JP2014041931A - Method for manufacturing solar cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a solar cell capable of improving production efficiency while suppressing an increase in a production cost by enabling thermal processing in the atmosphere.SOLUTION: A method for manufacturing a solar cell 100 with a light absorption layer 4 which performs photoelectric conversion includes the steps of: forming a zinc oxide-based transparent electrode 7 on the light absorption layer 4; forming a transparent insulation layer 9 on the transparent electrode 7; and thermally processing the solar cell 100 in which the transparent insulation layer 9 is formed at a temperature of not less than 150°C and not more than 300°C in the atmosphere.

Description

  The present invention relates to a method for manufacturing a solar cell including a zinc oxide-based transparent electrode, and in particular, is a manufacturing method suitable for heat-treating a zinc oxide-based transparent electrode.

Conventionally, zinc oxides such as ZnO and ZnAlO have been used as transparent electrode materials for solar cells.
In the production of solar cells, the transparent electrode may be heat-treated at 150 ° C. or higher in order to improve the crystallinity of the zinc oxide-based transparent electrode.

On the other hand, according to Patent Document 1 below, heat treatment of the transparent electrode is performed in an oxidizable atmosphere, and oxygen is prevented from adsorbing to the transparent electrode by being taken out into the atmosphere after being 150 ° C. or lower. Technology is disclosed.
Here, the oxidizable atmosphere includes an inert gas atmosphere (see Example 1 and Example 2 of Patent Document 1) and a vacuum (see Example 3).
The reason for preventing oxygen from being adsorbed on the transparent electrode is to avoid the problem that the potential of the transparent electrode is increased due to the adsorption of oxygen to the transparent electrode and the resistance of the transparent electrode is increased.

JP 2008-53118 A

  However, according to the manufacturing method disclosed in Patent Document 1, there is a need to hermetically seal the heat treatment apparatus in order to be in an oxidizable atmosphere. For this reason, an increase in equipment costs and an increase in maintenance costs due to the complexity of the heat treatment apparatus have led to an increase in production costs for solar cells.

  Moreover, like Example 1 and Example 2 of the said patent document 1, use of the inert gas became a factor which raises production cost further.

  Further, according to the manufacturing method disclosed in Patent Document 1, since it cannot be taken out into the atmosphere unless the temperature is 150 ° C. or lower, it is necessary to wait until the temperature is 150 ° C. or lower. did.

  In addition, as in Example 3 of Patent Document 1 described above, heat treatment in a vacuum tends to have a non-uniform temperature distribution, making it difficult to heat treat many solar cells at once. Therefore, since only a small amount of solar cells can be heat-treated, it has been a factor that further reduces the production efficiency.

  Therefore, the present invention was devised in view of the above-described background, and by enabling heat treatment in the atmosphere, it is possible to improve production efficiency while suppressing an increase in production cost. It is an object to provide a method for manufacturing a solar cell.

  In order to solve the above problems, a method for manufacturing a solar cell according to the present invention is a method for manufacturing a solar cell including a light absorption layer that performs photoelectric conversion, and a zinc oxide-based transparent electrode is provided on the light absorption layer. A step of forming, a step of forming a transparent insulating layer on the transparent electrode, a step of heat-treating the solar cell on which the transparent insulating layer is formed at a temperature of 150 ° C. to 300 ° C. in the atmosphere, It is characterized by including.

