JP2004281938A - Solar cell and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solar cell which uses a layer comprising Zn, Mg and O and can further improve the efficiency when compared to a conventional one, and its manufacturing method. <P>SOLUTION: The cell comprises a substrate 11, a first electrode layer 12 laminated on the substrate 11 one by one from the substrate 11 side, a p-type semiconductor layer 13, a layer A15 and a second electrode layer 16, and produces photovoltaic force by light projected from the second electrode layer 16 side. The layer A15 consists of oxide containing Zn, Mg and O, and the second electrode layer 16 comprises at least one element R selected from the group consisting of Al, Ga and In, Zn, Mg and O. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a solar cell and a method for manufacturing the same.
[0002]
[Prior art]
CuInSe ₂ (hereinafter sometimes referred to as CIS), which is a compound semiconductor thin film (chalcopyrite structure compound semiconductor thin film) composed of a group Ib element, a group IIIb element, and a group VIb element, or Cu (In, Ga) A thin-film solar cell using Se ₂ (hereinafter sometimes referred to as CIGS) as a light absorbing layer (hereinafter sometimes referred to as a CIS-based solar cell) exhibits high energy conversion efficiency, and the conversion efficiency by light irradiation or the like is high. It has been reported to have the advantage of no degradation.
[0003]
Conventional high-efficiency CIS-based solar cells generally use an ITO or ZnO: Al layer as a window layer. In recent years, however, ZnO and ZnO: Al have been used to optimize the conduction band offset between the light absorbing layer and the window layer. Instead, a solar cell using a layer containing Zn, Mg, and O (Zn _1-x Mg _x O layer) is being studied. In addition, a CIS solar cell that does not require a buffer layer used in a conventional solar cell by using a Zn _1-x Mg _x O layer has been developed (for example, Patent Document 1). Generally, ITO or ZnO: Al is used as the transparent conductive film.
[0004]
[Patent Document 1]
US Pat. No. 6,259,016
[Problems to be solved by the invention]
However, when ITO or ZnO: Al is used for the transparent conductive film, the conduction band is lower than that of the Zn _1-x Mg _x O layer which is the window layer, so that the conduction band offset between the two layers becomes large, It may cause deterioration of characteristics.
[0006]
In view of such circumstances, an object of the present invention is to provide a solar cell and a method of manufacturing the same that can achieve higher efficiency than in the past.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, the semiconductor device includes a substrate, a first electrode layer, a p-type semiconductor layer, a layer A, and a second electrode layer which are sequentially arranged on the substrate from the substrate side, A solar cell that generates photovoltaic power by light incident from an electrode layer side, wherein the layer A is made of an oxide containing Zn, Mg, and O (oxygen), and the second electrode layer is made of Al, It is characterized by containing at least one element selected from the group consisting of Ga and In, R, Zn, Mg, and O. In this solar cell, the conduction band offset between the layer A constituting the window layer and the second electrode layer can be made favorable, so that a solar cell with high characteristics can be obtained.
[0008]
In the above solar cell, the p-type semiconductor layer is preferably made of a p-type compound semiconductor containing Cu, at least one element selected from In and Ga, and at least one element selected from Se and S. .
[0009]
The solar cell further includes an n-type semiconductor layer disposed between the p-type semiconductor layer and the layer A, wherein the n-type semiconductor layer includes Cu, at least one element selected from In and Ga. , Se and S may be an n-type compound semiconductor containing at least one element selected from Zn and Zn.
[0010]
In the solar cell, the atomic ratio of Zn, Mg, and O in the layer A is Zn: Mg: O = (1-x): x: 1 (provided that 0.05 ≦ x ≦ 0.35). You may.
[0011]
In the above solar cell, the layer A contains at least one element M selected from Ca, Sr and Ba, the content of the element M in the layer A is 20 atom% or less, The total content of Mg and O is preferably at least 80 atomic%.
[0012]
In the above solar cell, the atomic ratio of Zn, Mg, and O in the second electrode layer is Zn: Mg: O = (1-x): x: 1 (where 0.05 ≦ x ≦ 0. 35).
[0013]
In the above solar cell, the content of the element R in the second electrode layer is 20 atomic% or less, and the total content of Zn, Mg, and O in the second electrode layer is 80 atomic% or more. Is preferred.
