JPH11284209A - Manufacture of compound semiconductor thin film having chalcopyrite structure and manufacture of solar cell having the thin film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a chalcopyrite structure compound semiconductor thin film which has a highly uniform composition. in the plane direction and low surface roughness with high reproducibility at low cost, and a method for manufacturing a solar battery which has the thin film and is improved in energy conversion efficiency. SOLUTION: A compound semiconductor thin film having a chalcopyrite structure is manufactured by forming a laminated film by successively forming an In oxide film 4, a Ga oxide film 3, and a metallic Cu film 5 on a substrate 1 and heating the laminated film to, for example, 400-550 deg.C in a selenium atmosphere. The above-mentioned In oxide is, for example, In2 O3 and the Ga oxide is, for example, Ga2 O3 . The preferable forming methods of the films 4, 3, and 5 are the sputtering. The above-mentioned selenium atmosphere is produced by generating selenium vapor by heating a single selenium substance. The substrate 1 is a soda lime glass plate carrying, for example, a single film or laminated film composed at least of one kind of metal selected from among, for example, Mo, Cr, Ta, W, and Ti on its surface.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a chalcopyrite structure compound semiconductor thin film and a method for producing a solar cell having the same.

[0002]

2. Description of the Related Art Group Ib and IIIb elements of the periodic table
Semiconductor thin film composed of elements of group VIb and VIb
As a compound semiconductor thin film having a pyrite structure,
Are known. Such a compound semiconductor thin film is, for example,
For example, CuInSe_Two , CuInS _Two, Cu (In_1-xGa
_x) Se_Two, CuIn (S_xSe_1-x)_Two, Cu (In_1-x
Ga_x) (S_ySe_1-Y)_TwoEtc. are composed of compounds
You. Compound semiconductor thin film composed of these compounds
Is called a CIS-based compound semiconductor thin film and is a thin film solar cell
As a light absorbing layer.

A method for manufacturing such a CIS-based compound semiconductor thin film (hereinafter referred to as "prior art A") is disclosed in
No. 2,313,313. FIG. 2 is an explanatory sectional view of such a conventional CIS-based compound semiconductor thin film. As shown in FIG. 2, a Cu film 13 is first deposited by magnetron sputtering on a substrate 11 having a Mo film 12 on its surface, and then an In film 14 is deposited. By such magnetron sputtering,
Since the Cu film 13 and the In film 14 are instantaneously alloyed or mixed, a composite film of Cu and In is formed. Next, a Se film 15 is deposited on the composite film by a thermal evaporation method, and the obtained laminated film is heated in the presence of a hydrogen-containing gas to form a p-type CuInSe ₂ 16 film.

A semiconductor made of CuInSe ₂ has a low band gap energy of 1.04 eV, so that
Attempts have been made to increase the band gap energy to 1.4 to 1.50 eV, which is optimal for a solar cell, by adding. For example, 5 December 1994
Miguel A. Contreras et al. Announced “HIGH EFFICIENCY Cu (In, Ga) Se ₂ -BASED SO at the 1st WCPEC held on September 9.
LAR CELLS: PROCESSINGOF NOVEL ABSORBER STRUCTURER
On pages 68 to 75 of S ", Cu (In, Ga) having a large band gap energy near the substrate and a small band gap energy near the surface which comes into contact with the n-type semiconductor is described. ) In order to obtain a chalcopyrite structure compound semiconductor thin film composed of Se _2, Ga contained in the chalcopyrite structure compound semiconductor thin film is used.
And In composition. Such a bandgap structure is called a graded bandgap structure, and attempts to reduce the recombination of carriers by tilting the conductor of the band structure and to effectively extract current.

Japanese Patent Application Laid-Open No. Hei 6-37342 discloses that
A group I-III oxide containing a group Ib element such as Cu and a group IIIb element such as In or Ga is reduced to a reducing atmosphere containing a group VIb element such as S or Se, or to a reduction such as H ₂ S or H ₂ Se. Sex V
A heat treatment in an atmosphere containing a group Ib compound converts the oxide into a chalcopyrite-type compound such as CuInS or CuInSe ₂ to form a semiconductor thin film (hereinafter referred to as “prior art B”). Have been. In addition, it is described that a uniform chalcopyrite-type compound having no composition or microscopic variation can be obtained by using the group I-III oxide.

