JP3311286B2 - Manufacturing method of thin film solar cell - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a hetero-junction thin-film solar cell using multinary compound semiconductor thin film as a light absorbing layer, in particular Cu-III-VI ₂ Group Karukopaito semiconductor as a light absorbing layer, for example, copper indium diselenide ( CIS), copper indium gallium diselenide (CIGS) or copper indium gallium indium selenide (CIGSS), thin-film copper indium gallium diselene indium gallium (CIGS)
The present invention relates to a method for manufacturing a thin-film solar cell having a pn heterojunction and a light absorbing layer of a p-type semiconductor such as copper indium gallium diselenide (CIGS) having a GSS) layer as a surface layer.

[0002]

2. Description of the Related Art Conventionally, thin film solar cells of the above type have been considered to be widely practicable and are disclosed in US Pat.
Cadmium sulfide (CdS) on a light-absorbing layer comprising CIS as described in US Pat. No. 226, issued June 15, 1982 by Michelsen et.al, and to provide a thin-film solar cell with high conversion efficiency. It discloses growing a layer.

[0003] Among many publications aimed at developing a thin film solar cell having such a high conversion efficiency,
U.S. Pat. No. 4,610,091 (Choudray et.al, issued September 9, 1986) and U.S. Pat.
No. 5409 (1992 by Eberspacher et.al).
(Issued September 3, 2001) is important.

US Pat. No. 5,045,409 describes a method for improving selenization of a CIS thin film light absorbing layer, and US Pat. No. 4,611,091 chemically grows a solution on a CIS thin film light absorbing layer from a solution. By growing a transparent and conductive n-type semiconductor thin film layer having a wide band gap such as zinc oxide formed by metal organic chemical vapor deposition (MOCVD) on the CdS thin film,
A manufacturing method is disclosed that significantly reduces the thickness of the layer.

The above two patent specifications minimize the use of highly toxic components such as hydrogen selenide and CdS, which are considered to be extremely important in a method for manufacturing a large-area thin-film solar cell module. Disclosed are methods of manufacture that are useful for minimizing or eliminating.

The method of growing a CdS thin film chemically from a solution described in the above-mentioned US Pat. No. 4,611,091 uses a CIS thin film light absorbing layer and a higher quality than a thick CdS formed by other methods. Form a heterojunction,
In addition, it has the effect of increasing the shunt resistance, but such an improvement is attributable to the etching or selective cleaning effect of the heterojunction interface formed by immersing the CIS thin film light absorbing layer in a solution, particularly the thin film light absorbing layer surface. It is considered included.

[0007]

In recent years, attempts have been actively made or attempted to essentially eliminate toxic materials such as cadmium from thin-film solar cells. However, it has not been successful to form a high-quality heterojunction without using a toxic material such as cadmium to produce a thin-film solar cell with high conversion efficiency. For example,
A zinc compound layer grown from a solution of zinc acetate dissolved in ammonium hydroxide is a zinc oxide thin film containing a large amount of zinc hydroxide up to about 30 mol% even after being dried by annealing in air after film formation. Therefore, hydroxyl groups are present on the surface, the film density is reduced, and the surface is insufficiently coated, and Cd
There is a problem that a thin film layer as good as that using S cannot be obtained.

As a thin-film solar cell using a material which does not contain toxicity such as cadmium, a metal back electrode 2 having a p-type conductive type on a glass substrate 2 as shown in FIG. A first multi-component compound semiconductor thin film 4 serving as a light absorbing layer, formed at an interface between the first multi-component compound semiconductor thin film 4 and the second metal oxide semiconductor thin film 6,
Sulfur-containing zinc mixed crystal compound semiconductor thin film 5 which is transparent and has high resistance and is provided as an interface layer, formed on the sulfur-containing zinc mixed crystal compound semiconductor thin film 5 and opposite to the first multi-element compound semiconductor thin film Having a conductivity type, serving as a window layer,
Second metal oxide semiconductor thin film 6 having a wide band gap, being transparent and conductive, and upper electrode or scribe line 7
Were formed in this order. However, in the case of manufacturing a thin film solar cell having the above structure, particularly in a manufacturing process of a sulfur-containing zinc mixed crystal compound semiconductor thin film serving as the interface layer, in a conventional manufacturing method, the first multi-element compound semiconductor thin film is formed. After growing a sulfur-containing zinc mixed crystal compound semiconductor thin film by chemical growth, it is heated and dried in the air, so that the thin film using a material such as cadmium in the device characteristics such as conversion efficiency and yield. There was a problem that it was inferior to solar cells.