[0014]
Also, the method of the present invention for manufacturing a solar cell includes: (i) forming a first electrode layer and a p-type semiconductor layer in this order above a substrate; and (ii) forming the p-type semiconductor layer. A step of forming a layer A made of an oxide containing Zn, Mg and O by a sputtering method above; and (iii) a step of forming a second electrode layer above the layer A by a sputtering method. And the second electrode layer includes at least one element selected from the group consisting of Al, Ga, and In, R, Zn, Mg, and O. According to this manufacturing method, the solar cell of the present invention can be easily manufactured.
[0015]
The above manufacturing method may include a step of heat-treating the layer A after the step (ii).
[0016]
In the above method, the p-type semiconductor layer is preferably made of a p-type compound semiconductor containing Cu, at least one element selected from In and Ga, and at least one element selected from Se and S. .
[0017]
In the above-described manufacturing method, after the step (i) and before the step (ii), the surface of the p-type semiconductor layer is doped with Zn by doping the surface of the p-type semiconductor layer with n. It may further include the step of shaping.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described.
[0019]
(Embodiment 1)
Embodiment 1 describes a solar cell of the present invention. FIG. 1 shows a cross-sectional view of the solar cell 10 of the first embodiment.
[0020]
With reference to FIG. 1, a solar cell 10 includes a substrate 11, a first electrode layer 12, a p-type semiconductor layer 13, an n-type semiconductor layer 14, a layer A15, and a second And an electrode layer 16. On the first electrode layer 12 and the second electrode layer 16, extraction electrodes 17 and 18 are formed, respectively. The solar cell 10 is an example of the solar cell of the present invention. The solar cell of the present invention may include at least the second electrode layer 16, the layer A15, the p-type semiconductor layer 13, and the first electrode layer 12, which are arranged in this order from the light incident side. A solar cell not including the n-type semiconductor layer 14 is also included in the solar cell of the present invention.
[0021]
As the substrate 11, for example, a glass substrate, a stainless steel substrate, a polyimide substrate, or the like can be used. When the solar cell of the present invention is an integrated type and the substrate is a conductive substrate (for example, a stainless steel substrate), a process of forming an insulating layer on the surface of the substrate or insulating the surface of the substrate is performed. There is a need to do.
[0022]
The first electrode layer 12 is made of a metal and can be formed of, for example, molybdenum (Mo).
[0023]
The p-type semiconductor layer 13 is a semiconductor layer that functions as a light absorption layer. The p-type semiconductor layer can be formed using a semiconductor having a chalcopyrite structure (hereinafter, sometimes referred to as an I-III-VI compound semiconductor) with a group Ib element, a group IIIb element, and a group VIb element as main constituent elements. . Specifically, it can be formed of a p-type compound semiconductor having a chalcopyrite structure, including Cu, at least one element selected from In and Ga, and at least one element selected from Se and S. For example, it can be formed of CuInSe ₂ , Cu (In, Ga) Se ₂ , or a semiconductor in which part of Se is replaced with sulfur (S).
[0024]
The n-type semiconductor layer 14 can be formed of a compound semiconductor containing Cu, at least one element selected from In and Ga, at least one element selected from Se and S, and Zn. For example, an n-type semiconductor layer obtained by doping Zn into the p-type semiconductor layer 13 can be used.
[0025]
The layer A15 contains at least one element M selected from the group consisting of Ca, Sr and Ba, Zn, Mg and O. Among these, Ca is preferable as the element M. Specifically, for the layer A15, (Zn, Mg, M) O, that is, an oxide in which the total atomic ratio of Zn, Mg, and the element M is substantially equal to the atomic ratio of oxygen can be used.
[0026]
The main constituent elements of the layer A15 are Zn, Mg and O, and the total content of these elements is 80 atom% or more (preferably 90 atom% or more), for example, 99 atom% or more. The atomic ratio between Zn, Mg, and O in the layer A15 is preferably Zn: Mg: O = (1-x): x: 1 (provided that 0.05 ≦ x ≦ 0.35). That is, the layer A15 has a composition obtained by adding an element M (for example, Ca alone) to a material represented by a composition formula Zn _1-x Mg _x O (0.05 ≦ x ≦ 0.35). Is preferred.
[0027]
The content of the element M in the layer A15 is 20 atomic% or less (preferably 10 atomic% or less), for example, 1 atomic% or less. The element M has the effect of reducing the resistivity even in a very small amount, and the effect can be obtained even when the content of the element M (for example, Ca alone) is, for example, 0.02 atomic% or more (preferably 0.035 atomic% or more). . When the layer A15 contains the element M, the resistivity of the layer A15 decreases. The volume resistivity of the layer A15 is, for example, 1 × 10 ¹² Ω · cm or less (preferably 1 × 10 ¹¹ Ω · cm or less). The thickness of the layer A is, for example, about 0.08 μm to 0.2 μm (preferably, about 0.1 μm to 0.15 μm).