[0006]

SUMMARY OF THE INVENTION As described in the prior art A,
When metal In is used, the surface roughness of In is large.
In addition, the variation in the composition in the plane direction increases,
CuInSe generated in _Two The ancestral surface of the thin film has also grown
I will. “Planar composition variation” means that
When creating a pond cell, it doesn't matter much
But when making large things such as solar cell modules
Has been pulled to a place with poor performance,
There is a problem that the performance becomes poor. Also,
This kind of chalcopyrite structure compound semiconductor thin film is mainly used
As a light absorbing layer of a solar cell.
When the surface roughness increases, photovoltaic power is generated at the pn junction surface
When this happens, a weak part is created
The open-circuit voltage, which is one of the characteristics of the pond, is reduced,
As a result, the problem of reduced energy conversion efficiency
is there.

[0007] When a metal oxide of a group I element and a metal oxide of a group III element are used as in the prior art B, the uniformity of the finally formed chalcopyrite film in the planar direction is improved. In view of the price, the metal oxide of the group I element is more expensive than the metal of the group I element, and thus there is a problem that the production cost is increased.

An object of the present invention is to solve such a problem. That is, the present invention provides a method for producing a chalcopyrite structure compound semiconductor thin film having good uniformity in the composition in the plane direction and a small surface roughness with good reproducibility at low cost, and improved energy conversion efficiency having the method. An object is to provide a method for manufacturing a solar cell.

[0009]

Means for Solving the Problems When the present inventors formed a metallic copper film on an indium oxide film and a gallium oxide film, which are nonmetallic films, respectively, the surface roughness of the film can be reduced. Therefore, it has been found that the composition variation in the planar direction of the film can be suppressed small, and the present invention has been completed.

That is, in order to achieve the above object, the first aspect of the present invention is to form a stacked film by forming an In oxide film, a Ga oxide film, and a metal Cu film on a substrate. A method for producing a chalcopyrite structured compound semiconductor thin film, comprising heating the film in a selenium atmosphere.

A second invention is the first invention, wherein the oxide of In is In ₂ O ₃ and the oxide of Ga is Ga ₂
O ₃ .

A third invention is the first or second invention, wherein the I
An oxide film of n, an oxide film of Ga, and a metal Cu film are formed by sputtering, respectively.

A fourth invention is characterized in that, in the first, second, or third invention, a selenium atmosphere is created by generating selenium by heating selenium alone.

According to a fifth aspect of the present invention, in the first, second, third or fourth aspect of the present invention, the substrate has a single film or a laminated film made of at least one metal selected from Mo, Cr, Ta, W and Ti. Characterized by being a soda lime glass plate.

A sixth invention is characterized in that, in the first, second, third, fourth or fifth invention, heating of the laminated film is performed at 400 to 550 ° C.

According to a seventh invention, a cadmium sulfide layer is formed on a chalcopyrite-structured compound semiconductor thin film obtained by any one of the first to sixth inventions by a solution growth method or a vacuum evaporation method. A method for manufacturing a solar cell, comprising forming a zinc oxide layer thereon.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The substrate used in the present invention is, for example, soda lime glass. However, as long as the object of the present invention is not contradicted, the heat resistance of ceramic substrates and the like conventionally used in the manufacture of solar cells is used. Substrate can be used.

In the present invention, the laminated film formed on the substrate is composed of an In oxide film, a Ga oxide film and a metal Cu film. When the laminated film is heated in a selenium atmosphere, a chemical reaction occurs. Progresses, and a uniform chalcopyrite structure compound semiconductor thin film is generated. Therefore, the In oxide film, the Ga oxide film, and the metal Cu film can be formed in any order to form a stacked film.

The selenium atmosphere in the present invention is, for example,
It can be produced by heating Se alone to generate Se vapor. Se in the Se vapor is Se
Does not mean a single atom of Se ₆ , Se ₂ , S
It is a generic term for e and other Se molecules.

In order to use the chalcopyrite structure compound semiconductor thin film produced by the present invention as a solar cell, for example, a cadmium sulfide layer as an N-type semiconductor is formed on the chalcopyrite structure compound semiconductor thin film by a solution growth method or a vacuum evaporation method. Is formed, and a zinc oxide layer is formed thereon as a transparent conductive film.

[0021]

Embodiments of the present invention will be described below. FIG.
BRIEF DESCRIPTION OF THE DRAWINGS It is sectional drawing of the manufacturing process of the chalcopyrite structure compound semiconductor thin film for explaining one Example of this invention, and the manufacturing process of the solar cell which has it.

