JP2012204617A - Photovoltaic element and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photovoltaic element having a high energy conversion efficiency and a method of manufacturing the same.SOLUTION: A photovoltaic element has a glass substrate, a rear face electrode layer, a p-type semiconductor optical absorption layer comprising a compound having a chalcopyrite structure, a transparent n-type buffer layer that can form PN junction with the p-type semiconductor optical absorption layer, and a transparent electrode layer that is an oxide thin film containing InOand ZnO, and oxide of one or more elements selected from a group comprising Al, Ga, B, Zr, Hf, and Ti and satisfying a specific atom ratio, in this order. The photovoltaic element has a groove penetrating through the p-type semiconductor optical absorption layer and the transparent n-type buffer layer to make a part of the rear face electrode layer expose. The groove is filled with the transparent electrode layer, and thereby, the transparent electrode layer contacts with the rear face electrode layer.

Description

  The present invention relates to a photovoltaic device and a method for manufacturing the photovoltaic device. More specifically, the present invention relates to a photovoltaic device having a p-type light absorption layer formed as a thin film of a compound semiconductor having a chalcopyrite structure, and a method for manufacturing the photovoltaic device.

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 includes an element that can use photovoltaic power generated in a photoelectric conversion material such as silicon or a compound semiconductor when light such as sunlight enters.
Although solar cells can be classified into several categories, single crystal silicon solar cells and polycrystalline silicon solar cells generally use expensive high purity and thick crystalline silicon substrates. For this reason, research on solar cells having a thin film structure, which is expected to significantly reduce material costs, has been actively conducted.

  As a solar cell having a thin film structure, a compound having a chalcopyrite type crystal structure, which is a non-silicon-based semiconductor material as a photoelectric conversion material, among others, copper (Cu), indium (In), gallium (Ga), A CIGS solar cell using a CIGS compound composed of selenium (Se) and sulfur (S) 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 A buffer layer thin film formed of InS, ZnS, CdS, ZnO or the like and an upper electrode thin film formed of ZnO: Al or the like (for example, Patent Document 1).
The CIGS solar cell disclosed in Patent Document 1 has a high light absorption rate of the CIGS semiconductor material, and the power generation layer can be formed by a method such as vapor deposition or sputtering, so that the thickness can be reduced to several μm. . Therefore, downsizing and material cost can be kept low, and energy saving at the time of manufacturing a solar cell can be achieved. However, the CIGS solar cell of Patent Document 1 is not a solar cell having sufficient energy conversion efficiency.

JP 2007-317885 A

  The objective of this invention is providing the photovoltaic device which has high energy conversion efficiency, and the manufacturing method of the said photovoltaic device.

According to the present invention, the following photovoltaic elements and the like are provided.
1. Glass substrate,
Back electrode layer,
A p-type semiconductor light-absorbing layer comprising a compound having a chalcopyrite structure;
A transparent n-type buffer layer capable of forming a pn junction with the p-type semiconductor light absorption layer, and at least one selected from the group consisting of In ₂ O ₃ and ZnO, and Al, Ga, B, Zr, Hf, and Ti A transparent electrode layer that is an oxide thin film containing an oxide of an element and that satisfies the following atomic ratios (1) and (2) in this order,
A photocathode that penetrates the p-type semiconductor light absorption layer and the transparent n-type buffer layer and exposes a part of the back electrode layer, and the transparent electrode layer fills the groove and contacts the back electrode layer; Power element.
In / (In + Zn) = 0.5 to 0.9 (1)
X / (In + Zn + X) = 0.015 to 0.03 (2)
(In the formula, X is the total number of atoms of Al, Ga, B, Zr, Hf and Ti.)
2. 1 comprising a transparent high-resistance buffer layer that is n-type to the p-type semiconductor light absorption layer and has a higher resistance than the transparent n-type buffer layer between the transparent n-type buffer layer and the transparent electrode layer. The photovoltaic element as described.
3. The photovoltaic element of 1 or 2 provided with the transparent surface antireflection layer whose refractive index is smaller than the said transparent electrode layer on the said transparent electrode layer.
4). Sintering including oxides of one or more elements selected from the group consisting of In ₂ O ₃ and ZnO, and Al, Ga, B, Zr, Hf, and Ti, and satisfying the following atomic ratios (1) and (2) Using a sputtering target consisting of a body,
The oxide thin film is formed in a mixed gas composed of argon (Ar) and oxygen (O ₂ ) having an oxygen partial pressure of 3 × 10 ⁻² Pa or less and / or a substrate temperature of 200 ° C. or less. The manufacturing method of the photovoltaic element in any one.
In / (In + Zn) = 0.5 to 0.9 (1)
X / (In + Zn + X) = 0.015 to 0.03 (2)
(In the formula, X is the total number of atoms of Al, Ga, B, Zr, Hf and Ti.)
A photovoltaic element obtained by the method for producing a photovoltaic element according to 5.4.

