JP2000332280A - Method for forming ZnO-based semiconductor thin film and method for manufacturing solar cell using the same - Google Patents

Abstract

[PROBLEMS] To provide a method of manufacturing a ZnO-based semiconductor thin film that does not damage a substrate when a ZnO-based semiconductor thin film is formed, and a method of manufacturing a solar cell using the same. A ZnO-based semiconductor thin film is formed on a substrate by bringing the substrate into contact with an aqueous solution. The aqueous solution 11 contains a compound containing zinc, a compound containing sulfur, and an ammonium salt as solutes.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for forming a ZnO-based semiconductor thin film and a method for manufacturing a solar cell using the same.

[0002]

2. Description of the Related Art CuInSe ₂ (CIS) or a compound semiconductor (chalcopyrite structure compound semiconductor) comprising a group Ib element, a group IIIb element and a group VIb element is used.
A thin-film solar cell using Cu (In, Ga) Se ₂ (CIGS) in which a is dissolved as a solid solution has a high energy efficiency and has an advantage that the conversion efficiency is not deteriorated by light irradiation or the like. It has been reported.

In a conventional CIS or CIGS solar cell, a buffer layer is formed on a CIS film or a CIGS film by a chemical deposition method. Ya, Ap
application of Zn-Compound
Buffer Layer for Polycrys
talline CuInSe ₂ -Based Thin
-Film SolarCells, Jpn. App
l. Phys. Vol. 35 (1996) pp 4383
-4388).

FIG. 3 shows an example of a conventional CIS or CIGS solar cell. As shown in FIG. 3, a conventional solar cell 1 includes a substrate 2, a back electrode 3 laminated on the substrate 2, a p-type compound semiconductor thin film 4 made of a CIS film or a CIGS film, a buffer layer 5, a window layer 6, Transparent conductive film 7, p
Buffer electrode 5 includes a side electrode 8 and an n-side electrode 9.
It consists of an nO-based semiconductor thin film.

A buffer layer 5 composed of a ZnO-based semiconductor thin film
Has conventionally been formed using an aqueous solution containing zinc ions and a large amount of ammonia.

[0006]

However, in the above-mentioned conventional method for manufacturing a ZnO-based semiconductor thin film, a solution in which a high concentration of ammonia (2 mol / l or more) is dissolved when forming the ZnO-based semiconductor thin film is used. An underlayer (a layer on which the buffer layer 5 is formed;
In FIG. 3, there is a problem that the p-type compound semiconductor thin film 4) is damaged and the conversion efficiency of the solar cell is reduced. On the other hand, when the concentration of ammonia is reduced, Zn (O
H) Since precipitation of ₂ occurs, it is difficult to produce a ZnO-based semiconductor thin film.

The present invention provides a method of forming a ZnO-based semiconductor thin film capable of forming a ZnO-based semiconductor thin film without damaging an underlayer, and a method of manufacturing a solar cell using the same, in order to solve the above conventional problems. The purpose is to do.

[0008]

In order to achieve the above object, a method for forming a ZnO-based semiconductor thin film (semiconductor thin film containing ZnO) according to the present invention comprises a compound containing zinc, a compound containing sulfur, A ZnO-based semiconductor thin film is formed on the substrate by bringing the substrate into contact with an aqueous solution containing a salt as a solute. According to the above formation method, a ZnO-based semiconductor thin film can be formed without using an aqueous solution in which high-concentration ammonia is dissolved. Therefore, according to the method for forming a ZnO-based semiconductor thin film of the present invention, the ZnO-based semiconductor
A system semiconductor thin film can be formed.

In the method of forming a ZnO-based semiconductor thin film,
The aqueous solution may further include ammonia having a concentration of 0.5 mol / l or less. This makes it possible to reduce the damage to the substrate and to form a ZnO-based semiconductor thin film with high film quality.

In the method of forming a ZnO-based semiconductor thin film,
The compound containing zinc is Zn (CH ₃ COO) ₂ ,
It is preferably at least one compound selected from ZnCl ₂ , ZnI ₂ and ZnSO ₄ .