(Embodiment 1) This embodiment will be described with reference to FIG. On a substrate 1 made of soda lime glass, a Mo film 2 was formed in advance to a thickness of about 1 μm by sputtering. Mo can form ohmic contact with a p-type conduction chalcopyrite semiconductor thin film when a solar cell is made, and furthermore, because it is difficult to react with Se, Mo is thus made in advance of a substrate made of soda-lime glass. A film was formed thereon. Substrate 1 on which Mo film 2 is formed
A Ga ₂ O ₃ film 3 and an In ₂ O ₃ film 4 were formed thereon at a substrate heating temperature of 300 ° C. by a vacuum evaporation method. Next, a Cu film 5 was formed on this film by DC magnetron sputtering without heating the substrate. When the atomic ratio of the laminated film thus formed was examined, Cu / (I
n + Ga) is 0.90 and Ga / (In
+ Ga) was 0.20. [FIG. 1 (a)]

This laminated film is placed in a Se atmosphere for 500
C. for 2 hours, CuIn _0.8Ga_0.2Se_Two Yo
Chalcopyrite structure compound with thickness of about 2μm
A body thin film 6 was formed. [FIG. 1 (b)]

When the surface roughness of the thus obtained chalcopyrite structure compound semiconductor thin film 6 was measured,
The results shown in the following Table 1 were obtained. The "surface roughness" is,
50 mm of chalcopyrite structure compound semiconductor thin film 6
Five center line average roughnesses randomly selected within a 50 mm square surface; measured by Ra (Ｒ) (hereinafter, in the present specification, “surface roughness” means the same measured value Do). When the composition uniformity was measured, the results shown in the following Table 2 were obtained. The “composition uniformity” was measured five times at randomly selected five points of a 50 mm × 50 mm square of the chalcopyrite structure compound semiconductor thin film 6 by X-ray fluorescence analysis (hereinafter, in this specification, “composition uniformity”). "Gender" means those measured similarly).

[0025]

[Table 1]

[0026]

[Table 2]

Then, a CdS film 7 was formed on the chalcopyrite structure compound semiconductor thin film 6 to a thickness of 0.3 μm at a substrate heating temperature of 200 ° C. by a vacuum evaporation method. Next, a ZnO film 8 is formed on the CdS film 7 by RF magnetron sputtering to a thickness of 0.1 μm at a substrate heating temperature of 200 ° C., and subsequently, a ZnO film doped with Al (hereinafter, referred to as “herein The “ZnO: Al film”) 9 was heated at a substrate heating temperature 2 by DC magnetron sputtering.
A film having a thickness of 0.7 μm was formed at 00 ° C. to obtain a solar cell. [FIG. 1 (c)] When the energy conversion of the solar cell was measured by irradiating the solar cell with light of 0.1 W / cm ₂ using a solar simulator, the result of the measurement was an open-circuit voltage;
50 mV, short-circuit current density; 32 mA / cm ₂ , fill factor: 55%, and energy conversion rate: 7.9%
Met.

(Example 2) As in Example 1, a Mo film was previously formed on a substrate made of soda lime glass to a thickness of about 1 μm by sputtering. This M
On the substrate on which the o film was formed, a Ga ₂ O ₃ film and an In ₂ O ₃ film were formed at a substrate heating temperature of 250 ° C. by RF magnetron sputtering. Next, a Cu film was formed on this film by DC magnetron sputtering without heating the substrate. When the atomic ratio of the laminated film thus formed was examined, Cu / (In + Ga) was found to be:
0.95 and Ga / (In + Ga) is
0.15.

This laminated film is placed in a Se atmosphere at 550
C. for 2 hours, CuIn _0.85Ga_0.15Se_Two 
Chalcopyrite structure compound half of about 2 μm thick
A conductor thin film was formed.

When the surface roughness of the thus obtained chalcopyrite structure compound semiconductor thin film was measured, the results shown in the following Table 3 were obtained.

[0031]

[Table 3]

Then, a CdS film was formed on the chalcopyrite structure compound semiconductor thin film to a thickness of 0.3 μm at a substrate heating temperature of 200 ° C. by a vacuum evaporation method. Next, this C
A ZnO film is formed on the dS film by RF magnetron sputtering to a thickness of 0.1 μm at a substrate heating temperature of 200 ° C., and then a ZnO: Al film is formed by DC magnetron sputtering to a thickness of 0.7 μm at a substrate heating temperature of 200 ° C. The film was formed into a solar cell. When the energy conversion rate of the solar cell was measured by irradiating the solar cell with light of 0.1 W / cm ₂ using a solar simulator, the measurement result was as follows: open-circuit voltage: 440 mV, short-circuit current density: 33.5 m
A / cm ₂ , fill factor; 56%, and energy conversion rate: 8.5%.