According to the method for manufacturing a solar cell according to the present invention, the transparent insulating layer is formed on the transparent electrode, and the transparent electrode is not exposed to the atmosphere. Therefore, even if heat treatment is performed in the air to improve the crystal ratio of the transparent electrode, oxygen in the air is prevented from adsorbing to the transparent electrode, and the increase in resistance of the transparent electrode due to oxygen adsorption can be suppressed.
Moreover, according to the manufacturing method which concerns on this invention, since it heat-processes in air | atmosphere, it is not necessary to seal a heat processing apparatus, and the raise of production cost can be suppressed.
Moreover, according to the manufacturing method which concerns on embodiment, since it heat-processes in air | atmosphere, the raise of the production cost by inert gas use can be avoided.
Moreover, according to the manufacturing method which concerns on this invention, there is no restriction | limiting that it cannot put out in air | atmosphere until it becomes 150 degrees C or less like the technique of patent document 1. FIG. Therefore, the production efficiency of the solar cell can be improved as compared with the prior art.
Furthermore, according to the manufacturing method according to the present invention, since the heat treatment is performed in the atmosphere, it is difficult to heat treat many solar cells at a time as the temperature distribution is likely to be non-uniform as in the case of the heat treatment in a vacuum. There is no problem. Therefore, it is possible to avoid a decrease in production efficiency of the solar cell.

  The transparent insulating layer preferably contains one or more materials selected from magnesium fluoride, zinc oxide, and silicon oxide.

According to the configuration described above, in order to modularize a solar cell, when a solar cell having a transparent insulating layer formed on the outermost surface is sealed with glass, the refractive index between the refractive index of the glass and the refractive index of the transparent electrode A transparent insulating layer having a refractive index is sandwiched between the glass and the transparent electrode.
Therefore, since the refractive index does not change greatly among the glass, the transparent insulating layer, and the transparent electrode, the reflected light can be reduced and the power generation efficiency can be improved.

  Further, the light absorption layer is a chalcopyrite type compound, and includes a formation step of forming a buffer layer on the light absorption layer as a pre-step of the step of forming the transparent electrode, Heat treatment is preferably performed at a temperature of 150 ° C. to 200 ° C. in the air.

  The light absorption layer of the chalcopyrite type compound described above has a small secular change and a high light absorption coefficient. Further, according to the above-described process, the crystallinity of the interface between the light absorption layer and the buffer layer of the chalcopyrite type compound can be improved, and the efficiency of the efficiency is improved by reducing the trapping of electrons due to the defect level at the interface. Can be made.

  According to the present invention, it is possible to provide a method for manufacturing a solar cell that can suppress an increase in production cost and can improve production efficiency.

It is a figure which shows the cross section which cut the solar cell module which concerns on embodiment in the lamination direction. It is a figure which shows the process of the first half in the manufacturing process of a solar cell. It is a figure which shows the latter process in the manufacturing process of a solar cell. It is the graph which represented relatively the resistivity (rho) of Examples 1-3 and the comparative example 1 by Hall measurement. It is the graph which relatively represented FF of Example 2-Example 4 and the comparative example 1. FIG.

  Next, solar cells according to embodiments of the present invention will be described with reference to the drawings as appropriate. In addition, in FIGS. 1-3, in order to make the component of a solar cell easy to see, the thickness, width | variety, and space | interval about a component may be exaggerated.

As shown in FIG. 1, the solar cell 100 according to the embodiment includes a substrate 1, a plurality of unit cells 10 formed on the substrate 1, and a plurality of contact electrodes 6 that connect the plurality of unit cells 10 in series. Prepare.
The unit cell 10 includes a lower electrode 2 formed on the substrate 1, a p-type light absorption layer 4 formed on the lower electrode 2, and an n-type buffer layer formed on the light absorption layer 4. 5, an n-type transparent electrode 7 formed on the buffer layer 5, and a transparent insulating layer 9 formed on the transparent electrode 7.
Furthermore, the light absorption layer 4 is a chalcopyrite type compound containing copper, indium, gallium, and selenium, and has characteristics such as a small secular change and a high light absorption coefficient.

When the unit cell 10 is irradiated with light such as sunlight, electrons gather at the interface of the transparent electrode 7 at the junction interface between the p-type light absorption layer 4 and the n-type transparent electrode 7, while holes are generated. Collecting at the interface of the light absorption layer 4, an electromotive force is generated between the light absorption layer 4 and the transparent electrode 7.
Thereby, a current I proportional to the number of unit batteries 10 connected in series is output to the outside as an output current of the solar battery 100.