The present invention has been made to solve the above problems, and provides a method of manufacturing a thin film solar cell having a heterojunction using the multiplexed compound semiconductor thin film of high conversion efficiency containing no cadmium as a light absorbing layer. The purpose is to provide.

Another object of the present invention is to provide a method of manufacturing a thin-film solar cell in which the device characteristics of the thin-film solar cell having the heterojunction, that is, the conversion efficiency and the yield (yield) are improved.

Another object of the present invention is to provide a method of manufacturing a thin-film solar cell which can be mass-produced and which reduces the use and concentration of chemicals when manufacturing the thin-film solar cell having the heterojunction. And

[0012]

SUMMARY OF THE INVENTION The present invention provides a metal back electrode and a first multi-element compound semiconductor formed on the metal back electrode, having a p-type conductivity and serving as a light absorbing layer. A thin film, formed on the first multi-compound semiconductor thin film, having a conductivity type opposite to that of the first multi-compound semiconductor thin film, serving as a window layer, having a wide band gap, being transparent and having conductivity. Formed at the interface between the second metal oxide semiconductor thin film and the first multi-component compound semiconductor thin film and the second metal oxide semiconductor thin film, which is transparent, has high resistance, and serves as an interface layer. A sulfur-containing zinc mixed crystal compound semiconductor thin film,
In a method for manufacturing a thin-film solar cell comprising an upper electrode,
After chemically growing the sulfur-containing zinc mixed crystal compound semiconductor thin film containing oxygen, sulfur and hydroxyl groups on the first multi-component compound semiconductor thin film from a solution, the sulfur-containing zinc mixed crystal compound semiconductor thin film is By annealing at a temperature of less than 100 to 250 ° C. in a vacuum of 1 to 100 Torr, zinc hydroxide in the sulfur-containing zinc mixed crystal compound semiconductor thin film is converted into zinc oxide, and has a transparent and high resistance. This is a method for manufacturing a thin-film solar cell for forming an interface layer.

The present invention is a method for manufacturing a thin-film solar cell, wherein the sulfur-containing zinc mixed crystal compound semiconductor thin film is annealed for 10 to 120 minutes.

In the present invention, a zinc salt is used to form a sulfur-containing zinc mixed crystal compound semiconductor thin film serving as the interface layer, and the zinc salt is one of zinc sulfate, zinc chloride and zinc acetate. This is a method for manufacturing a thin-film solar cell selected from the following.

The present invention is a method for producing a thin-film solar cell containing a sulfur-containing salt in addition to a zinc salt to form a sulfur-containing zinc mixed crystal compound semiconductor thin film serving as the interface layer.

In the present invention, the first multi-element compound semiconductor thin film serving as the light absorbing layer may be made of copper indium diselenide (CIS) or copper indium gallium diselenide (CI).
GS), copper indium gallium diselenide gallium (CIGS) or copper indium gallium diselenide gallium (CIGS) having a thin layer of copper selenide-copper indium gallium (CIGSS) as a surface layer This is a method for manufacturing a battery.

The present invention is a method for manufacturing a thin-film solar cell, wherein the second metal oxide semiconductor thin film serving as the window layer is made of zinc oxide.

[0018]

Embodiments of the present invention will be described below. As a thin-film solar cell using a material that does not contain toxicities such as cadmium, a first multi-element compound having a metal back electrode, a p-type conductivity type, and serving as a light absorbing layer on a glass substrate is conventionally used. A semiconductor thin film, a sulfur-containing zinc mixed crystal compound semiconductor formed at an interface between the first multi-component compound semiconductor thin film and the second metal oxide semiconductor thin film, having high transparency and being provided as an interface layer; A thin film, formed on the sulfur-containing zinc mixed crystal compound semiconductor thin film, having a conductivity type opposite to that of the first multi-component compound semiconductor thin film, serving as a window layer, and having a wide band gap and being transparent and conductive. The thin film solar cell has a structure in which the second metal oxide semiconductor thin film and the upper electrode or the scribe line are sequentially formed.

