JP5465859B2 - Photovoltaic element and manufacturing method thereof - Google Patents

Description

  The present invention relates to a photovoltaic element having a light-absorbing layer formed into a thin film from a p-type chalcopyrite structure compound having conductivity, and a method for manufacturing the photovoltaic element.

Solar cells are widely used for various applications because they are clean power generation elements using inexhaustible sunlight as an energy source. A solar cell uses silicon, a compound semiconductor, or the like as a photoelectric conversion material, and includes an element that uses a photovoltaic force generated in the photoelectric conversion material when light such as sunlight enters the photoelectric conversion material.
And although a solar cell can be classified into some, a monocrystalline silicon solar cell and a polycrystalline silicon solar cell use an expensive silicon substrate. For this reason, a solar cell having a thin film structure, which is expected to greatly reduce the material cost, is used.

Thin-film solar cells include non-silicon-based semiconductor materials as photoelectric conversion materials, compounds with chalcopyrite-type crystal structures, especially copper (Cu), indium (In), gallium (Ga), and selenium. A CIGS solar cell using a CIGS compound made of (Se) has attracted attention.
As a configuration of the CIGS solar cell, for example, a lower electrode thin film formed on a glass substrate, a light absorbing layer thin film made of a CIGS compound containing copper, indium, gallium, and selenium, and a light absorbing layer thin film It is composed of a high-resistance buffer layer thin film formed of InS, ZnS, CdS, ZnO or the like and an upper electrode thin film formed of ZnOAl or the like (for example, see Patent Document 1).
The CIGS solar cell as described in Patent Document 1 has a thickness of several μm because the CIGS semiconductor material has a high light absorption rate and a power generation layer can be formed by a method such as vapor deposition or sputtering. And can be thin. Therefore, downsizing and material cost can be kept low, and energy saving at the time of manufacturing a solar cell can be achieved.

JP 2007-317885 A

However, the upper electrode thin film formed of ZnOAl or the like is a material that can realize low resistance by crystallization. When crystallized, the n-type formed between the buffer layer or the buffer layer and the transparent electrode layer. A boundary is formed at the interface with the semiconductor layer, which becomes an energy barrier, and electrical bonding properties are reduced.
In the case of the solar cell element in which the boundary is formed in this way, since the junction area at the interface is small, there is a problem in reliability due to a decrease in electrical connectivity while the solar cell element is used for a long time.
In view of these points, the present invention reduces the energy barrier due to the boundary with the transparent electrode layer even in a light absorption layer formed of a compound having a chalcopyrite type crystal structure, and has a long-term electrical connection property. It is an object of the present invention to provide a photovoltaic device capable of obtaining stable characteristics and a method for manufacturing the photovoltaic device.

The photovoltaic device according to the present invention has a glass substrate, a back electrode layer provided on one surface of the glass substrate, and a conductive p laminated on the back electrode layer with a chalcopyrite structure compound. Type light-absorbing layer, a light-transmitting n-type buffer layer laminated on the light-absorbing layer and pn-junction with the light-absorbing layer, and the light-absorbing layer laminated on the buffer layer and laminated A translucent transparent electrode layer provided from one side of the buffer layer to the back electrode layer , the transparent electrode layer comprising indium oxide and zinc oxide as main components, and an atomic force microscope (Atomic microscope). It is characterized by being formed into an amorphous thin film having a particle diameter of 0.001 μm or less by surface observation of a Force Microscope.

In the present invention, the transparent electrode layer is formed by sputtering film formation using a mixed gas of argon (Ar) and oxygen (O ₂ ), and the oxygen partial pressure of the mixed gas is 1 × 10 ⁻³ Pa or more and 5 ×. A structure in which at least one of a condition of 10 ⁻² Pa or less and a condition of a substrate temperature of 100 ° C. or more and 200 ° C. or less is set to form an amorphous thin film. Is preferred.

In the present invention, it is preferable that the transparent electrode layer has a composition In ₂ O ₃ / (In ₂ O ₃ + ZnO) formed to be 50% by mass to 95% by mass.

  Furthermore, in the present invention, the transparent electrode layer preferably has a configuration in which the amount of the third component in the composition containing indium oxide and zinc oxide as main components is 20% by mass or less.

  And in this invention, it is preferable to set it as the structure provided with the translucent n-type semiconductor layer laminated | stacked on the said buffer layer and becoming n-type with respect to the said light absorption layer with higher resistance than the said buffer layer.

  In the present invention, the n-type semiconductor layer is preferably formed in an amorphous thin film having a particle size of 0.001 μm or less as observed by an atomic force microscope.

  Furthermore, in the present invention, the n-type semiconductor layer is preferably formed of the same constituent material as the transparent electrode layer.

Further, in the present invention, the n-type semiconductor layer is formed by sputtering film formation using a mixed gas of argon (Ar) and oxygen (O ₂ ), and the oxygen partial pressure of the mixed gas is 1 × 10 ⁻² Pa or more. At least one of a condition of 0.2 Pa or less and a condition of a substrate temperature of 100 ° C. or more and 200 ° C. or less is set, and the amorphous thin film is formed. preferable.

  In addition, it is preferable that the transparent electrode layer is provided with a surface transparent electrode layer that is laminated and has conductivity and translucency and has a refractive index smaller than that of the transparent electrode layer.

  In the present invention, the surface transparent electrode layer is preferably formed of the same constituent material as the transparent electrode layer.

In the present invention, the surface transparent electrode layer is formed by sputtering using a mixed gas of argon (Ar) and oxygen (O ₂ ), so that the oxygen partial pressure of the mixed gas is 1 × 10 ⁻³ Pa or more. At least one of a condition of × 10 ⁻² Pa or less and a condition of a substrate temperature of 100 ° C. or more and 200 ° C. or less is set to form an amorphous thin film. It is preferable.

  The method for manufacturing a photovoltaic device according to the present invention includes a back electrode layer forming step of forming a back electrode layer on a glass substrate as a thin film, and a p-type light absorption with a chalcopyrite structure compound on the back electrode layer. A light absorption layer forming step of forming a thin film layer, a buffer layer forming step of forming an n-type buffer layer pn-junctioned with the light absorption layer on the light absorption layer, and a transparent electrode layer on the buffer layer. A transparent electrode layer forming step, wherein the transparent electrode layer forming step includes indium oxide and zinc oxide as main components, and an atomic force A thin film is formed in an amorphous state having a particle diameter of 0.001 μm or less by surface observation with a microscope (Atomic Force Microscope).