In the above method for forming a ZnO-based semiconductor thin film,
It is preferable that the compound containing sulfur is at least one compound selected from thiourea and thioacetamide.

In the above method for forming a ZnO-based semiconductor thin film,
The ammonium salt is CH ₃ COONH ₄ , NH ₄ C
Preferably, the compound is at least one compound selected from the group consisting of 1, NH ₄ I and (NH ₄ ) ₂ SO ₄ .

In the method of forming a ZnO-based semiconductor thin film,
It is preferable that the temperature of the aqueous solution is 10 ° C or more and 100 ° C or less. By setting the temperature of the aqueous solution within the above range, an appropriate reaction for film formation can be caused.

In the above method for forming a ZnO-based semiconductor thin film,
The pH of the aqueous solution is preferably 9 or more and 11 or less. By setting the pH of the aqueous solution within the above range, a high-quality semiconductor thin film can be formed.

In the above method for forming a ZnO-based semiconductor thin film,
It is preferable that the contact between the aqueous solution and the substrate is performed by immersing the substrate in the aqueous solution.

The method of manufacturing a solar cell according to the present invention includes an upper electrode film and a lower electrode film, a light absorbing layer disposed between the upper electrode film and the lower electrode film, 9. A method for manufacturing a solar cell, comprising: a ZnO-based semiconductor thin film disposed between an absorbing layer and a solar cell;
Wherein the ZnO-based semiconductor thin film is formed by using the ZnO-based semiconductor thin film forming method according to any one of the above. According to the method for manufacturing a solar cell, a ZnO-based semiconductor thin film can be formed without damaging the underlayer, so that a solar cell with high characteristics can be obtained.

In the method for manufacturing a solar cell, it is preferable that the light absorbing layer is formed of a compound semiconductor thin film containing a group Ib element, a group IIIb element, and a group VIb element. As a result, a solar cell having particularly high characteristics can be obtained.

In the method of manufacturing a solar cell, the group Ib element is Cu, and the group IIIb element is In and Ga.
It is preferable that there is at least one element selected from the group consisting of Se and S.

[0019]

Embodiments of the present invention will be described below.

Embodiment 1 In Embodiment 1, an example of a method for forming a ZnO-based semiconductor thin film of the present invention will be described. Here, the ZnO-based semiconductor thin film is a semiconductor thin film containing ZnO, for example, a Zn (O, OH, S) thin film (a thin film containing a Zn—O bond, a Zn—OH bond, and a Zn—S bond). Applicable.

In the method of forming a ZnO-based semiconductor thin film according to the first embodiment, as shown in FIG. 1, a substrate 10 is brought into contact with an aqueous solution 11 to form a ZnO-based semiconductor thin film on the substrate 10. Note that in FIG. 1, the substrate 10 is
Although the case where the substrate 10 is brought into contact with the aqueous solution 11 by immersing the substrate 10 in the aqueous solution 11 is shown, another method may be used for bringing the substrate 10 into contact with the aqueous solution 11.

The substrate 10 includes a metal thin film and a semiconductor thin film as required. When the substrate 10 includes a semiconductor thin film on the surface, this semiconductor thin film serves as a base layer, and Zn
An O-based semiconductor thin film is formed.

The aqueous solution 11 contains a zinc-containing compound,
It contains a sulfur-containing compound and an ammonium salt as solutes. Moreover, the aqueous solution 11 further contains ammonia as needed.

Compounds containing zinc which is a solute of the aqueous solution 11 include, for example, Zn (CH ₃ COO) ₂ , ZnCl
₂ , at least one compound selected from ZnI ₂ and ZnSO ₄ can be used.

As the compound containing sulfur which is a solute of the aqueous solution 11, for example, at least one compound selected from thiourea (NH ₂ CSNH ₂ ) and thioacetamide (C ₂ H ₅ NS) can be used.

