JPH1074967A - Thin-film solar cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a thin-film solar cell, used as a light absorbing layer having a proper carrier concentration by forming a p-type compound semiconductor thin film, containing Ib group element, III group element and VIb group element in a range where the ratio of Ib group element to III group element has a particular value. SOLUTION: An Mo film 11 is formed on a blue plate glass substrate 10. On this film, Na is added together with Cu vapor deposition in the first half of the film formation, in the last half of the film formation, a p-type Cu (In1-x Gax )3 Se5 film 12 is formed by creating no Cu state or an insufficient state for Cu, without adding Na. By doing this, Cu/(In+Ga) is in the ronge of more than 0.22 but less than 0.75. Thereafter, the surface of p-type Cu (In1-x Gax )3 Se5 film 12 is washed, a CdS film of a high resistance n-type buffer layer 13 is formed, moreover, ZnO:Al film 14 of the transparent conductive film is formed, by doing this, a thin-film solar cell having a p-type CIS-based material in a new range of composition as a light-absorbing layer can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a solar cell using a thin film of a CIS material represented by CuInSe ₂ for a light absorbing layer.

[0002]

2. Description of the Related Art A p-type CI is used as an inexpensive thin-film solar cell.
Development of a thin film solar cell using an S-based thin film as a light absorbing layer has been performed.

In recent years, among solar cells using CIS-based thin films, those using soda glass as a substrate have been reported to exhibit high energy conversion efficiency.
Studies have been conducted to introduce element a into CIS-based thin films.

[0004] For example, Japanese Patent Application Laid-Open No. Hei 8-102546 discloses a semiconductor thin film in which a compound comprising a group Ia and a group VIa element is simultaneously deposited when depositing a compound semiconductor thin film comprising a group Ib group, a group IIIa and a group VIa element. And a solar cell using a semiconductor thin film formed by alternately depositing at least two or more compound semiconductor thin films composed of a group Ib group, a IIIa group and a VIa element, and a compound thin film composed of a group Ia and a VIa group element. It has been disclosed.

[0005]

However, in a conventional solar cell using a CIS-based thin film, the conversion efficiency greatly depends on the composition of the CIS-based thin film, and the range in which high efficiency can be obtained depends on the composition CuIn _y Se. in _z Cu / (in + G
a) is about 0.85 to 0.95, that is, 1.05 ≦ y
It was limited to a narrow composition range of about ≦ 1.18. This is because, if the y composition deviates from this range, the carrier concentration sharply decreases and further becomes n-type, so that a pn junction cannot be formed.

[0006] CuIn _y Se _z has a bandgap of about 1.04 eV.
By the u (an In 1 _{over x} Ga _{x) y} Se _z, it is known that can be brought close to the band gap 1.4 corresponding to the wavelength of the sunlight. However, when the x composition is increased, a solar cell with high conversion efficiency cannot be obtained due to the deterioration of crystallinity, so that there is a problem that the x composition must be suppressed to 0.25 to 0.35. Therefore, the conventional C
In an IS-based thin film solar cell, the forbidden band width of the light absorbing layer is set to 1.2.
It could not be made larger than eV.

An object of the present invention is to provide a method for manufacturing a solar cell using a p-type CIS-based material having a novel composition, which could not be used conventionally, as a light absorbing layer.

[0008]

In order to achieve the above object, according to the present invention, the following solar cell is provided.

That is, the light absorbing layer includes a p-type compound semiconductor thin film containing a group Ib element, a group III element, and a group VIb element, wherein the compound semiconductor thin film is doped with a group Ia element. The ratio of the group Ib element to the group III element contained in the compound semiconductor thin film is 0.22 or more and 0.75 or more.
It is a thin film solar cell characterized by the following.

[0010]

An embodiment of the present invention will be described with reference to the drawings.

The inventors fixed the z composition and the x composition and changed the y composition to form a Cu (In _{1 -x} Ga _x ) _y Se _z film by using a film formation method to add Na described later. Was prepared and its characteristics were measured. As a result, as shown in FIG. 10, even in the composition of Cu / (In + Ga) ≦ 0.75, that is, 1.33 ≦ y, which was conventionally unsuitable as a light absorption layer of a solar cell due to a low carrier concentration, 10 ¹⁶ to 10 ¹⁷ c
It was found that the carrier concentration was suitable as a solar cell material of about m ⁻³ . The measurement of the thermoelectromotive force also revealed that in this composition region, n-type conduction was conventionally performed, but the addition of Na inverts to p-type conduction. Although the reason for the reversal of the conductivity type from n-type to p-type due to the addition of Na is not clear at present, trivalent I which forms a crystal lattice is present.
It is considered that n was substituted by monovalent Na and an acceptor was generated.