According to the present invention, a back electrode layer provided on one surface of a glass substrate has a light-transmitting n-type that is pn-junctioned to the light-absorbing layer to a p-type light-absorbing layer having conductivity with a compound having a chalcopyrite structure. A transparent electrode layer in a photovoltaic device in which a buffer layer is laminated and laminated on the buffer layer and a light-transmitting transparent electrode layer is provided from one side of the light absorption layer and the buffer layer to one of the back electrode layers Is formed into an amorphous thin film having a particle diameter of 0.0001 μm or more and 0.001 μm or less by surface observation with an atomic force microscope, with indium oxide and zinc oxide as main components. without a boundary is formed between the n-type semiconductor layer provided between the layer and the transparent electrode layer, also, by small particle size, it is possible to earn the surface area of the joint surface, stable It is possible to secure the gas-bonding property. Therefore, the photovoltaic device obtained in this configuration has stable electrical bonding even when used for a long period of time, and can provide stable energy conversion efficiency for a long period of time.

Hereinafter, an embodiment according to a photovoltaic device of the present invention will be described with reference to the drawings.
FIG. 1 is a cross-sectional view showing a schematic configuration of a photovoltaic element constituting the solar cell in the present embodiment.

[Configuration of photovoltaic element]
In FIG. 1, reference numeral 100 denotes a photovoltaic element, and this photovoltaic element 100 is an element that generates an electromotive force upon incidence of light. A plurality of photovoltaic elements 100 are connected in series, for example, and configured as a solar cell that can be taken out as electric energy.
In the photovoltaic device 100, the back electrode layer 120, the light absorption layer 130, the buffer layer 140, the n-type semiconductor layer 150, the transparent electrode layer 160, and the surface transparent electrode layer 170 are sequentially laminated on the glass substrate 110. It has a layered structure.
The glass substrate 110 is made of alkali glass such as soda lime glass, but is not limited thereto.

(Back electrode layer)
The back electrode layer 120 is formed as a thin film on one surface of the glass substrate 110 with a conductive material. A plurality of the back electrode layers 120 are provided in parallel with an insulating distance in a state where the planar region has a predetermined width. The back electrode layer 120 is formed by, for example, forming Mo (molybdenum) by DC sputtering or the like and then dividing the film by the width of the insulation distance by laser light irradiation or the like. A groove between the back electrode layers 120 having the width of the insulation distance is shown in FIG.
As the conductive material, Mo will be exemplified since the CIGS type is exemplified as the light absorption layer 130 as will be described in detail later. However, the conductive material is not limited to this, but gold, silver, copper, aluminum, nickel, iron, chromium, molybdenum , Tungsten, titanium, cobalt, tantalum, niobium, zirconium, and other metals or alloys. In particular, a metal with high reflectance is preferable. Further, the film forming method is not limited to DC sputtering, and examples thereof include a vapor deposition method, various sputtering methods, a CVD method, a spray method, a spin-on method, and a dip method.
The back electrode layer 120 is preferably formed with a thickness dimension of 0.01 μm to 1 μm, preferably 0.1 μm to 1 μm. Here, if the thickness is less than 0.01 μm, the resistance value may increase. On the other hand, if it is thicker than 1 μm, there is a risk of peeling. Thus, the thickness dimension of the back electrode layer 120 is set to 0.01 μm or more and 1 μm or less, preferably 0.1 μm or more and 1 μm or less.
Further, the back electrode layer 120 is not limited to a flat surface, and may have a function of irregularly reflecting light by forming an uneven shape on the surface. That is, the long wavelength light that could not be absorbed by the laminated light absorption layer 130 is scattered to increase the optical path length in the light absorption layer 130, thereby improving the long wavelength sensitivity of the photovoltaic device 100, Short circuit current increases. As a result, the photoelectric conversion efficiency can be improved. Note that it is desirable that the uneven shape for scattering light has a difference in height between peaks and valleys of the unevenness of Rmax, which is 0.2 μm or more and 2.0 μm or less. Here, when Rmax is larger than 2.0 μm, the coverage property is lowered, film thickness unevenness may occur, and the resistance value may be uneven. Therefore, when an uneven shape is provided, Rmax is 0.2 μm or more. It is preferable to set it to 0 μm or less. Various methods such as dry etching, wet etching, sand blasting, and heating can be applied as the processing of the uneven shape.

(Light absorption layer)
The light absorption layer 130 is a thin film formed in a state of being cross-linked across the back electrode layer 120 adjacent to the top surface of the back electrode layer 120 with a chalcopyrite compound which is a compound of a chalcopyrite structure having p-type conductivity. Yes.
Specifically, the light absorption layer 130 is made of a group II-VI semiconductor such as ZnSe, CdS, or ZnO, a group III-V semiconductor such as GaAs, InP, or GaN, a group IV compound semiconductor such as SiC or SiGe, Cu (In , Ga) Se ₂ , Cu (In, Ga) (Se, S) ₂ , or chalcopyrite semiconductors (I-III-VI group semiconductors) such as CuInS ₂ can be used. In this embodiment, a configuration in which a so-called CIGS-based light absorption layer 130 in which Cu, In, Ga, and Se are formed into a thin film by sputtering or vapor deposition is illustrated. That is, the film is formed by various film forming methods using various materials so as to have a chalcopyrite structure composition in the film forming state.
This film formation is manufactured by, for example, a multi-source deposition method using a molecular beam epitaxy apparatus.
The light absorption layer 130 is preferably formed with a thickness dimension of 0.1 μm to 10 μm, preferably 0.5 μm to 5 μm. Here, if the thickness is less than 0.1 μm, the amount of light absorbed from outside light may be reduced. On the other hand, if it is thicker than 10 μm, the productivity may be reduced or the film may be easily peeled off due to film stress. Accordingly, the thickness dimension of the light absorption layer 130 is set to 0.1 μm to 10 μm, preferably 0.5 μm to 5 μm.
The light absorption layer 130 is formed on the back electrode layer 120, and after the buffer layer 140 described later is further formed, the light absorption layer 130 is divided into a state in which the back electrode layer 120 is exposed by, for example, mechanical scribing. The back electrode layer 120 is formed so as to be cross-linked. The light absorption layer 130 is not limited to these methods, and various methods such as selenization of Cu—In—Ga by annealing can be used. Further, the light absorption layer 130 is not limited to Cu, In, Ga, and Se.

