WO2011108033A1 - Compound thin film solar cell and method for manufacturing same - Google Patents

Abstract

Provided is a highly-efficient compound thin film solar cell in which a light absorption layer (14) is adjusted to have the most suitable band gap for light absorption by controlling the crystal particle size thereof, and a method for manufacturing the same. Specifically provided is a compound thin film solar cell characterized by being provided with at least a substrate (11), a back surface electrode (12) provided on the substrate (11), a first extraction electrode (13) provided on the back surface electrode (12), a light absorption layer (14) provided on the back surface electrode (12) and including a compound semiconductor thin film represented by Cu(Al_1-x-yGa_xIn_y)(Te_1-a-bSe_aS_b)₂ (where 0≤x≤1, 0≤y≤1, 0≤a≤1, 0≤b≤1, 0≤x+y≤1, 0≤a+b≤1), a buffer (15) provided on the light absorption layer (14), a transparent electrode layer (16) provided on the buffer layer (15), and a second extraction electrode (17) provided on the transparent electrode layer (16), and the mean crystal particle size of the compound semiconductor thin film is 1-100 nm.

Description

Compound thin film solar cell and manufacturing method thereof

The present invention relates to a compound thin film solar cell.

For compound thin film solar cells, as the light absorption layer, II-VI group II-VI CdTe or I, III, VI group I-III-VI _2- type CuInSe ₂ having a chalcopyrite structure is used. Cu (In, Ga) Se ₂ (CIGS) is widely used. By selecting a constituent element of the chalcopyrite type compound semiconductor, the band gap (Eg) can be greatly modulated.

As one of high efficiency technologies in CIGS solar cells, there is a technology for forming a distribution in the band gap by changing the composition ratio of In and Ga in the light absorption layer to control the band gap. However, when the band gap is controlled by changing the composition ratio of In, Ga, or the like in the light absorption layer, it is essential to strictly control the supply of the constituent elements when forming the film by vacuum deposition. In addition, by stacking a plurality of compound semiconductor layers having different constituent elements and composition ratios of the light absorption layer, a solar cell including light absorption layers having different band gaps can be formed, and the wavelength sensitivity can be broadened.

Also, as a method for increasing the efficiency of a compound thin film solar cell, it is widely recognized that it is generally important to promote crystal growth and increase the crystal grain size. For example, in Patent Document 1, in order to obtain a large crystal grain size of 500 nm or more, when a chalcopyrite type compound thin film is deposited by vacuum evaporation or sputtering, a chalcogenide element and a rare gas element are irradiated with an ion beam. A method of manufacturing a pyrite-type compound thin film is disclosed. On the other hand, unlike Si-based solar cells, carriers of chalcopyrite type compound thin-film solar cells represented by CIGS are insensitive to crystal grain boundaries, and it is known that crystal grain boundaries are less likely to become recombination centers of carriers. Yes.

JP 2000-144377 A

In conventional technology for improving the efficiency of compound thin-film solar cells, precise control such as control of the composition ratio of compound semiconductor thin films, multilayered light absorption layers, and ion beam irradiation is essential, which increases the manufacturing cost of solar cells. There is a problem.

The present invention aims to solve such problems, and by controlling the crystal grain size of the light absorption layer, a highly efficient compound thin film solar cell including a light absorption layer adjusted to a band gap optimal for light absorption, and its An object is to provide a manufacturing method.

The compound thin film solar cell 10 includes a substrate 11, a back electrode 12 provided on the substrate 11, a first extraction electrode 13 provided on the back electrode 12, and a Cu provided on the back electrode 12. Light absorbing layer 14 containing a compound semiconductor thin film represented by (Al _1-xy Ga _x In _y ) (Te _1-ab Se _a S _b ) ₂ (where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ a ≦ 1, 0 ≦ b ≦ 1, 0 ≦ x + y ≦ 1, 0 ≦ a + b ≦ 1), the buffer 15 provided on the light absorption layer 14, and the buffer layer 15 It has at least a transparent electrode layer 16 provided thereon and a second extraction electrode 17 provided on the transparent electrode layer 16, and the compound semiconductor thin film has an average crystal grain size of 1 nm to 100 nm. It is characterized by.

According to the present invention, a highly efficient compound thin film solar cell is provided by controlling the particle size of the light absorption layer.