[0028]
The second electrode layer 16 contains at least one element selected from the group consisting of Al, Ga, and In, R, Zn, Mg, and O. Among these, Ga is preferable as the element R. Specifically, for the second electrode layer 16, (Zn, Mg, R) O, that is, an oxide in which the total atomic ratio of Zn, Mg, and the element R is substantially equal to the atomic ratio of oxygen is used. be able to.
[0029]
The main constituent elements of the second electrode layer 16 are Zn, Mg, and O, and the total content of these elements is 80 atom% or more (preferably 97 atom% or more). The atomic ratio of Zn, Mg, and O in the second electrode layer 16 is Zn: Mg: O = (1-x): x: 1 (provided that 0.05 ≦ x ≦ 0.35). Is preferred. That is, the second electrode layer 16 is obtained by adding the element R (for example, Ga alone) to a material represented by the composition formula Zn _1-x Mg _x O (0.05 ≦ x ≦ 0.35). Preferably, it is a composition.
[0030]
The content ratio of the element R in the second electrode layer 16 is 20 atomic% or less (preferably 3 atomic% or less). By adding the element R to the oxides of Zn and Mg, the matching of the conduction band offset with the window layer can be made favorable. Further, by adding the element R, the resistance value of the second electrode layer 16 can be reduced. Such an effect can be obtained even when the amount of the element R is very small, and the effect can be obtained even when the content of the element R (for example, Ga alone) is, for example, 0.01 atomic% or more (preferably 0.1 atomic% or more). .
[0031]
The sheet resistance of the second electrode layer 16 is, for example, 30Ω / □ or less (preferably 10Ω / □ or less) when the thickness is 0.1 μm. The thickness of the layer A is, for example, about 0.08 μm to 0.2 μm (preferably, about 0.1 μm to 0.15 μm).
[0032]
In the solar cell of Embodiment 1, the window layer in contact with the second electrode layer is made of an oxide containing Zn, Mg, and O (preferably further containing the element M). The second electrode layer is made of an oxide containing Zn, Mg, O, and the element R. With such a configuration, the offset of the conduction band between the window layer and the second electrode layer can be made preferable. Further, the resistance values of the window layer and the second electrode layer can be reduced. As a result, according to the present invention, a solar cell that can achieve higher efficiency than before can be obtained.
[0033]
(Embodiment 2)
Embodiment 2 describes a method for manufacturing a solar cell of the present invention. According to the manufacturing method of the second embodiment, the solar cell described in the first embodiment can be manufactured.
[0034]
First, the first electrode layer 12 and the p-type semiconductor layer 13 are formed in this order above the substrate 11 (step (i)). The first electrode layer 12 can be formed by, for example, a sputtering method or an evaporation method. The p-type semiconductor layer 13 made of a group I-III-VI compound semiconductor can be formed by, for example, an evaporation method, and can be formed by, for example, a known three-stage evaporation method.
[0035]
When the solar cell to be manufactured includes the n-type semiconductor layer 14, the n-type semiconductor layer 14 is formed on the p-type semiconductor layer 13. The n-type semiconductor layer 14 can be formed by a vapor deposition method similarly to the p-type semiconductor layer 13. Further, the surface of the p-type semiconductor layer 13 made of a group I-III-VI compound semiconductor may be doped with Zn to form the n-type semiconductor layer 14 with the surface of the p-type semiconductor layer 13 being n-type. .
[0036]
Next, a layer A15 is formed above the p-type semiconductor layer 13 (on the n-type semiconductor layer 14 if it exists) by a sputtering method (step (ii)). Since the composition of the layer A15 has been described in the first embodiment, a duplicate description will be omitted. The composition of the layer A15 can be easily controlled by changing the composition of the target to be sputtered. The target used for forming the layer A15 includes at least one element R selected from the group consisting of Al, Ga, and In, Zn, Mg, and O. Note that a plurality of targets may be used.
[0037]
After forming the layer A15, a step of heat-treating the layer A may be included. The heat treatment is preferably performed in an inert gas, and is preferably performed in an atmosphere composed of a nitrogen gas, a rare gas, or a gas containing these gases. As the rare gas, for example, an argon gas can be used. The heat treatment is performed at a temperature in the range of 100C to 300C. The heat treatment time varies depending on the temperature of the heat treatment, but is usually about 5 to 15 minutes.