(Buffer layer)
The buffer layer 140 is formed as a thin film on the upper surface of the light absorption layer 130. The buffer layer 140 is a light-transmitting and relatively low-resistance n-type semiconductor layer that is stacked on the light absorption layer 130 and forms a pn junction. Further, the buffer layer 140 remains on the surface of the light absorption layer 130 and also functions as a barrier against a semimetal resistance layer such as Cu ₂ Se that functions as a shunt path.
The buffer layer 140 is formed into a thin film by growing an InS solution, for example. As this film formation, it manufactures, for example on the manufacturing conditions of CBD (Chemical Bath Deposition).
The buffer layer 140 is preferably formed to have a thickness dimension of 0.01 μm to 0.5 μm, preferably 0.1 μm to 0.5 μm. Here, if the thickness is less than 0.01 μm, pn junction spots may occur. On the other hand, when the thickness is greater than 0.5 μm, light from outside light is inhibited, and the light absorption of the light absorption layer 130 may be reduced. Accordingly, the thickness dimension of the buffer layer 140 is set to 0.01 μm or more and 0.5 μm or less, preferably 0.1 μm or more and 0.5 μm or less.
In addition, although CIS system is illustrated as the light absorption layer 130, InS is illustrated. However, the present invention is not limited to this, and any material can be used as long as it is a material that can be pn-bonded favorably with the light absorption layer 130.
The buffer layer 140 is divided together with the light absorption layer 130 by mechanical scribing or the like of the light absorption layer 130 described above.

(N-type semiconductor layer)
The n-type semiconductor layer 150 is an amorphous layer formed in a thin film on the upper surface of the buffer layer 140. The n-type semiconductor layer 150 is light-transmitting and has an n-type relatively high resistance to the light absorption layer 130, that is, the light absorption layer 130 that functions as a hole carrier. Functions as an electronic carrier. Further, the n-type semiconductor layer 150 prevents a decrease in open-circuit voltage.
The n-type semiconductor layer 150 has a resistance value of 10 kΩ / □ or more and 1000 kΩ / □ or less. Here, when the resistance value is smaller than 100 kΩ / □, the electrons formed in the light absorption layer easily move to the anode side, the open-circuit voltage is lowered, and the photoelectric conversion efficiency may be lowered. On the other hand, when the resistance value is greater than 1000 kΩ / □, the open-circuit voltage is improved, but the drive voltage of the photoelectric conversion element may be increased. Thereby, the resistance value of the n-type semiconductor layer 150 is set to 10 kΩ / □ or more and 1000 kΩ / □ or less.
The n-type semiconductor layer 150 is formed, for example, by sputtering using a mixed gas of argon (Ar) and oxygen (O ₂ ), particularly in direct current sputtering, with an oxygen partial pressure pO ₂ of 1 × 10 ^{− At} least one of the conditions of ² Pa to 0.2 Pa and the substrate temperature of 100 ° C. to 200 ° C. is set, and the surface of the atomic force microscope is set. It is produced in an amorphous state with a particle size of 0.001 μm or less by observation.
Here, if the oxygen partial pressure pO ₂ is lower than 1 × 10 ⁻² Pa, a low resistance film may be formed. On the other hand, if the oxygen partial pressure pO ₂ is higher than 0.2 Pa, the plasma discharge becomes unstable in the DC sputtering film forming method, and there is a possibility that stable film formation cannot be performed. Further, when the substrate temperature is lower than 100 ° C., the interface reaction between the n-type buffer layer 140 component (such as sulfur (S)) and the n-type semiconductor layer 150 does not proceed, and the n-type semiconductor layer 150 does not increase in resistance. There is a fear. On the other hand, when the substrate temperature is higher than 200 ° C., the n-type buffer layer 140 may be deteriorated.
Further, in the formation of the n-type semiconductor layer 150, the main component is indium oxide and zinc oxide, and the amorphous particle having a particle size of 0.001 μm or less by surface observation with an atomic force microscope (AFM) is used. Manufactured. Here, if the particle diameter by AFM surface observation becomes coarser than 0.001 μm, the interfacial bonding property with the n-type buffer layer 140 may be deteriorated and an energy barrier may be generated. As a result, the particle diameter of the AFM surface observed is set to 0.001 μm or less.
The n-type semiconductor layer 150 is preferably formed with a thickness of 0.01 μm to 1 μm, preferably 0.1 μm to 1 μm. Here, if the thickness is less than 0.01 μm, the blocking effect of holes generated in the light absorption layer 130 may be reduced. On the other hand, when the thickness is greater than 1 μm, the transmittance is lowered, and the absorption of external light in the light absorption layer 130 may be hindered. Thereby, the thickness dimension of the n-type semiconductor layer 150 is set to 0.01 μm or more and 1 μm or less, preferably 0.1 μm or more and 1 μm or less.
In addition, as described above, the n-type semiconductor layer 150 is divided together with the light absorption layer 130 and the buffer layer 140 by mechanical scribing or the like. A groove formed by mechanical scribing or the like and exposing the back electrode layer 120 between the light absorption layer 130, the buffer layer 140, and the n-type semiconductor layer 150 is shown as a first processed groove 131 in FIG.