It is a conceptual diagram of the basic structure of a compound thin film solar cell. A low-temperature heat treatment was CuAlTe ₂ thin film optical property evaluation results of the cross-section SEM images. An optical property evaluation result and a cross-sectional SEM image of CuAlTe ₂ thin film high temperature heat treatment. This is a change in the particle size in the film thickness direction of the band graded light absorption layer 14. It is a conceptual diagram of the light absorption layer 14 of a multilayer coupling type solar cell.

Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings.
The compound thin film solar cell 10 shown in the conceptual diagram of FIG. 1 includes a substrate 11, a back electrode 12 provided on the substrate, a first extraction electrode 13 provided on the back electrode 12, and the back electrode. 12, a light absorption layer 14 provided on the buffer layer 15, a buffer layer 15 (15 a, 15 b) provided on the light absorption layer 14, a transparent electrode layer 16 provided on the buffer layer 15, and the transparent electrode And a second extraction electrode 17 provided on the layer 16.

As a manufacturing method of the compound thin film solar cell 10 of FIG. 1, the following method is mentioned as an example.
In addition, it is an example of the following manufacturing method, You may change suitably. Therefore, the order of the steps may be changed, or a plurality of steps may be combined.

[Step of forming back electrode on substrate]
A back electrode 12 is formed on the substrate 11. Examples of the film forming method include a sputtering method.

[Step of forming light absorption layer on back electrode]
After the back electrode 12 is deposited, a compound semiconductor thin film that becomes the light absorption layer 14 is deposited. Since the light absorption layer 14 and the first extraction electrode 13 are deposited on the back electrode 12, the light absorption layer 14 is deposited on a part of the back electrode 12 excluding at least the portion where the first extraction electrode 13 is deposited. To do. Examples of the film forming method include vacuum processes such as sputtering and vacuum deposition. In the sputtering method, all the constituent elements of the light absorption layer are supplied from the sputtering target. There may be one source target or a plurality of targets. It is desirable to adjust the preparation composition of the target constituent elements so that the formed thin film has a stoichiometric composition and, in some cases, the Group III element is slightly excessive, and the insufficient elements are supplied from other targets. May be.

[Step of heat-treating light absorption layer]
After film formation, the film formation chamber is evacuated and annealed in an ultra-high vacuum atmosphere. The compound semiconductor thin film immediately after sputtering is amorphous and has a very small particle size. Therefore, the compound semiconductor thin film can be crystallized by performing annealing at a high temperature. The average crystal grain size varies depending on the annealing temperature.
The crystallization of the compound semiconductor thin film may be annealed during the film formation of the compound semiconductor thin film in addition to the annealing after the film formation. The heating means is not particularly limited, such as annealing or infrared laser.

[Step of forming a buffer layer on the light absorption layer]
Buffer layers 15 a and 15 b are deposited on the obtained light absorption layer 14.
Examples of the method for forming the buffer layer 15a include a sputtering method in a vacuum process, a vacuum deposition method or metal organic chemical vapor deposition (MOCVD), and a chemical deposition (CBD) method in a liquid phase process.
Examples of the method for forming the buffer layer 15b include sputtering in a vacuum process, vacuum deposition, or metal organic chemical vapor deposition (MOCVD).

[Step of forming transparent electrode on buffer layer]
Subsequently, the transparent electrode 16 is deposited on the buffer layer 15b.
Examples of the film forming method include sputtering in a vacuum process, vacuum vapor deposition, or metal organic chemical vapor deposition (MOCVD).

[Step of forming the electrode on the back electrode and the transparent electrode]
The first extraction electrode 13 is deposited on a portion excluding at least the portion where the light absorption layer is formed on the back electrode 12.
The second extraction electrode 17 is deposited on a portion excluding at least a portion where the antireflection film is formed on the transparent electrode 16.
Examples of the film forming method include a sputtering method and a vacuum deposition method.
The film formation of the first and second extraction electrodes may be performed in one step, or may be performed after any step as a separate step.

[Step of forming an antireflection film on a transparent electrode]
Finally, an antireflection film 18 is deposited on the transparent electrode 16 except at least the portion where the second extraction electrode 17 is formed.
Examples of the film forming method include a sputtering method and a vacuum deposition method.
The compound thin film solar cell shown in the conceptual diagram of FIG. 1 is produced through the above steps.
In the case of producing a compound thin film solar cell module, after the step of forming the back electrode on the substrate, the step of dividing the back electrode with a laser, the step of forming the buffer layer on the light absorption layer, and the buffer layer After the step of forming the transparent electrode, the step of dividing the sample by mechanical scribing is sandwiched between the layers, thereby enabling integration.