  ADVANTAGE OF THE INVENTION According to this invention, the photovoltaic device which has high energy conversion efficiency, and the manufacturing method of the said photovoltaic device can be provided.

It is a figure which shows one Embodiment of the photovoltaic device of this invention. It is a figure which shows other embodiment of the photovoltaic device of this invention. It is a figure which shows other embodiment of the photovoltaic device of this invention.

[Photovoltaic element]
FIG. 1 is a diagram showing an embodiment of the photovoltaic device of the present invention.
The photovoltaic device 100 includes a glass substrate 110, a back electrode layer 120, a p-type semiconductor light absorption layer 130 made of a compound having a chalcopyrite structure, and a transparent n-type buffer layer capable of forming a pn junction with the p-type semiconductor light absorption layer. 140, and transparent electrode layer 160 which is an oxide thin film including an oxide of one or more elements selected from the group consisting of In ₂ O ₃ and ZnO, and Al, Ga, B, Zr, Hf and Ti in this order. Prepare.
The photovoltaic element 100 has a first processed groove 131 that penetrates the p-type semiconductor light absorption layer 130 and the transparent n-type buffer layer 140 and exposes a part of the back electrode layer 120. The processed groove 131 is filled so that the back electrode layer 120 is in contact with the exposed portion of the back electrode layer 120.
The back electrode layer 120 has a dividing groove 121 that exposes a part of the glass substrate 110, and the p-type semiconductor light absorption layer 130 fills the dividing groove 121 and is in contact with the glass substrate 110, and is transparent. The electrode layer 160 has a second processed groove 171 that exposes a part of the n-type buffer layer 140.

Photovoltaic elements are elements that generate an electromotive force upon incidence of light. For example, a photovoltaic cell that is connected in series and can be extracted as electric energy can be configured.
Hereinafter, each member which comprises the photovoltaic element of this invention is demonstrated.

[Transparent electrode layer]
The transparent electrode layer is an oxide thin film containing an oxide of one or more elements selected from the group consisting of In ₂ O ₃ and ZnO, and Al, Ga, B, Zr, Hf, and Ti.
Examples of the oxide of one or more elements selected from the group consisting of Al, Ga, B, Zr, Hf, and Ti included in the oxide thin film include Al ₂ O ₃ , Ga ₂ O ₃ , B ₂ O ₃ , and ZrO _2. , HfO ₂ and TiO ₂ are preferable, and Al ₂ O ₃ and Ga ₂ O ₃ are preferable.

  The photovoltaic element can be formed by, for example, sputtering, but oxygen introduced at the time of formation may damage the light absorption layer and the buffer layer of the element. Al, Ga, B, Zr, Hf, and Ti contained in the transparent electrode layer are elements having an effect of incorporating oxygen into the transparent electrode layer. The oxygen incorporation effect improves the internal quantum efficiency of the device and improves the parallel resistance. The conversion efficiency can be prevented from being lowered. In addition, by incorporating oxygen into the transparent electrode layer, it is possible to suppress the formation of lower oxides and metals in the transparent electrode, and the vicinity of 600 nm, which is the strongest wavelength region of the sunlight spectrum due to these. The optical absorption of the transparent electrode layer can be reduced.

Al, Ga, B, Zr, Hf, and Ti contained in the transparent electrode layer can reduce carrier density and improve mobility while maintaining high conductivity.
By the effect, the transmittance in the infrared region (800 to 1300 nm) of the transparent electrode layer is improved, and conversion efficiency can be improved by incorporating more photons.

The oxide thin film contains, for example, indium oxide (In ₂ O ₃ ) and zinc oxide (ZnO) as main components, and oxidizes one or more elements selected from the group consisting of Al, Ga, B, Zr, Hf, and Ti. It is an amorphous film containing a small amount of matter, and satisfies the following atomic ratios (1) and (2). An oxide thin film, which is an amorphous film mainly composed of indium oxide and zinc oxide, has excellent heat resistance and light resistance, can be formed with stable characteristics that do not cause changes in optical characteristics, and has long-term stable energy conversion efficiency. can get. Further, the surface area of the interlayer interface to be connected is increased, and the interface connection reliability can be improved.
In / (In + Zn) = 0.5 to 0.9 (1)
X / (In + Zn + X) = 0.015 to 0.03 (2)
(In the formula, X is the total number of atoms of Al, Ga, B, Zr, Hf and Ti in the oxide thin film.)
About the said Formula (2), More preferably, it is X / (In + Zn + X) = 0.0025-0.015, More preferably, it is X / (In + Zn + X) = 0.004-0.006.