The ammonium salt which is a solute of the aqueous solution 11 includes CH ₃ COONH ₄ , NH ₄ Cl, NH ₄ I and (N
At least one compound selected from H ₄ ) ₂ SO ₄ can be used. The concentration of ammonium salt is 0.1m
It is preferably from ol / l to 0.3 mol / l. 0.1 mol / l to 0.3 mol of ammonium salt
By setting / l, damage to the underlayer can be particularly reduced.

When the aqueous solution 11 contains ammonia, the concentration of the dissolved ammonia is preferably 0.5 mol / l or less. 0.5m ammonia concentration
By setting the ratio to ol / l or less, damage to the underlying layer can be reduced. Further, by setting the concentration of ammonia to 0.3 mol / l or less, damage to the underlying layer can be particularly reduced. The concentration of ammonia dissolved in the aqueous solution 11 is 0.5 mol /
l, the concentration of ammonium salt is 0.05 mol /
It is preferably 1 to 0.2 mol / l.

The pH of the aqueous solution 11 is preferably 9 or more and 11 or less.

The substrate 10 may include a compound semiconductor thin film containing a group Ib element, a group IIIb element, and a group VIb element. By forming a ZnO-based semiconductor thin film on a compound semiconductor thin film containing a group Ib element, a group IIIb element, and a group VIb element, a semiconductor thin film suitable for a solar cell can be obtained. At this time, the group Ib element is preferably Cu, the group IIIb element is at least one element selected from In and Ga, and the group VIb element is preferably at least one element selected from Se and S.

According to the method for forming a ZnO-based semiconductor thin film of the first embodiment, the ZnO-based semiconductor thin film can be formed without damaging the substrate.
An O-based semiconductor thin film can be formed.

(Embodiment 2) In Embodiment 2, an example of a method for manufacturing a solar cell of the present invention will be described.

In the manufacturing method according to the second embodiment, first, FIG.
As shown in (a), a lower electrode film 22 is formed on a substrate 21. As the substrate 21, a glass substrate, a resin film, a stainless steel substrate, or the like can be used. The lower electrode film 22 is made of a conductive material such as a metal, and can be formed by a sputtering method, an evaporation method, or the like.

Thereafter, as shown in FIG. 2B, a light absorbing layer 23 is formed. For example, Ib
A p-type compound semiconductor containing a group III element, a group IIIb element, and a group VIb element can be used. Specifically, CuInS
e ₂ and Cu (In, Ga) Se ₂ can be used.
CuInSe ₂ or Cu (In, Ga) Se ₂ is formed by a vapor deposition method,
It can be formed by a sputtering method, a plating method, or the like.

Thereafter, as shown in FIG. 2C, a buffer layer 24 is formed on the light absorbing layer 23. Buffer layer 24
Is made of a ZnO-based semiconductor thin film and is formed by the method described in the first embodiment.

Thereafter, as shown in FIG.
5 and an upper electrode film 26 are formed. The window layer 25 is made of, for example, ZnO and can be formed by a sputtering method or the like. The upper electrode film 26 is made of, for example, ITO (Ind
(Im Tin Oxide) and can be formed by a sputtering method or the like.

Then, as shown in FIG. 2E, after removing the light absorbing layer 23 and the like at the portion where the extraction electrode 27 is formed, the extraction electrodes 27 and 28 are formed on the lower electrode film 22 and the upper electrode film 23. Form. The removal of the light absorption layer 23 and the like can be performed by, for example, a scribe method such as a laser scribe method, a dry etching method, or a wet etching method. Also, the extraction electrodes 27 and 28
Can be performed by, for example, an evaporation method or a sputtering method. Thus, the lower electrode film 2 is formed on the substrate 21.
2. A solar cell is formed in which the light absorbing layer 23, the buffer layer 24, the window layer 25, and the upper electrode film 26 are sequentially laminated.

In the method of manufacturing a solar cell, the method described in the first embodiment is used when forming the buffer layer 24. Therefore, according to the method for manufacturing a solar cell, damage to the underlying layer (the light absorbing layer 23 in the second embodiment) can be suppressed when the buffer layer 24 is formed, so that a solar cell with high characteristics can be obtained.