A preferred band gap for converting sunlight into energy is 1.0 eV to 1.5 eV. The band gap for the optimal sunlight spectrum is often 1.4 eV to 1.5 eV. There is also a report that the conversion efficiency becomes maximum in the vicinity of 1.2 eV.
In addition, even if it is outside the range of said preferable band gap, it can use for the light absorption layer 14 for converting the light of the short wavelength side of sunlight. The conversion efficiency of the compound thin-film solar cell using the light absorption layer 14 for converting light on the short wavelength side alone is not high. However, it is possible to improve the conversion efficiency of the solar cell by combining the light absorption layer 14 in the above preferable range and the light absorption layer 14 that converts light on the short wavelength side.

The light absorption layer 14 includes a chalcopyrite type compound semiconductor thin film that can be represented by ABC ₂ (the alphabet of ABC ₂ is not an element symbol). A is Cu. B is one or more elements selected from the group consisting of Al, In and Ga. C is one or more elements selected from the group consisting of S, Se and Te.
The conditions of the light absorption layer 14 can be summarized as follows.
The light absorption layer 14 is Cu (Al _1-xy Ga _x In _y ) (Te _1-ab Se _a S _b ) ₂ (where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ a ≦ 1, 0 ≦ b ≦ 1, 0 ≦ x + y ≦ 1, and 0 ≦ a + b ≦ 1).
The light absorption layer 14 is preferably formed on the back electrode by sputtering.
The thickness of the light absorption layer 14 is preferably 0.5 to 3.0 μm. If the thickness of the light absorbing layer 14 is thinner than 0.5 μm, it is too thin to function as the light absorbing layer, and if it is thicker than 3.0 μm, it is not preferable that the manufacturing cost of the light absorbing layer 14 increases. .

The crystal grain size of the compound thin film semiconductor of the light absorption layer 14 is adjusted by heat treatment during or after the film formation. The higher the heating temperature, the larger the crystal grain size of the compound thin film semiconductor.
When the average crystal grain size of the compound semiconductor thin film is adjusted to 1 nm or more and 100 nm or less, it is preferable that the band gap is suitable for absorption of sunlight. When a compound semiconductor having a wide gap is used in advance, it can be controlled to a band gap suitable for absorption of sunlight by heat treatment at a relatively low temperature.
In addition, since the crystal grain size is controlled by heat treatment after film formation, in the range where the average crystal grain size is 10 nm or less, the crystallinity is low and an appropriate band gap may not be formed. The crystal grain size is preferably 10 nm or more and 100 nm or less.

In order to convert sunlight into energy with high efficiency, it is preferable that a light absorption layer that absorbs light in the vicinity of the visible light region where the radiant energy of the solar energy spectrum is strong is included. Therefore, it is preferable that the light absorption layer 14 includes a compound semiconductor thin film having an average crystal grain size of 1 nm to 50 nm. In order to convert sunlight into energy with higher efficiency, a compound semiconductor thin film having an average crystal grain size of 1 nm to 50 nm and a compound semiconductor thin film having an average crystal grain size of more than 50 nm and not more than 100 nm are laminated as the light absorption layer 14. It is preferable. It is more preferable that the number of stacked compound thin film semiconductors is 2 or more because a wide range of wavelengths can be absorbed and converted in sunlight. In addition, when stacking compound semiconductors having different average crystal grain sizes, a compound semiconductor thin film having an average crystal grain size of 50 nm or more and 100 nm or less capable of capturing light with a short wavelength may be disposed on the side irradiated with sunlight. preferable.

As the heat treatment of the light absorption layer 14, annealing in an ultrahigh vacuum atmosphere is preferable. The annealing temperature is preferably 200 ° C. or more and 500 ° C. or less at the substrate temperature. When the annealing temperature is within this range, it is preferable that the band gap has a crystal grain size that is suitable for the light absorption layer 14 of the solar cell.
Further, since crystal growth proceeds in the initial stage of annealing and gradually reaches a steady state, the annealing time is preferably 10 minutes or more and 120 minutes or less.