In the composition range of Cu / (In + Ga) ≦ 0.75, that is, 1.33 ≦ y, as shown in the pseudo binary phase diagram of FIG. 5, a defect pseudo chalcopyrite type structure CuIn ₃ S
e ₅ crystal phase (beta-phase in Fig. 5) has been known to exist. Therefore, the Cu obtained by the film forming method of the present invention
(An In _{1 over x} Ga x) _y Se _z film Cu / (In + Ga) ≦ 0.
It is considered that at least 75, that is, a composition range of 1.33 ≦ y contains at least the CuIn ₃ Se ₅ crystal phase. Therefore, the X-ray diffraction, the film formation was Cu (an In _{1 over} x Ga _x) which is obtained by the process _y Se _z film of the present invention (Cu / (In + Ga)
= 0.5), a diffraction peak peculiar to the defect pseudo chalcopyrite structure was observed as shown by a black circle in FIG. 4, and it was confirmed that a CuIn ₃ Se ₅ crystal phase was present.

The uniform band width of the CuIn ₃ Se ₅ crystal is as follows:
1.3 eV, and CuInSe ₂
The bandgap is 0.2 eV wider than that of the system, and the matching with the solar spectrum is improved, which is advantageous for realizing a high-efficiency solar cell.

As described above, by using the film formation method of adding Na according to the present invention, Cu (In _{1 -Cu) having} a composition which could not be used as a layer as a light absorbing layer because the carrier concentration was extremely low conventionally. It has become possible to obtain a thin film solar cell using the _x Ga _x ) _y Se _z film as a p-type light absorbing layer having an appropriate carrier concentration. Therefore, the composition of the light absorbing layer of the thin film solar cell of the present invention is represented by C in the phase diagram of FIG.
This is the range where uIn ₃ Se ₅ crystals are formed, and Cu / (I
n + Ga) is in the range of 0.22 or more and 0.75 or less, that is, 1.33 ≦ y ≦ 4.5. Particularly preferably, C
This is a range where only uIn ₃ Se ₅ crystal is formed, and Cu /
(In + Ga) is in the range of 0.28 to 0.52, that is, 1.92 ≦ y ≦ 3.57. In addition, Cu /
The range of Se is 0.2 or more and 0.5 or less, that is, 2 ≦ z ≦ 5.

Here, Cu to which Na according to the present invention is added is used.
(An In _{1 over x} Ga x) _y Se _z film (hereinafter, also referred to as CIGS film)
A method for forming a film will be described.

In this embodiment, the film is formed by using a multi-source vacuum evaporation method. Cu, In, Ga, S as an evaporation source
Na ₂ Se is used as each e source and the Na source. The CIGS film is formed by controlling the temporal change of the evaporation amount of each evaporation source as shown in any of FIGS.

That is, when a CIGS film is formed, the film formation time for obtaining a required film thickness is divided into two stages, a first half and a second half, and the first half is made to have an excess of Cu (Cu / (In + Ga)> 1). , Na ₂ Se is evaporated. On the other hand, in the latter half, Cu is less than in the first half, and Na ₂ Se is not evaporated. The evaporation amount of Se is kept constant throughout the first half. In the present embodiment, Se / (Cu + In + G
a) was 2-3.

Specifically, a CIGS film, ie, Cu
Is determined in advance of (an In _{1 over x} Ga x) _y Se _z composition xyz which is an object of the film, Cu evaporation required the composition of Cu (an In _{1 over x} Ga x) _y Se _z film in order to obtain by evaporation Amount, In evaporation amount,
The Ga evaporation amount and the Se evaporation amount are obtained in advance by calculation or experiment according to the adhesion rate of each element to the substrate.

Then, actually, Cu (In _1−x Ga _x ) _y S
When the _ez film is formed, for example, when the control method of FIG. 8 is used, the above-described C
In the latter half, the amount of Cu evaporated is controlled so as to evaporate less Cu than the previously determined amount of Cu evaporation, and the amount of C deposited as a result on the substrate is determined.
u (an In 1 _{over x} Ga _{x) y} Se _z film is to such that the predetermined composition.

