined temperature (the temperature at which the sulfide reaction starts) as the start time, the selenium source gas is introduced at the start time. It may be introduced before the start, or after the start.

-The heating furnace seleniumization step and the sulfurization step may be carried out in the same heating furnace, or may be carried out separately in different heating furnaces. In the former case, since it is not necessary to transport the substrate in the seleniumization step and the sulfurization step, the manufacturing time can be shortened and the manufacturing cost can be reduced. Further, in the latter case, the controllability of the seleniumization step and the sulfurization step can be improved by the two heating furnaces.

-Increasing step In carrying out the sulfurization step, the temperature in the heating furnace may be continuously raised from normal temperature to a temperature higher than a predetermined temperature (the temperature at which the sulfurization reaction starts), or a plurality of steps may be performed. You may raise it via. In the latter case, the temperature in the heating furnace is set to, for example, a second temperature higher than a predetermined temperature (the temperature at which the sulfurization reaction starts) from the first temperature after being set to the first temperature from normal temperature. You may.

In particular, when the seleniumization step and the sulphurization step are carried out in the same heating furnace, for example, after the temperature in the heating furnace is set from normal temperature to the first temperature, the seleniumization is carried out at the first temperature. Moreover, after the temperature in the heating furnace is set to a second temperature higher than a predetermined temperature (the temperature at which the sulfide reaction starts) from the first temperature, sulfide may be carried out at the second temperature.

-Temperature during the sulfurization step The temperature in the heating furnace during the sulfurization step may be constant or may be changed stepwise. For example, the temperature profile during the sulfurization step may be constant within the range of 450 ° C. or higher and 650 ° C. or lower, or may be maintained at a value within the range of 550 ° C. or higher and 570 ° C. or lower and then 580 ° C. It may be held in the range of ° C. or higher and 620 ° C. or lower, and then kept in the range of 550 ° C. or higher and 570 ° C. or lower. If the temperature profile during the sulfurization step changes stepwise, a sulfur source gas may be introduced each time the temperature changes.

-Temperature lowering step In completing the sulfurization step, the temperature in the heating furnace may be continuously lowered from a temperature higher than a predetermined temperature (the temperature at which the sulfurization reaction starts) to room temperature, or via a plurality of steps. You may lower it. In the latter case, the temperature in the heating furnace is, for example, from a second temperature (temperature of 500 ° C. or higher) higher than a predetermined temperature (temperature at which the sulfurization reaction starts) to a third temperature (temperature of 450 ° C. or lower). After being set, it may be set to room temperature from the third temperature.

-Seleniumization process The same can be said for the gas introduction timing and heating timing in the seleniumization process as in the sulfurization process. For example, the selenium source gas may be introduced into the heating furnace only once, or may be divided into a plurality of times. Further, the heating by the heating furnace may be performed before the selenium source gas is introduced into the heating furnace or after being introduced into the heating furnace.

Further, after a part of the selenium source gas is introduced into the heating furnace, heating by the heating furnace may be started. Further, the selenium source gas may be introduced into the heating furnace during the temperature rise by the heating furnace or after the inside of the heating furnace reaches a predetermined temperature.

In carrying out the seleniumization step, the temperature in the heating furnace may be continuously raised from normal temperature to a temperature higher than a predetermined temperature (the temperature at which the seleniumization reaction starts), or via a plurality of steps. You may raise it. In the latter case, the temperature in the heating furnace is maintained at, for example, a temperature within the range of 300 ° C. or higher and 400 ° C. or lower, and then maintained at a temperature of 400 ° C. or higher.

<Experimental example>
An experimental example will be described. The following experimental examples aim to find a more effective molar ratio of selenium source gas for improving characteristics such as photoelectric conversion efficiency in the sulfurization step.