When manufacturing a thin film solar cell having the above structure,
In particular, in the manufacturing process of the sulfur-containing zinc mixed crystal compound semiconductor thin film serving as the interface layer, in the conventional manufacturing method, the sulfur-containing zinc mixed crystal compound semiconductor thin film is formed by chemical growth on the first multi-component compound semiconductor thin film. After growing, heat drying treatment was performed in the air, but in the manufacturing method of the present invention, instead of the conventional heat drying treatment in the air, the heat drying treatment is performed in a vacuum. Thereby, device characteristics such as conversion efficiency and yield can be improved.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A thin-film solar cell 1 comprises a glass substrate 2, a metal back electrode 3, a first multi-component semiconductor thin film 4, a sulfur-containing zinc mixed crystal compound semiconductor thin film 5, a second metal oxide semiconductor thin film 6, This is a structure in which upper electrodes or scribe lines 7 are sequentially formed.

The present invention relates to a method for manufacturing a thin-film solar cell. The thin-film solar cell 1 has a structure as shown in FIG. 1, and a metal back electrode 3, a first multi-component compound semiconductor thin film 4, a sulfur-containing zinc mixed crystal compound semiconductor thin film 5, a second metal The oxide semiconductor thin film 6 and the upper electrode or scribe line 7 are sequentially formed in a laminated structure.

Further, details of the thin-film solar cell 1 will be described.
The glass substrate 2 has a thickness of 1 to 3 mm. The metal back electrode 3 is made of a metal such as molybdenum, titanium or tantalum or a metal laminated structure having a thickness of 1 to 2 μm. The first multi-element compound semiconductor thin film 4 serves as a light absorbing layer and has a thickness of 1 to 3 of a p-type conductivity type Cu-III-VI group ₂ chalcopyrite structure.
3 μm thin film, CIS, CIGS, CIGSS or CI
It is composed of a thin film of a multiple compound semiconductor such as CIGS having a GSS layer as a surface layer. Sulfur-containing zinc mixed crystal compound semiconductor thin film 5
Are high resistance, serve as an interfacial layer, and use a zinc salt, specifically a solution selected from one of zinc sulfate, zinc chloride or zinc acetate to form this thin film. If necessary, a sulfur-containing salt can be used in addition to the zinc salt. The second metal oxide semiconductor thin film 6 is provided as a window layer, and is made of zinc oxide having a wide bandgap having an n-type conductivity type and a thickness of 0.5 to 3 μm which is transparent and conductive.
An upper electrode or scribe line 7 is formed on an exposed surface of the second metal oxide semiconductor thin film 6.

The method of manufacturing a thin-film solar cell according to the present invention is characterized by the following step of manufacturing a sulfur-containing zinc mixed crystal compound semiconductor thin film 5. After chemically growing a thin film containing oxygen, sulfur and hydroxyl groups from a solution containing a zinc salt or a sulfur-containing salt on the first multi-component compound semiconductor thin film 4 serving as a light absorbing layer, By heating and drying, a high-resistance sulfur-containing zinc mixed crystal compound semiconductor thin film 5 is formed.

The vacuum heating and drying process in the method for manufacturing a thin film solar cell will be described in detail below. The first multi-component semiconductor thin film 4 serving as a light absorbing layer is immersed in a solution containing a zinc salt or a sulfur-containing salt to form a sulfur-containing zinc mixed crystal compound semiconductor on the first multi-component semiconductor thin film 4. After chemically growing the thin film 5, the grown sulfur-containing zinc mixed crystal compound semiconductor thin film 5 is annealed in a vacuum of 1 to 100 Torr at a set temperature of 100 to 250 ° C. for 10 to 120 minutes to dry and At the same time as converting zinc hydroxide in the film to zinc oxide, it promotes the reforming of the surface of the first multi-component compound semiconductor thin film 4 with sulfur.

The test results of the element characteristics of the thin-film solar cell 1 manufactured by the method for manufacturing a thin-film solar cell of the present invention will be described below.

The effects of the vacuum drying treatment on the conversion efficiency and the yield (yield) will be described with reference to Tables 1 to 4.