In the case of the control method shown in FIG.
All of the Cu elements necessary for forming the S film into the desired composition are evaporated in the first half of the film formation, and the evaporation of Cu is stopped in the second half.

In the case of the control method shown in FIG. 7, control is performed such that the evaporation amount of Cu is constant throughout the film formation, and the evaporation amounts of In and Ga are reduced in the first half of the film formation and increased in the second half. As a result, the first half of the film formation is excessive in Cu.

In the control methods shown in FIGS. 6 to 8, Se,
In order to accurately control the evaporation amount of In, Ga, Cu, and Na ₂ Se, the shutter of the evaporation apparatus is opened when the evaporation amount from each evaporation source becomes constant.

It is also possible to use a method of starting evaporation of Cu and Na ₂ Se after the shutter is opened, as in the control method of FIG.

In each of the control methods shown in FIGS.
The temperature of the substrate during the formation of the CIGS film was 550 ° C. Further, in order to prevent Se from re-evaporating from the surface of the CIGS film, the evaporation of Cu, In, and Ga is stopped, and Se is continuously evaporated until the substrate temperature becomes 350 ° C. or lower.

CIGS obtained by the film forming method of the present invention
The films were analyzed by Auger electron spectroscopy (AES). It should be noted that a method for controlling a temporal change in the evaporation amount during film formation is shown in FIG.
Was used. As a result, in the thickness direction of the obtained CIGS film, each element of Cu, In, Ga, and Se is detected at a substantially constant concentration, and the composition of Cu, In, Ga, and Se is substantially uniform in the thickness direction. It turned out to be. This is probably because Cu diffused in the film thickness direction.

Further, Na element was detected only near the surface. From this, Na supplied in the first half of film formation is:
It was found that it diffused and moved to the surface. Also,
It is considered that Na was present in the film at a concentration lower than the AES detection limit.

In the film forming method of the present invention, the reason why the carrier concentration is high even in the range of y composition of 1.33 or more is as follows.
Although it is not clear at this time, the inventors believe that the reason is related to the timing of adding Na.

Therefore, in order to examine how the carrier concentration changes when the film is formed by changing the timing of adding Na, the following comparative sample was prepared and the carrier concentration was measured. .

First, as a first comparative example, when forming a CIGS film, Na ₂ Se was formed while controlling the evaporation amounts of Cu, In, Ga, and Se in the same manner as in the film forming method of the present invention. Using a method that evaporates during all the time in the film, CIG
An S film sample was prepared.

Further, as a second comparative example, CIG
When forming the S film, Na ₂ S was formed while controlling the amount of evaporation of Cu, In, Ga, and Se in the same manner as the film forming method of the present invention.
A CIGS film sample was prepared by a method in which e was not evaporated in the first half of the film formation, but only in the second half.

The CIGs of the first and second comparative examples
Measurement of the carrier concentration of the S film, as shown in FIG. 10, the range is 10 ¹⁶ or more carrier concentration obtained,
Cu / (Ga + In) is 0.8 or more, that is, y ≦
1.25, conventional CIGS without Na added
Same as membrane.

From this, it is understood that even if the method of continuously adding Na during the film formation or the method of adding Na in the latter half of the film formation lacking Cu is used, a CIGS film that can tolerate composition fluctuation cannot be obtained. Was. This confirmed that it is desirable to add Na at the same time as Cu deposition in the first half of film formation.

As described above, in the present embodiment, CIGS
When depositing a film, Na is added together with Cu vapor deposition in the first half of the film formation, and no Cu or C is added in the latter half of the film formation.
By making the conditions insufficient, and by not adding Na, Cu (In _{1 -x} Ga _x ) _y Se _z is added.
It can be p-type within the range of 33 ≦ y. This allows the solar cell structure using a novel p-type Cu (an In _{1 over} x Ga _x) composition _y Se _z film.

In the above description, the film formation method in which the Na element is added has been described. However, the film formation method in which another Ia group element such as K or Li is added instead of Na may be used.
Experiments have confirmed that a p-type CIGS film can be obtained in a new composition range of 1.33 ≦ y.

Next, was formed by the film forming method of the present invention, p-type Cu (an In _{1 over x} Ga x) _y Se _z film (1.33 ≦ y ≦
4.5, 2 ≦ z ≦ 5) will be described. In the following description, as an example, a solar cell using a Cu (In _{1 -x} Ga _x ) ₃ Se ₅ film formed by the film forming method of the present invention will be described.