In the experimental example, seven samples SA1 to SA7 were prepared. The samples SA1 to SA4 adopted a small size glass substrate of about 2.5 cm × about 2.5 cm, and the samples SA5 to SA7 adopted a large size glass substrate of about 90 cm × about 120 cm. The methods for producing the samples SA1 to SA7 are the same except for the step of sulfurizing, which will be described later, and are as follows.

First, a molybdenum (Mo) layer as a first electrode layer is formed on a glass substrate. Further, a precursor layer containing copper (Cu), indium (In), and gallium (Ga) is formed on the molybdenum layer. After that, this precursor layer is seleniumized in the atmosphere of hydrogen selenide gas (H ₂ Se). As a result, the precursor layer on the molybdenum layer is converted into a Cu (In _x , Ga _1-x ) Se ₂ compound semiconductor layer as a photoelectric conversion layer.

Next, the atmosphere of the hydrogen selenium gas used for seleniumization is exhausted. After this, Cu (In _x , Ga _1-x ) Se ₂ is sulfurized in the atmosphere of hydrogen sulfide (H ₂ S) and hydrogen selenide (H ₂ Se). However, the molar ratio of hydrogen sulfide to the entire atmosphere (for example, the entire atmosphere in the heating furnace) was 30%, and the molar ratio of hydrogen selenide to the entire atmosphere was prepared in the following six types as parameters.
0% (samples SA1 and SA5)
・ 0.3% (Sample SA6)
・ 0.5% (Sample SA2)
・ 0.6% (Sample SA7)
・ 1.0% (Sample SA3)
・ 2.0% (Sample SA4)

Finally, a buffer layer and a second electrode layer are formed on the sulfurized photoelectric conversion layer.

The manufacturing method of the samples SA1 to SA7 is a manufacturing method for forming a photoelectric conversion layer by the SAS method. The SAS method was used in this experimental example because the variation in the thickness of the photoelectric conversion layer on the glass substrate is suppressed by adopting the vapor phase seleniumization method in which the precursor layer is seleniumized in the gas phase. That is, the in-plane uniformity is improved. For example, the photoelectric conversion layer by the SAS method realizes the increase in the size of the substrate and the improvement of characteristics such as the photoelectric conversion efficiency by improving the in-plane uniformity as compared with the photoelectric conversion layer by the vapor deposition method or the ink coating method. can.

Tables 1 and 2 show the results of evaluating the characteristics of the photoelectric conversion element for these seven samples SA1 to SA7. In Tables 1 and 2, Eff is the photoelectric conversion efficiency, Voc is the open circuit voltage, Isc is the short circuit current, FF is the curve factor, Rs is the series resistance, and Rsh is the series resistance. , Parallel resistance.

Eff, Voc, Isc, FF, and Rsh are preferably large, and Rs is preferably small. That is, if Voc, Isc, and FF are large, Eff is large. Further, if Rsh is large, the leakage current of the photoelectric conversion element becomes small. Further, if Rs is small, the resistance loss of the electromotive force of the photoelectric conversion element becomes small.

In Tables 1 and 2, the samples SA1 and SA5 are formed by a conventional method of sulfurizing without hydrogen selenide gas, and when standardized based on this, Eff, Voc, Isc, FF, and Rsh If the result is larger than 1, it means that it is better than the conventional method, and for Rs, if the result is smaller than 1, it means that it is better than the conventional method.

As can be seen from Tables 1 and 2, for the short-circuit current Isc and the parallel resistance Rsh, all the samples SA2 to SA4, SA6, and SA7 other than the samples SA1 and SA5 formed by the conventional method are used as samples SA1 and SA5. Better than the result of. That is, according to Tables 1 and 2, the characteristics of the photoelectric conversion element are obtained by sulphurizing with a mixed gas containing a sulfur source gas and a selenium source gas having a number of moles smaller than the number of moles of the sulfur source gas. Is confirmed to improve.

Here, we focus on the photoelectric conversion efficiency Eff among the characteristics of the photoelectric conversion element.

