JP2018056541A - Solar cell, junction type solar cell, solar cell module and solar power generation system - Google Patents

Abstract

A solar cell, a multi-junction solar cell, a solar cell module, and a solar power generation system with improved conversion efficiency are provided. A solar cell includes a substrate, a first electrode on the substrate, and a light absorption layer and an n-type layer between the first electrode and the second electrode. The light absorption layer 3 is provided between the first electrode 2 and the n-type layer 5. Further, a dot region 4 is provided between the first electrode 2 and the light absorption layer 3. The dots are made of at least one of a metal, an alloy, and a conductive oxide. The first electrode 2 is a transparent electrode including a semiconductor film. [Selection] Figure 1

Description

  Embodiments relate to a solar cell, a multi-junction solar cell, a solar cell module, and a solar power generation system.

  As a highly efficient solar cell, there is a multi-junction type (tandem) solar cell. Since an efficient cell can be used for each wavelength band, higher efficiency than a single junction is expected. A chalcopyrite solar cell such as CIGS is known to have high efficiency, and can be a top cell candidate by forming a wide gap. However, when used as a top cell, it is necessary to use a transparent electrode in order to transmit light having a band gap or less. If the light absorption layer is formed directly on the transparent electrode, the interface is oxidized and a good contact cannot be formed, and the efficiency is not easily increased.

Patent No. 5875124

  Embodiments provide a solar cell, a multi-junction solar cell, a solar cell module, and a solar power generation system with improved conversion efficiency.

  The solar cell of the embodiment includes the first electrode, the second electrode, and the light absorption layer 3 between the first electrode and the second electrode, and the aperture ratio is between the first electrode and the light absorption layer 3. It has a dot area of 50% or more and 99.95% or less.

The cross-sectional conceptual diagram of the solar cell in connection with embodiment. The image figure in connection with embodiment. The image figure in connection with embodiment. The cross-sectional conceptual diagram of the solar cell in connection with embodiment. The cross-sectional conceptual diagram of the solar cell in connection with embodiment. The cross-sectional conceptual diagram of the solar cell in connection with embodiment. 1 is a conceptual cross-sectional view of a part of a solar cell according to an embodiment. 1 is a conceptual cross-sectional view of a part of a solar cell according to an embodiment. The optical microscope image concerning embodiment. The optical microscope image concerning embodiment. The optical microscope image concerning embodiment. The optical microscope image concerning embodiment. The cross-sectional conceptual diagram of the solar cell in connection with embodiment. The cross-sectional conceptual diagram of the multijunction solar cell in connection with embodiment. The conceptual diagram of the solar cell module in connection with embodiment. The conceptual diagram of the solar energy power generation system in connection with embodiment.

Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the drawings.
(First embodiment)
As shown in FIG. 1, a solar cell 100 according to this embodiment includes a substrate 1 and a first electrode 2 on the substrate 1. Between the first electrode 2 and the second electrode 6, the light absorption layer 3 and the n-type layer 5 exist. Further, the light absorption layer 3 exists between the first electrode 2 and the n-type layer 5. A dot region 4 is provided between the first electrode 2 and the light absorption layer 3.

(substrate)
As the substrate 1 of the embodiment, it is desirable to use soda lime glass, general glass such as quartz, white plate glass, chemically tempered glass, metal plate such as stainless steel, Ti (titanium) or Cr (chromium), polyimide, acrylic, etc. Resin can also be used.

(First electrode)
The first electrode 2 of the embodiment is an electrode of the solar cell 100. The first electrode 2 is, for example, a transparent electrode including a semiconductor film formed on the substrate 1. The first electrode 2 exists between the substrate 1 and the light absorption layer 3. As the first electrode 2, a semiconductor film containing at least indium tin oxide (ITO) can be used. A layer containing SnO ₂ , TiO ₂ , carrier-doped oxide such as ZnO: Ga, ZnO: Al, or the like may be stacked on the ITO on the light absorption layer 3 side. It may be a laminate of ITO and SnO ₂ from the substrate 1 side to the light absorption layer 3 side, or a laminate of ITO, SnO ₂ and TiO ₂ from the substrate 1 side to the light absorption layer 3 side. The layer in contact with the light absorption layer of the first electrode 2 is preferably an oxide layer of any one of ITO, SnO ₂ and TiO ₂ . Further, a layer containing an oxide such as SiO ₂ may be further provided between the substrate 1 and ITO. The first electrode 2 can be formed by sputtering the substrate 1 or the like. The film thickness of the first electrode 2 is, for example, not less than 100 nm and not more than 1000 nm. When the solar cell of the embodiment is used for a multi-junction solar cell, the solar cell of the embodiment is present on the top cell side or the middle cell side, and the first electrode 2 is a light-transmitting semiconductor film. preferable.

