JPH0888379A - Chalcopyrite type compound thin film solar battery - Google Patents

Abstract

PURPOSE: To restrain recombination in a heterojunction interface and to improve an open voltage by forming an intermediate layer consisting of a specified chalcopyrite type compound between a p-type chalcopyrite type compound layer and an n-type compound semiconductor layer. CONSTITUTION: A p-type chalcopyrite type compound layer 3 consisting of a group Ib element, a group IIIb element and a chalcogen element and an n-type compound semiconductor layer 5 consisting of a group IIb element and a group VIb element are provided on a substrate 1. An intermediate layer 4 consisting of a chalcopyrite type compound whose mole ratio of a group Ib element to a group Wb element is small when compared to a p-type chalcopyrite type compound is formed between the p-type chalcopyrite type compound layer 3 and the n-type compound semiconductor layer 5. Thereby, recombination caused between the p-type chalcopyrite compound layer 3 and the n-type compound semiconductor layer 5 can be restrained, thus improving an open voltage. High photoelectric conversion efficiency can be obtained in this way.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solar cell using a chalcopyrite type compound thin film.

[0002]

2. Description of the Related Art Chalcopyrite type compounds are materials expected to be applied to solar cells, light emitting devices and the like. In particular,
Since CuInSe ₂ , CuGaSe ₂ , CuInS ₂ and their mixed crystal compounds are direct transition type, they have a large optical absorption coefficient and their band gaps match the solar spectrum, so they are applied as solar cell materials. Is expected. As the structure of the solar cell, a Mo electrode layer is formed on a glass substrate, and p-type CuInS is formed on the Mo electrode layer.
stacking compound semiconductors such as e ₂ or CuInS ₂ ,
Then, Cd _x Zn _1-x S (0 ≦ x ≦ 1), Z
An n-type semiconductor having a wide optical band gap such as nSe or ZnO is stacked, and Al-doped ZnO or Sn-doped In is further stacked.
It is known that a transparent electrode such as ₂ O ₃ is formed.

However, the solar cells having these structures have the following problems. Due to the heterojunction of two different semiconductors, there are defect levels at the junction interface.
The holes of p-type CuInSe ₂ and the electrons of n-type CdS are recombined via the defect level. Therefore, the open circuit voltage is lowered, and further the conversion efficiency is lowered.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a solar cell having high conversion efficiency by suppressing recombination at the heterojunction interface and improving open circuit voltage.

[0005]

In such a situation,
As a result of intensive studies to solve the above problems, the present inventors have found that a p-type chalcopyrite-type compound layer and an n-type II
When a chalcopyrite type compound layer having a smaller molar ratio of the group Ib element to the group IIIb element than the p-type chalcopyrite compound, that is, a hole density lower than that of the p-type chalcopyrite compound, is inserted between the group b element-containing compound semiconductor layer and the p-type chalcopyrite compound. The inventors have found that recombination is reduced and have completed the present invention.

