JPH1126790A - Semiconductor thin film, method for manufacturing the same and thin film solar cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To raise light collection efficiency by allowing a semiconductor thin film to comprise a solid solution represented by a specific equation as main component. SOLUTION: A main component is (Inx Ga1-x )(Sey S1-y )2 (where, x and y are value of 0-1, z is value of 1-1.5). On a CuInSe2 thin film formed on a soda lime glass substrate through an Mo thin film, In, Se, and S are simultaneously vapor- deposited while substrate temperature set to 100-300 deg.C, vacuum level set to 10<-5> toor or less. Here, with evaporation rate of vapor-deposition source as In; 5 Å/s, Se; 10 Å/s, S; 5 Å/s, a film of film thickness about 500 Å, In:Se:S =40:50:10 is formed. An absorption-end wavelength of a solid solution thin film moves to the short wavelength side as x becomes large, for wider band gap. Therefor, as the band gap of a film becomes larger, the number of photons P incident on a p-n joint interface increases, resulting in larger current value for raised light collection efficiency.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a semiconductor thin film, a method for producing the same, and a thin film solar cell using the same as a buffer layer of the solar cell.

[0002]

2. Description of the Related Art FIG. 2 is a schematic sectional view of a conventional chalcopyrite solar cell. As shown in FIG. 2, a Mo film 2 is formed on a glass plate substrate 1 as an electrode, and a p-type semiconductor layer having a chalcopyrite structure made of a CuInSe ₂ film 3 is formed thereon. Then, on this p-type semiconductor layer, an n-type semiconductor layer made of a CdS film 4 is formed as a buffer layer, and a transparent electrode layer made of a ZnO film 5 is formed.

As described above, a thin film of CdS (band gap: 2.4 eV) is generally used as a buffer layer of a chalcopyrite solar cell. This Cd
As described in Applied Physics Vol. 62, No. 2 (issued in February, 1993), pages 139-142,
The film is mainly formed by a wet method called a solution growth method.

[0004]

However, such a conventional chalcopyrite type solar cell discharges harmful Cd waste during its production and disposal, and thus has a problem from the viewpoint of environmental conservation. Recently, as an alternative to Cd, I
The chalcogenide of n has been proposed, but the chalcogenide of In has a band gap of C such that the band gap of In ₂ Se ₃ is 1.70 eV, for example.
Since it is smaller than the band gap of dS (2.4 eV), there is a problem that light collection efficiency is reduced.

Further, as a buffer layer of a chalcopyrite solar cell, a ZnX—MgX solid solution thin film (X = S,
Although Se or Te) has been proposed, it has been reported that it has disadvantages such as unstable conversion efficiency.

An object of the present invention is to solve such a problem. That is, an object of the present invention is to provide a semiconductor thin film which maintains high light collection efficiency without discharging harmful Cd waste, a method for manufacturing the same, and a thin film solar cell using the same.

[0007]

As described above, the band gap of In ₂ Se ₃ , which is a chalcogenide of In, is 1.70 eV, as described above. The inventors have found that the band gap of the film gradually increases as Ga or both of them are doped, and have completed the present invention.

In the first invention, the semiconductor thin film is formed of (In _x Ga).
_1-x ) (Se _y S _1-y ) _{z wherein} x and y are values from 0 to 1 and z is a value from 1 to 1.5. ] It is characterized by being mainly composed of a solid solution.

According to a second aspect of the present invention, in the manufacture of the semiconductor thin film of the first aspect, at least two or more elements of In, Ga, Se, and S are simultaneously deposited on the substrate as separate deposition sources. Features.

According to a third aspect of the present invention, in the production of the semiconductor thin film of the first aspect, In, Ga, Se and S are formed on a substrate by adding a compound containing two or more of these elements and a simple substance of each of the elements. It is characterized in that they are simultaneously deposited as separate deposition sources.

The fourth invention is the third invention, wherein the I
n, Ga, Se and S are represented by In _x S _1-x (where x is 0
１1. ), Ga, Se and S as separate evaporation sources, and are simultaneously evaporated.

The fifth invention is characterized in that, in the first invention, In, Ga, Se and S are simultaneously vapor-deposited on a substrate, using compounds containing two or more of them as separate vapor deposition sources. I have.