The method of manufacturing a solar cell described above is an example, and the method of manufacturing a solar cell according to the present invention may be applied to another embodiment as long as the method of forming a ZnO-based semiconductor thin film described in Embodiment 1 is used. Can be applied.

For example, the structure of the solar cell is not limited to the structure of the above embodiment, but may be any as long as a buffer layer is formed between the light absorbing layer and the upper electrode film. For example,
Another layer may be included between the light absorbing layer and the buffer layer. Further, in the above embodiment, the solar cell that generates an electromotive force by light incident from the opposite side of the substrate 21 has been described, but a solar cell that generates an electromotive force by light incident from the substrate 21 side may be used. In this case, a transparent conductive film (upper electrode film), a window layer, a buffer layer, a light absorbing layer, and a lower electrode film may be formed from the substrate side.

[0040]

The present invention will be described below more specifically with reference to examples. However, the present invention is not limited only to the following examples.

Example 1 In Example 1, CuInSe was used.
₂ thin film, by contacting the aqueous solution containing Zn ions, describes an example of forming a ZnO-based semiconductor thin film CuInSe ₂ thin film.

First, a Mo film was formed on a glass substrate by a sputtering method, and a CuInSe ₂ thin film was formed thereon by a vapor deposition method.

Next, an aqueous solution containing zinc chloride (ZnCl ₂ ), thiourea (NH ₂ CSNH ₂ ), and ammonium chloride (NH ₄ Cl), which are zinc-containing compounds (salts), was prepared. The concentration of zinc chloride in the aqueous solution is 0.01 mol /
1, the concentration of thiourea was 0.2 mol / l, and the concentration of ammonium chloride was 0.5 mol / l. The container containing the aqueous solution was allowed to stand in a hot water tank maintained at 85 ° C. The substrate on which the CuInSe ₂ thin film was formed was immersed in this aqueous solution for about 20 minutes. Thereafter, the substrate was pulled up from the aqueous solution and washed with pure water.

The composition of the film formed by the above method was analyzed by X-ray photoelectron spectroscopy. Zn, O and S were detected from the formed film. The concentration of each element is Zn at 50 at.
omic%, O is 36 atomic%, S is 14atom
mic%. Also, as a result of measuring the binding energy of the oxygen in the 1s orbit, oxygen in the formed film is O and O
H was found to exist in two states.

Thus, a Zn (O, OH, S) film could be easily formed on the CuInSe ₂ thin film. Here, chloride is used as the salt of Zn, but the same result can be obtained by using iodide, bromide, nitrate, sulfate, acetate, or the like.

Example 2 In Example 2, CuInSe was used.
₂ thin film, by contacting the aqueous solution containing Zn ions, explaining another example of forming a ZnO-based semiconductor thin film CuInSe ₂ thin film.

First, a Mo film was formed on a glass substrate by a sputtering method, and a CuInSe ₂ thin film was formed thereon.

Next, zinc acetate (Zn (CH ₃ COO) ₂ ) which is a compound (salt) containing zinc and thiourea (NH ₂ CS
NH ₂ ), ammonia and ammonium acetate (CH ₃ COO)
And an aqueous solution containing NH ₄ ). The concentration of zinc acetate in the aqueous solution was 0.02 mol / l, the concentration of thiourea was 0.2 mol / l, and the concentration of ammonia was 0.5 mol / l.
1 and the concentration of ammonium acetate were 0.1 mol / l. The container containing the aqueous solution was allowed to stand in a hot water tank maintained at 85 ° C. The substrate on which the CuInSe ₂ thin film was formed was immersed in this aqueous solution for about 20 minutes. Thereafter, the substrate was pulled up from the aqueous solution and washed with pure water.

The composition of the film formed by the above method was analyzed by X-ray photoelectron spectroscopy. As a result, Zn,
O and S were detected. The concentration of each element is Zn at 51 at.
omic%, O is 35 atomic%, S is 14ato
mic%. Also, as a result of measuring the binding energy of the oxygen in the 1s orbit, the oxygen in the formed film was O and OH
It was found to exist in two states.