That is, the present invention is as follows. 1. A p-type chalcopyrite type compound layer composed of an Ib group element, a IIIb group element and a chalcogen element (S, Se and Te) of the Periodic Table of Elements, and an n type compound semiconductor layer composed of a IIb group element and a VIb group element In the thin-film solar cell having, the mol of the lb group element relative to the IIIb group element between the p-type chalcopyrite-type compound layer and the n-type compound semiconductor layer is higher than that of the p-type chalcopyrite-type compound. A thin-film solar cell, wherein an intermediate layer made of a chalcopyrite type compound having a small ratio is formed. 2. 2. The thin-film solar cell according to the above 1, wherein the chalcopyrite type compound formed as the intermediate layer is an n-type semiconductor. 3. The band gap of the chalcopyrite type compound formed as the intermediate layer is larger than the band gap of the p type chalcopyrite type compound, and the IIb group element and V
The thin film solar cell according to the above 1, wherein the band gap is smaller than that of an n-type compound semiconductor layer made of an Ib group element. 4. The p-type chalcopyrite type compound is CuInS ₂ ; 5. Compared to the p-type chalcopyrite-type compound layer and the chalcopyrite-type compound, I for the group IIIb element
In a method for producing a laminated film including a chalcopyrite type compound layer having a small molar ratio of a b-group element, after forming a p-type chalcopyrite type compound layer, the p-type chalcopyrite is formed at a temperature lower than the formation temperature. A method for producing a chalcopyrite type compound laminated film, comprising forming a chalcopyrite type compound layer as an intermediate layer by reducing a molar ratio of a group Ib element to a group IIIb element as compared with a type compound. 6. p-type and CuInS ₂ layer of a method for manufacturing a laminated film molar ratio of Group Ib element to the Group IIIb element in comparison with the CuInS ₂ is composed of a small chalcopyrite-type compound layer, the CuInS ₂ layer of the p-type 450 ~ 600
After the formation in the range of ° C, the molar ratio of the group Ib element to the group IIIb element is made smaller than that of the p-type CuInS ₂ layer to form a chalcopyrite type compound layer as an intermediate layer in the range of 300 to 450 ° C. A method for producing a chalcopyrite type compound laminated film, which is characterized in that the film is formed.

The thin film solar cell according to the present invention has the structure shown in FIG. 0.5 ~ 2μ film thickness on the substrate 1 such as glass
m conductive film 2 such as Mo is formed, and 1-3 μm is formed on the conductive thin film 2.
m p-type chalcopyrite compound layer 3 is further formed, and a chalcopyrite compound layer 4 as an intermediate layer having a thickness of 5 to 1000 nm is further formed thereon, and a layer having a thickness of 5 to 1000 nm is formed thereon.
N-type semiconductor layer 5 such as CdS and Zn of 0.1 to 2 μm
By sequentially forming the transparent electrode layer 6 such as O: Al,
Thin film solar cells are fabricated.

The chalcopyrite compound in the present invention means an element of Group Ib of the Periodic Table of Elements such as Cu and Ag and Al,
Group IIIb elements of the periodic table of elements such as Ga and In, and S,
Compounds composed of chalcogen elements such as Se and Te and having a chalcopyrite (chalcopyrite) type structure are collectively referred to as CuInS ₂ , AgInS ₂ , CuInSe ₂ , C
uGaSe ₂ , AgInSe ₂ , AgGaSe ₂ , Cu
InTe ₂ , CuGaTe ₂ , AgInTe ₂ , AgG
aTe ₂ or a solid solution thereof has an appropriate band gap and is preferable as a material for a thin film solar cell.

The p-type chalcopyrite compound of the present invention is not particularly limited as long as its conductivity type is p-type.
The molar ratio of the group Ib element to the group IIb element is 0.9 to
It is preferably in the range of 1.2. The chalcopyrite type compound as the intermediate layer is not particularly limited as long as the molar ratio of the group Ib element to the group IIIb element is smaller than that of the p type chalcopyrite type compound.
It is preferably in the range of 0.6 to 1.0, and more preferably the conductivity type is n type. Furthermore, for example, the p-type chalcopyrite-type compound is CuI.
In the case of nS ₂ , Cu (In, Ga) S _{2 is used} as the intermediate layer.
It is preferable to use a compound having a large band gap, such as the above because the effect of the present invention is large. However, the band gap of the intermediate layer in this case needs to be in a range not larger than the band gap of the IIb group element-containing compound. According to the present invention, the holes of the p-type chalcopyrite compound layer and the electrons of the IIb-group element-containing semiconductor layer can be spatially separated by inserting the intermediate layer. Recombination at the bonding interface of the semiconductor layers can be suppressed, and good characteristics are exhibited in thin film solar cells.

As a method of forming the chalcopyrite type compound thin film of the p-type layer and the intermediate layer, any method such as a sputtering method, a vacuum deposition method, a MOCVD method or a chalcogenization method can be used. For example, p-type CuInS ₂ is formed by a vacuum vapor deposition method using Cu, In, and S as separate evaporation sources.
This can be carried out by forming a layer, then reducing the supply amount of Cu, and similarly forming an intermediate CuInS ₂ layer.