(Light absorption layer)
The light absorption layer 3 of the embodiment is a p-type compound semiconductor layer. The light absorption layer 3 exists between the first electrode 2 and the n-type layer 5. The light absorption layer 3 is a layer containing a compound containing a group I, group III and group VI element. The group I element preferably contains at least Cu. The group III element preferably contains at least Ga. The group VI element preferably contains at least Se. For example, Cu (In, Ga) Se ₂ , CuInTe ₂ , CuGaSe ₂ , Cu (In, Al) Se ₂ containing a Group I (Group Ib) element, a Group III (IIIb) group element, and a Group VI (Group VIb) element. , Cu (Al, Ga) (S, Se) ₂ , Cu (In, Ga) (S, Se) ₂ , CuGa (S, Se) ₂ , Ag (In, Ga) Se _{2 and} other compounds having a chalcopyrite structure A semiconductor layer can be used as a light absorption layer. The group Ib element is made of Cu or Cu and Ag, the group IIIb element is one or more elements of Ga, Al and In, and the group VIb element is one or more elements of Se, S and Te It is preferable that Among these, it is more preferable that the group Ib element is made of Cu, the group IIIb element is made of Ga, Al, or Ga and Al, and the group VIb element is made of Se, S, or Se and S. When the group IIIb element contains a small amount of In, it is preferable that the band gap of the light absorption layer 3 is easily adjusted to a suitable value as a top cell of a multijunction solar cell. The film thickness of the light absorption layer 3 is, for example, not less than 800 nm and not more than 3000 nm.

  By combining the elements, the size of the band gap can be easily adjusted to a target value. The target band gap value is, for example, 1.0 eV or more and 2.7 eV or less.

  The film forming method of the light absorption layer 3 includes a vapor deposition process such as a three-stage method, and is not limited as long as the film can be formed on the first electrode 2 having the dot region 4. Even in the case of a solar cell having an intermediate layer on the first electrode 2 and having the dot region 4 on the intermediate layer, the method for forming the light absorption layer 3 is the same.

(Dot area)
The dot region 4 of the embodiment is a region having dots that exist between the first electrode 2 and the light absorption layer 3. The dot area 4 is an area where dots are present and the aperture ratio is 50% or more. Dots exist in non-opening portions. In the non-opening portion, the dots are in contact with the surface of the light absorption layer 3 facing the first electrode 2 direction. Further, the surface opposite to the surface where the dots are in contact with the light absorption layer 3 is in contact with the surface of the first electrode 2 facing the light absorption layer 3. The light absorbing layer 3 is present in the opening, that is, in the region where no dot exists. The dot region 4 has high translucency to the first electrode 2 and has an effect of suppressing oxidation of the compound semiconductor constituting the light absorption layer 3. It also has a function of suppressing the formation of an oxidized region at the interface between the compound semiconductor and the first electrode 2, and the contact portion becomes a dot, so that an electric field can be concentrated on the dot portion and interface recombination can be suppressed to improve the open circuit voltage. When the oxidation of the light absorption layer 3 is suppressed, the open circuit voltage is improved and the conversion efficiency is also improved. Introducing an insulating layer on the first electrode 2 physically reduces the contact portion between the electrode and the compound semiconductor (the insulating region corresponds to a passivation film), further suppresses interface recombination, and maintains a high open-circuit voltage. Can do. High translucency is a suitable characteristic when used as a top cell of a multijunction solar cell. Moreover, the solar cell of the embodiment is suitable not only for use in multi-junction solar cells but also for solar cell applications that require transparency.