In this manner, a Zn (O, OH, S) film could be easily formed on the CuInSe ₂ thin film. Here, acetate was used as the salt of Zn,
Similar results can be obtained by using chloride, iodide, bromide, nitrate, sulfate and the like.

Embodiment 3 In Embodiment 3, an example of manufacturing a solar cell including a buffer layer made of a ZnO-based semiconductor thin film will be described.

The solar cell of Example 3 will be described with reference to FIG.

In the third embodiment, a Mo film (film thickness: 1 μm) as a lower electrode film 22 is formed on a glass substrate as a substrate 21 by a sputtering method, and a light absorbing layer 23 is formed thereon.
Formed by Cu (In, Ga) Se ₂ film deposition method (film thickness 2 [mu] m) is (see FIG. 2 (a)). Thereafter, Zn (O,
(OH, S) film was formed.

Further, the window layer 25 is formed on the buffer layer 24.
A ZnO film having a thickness of 100 nm and an ITO film serving as the upper electrode film 26 were formed by a sputtering method. Sputtering is performed using an argon gas of 8 × 10 ⁻³ Torr.
r, and a high frequency power of 500 W was applied to the target in an atmosphere of r. Thereafter, the extraction electrodes 27 and 28
(Thickness: 350 nm). The extraction electrodes 27 and 28 were formed by laminating a NiCr film and an Au film by an electron beam evaporation method.

The solar cell fabricated in this manner has AM
The solar cell characteristics were measured by irradiating 1.5 or 100 mW / cm ² pseudo sunlight.

As a result of measuring the characteristics of the solar cell prepared by the above-described method, an open circuit voltage of 0.63 showing the characteristics of the solar cell was obtained.
V, short-circuit current 35 mA / cm ² , fill factor 0.66, and solar cell conversion efficiency 14.6%.

For comparison, a buffer layer containing Zn was formed under the condition that no ammonium salt was added. Compound containing zinc (salt) to make buffer layer for comparison
An aqueous solution containing zinc acetate, thiourea, and ammonia was prepared. The concentration of zinc acetate in the aqueous solution is 0.02
mol / l, the concentration of thiourea was 0.2 mol / l, and the concentration of ammonia was 3 mol / l. The container containing the aqueous solution was allowed to stand in a hot water tank maintained at 85 ° C. The substrate on which the Cu (In, Ga) Se ₂ thin film was formed was immersed in this aqueous solution for about 20 minutes. Thereafter, the substrate was pulled up from the aqueous solution and washed with pure water.

The composition of the film formed by the above method was analyzed by X-ray photoelectron spectroscopy. As a result, the composition of the film formed was the same as that prepared by the manufacturing method of the present invention. A solar cell was manufactured in the same manner as described above, and the solar cell characteristics were measured. As a result of measuring the characteristics of the solar cell prepared by the above-described method, an open-circuit voltage of 0.47 V, a short-circuit current of 32 mA / cm ² , a fill factor of 0.48, and a solar cell conversion efficiency of 7.2% showing the solar cell characteristics were shown. . This characteristic decrease is caused by a very high ammonia concentration at the time of forming the buffer layer.
It is considered that the Ga) Se ₂ film was damaged.

Fourth Embodiment In a fourth embodiment, another example in which a solar cell including a buffer layer containing Zn is manufactured will be described.

The method of manufacturing a solar cell differs from that of Example 3 only in the method of forming a buffer layer containing Zn.
Duplicate descriptions are omitted.

In the fourth embodiment, the buffer layer 24 of Zn
The (O, OH, S) film was formed by the method described in Example 2.

The characteristics of the solar cell were measured in the same manner as in Example 3.

As a result of measuring the characteristics of the solar cell prepared by the above-described method, an open circuit voltage of 0.64 showing the characteristics of the solar cell was obtained.
V, short-circuit current 35 mA / cm ² , fill factor 0.67, and solar cell conversion efficiency 15.0%. In the method of Embodiment 4, the addition of ammonia causes some damage to the substrate.
Since the film quality of the (O, OH, S) film was improved, a solar cell having high characteristics was obtained.