The temperature for forming the p-type chalcopyrite compound layer and the intermediate layer is not particularly limited as long as it is a temperature at which the chalcopyrite compound is formed, but is preferably 300 ° C. or higher from the viewpoint of crystallinity. When forming a thin film on an inexpensive substrate such as soda lime glass, the temperature is preferably 600 ° C. or lower in consideration of the properties of glass.
Furthermore, by setting the formation temperature of the intermediate layer lower than the formation temperature of the p-type chalcopyrite compound layer, mutual diffusion of elements at the interface between the two is suppressed, and a sharp composition change can be realized. It is considered that the steeper the compositional change, the more effectively the electrons and holes are spatially separated, and the greater the effect of the intermediate layer. For example, in the case of CuInS ₂ , the p-type CuInS ₂ layer, which is a light absorption layer, has high crystallinity, and therefore the formation temperature thereof is preferably in the range of 450 to 600 ° C., more preferably 500 to 550 ° C. Is the range.
550 ° C. is a temperature sufficiently lower than the temperature at which the soda lime glass substrate is distorted. Further, the formation temperature of the intermediate layer laminated on the p-type CuInS ₂ layer is preferably in the range of 300 to 450 ° C., but more preferably in the range of 400 to 450 ° C. from the viewpoint of crystallinity.

[0012]

EXAMPLES Examples of the present invention will be specifically described below.

[0013]

[Example 1] 1 μm on a glass substrate by sputtering
Mo electrode is formed, and then the Cu / In molar ratio is 1.0 by the vacuum co-evaporation method using Cu, In, and S as evaporation sources.
Of the p-type CuInS ₂ layer of Cu / Cu at the substrate temperature of 550 ° C.
CuInS ₂ as an intermediate layer having an In molar ratio of 0.9
The layers were sequentially formed at a substrate temperature of 425 ° C. Further, an n-type CdS layer is further formed thereon by a solution growth method to a thickness of 50 nm and Zn.
A thin film solar cell having the same structure as that of FIG. 1 was produced by sequentially forming an O: Al transparent electrode with a thickness of 2 μm by a sputtering method. The p-type CuInS ₂ layer has a thickness of about 2 μm, and the intermediate CuInS ₂ layer has a thickness of 5 nm to 1000 n.
It was changed in the range of m. The conductivity type of the intermediate layer was a high resistance p-type.

The characteristics of the solar cell element were evaluated by irradiating it with light of AM 1.5. The open circuit voltage increased as the film thickness of the intermediate layer increased, and was almost saturated at a film thickness of about 300 nm. Also, the fill factor is as the thickness of the intermediate layer increases,
It increases due to the suppression of interfacial leakage current.
When the thickness is more than 00 nm, the series resistance component becomes large and conversely tends to decrease. When the 500 nm intermediate layer was formed, the conversion efficiency reached the maximum and was 10.8%.

[0015]

[Example 2] 1 μm on a glass substrate by sputtering
Mo electrode is formed, and then the Cu / In molar ratio is 1.0 by the vacuum co-evaporation method using Cu, In, and S as evaporation sources.
P-type CuInS ₂ layer of Cu / I at a substrate temperature of 550 ° C.
A CuInS ₂ layer as an intermediate layer having an n molar ratio of 0.7 was sequentially formed at a substrate temperature of 425 ° C. Further, an n-type CdS layer is further formed thereon by a solution growth method to a thickness of 50 nm and Zn.
A thin film solar cell having the same structure as that of FIG. 1 was produced by sequentially forming an O: Al transparent electrode with a thickness of 2 μm by a sputtering method. The p-type CuInS ₂ layer has a thickness of about 2 μm, and the intermediate CuInS ₂ layer has a thickness of 5 nm to 1000 nm.
Was changed in the range. The conductivity type of the intermediate layer was n-type.