The sixth invention is the fifth invention, wherein the I
It is characterized in that n, Ga, Se and S are simultaneously evaporated using In ₂ Se ₃ and Ga ₂ Se ₃ as separate evaporation sources.

According to a seventh aspect of the present invention, in the first aspect, vapor deposition is performed from a vapor deposition source of a solid solution of In, Ga, Se and S on the substrate.

According to an eighth aspect of the present invention, in the first aspect, at least three thin films of In, Ga, Se and S are stacked on the substrate, and the thin films are formed in a vacuum atmosphere, an inert gas atmosphere,
The heat treatment is performed in at least one of the Se atmosphere and the S atmosphere.

According to a ninth aspect of the present invention, in the first aspect, a thin film of In or Ga or a thin film of both of them is laminated on a substrate, and the thin film is formed in an S atmosphere or a Se atmosphere or
The heat treatment is performed in an atmosphere in which the two are combined.

According to a tenth aspect of the present invention, there is provided a solar cell having a semiconductor layer having a chalcopyrite structure, a buffer layer, and a transparent electrode layer on a substrate in that order.
_x Ga _1-x ) (Se _y S _1-y ) _z [where x and y are from 0 to
Is a value of 1 and z is a value of 1 to 1.5. ] It is characterized by having a semiconductor thin film mainly composed of a solid solution.

According to the eleventh invention, in the tenth invention,
The semiconductor layer having a chalcopyrite structure is made of CuInSe ₂ , C
u (In, Ga) Se ₂ , CuIn (S, Se) ₂ , C
u (In, Ga) (S , Se) is characterized by consisting of ₂ or CuInS _2.

According to a twelfth aspect of the present invention, in the tenth or eleventh aspect, the transparent electrode layer is made of ZnO or a semiconductor thin film obtained by doping ZnO with a Group IIIb element.

According to a thirteenth aspect, in the twelfth aspect,
It is characterized in that the group IIIb element is B or Al.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION
The compounds that make up the pyrite structure semiconductor layer are, for example,
For example, CuInSe_Two , CuInS_Two, Cu (In, G
a) Se_Two, CuIn (S, Se)_Two, Cu (In, G
a) (S, Se)_TwoOr Cu (In, Ga) S _Two Is raised
Is not limited to these compounds,
Other chalcopies as long as they meet the purpose of the present invention
It also includes a compound constituting a semiconductor layer having a light structure.

The absorption edge wavelength (nm) and band gap (eV) of the solid solution film of In ₂ (Se _1-x S _x ) ₃ of the present invention.
Are shown in Table 1 below, and the results of measuring their spectral transmittances are shown in FIG. Each film thickness is
4000 $.

[0023]

[Table 1]

From Table 1 and FIG. 1, it can be seen that the absorption edge wavelength shifts to the edge wavelength side as x increases, and the band gap increases. In a solar cell, when the band gap of the film increases, the number of photons incident on the pn junction interface increases, so that the current value increases and the conversion efficiency improves. Here, the wavelength at which Tr = 0.5 is the absorption edge wavelength, and the energy corresponding to this is the band gap. Each of these films shows n-type conductivity and a resistivity of 10 to 10 ⁴ Ω · cm, which is a property suitable for a buffer layer.

[0025]

【Example】

(Example 1) A CuInSe ₂ thin film formed on a soda lime glass substrate via a Mo thin film, and a substrate temperature of 100
~ 300 ° C and vacuum degree 10 ^-5 torr or less,
n, Se and S were simultaneously ternary deposited. At this time, the evaporation rates of these evaporation sources were set to In: 5 ° / s, Se: 10 °.
/ S and S; 5 ° / s, and vapor deposition was performed for about 2 minutes. As a result, the film thickness was about 500 °, and In: Se: S = 40: 5.
A 0:10 film was formed.

Example 2 A soda lime glass substrate was coated with M
oCuInSe formed via a thin film_Two On a thin film,
Plate temperature 100-300 ° C and degree of vacuum 10^-Fivebelow torr
Set to In _TwoSe_ThreeAnd S were simultaneously deposited in a binary manner.
At this time, the evaporation rate of these evaporation sources was set to In._TwoSe_Three; 5
Å / s and S; 5Å / s, vapor deposition for about 3 minutes
As a result, the film thickness was about 500 °, In: Se: S = 40: 5.
A 5: 5 film was formed.