(Transparent electrode layer)
The transparent electrode layer 160 is formed in the first processed groove 131 extending from the upper surface of the n-type semiconductor layer 150 to the back electrode layer 120 from one side of the scribed light absorption layer 130, the buffer layer 140, and the n-type semiconductor layer 150. It is formed as a thin film. The transparent electrode layer 160 is made of the same material as that of the n-type semiconductor layer 150, that is, the main composition is (In ₂ O ₃ + ZnO), and the surface of an atomic force microscope is formed by DC sputtering or vapor deposition. A thin film is formed with an amorphous particle size of 0.001 μm or less by observation. In other words, the same material can be used to form a film with the same apparatus.
Further, the transparent electrode layer 160 has a resistance value of 5Ω / □ or more and 20Ω / □ or less. Here, when the resistance value is smaller than 5Ω / □, the film thickness is increased and the transmittance may be reduced. On the other hand, if the resistance value is larger than 20Ω / □, a sufficient threshold voltage for moving electrons and holes generated in the light absorption layer 130 or the like is not applied, which may cause a disadvantage that energy conversion efficiency is lowered. There is. Thereby, the resistance value of the transparent electrode layer 160 is set to 5Ω / □ or more and 20Ω / □ or less.
The transparent electrode layer 160 is formed by sputtering using, for example, a mixed gas of Ar and O _2, and in particular by direct current sputtering that is the same as the film forming method of the n-type semiconductor layer 150, the oxygen partial pressure pO _{2 is set} to 1. At least one of a condition of × 10 ⁻³ Pa to 5 × 10 ⁻² Pa and a condition of the substrate temperature of 100 ° C. to 200 ° C. is set, and an atomic force microscope ( It is manufactured in an amorphous form having a particle size of 0.001 μm or less by surface observation with an atomic force microscope.
Here, when the oxygen partial pressure pO ₂ is lower than 1 × 10 ⁻³ Pa, the transmittance may be lowered. On the other hand, when the oxygen partial pressure pO ₂ is higher than 5 × 10 ⁻² Pa, there is a concern that the resistance of the transparent electrode layer 160 increases. Further, when the substrate temperature is lower than 100 ° C., the stability of the transparent electrode layer 160 may be lowered. On the other hand, when the substrate temperature is higher than 200 ° C., the n-type buffer layer 140 may be deteriorated.
Further, in forming the transparent electrode layer 160, indium oxide and zinc oxide are used as main components, and a constituent material having a particle size of 0.001 μm or less by surface observation with an atomic force microscope (AFM) is used. Here, when the particle diameter by surface observation of AFM becomes coarser than 0.001 μm, the interfacial bonding property with the n-type semiconductor layer 150 is lowered, and an energy barrier may be generated. As a result, the particle diameter of the AFM surface observed is set to 0.001 μm or less.
The transparent electrode layer 160 is preferably formed with a thickness of 0.01 μm to 1 μm, preferably 0.1 μm to 1 μm. Here, if the thickness is less than 0.01 μm, a predetermined low resistance film may not be obtained. On the other hand, if it is thicker than 1 μm, the transmittance is lowered, and the light absorption efficiency in the light absorption layer 130 may be reduced. Thus, the thickness dimension of the transparent electrode layer 160 is set to 0.01 μm to 1 μm, preferably 0.1 μm to 1 μm.
The transparent electrode layer 160 is divided into a state in which the n-type semiconductor layer 150 is exposed to a state in which the photovoltaic elements 100 are connected in series by, for example, mechanical scribing after a surface transparent electrode layer 170 described later is formed. The

(Surface transparent electrode layer)
The surface transparent electrode layer 170 has a refractive index smaller than that of the transparent electrode layer 160, and is formed as a thin film on the upper surface of the transparent electrode layer 160 with the same constituent material, that is, the main composition is (In ₂ O ₃ + ZnO), atoms An amorphous film having a particle size of 0.001 μm or less by surface observation with an atomic force microscope is formed.
Further, the surface transparent electrode layer 170 has a resistance value of 100Ω / □ or less. Here, when the resistance value is larger than 100Ω / □, there is a risk of increasing the connection resistance with the metal extraction electrode formed on the element when the element is formed. Thus, the resistance value of the surface transparent electrode layer 170 is set to 100Ω / □ or less.
The surface transparent electrode layer 170 is formed, for example, by sputtering using a mixed gas of Ar and O ₂ , particularly in the same direct current sputtering as the method for forming the n-type semiconductor layer 150 and the transparent electrode layer 160, At least one of a condition for setting the partial pressure pO ₂ to 1 × 10 ⁻³ Pa to 5 × 10 ⁻² Pa and a condition for setting the substrate temperature to 100 ° C. to 200 ° C. is set. It is manufactured in an amorphous form having a particle size of 0.001 μm or less by surface observation with an atomic force microscope.
Here, when the oxygen partial pressure pO ₂ is lower than 1 × 10 ⁻³ Pa, the transmittance may be lowered. On the other hand, when the oxygen partial pressure pO ₂ is higher than 5 × 10 ⁻² Pa, there is a risk that the resistance of the surface transparent electrode layer 170 increases. Further, when the substrate temperature is lower than 100 ° C., there is a risk that the stability of the surface transparent electrode layer 170 is lowered. On the other hand, when the substrate temperature is higher than 200 ° C., the n-type buffer layer 140 may be deteriorated.
The surface transparent electrode layer 170 is preferably formed to have a thickness dimension of 0.01 μm to 1 μm, preferably 0.1 μm to 1 μm. Here, when the thickness is less than 0.01 μm, the antireflection effect is reduced, light from outside light to the light absorption layer 130 is inhibited, and light absorption of the light absorption layer 130 may be reduced. On the other hand, when the thickness is greater than 1 μm, the transmittance decreases, light from outside light to the light absorption layer 130 is inhibited, and light absorption of the light absorption layer 130 may be decreased. Thereby, the thickness dimension of the surface transparent electrode layer 170 is set to 0.01 μm or more and 1 μm or less, preferably 0.1 μm or more and 1 μm or less.
The surface transparent electrode layer 170 is divided together with the transparent electrode layer 160 by mechanical scribing of the transparent electrode layer 160 described above. A groove formed by this mechanical scribing or the like and exposing the n-type semiconductor layer 150 between the transparent electrode layer 160 and the surface transparent electrode layer 170 is shown as a second processed groove 171 in FIG.

[Manufacturing operation of photovoltaic element]
Next, an operation for manufacturing the photovoltaic element 100 will be described.
In the production of the photovoltaic device 100, a back electrode layer forming step, a light absorbing layer forming step, a buffer layer forming step, an n-type semiconductor layer forming step, a first scribing step, a transparent electrode layer forming step, The surface transparent electrode layer forming step and the second scribing step are sequentially performed.