If In / (In + Zn) of atomic ratio (1) is less than 0.5, zinc oxide microcrystals are formed in the oxide thin film, which may increase the resistance. When In / (In + Zn) is more than 0.9, indium oxide microcrystals are formed in the oxide thin film, which may increase the resistance.
When the atomic ratio (2) X / (In + Zn + X) is less than 0.0015, the effect of reducing the partial pressure of oxygen in the introduced gas used when forming the transparent electrode layer cannot be obtained, and the buffer layer or the light absorption layer May cause damage. On the other hand, when X / (In + Zn + X) is more than 0.03, the resistance of the transparent electrode layer is increased and the series resistance of the photovoltaic device is increased, which may reduce the photoelectric conversion efficiency.

Indium oxide (In ₂ O ₃ ) and zinc oxide (ZnO) in the oxide thin film have an atomic ratio of In / (In + Zn) of 50 atomic% to 90 atomic%.
When the atomic ratio of In / (In + Zn) is less than 0.50, zinc oxide microcrystals are generated in the transparent electrode layer, which may increase the resistance. If it exceeds 0.90, indium oxide microcrystals are formed in the transparent electrode layer, which may increase the resistance.

The resistance value of the transparent electrode layer is, for example, 5Ω / □ or more and 30Ω / □ or less. When the resistance value is within this range, a sufficient threshold voltage for transferring electrons and holes generated in the light absorption layer can be applied, and the energy conversion efficiency of the device can be improved.
When the resistance value of the transparent electrode layer is less than 5Ω / □, the film thickness is increased and the transmittance may be reduced. On the other hand, when the resistance value of the transparent electrode layer is more than 30Ω / □, a sufficient threshold voltage for the movement of electrons and holes generated in the light absorption layer or the like is not applied, and the energy conversion efficiency may be reduced. .
Note that the work function of the transparent electrode layer may be appropriately set according to the energy band set for the p-type semiconductor light absorption layer.

  The thickness of the transparent electrode layer is, for example, from 0.01 μm to 1 μm, and preferably from 0.1 μm to 1 μm. When the thickness of the transparent electrode layer is less than 0.01 μm, the transparent electrode layer may not obtain a predetermined low resistance. On the other hand, when the thickness of the transparent electrode layer exceeds 1 μm, the transmittance is lowered, and the light absorption efficiency of the p-type semiconductor light absorption layer may be reduced.

[Glass substrate]
As the glass substrate, for example, alkali glass such as soda lime glass can be used, but is not limited thereto.

[Back electrode layer]
The back electrode layer is a layer made of a conductive material, for example, a thin film is formed on one surface of a glass substrate, and a plurality of the back electrode layers are provided in parallel via an insulating distance in a state where the planar region has a predetermined width. Yes.
Examples of the conductive material for the back electrode layer include metals or alloys such as gold, silver, copper, aluminum, nickel, iron, chromium, molybdenum, tungsten, titanium, cobalt, tantalum, niobium, and zirconium, and particularly reflectivity. A metal having a high extinction coefficient and a low extinction coefficient is preferable.
For example, when the p-type semiconductor light absorption layer is a CIGS-based layer, the back electrode layer is preferably a layer made of molybdenum.

  The thickness of the back electrode layer is, for example, 0.01 μm or more and 1 μm or less, preferably 0.1 μm or more and 1 μm or less. When the thickness of the back electrode layer is less than 0.01 μm, the resistance value of the photovoltaic element may increase. On the other hand, when the thickness of the back electrode layer is more than 1 μm, peeling may occur.

  The surface of the back electrode layer is not limited to a flat surface, and may have an uneven shape that diffusely reflects light. The back electrode layer having an uneven shape can scatter long-wavelength light that could not be absorbed by the p-type semiconductor light absorption layer, thereby extending the optical path length in the p-type semiconductor light absorption layer. Thereby, the long wavelength sensitivity of a photovoltaic device improves, a short circuit current increases, and photoelectric conversion efficiency can be improved.

The uneven shape for scattering the light of the back electrode layer is preferably set to Rmax of 0.2 μm or more and 2.0 μm or less, where Rmax is the difference in height between the peaks and valleys of the unevenness. When Rmax is larger than 2.0 μm, the coverage is deteriorated, the film thickness is uneven, and the resistance value may be uneven.
The uneven shape can be processed by applying various methods such as dry etching, wet etching, sand blasting, and heating.

[P-type semiconductor light absorption layer]
The p-type semiconductor light absorption layer is a layer made of a chalcopyrite compound that is a compound of a chalcopyrite structure having p-type conductivity, and is formed into a thin film so that a part of the back electrode layer is exposed.