  Next, a method for manufacturing the solar cell 100 according to the embodiment will be described with reference to FIGS.

  First, as shown in FIG. 2A, a substrate 1 for forming a unit cell 10 is prepared. The material of the substrate 1 is not particularly limited in the present invention, but is preferably soda glass. This is because, in the case of soda glass, sodium contained in the soda glass is taken into the light absorption layer 4 and the performance of the light absorption layer 4 is improved.

  Next, the lower electrode single layer 2a is formed on the substrate 1 by sputtering using a Mo target (see FIG. 2B).

  Next, the lower electrode single layer 2a is cut by a mechanical scribe means having a scribe blade or a laser scribe means for cutting by irradiating a laser to form a groove 3 (see FIG. 2C). As a result, a plurality of lower electrodes 2 divided by the grooves 3 are formed on the substrate 1.

Next, a light absorption layer precursor composed of an In layer and a Cu—Ga layer is formed on the lower electrode 2 by a sputtering method using a metal In target and a Cu—Ga alloy target.
Then, heat treatment is performed at a temperature of about 400 ° C. to 600 ° C. in an H ₂ Se atmosphere. Thereby, Se diffuses in the light absorption layer precursor, and a p-type light absorption single layer 4a made of Cu—In—Ga—Se can be obtained (see FIG. 2D). In addition, the light absorption single layer 4a is formed also in the groove | channel 3 by this process.

  Next, an n-type buffer single layer 5a such as CdS, ZnS or InS is formed on the light absorption single layer 4a by, for example, CBD (Chemical Bath Deposition) (see FIG. 2E).

Next, a part of the light absorption single layer 4a is irradiated with laser light to modify a part of the light absorption single layer 4a. Thereby, as shown in FIG. 3A, the contact electrode 6 having higher conductivity than the light absorption single layer 4a can be obtained, and the light absorption single layer 4a and the buffer single layer 5a are divided, A light absorption layer 4 and a buffer layer 5 are formed on the lower electrode 2.
In the present invention, the wavelength of the laser beam, the irradiation time of the laser beam, and the like are not particularly limited. In the embodiment, the contact electrode 6 is obtained by irradiating a part of the light-absorbing single layer 4a with laser light. However, the present invention is not limited to this. For example, the buffer single layer 5 a and the light absorption single layer 4 a may be cut by a scribing means, and a part of the transparent electrode 7 may be formed on the lower electrode 2.

  Next, a zinc oxide-based transparent electrode single layer 7a made of ZnO or ZnAlO is formed by sputtering using a ZnO target or a ZnAlO alloy target (see FIG. 3B).

  Next, as shown in FIG. 3C, a transparent insulating single layer 9a is formed on the transparent electrode single layer 7a. Examples of the method for forming the transparent insulating single layer 9a include a vacuum vapor deposition method, a sputtering method, and a CVD (Chemical Vapor Deposition) method.

The transparent insulating single layer 9a needs to be a highly transparent and insulating material. The reason why the transparency needs to be high is to avoid a situation where power generation efficiency is reduced. The reason for being insulative is to avoid power loss by using only the transparent electrode single layer 7a as a current path and not passing a current therethrough.
The transparent insulating single layer 9a preferably includes one or more materials selected from magnesium fluoride, zinc oxide, and silicon oxide.
According to this, when the solar cell 100 is sealed with glass (not shown) to manufacture a solar cell module (not shown), the reflectance between the reflectance of the glass and the reflectance of the transparent electrode 7 is intermediate. Since the transparent insulating layer 9 having n is sandwiched between the glass and the transparent electrode 7, a laminated structure in which the refractive index does not change greatly between the glass, the transparent insulating layer 9, and the transparent electrode 7 is obtained.
Therefore, the light reflected between the glass, the transparent insulating layer 9 and the transparent electrode 7 can be reduced, and the power generation efficiency can be improved.