Further, as a heat treatment method for the light absorption layer 14, a method using an infrared laser is also preferable. Examples of the infrared laser include CW Nd: YAG or a semiconductor laser. Also in the heat treatment with an infrared laser, the heating temperature is preferably 200 ° C. or higher and 500 ° C. or lower from the viewpoint of conversion efficiency of sunlight. Also in the heat treatment using an infrared laser, the preferred range of the average crystal grain size of the compound semiconductor thin film is the same as that of annealing. In addition, by controlling the irradiation site and irradiation temperature of the infrared laser, the light absorption layer 14 in which the average crystal grain size is changed in the film thickness direction as shown in the conceptual diagram of the correlation between the film thickness direction and the particle size in FIG. It is also possible. By changing the grain size stepwise, the band structure of the conduction band changes in synchronization with it. The light absorption layer 14 in which the average crystal grain size is changed stepwise in the film thickness direction is preferable because it can improve carrier collection efficiency by forming an internal electric field and increase open circuit voltage by reducing carrier recombination at the pn junction interface. . The change in the grain size in the film thickness direction is preferably the shape shown in the correlation conceptual diagram of FIG. 4, but may be a shape that monotonously increases from the pn junction interface.

When the light absorption layer 14 is formed, a crystal growth inhibitor may be added to the chalcopyrite type semiconductor.
When a crystal growth inhibitor is added, the growth of the crystal grain size can be adjusted (suppressed). In the case where the heat treatment is performed at the same temperature, if a crystal growth inhibitor is added, crystal growth can be suppressed as compared with a case where a crystal growth inhibitor is not added. Examples of the crystal growth inhibitor include elements such as B, Ti, Fe, Ni, and Nb. The amount of the crystal growth inhibitor added is preferably 5 at% or more and 30 at% or less with respect to the atomic weight of the light absorption layer 14, for example. As described above, when a crystal growth inhibitor is added, the band gap can be easily adjusted, and light in a wide range of wavelengths suitable for absorption of sunlight can be absorbed and converted.

Further, the light absorption layer 14 to which the crystal growth inhibitor is added so that the concentration of the crystal growth inhibitor has a gradient distribution in the film thickness direction of the light absorption layer 14 is formed, and the band graded film shown in FIG. The light absorption layer 14 may be used. As described above, the light absorption layer 14 whose average crystal grain size is changed stepwise in the film thickness direction by the addition of the crystal growth inhibitor improves carrier collection efficiency by forming an internal electric field and carriers at the pn junction interface. It is preferable because the open circuit voltage can be improved by reducing recombination. The change in the grain size in the film thickness direction is preferably the shape shown in the correlation conceptual diagram of FIG. 4, but may be a shape that monotonously increases from the pn junction interface.

Alternatively, a light absorption layer 14 having a multilayer structure may be formed by laminating compound semiconductor thin films to which different concentrations of crystal growth inhibitors are added.
By forming a narrow gap and wide gap compound semiconductor as the light absorption layer 14 and heat-treating it, a light absorption layer capable of converting light in a wider wavelength range into energy in sunlight is obtained. More preferably.

Hereinafter, in the examples, configurations other than the light absorption layer 14 used in the compound thin film solar cell will be described.
As the substrate 11, it is desirable to use blue plate glass, and it is also possible to use a metal plate such as stainless steel, Ti or Cr, or a resin such as polyimide.

As the back electrode 12, a metal film such as Mo or W can be used. Among these, it is desirable to use a Mo film.

As the extraction electrodes 13 and 17, for example, Al, Ag, or Au can be used. Furthermore, in order to improve the adhesion with the transparent electrode 15, after depositing Ni or Cr, Al, Ag or Au may be deposited.

As the buffer layer 15, CdS, Zn (O, S, OH), or ZnO added with Mg can be used. The chalcopyrite compound semiconductor of the light absorption layer 14 functions as a p-type semiconductor, the buffer layer 15a typified by CdS or ZnO: Mg functions as an n-type semiconductor, and the buffer layer 15b typified by ZnO functions as an n ⁺ -type layer. Conceivable. By selecting the material of the buffer layer 15a so as to induce a conduction band discontinuity (CBO) ΔEc at the pn junction interface, carrier recombination can be reduced.

The transparent electrode layer 16 is required to transmit sunlight and have conductivity, for example, ZnO containing 2 wt% of alumina (Al ₂ O ₃ ): ZnO containing Al or B from diborane as a dopant. : B can be used.

Since sunlight can be taken in with high efficiency, it is desirable to provide the antireflection film 18. For example, MgF ₂ is desirably used as the antireflection film 18.
Hereinafter, the present invention will be described in detail by way of examples.