(Back electrode layer forming process)
In the back electrode layer forming step, the back electrode layer 120 is formed as a thin film on the glass substrate 110.
Specifically, an electrode material such as Mo (molybdenum) is formed on the glass substrate 110 so as to have a thickness of 0.01 μm to 1 μm, preferably 0.1 μm to 1 μm, by various film forming methods such as DC sputtering. To form a film.
Then, after the film formation, the dividing grooves 121 whose width dimension is the insulation distance are formed in parallel so that the planar region becomes the back electrode layer 120 having a predetermined width by laser light irradiation, mechanical scribing, etching processing, or the like. Divide into

(Light absorption layer forming process)
In the light absorbing layer forming step, the light absorbing layer 130 is formed in a thin film on the back electrode layer 120 formed on the glass substrate 110 in the back electrode layer forming step so as to be bridged across the dividing grooves 121. In the present embodiment, the light absorption layer 130 is formed on the substantially entire surface of the one surface side of the glass substrate 110 by the first scribing process described later after film formation. The stage will be described as a process for forming the light absorption layer 130.
In film formation, II-VI group semiconductors such as ZnSe, CdS and ZnO, III-V group semiconductors such as GaAs, InP and GaN, IV group compound semiconductors such as SiC and SiGe, Cu (In, Ga) Se ₂ and the like A semiconductor material such as chalcopyrite semiconductor (I-III-VI group semiconductor) such as Cu (In, Ga) (Se, S) ₂ or CuInS ₂ is used. These semiconductor materials are formed into a chalcopyrite structure composition with a thickness of 0.1 μm to 10 μm, preferably 0.5 μm to 5 μm, by various film forming methods such as sputtering and vapor deposition.

(Buffer layer forming step)
In the buffer layer forming step, a light-transmitting n-type buffer layer 140 that forms a pn junction with the light absorbing layer 130 is formed on the light absorbing layer 130 formed in the light absorbing layer forming step. In the present embodiment, similarly to the light absorption layer 130 described above, a film that forms the light absorption layer 130 is formed on almost the entire surface on one side of the glass substrate 110 , and then formed in a first scribing step described later. The buffer layer 140 is formed together with the light absorption layer 130 in a divided manner. For convenience of explanation, the step of forming the film will be described as a process for forming the buffer layer 140.
In film formation, for example, InS is grown as a solution under CBD (Chemical Bath Deposition) production conditions, and a thin film is formed with a thickness dimension of 0.01 μm to 0.5 μm, preferably 0.1 μm to 0.5 μm.

(N-type semiconductor layer forming step)
In the n-type semiconductor layer forming step, a light-transmitting and amorphous n-type is formed on the buffer layer 140 formed in the buffer layer forming step and has a higher resistance than the buffer layer 140 and becomes n-type with respect to the light absorption layer 130. The semiconductor layer 150 is formed as a thin film. In the present embodiment, similarly to the light absorption layer 130 and the buffer layer 140 described above, a film that forms the buffer layer 140 is formed on almost the entire surface of the one surface side of the glass substrate 110, and then a first layer to be described later is formed. The n-type semiconductor layer 150 is formed together with the light absorption layer 130 and the buffer layer 140 by being divided in a scribing process. For convenience of explanation, the stage of film formation will be described as a process for forming the n-type semiconductor layer 150.
In forming the n-type semiconductor layer 150, for example, In and zinc (Zn) are formed under appropriate conditions. Specifically, in sputtering film formation using a mixed gas of argon (Ar) and oxygen (O ₂ ), particularly in direct current sputtering, the oxygen partial pressure pO _{2 is set} to 1 × 10 ⁻² Pa or more and 0.2 Pa or less. A composition comprising, as a main component, indium oxide and zinc oxide, or a thin film by DC sputtering, vapor deposition, or the like, under at least one of the above conditions and the condition in which the substrate temperature is 100 ° C. or higher and 200 ° C. or lower. DC sputtering or vapor deposition is used.
In this way, a thin film is formed with (In ₂ O ₃ + ZnO) as the main composition and a thickness dimension of 0.01 μm to 1 μm, preferably 0.1 μm to 1 μm. Under this manufacturing condition, the n-type semiconductor layer 150 is formed in an amorphous state having a particle size of 0.001 μm or less by surface observation with an atomic force microscope.

(First scribing process)
In the first scribing process, after forming the buffer layer 140 on the light absorption layer 130 in the buffer layer formation process, an element process for generating an electromotive force in an effective area where the back electrode layer 120 and the light absorption layer 130 face each other. Is a mechanical scribing process.
For example, the n-type semiconductor layer 150, the buffer layer 140, and the light absorption layer 130 to be stacked are scribed by a laser irradiation method using a 248 nm excimer laser, the first processed groove 131 is formed and divided, and the back electrode layer 120 surfaces are exposed.

(Transparent electrode layer forming process)
In the transparent electrode layer forming step, the back electrode layer 120 facing the first processed groove 131 from the upper surface of the n-type semiconductor layer 150 provided with the first processed groove 131 and divided in the first scribing step. The amorphous transparent electrode layer 160 is formed as a thin film in the region up to the above.
When forming the transparent electrode layer 160, the same constituent material as that of the n-type semiconductor layer 150 is used to form the transparent electrode layer 160 by the same film forming method. Specifically, in sputtering film formation using a mixed gas of Ar and O ₂ , particularly in direct current sputtering, the oxygen partial pressure pO _{2 is set} to 1 × 10 ⁻³ Pa to 5 × 10 ⁻² Pa, The film was formed under at least one of the conditions in which the substrate temperature was 100 ° C. or higher and 200 ° C. or lower.
In this manner, an amorphous film having a main composition of (In ₂ O ₃ + ZnO) and a thickness of 0.01 μm to 1 μm, preferably 0.1 μm to 1 μm is formed. Under this manufacturing condition, the transparent electrode layer 160 is formed in an amorphous state having a particle diameter of 0.001 μm or less by surface observation with an atomic force microscope.

(Surface transparent electrode layer forming process)
In the surface transparent electrode layer forming step, the upper electrode of the transparent electrode layer 160 formed in the transparent electrode layer forming step is manufactured by the same film forming method using the same constituent material as that of the n-type semiconductor layer 150 and the transparent electrode layer 160. Film. Specifically, in sputtering film formation using a mixed gas of Ar and O ₂ , particularly in direct current sputtering, the oxygen partial pressure pO _{2 is set} to 1 × 10 ⁻³ Pa to 5 × 10 ⁻² Pa, The film was formed under at least one of the conditions in which the substrate temperature was 100 ° C. or higher and 200 ° C. or lower.
In this manner, an amorphous film having a main composition of (In ₂ O ₃ + ZnO) and a thickness of 0.01 μm to 1 μm, preferably 0.1 μm to 1 μm is formed. Under this manufacturing condition, the surface transparent electrode layer 170 is formed in an amorphous state having a particle size of 0.001 μm or less by surface observation with an atomic force microscope.