For the p-type semiconductor light absorption layer, a chalcopyrite compound such as CIS (Cu, In, S, Se), CZTS (Cu, Zn, Sn, S, Se) can be used in addition to CIGS.
Specific examples of the chalcopyrite compound of the p-type semiconductor light absorption layer include: II-VI group semiconductors such as ZnSe, CdS, ZnO; III-V group semiconductors such as GaAs, InP, and GaN; IV group compounds such as SiC and SiGe _{semiconductor; Cu (in, Ga) Se} 2, Cu (in, Ga) (Se, S) 2, CuInS 2 , etc. chalcopyrite semiconductor (I-III-VI group semiconductor) of the like.

The thickness of the p-type semiconductor light absorption layer is, for example, from 0.1 μm to 10 μm, preferably from 0.5 μm to 5 μm.
When the thickness of the p-type semiconductor light absorption layer is less than 0.1 μm, the amount of light absorbed from outside light may be reduced. On the other hand, when the thickness of the p-type semiconductor light absorption layer exceeds 10 μm, the productivity may decrease, the film may be easily peeled due to film stress, or the conversion efficiency may decrease due to an increase in direct resistance. As a result,

[Transparent n-type buffer layer]
The transparent n-type buffer layer is a relatively low-resistance n-type semiconductor layer that is formed in a thin film on the upper surface of the p-type semiconductor light absorption layer and is pn-junction with the p-type semiconductor light absorption layer. Like the layer, the back electrode layer is partly exposed. In addition, the n-type buffer layer can also function as a barrier against a semi-metal resistance layer such as Cu ₂ Se remaining on the surface of the p-type semiconductor light absorption layer and functioning as a shunt path.

The transparent n-type buffer layer is not particularly limited as long as it is a layer made of a material that can satisfactorily pn-join with the p-type semiconductor light absorption layer, and examples thereof include a layer made of CdS or InS.
As a preferable combination of the p-type semiconductor light absorption layer and the n-type buffer layer, the p-type semiconductor light absorption layer is a CIGS light absorption layer, and the n-type buffer layer is a layer made of CdS and / or InS.

  The thickness of the n-type buffer layer is, for example, 0.01 μm or more and 0.5 μm or less, preferably 0.1 μm or more and 0.5 μm or less. When the thickness of the n-type buffer layer is less than 0.01 μm, pn junction spots may occur. On the other hand, when the thickness of the n-type buffer layer is more than 0.5 μm, the light from outside light is hindered and the light absorption of the p-type semiconductor light absorption layer may be lowered.

[High resistance buffer layer]
FIG. 2 is a diagram showing another embodiment of the photovoltaic element of the present invention.
The photovoltaic element 100 of FIG. 2 is the same as that of FIG. 1 except that a high resistance buffer layer 150 is further provided between the transparent n-type buffer layer 140 and the transparent electrode layer 160. Similar to the transparent n-type buffer layer 140 and the p-type semiconductor light absorption layer 130, the transparent high-resistance buffer layer 150 is formed so that a part of the back electrode layer 120 is exposed.

The high resistance buffer layer is a layer that is arbitrarily stacked, and is a crystalline layer that is n-type with respect to the p-type semiconductor light absorption layer and has a higher resistance than the n-type buffer layer.
When the photovoltaic device includes the high-resistance buffer layer, it can function as an electron carrier for the p-type semiconductor light absorption layer that functions as a hole carrier. In addition, the high resistance buffer layer can prevent a decrease in open-circuit voltage.

The high resistance buffer layer is a crystalline layer made of, for example, zinc oxide (ZnO), and its resistance value is usually 10 kΩ / □ or more and 1000 kΩ / □ or less. By providing the high resistance buffer layer, it is possible to prevent a decrease in the open-circuit voltage.
When the resistance value of the high-resistance buffer layer is less than 100 kΩ / □, electrons formed in the light absorption layer easily move to the anode side, and the open end voltage may be reduced, leading to a decrease in photoelectric conversion efficiency. On the other hand, when the resistance value of the high-resistance buffer layer is more than 1000 kΩ / □, the open-circuit voltage is improved, but there is a risk of increasing the driving voltage of the photoelectric conversion element.

  By using a material mainly composed of ZnO for the formation of the high-resistance buffer layer, ZnO is also a material for the transparent electrode layer. Therefore, the transparent electrode layer can be formed using, for example, the same apparatus and opened to the atmosphere. Therefore, it is possible to improve the productivity and reduce the manufacturing cost. Further, the continuous film formation can prevent the performance degradation of the bonding interface due to surface contamination.