Example 1
A blue glass substrate was used as the substrate 11, and a Mo thin film serving as the back electrode 12 was deposited by about 700 nm by sputtering. Sputtering was performed by applying RF 200 W in an Ar gas atmosphere using Mo as a target.
After the Mo thin film serving as the back electrode 12 was deposited, a CuAlTe ₂ thin film serving as the light absorption layer 14 was similarly deposited by about 2 μm by RF sputtering. Film formation was performed by applying RF 200 W in an Ar gas atmosphere.

After film formation, the film formation chamber was evacuated and annealed in an ultra-high vacuum atmosphere at 200 ° C. The CuAlTe ₂ thin film immediately after sputtering is amorphous and has a very small particle size. Therefore, by performing annealing at a high temperature, the CuAlTe ₂ thin film crystallized and the particle size became about 10 nm. As a result, the CuAlTe ₂ thin film had a band gap value suitable for the light absorption layer 14.

A ZnO thin film to which Mg was added as a buffer layer 15a was deposited on the obtained light absorption layer 14 to a thickness of about 50 nm. RF sputter was used for film formation, but it was performed at an output of 50 W in consideration of plasma damage at the interface. A ZnO thin film was deposited as a buffer layer 15b on the buffer layer 15a, and then ZnO: Al containing 2 wt% of alumina (Al ₂ O ₃ ) to be the transparent electrode 16 was deposited to a thickness of about 1 μm. As the extraction electrodes 13 and 17, NiCr and Au were deposited by an evaporation method. The film thickness was 100 nm and 300 nm, respectively. Finally, MgF ₂ was deposited by sputtering as the antireflection film 18 to produce the compound thin film solar cell shown in FIG.
The optical property evaluation result (a) and cross-sectional SEM image (b) of the light absorption layer of the manufactured compound thin film solar cell are shown in FIG. From the optical property evaluation results, the band gap of the light absorption layer 14 of Example 1 was estimated to be 1.05 eV. Moreover, the thin film which consists of a compound semiconductor with a very small particle size was confirmed from the SEM image.

(Example 2)
A compound thin-film solar cell was manufactured in the same manner as in Example 1 except that Cu (Al _1-x In _x ) Te ₂ to be the light absorption layer 14 was formed by RF sputtering.
x is a numerical value larger than 0 and smaller than 1.
Even when Cu (Al _1-x In _x ) Te ₂ is used as the light absorption layer 14, it was amorphous before high-temperature heat treatment, but by annealing at 200 ° C., Cu (Al _1-x In _x ) Te ₂ is crystallized, and a compound thin film solar cell having a band gap value suitable as the light absorption layer 14 is obtained.

(Example 3)
A compound thin-film solar cell is manufactured in the same manner as in Example 1 except that Cu (Al _1-x Ga _x ) Te ₂ to be the light absorption layer 14 is formed by RF sputtering.
x is a numerical value larger than 0 and smaller than 1.
Even when Cu (Al _1-x Ga _x ) Te ₂ is used as the light absorption layer 14, it was amorphous before high-temperature heat treatment, but by annealing at 200 ° C., Cu (Al _1-x Ga _{x) x} ) Te ₂ crystallizes, and a compound thin film solar cell having a band gap value suitable as the light absorption layer 14 is obtained.

Example 4
A compound thin-film solar cell is manufactured by the same method as in Example 1 except that Cu (Al _1-xy In _x Ga _y ) Te ₂ to be the light absorption layer 14 is formed by RF sputtering.
x and y are numerical values larger than 0 and smaller than 1.
Even when Cu (Al _1-xy In _x Ga _y ) Te ₂ is used as the light absorption layer 14, it was amorphous before high-temperature heat treatment, but by annealing at 200 ° C., Cu (Al _1-xy In _x Ga _y ) Te ₂ is crystallized, and a compound thin film solar cell having a band gap value suitable as the light absorption layer 14 is obtained.

(Example 5)
A compound thin film solar cell is manufactured by the same method as in Example 1 except that CuAlSe ₂ to be the light absorption layer 14 is formed by RF sputtering.
Even when CuAlSe ₂ is used as the light absorption layer 14, it was amorphous before the high-temperature heat treatment, but by annealing at 200 ° C., CuAlSe ₂ crystallized, and a band gap value suitable for the light absorption layer 14. The compound thin film solar cell is obtained.