(Second scribing process)
In the second scribing step, after forming the surface transparent electrode layer 170 in the surface transparent electrode layer forming step, the transparent electrode layer 160 and the surface transparent electrode layer 170 are divided and connected in series as an element structure. The mechanical scribing process.
For example, the transparent electrode layer 160 and the surface transparent electrode layer 170 to be laminated by a mechanical scribing method using a metal needle are mechanically scribed, and a second processed groove 171 is formed and divided to expose the surface of the n-type semiconductor layer 150. Let By this process, the adjacent photovoltaic elements 100 which are thin film laminated semiconductor structures on the glass substrate 110 are connected in series.

[Function and effect of photovoltaic element]
As described above, in the photovoltaic device 100 of the above embodiment, the p-type having conductivity with a chalcopyrite structure compound across the pair of back electrode layers 120 provided on one surface of the glass substrate 110. A light-transmitting n-type buffer layer 140 is formed on the light absorption layer 130 so as to be pn-junction with the light absorption layer 130. The light absorption layer 130 is laminated on the buffer layer 140, and the back surface from one side of the light absorption layer 130 and the buffer layer 140. The transparent electrode layer 160 in the photovoltaic device 100 in which the translucent transparent electrode layer 160 is provided over one of the electrode layers 120 is formed into an amorphous thin film containing indium oxide and zinc oxide as main components. Yes.
For this reason, the transparent electrode that collects the electromotive force generated by the incidence of light at the pn junction can be satisfactorily processed without causing inconveniences such as cracks and missing even with mechanical scribing that is easy to process. Therefore, manufacturability is improved, yield can be improved, and manufacturing cost can be reduced.
Furthermore, since it is an amorphous material mainly composed of indium oxide and zinc oxide, it can be formed with stable characteristics that are excellent in heat resistance and light resistance and do not cause changes in optical characteristics, and can provide stable energy conversion efficiency over a long period of time. . Further, the surface area of the interlayer interface to be connected is increased, and high interface connection reliability can be provided.

Then, by sputtering film formation using a mixed gas of Ar and O ₂ , the oxygen partial pressure of the mixed gas is set to 1 × 10 ⁻³ Pa to 5 × 10 ⁻² Pa and the substrate temperature is set to 100 ° C. or more and 200 ° C. The transparent electrode layer 160 is formed on the amorphous thin film by setting at least one of the conditions set to be equal to or lower than the temperature.
For this reason, pattern processing can be performed with high accuracy by a simple mechanical scribing method using, for example, a metal needle, and productivity can be improved.

Further, when the transparent electrode layer 160 is formed, an amorphous thin film is formed using a constituent material having a particle size of 0.001 μm or less by surface observation with an atomic force microscope.
For this reason, the bondability with the n-type semiconductor layer 150 can be improved, the energy barrier can be reduced, the stability of the bond can be improved, and the durability can be improved.

Furthermore, the transparent electrode layer 160 has a resistance value of 5Ω / □ or more and 20Ω / □ or less.
For this reason, a sufficient threshold voltage for moving electrons and holes generated in the light absorption layer 130 is applied, and the energy conversion efficiency can be improved.

In addition, a light-transmitting n-type semiconductor layer 150 that has higher resistance than the buffer layer 140 and is n-type with respect to the light absorption layer 130 is stacked on the buffer layer 140.
For this reason, the fall of an open end voltage can be prevented.

Then, the n-type semiconductor layer 150 is formed with high resistance by sputtering at a predetermined oxygen concentration, that is, the oxygen partial pressure of the mixed gas is set to 1 × 10 ⁻² Pa by sputtering film formation using a mixed gas of Ar and O _2. An amorphous thin film is formed by setting at least one of a condition of 0.2 Pa or less and a condition of a substrate temperature of 100 ° C. or more and 200 ° C. or less.
For this reason, the layer which can prevent the fall of an open end voltage easily is obtained.

Further, the n-type semiconductor layer 150 is formed of the same constituent material as that of the transparent electrode layer 160.
For this reason, the n-type semiconductor layer 150 and the transparent electrode layer 160 can be formed using the same apparatus, and the productivity can be improved. Therefore, the manufacturing cost can be reduced. Furthermore, since it can be continuously produced by the sputtering apparatus of the same apparatus, the transparent electrode layer 160 can be continuously formed without being exposed to the atmosphere, and the performance deterioration of the bonding interface due to surface contamination can be prevented.

The constituent materials of the n-type semiconductor layer 150 and the transparent electrode layer 160 are indium oxide and zinc oxide.
For this reason, it is possible to form a conductive thin film that is amorphous and has favorable characteristics under relatively low temperature conditions, is less prone to cracks, has high adhesion to the back electrode layer 120, and can be manufactured with a good yield.

Further, a surface transparent electrode layer 170 having conductivity and translucency and having a refractive index smaller than that of the transparent electrode layer 160 is laminated on the transparent electrode layer using the same constituent material as that of the transparent electrode layer 160.
Therefore, efficient light incidence can be obtained, and light energy can be efficiently converted into electrical energy. Furthermore, as described above, since it can be continuously produced by the same sputtering apparatus, the surface transparent electrode layer 170 can be continuously formed without opening to the atmosphere, and the performance degradation of the bonding interface due to surface contamination can be prevented. .

[Modification of Embodiment]
The aspect described above shows one aspect of the present invention, and the present invention is not limited to the above-described embodiment, and is within a range where the object and effect of the present invention can be achieved. Modifications and improvements are included in the content of the present invention. In addition, the specific configuration and shape in carrying out the present invention are not problematic as other configurations and shapes within the range in which the object and effect of the present invention can be achieved.

That is, as the photovoltaic element of the present invention, the light absorption layer 130 is formed of a so-called CIGS system, but may be formed of a chalcopyrite structure compound such as CIS.
The configuration in which the n-type semiconductor layer 150 is provided has been described as an example, but this layer may not be provided. Similarly, the surface transparent electrode layer 170 may not be provided.
In addition, the first scribing process, the second scribing process, and the like are performed to form the divided grooves 121, the first processed grooves 131, and the second processed grooves 171. However, for example, printing or a mask is used. For example, the film may be formed in a state of being divided by the dividing groove 121, the first processing groove 131, and the second processing groove 171 in advance.
And although the n-type semiconductor layer 150, the transparent electrode layer 160, and the surface transparent electrode layer 170 were formed with the same structural material, it is not this limitation.
Further, the refractive index can be appropriately set according to the film forming situation of the n-type semiconductor layer 150, the transparent electrode layer 160, and the surface transparent electrode layer 170. Note that it is preferable that light be efficiently incident and reflected so as to be confined in the layer.
Furthermore, the work function may be set as appropriate according to the energy band set for the light absorption layer 130.