  The thickness of the high resistance buffer layer is, for example, not less than 0.01 μm and not more than 1 μm, and preferably not less than 0.1 μm and not more than 1 μm. When the thickness of the high resistance buffer layer is less than 0.01 μm, the blocking effect of holes generated in the p-type semiconductor light absorption layer may be reduced. On the other hand, when the thickness of the high-resistance buffer layer is more than 1 μm, the transmittance of the high-resistance buffer layer is lowered, and there is a possibility that the absorption of external light in the p-type semiconductor light absorption layer is hindered.

[Surface antireflection layer]
FIG. 3 is a diagram showing another embodiment of the photovoltaic device of the present invention.
The photovoltaic element 100 of FIG. 3 is the same as FIG. 2 except that a transparent surface antireflection layer 170 is further provided on the transparent electrode layer 160. Similar to the transparent electrode layer 160, the surface antireflection layer 170 is formed so that a part of the high resistance buffer layer is exposed.

The surface antireflection layer is a layer having a refractive index smaller than that of the transparent electrode layer and is arbitrarily laminated. By making the refractive index smaller than that of the transparent electrode layer, efficient light incidence can be obtained and light can be reflected so as to be confined in the layer, and the device can efficiently convert light energy into electric energy. .
The refractive index of the surface antireflection layer can be appropriately set depending on the refractive indexes of the high resistance buffer layer and the transparent electrode layer.

The surface antireflection layer is a layer made of, for example, MgF.
The thickness of the surface antireflection layer is, for example, from 0.01 μm to 1 μm, preferably from 0.1 μm to 1 μm. When the thickness of the surface antireflection layer is less than 0.01 μm, the antireflection effect of the surface antireflection layer is reduced, light from outside light to the light absorption layer is inhibited, and the light absorption of the light absorption layer may be reduced. There is. On the other hand, when the thickness is larger than 1 μm, the transmittance decreases, light from outside light to the light absorption layer 130 is hindered, and light absorption of the light absorption layer 130 may decrease. 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.

[Method for producing photovoltaic element]
The photovoltaic element of the present invention can be produced by the following method.
For example, the photovoltaic device of the present invention having the configuration of FIG. 3 includes a step of forming a back electrode layer on a glass substrate, a step of forming a light absorption layer on the back electrode layer, and an n-type buffer layer on the light absorption layer. Forming a high resistance buffer layer on the n-type buffer layer, a first scribing step, forming a transparent electrode layer in contact with the back electrode layer on the high resistance buffer layer, on the transparent electrode layer It can be manufactured by sequentially performing the step of forming the surface antireflection layer and the second scribing step.

In the photovoltaic device manufacturing method of the present invention, the oxide thin film that is the transparent electrode layer is selected from the group consisting of In ₂ O ₃ and ZnO, and Al, Ga, B, Zr, Hf, and Ti. A sputtering target made of a sintered body containing an oxide of the element and satisfying the following atomic ratios (1) and (2) is used, and argon (Ar) and oxygen (with an oxygen partial pressure of 3 × 10 ⁻² Pa or less) The film is formed in a mixed gas composed of O ₂ ) and / or at a substrate temperature of 200 ° C. or lower.
In / (In + Zn) = 0.5 to 0.9 (1)
X / (In + Zn + X) = 0.015 to 0.03 (2)
(In the formula, X is the total number of atoms of Al, Ga, B, Zr, Hf and Ti.)
In a photovoltaic device having a p-type semiconductor light absorption layer made of a compound having a chalcopyrite structure, an n-type buffer layer formed of InS, ZnS, CdS, ZnO, and the like, and a transparent electrode layer in this order, the transparent electrode layer When oxygen is introduced as a film forming gas during the formation by sputtering, the light absorption layer may be damaged and the power generation efficiency of the device may be adversely affected. This is the same situation as annealing in oxygen due to introduction of oxygen gas and substrate heating and curing by plasma during sputtering, oxygen diffuses to the light absorption layer through grain boundaries and defects of the buffer layer, and S and This is to replace Se.
In the manufacturing method of the present invention, the performance degradation of the element can be prevented by setting the oxygen partial pressure and / or the substrate temperature within a specific range.

  For the back electrode layer, an electrode material such as Mo (molybdenum) is formed on the glass substrate by various film forming methods such as vapor deposition, CVD, spraying, spin-on, dipping, and DC sputtering. After film formation, the back electrode layer is divided in parallel by forming split grooves with an insulation distance width by laser light irradiation, mechanical scribing, etching processing, etc. so that the planar area of the back electrode layer becomes a predetermined area To do.