(Example 6)
A compound thin film solar cell is manufactured by the same method as in Example 1 except that CuGaSe ₂ to be the light absorption layer 14 is formed by RF sputtering.
Even when CuGaSe ₂ is used as the light absorption layer 14, it was amorphous before the high-temperature heat treatment, but by annealing at 200 ° C., CuGaSe ₂ crystallizes, and a band gap value suitable for the light absorption layer 14. The compound thin film solar cell is obtained.

Examples 5 and 6 are not examples in which any one of Al, In, and Ga is combined, but Al, In, and Ga may be used in combination.

(Example 7)
A compound thin film solar cell is manufactured by the same method as in Example 1 except that CuAlS ₂ to be the light absorption layer 14 is formed by RF sputtering.
Even when CuAlS ₂ is used as the light absorption layer 14, it was amorphous before high-temperature heat treatment, but by annealing at 200 ° C., CuAlS ₂ crystallized, and a band gap value suitable for the light absorption layer 14. The compound thin film solar cell is obtained.

(Example 8)
A compound thin film solar cell is manufactured by the same method as in Example 1 except that CuInS ₂ to be the light absorption layer 14 is formed by RF sputtering.
Even when CuInS ₂ is used as the light absorption layer 14, it was amorphous before high-temperature heat treatment, but by annealing at 200 ° C., CuInS ₂ crystallized, and a band gap value suitable for the light absorption layer 14. The compound thin film solar cell is obtained.

Example 9
A compound thin film solar cell is manufactured by the same method as in Example 1 except that CuGaS ₂ to be the light absorption layer 14 is formed by RF sputtering.
Even when CuGaS ₂ is used as the light absorption layer 14, it was amorphous before the high-temperature heat treatment, but CuGaS ₂ was crystallized by annealing at 200 ° C., which is suitable for the light absorption layer 14. Value compound thin film solar cells are obtained.

Example 7-9 is not an example in which any of Al, In, and Ga is combined, but Al, In, and Ga may be used in combination.

(Example 10-18)
Except that the light absorption layer 14 is heat-treated at an annealing temperature of 500 ° C., it is the same as in Examples 1 to 9. In the present embodiment, the treatment is performed at a higher temperature than in the first embodiment, and as a result, the crystal of the light absorption layer 14 grows greatly. FIG. 3 shows an optical property evaluation result (a) and a cross-sectional SEM image (b) of the light absorption layer 14 when CuAlTe ₂ is used for the light absorption layer in this example. In this case, the band gap of the light absorption layer 14 was estimated to be 2.25 eV. Moreover, the thin film which consists of a compound semiconductor whose average crystal grain diameter is about 100 nm was confirmed from the SEM image. Since the band gap increases as the average crystal grain size increases, it is suitable as the light absorption layer 14 for converting light on the short wavelength side.

(Comparative Example 1-9)
The same as in Examples 1 to 9, except that the annealing temperature is 100 ° C. In this embodiment, the processing is performed at a lower temperature than in the first embodiment. By processing at a lower temperature than in Example 1, the crystal of the light absorption layer 14 hardly grows. In the case of this comparative example, CuAlTe ₂ is generally amorphous, and the crystal grain size and the band gap of the compound of the light absorption layer 14 cannot be suitably controlled.

(Comparative Example 10)
A compound thin-film solar cell is manufactured by the same method as in Example 1 except that CuInTe _{2 serving} as the light absorption layer 14 is formed by RF sputtering.
When using CuInTe ₂ as the light absorption layer 14, the bulk value of the band gap is originally 1.0 eV or less, and the band gap cannot be suitably controlled by controlling the crystal grain size of the light absorption layer.

(Comparative Example 11)
A compound thin film solar cell is manufactured by the same method as in Example 1 except that CuGaTe _{2 serving} as the light absorption layer 14 is formed by RF sputtering.
Even when CuGaTe ₂ is used as the light absorption layer 14, it was amorphous before the high-temperature heat treatment, but can be crystallized by annealing at 200 ° C. However, since the bulk value of the band gap is originally 1.5 eV or less, when the annealing temperature is 200 ° C., the band gap cannot be suitably controlled by controlling the crystal grain size of the light absorption layer.