Although the embodiments of the present invention have been described with reference to the examples, the present invention is not limited to the above embodiments, but can be applied to other embodiments based on the technical idea of the present invention. .

[0065]

As described above, in the method for manufacturing a ZnO-based semiconductor thin film of the present invention, a ZnO-based semiconductor thin film is formed without using high-concentration ammonia. Therefore, according to the method for producing a ZnO-based semiconductor thin film of the present invention,
A ZnO-based semiconductor thin film can be formed without damaging the substrate (underlying layer).

According to the method for manufacturing a solar cell of the present invention, a solar cell having high characteristics can be obtained without using Cd for the buffer layer.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an example of one step in a method for forming a ZnO-based semiconductor thin film of the present invention.

FIG. 2 is a process chart showing one example of a method for manufacturing a solar cell of the present invention.

FIG. 3 is a cross-sectional view illustrating an example of a conventional solar cell.

[Explanation of symbols]

 10, 21 Substrate 11 Aqueous solution 22 Lower electrode film 23 Light absorbing layer 24 Buffer layer 25 Window layer 26 Upper electrode film 27, 28 Extraction electrode

Continued on the front page (72) Inventor Shigeo Hayashi 1006 Kazuma Kadoma, Osaka Pref. Matsushita Electric Industrial Co., Ltd. ) 5F051 AA10 CB11 GA03 GA06 5F053 AA03 AA45 DD20 FF01 HH05 LL05 RR03 RR12

Claims (11)

[Claims] 1. A substrate is brought into contact with an aqueous solution containing a zinc-containing compound, a sulfur-containing compound, and an ammonium salt as a solute to form a Zn on the substrate.
A method for forming a ZnO-based semiconductor thin film, comprising forming an O-based semiconductor thin film. 2. The aqueous solution has a concentration of 0.5 mol / l.
The ZnO according to claim 1, further comprising the following ammonia:
Method of forming a system-based semiconductor thin film. 3. The method according to claim 1, wherein the zinc-containing compound is Zn (C
The method for forming a ZnO-based semiconductor thin film according to claim 1, wherein the method is at least one compound selected from the group consisting of H ₃ COO) ₂ , ZnCl ₂ , ZnI _2, and ZnSO ₄ . 4. The method for forming a ZnO-based semiconductor thin film according to claim 1, wherein said compound containing sulfur is at least one compound selected from thiourea and thioacetamide. 5. The method according to claim 1, wherein the ammonium salt is CH ₃ COON.
The compound according to claim 1, wherein the compound is at least one compound selected from H ₄ , NH ₄ Cl, NH ₄ I, and (NH ₄ ) ₂ SO _4.
3. The method for forming a ZnO-based semiconductor thin film according to item 1. 6. The temperature of the aqueous solution is 10 ° C. or more and 100 ° C.
The Zn according to any one of claims 1 to 5, which is not higher than 0 ° C.
A method for forming an O-based semiconductor thin film. 7. The method for forming a ZnO-based semiconductor thin film according to claim 1, wherein the pH of the aqueous solution is 9 or more and 11 or less. 8. The method for forming a ZnO-based semiconductor thin film according to claim 1, wherein the contact between the aqueous solution and the substrate is performed by immersing the substrate in the aqueous solution. 9. An upper electrode film and a lower electrode film, a light absorbing layer disposed between the upper electrode film and the lower electrode film, and a light absorbing layer disposed between the upper electrode film and the light absorbing layer. A method of manufacturing a solar cell, comprising: a ZnO-based semiconductor thin film, comprising: forming the ZnO-based semiconductor thin film by using the ZnO-based semiconductor thin film forming method according to claim 1. Solar cell manufacturing method. 10. The light-absorbing layer comprises a group Ib element,
The method for manufacturing a solar cell according to claim 9, comprising a compound semiconductor thin film containing a group b element and a group VIb element. 11. The method according to claim 11, wherein the group Ib element is Cu,
The method for manufacturing a solar cell according to claim 10, wherein the group Ib element is at least one element selected from In and Ga, and the group VIb element is at least one element selected from Se and S.