The p-type semiconductor light absorption layer is formed by sputtering such as Cu, In, Ga, and Se (CIGS) so as to have a chalcopyrite structure, vapor deposition including multi-source vapor deposition using a molecular beam epitaxy apparatus, or the like. . The light absorption layer can also be formed by, for example, selenizing Cu—In—Ga by annealing.
Note that the p-type semiconductor light absorption layer is divided by mechanical scribing or the like to be described later so that the back electrode layer is exposed.

The n-type buffer layer can be formed, for example, by growing a solution of CdS or InS by CBD (Chemical Bath Deposition) or the like.
The n-type semiconductor buffer layer is divided by mechanical scribing or the like, which will be described later, so that the back electrode layer is exposed.

The high-resistance buffer layer, preferably a material such as zinc oxide (ZnO), in an argon (Ar) and oxygen (O ₂₎ sputtering film formation using a mixed gas containing (especially DC sputtering), the oxygen partial pressure pO ₂ Is set to 1 × 10 ⁻² Pa to 0.2 Pa and / or the substrate temperature is set to 100 ° C. to 200 ° C. to form a crystalline film by DC sputtering or vapor deposition.
When the oxygen partial pressure pO ₂ is less than 1 × 10 ⁻² Pa, a low resistance film may be formed. On the other hand, when the oxygen partial pressure pO ₂ exceeds 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.
When the substrate temperature is lower than 100 ° C., the interface reaction between the n-type semiconductor buffer layer component (sulfur (S) or the like) and the high resistance buffer layer does not proceed, and the high resistance buffer layer may not increase in resistance. On the other hand, when the substrate temperature is higher than 200 ° C., the components (Cd and the like) of the n-type buffer layer may penetrate deeply into the light absorption layer, and the light absorption layer may be deteriorated.

The high resistance buffer layer is divided by mechanical scribing or the like described later so that the back electrode layer is exposed.
The high resistance buffer layer is an arbitrary layer, and the lamination of the layer may be omitted.

In the first scribing step, a first processed groove penetrating the laminated body including the p-type semiconductor light absorption layer, the n-type buffer layer, and the high-resistance buffer layer is provided, and a part of the back electrode layer is exposed.
The first processed groove is for generating an electromotive force in an effective area where the back electrode layer and the p-type semiconductor light absorption layer face each other, and the first processed groove can be formed by, for example, a mechanical scribing process. Examples of the mechanical scribing treatment include a laser irradiation method using a 248 nm excimer laser.

The transparent electrode layer is formed so as to be in contact with the back electrode layer by filling the first processed groove, and is selected from the group consisting of In ₂ O ₃ and ZnO, and Al, Ga, B, Zr, Hf, and Ti. In a mixed gas composed of argon (Ar) and oxygen (O ₂ ) having an oxygen partial pressure of 3 × 10 ⁻² Pa or less, using a sputtering target composed of a sintered body containing an oxide of one or more elements In addition, the substrate temperature is set to 200 ° C. or less, and the film is formed by DC sputtering, vapor deposition, or the like.
According to the above method, the transparent electrode layer can be formed as an amorphous layer having a particle size of 0.001 μm or less by surface observation with an atomic force microscope (Atomic Force Microscope). Such a transparent electrode layer has good bonding properties with the back electrode layer and the high-resistance buffer layer, can reduce the energy barrier, and can improve the durability of the element.
When the oxygen partial pressure pO ₂ exceeds 3 × 10 ⁻² Pa, the resistance of the transparent electrode layer may increase, and the performance of the light absorption layer may be deteriorated due to damage to the element due to oxygen. In addition, when the substrate temperature is higher than 200 ° C., the components (Cd and the like) of the n-type buffer layer may penetrate deeply into the light absorption layer, the light absorption layer may be deteriorated, and cracks may be generated.

Projection electrode layer that is an amorphous film obtained in a mixed gas composed of argon (Ar) and oxygen (O ₂ ) having an oxygen partial pressure of 3 × 10 ⁻² Pa or less and / or a substrate temperature of 200 ° C. or less. Can be processed with high accuracy without causing inconveniences such as cracks or missing even in the mechanical scribing process.
Since simple machining such as mechanical scribing can be performed, productivity can be improved, yield can be improved, and manufacturing cost can be reduced.

The target used for forming the transparent electrode layer is a target that satisfies the following atomic ratios (1) and (2).
In / (In + Zn) = 0.5 to 0.9 (1)
X / (In + Zn + X) = 0.015 to 0.03 (2)
(In the formula, X is the total number of atoms of Al, Ga, B, Zr, Hf and Ti.)

  The transparent electrode layer is divided so that a part of the high resistance buffer layer to which the photovoltaic elements can be connected in series is exposed by, for example, mechanical scribing after a surface antireflection layer described later is formed.