Influence on conversion efficiency and yield (yield) by processing time in vacuum drying processing

[0028]

[Table 1]

The above Table 1 shows the element characteristics of the thin-film solar cell manufactured by the conventional drying method by heating and drying in air (temperature: 200 ° C., pressure: normal pressure, drying time: 15 minutes). .

[0030]

[Table 2]

Table 2 shows that temperature: 200 ° C., pressure: 30
This shows the device characteristics of a thin-film solar cell manufactured at a constant Torr while varying the drying time.

Compared with the thin-film solar cell manufactured by heating and drying in air (temperature: 200 ° C., pressure: normal pressure, drying time: 15 minutes), which is the conventional manufacturing method shown in Table 1 above, As shown in Table 2, temperature: 200 ° C., pressure: 30 Torr
In the case of a thin-film solar cell manufactured with a constant drying time, the conversion efficiency and the standard deviation β are improved when the drying time is 15 to 120 minutes. When the drying time is 15 to 60 minutes, the conversion efficiency and the standard deviation β are improved as the drying time increases.

The standard deviation β is the variation α of the conversion efficiency.
And the variation α = (conversion efficiency × β) ÷ 2.

For example, those manufactured by the conventional manufacturing method by heating and drying in the air shown in Table 1 and Table 2
In comparison with the case where the drying time is 60 minutes, the conversion efficiency is 10.0 ± 1.105 (10.0 × 1.
0.0221 ÷ 2) solar cells can be obtained with a yield (yield) of 65%, while those with a drying time of 60 minutes have a conversion efficiency of 11.0 ± 0.0462 (11.0 ×
The yield (yield) of the solar cell of 0.0084 ÷ 2) is 65%, and both the efficiency and the yield (yield) are improved.

The yield (yield) of the two is the same.
Even if it is 5%, the variation α is 0.0462.
On the other hand, since the former is 1.105, the latter substantially has a higher yield (yield).

However, when the drying time is 60 minutes is the maximum, and when the drying time is 120 minutes, both the conversion efficiency and the standard deviation β decrease. β is improving.

The reason why the conversion efficiency and the standard deviation β decrease when the drying time is too long is considered to be the deterioration of the interface state.

Effect of Drying Temperature in Vacuum Drying on Conversion Efficiency and Yield (Yield)

[0039]

[Table 3]

Table 3 shows that time: 60 minutes, pressure: 30 To.
rr Indicates the device characteristics of a thin-film solar cell manufactured at a constant temperature while varying.

As shown in Table 1 above, a conventional manufacturing method of heating and drying in air (temperature: 200 ° C., pressure: normal pressure,
(Drying time: 15 minutes) compared with the thin-film solar cell manufactured by the method shown in Table 3 above, time: 60 minutes, pressure: 30 Torr.
In the case of a thin-film solar cell manufactured at a constant temperature while changing the temperature, when the drying temperature is 100 to 230 ° C., Table 1
Both the conversion efficiency and the standard deviation β are improved over the conventional one shown in FIG. Up to 200 ° C., the conversion efficiency and the standard deviation β increase as the temperature rises. However, as the temperature rises to 230 ° C., the conversion efficiency and the standard deviation β are more excellent than those of the related art shown in Table 1. , But slightly lower. The cause is considered to be the influence of interdiffusion of the interface due to the temperature rise.

Effect of Drying Pressure on Conversion Efficiency and Yield (Yield) in Vacuum Drying

[0043]

[Table 4]

Table 4 shows that time: 60 minutes and temperature: 200.
This shows the device characteristics of a solar cell manufactured at a constant ° C and a varied drying pressure.

As compared with the solar cell manufactured by the conventional method of heating and drying in air (temperature: 200 ° C., pressure: normal pressure, drying time: 15 minutes) as shown in Table 1, In the case of a solar cell manufactured by changing the drying pressure at a constant time of 60 minutes and at a temperature of 200 ° C. as shown in FIG. 4, when the drying pressure is in the range of 1 to 50 Torr, the conversion efficiency and the conventional one shown in Table 1 are higher. Both the standard deviation β improve. However, at 100 Torr, the value is almost the same as the conventional one shown in Table 1. This is considered to be because the effect of drying moisture decreases as the pressure increases.