The characteristics of the solar cell element were evaluated by irradiating it with light of AM 1.5. The open circuit voltage increased as the film thickness of the intermediate layer increased, and was almost saturated at a film thickness of about 100 nm. Also, the fill factor is as the thickness of the intermediate layer increases,
Increased due to the suppression of interfacial leakage current.
When the thickness is more than 00 nm, the series resistance component becomes large and conversely tends to decrease. When the 200 nm intermediate layer was formed, the conversion efficiency reached its maximum and was 11.5%.

[0017]

[Example 3] 1 μm on a glass substrate by sputtering
Mo electrode is formed, and then the Cu / In molar ratio is 1.0 by the vacuum co-evaporation method using Cu, In, and S as evaporation sources.
Of p-type CuInS ₂ layer of Cu, I at a substrate temperature of 550 ° C.
Cu / Cu by the vacuum evaporation method using n, Ga, and S as evaporation sources.
A Cu (In, Ga) S ₂ layer as an intermediate layer having an (In + Ga) molar ratio of 0.7 and a Ga / In molar ratio of 0.2 was sequentially formed at a substrate temperature of 425 ° C. Further, an n-type CdS layer is further formed thereon by a solution growth method to a thickness of 50 nm and Zn.
A thin film solar cell having the same structure as that of FIG. 1 was produced by sequentially forming an O: Al transparent electrode with a thickness of 2 μm by a sputtering method. The p-type CuInS ₂ layer has a thickness of about 2 μm, and the intermediate layer Cu (In, Ga) S ₂ layer has a thickness of 5 nm to 1 nm.
It was changed in the range of 000 nm. The conductivity type of the intermediate layer was n-type.

The characteristics of the solar cell element were evaluated by irradiating it with light of AM 1.5. The open circuit voltage increased as the film thickness of the intermediate layer increased, and was almost saturated at a film thickness of about 50 nm. Further, the fill factor increases as the film thickness of the intermediate layer increases, because the interface leak current is suppressed.
When it was 0 nm or more, the series resistance component increased, and on the contrary, it tended to decrease. Further, the short-circuit current tended to decrease slightly as the film thickness of the intermediate layer having a large band gap increased. When the 100 nm intermediate layer was formed, the conversion efficiency reached the maximum and was 12.0%.

[0019]

[Comparative Example 1] 1 μm on a glass substrate by sputtering
Mo electrode is formed, and then the Cu / In molar ratio is 1.0 by the vacuum co-evaporation method using Cu, In, and S as evaporation sources.
The p-type CuInS ₂ layer was formed at a substrate temperature of 550 ° C. to a thickness of about 2 μm. Further, an n-type CdS layer having a thickness of 50 nm and a ZnO: Al transparent electrode having a thickness of 2 μm were sequentially formed on the n-type CdS layer by a solution growth method to form a thin film solar cell having the structure shown in FIG. A for this solar cell element
When the characteristics were evaluated by irradiation with M1.5 light, the conversion efficiency was 8.0%.

[0020]

[Example 4] 1 μm on a glass substrate by sputtering
Mo electrode was formed, and then the Cu / In molar ratio was 1. by the vacuum co-evaporation method using Cu, In, and Se as evaporation sources.
0 p-type CuInSe ₂ layer at a substrate temperature of 550 ° C.
/ In molar ratio of 0.7 CuInS as an intermediate layer
The e ₂ layer was sequentially formed at a substrate temperature of 425 ° C. Further, an n-type CdS layer is further formed thereon by a solution growth method at 50 nm, Z
A thin film solar cell having the same structure as in FIG. 1 was produced by sequentially forming nO: Al transparent electrodes with a thickness of 2 μm by a sputtering method. The thickness of the p-type CuInSe ₂ layer is about 2 μm, and the thickness of the intermediate layer CuInSe ₂ layer is 5 nm to 100 nm.
It was changed in the range of 0 nm. The conductivity type of the intermediate layer is n.
It was a mold.