According to Table 1, the photoelectric conversion efficiency Eff is better than that of sample SA1 in samples SA2 and SA3, and worse than that of sample SA1 in sample SA4. This means that the thresholds for improving and decreasing the photoelectric conversion efficiency Eff are between 1.0% and 2.0% when the molar ratio of hydrogen selenide to the entire atmosphere is used as a parameter.

Further, according to Table 2, the photoelectric conversion efficiency Eff is better than that of the sample SA5 in the samples SA6 and SA7. This means that the photoelectric conversion efficiency Eff is improved when the molar ratio of hydrogen selenide to the entire atmosphere is 0.3% and 0.6%. Here, in the samples SA6 and SA7, the effect of improving the photoelectric conversion efficiency Eff is smaller than that of the samples SA2 and SA3 because the substrate size is larger than that of the sample in Table 1.

That is, as the substrate size increases, the in-plane uniformity of the photoelectric conversion layer inevitably deteriorates. It is considered that the deterioration of the in-plane uniformity has an effect on the effect of improving the photoelectric conversion efficiency Eff. Assuming that the in-plane uniformity of the samples SA6 and SA7 is the same as that of the samples SA2 to SA4 in Table 1, the photoelectric conversion efficiency (standard value) of the sample SA6 is estimated to be about 1.020, and the photoelectric of the sample SA7 is estimated to be about 1.020. The conversion efficiency (standard value) is estimated to be about 1.040.

Taking the above into consideration, as a result of further accumulating data, it was found that the relationship between the molar ratio [%] of the selenium source gas to the entire atmosphere used for sulfurization and the photoelectric conversion efficiency Eff is as shown in FIG. bottom. According to FIG. 7, the threshold value for improving and decreasing the photoelectric conversion efficiency Eff is 1.5%. That is, when the molar ratio of the selenium source gas to the entire atmosphere is 1.5% or less, the effect of improving the photoelectric conversion efficiency is realized. Further, when the molar ratio of the selenium source gas to the entire atmosphere is 0.3% or more and 1.0% or less, the photoelectric conversion efficiency is improved by 2% or more as compared with the conventional method.

FIG. 8 shows the result of changing the horizontal axis of FIG. 7 to “molar ratio of selenium source gas to sulfur source gas in atmosphere”. That is, in the experimental example, the molar ratio of the sulfur source gas to the entire atmosphere is 30%, so the value obtained by dividing the value on the horizontal axis of FIG. 7 by 30 is the “selenium source to the sulfur source gas in the atmosphere” in FIG. It becomes the molar ratio of gas.

According to FIG. 8, the threshold value for improving and decreasing the photoelectric conversion efficiency Eff is 5%. That is, when the molar ratio of the selenium source gas to the sulfur source gas in the atmosphere is 5% or less, the effect of improving the photoelectric conversion efficiency is realized. Further, when the molar ratio of the selenium source gas to the sulfur source gas in the atmosphere is 1.0% or more and 3.3% or less, the photoelectric conversion efficiency is improved by 2% or more as compared with the conventional method.

Next, the reason why the effect of improving the photoelectric conversion efficiency Eff can be obtained will be verified.

FIG. 9 shows the results of structural analysis of samples SA1 and SA3 by XRD (X-ray diffraction).
The target of the structural analysis is the surface portion of the photoelectric conversion layer, for example, the surface portion 13-2 in FIG. That is, in the photoelectric conversion layer, the crystal structure from the surface opposite to the glass substrate side to the depths d1, d2, and d3 was analyzed by XRD. However, d1 (for example, about 50 nm) <d2 (for example, about 130 nm) <d3 (for example, about 1 μm) <t, and t is the thickness of the photoelectric conversion layer.

According to the figure, the XRD pattern of the sample SA3 is substantially the same and steep at the three depths d1, d2, and d3. That is, the half width of the diffraction intensity (vertical axis) of the XRD pattern of the sample SA3 is small. This is because in the sample SA3, sulfurization (substitution of selenium element to sulfur element) is effectively performed at any of the depths d1, d2, and d3, and almost the same crystal, that is, Cu (In _x) . , Ga _1-x ) S ₂ or Cu (In _x , Ga _1-x ) (Sey, S _{1-y ) 2} is present.