(Embodiment 3) M is applied to a soda-lime glass substrate.
On the CuInSe ₂ thin film formed via the o thin film, In ₂ Se ₃ and Ga ₂ S ₃ were simultaneously vapor-deposited at a substrate temperature of 100 to 300 ° C. and a degree of vacuum of 10 ⁻⁵ torr or less. . At that time, the evaporation rate of these evaporation sources was set to In ₂ S
e ₃ ; 5 ° / s and Ga ₂ S ₃ ; 5 ° / s, about 4
Minutes, a film thickness of about 500 °, In: G
A film of a: Se: S = 30: 10: 50: 10 was formed.

Example 4 A bulk of (In, Ga) ₂ (Se, S) ₃ was prepared by inserting a simple substance of In, Ga, Se and S into a quartz tube and heating to 1200 ° C.
The bulk composition ratio is In: Ga: Se: S = 30: 1.
0:50:10. Then, a substrate temperature of 100 to 300 ° C. and a degree of vacuum of 10 ⁻⁵ torr are formed on a CuInSe ₂ thin film formed on a soda lime glass substrate via a Mo thin film.
The deposition was performed using the bulk as a deposition source under the following conditions. At this time, when the evaporation rate of the evaporation source was 10 ° / s and the evaporation was performed for about 2 minutes, the film thickness was about 500 °, and I
A film of n: Ga: Se: S = 30: 10: 50: 10 was formed.

(Embodiment 5) A soda-lime glass substrate was coated with M
o On a CuInSe ₂ thin film formed via a thin film, the substrate temperature is set to 100 to 300 ° C. and the degree of vacuum is set to 10 ⁻⁵ torr or less.
e; 500 ° and S; 200 °. When this was heat-treated at 300 ° C., a film thickness of about 5
00 °, a film of In: Se: S = 40: 50: 10 was formed.

(Embodiment 6) A soda-lime glass substrate was coated with M
On the CuInSe ₂ thin film formed via the o thin film, In is deposited at a substrate temperature of 100 to 300 ° C. and a degree of vacuum of 10 ⁻⁵ torr or less, and In is deposited to a thickness of 200 °, and then Se and S Was co-evaporated. At this time, the evaporation rates of the deposition sources of Se and S are set to Se; 5 ° / s and S; 5 ° / s.
And when vapor deposition was performed for about 3 minutes,
A film of In: Se: S = 40: 50: 10 was formed.

(Example 7) On a glass substrate having a thickness of about 1 mm
Then, Mo was formed to a thickness of 1.0 μm by sputtering as an electrode.
Then, Cu, In and Se are ternarily deposited on the Mo thin film.
When deposited, CuInSe_TwoDeposits a thin film about 2μm thick
did. Furthermore, this CuInSe_TwoOn the thin film, In and
By the simultaneous binary deposition of Se, the InSe thin film is reduced to about 0.2.
μm thick, and subsequently, a film is formed on the InSe thin film.
ZnO: Al [2 to 3% by weight of Al in ZnO]
(Hereinafter referred to as “wt%”).
A film was formed to a thickness of 1.0 μm. Solar cell solar cell obtained
0.1W / cm by simulator ^Two Under light irradiation
When the energy conversion efficiency was measured, the energy conversion
The conversion efficiency was 9.3%.

(Embodiment 8) On a glass substrate having a thickness of about 1 mm, Mo was formed as a back electrode to a thickness of 1.0 μm by sputtering, and Cu, In, Ga and S were formed on the Mo thin film.
e is quaternary deposited to obtain CuIn _0.75 Ga _0.25 Se ₂
A thin film was formed to a thickness of about 2 μm. Furthermore, this CuIn
_{On the 0.75} Ga _0.25 Se ₂ thin film, an In ₂ S ₃ thin film is vacuum-deposited to form an InS thin film with a thickness of about 0.2 μm. Then, Zn is deposited on the InS thin film by sputtering.
O: Al (ZnO doped with 2 to 3 wt% of Al) was formed to a thickness of about 1.0 μm. When the energy conversion efficiency of the obtained solar cell under irradiation of light of 0.1 W / cm ² by a solar simulator was measured, the energy conversion efficiency was 9.6%.