  If the aperture ratio of the dot region 4 ([area of the region where the dot exists] / [area of the first electrode 2]) is high, the transparency is excellent. The function of preventing the oxidation of the light absorption layer 3 occurs even at an extremely high aperture ratio. The specific aperture ratio of the dot region 4 is preferably 50% or more and 99.95% or less. If the aperture ratio is less than 50%, the translucency is lowered, which is not preferable. When the aperture ratio is less than 99%, it is represented by 2 significant digits (rounded off), and when it is 99% or more, it is represented by 3 or 4 significant digits (rounded off). On the other hand, when the aperture ratio exceeds 99.95%, the effect of preventing the light absorption layer 3 from being oxidized due to the presence of the dot region 4 is hardly seen, and it becomes difficult to contribute to the improvement of the conversion efficiency. A more preferable aperture ratio is 61% or more and 99.95% or less, and 80% or more and 99.95% or less. The reason for having an anti-oxidation function even at such a high aperture ratio is that the dots are dispersed and exist between the light absorption layer 3 and the first electrode 2 to inhibit the formation of an oxide film. Conceivable. Contact resistance occurs between the compound semiconductor and the electrode, but the conduction through the low-resistance dot is dominant in that portion, and the oxide film is difficult to be formed in the portion where the dot exists. A contact is formed. Therefore, current is collected at the dot portion, and functions effectively while maintaining a high aperture ratio.

The dots are preferably made of a material that does not react or hardly reacts with the light absorption layer 3. Therefore, it is preferable that the dots include one or more of metals, alloys, and conductive oxides. When the light absorption layer 3 contains Se or S, the material constituting the dots is preferably a material that can withstand corrosion due to Se or S. If it is a metal, a noble metal element and Mo are preferable. Therefore, it is desirable that the metal contained in the dot metal or alloy is at least one of Mo, Ru, Rh, Pd, Ag, Ir and Pt. As the conductive oxide, RuO ₂ , PdO, Rh ₂ O ₃ , PtO ₂ , IrO _{2 and the} like are preferable from the viewpoint of Se and S corrosion resistance. Further, a metal capable of ohmic connection with the light absorption layer 3 is preferable. A metal or compound (oxide) having a deep work function is preferred. The work function is preferably a metal or compound (oxide) of 5.4 eV or more. For these reasons, it is more preferable that the dots include one or more of Mo, Pt, Ir, and Pd. These dots may be composed of one kind or a combination of two or more kinds of materials.

  The shape of the dot is not particularly limited. Specific examples of the shape of the dot include a circle, an ellipse, and a polygon. These circular, elliptical, and polygonal shapes may have a hollow shape (such as an O shape) or an opening (such as a C shape or a parenthesis shape), and are not particularly limited. The size of the dot is preferably 2 nm or more and 20 μm or less. The size of the dots is more preferably 6 nm or more and 10 μm or less. If the dots are too small, it is difficult to disperse them on the first electrode 2 surface. On the other hand, if the dot is too large, it is not preferable because variations in translucency occur or the light absorption layer 3 is easily oxidized. The dot height of the dot region 4 is not particularly limited, but is preferably 2 nm or more and 50 μm or less from the viewpoint of ease of manufacture. When the mobility of the light absorption layer 3 is not so high, it is preferable in that the aperture ratio can be increased while the distance between the metals is reduced by using a hollow dot with a hole. When the dots are formed on the first electrode 2 by applying and drying a solution containing metal particles, the metal particles may be partially aggregated.

  It is preferable that the dots are dispersed and exist between the light absorption layer 3 and the first electrode 2. Therefore, it is preferable that the dot area satisfies the above aperture ratio as a whole.