On the other hand, the XRD pattern of the sample SA1 becomes wider as it gets closer to the surface of the photoelectric conversion layer. That is, the half width of the diffraction intensity (vertical axis) of the XRD pattern of the sample SA1 becomes larger as it gets closer to the surface of the photoelectric conversion layer. This is because in sample SA1, sulfide (substitution of selenium element to sulfur element) is not effectively performed on the surface of the photoelectric conversion layer, and in particular, a large number of crystals, that is, near the surface of the photoelectric conversion layer. In addition to Cu (In _x , Ga _1-x ) S ₂ and Cu (In _x , Ga _1-x ) (Se _y , S _1-y ) ₂ , Cu (In _x , Ga _1-x ) Se It means that ₂ exists separately from these.

Therefore, in order to improve the photoelectric conversion efficiency in the sample SA3, selenium as a Group VI element is effectively replaced with sulfur on the surface portion of the photoelectric conversion layer by sulfurization, and Cu (In _x , Ga _1- ) is formed on the surface portion of the photoelectric conversion layer. _x ) It can be concluded that the result is that Se ₂ does not remain or is less likely to remain than the conventional method.

<Application example>
FIG. 10 shows an example of a solar cell submodule as an application example.
The solar cell submodule of this example has a so-called integrated structure. That is, the solar cell submodule includes a plurality of photoelectric conversion elements 10-1, 10-2, ... 10-k connected in series. However, k is a natural number of 2 or more.

The substrate 11 is common to a plurality of photoelectric conversion elements 10-1, 10-2, ... 10-k. The substrate 11 is, for example, a flexible substrate having a laminated structure of stainless steel (SUS), aluminum, and aluminum oxide.

The plurality of first electrode layers 12-1, 12-2, ... 12-k, 12- (k + 1) are arranged side by side on the substrate 11. The plurality of first electrode layers 12-1, 12-2, ... 12-k, 12- (k + 1) formed a metal layer such as molybdenum (Mo), titanium (Ti), and chromium (Cr). Later, it can be formed by patterning the metal layer (first patterning).

Each photoelectric conversion element 10-1, 10-2, ... 10-k has a photoelectric conversion layer 13 and a buffer layer 14. The photoelectric conversion layer 13 and the buffer layer 14 correspond to the photoelectric conversion layer 13 and the buffer layer 14 described with reference to FIGS. 1 to 9. The photoelectric conversion layer 13 and the buffer layer 14 of the photoelectric conversion elements 10-1, 10-2, ... 10-k formed the photoelectric conversion layer 13 and the buffer layer 14 by, for example, the manufacturing methods of FIGS. 3 to 6. Later, these can be formed by patterning (second patterning).

In each photoelectric conversion element 10-1, 10-2, ... 10-k, the second electrode layer 15 is one of a plurality of first electrode layers 12-1, 12-2, ... 12-k. Connected to. For example, the second electrode layer 15 of the photoelectric conversion element 10-1 is connected to the first electrode layer 12-2 of the photoelectric conversion element 10-2 located next to the second electrode layer 15. The same applies to the remaining photoelectric conversion elements 10-2, ... 10-k. As a result, the plurality of photoelectric conversion elements 10-1, 10-2, ... 10-k are connected in series with each other.

The second electrode layer 15 of each photoelectric conversion element 10-1, 10-2, ... 10-k is formed after forming the second electrode layer 15 by, for example, the manufacturing method of FIGS. 3 to 6. It can be formed by patterning (third patterning).

The first electrode layer 12-1 is connected to, for example, the positive electrode 18, and the first electrode layer 12- (k + 1) is connected to, for example, the negative electrode 19.