(Comparative Example 1) An Mo film was previously formed on a substrate made of soda lime glass to a thickness of about 1 μm by sputtering. On the substrate on which the Mo film was formed, an In—Ga—Se film was formed from a ternary source of In, G, and Se by a simultaneous evaporation method. Next, a Cu film was formed on this film by sputtering. This laminated film was heated at 500 ° C. for 1 hour in a Se atmosphere to form a conventional chalcopyrite structure compound semiconductor thin film of CuIn _0.8 Ga _0.2 Se _{2 having} a thickness of about 2 μm.

When the surface roughness of the conventional chalcopyrite structure compound semiconductor thin film thus obtained was measured, the results shown in the following Table 4 were obtained. When the composition uniformity was measured, the results shown in the following Table 5 were obtained.

[0035]

[Table 4]

[0036]

[Table 5]

Then, a CdS film was formed on this conventional chalcopyrite structure compound semiconductor thin film to a thickness of 0.3 μm by vacuum evaporation. Next, Z is formed on this CdS film.
The nO film is 0.1 magnetized by RF magnetron sputtering.
Then, a ZnO: Al film was formed to a thickness of 0.7 μm at a substrate heating temperature of 200 ° C. by DC magnetron sputtering to obtain a solar cell. When the solar cell was irradiated with light of 0.1 W / cm ₂ by a solar simulator and the energy conversion rate of the solar cell was measured,
The measurement results were: open-circuit voltage: 425 mV, short-circuit current density: 31.5 mA / cm ₂ , fill factor: 54
% And energy conversion; 7.23%.

As described above, according to the results of Examples 1 and 2 and Comparative Example 1 (conventional example), in Examples 1 and 2, their open-end voltages are higher than that of Comparative Example 1 of the prior art. It can be seen that their surface roughness is significantly better than Comparative Example 1. Then, the chalcopyrite structure compound semiconductor thin films in Example 1 and Comparative Example 1 are composed of CuIn _0.8 Ga _0.2 Se ₂ having substantially the same composition and thickness,
Moreover, their n-type semiconductors are almost the same CdS, ZnO
In view of the fact that they are composed of Zn: Al and Zn: Al, it can be said that the improvement of the open-circuit voltage in the above embodiment is due to the improvement in the surface roughness of the chalcopyrite structure compound semiconductor thin films. The reason why the open-end voltage of Example 2 is slightly lower than that of Example 1 is that the bandgap energy of the light absorbing layer is reduced because the Ga content of the chalcopyrite structure compound semiconductor thin film is small. it is conceivable that.

Hereinafter, the operation of the present invention will be described as follows.
I'm sorry. (1) About the first and second inventions In has a low melting point of about 157 ° C. and is a soft metal even at room temperature.
It is. When a thin film is made of this material, the surface becomes very concave.
It will be convex. For example, soda lime moth
When In is vacuum-deposited on the glass at a substrate temperature of 100 ° C.,
Is the center line surface roughness (R_a ) Is 300Å
You. This is In_TwoO_ThreeThe surface roughness is
It can be seen that the angle is 30 ° or less, which is extremely small. Ma
Ga has a melting point of about 28 ° C.,
If it exceeds 0 ° C., it becomes liquid. Then on the board
Droplets of Ga liquid appear on the surface
The compositional uniformity of the composition becomes poor. This is Ga_TwoO_Three
In other words, the surface roughness is In_TwoO_Three  Same as
Will be smaller. Moreover, Ga_TwoO_ThreeIs In _TwoO_Three
It has a melting point as high as that of. In addition, the metal copper film
Even if it is formed on an indium film or a gallium oxide film,
The roughness can be reduced, so that the
Variations in the composition of the directions can be kept small.

Therefore, an In oxide film, a Ga oxide film and a metal Cu film are formed on a substrate to form a laminated film, and this laminated film is formed by heating in a selenium atmosphere. The surface roughness of the chalcopyrite structure compound semiconductor thin film can be remarkably improved, and therefore, even if this chalcopyrite structure compound semiconductor thin film is used for the light absorption layer of a solar cell, the open-circuit voltage is small as in the conventional case. It does not become. Further, since the metal Cu film is used, the manufacturing cost can be reduced.

(2) Third Invention Since the In oxide film and the Ga oxide film are formed by hydrogen sputtering, a uniform film can be easily formed with good reproducibility. Since a uniform Cu film can be easily formed with good reproducibility by sputtering or vacuum deposition, the metal Cu film is formed by the same sputtering as the formation of the In oxide film and the Ga oxide film. Is efficient.