The surface of the light absorption layer 3 facing the first electrode 2 is equally divided into 12 regions (2 horizontal and 6 vertical) in a lattice shape as shown in the image diagram of FIG. 2, and the cross section including the central portion of each region is, for example, 40k times. Observe SEM (Scanning Electron Microscope). The region is divided into six in the long side direction and two in the short side. If the shape is a square, either may be divided into six. The cross section to be observed is a surface including the light absorption layer 3, the dot region 4, and the first electrode 2 in a direction perpendicular to the surface of the light absorption layer 3 facing the first electrode 2. Further, the 12 cross sections to be observed are all cross sections in the same direction as the cross sections on the imaginary lines X1 to X6 in FIG. The angle of each line passing through the center of the lattice region is arbitrarily selected so that the dot region 4 can be observed. A surface where seven dot regions 4 can be confirmed in the SEM image is observed. An area of ⁶ × 10 ⁻⁶ mm ² in the observation surface is observed, and an SEM image as shown in the image diagram of FIG. 3 is obtained. Then, as shown in the image diagram of FIG. 3, each dot (4A, 4B, 4C, 4D, 4E, 4F, 4G in FIG. 3) in the dot region 4 is projected to the first electrode 2 side. The length when each dot is projected is defined as L ₁ , L ₂ ... L _n (L ₁ to L _{7 in} FIG. 3). This is from _{L 1} to _{L n} and the size of the dots. A first width of the electrodes 2 of the observation plane is L _0. The sum of _{L n} and _{L S} from L _1. And that the aperture ratio calculated | required by (L _S / L ₀ ) ² means satisfy | filling the said aperture ratio means that the dot area | region 4 satisfy | fills the said aperture ratio. That is, 50% ≦ (L _S / L ₀ ) ² ≦ 99.5% is preferable. 61% ≦ (L _S / L ₀ ) ² ≦ 99.5% is more preferable. 80% ≦ (L _S / L ₀ ) ² ≦ 99.5% is more preferable. And the state which satisfy | filled the said aperture ratio in all the 12 cross sections is more preferable. In this state, it is assumed that the dot area 4 generally satisfies the above aperture ratio. When seven dot regions cannot be confirmed in the SEM observation image, the magnification is appropriately changed, and in some cases, TEM (Transmission Electron Microscope) observation is performed.

Moreover, it is preferable that the difference in dot size is small. Here, the average value of L ₁ , L ₂ ... L _n is L _AVE . _Let L _{MAX be} the maximum value of L ₁ , L ₂ ... L _n . _Let L _{MIN be} the minimum value among L ₁ , L ₂ ... L _n . At this time, when 0.8 L _AVE ≦ L _MIN ≦ L _MAX ≦ 1.2 L _AVE is satisfied, the minimum value and the maximum value of the dot size in the dot region 4 are 0.8 times or more the average value of the dots 1 . Means that it is 2 times or less, which is preferable. Similarly, when 0.9 L _AVE ≦ L _MIN ≦ L _MAX ≦ 1.1 L _AVE is satisfied, the minimum value and the maximum value of the dot size in the dot region 4 are 0.9 of the average value of the dot sizes. It means that the ratio is not less than twice and not more than 1.1 times, and is more preferable. Moreover, it is preferable that the difference in the size of each dot is small in all the 12 cross sections. In this state, it is assumed that the dot region 4 satisfies the condition that the difference in dot size is small as a whole.

In addition, if the dots are unevenly distributed, the translucency is low in a region with many dots, and the surface facing the first electrode 2 of the light absorption layer 3 is easily oxidized in a region with few dots. Therefore, it is preferable that the difference in dot interval in the dot region 4 is small. The minimum value and the maximum value of the dot interval in the dot region 4 are preferably 0.8 times or more and 1.2 times or less of the average value of the dot intervals. The minimum value and the maximum value of the dot interval in the dot region 4 are more preferably 0.9 times to 1.1 times the average value of the dot intervals. The variation in the dot interval will be described with reference to the image diagram of FIG. The SEM image used for obtaining the dot interval is the same as the SEM image for obtaining the aperture ratio. Each dot (4A, 4B, 4C, 4D, 4E, 4F, 4G in FIG. 3) in the dot region 4 is projected to the first electrode 2 side. _Let the distances between the projected portions L ₁ , L ₂ ... L _n (in FIG. 3, L ₁ to L ₇ ) be D ₁ , D ₂ ... D _n (in FIG. 3, D ₁ to D ₆ ). An average value of D ₁ , D ₂ ... D _n is D _AVE . _Let D _{MAX be} the maximum value of D ₁ , D ₂ ... D _n . _Let D _{MIN be} the minimum value of D ₁ , D ₂ ... D _n . At this time, when 0.8D _AVE ≦ D _MIN ≦ D _MAX ≦ 1.2D _AVE is satisfied, the minimum value and the maximum value of the dot interval in the dot region 4 are 0.9 times or more the average value of the dot interval. It means that it is 1 time or less. Similarly, when 0.9D _AVE ≦ D _MIN ≦ D _MAX ≦ 1.1D _AVE is satisfied, the minimum value and the maximum value of the dot interval in the dot region 4 are 0.8 times or more the average value of the dot intervals. It means 2 times or less. From the same viewpoint, the dot interval is preferably 0.8 nm or more and 24 μm or less. When the dots are uniformly dispersed in this way, there is little variation in light transmittance, the optical characteristics of the solar cell 100 are improved, and when the dots have the same aperture ratio and the same size, they are uniformly dispersed. The better the anti-oxidation function of the light absorption layer 3, the better. This is because oxidation is likely to proceed in a region where there are very few or no dots, and even if there are even a few dots, the formation of an oxide film is hindered, and as a result, conversion efficiency is considered to improve. Therefore, it is also preferable that all the 12 cross sections satisfy the dot interval. In this state, the dot area 4 as a whole satisfies the dot interval.