The surface antireflection layer can be formed, for example, by sputtering or vapor deposition.
When forming the surface prevention layer, the substrate temperature is preferably 200 ° C. or lower. When the substrate temperature is higher than 200 ° C., components (Cd and the like) of the n-type buffer layer may penetrate deeply into the light absorption layer, and the light absorption layer may be deteriorated.

The surface antireflection layer is divided by mechanical scribing or the like described later so that the high resistance buffer layer is exposed.
The surface antireflection layer is an arbitrary layer, and the lamination of the layer may be omitted.

In the second scribing step, a second processed groove penetrating the laminated body including the transparent electrode layer and the surface antireflection layer is provided, and a part of the high resistance buffer layer is exposed.
The second scribing process is a mechanical scribing process for forming elements connected in series. Examples of the scribing process include mechanical scribing using a metal needle.

  In the photovoltaic device manufacturing method described above, the dividing grooves and the processed grooves are formed by a scribing process or the like. For example, the layers are laminated so that the divided grooves and the processed grooves are formed in advance by printing, a mask, or the like. Also good.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples.

Example 1
A photovoltaic device having the configuration shown in FIG. 3 was produced by the following procedure.
[Selection of optimal oxygen amount]
On a soda-lime glass substrate having a vertical dimension of 10 cm and a horizontal dimension of 10 cm, a sputtering pressure of 0 was applied using a DC magnetron sputtering apparatus and a sputtering target of In ₂ O ₃ : ZnO = 70 [mass%]: 30 [mass%]. .3 Pa, a mixed gas of argon (Ar) and oxygen (O ₂ ) was adjusted so that the partial pressures of oxygen were 0.001 Pa, 0.002 Pa, 0.003 Pa, and 0.005 Pa, respectively, and 0.1 μm at room temperature. A transparent electrode thin film having a thickness was formed.
The resistance values of the transparent electrode thin films formed at oxygen partial pressures of 0.001 Pa, 0.002 Pa, 0.003 Pa, and 0.005 Pa were measured by a four-end needle method using Loresta EP manufactured by Mitsubishi Yuka. As a result, the oxygen partial pressure at which the resistance was the lowest was 0.001 Pa. Therefore, 0.001 Pa was determined as the optimum oxygen partial pressure for forming the transparent electrode layer.

[Production of element substrate]
On a soda lime glass substrate having a vertical dimension of 10 cm and a horizontal dimension of 10 cm, a back electrode layer containing Mo (molybdenum) as a main component was formed to a thickness of 0.1 μm at room temperature using a DC magnetron sputtering apparatus. On the back electrode layer, CuS, InS, GaS, and SeS were used as a deposition source, and a light absorption layer mainly composed of CIGS was formed at 350 ° C. by a co-evaporation method using a molecular beam epitaxy apparatus with a film thickness of 1 μm. . On the light absorption layer, a buffer layer containing InS as a main component was formed at 100 ° C. to a thickness of 0.1 μm by the CBD method to manufacture an element substrate.
In addition, the film thickness of each layer on the substrate is the back electrode by installing soda lime glass in which a film thickness measurement mask is formed together with the element substrate for each film forming process, and removing the measurement mask after forming each layer. A first groove for penetrating the layer and exposing a part of the glass substrate, a first processed groove for penetrating the light absorption layer and the buffer layer and exposing a part of the back electrode layer, and a depth of the groove; Was measured by the stylus method (device used: DEKTAK3030 manufactured by Sloan).

[Manufacture of photovoltaic elements]
On the obtained element substrate, using a DC magnetron sputtering device and a ZnO target (ZnO = 100 [mass%]), the sputtering pressure was set to 0.5 Pa, and argon (adjusted so that the oxygen partial pressure was 0.2 Pa). A mixed gas composed of Ar) and oxygen (O ₂ ) was supplied to form a high resistance buffer layer with a thickness of 0.1 μm at room temperature. Sputtering is performed using an Al ₂ O ₃ doped IZO target (main component is In ₂ O ₃ : ZnO = 70 [atomic%]: 30 [atomic%] and Al ₂ O ₃ is added at 1500 atomic ppm) on the high resistance buffer layer. Supplying a mixed gas composed of argon (Ar) and oxygen (O ₂ ) adjusted to a pressure of 0.3 Pa and an oxygen partial pressure of 0.001 Pa, the transparent electrode layer is a 0.3 μm film at room temperature Formed with thickness. The sheet resistance of the transparent electrode layer was 14.7Ω / □. A surface antireflection layer was formed to a thickness of 100 nm by RF magnetron sputtering using MgF on the formed transparent electrode layer. In the same manner as the first processed groove, a second processed groove exposing a part of the high resistance buffer layer was formed to manufacture a photovoltaic device.
The sheet resistance of the transparent electrode layer is determined by installing a soda lime glass substrate for film thickness measurement together with the element substrate in the transparent electrode layer film forming step, and after the transparent electrode layer film forming step, the four-end needle method (applicable equipment: Measured by Loresta EP (Mitsubishi Yuka).