(Comparative Example 12)
A compound thin-film solar cell is manufactured by the same method as in Example 1 except that Cu (In _1-x Ga _x ) Te ₂ to be the light absorption layer 14 is formed by RF sputtering.
x is a numerical value larger than 0 and smaller than 1.
Even when Cu (In _1-x Ga _x ) Te ₂ is used as the light absorption layer 14, it was amorphous before high-temperature heat treatment, but can be crystallized by annealing at 200 ° C. However, since the bulk value of the band gap is originally 1.5 eV or less, the band gap cannot be suitably controlled by controlling the crystal grain size of the light absorption layer at an annealing temperature of 200 ° C.

(Comparative Example 13)
A compound thin film solar cell is manufactured by the same method as in Example 1 except that CuInSe ₂ to be the light absorption layer 14 is formed by RF sputtering.
Even when CuInSe ₂ is used as the light absorption layer 14, it was amorphous before high-temperature heat treatment, but can be crystallized by annealing at 200 ° C. However, since the bulk value of the band gap is originally 1.5 eV or less, when the annealing temperature is 200 ° C., the band gap cannot be suitably controlled by controlling the crystal grain size of the light absorption layer.

(Example 19)
Example 1 is the same as Example 1 except that the light absorption layer 14 is heat-treated at 200 ° C. during film formation. Even when heat treatment is performed during the formation of the light absorption layer, CuAlTe ₂ grows to a crystal grain size suitable for the light absorption layer 14.

(Example 20)
The same as Example 1 except that B is added to the material of the light absorption layer 14 to form a light absorption layer and anneal at 500 ° C. The addition of B is 20 at% on the front side and 5 at% on the back side with respect to the atomic weight of the light absorption layer 14. The addition amount of B is controlled so that the addition amount of B has a gradient distribution from the front side to the back side. By changing the band gap in the film thickness direction of the light absorption layer 14, a band-graded light absorption layer 14 is obtained.

(Example 21)
It is the same as that of Example 1 except performing heat processing from the both sides of the light absorption layer 14 with a CW Nd: YAG laser instead of annealing. In this embodiment, heat treatment is performed with an infrared laser, to control the average crystal grain size of CuAlTe ₂ in a suitable range can be adjusted to a suitable band gap value CuAlTe ₂ thin film as a light absorbing layer 14 .

(Example 22)
Example 21 is the same as Example 21 except that the intensity of the CW Nd: YAG laser is adjusted and heat treatment is performed only from the back surface of the light absorption layer 14. In the present embodiment, heat treatment is performed only with the infrared laser from the back surface of the light absorption layer, and the average crystal grain size of CuAlTe ₂ of the light absorption layer 14 is distributed in the film thickness direction. The obtained light absorption layer 14 is band graded.

(Example 23)
Example 12 is the same as Example 12 except that the back side of the light absorption layer 14 is irradiated with a strong laser with a CW Nd: YAG laser and a weak laser is irradiated from the front side. In this example, the distribution of the average crystal grain size of CuAlTe ₂ in the light absorption layer 14 is caused in the film thickness direction as in Example 22. The obtained light absorption layer 14 is band graded.

(Example 24)
B is added to the material of the light absorption layer 14, and the addition of B is performed by laminating the light absorption layer 1 μm at a time so that the front side is 20 at% and the back side is 5 at% with respect to the atomic weight of the light absorption layer 14. Except for this, this is the same as Example 21.
By controlling the addition amount of B so that the addition amount of B is different between the front side and the back side, the light absorption layer after heating becomes a light absorption layer 14 in which layers having different average crystal grain sizes are laminated.

(Example 25)
After laminating 1 μm of CuAlTe ₂ to which 20 at% of B is added as the light absorption layer 14 with respect to the atomic weight of the light absorption layer 14, 1 μm of CuAlTe ₂ having no addition of B or the like is further laminated and annealed at 500 ° C. Other than the above, this embodiment is the same as the first embodiment.

In Examples 24 and 25, depending on the presence or absence of the crystal growth inhibitor or a difference in concentration, the obtained light absorption layer 14 changed the short wavelength light 23 on the front side like the light absorption layer 14 of the multi-junction solar cell of FIG. The wide gap CuAlTe ₂ layer 21 that absorbs has a large crystal grain size, and the narrow gap CuAlTe ₂ layer 22 that absorbs the long wavelength light 24 on the back side has a small grain size. Accordingly, the light absorption layer 14 having layers having different band gaps can be obtained.
By laminating both of the crystal growth inhibitor added and the crystal growth inhibitor not added, heat treatment is performed to obtain the light absorption layer 14 in which the front side absorbs the short wavelength and the back side absorbs the long wavelength.