  The dot region 4 is a method of applying and drying a liquid containing metal particles to be dots, or a method of forming a metal film, an oxide film or a nitride film and processing it into an arbitrary dot pattern using a mask Alternatively, it can be formed by imprinting using a template having a dot pattern shape.

  The average diameter in the in-plane direction of the dots in the dot region 4 is preferably smaller than the average crystal grain size in the in-plane direction of the interface on the first electrode side of the light absorption layer 3. It is desirable that the crystal size of the compound semiconductor constituting the light absorption layer 3 is smaller. As a result, the transport and collection of the generated charge to the dot region are completed within the generated crystal, and a current drop due to charge recombination deactivation at the grain boundary and a voltage drop due to the passage through the grain boundary. Can be avoided.

  4 and 5 are conceptual cross-sectional views of the solar cell 100 of the embodiment. The conceptual diagram of FIG. 4 represents the solar cell 100 in which the average diameter in the in-plane direction of the dots in the dot region 4 is smaller than the average crystal grain size in the in-plane direction of the interface on the first electrode 2 side of the light absorption layer 3. ing. The conceptual diagram of FIG. 5 represents the solar cell 100 in which the average diameter in the in-plane direction of the dots in the dot region 4 is smaller than the average crystal grain size in the in-plane direction of the interface on the first electrode 2 side of the light absorption layer 3. ing. The average diameter in the in-plane direction of the dots in the dot region 4 and the average crystal grain size in the in-plane direction of the interface on the first electrode 2 side of the light absorption layer 3 are obtained from the same SEM image as the SEM image for obtaining the aperture ratio. The average diameter in the in-plane direction of the dots in the dot region 4 is the average value of the lengths in the width direction of the dots of the SEM image. The average crystal grain size in the in-plane direction of the interface on the first electrode 2 side of the light absorption layer 3 is the length in the width direction of the interface on the first electrode 2 side of the light absorption layer 3 in the SEM image (d1- d6, d7−d11) is an average value. In FIG.4 and FIG.5, the grain boundary of the light absorption layer 3 is represented with the broken line. 4 and 5, a star mark is marked on the crystal of the light absorption layer 3 that is not in direct contact with the dot.

  4 and FIG. 5, the solar cell 100 shown in the conceptual diagram of FIG. 4 has an average crystal in the in-plane direction of the interface on the first electrode 2 side of the light absorption layer 3 with respect to the average diameter in the in-plane direction of the dots. Since the particle size is small, there are more crystals of the light absorption layer 3 that are not in direct contact with the dots compared to the solar cell 100 shown in the conceptual diagram of FIG. In the crystal of the light absorption layer 3 that is not in direct contact with the dot, holes generated by power generation reach the dot through the grain boundary of the light absorption layer 3. When holes pass through the grain boundary, it is not preferable because recombination deactivation or voltage drop occurs. By satisfying the relationship that the average diameter in the in-plane direction of the dots in the dot region 4 is smaller than the average crystal grain size in the in-plane direction of the interface on the first electrode 2 side of the light absorption layer 3, the light absorption layer 3 This has the advantage that the generated power can be transmitted efficiently.