First, as shown in FIG. 1, a thin-film solar cell according to the first embodiment has a Mo film 11 as a lower electrode and a p-type Cu (In _{1 -x} G
This is a so-called substrate type solar cell having a configuration in which an a _x ) ₃ Se ₅ film 12, an i-type or high-resistance n-type buffer layer 13, and an n ⁺ -type transparent conductive film 14 are sequentially stacked.

The p-type Cu (In _{1 -x} Ga _x ) ₃ Se ₅ film 1
In No. 2, Na is added as a group Ia element.

As the transparent conductive film 14, a ZnO film to which Al is added is used, and the i-type or high-resistance n-type buffer layer 13 is used.
Is a CdS film.

The thickness of the Mo film 11 is about 0.8 μm, the thickness of the CIGS film 12 is 1 μm to 4 μm, and the thickness of the i-type or high-resistance n-type buffer layer 13 is several nm to 0.1 μm.
3 μm, the thickness of the transparent conductive film 14 is 0.3 μm to 2 μm
And

The substrate type solar cell shown in FIG.
This is an in-hetero junction type solar cell. Light is irradiated from the transparent conductive film 14 side, passes through the transparent conductive film 14 and the i-type or high-resistance n-type buffer layer 13, and is p-type Cu (In _1−x
The Ga _x ) ₃ Se ₅ film 12 absorbs the electrons and generates an electron-hole pair, and a current flows.

The manufacturing method of the present embodiment for manufacturing the solar cell of FIG. 1 will be described.

First, a Mo film 11 is formed on a blue glass substrate 10.
Is formed by a sputtering method.

Next, a p-type Cu (In _{1 -x} Ga _x ) ₃ Se ₅ film 12 is formed on the Mo film 11 by the above-described film forming method.

Thereafter, the surface of the p-type Cu (In _{1 -x} Ga _x ) ₃ Se ₅ film 12 is washed, and a CdS film of an i-type or high-resistance n-type buffer layer 13 is formed by a solution growth method. further,
A ZnO: Al film as a transparent conductive film is formed as a transparent conductive film by a high-frequency magnetron sputtering method. As described above, the substrate type solar cell of the present embodiment is manufactured.

The cleaning of the surface of the CIGS film 12 is performed by the following method.
This is performed in order to wash out the alkali metal element and the like existing on the surface of the IGS film 12 and to form a CdS film favorably. In the present embodiment, the cleaning method uses the substrate 10 with the CIGS film 12.
Was repeatedly immersed in pure water for several minutes. Then, the substrate 10 removed from the pure water is transferred into a solution for growing a CdS film, and the CIGS film 12 is grown by a solution growing method.
A CdS film is formed thereon. Thereby, the cleaned CIG
A heterojunction between the CdS film and the CIGS film 12 can be formed in a clean state without the surface of the S film 12 being contaminated by dust and the like in the air. In this embodiment, an aqueous solution in which CdI ₂ , thiourea, and ammonia are dissolved is used as a solution for growing CdS. When the surface of the CIGS film 12 is immersed in pure water for cleaning, ultrasonic cleaning may be used.

The configuration of the pn homojunction type thin-film solar cell according to the second embodiment will be described with reference to FIG.

The solar cell shown in FIG. 2 has a Mo film 11 as an electrode and a p-type Cu (In
_The structure having the _1-x Ga _x ) ₃ Se ₅ film 12 is the same as that of FIG. 1, but an n-type Cu (In _{1 -x} Ga _x ) ₃ Se ₅ film 2
3 and a transparent conductive film 24 are sequentially laminated. This configuration constitutes a pn homojunction thin-film solar cell using p-type and n-type films while having the same composition.

A pn homojunction thin-film solar cell has become possible for the first time since the Cu (In _{1 -x} Ga _x ) ₃ Se ₅ film can be made p-type by the film forming method of the present invention. FIG. pn homojunction is, p-type, respectively with the same composition, for laminating n-type Cu (an In 1 _{over x} Ga _{x) 3} Se ₅ film, it is possible to match the lattice constant of the crystal, a problem in heterozygous Since problems such as band mismatch and interface state can be solved, high conversion efficiency can be expected.

The n-type Cu (In _{1 -x} Ga _x ) ₃ Se ₅ film 2
3 can be formed by a conventional film forming method without adding Na.