[0038]
Finally, a second electrode layer 16 is formed above the layer A15 by a sputtering method (step (iii)). Since the composition of the second electrode layer 16 has been described in the first embodiment, a duplicate description will be omitted. The composition of the second electrode layer 16 can be easily controlled by changing the composition of the target to be sputtered. The target used for forming the second electrode layer 16 includes at least one element R selected from the group consisting of Al, Ga, and In, Zn, Mg, and O. Note that a plurality of targets may be used.
[0039]
Next, an extraction electrode is formed on the first electrode layer 12 and the second electrode layer 16 as necessary. Thus, the solar cell described in Embodiment 1 can be manufactured.
[0040]
【Example】
Hereinafter, the present invention will be described more specifically with reference to examples.
[0041]
(Example 1)
Example 1 describes an example in which the transparent conductive film of the present invention was manufactured.
[0042]
A Zn _0.9 Mg _0.1 Ga _0.003 O film (thickness: 300 nm) was formed on an insulating substrate by ternary sputtering using a ZnO target, an MgO target, and a Ga ₂ O ₃ target. Formed. At this time, the argon gas pressure was 2.7 Pa (2 × 10 ⁻² Torr), the high-frequency power applied to the ZnO target was 200 W, the high-frequency power applied to the MgO target was 100 W, and the Ga ₂ O ₃ target was used. Was 20 W. The sheet resistance of the produced film was 60Ω / □.
[0043]
In this embodiment, the oxide thin film has a composition represented by a composition in which Ga is added to Zn _1-x Mg _x O. Similarly, even if Al or In is added instead of Ga, a thin film having a lower sheet resistance than the Zn _1-x Mg _x O film can be obtained.
[0044]
(Example 2)
Example 2 describes an example in which the solar cell of the present invention was manufactured.
[0045]
First, a Mo film was formed on a glass substrate by a sputtering method, and a Cu (In, Ga) Se ₂ film (thickness: 2 μm) was formed thereon by a vapor deposition method. Thereafter, the substrate temperature was set to 300 ° C., Zn was deposited on the Cu (In, Ga) Se ₂ film for 3 minutes, and Zn was added to a depth of 50 nm from the surface.
[0046]
Next, a layer A (thickness: 100 nm) made of Zn _0.9 Mg _0.1 Ca _0.0007 O was formed on the Zn (Cu, In, Ga) Se ₂ film doped with Zn by a sputtering method. This layer A was formed by a binary sputtering method using an MgO target containing 1 wt% Ca and a ZnO target. At this time, the argon gas pressure was 2.7 Pa (2 × 10 ⁻² Torr), the high frequency power applied to the ZnO target was 200 W, and the high frequency power applied to the MgO target was 100 W.
[0047]
Next, a second electrode layer which was a transparent conductive film was formed over the layer A. Specifically, a Zn _0.9 Mg _0.1 O: Ga film (thickness: 300 nm), which is Zn _1-x Mg _x O to which Ga was added, was formed. This second electrode layer was formed by a ternary sputtering method using a ZnO target, an MgO target, and a Ga ₂ O ₃ target. At this time, the argon gas pressure was 2.7 Pa (2 × 10 ⁻² Torr), the high-frequency power applied to the ZnO target was 200 W, the high-frequency power applied to the MgO target was 100 W, and the Ga ₂ O ₃ target was used. Was 20 W.
[0048]
Finally, an extraction electrode was formed by laminating a NiCr film and an Ag film by an electron beam evaporation method. Thus, the solar cell of the present invention was manufactured.
[0049]
_Further, Zn _{0.9 Mg} 0.1 O: ZnO in place of Ga film: it was also prepared solar cell using Ga film (ZnO film doped with Ga).
[0050]
The two types of solar cells thus manufactured were irradiated with pseudo sunlight of AM 1.5 and 100 mW / cm ² to measure the solar cell characteristics.
[0051]
As a result of evaluating the characteristics of the solar cell using the Zn _0.9 Mg _0.1 O: Ga film as the transparent conductive film, a short-circuit current of 31.2 mA / cm ² , an open voltage of 0.474 V, a fill factor of 0.581, and conversion were obtained. The efficiency was 8.6%. Furthermore, when this solar cell was annealed at 200 ° C. for 10 minutes in a nitrogen gas atmosphere, the short-circuit current was 36.2 mA / cm ² , the open voltage was 0.601, the fill factor was 0.665, and the conversion efficiency was 14.5%.