Although omitted in the embodiments, Te, Se, and S are not limited to one, but may be a combination of two or more.
The above example is an example of an embodiment of the present invention. Therefore, the compound thin film solar cell provided with the element of the present invention and the manufacturing method thereof are included in the scope of the present invention.

DESCRIPTION OF SYMBOLS 10 ... Compound thin film solar cell, 11 ... Board | substrate, 12 ... Back electrode, 13 ... 1st extraction electrode, 14 ... Light absorption layer, 15a ... Buffer layer, 15b ... Buffer layer, 16 ... Transparent electrode layer, 17 ... 2nd 18 ... Antireflection film, 21 ... Wide gap CuAlTe ₂ layer, 22 ... Narrow gap CuAlTe ₂ layer, 23 ... Short wavelength light, 24 ... Long wavelength light

Claims (10)

A substrate,
A back electrode provided on the substrate;
A first extraction electrode provided in a part on the back electrode;
Cu (Al _1-xy Ga _x In _y ) (Te _1-ab Se _a S _b ) ₂ provided at a portion excluding at least the portion where the first extraction electrode is provided on the back electrode. A light-absorbing layer containing a compound semiconductor thin film represented by the formula (where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ a ≦ 1, 0 ≦ b ≦ 1, 0 ≦ x + y ≦ 1, 0 ≦ a + b ≦) 1)
A buffer layer provided on the light absorption layer;
A transparent electrode layer provided on the buffer layer;
At least a second extraction electrode provided on the transparent electrode layer,
A compound thin film solar cell, wherein the compound semiconductor thin film has an average crystal grain size of 1 nm or more and 100 nm or less. The compound thin film solar cell according to claim 1, wherein the compound semiconductor thin film has an average crystal grain size of 10 nm or more and 100 nm or less. The compound thin film solar cell according to claim 1, wherein the compound semiconductor thin film has an average crystal grain size of 1 nm or more and 50 nm or less. 2. The compound thin film solar cell according to claim 1, wherein the compound semiconductor thin film is a layer having an average crystal grain size of 1 nm or more and 50 nm or less and a layer having an average crystal grain size of greater than 50 nm and 100 nm or less. 2. The compound thin film solar cell according to claim 1, wherein the light absorption layer contains one or more selected from B, Ti, Fe, Ni and Nb. 6. The compound thin film solar cell according to claim 1, wherein an average crystal grain size of the compound semiconductor thin film changes stepwise in a film thickness direction of the light absorption layer. Forming a back electrode on the substrate;
A light absorption layer containing a compound semiconductor thin film represented by Cu (Al _1-xy Ga _x In _y ) (Te _1-ab Se _a S _b ) ₂ on the back electrode (where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ a ≦ 1, 0 ≦ b ≦ 1, 0 ≦ x + y ≦ 1, 0 ≦ a + b ≦ 1)
A step of heat-treating the light absorbing layer during the step of forming the light absorbing layer or after the step of forming the light absorbing layer;
Forming a buffer layer on the light absorbing layer;
Forming a transparent electrode layer on the buffer layer;
Forming a first extraction electrode on the back electrode;
Forming a second extraction electrode on the transparent electrode layer;
A method for producing a compound thin-film solar cell comprising: In the step of heat-treating the light absorption layer,
The heating method is annealing or infrared laser irradiation,
The method for producing a compound thin-film solar cell according to claim 7, wherein the heating temperature is 200 ° C. or more and 500 ° C. or less. In the step of heat-treating the light absorption layer,
8. The method of manufacturing a compound thin-film solar cell according to claim 7, wherein the light absorption layer is heat-treated by irradiating a local area of the light absorption layer with an infrared laser. In the step of forming the light absorption layer,
The compound thin film solar according to claim 7, wherein a light absorption layer is formed by adding a crystal growth inhibitor satisfying the following condition (1) or (2) to a material for forming the compound semiconductor thin film. Battery manufacturing method.
(1) Crystal growth inhibitor which is one or more elements selected from B, Ti, Fe, Ni and Nb and has a constant concentration with respect to the light absorption layer (2) B, Ti, Fe A crystal growth inhibitor which is one or more elements selected from Ni and Nb and whose concentration changes stepwise in the film thickness direction of the light absorption layer

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