(3) Lower Surface of the Rotating Body Regarding the Fourth Invention Since the selenium atmosphere is created by generating selenium by heating selenium alone, it does not generate toxic gas such as H ₂ Se which has been conventionally used. A high quality chalcopyrite structure compound semiconductor thin film can be formed.

(4) Regarding the Fifth Invention A single film or a laminated film composed of at least one metal selected from Mo, Cr, Ta, W and Ti on a substrate has a work function of the metal. Since it is relatively large, it becomes easy to make ohmic contact with the p-type conduction chalcopyrite structure compound semiconductor thin film to be formed thereon. In addition, since these metal films do not easily react with Se, they do not peel off even when exposed to a high temperature of about 400 to 450 ° C. in selenium vapor.

(5) Regarding the Sixth Invention When the heating temperature is lower than 400 ° C., the crystals having a chalcopyrite structure become incomplete, and copper selenide (Cu _2-x Se) is used.
, CuSe, etc.), indium selenide (InSe, I
n ₆ Se ₇ etc.), gallium selenide (GaSe, Ga ₂ S)
e _3, etc.) remain without reacting. When a solar cell having such a chalcopyrite-structured compound semiconductor thin film is produced, these binary compounds become recombination centers of carriers, resulting in poor solar cell characteristics. It will have an adverse effect. Further, this kind of chalcopyrite structure compound semiconductor thin film is used as a light absorbing layer of a solar cell, and in most cases, soda lime glass is used as a substrate of the solar cell. A substrate made of soda lime glass softens at 570 ° C. and has a slightly lower temperature of 55 ° C.
Warping occurs at temperatures above 0 ° C. Therefore, by setting the heating temperature to 400 to 550 ° C., a chalcopyrite structure compound semiconductor thin film having good crystallinity can be formed without deforming the substrate.

(6) Seventh invention A cadmium sulfide layer is formed by a solution growth method or a vacuum evaporation method on the chalcopyrite structure compound semiconductor thin film obtained by any one of the first to sixth inventions. Further, by forming a zinc oxide layer thereon by a sputtering method, it is possible to provide a solar cell with improved energy conversion efficiency in order to particularly improve the open-circuit voltage among the solar cell characteristics. .

[0046]

According to the present invention, it is possible to provide a method for producing a chalcopyrite structure compound semiconductor thin film having good composition uniformity in the plane direction and small surface roughness with good reproducibility and at low cost. A method for manufacturing a solar cell with improved energy conversion efficiency can be provided.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a process for manufacturing a chalcopyrite structure compound semiconductor thin film and a process for manufacturing a solar cell having the same, for explaining one embodiment of the present invention.

FIG. 2 is an explanatory cross-sectional view of a conventional CIS-based compound semiconductor thin film.

[Explanation of symbols]

Reference Signs List 1 substrate 2 Mo film 3 Ga ₂ O ₃ film 4 In ₂ O ₃ film 5 Cu film 6 chalcopyrite structure compound semiconductor thin film 7 CdS film 8 ZnO film 9 ZnO: Al film

Claims (7)

[Claims] An oxide film of In, a oxide film of Ga, and a metal Cu film are formed on a substrate to form a laminated film, and the laminated film is heated in a selenium atmosphere. A method for producing a pyrite structure compound semiconductor thin film. 2. The method of manufacturing a chalcopyrite structure compound semiconductor thin film according to claim 1, wherein the oxide of In is In ₂ O ₃ , and the oxide of Ga is Ga ₂ O ₃ . 3. The method for producing a chalcopyrite structure compound semiconductor thin film according to claim 1, wherein the In oxide film, the Ga oxide film, and the metal Cu film are each formed by sputtering. 4. The method for producing a chalcopyrite structured compound semiconductor thin film according to claim 1, wherein the selenium atmosphere is created by generating selenium by heating selenium alone. 5. A soda-lime glass plate having on its surface a single film or a laminated film made of at least one metal selected from Mo, Cr, Ta, W and Ti. Item 10. The method for producing a chalcopyrite structure compound semiconductor thin film according to item 1, 2, 3, or 4. 6. The method for producing a chalcopyrite structured compound semiconductor thin film according to claim 1, wherein the heating of the laminated film is performed at 400 to 550 ° C. 7. A cadmium sulfide layer is formed on a chalcopyrite-structured compound semiconductor thin film obtained by the method according to claim 1 by a solution growth method or a vacuum deposition method, and A method for manufacturing a solar cell, comprising forming a zinc oxide layer thereon.