According to the above solar cell submodule, when a plurality of photoelectric conversion elements 10-1, 10-2, ... 10-k are regarded as one unit, a plurality of units are arranged in parallel between the positive electrode 18 and the negative electrode. You can connect. Moreover, these plurality of units can be formed on one substrate 11. Therefore, a solar cell panel using such a solar cell submodule has a limited decrease in power generation even if it is partially shaded. That is, a solar cell panel that stably generates power is realized.

Further, the above-mentioned solar cell submodule can be formed by patterning three times (for example, laser patterning or mechanical patterning using a needle). In the manufacturing process of the solar cell submodule, the number of patterning is proportional to the manufacturing cost of the solar cell submodule. That is, the fact that the solar cell submodule can be manufactured by patterning three times means that the manufacturing cost of the solar cell submodule can be reduced.

Therefore, by applying the photoelectric conversion element according to the embodiment to the above-mentioned solar cell submodule, a solar cell submodule having high photoelectric conversion efficiency and capable of obtaining a stable power generation amount can be manufactured at a low level. It can be formed at cost.

<Conclusion>
As described above, according to the embodiment of the present invention, selenium can be effectively replaced with sulfur by sulfurization on the surface portion of the photoelectric conversion layer containing the group I element, the group III element, and selenium.

Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various forms other than those described above, and various omissions, substitutions, changes, etc. can be made without departing from the gist of the present invention. These embodiments and variations thereof are included in the scope and gist of the present invention, and the inventions described in the claims and their equivalents are also included in the scope and gist of the present invention.

11: Substrate, 12: First electrode layer, 13: Photoelectric conversion layer, 13-1: Internal, 13-2: Surface part, 13-p: Precaser layer, 14: Buffer layer, 15: Second electrode layer , 16, 17-2: Selenium source gas, 17-1: Sulfur source gas, 18: Positive electrode, 19: Negative electrode.

Claims (8)

A step of forming a precursor layer containing at least Group I elements and Group III elements on the substrate, and
A step of seleniumizing the precursor layer in the atmosphere of a selenium source gas having selenium to form at least a photoelectric conversion layer containing the group I element, the group III element, and the selenium.
A step of sulfurizing the photoelectric conversion layer in an atmosphere of a sulfur source gas having sulfur and a mixed gas containing the selenium source gas.
Equipped with
In the atmosphere of the mixed gas, the number of moles of the selenium source gas is smaller than the number of moles of the sulfur source gas.
The molar ratio of the selenium source gas to the entire atmosphere of the mixed gas is 1.5% or less.
Manufacturing method of photoelectric conversion element. The method for manufacturing a photoelectric conversion element according to claim 1 , wherein the molar ratio of the selenium source gas to the entire atmosphere of the mixed gas is 0.3% or more and 1.0% or less. The method for manufacturing a photoelectric conversion element according to claim 1, wherein the molar ratio of the selenium source gas to the sulfur source gas in the atmosphere of the mixed gas is 5% or less. The method for manufacturing a photoelectric conversion element according to claim 3 , wherein the molar ratio of the selenium source gas to the sulfur source gas in the atmosphere of the mixed gas is 1.0% or more and 3.3% or less. The method for manufacturing a photoelectric conversion element according to any one of claims 1 to 4 , wherein the sulfur source gas is hydrogen sulfide. The method for manufacturing a photoelectric conversion element according to any one of claims 1 to 5 , wherein the selenium source gas is hydrogen selenide. The selenium formation is performed in a heating furnace containing a selenium source gas, and the selenium formation is performed.
After the selenium source gas used in the selenium formation is discharged from the heating furnace, the sulfidation is performed in the heating furnace containing the mixed gas.
The method for manufacturing a photoelectric conversion element according to any one of claims 1 to 6 . The method for manufacturing a photoelectric conversion element according to claim 7 , wherein the temperature in the heating furnace is 500 ° C. or higher during the sulfurization.

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