In view of the above experimental examples, the processing time was determined for the entire time range of the experiment, ie, 15 to 12 hours.
In the range of 0 minutes, the drying temperature was in the entire temperature range tested, that is, in the range of 100 to 230 ° C., and the drying pressure was in the range of 1 to 100 Torr. And the standard deviation β are both improved.

[0047]

According to the manufacturing method of the present invention, a thin-film solar cell having high conversion efficiency and high yield can be manufactured without using toxic materials such as cadmium.

Further, since the manufacturing method of the present invention is manufactured using an existing relatively simple apparatus called a vacuum heating and drying treatment, when manufacturing a thin film solar cell, it can be mass-produced and the amount of chemicals used can be reduced. And the concentration can be reduced, so that the manufacturing cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a view showing a schematic structure of a thin film solar cell to be manufactured by a manufacturing method of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Thin film solar cell 2 Substrate 3 Metal back electrode 4 First multi-component compound semiconductor thin film (light absorption layer: p-type semiconductor) 5 Sulfur-containing zinc mixed crystal compound semiconductor thin film (interface layer) 6 Second metal oxide semiconductor thin film ( (Window layer: n-type semiconductor) 7 Upper electrode or scribe line

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-8-330614 (JP, A) JP-A-57-162475 (JP, A) JP-A-8-97450 (JP, A) Kushiya et al, A pplication of Zn-c ompound Buffer Lay er for Polycrystal line CuInSe2-Based Thin-Film Solar C ells, Japanese Jour nal of Applied Phy sics, Japan, The Japan Society of Applied Physics, vol. 35 no. 8, 4383-4388 (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 31/04-31/078 H01L 21/368

Claims (6)

(57) [Claims] 1. A metal back electrode, a first multi-compound semiconductor thin film formed on the metal back electrode, having a p-type conductivity, and serving as a light absorbing layer; A second metal oxide semiconductor formed on the compound semiconductor thin film, having a conductivity type opposite to that of the first multi-element compound semiconductor thin film, serving as a window layer, and having a wide bandgap, and being transparent and conductive; A thin film, the first multi-component compound semiconductor thin film, and a second
A thin-film solar cell manufacturing method comprising: a sulfur-containing zinc mixed crystal compound semiconductor thin film formed at an interface between a metal oxide semiconductor thin film of the present invention, which is transparent, has high resistance and serves as an interface layer, and an upper electrode In the above, after the sulfur-containing zinc mixed crystal compound semiconductor thin film containing oxygen, sulfur and hydroxyl groups is chemically grown from a solution on the first multi-component compound semiconductor thin film, the sulfur-containing zinc mixed crystal compound semiconductor thin film To
By annealing at a temperature of less than 100 to 250 ° C. in a vacuum of 1 to 100 Torr, zinc hydroxide in the sulfur-containing zinc mixed crystal compound semiconductor thin film is converted into zinc oxide, and has a transparent and high resistance. A method for manufacturing a thin-film solar cell, comprising forming an interface layer. 2. The method according to claim 1, wherein the annealing time of the sulfur-containing zinc mixed crystal compound semiconductor thin film is 10 to 120 minutes. 3. A zinc salt is used for forming a sulfur-containing zinc mixed crystal compound semiconductor thin film serving as the interface layer, wherein the zinc salt is formed from one of zinc sulfate, zinc chloride and zinc acetate. 2. The method according to claim 1, wherein the selection is performed.
A method for manufacturing the thin-film solar cell according to the above. 4. The thin-film solar cell according to claim 1, wherein a sulfur-containing salt is contained in addition to the zinc salt to form the sulfur-containing zinc mixed crystal compound semiconductor thin film serving as the interface layer. Production method. 5. The method according to claim 1, wherein the first multi-element compound semiconductor thin film serving as the light absorbing layer is made of copper indium diselenide (CI).
S), copper indium gallium diselenide (CIG
S), indium / gallium diselene / copper iodide (C
2. A thin-film solar cell according to claim 1, wherein said thin-film solar cell is made of copper indium gallium diselenide (IGGS) or a thin layer of copper indium gallium indium selenide (CIGS) as a surface layer. Method. 6. The method according to claim 1, wherein the second metal oxide semiconductor thin film serving as the window layer is made of zinc oxide.