In the configuration shown in FIG. 2, the n-type Cu (In _1−x
To prevent light from being absorbed by Ga _{x) 3} Se ₅ film 23, it is desirable to reduce the thickness of the n-type Cu (an In _{1 over x} Ga x) ₃ Se ₅ film 23. Further, n-type Cu (In _1−x Ga _x )
_{The 3} Se ₅ film 23 can be doped with an impurity to optimize the carrier concentration.

As a third embodiment, the structure of a buried heterojunction solar cell will be described with reference to FIG.

2, a Mo film 11 of an electrode and a p-type Cu (In _{1 -x} Ga)
_x ) ₃ Se ₅ film 12, n-type Cu (In _{1 -x} Ga _x ) ₃ Se ₅ film 23
Are stacked, and an i-type or high-resistance n-type buffer layer 34 and an n ⁺ -type transparent conductive film 35 are further stacked thereon. i
The type or high-resistance n-type buffer layer 34, a CdS film, the n ⁺ -type transparent conductive film 35, was added Al Z
An nO film can be used.

[0053] As described above, the use of the deposition method of the present invention, Cu and (an In _{1 over x} Ga x) _y Se _z film 1.
Since it can be p-type within a new range of 33 ≦ y,
A light absorbing layer having a novel composition can be provided. Also,
By using this p-type Cu (an In 1 _{over x} Ga _{x) y} Se _z film as the light absorbing layer, it is possible to obtain a novel thin-film solar cells. In particular, p-type and n-type Cu
(An In _{1 over} x Ga _x) it is possible to form a _y Se _z film,
It is possible to obtain a homojunction thin-film solar cell that could not be formed conventionally.

In the thin-film solar cells of FIGS. 1, 2 and 3, even when the composition of the p-type Cu (In _{1 -x} Ga _x ) ₃ Se ₅ film 12 fluctuates, as shown in FIG. Since a high carrier concentration can be maintained in a wide composition range, a large-area thin-film solar cell can be easily manufactured. Also, p-type C
Since the composition variation of the u (In _1−x Ga _x ) ₃ Se ₅ film 12 can be tolerated, it is suitable for mass production.

The band gap of CuIn ₃ Se ₅ is 1.3 eV (D. Schmid et al,
J. Appl. Phys. 73 (6), 15 March 1993). Therefore, a very small x composition, slightly by adding Ga, p-type Cu (an In _{1 over} x Ga _{x) y} Se _z film (1.33 ≦ y ≦ 4.5,2 ≦ z ≦ according to the invention The bandgap of 5) can be set to 1.4 eV. Thus, p-type Cu (an In _{1 over} x Ga _x) of the present invention _y Se _z film (1.33 ≦ y ≦ 4.5,
By using (2 ≦ z ≦ 5) as the light absorbing layer, it is possible to obtain a solar cell having a high absorption rate of the light absorbing layer.
Further, p-type Cu (an In _{1 over} x Ga _x) of the present invention _y Se _z film (1.
33 ≦ y ≦ 4.5, 2 ≦ z ≦ 5), the forbidden band width is 1.4.
Since the amount of Ga added for eV is small, the crystallinity may not be impaired by a large amount of Ga added. Accordingly, a band gap can be widened with a film having good crystallinity, so that high conversion efficiency can be obtained.

In the above embodiment, the N
Na ₂ Se was used as the vapor deposition source of “a”.
Alternatively, a compound containing Na or an alloy containing Na can be used. For example, an alloy composed of Cu and a group Ia element, for example, CuNa can be used. Group Ia elements such as Na ₂ O, Na ₂ S, and Na ₂ Te—VI
Group b element compounds can be used. Further, Na
Group Ia element-Group VIIb element compounds such as F, NaCl, and NaBr can be used. When an alloy composed of Cu and a Group Ia element or a Group Ia-Group VIb element compound is used, Cu or a Group VIb element is Cu (In _1−x Ga _x ) _y Se.
_Since it belongs to the same group as the group VIb element originally contained in the _z film, even if it is contained as an impurity in the crystal, it does not adversely affect the film. When using a Ia group element -VIIb group element compound, VIIb group element is evaporated by high temperature of the substrate temperature above 500 ℃, Cu (In _{1 over} x Ga _x) is not taken into _y Se _z film 12.