Example 9 On a glass substrate having a thickness of about 1 mm
Then, Mo was formed to a thickness of 1.0 μm by sputtering as an electrode.
Then, on this Mo thin film, a Cu thin film and a
And In thin films to a thickness of 0.2 μm and 0.5 μm, respectively.
Continuous lamination film formation, and this laminate is put in a sulfur atmosphere
Heat treatment at 550 ° C for 1 hour_Two Thin film
Was formed to a thickness of about 2 μm. Furthermore, this CuInS_Two Thin
On the film, In, S and Se are ternary deposited to form In
_Two(S, Se)_ThreeA thin film is formed to a thickness of about 0.2 μm,
This In _Two On the (S, Se) thin film, Z
nO: Al (ZnO doped with 2-3 wt% of Al
Was formed to a thickness of about 1.0 μm. Of the obtained solar cell
0.1W / cm by solar simulator^Two Light irradiation of
When measuring the energy conversion efficiency below, the energy
The energy conversion efficiency was 6.1%.

Example 10 Mo was deposited as a back electrode to a thickness of 1.0 μm on a glass substrate having a thickness of about 1 mm by sputtering, and Cu, In and Se were deposited on the Mo thin film in a thickness of 3 μm.
The CuInSe ₂ thin film was formed to a thickness of about 2 μm by simultaneous vapor deposition. Further, Ga on the CuInSe ₂ thin film
By vacuum vapor deposition of ₂ Se ₃ , a GaSe thin film is formed to a thickness of about 0.2 μm, and then ZnO: Al (2 to 3 wt.
% Doped) to a thickness of about 1.0 μm. 0.1 W / of the obtained solar cell by a solar simulator
When the energy conversion efficiency under irradiation with light of cm ² was measured, the energy conversion efficiency was 9.1%.

(Conventional Example 1) Mo was formed as a back electrode to a thickness of 1.0 μm on a glass substrate having a thickness of about 1 mm by sputtering, and Cu, In and Se were deposited on the Mo thin film in a thickness of 3 μm.
The CuInSe ₂ thin film was formed to a thickness of about 2 μm by simultaneous vapor deposition. Further, a CdS thin film is formed to a thickness of about 0.4 μm on the CuInSe ₂ thin film by a vacuum evaporation method.
On this CdS thin film, ZnO: Al (ZnO
Doped with 2-3 wt% of Al) to about 1.0 μm
A thick film was formed. When the energy conversion efficiency of the obtained solar cell under irradiation of light of 0.1 W / cm ² by a solar simulator was measured, the energy conversion efficiency was:
It was 9.0%.

(Conventional Example 2) Mo was formed as a back electrode to a thickness of 1.0 μm on a glass substrate having a thickness of about 1 mm by a sputtering method, and Cu, In, Ga and S were formed on the Mo thin film.
e is quaternary deposited to obtain CuIn _0.75 Ga _0.25 Se ₂
A thin film was formed to a thickness of about 2 μm. Furthermore, this CuIn
_A CdS thin film is formed in a thickness of about 0.4 μm on a _0.75 Ga _0.25 Se ₂ thin film by a vacuum evaporation method, and then ZnO: Al (AlO is added to ZnO: 2 to 3) on the CdS thin film by a sputtering method.
wt.% doped) to a thickness of about 1.0 μm.
0.1 of the obtained solar cell was measured using a solar simulator.
When the energy conversion efficiency under irradiation with light of W / cm ² was measured, the energy conversion efficiency was 9.5%.

(Conventional Example 3) Mo was formed as a electrode to a thickness of 1.0 μm on a glass substrate having a thickness of about 1 mm by a sputtering method, and a Cu thin film and an In thin film were formed on the Mo thin film by a vacuum evaporation method. Each layer was continuously formed into a layer having a thickness of 0.2 μm and a layer having a thickness of 0.5 μm, and the layered body was heated in a sulfur atmosphere at 550 ° C. for 1 hour to form a CuInS ₂ thin film having a thickness of about 2 μm. Further, a CdS thin film is formed to a thickness of about 0.4 μm on the CuInS ₂ thin film by a vacuum evaporation method, and then Zn is formed on the CdS thin film by a sputtering method.
O: Al (ZnO doped with 2 to 3 wt% of Al) was formed to a thickness of about 1.0 μm. When the energy conversion efficiency of the obtained solar cell under irradiation of light of 0.1 W / cm ² by a solar simulator was measured, the energy conversion efficiency was 6.0%.