[0052]
On the other hand, as a result of evaluating characteristics of a solar cell using a ZnO: Ga film as a transparent conductive film, a short-circuit current of 30.8 mA / cm ² , an open-circuit voltage of 0.460 V, a fill factor of 0.572, and a conversion efficiency of 8.1% were obtained. there were. When this solar cell was annealed in the same manner as the solar cell of the present invention, the short-circuit current was 34.9 mA / cm ² , the open-circuit voltage was 0.588, the fill factor was 0.652, and the conversion efficiency was 13.4%.
[0053]
Therefore, the solar cell using the Zn _0.9 Mg _0.1 O: Ga film as the transparent conductive film had a higher conversion efficiency by 1% or more than the solar cell of the comparative example.
[0054]
In this embodiment, the case where Ga is added has been described, but a high-efficiency solar cell can be similarly manufactured by adding Al or In.
[0055]
As described above, the embodiments of the present invention have been described by way of examples. However, the present invention is not limited to the above embodiments, and can be applied to other embodiments based on the technical idea of the present invention.
[0056]
【The invention's effect】
As described above, in the present invention, a film containing Zn, Mg, and O is used for the window layer, and a film containing at least one element R selected from Al, Ga, and In, Zn, Mg, and O is used. Used as a transparent conductive film. According to the present invention, a highly efficient solar cell can be obtained. In particular, according to the present invention, a highly efficient CIS or CIGS solar cell can be obtained.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view schematically showing one example of the solar cell of the present invention.
[Explanation of symbols]
Reference Signs List 10 solar cell 11 substrate 12 first electrode layer 13 p-type semiconductor layer 14 n-type semiconductor layer 15 layer A
16 Second electrode layer 17, 18 Extraction electrode

Claims (11)

A substrate, and a first electrode layer, a p-type semiconductor layer, a layer A, and a second electrode layer which are arranged on the substrate in order from the substrate side, and the light incident from the second electrode layer side includes A photovoltaic solar cell,
The layer A is made of an oxide containing Zn, Mg, and O;
A solar cell, wherein the second electrode layer includes at least one element selected from the group consisting of Al, Ga, and In, R, Zn, Mg, and O. The solar cell according to claim 1, wherein the p-type semiconductor layer is made of a p-type compound semiconductor containing Cu, at least one element selected from In and Ga, and at least one element selected from Se and S. . Further comprising an n-type semiconductor layer disposed between the p-type semiconductor layer and the layer A;
The n-type semiconductor layer according to claim 2, wherein the n-type semiconductor layer is made of an n-type compound semiconductor containing Cu, at least one element selected from In and Ga, at least one element selected from Se and S, and Zn. Solar cell. The atomic ratio of Zn: Mg: O in the layer A is Zn: Mg: O = (1-x): x: 1 (provided that 0.05 ≦ x ≦ 0.35). The solar cell according to any one of the above. The layer A contains at least one element M selected from Ca, Sr, and Ba;
The content of the element M in the layer A is 20 atomic% or less;
The solar cell according to claim 4, wherein the total content of Zn, Mg, and O in the layer A is 80 atomic% or more. The atomic ratio of Zn, Mg, and O in the second electrode layer is Zn: Mg: O = (1-x): x: 1 (where 0.05 ≦ x ≦ 0.35). Item 4. The solar cell according to any one of Items 1 to 3. 4. The content of the element R in the second electrode layer is 20 atomic% or less, and the total content of Zn, Mg and O in the second electrode layer is 80 atomic% or more. The solar cell according to any one of the above. (I) forming a first electrode layer and a p-type semiconductor layer in this order over a substrate;
(Ii) a step of forming a layer A made of an oxide containing Zn, Mg and O by a sputtering method above the p-type semiconductor layer;
(Iii) forming a second electrode layer on the layer A by a sputtering method,
The method of manufacturing a solar cell, wherein the second electrode layer includes at least one element selected from the group consisting of Al, Ga, and In, R, Zn, Mg, and O. The method for manufacturing a solar cell according to claim 8, further comprising a step of heat-treating the layer A after the step (ii). 10. The p-type semiconductor layer according to claim 8, wherein the p-type semiconductor layer is made of a p-type compound semiconductor containing Cu, at least one element selected from In and Ga, and at least one element selected from Se and S. Solar cell manufacturing method. After the step (i) and before the step (ii), doping Zn to the surface of the p-type semiconductor layer to make the surface of the p-type semiconductor layer n-type is performed. The method for manufacturing a solar cell according to claim 8, further comprising:

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