Similarly, as a vapor deposition source when adding another Group Ia element such as Li or K, a Li-VIb group element compound, a K-VIb group element compound, a Li-VIIb group element compound, a K Group VIIb element compounds can be used.

In FIGS. 6 to 9, the CIGS film formation time is divided into the first half and the second half, and the first half is made to be excessive in Cu. However, it is not always necessary to divide the first half into the second half. It may be divided into an excessive first stage and a Cu-deficient second stage. Therefore, the time distribution at each stage can be set freely.

It is not necessary to completely match the timing for terminating the evaporation of the Na element with the timing for switching Cu from excess to insufficient as shown in FIGS. Na
The element evaporation time can be made shorter or longer than the Cu excess time.

Further, in this embodiment, the composition is Cu
(An In _{1 over} x Ga _x) has been described _y Se _z film is not limited thereto, CuIn _y Se _z film, CuGa _y Se _z film, CuIn
_y S _z film, CuIn _y (S _m Se _{1 over} m) _z film, Cu (In _{1 over} x G
a _x ) _y (S _m Se _{1 -m} ) _z film. When films having these compositions are used, Cu is excessively added in the first half of film formation, and a Group Ia element such as Na is added, and Cu is added in the second half.
By making it insufficient, a p-type film can be obtained in a novel composition range.

In this embodiment, the transparent conductive film 14
Is a ZnO film to which Al is added, but n ⁺
Any other type of transparent conductive film may be used. For example, a ZnO film to which an element such as B, Ga, or In is added;
A so-called ITO film obtained by adding 10% of SnO ₂ to ₂ O ₃ , a SnO ₂ film obtained by adding an element such as F, and the like can be used.

The i-type or high-resistance n-type buffer layer 1
CdS was used for No. 3, but in addition to CdS, Zn
O, Zn (OH) ₂ , ZnS, In ₂ O ₃ , InN, Ga
N, In ₂ S ₃ , ZnSe, InSe, ZnInSe, or the like can be used.

Further, in the present embodiment, the substrate type solar cell shown in FIGS. 1, 2 and 3 has been described as the type of solar cell, but the type of solar cell is limited to this type. Not something. For example, contrary to the configuration of FIG. 1, a transparent conductive film 14, an i-type or high-resistance n-type buffer layer 13, a p-type Cu (In _{1 -xG)}
a _x ) ₃ Se ₅ 12 and the Mo film 11 may be laminated in this order to form a super-straight type thin-film solar cell in which light is irradiated from the substrate 20 side.

In the structure of the solar cell shown in FIGS. 1, 2 and 3, the Na element contained in the blue glass substrate 10 is C
In order to prevent diffusion to the IGS film 12, an SiO ₂ film or the like can be disposed between the blue glass substrate 10 and the Mo film 11 as a block layer of an alkali metal such as Na.

Further, in this embodiment, a multi-source vacuum evaporation method is used as a method of forming a CIGS film, but a method other than the multi-source vacuum evaporation method can be used. For example,
A Cu film, an In-Ga film, and a Se film are sequentially laminated on a substrate, and a solid-phase selenization method in which a CIGS film is formed by heating and diffusing, or a Cu film and an In-Ga film are sequentially laminated on a substrate. In addition, a vapor-phase selenization method in which they are mutually diffused and selenized by Se vapor or H ₂ Se gas, a sputtering method, or the like can be used. In the case of selenization, Cu
It is considered that by adding Na to the film, a p-type CIGS film can be obtained in a novel composition range as in the present embodiment. Further, in the case of the sputtering method, as in the case of the present embodiment, an excessive amount of Cu and an N
It is considered that by adding a, a p-type CIGS film can be obtained in a novel composition range as in the present embodiment.

[0066]

As described above, according to the present invention,
It is possible to provide a thin-film solar cell using a p-type CIS-based material as a light absorbing layer in a novel composition range.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a configuration of a pin heterojunction thin-film solar cell according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view illustrating a configuration of a pn homojunction thin-film solar cell according to an embodiment of the present invention.

FIG. 3 is a sectional view showing a configuration of a buried heterojunction thin-film solar cell according to an embodiment of the present invention.

FIG. 4 is a graph showing an analysis result of a CIGS film obtained by a film forming method of the present invention by X-ray diffraction.

FIG. 5 is an explanatory diagram showing a crystal phase state of CuIn _y Se _z .

FIG. 6 is a diagram illustrating a CI method according to an embodiment of the present invention.
7 is a graph showing a temporal change in the evaporation amount of each evaporation source when forming a GS film.