The characteristics of the solar cell element were evaluated by irradiating it with light of AM 1.5. The open circuit voltage increased as the film thickness of the intermediate layer increased, and was almost saturated at a film thickness of about 200 nm. Also, the fill factor is as the thickness of the intermediate layer increases,
It increases by suppressing the interface leak current, but
When the thickness is more than 00 nm, the series resistance component becomes large and conversely tends to decrease. When the 250 nm intermediate layer was formed, the conversion efficiency reached the maximum and was 13.0%.

[0022]

Comparative Example 2 1 μm on a glass substrate by sputtering method
Mo electrode was formed, and then the Cu / In molar ratio was 1. by the vacuum co-evaporation method using Cu, In, and Se as evaporation sources.
0 p-type CuInSe ₂ layer of 2 μm at a substrate temperature of 550 ° C.
Formed to a degree. Further, an n-type CdS layer having a thickness of 50 nm and a ZnO: Al transparent electrode having a thickness of 2 μm were sequentially formed on the n-type CdS layer by a solution growth method to form a thin film solar cell having the structure shown in FIG. When the characteristics of this solar cell element were irradiated with light of AM1.5, the conversion efficiency was 11.5%.

[0023]

According to the present invention, the open circuit voltage can be improved and a solar cell with high conversion efficiency can be provided, which is very useful.

[Brief description of drawings]

FIG. 1 is an explanatory sectional view showing an example of an element structure of a solar cell using a chalcopyrite type compound layer of the present invention.

FIG. 2 is an explanatory cross-sectional view showing an example of a device structure of a solar cell using a conventional chalcopyrite type compound layer.

[Explanation of symbols]

 1. Substrate 2. Conductive thin film 3. 3. P-type chalcopyrite compound layer 4. Chalcopyrite compound intermediate layer 5. n-type semiconductor layer 6. Transparent electrode layer

Claims (6)

[Claims] 1. A p-type chalcopyrite type compound layer composed of an Ib group element, a IIIb group element and a chalcogen element (S, Se and Te) of the Periodic Table of Elements, and an n type composed of a IIb group element and a VIb group element. In a thin film solar cell having the compound semiconductor layer of p.
A thin-film solar cell, wherein an intermediate layer made of a chalcopyrite type compound having a smaller molar ratio of the group Ib element to the group IIIb element than that of the type chalcopyrite type compound is formed. 2. The thin film solar cell according to claim 1, wherein the chalcopyrite type compound formed as the intermediate layer is an n-type semiconductor. 3. The band gap of the chalcopyrite-type compound formed as the intermediate layer is larger than the band gap of the p-type chalcopyrite-type compound, and the band of the n-type compound semiconductor layer composed of the IIb group element and the VIb group element. It is smaller than a gap, The thin film solar cell of Claim 1 characterized by the above-mentioned. 4. The p-type chalcopyrite compound is CuI.
thin-film solar cell of claim 1, 2 or 3, wherein the a nS _2. 5. A p-type chalcopyrite type compound layer,
In a method for producing a laminated film comprising a chalcopyrite type compound layer having a smaller molar ratio of the Ib group element to the IIIb group element than the chalcopyrite type compound, after forming a p type chalcopyrite type compound layer, A chalcopyrite-type compound layer as an intermediate layer is formed at a temperature lower than the formation temperature to reduce the molar ratio of the group Ib element to the group IIIb element as compared with the p-type chalcopyrite type compound. A method for producing a chalcopyrite type compound laminated film. 6. A p-type CuInS ₂ layer and the CuInS
_{In the} method for producing a laminated film comprising a chalcopyrite type compound layer in which the molar ratio of the group Ib element to the group IIIb element is smaller than that of ₂ , the p-type CuInS ₂ layer is
After forming in the range of 0 to 600 ° C., the p-type CuIn
A chalcopyrite-type compound laminate, characterized by forming a chalcopyrite-type compound layer as an intermediate layer in the range of 300 to 450 ° C. by reducing the molar ratio of the Ib-group element to the IIIb-group element as compared with the S ₂ layer. Membrane fabrication method.