  The average diameter of the dots in the dot region 4 in the in-plane direction is preferably about several hundred nm. In the case of a multi-junction solar cell, light passes through a solar cell having a second photoelectric conversion site called a bottom cell through which light cannot be absorbed by a solar cell having a first photoelectric conversion site called a top cell. It is necessary to make it. In order to increase the light transmittance of the top cell, it is sufficient to reduce the dot area and increase the aperture ratio. In this case, however, the charge collection area decreases, and as a result, the output of the solar cell decreases. However, when the dot has the same size as the incident wavelength of about several hundred nm or smaller than that, the light transmittance is not greatly reduced even if the aperture ratio is not large. Therefore, it is desirable that the aperture ratio is not greatly changed, and the dot size is set to be equal to or less than the wavelength to be transmitted.

  FIG. 6 and FIG. 7 show an enlarged sectional conceptual view of the solar cell 100 of the embodiment. Depending on the material constituting the dot region 4, there is a possibility of blocking an element diffusing from the base substrate. Thereby, there exists a performance fall of a light absorption layer, and inhibition of formation. On the other hand, by setting the dot size to about several hundreds of nanometers, the elements from the area without dots diffuse into the dot area, so that there is no obstacle to the formation of the light absorption layer.

  FIG. 6 shows a conceptual diagram when the average diameter in the in-plane direction of the dots in the dot region is large, for example, 200 nm or more. In the conceptual diagram shown in FIG. 6, the crystal of the light absorption layer 3 on the dots tends to be small, and the crystal of the light absorption layer 3 on the first electrode 2 (transparent electrode) tends to be large. In addition, it is confirmed that the crystals of the light absorption layer 3 tend to grow along the dots, and the crystals on the first electrode 2 have a large particle size and tend to be in direct contact with the dots. is there. On the other hand, the crystal of the light absorption layer 3 on the dot has a smaller particle diameter than the crystal on the first electrode 2. If there are many crystals with a small particle size, the grain boundaries increase, and the power generation efficiency decreases for the reasons described above.

  FIG. 7 shows a conceptual diagram when the average diameter in the in-plane direction of the dots in the dot region is small, for example, 100 nm or less. In the conceptual diagram shown in FIG. 7, the crystal of the light absorption layer 3 on the dots tends to be small and the crystal of the light absorption layer 3 on the first electrode 2 (transparent electrode) tends to be large, similar to that shown in the conceptual diagram of FIG. There is. In addition, it is confirmed that the crystals of the light absorption layer 3 tend to grow along the dots, and the crystals on the first electrode 2 have a large particle size and tend to be in direct contact with the dots. is there. On the other hand, the crystal of the light absorption layer 3 on the dot has a smaller particle diameter than the crystal on the first electrode 2. If there are many crystals with a small particle size, the grain boundaries increase, and the power generation efficiency decreases for the reasons described above. In the form shown in the conceptual diagram of FIG. 7, since the size of a dot is small, it is preferable at a point with the high ratio of a crystal | crystallization with a large particle size. In addition, if the aperture ratio is the same, the smaller the dot size, the higher the ratio of direct contact with each crystal, and the lower the ratio of movement of holes through the grain boundary. When the dot size is small as shown in FIG. 7, the crystal of the light absorption layer 3 has a large particle size, which is effective in suppressing recombination activity and preventing voltage drop. In FIG.6 and FIG.7, the grain boundary of the light absorption layer 3 is represented with the broken line. 6 and 7, a star mark is marked on the crystal of the light absorption layer 3 that is not in direct contact with the dot.

  Therefore, when the average diameter in the in-plane direction of the dots is 100 nm or less, the crystal quality of the light absorption layer 3 is improved, and from the viewpoint of power generation efficiency, the crystal quality of the light absorption layer 3, that is, the light absorption layer 3 It is preferable that the crystal has a large particle size. For example, when the material constituting the dot region 4 is molybdenum, it is considered that a crystal growing on the dot region can be formed into a crystal having a large particle size by an element diffusing from outside the dot region. For these reasons, the average diameter in the in-plane direction of the dots is preferably 2 nm or more and 100 nm or less, and more preferably 6 nm or more and 50 nm or less.