FIG. 7 is a diagram showing a CI method according to an embodiment of the present invention.
7 is a graph showing a temporal change in the evaporation amount of each evaporation source when forming a GS film.

FIG. 8 is a diagram illustrating a CI method according to an embodiment of the present invention.
7 is a graph showing a temporal change in the evaporation amount of each evaporation source when forming a GS film.

FIG. 9 is a diagram illustrating a CI method according to an embodiment of the present invention.
7 is a graph showing a temporal change in the evaporation amount of each evaporation source when forming a GS film.

FIG. 10 is a graph showing the carrier concentration of a CIGS film obtained by the film forming method of the present invention.

[Explanation of symbols]

10 ... Blue plate glass, 11 ... Mo film, 12 ...
p-Cu (In _{1 over x} Ga x) ₃ Se ₅ film, 13, 34 · · · i
Type or high resistance n-type buffer layer, 14, 35... N ⁺
The transparent conductive film type, 23 ··· n-Cu (In 1 _over x Ga _{x) 3}
Se ₅ film, 24 ... Transparent conductive film.

Claims (13)

[Claims] 1. A light absorbing layer comprising a p-type compound semiconductor thin film containing a group Ib element, a group III element, and a group VIb element, wherein said compound semiconductor thin film is doped with a group Ia element, A thin-film solar cell, wherein a ratio of a group Ib element to a group III element contained in the compound semiconductor thin film is 0.22 or more and 0.75 or less. 2. The method according to claim 1, wherein the ratio of the group Ib element to the group VIb element contained in the compound semiconductor thin film is:
A thin-film solar cell characterized by being 0.2 or more and 0.5 or less. 3. The compound semiconductor thin film according to claim 1, wherein a ratio of a group Ib element to a group III element contained in the compound semiconductor thin film is:
A thin-film solar cell having a thickness of 0.28 or more and 0.52 or less. 4. The compound semiconductor thin film according to claim 1, wherein the compound semiconductor thin film contains Cu as the group Ib element, contains at least one of In and Ga as the group III element, and contains S as the group VIb element. And at least one of Se. 5. The method of claim 4, wherein the compound composition of the semiconductor thin film is represented by Cu (an In _{1 over x Ga x) y (S m} Se 1 _over m) _z film, 0 ≦ x ≦ 1,1. 33 ≦ y ≦ 4.5, 2 ≦ z ≦
5. A thin-film solar cell, wherein 0 ≦ m ≦ 1. 6. The compound semiconductor thin film according to claim 1, wherein Na, Li, K and R
b. A thin-film solar cell, wherein at least one of b is added. 7. The semiconductor device according to claim 1, further comprising an n-type compound semiconductor thin film disposed at a position in contact with said p-type compound semiconductor thin film, wherein said n-type compound semiconductor thin film comprises an Ib group element, A thin-film solar cell comprising: a group IV element and a group VIb element having the same composition as the p-type compound semiconductor thin film. 8. The compound semiconductor thin film according to claim 1, wherein the compound semiconductor thin film is formed on a substrate by a step of supplying a group Ib element, a group III element, and a group VIb element. The ratio of the amount to the supply of group III elements,
Ib contained in the compound semiconductor thin film having a desired composition
A first step of supplying the group Ia element onto the substrate while increasing the ratio of the group III element to the group III element, and the step of supplying the group Ib element supply amount to the group III element supply amount,
A second step of making the first step smaller than the first step. 9. The thin-film solar cell according to claim 8, wherein the supply amount of the Ib group element in the second step is set to zero. 10. The thin-film solar cell according to claim 8, wherein the supply amount of the group III element in the first step is set to zero. 11. The method according to claim 8, wherein said group Ia element and VIb are supplied to supply said group Ia element in said first step.
A thin-film solar cell characterized by supplying at least one of a compound with a Group I element and a compound with a Group Ia element and a Group VIIb element. 12. The compound according to claim 11, wherein the group VIb element of the compound of the group Ia element and the group VIb element is any of S, Se and Te.
The group VIIb element of the compound with the group element is F, Cl, and
A thin-film solar cell, which is any one of Br. 13. The method according to claim 8, wherein in the film forming step, a group Ib element, a group III element, a group VIb element, and a group Ia
A thin-film solar cell, wherein the method for supplying a group III element to a substrate is a vapor phase growth method.