As described above, according to the structure of the present invention, a p-type semiconductor thin film having a chalcopyrite type crystal structure, for example, CuInSe ₂ , Cu (In, Ga) Se
₂ , a thin film of CuInS ₂ or the like, as a buffer layer, containing no Cd instead of the conventional CdS thin film, (In _x G
a _1-x ) (Se _y S _1-y ) _z [where x and y are from 0 to 1
And z is a value from 1 to 1.5. ]
By contacting a semiconductor thin film mainly composed of a solid solution and further contacting this thin film with, for example, a ZnO: Al thin film, a solar cell which is non-polluting and exhibits the same energy conversion efficiency as when using a conventional CdS thin film Is obtained.

[0039]

As described above, it is possible to provide a semiconductor thin film having high light collection efficiency without discharging harmful Cd waste, a method of manufacturing the same, and a thin film solar cell using the same. And since each thin film can be formed in the same vacuum apparatus, there is great industrial merit.

[Brief description of the drawings]

FIG. 1 is a diagram showing the spectral transmittance of an In ₂ (Se _1-x S _x ) ₃ solid solution thin film of the present invention.

FIG. 2 is a schematic cross-sectional explanatory view of a conventional chalcopyrite solar cell.

[Explanation of symbols]

Reference Signs List 1 glass substrate 2 Mo film 3 CuInSe ₂ film 4 CdS film 5 ZnO film

Claims (13)

[Claims] (1) (In _x Ga _1-x ) (Se _y S _1-y ) _{z wherein} x and y are 0 to 1 and z is 1
１．５1.5. ] A semiconductor thin film mainly comprising a solid solution. 2. The method according to claim 1, wherein at least two elements of In, Ga, Se and S are simultaneously deposited on the substrate as separate deposition sources. 3. A method of simultaneously depositing In, Ga, Se and S on a substrate by using a compound containing two or more of these elements and a simple substance of each of these elements as separate evaporation sources. A method for manufacturing a semiconductor thin film according to claim 1. 4. An In _x S _{1 -x}
4. The method according to claim 3, wherein (x is a value of 0 to 1), and Ga, Se and S are simultaneously deposited as separate deposition sources. 5. The method of manufacturing a semiconductor thin film according to claim 1, wherein In, Ga, Se and S are simultaneously vapor-deposited on the substrate by using a compound containing two or more of them as separate vapor deposition sources. Method. 6. In, Ga, Se and S are represented by In ₂ Se ₃
And Ga and ₂ Se ₃ as separate deposition source, a method of manufacturing a semiconductor thin film according to claim 5, characterized in that the simultaneously deposited. 7. The method for producing a semiconductor thin film according to claim 1, wherein the vapor deposition is performed from a vapor deposition source of a solid solution of In, Ga, Se and S on the substrate. 8. At least three thin films of In, Ga, Se and S are stacked on a substrate, and the thin films are formed in a vacuum atmosphere.
2. The method according to claim 1, wherein the heat treatment is performed in at least one of an inert gas atmosphere, a Se atmosphere, and an S atmosphere. 9. A thin film of In or Ga on a substrate, or
Both of these thin films are laminated, and this is called S atmosphere or S atmosphere.
2. The method according to claim 1, wherein the heat treatment is performed in an e atmosphere or an atmosphere in which the two are combined. 10. A solar cell having a semiconductor layer having a chalcopyrite structure, a buffer layer, and a transparent electrode layer in that order on a substrate, wherein the buffer layer comprises (In _x Ga _{1 -x} )
(Se _y S _1-y ) _z [where x and y are values from 0 to 1, and z is a value from 1 to 1.5. ] A solar cell comprising a semiconductor thin film mainly composed of a solid solution. 11. A semiconductor layer having a chalcopyrite structure comprising C
uInSe ₂ , CuInS ₂ , Cu (In, Ga) S
e ₂ , CuIn (S, Se) ₂ , Cu (In, Ga)
(S, Se) ₂ or Cu (In, Ga) solar cell according to claim 10, wherein a formed of S _2. 12. The transparent electrode layer is made of ZnO or ZnO.
The solar cell according to claim 10, comprising a semiconductor thin film doped with a group Ib element. 13. The solar cell according to claim 12, wherein the group IIIb element is B or Al.