(N-type layer)
The n-type layer 5 of the embodiment is an n-type semiconductor layer. The n-type layer 5 exists between the light absorption layer 3 and the second electrode 6. The n-type layer 5 is a layer physically in contact with the surface of the light absorption layer 3 opposite to the surface facing the first electrode 2 side. The n-type layer 5 is a layer heterojunction with the light absorption layer 3. The n-type layer 5 is preferably an n-type semiconductor whose Fermi level is controlled so that a photoelectric conversion element having a high open circuit voltage can be obtained. n-type layer 5, for _{example, Zn 1-y M y O} 1-x S x, Zn 1-y-z Mg z M y O, ZnO 1-x S x, Zn 1-z Mg z O (M is At least one element selected from the group consisting of B, Al, In, and Ga), CdS, and the like can be used. The thickness of the n-type layer 5 is preferably 2 nm or more and 800 nm or less. The n-type layer 5 is formed by sputtering or CBD (Chemical Solution Deposition), for example. When the n-type layer 5 is formed by CBD, for example, a metal salt (for example, CdSO ₄ ), sulfide (thiourea), and a complexing agent (ammonia) can be formed on the light absorption layer 3 by a chemical reaction in an aqueous solution. . When a chalcopyrite compound containing no In in the IIIb group element such as a CuGaSe ₂ layer, an AgGaSe ₂ layer, a CuGaAlSe ₂ layer, a CuGa (Se, S) ₂ layer, or the like is used as the light absorption layer 3, CdS is preferred.

(Oxide layer)
The oxide layer of the embodiment is a thin film that is preferably provided between the n-type layer 5 and the second electrode 6. The oxide layer is a thin film containing any one compound of Zn _1-x Mg _x O, ZnO _1-y S _y and Zn _1-x Mg _x O _1-y S _y (0 ≦ x, y <1). is there. The oxide layer may not cover the entire surface of the n-type layer 5 facing the second electrode 6 side. For example, it is only necessary to cover 50% of the surface of the n-type layer 5 on the second electrode 6 side. Other candidates include Wurtz-type AlN, GaN, BeO, and the like. When the volume resistivity of the oxide layer is 1 Ωcm or more, there is an advantage that a leakage current derived from a low resistance component that may exist in the light absorption layer 3 can be suppressed. In the embodiment, the oxide layer can be omitted. These oxide layers are oxide particle layers, and preferably have a large number of voids in the oxide layer. The intermediate layer is not limited to the above-described compounds and physical properties, and may be any layer that contributes to improving the conversion efficiency of the solar cell. The intermediate layer may be a plurality of layers having different physical properties.

(Second electrode)
The second electrode 6 of the embodiment is an electrode film that transmits light such as sunlight and has conductivity. The second electrode 6 is in physical contact with the surface of the intermediate layer or n-type layer 5 opposite to the surface facing the light absorption layer 3 side. Between the second electrode 6 and the first electrode 2, the bonded light absorption layer 3 and n-type layer 5 exist. For example, the second electrode 6 is formed by sputtering in an Ar atmosphere. The second electrode 6 can be made of, for example, ZnO: Al using a ZnO target containing 2 wt% of alumina (Al ₂ O ₃ ) or ZnO: B with B as a dopant from diborane or triethylboron.

(Third electrode)
The third electrode of the embodiment is an electrode of the photoelectric conversion element 100 and is a metal film formed on the side opposite to the light absorption layer 3 side on the second electrode. As the third electrode, a conductive metal film such as Ni or Al can be used. The film thickness of the third electrode is, for example, not less than 200 nm and not more than 2000 nm. Further, when the resistance value of the second electrode 6 is low and the series resistance component can be ignored, the third electrode may be omitted.

(Antireflection film)
The antireflection film of the embodiment is a film for facilitating the introduction of light into the light absorption layer 3, and is formed on the second electrode 6 or on the side opposite to the light absorption layer 3 side on the third electrode. Yes. For example, MgF ₂ or SiO ₂ is preferably used as the antireflection film. In the embodiment, the antireflection film can be omitted. Although it is necessary to adjust the film thickness according to the refractive index of each layer, it is preferable to deposit 70-130 nm (preferably 80-120 nm).

(Second Embodiment)
As shown in FIG. 8, the solar cell 101 according to this embodiment includes a substrate 1 and a first electrode 2 on the substrate 1. Between the first electrode 2 and the second electrode 6, the light absorption layer 3 and the n-type layer 5 exist. Further, the light absorption layer 3 exists between the first electrode 2 and the n-type layer 5. A dot region 4 is provided between the first electrode 2 and the light absorption layer 3. Between the dots in the dot region 4, the first insulating film 7 exists. When the dots in the dot region 4 are hollow, it is preferable that the first insulating film 7 exists also in the hollow portion. Except for the first insulating film 7, the solar cell 100 is the same as that of the first embodiment. Descriptions common to the first embodiment and the second embodiment are omitted.