The thickness of the transparent insulating single layer 9a is not particularly limited as long as oxygen can be prevented from being adsorbed to the transparent electrode 7 in the heat treatment step, but it is preferably in the range of 100 to several thousand.
When the thickness of the transparent insulating single layer 9a is, for example, about several tens of millimeters, the resistance of the transparent electrode 7 is less than that when the thickness of the transparent insulating layer 9 is 100 inches or more due to the influence of oxygen adsorbed on the transparent insulating layer 9. This is because the value may increase.
On the other hand, if the thickness of the transparent insulating single layer 9a exceeds several thousand Å, the power generation efficiency is reduced due to the reduction in transmittance, which is not preferable.

  Next, the transparent electrode single layer 7a and the transparent insulating single layer 9a are cut by mechanical scribe means or laser scribe means to form the grooves 8. Thereby, the transparent electrode 7 and the transparent insulating layer 9 divided | segmented by the groove | channel 8 are formed (refer FIG.3 (d)).

Next, the solar cell 100 is heat-treated in the atmosphere by a heat treatment apparatus.
Here, the heat treatment temperature is a temperature of 150 ° C. or higher and 300 ° C. or lower. According to this, the crystallinity of the transparent electrode 7 is improved, and the conductivity of the transparent electrode 7 can be increased.
Further, as shown in the embodiment, when the light absorption layer 4 is a chalcopyrite type compound, it is preferable that the heat treatment is performed at a temperature of 150 ° C. or higher and 200 ° C. or lower.
In the step of forming the buffer single layer 5a on the light absorption single layer 4a, a defect level may occur at the junction interface between the light absorption single layer 4a and the buffer single layer 5a. The crystallinity of the interface between the light absorption layer and the buffer layer can be improved, and the trapping of electrons due to the defect level at the interface can be reduced to improve the efficiency.

As described above, the solar cell 100 including the plurality of unit cells 10 on the substrate 1 can be manufactured by the above-described steps as shown in FIG.
In addition, in the manufacturing process of the solar cell 100, there is a component that does not define the thickness, but the present invention is not particularly limited, and the thickness is appropriately set as long as the solar cell 100 can be used. You can do it.

As described above, according to the method for manufacturing the solar cell 100 according to the embodiment, even if the solar cell 100 is heat-treated in the atmosphere, oxygen is adsorbed on the transparent insulating layer 9 disposed on the outermost surface (uppermost surface) of the solar cell 100. And since it can prevent that oxygen adsorb | sucks to the transparent electrode 7, the high resistance of the transparent electrode 7 can be suppressed.
In particular, when the thickness of the transparent insulating layer 9 is in the range of 100 to several thousand, the resistance value of the transparent electrode 7 does not increase due to oxygen adsorbed on the transparent insulating layer 9, and the transmittance It is possible to avoid a decrease in the temperature.

Further, according to the manufacturing method according to the embodiment, since heat treatment is performed in the atmosphere, there is no need to seal the heat treatment apparatus as in the technique of Patent Document 1, and an increase in production cost is suppressed compared to the conventional technique. it can.
Furthermore, according to the manufacturing method according to the embodiment, since the heat treatment is performed in the atmosphere, an increase in production cost due to the use of an inert gas can be avoided.

Moreover, according to the manufacturing method which concerns on embodiment, since there is no restriction | limiting that it cannot put out in air | atmosphere until it becomes 150 degrees C or less like the technique of patent document 1, Compared with a prior art, the solar cell 100 of FIG. Production efficiency can be improved.
Furthermore, according to the manufacturing method according to the embodiment, since the heat treatment is performed in the atmosphere, the temperature distribution is likely to be non-uniform as in the case of the heat treatment in a vacuum, and it is difficult to heat treat many solar cells 100 at one time. The problem does not occur. Therefore, a decrease in production efficiency of solar cell 100 can be avoided.