About the manufactured photovoltaic element, the photoelectric conversion efficiency was evaluated with the following method. The evaluation results are shown in Table 1.
The produced photovoltaic element has a transparent electrode layer as a positive electrode, a back electrode layer as a negative electrode, and a screen printing method using an Ag paste, and the film thickness is 30 μm □ and a film thickness is 0.5 μm on the transparent electrode layer and the back electrode layer. Photoelectric conversion efficiency is obtained by forming each extraction electrode, irradiating the element with light, and evaluating each of open circuit voltage (Voc), short circuit current density (Isc), fill factor (FF) / standard incident power (Pin) Was calculated. Further, the produced photovoltaic device was exposed for 2000 hours under the condition of 1 SUN using a solar simulator, and the photoelectric conversion efficiency was calculated for the exposed photovoltaic device in the same manner as described above.
In addition, the light (solar simulation) which adjusted the light from a xenon lamp with the specific optical filter was used for the light source.

Examples 2-35 and Comparative Examples 1-20
Table 1 shows the dopant of the transparent electrode layer, the target used for the film formation of the high resistance buffer layer and the transparent electrode layer, the film formation conditions of the high resistance buffer layer and the transparent electrode layer, and the oxygen amount at the time of film formation of the transparent electrode layer A photovoltaic device was manufactured and evaluated in the same manner as in Example 1 except that.
The results of Examples 2 to 35 and Comparative Examples 1 to 20 are shown in Tables 1 to 3, respectively.

  The photovoltaic element of the present invention can be applied to various photoelectric conversion devices using a photoelectric conversion function, an optical rectification function, etc., for example, a photovoltaic cell such as a solar cell; an optical sensor, an optical switch, a phototransistor, etc. It is useful for optical recording materials such as electronic elements; and optical memories.

DESCRIPTION OF SYMBOLS 100 Photovoltaic element 110 Glass substrate 120 Back surface electrode layer 121 Dividing groove 130 P-type semiconductor light absorption layer 131 1st process groove 140 N-type buffer layer 150 High resistance buffer layer 160 Transparent electrode layer 170 Surface antireflection layer 171 2nd Machining groove

Claims (5)

Glass substrate,
Back electrode layer,
A p-type semiconductor light-absorbing layer comprising a compound having a chalcopyrite structure;
A transparent n-type buffer layer capable of forming a pn junction with the p-type semiconductor light absorption layer, and at least one selected from the group consisting of In ₂ O ₃ and ZnO, and Al, Ga, B, Zr, Hf, and Ti A transparent electrode layer that is an oxide thin film containing an oxide of an element and that satisfies the following atomic ratios (1) and (2) in this order,
A photocathode that penetrates the p-type semiconductor light absorption layer and the transparent n-type buffer layer and exposes a part of the back electrode layer, and the transparent electrode layer fills the groove and contacts the back electrode layer; Power element.
In / (In + Zn) = 0.5 to 0.9 (1)
X / (In + Zn + X) = 0.015 to 0.03 (2)
(In the formula, X is the total number of atoms of Al, Ga, B, Zr, Hf and Ti.)   The transparent high-resistance buffer layer which is n-type with respect to the p-type semiconductor light absorption layer and has a higher resistance than the transparent n-type buffer layer between the transparent n-type buffer layer and the transparent electrode layer. 2. The photovoltaic element according to 1.   The photovoltaic element of Claim 1 or 2 provided with the transparent surface antireflection layer whose refractive index is smaller than the said transparent electrode layer on the said transparent electrode layer. Sintering including oxides of one or more elements selected from the group consisting of In ₂ O ₃ and ZnO, and Al, Ga, B, Zr, Hf, and Ti, and satisfying the following atomic ratios (1) and (2) Using a sputtering target consisting of a body,
The oxide thin film is formed in a mixed gas composed of argon (Ar) and oxygen (O ₂ ) having an oxygen partial pressure of 3 × 10 ⁻² Pa or less and / or a substrate temperature of 200 ° C. or less. 4. A method for producing a photovoltaic device according to any one of 3 above.
In / (In + Zn) = 0.5 to 0.9 (1)
X / (In + Zn + X) = 0.015 to 0.03 (2)
(In the formula, X is the total number of atoms of Al, Ga, B, Zr, Hf and Ti.) A photovoltaic element obtained by the method for producing a photovoltaic element according to claim 4.

Images