  In addition, the specific configuration, shape, and the like in the implementation of the present invention may be other structures as long as the object of the present invention can be achieved.

Next, an Example is given and this invention is demonstrated more concretely.
In addition, this invention is not limited to the content of an Example etc. at all.
(Creation of element substrate)
On a soda-lime glass substrate 110 having a vertical dimension of 10 cm and a horizontal dimension of 10 cm, a back electrode layer 120 mainly composed of Mo (molybdenum) is formed with a film thickness of 0.1 μm at room temperature using a DC magnetron sputtering apparatus. In addition, a light-absorbing layer 130 mainly composed of CIGS at 350 ° C. is formed with a film thickness of 1 μm at 350 ° C. by co-evaporation using a molecular beam epitaxy apparatus, using CuS, InS, GaS, and SeS as an evaporation source. On top of that, a buffer layer 140 containing InS as a main component by a CBD method and having a thickness of 0.1 μm formed at 100 ° C. was used as an element substrate.

(Measurement of film thickness)
The film thickness of each layer provided on the element substrate in the above-mentioned element substrate and the following examples is set for each film forming process, in addition to the element substrate, soda lime glass in which a mask for measuring the film thickness is installed, A step was formed by removing the mask after film formation, and measurement was performed by a stylus method (device used: DEKTAK3030 manufactured by Sloan).

(Sheet resistance measurement)
The sheet resistance of each layer of the n-type semiconductor layer 150, the transparent electrode layer 160, and the surface transparent electrode layer 170 in the photovoltaic element manufactured in the following examples is not only the element substrate but also the film resistance for each layer forming process. A soda lime glass substrate for thickness measurement was installed, and after forming each layer, measurement was performed with a four-end needle method (device used: Loresta FP manufactured by Mitsubishi Oil Corporation).

(Measurement of particle size)
In the photovoltaic device manufactured in the following example, the particle size of each layer of the n-type semiconductor layer 150, the transparent electrode layer 160, and the surface transparent electrode layer 170 is determined by using the respective film-forming substrates used for the sheet resistance measurement. It was measured by surface observation with a force microscope (AFM).

(Element evaluation)
The photoelectric conversion efficiency of the photovoltaic device manufactured in the following examples is obtained by using a transparent electrode layer or a surface transparent electrode layer as a positive electrode and Mo as a negative electrode, and by screen printing using Ag paste, the transparent electrode layer or the surface transparent An extraction electrode having a thickness of 30 μm □ and a thickness of 0.5 μm was formed on the electrode layer and the Mo layer, and the open circuit voltage (Voc), the short circuit current density (Isc), and the fill factor (FF) were evaluated. In addition, what adjusted the light from a xenon lamp with the specific optical filter (solar simulation) was used as a light source as a light source.

(High temperature and high humidity test)
The high-temperature and high-humidity test of the photovoltaic device manufactured in the following example was conducted after exposing the photovoltaic device to a high-temperature and high-humidity bath at 80 ° C. and 85% RH for 1000 hours before Ag paste printing. After printing the Ag paste by the method, the photoelectric conversion efficiency was calculated by evaluating the open circuit voltage (Voc), the short circuit current density (Isc), and the fill factor (FF).

[Example 1]
(Formation of n- type semiconductor layer 150)
A DC magnetron sputtering apparatus and an IZO target (In ₂ O ₃ : ZnO = 90 [mass%]: 10 [mass%]) were used on the element substrate, with a sputtering pressure of 0.5 Pa, argon (Ar) and oxygen (O ₂ ) Was adjusted so that the partial pressure of oxygen was 0.2 Pa, and the n-type semiconductor layer 150 was formed to a thickness of 0.1 μm at room temperature.
When the particle size of the n-type semiconductor layer 150 formed on soda lime glass installed in the film forming apparatus at the same time as the element substrate was measured by AFM surface observation, it was 0.7 nm.
(Formation of transparent electrode layer 160)
On the n-type semiconductor layer 150, an IZO target (In ₂ O ₃ : ZnO = 90 [mass%]: 10 [mass%]) was used, a sputtering pressure of 0.5 Pa, argon (Ar) and oxygen (O ₂ ).
) Was adjusted so that the oxygen partial pressure was 0.001 Pa, and the transparent electrode layer 160 was formed to a thickness of 0.2 μm at room temperature.
When the sheet resistance of the transparent electrode layer 160 formed on the soda lime glass installed in the film forming apparatus at the same time as the element substrate was measured by the four-end needle method and the particle diameter was measured by surface observation by AFM, the sheet resistance was The resistance was 15Ω / □ and the particle size was 0.3 nm.
(Formation of surface transparent electrode layer 170)
On the transparent electrode layer 160, an IZO target (In ₂ O ₃ : ZnO = 90 [mass%]: 10 [mass%]) was used, a sputtering pressure of 0.5 Pa, argon (Ar) and oxygen (O ₂ ).
The surface transparent electrode layer 170 was formed to a thickness of 0.1 μm at 200 ° C.
When the particle diameter of the surface transparent electrode layer 170 formed on the soda lime glass installed in the film forming apparatus simultaneously with the element substrate was measured by surface observation by AFM, as shown in Table 1, the particle diameter was 0.3 nm. Met.