  In the present embodiment, the solar cell 100 in which the light absorption layer 4 is a chalcopyrite type compound has been described as an example. However, the present invention is not limited to this, and a compound such as an InGaAs type or a GaAs type is used. It may be a light absorption layer or a silicon-based light absorption layer.

(Example 1 to Example 4)
Next, examples manufactured by the manufacturing method according to the embodiment will be described with reference to FIGS. 4 and 5.

First, in order to measure the resistivity ρ [Ω · cm] of the transparent electrode of the unit cell in the solar cell, the solar cell having the transparent insulating layer (Example 1 to Example 4) and transparent by the above-described manufacturing method A solar cell having no insulating layer (Comparative Example 1) was produced. Examples 1 to 4 and Comparative Example 1 were heat-treated under the same conditions.
Further, the difference between the first to third embodiments is the thickness of the transparent insulating layer, and each of the first to third embodiments is 100, 200, and 850 [Å].

  In addition, 4 pieces were manufactured and measured for each of Examples 1 to 4 and Comparative Example 1.

And while measuring each resistivity (rho) of Example 1- Example 3 and the comparative example 1 by Hall measurement, the average value of measured resistivity (rho) was computed.
FIG. 4 shows the relative values of the average values of the resistivity ρ. Here, the horizontal axis of FIG. 4 shows the thickness of the transparent insulating layer, and the left end is the case where the thickness of the transparent insulating layer is 0 (Comparative Example 1), and as it goes to the right side, The thickness is increased. The vertical axis of FIG. 4 shows the relative value of the average value of the resistivity [rho (average value of the resistivity [rho _Z average value / Comparative Example 1 to the values of resistivity at [rho).

As shown in FIG. 4, the resistivity ρ (average value) of each of Examples 1 to 3 was lower than that of Comparative Example 1.
From the above, when the transparent insulating layer is formed (Example 1 to Example 3), the resistance of the transparent electrode is increased by the heat treatment as compared with the case where the transparent insulating layer is not formed (Comparative Example 1). It turned out that it can suppress.

Next, FIG. 5 shows a graph that relatively represents the average value of each FF of Examples 2 to 4 and the average value of the FF of Comparative Example 1. The thickness of the transparent insulating layer of Example 4 is 400 [４００]. 5 represents the relative value of the average value of FFs (average value of each FF / average value of FF _Z of Comparative Example 1).

  When considered based on the FF shown in FIG. 5, the average values of the FFs of Examples 2 to 4 are substantially equivalent values, and are higher than the average value of the FFs of Comparative Example 1. It became. From the above, when the transparent insulating layer was formed (Examples 2 to 4), an excellent solar cell could be obtained compared to the case where the transparent insulating layer was not formed (Comparative Example 1). I understood.

DESCRIPTION OF SYMBOLS 100 Solar cell 10 Unit cell 1 Board | substrate 2 Lower electrode 4 Light absorption layer 5 Buffer layer 6 Contact electrode 7 Transparent electrode 9 Transparent insulating layer

Claims (3)

A method for producing a solar cell comprising a light absorption layer for performing photoelectric conversion,
Forming a zinc oxide based transparent electrode on the light absorbing layer;
Forming a transparent insulating layer on the transparent electrode;
And a step of heat-treating the solar cell on which the transparent insulating layer is formed at a temperature of 150 ° C. or higher and 300 ° C. or lower in the atmosphere.   The method for manufacturing a solar cell according to claim 1, wherein the transparent insulating layer comprises one or more materials selected from magnesium fluoride, zinc oxide, and silicon oxide. The light absorbing layer is a chalcopyrite type compound,
As a pre-process of the step of forming the transparent electrode, including a step of forming a buffer layer on the light absorption layer,
3. The method for manufacturing a solar cell according to claim 1, wherein the heat treatment is performed in the atmosphere at a temperature of 150 ° C. or higher and 200 ° C. or lower.

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