A screen using Ag paste on the surface transparent electrode layer 170 and the Mo back electrode layer 120 of one photovoltaic element 100 in which the n-type semiconductor layer 150, the transparent electrode layer 160, and the surface transparent electrode layer 170 are laminated on the element substrate. When the extraction electrode was formed by printing and the photoelectric conversion efficiency was measured, as shown in Table 1, Voc was 620 mV, Isc was 39 mA, and FF (curve factor) / Pin (standard incident power) was 0.67. The photoelectric conversion efficiency calculated from the results was 16.2%.
Another photovoltaic element 100 in which an n-type semiconductor layer 150, a transparent electrode layer 160, and a surface transparent electrode layer 170 are stacked on an element substrate is subjected to a 1000 hour exposure test in a high temperature and high humidity condition of 80 ° C. and 85% RH. The extraction electrode was formed by screen printing using Ag paste on the surface transparent electrode layer 170 and the Mo back electrode layer 120 after the test, and when the photoelectric conversion efficiency was measured, Voc was 619 mV, Isc was 39 mA, FF / Pin was 0.67, and the photoelectric conversion efficiency calculated from these was 16.2%.
In the table, n layer represents the n- type semiconductor layer 150, TCO represents the transparent electrode layer 160, and S-TCO represents the surface transparent electrode layer 170.

[Examples 2-48 and Comparative Examples 1-24]
The n-type semiconductor layer 150, the transparent electrode layer 160, and the surface transparent electrode layer 170 are appropriately formed on the element substrate in the same manner as in Example 1 except for the film forming conditions, the target composition, and the presence or absence of the surface transparent electrode layer 170. The particle size, the sheet resistance of the transparent electrode layer 160, the initial device evaluation, and the device evaluation after the high-temperature and high-humidity test were performed, and the results are shown in Tables 1 to 4.

[result]
From the experimental results shown in Tables 1 to 4 above, by controlling the particle size of each constituent layer to 0.001 μm or less by optimizing the film forming conditions, the energy conversion efficiency is improved and the energy after the high-temperature and high-humidity test It can be seen that a decrease in conversion efficiency can be minimized.

  INDUSTRIAL APPLICABILITY The present invention can be used as a photovoltaic element having a conductive p-type light absorption layer formed into a thin film with a chalcopyrite structure compound.

It is sectional drawing which shows schematic structure of the photovoltaic device which concerns on one Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 ... Photovoltaic element 110 ... Glass substrate 120 ... Back surface electrode layer 121 ... Dividing groove 130 ... Light absorption layer 131 ... First processed groove 140 ... Buffer layer 150 ... N-type semiconductor layer 160 ... Transparent electrode layer 170 ... Surface transparent Electrode layer 171 ... second processed groove

Claims (12)

A glass substrate;
A back electrode layer provided on one surface of the glass substrate;
A p-type light-absorbing layer having conductivity formed by stacking on the back electrode layer with a compound of chalcopyrite structure;
A light-transmitting n-type buffer layer laminated on the light absorption layer and pn-junction with the light absorption layer;
A light-transmitting transparent electrode layer provided over the back electrode layer from one side of the light-absorbing layer and the buffer layer, which is laminated to the buffer layer,
The transparent electrode layer is formed in an amorphous thin film having indium oxide and zinc oxide as main components and having a particle diameter of 0.001 μm or less by surface observation with an atomic force microscope. Photovoltaic element. The photovoltaic device according to claim 1, wherein
The transparent electrode layer is formed by sputtering film formation using a mixed gas of argon (Ar) and oxygen (O ₂ ), and the oxygen partial pressure of the mixed gas is 1 × 10 ⁻³ Pa or more and 5 × 10 ⁻² Pa or less. A photovoltaic element characterized in that it is formed into an amorphous thin film by setting at least one of the following conditions: a condition in which the substrate temperature is 100 ° C. or more and 200 ° C. or less. The photovoltaic device according to claim 1 or 2, wherein
The photovoltaic device, wherein the transparent electrode layer has a composition In ₂ O ₃ / (In ₂ O ₃ + ZnO) of 50% by mass to 95% by mass. The photovoltaic device according to any one of claims 1 to 3, wherein
The photovoltaic device, wherein the transparent electrode layer has a third component amount of 20 mass% or less in a composition mainly composed of indium oxide and zinc oxide. The photovoltaic device according to any one of claims 1 to 4, wherein:
A photovoltaic element comprising: a light-transmitting n-type semiconductor layer that is laminated on the buffer layer and has a higher resistance than the buffer layer and becomes n-type with respect to the light absorption layer. The photovoltaic device according to claim 5, wherein
The photovoltaic element, wherein the n-type semiconductor layer is formed in an amorphous thin film having a particle size of 0.001 μm or less by surface observation with an atomic force microscope. The photovoltaic element according to claim 5 or 6, wherein
The n-type semiconductor layer is formed of the same constituent material as that of the transparent electrode layer. The photovoltaic device according to any one of claims 5 to 7, wherein
The n-type semiconductor layer is formed by sputtering film formation using a mixed gas of argon (Ar) and oxygen (O ₂ ) so that the oxygen partial pressure of the mixed gas is 1 × 10 ⁻² Pa or more and 0.2 Pa or less. And at least one of the conditions for setting the substrate temperature to 100 ° C. or higher and 200 ° C. or lower, and formed into an amorphous thin film. The photovoltaic device according to any one of claims 1 to 8, wherein
A photovoltaic element comprising a surface transparent electrode layer formed on the transparent electrode layer and having conductivity and translucency and having a refractive index smaller than that of the transparent electrode layer. The photovoltaic device according to claim 9, wherein
The surface transparent electrode layer is formed of the same constituent material as the transparent electrode layer. The photovoltaic device according to claim 9 or 10, wherein
The surface transparent electrode layer is formed by sputtering using a mixed gas of argon (Ar) and oxygen (O ₂ ), and the oxygen partial pressure of the mixed gas is 1 × 10 ⁻³ Pa or more and 5 × 10 ⁻² Pa or less. And at least one of a condition for setting the substrate temperature to 100 ° C. or more and 200 ° C. or less, and is formed into an amorphous thin film. . A back electrode layer forming step of forming a back electrode layer in a thin film on a glass substrate;
A light absorption layer forming step of forming a thin p-type light absorption layer with a chalcopyrite structure compound on the back electrode layer;
A buffer layer forming step of forming a thin n-type buffer layer that forms a pn junction with the light absorption layer on the light absorption layer;
A transparent electrode layer forming step of forming a transparent electrode layer on the buffer layer;
A method of manufacturing a photovoltaic device that implements
In the transparent electrode layer forming step, the transparent electrode layer is formed into an amorphous thin film whose main component is indium oxide and zinc oxide, and whose particle diameter is 0.001 μm or less by surface observation with an atomic force microscope. A method for producing a photovoltaic device, comprising: forming a photovoltaic device.

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