(First insulation film)
The first insulating film 7 exists on the entire surface or a part between the light absorption layer 3 between the dots and the first electrode 2. The first insulating film 7 is a translucent film that prevents oxidation of the light absorption layer 3. The surface of the first electrode 2 facing the light absorption layer 3 side is physically in contact with the surface of the first insulating film 7 facing the first electrode 2 side. The surface of the light absorption layer 3 facing the first electrode 2 side is physically in contact with the surface of the first insulating film 7 facing the light absorption layer 3 side. The side surface of the first insulating film 7, that is, the surface facing the dot region 4 side is in physical contact with the dots or the light absorption layer 3. The dot region 4 can partially prevent the light absorption layer 3 from being oxidized, but from the viewpoint of preventing oxidation, a lower aperture ratio of the dot region 4 is better, but it is not preferable because the light transmittance is lowered. Further, in the solar cell in which the first insulating film 7 is provided on the entire surface between the light absorption layer 3 and the first electrode 2 and the dot region 4 is not provided, the contact between the electrode and the light absorption layer is not good, and the conversion efficiency is not improved. If an insulating film is simply introduced, the series resistance component (Rs) of the solar cell is increased and the efficiency is reduced.

When the first insulating film 7 exists between the light absorption layer 3 and the first electrode 2, electrical conduction between the first electrode 2 and the light absorption layer 3 can be suppressed, the curvature factor FF is improved, and the conversion efficiency is increased. Will improve. As the first insulating film, either an oxide film or a nitride film can be given. Specifically, the oxide film is preferably one or more of AlO _x , SiO _x , MgO, and (Al, Si, Mg) O _x . The nitride film is preferably one or more of SiN _x , AlN _x , GaN _x, and (Si, Al, Ga) N _x . The thickness of the first insulating film 7 may be thicker than the dot height of the dot region 4, but is preferably not more than the dot height and not less than 1 nm and not more than 80 nm. The thickness of the 1st insulating film 7 is below the height of a dot, and 5 nm or more and 50 nm or less are more preferable. The first insulating film 7 has the above effect even if it does not cover the entire surface between the light absorption layer 3 and the first electrode 2 between the dots. From the viewpoint of preventing oxidation and improving FF, and from the viewpoint of the film forming process, the first insulating film 7 is preferably present on the entire surface between the light absorption layer 3 and the first electrode 2 between the dots.

9 to 12 show optical microscope images of members in which the dot region 4 and the first insulating film 7 are formed on the first electrode 2. The optical microscope images in FIGS. 9 to 12 are all on the same scale. FIG. 9 shows dots made of molybdenum, and has a hollow circle (O-type), a dot size of 5 μm, a dot interval of 8 μm, an aperture ratio of 82%, and a dot region 4 with a dot height of 50 nm. In FIG. 9, as the first insulating film 7, AlO _x having a thickness of 40 nm is formed. FIG. 10 is the same as FIG. 9 except that the dot shape is a hollow hexagon (hex nut type). FIG. 11 is the same as FIG. 9 except that SiN _x is used as the first insulating film 7. FIG. 12 is the same as FIG. 10 except that SiN _x is used as the first insulating film 7. A uniform dot pattern is formed in any optical microscope image. Note that the members shown in the optical microscope images of FIGS. 9 to 8 include a region in which some dots are not formed in the peripheral portion. When the dot shape is hollow and the dots are arranged in a uniform pattern as shown in FIGS. 9 to 12, regardless of the presence or absence of the first insulating film 7, the mobility of the light absorption layer 3 is not so high. It is preferable in that the aperture ratio can be increased while the interval between the metals is reduced by using the hollow-shaped dots with holes.

  A semiconductor manufacturing process can be adopted as a method of forming the first insulating film 7. For example, a metal film for the dot region 4 is formed on the first electrode 2 and processed into a dot pattern using a resist mask to form the dot region 4. Subsequently, a material to be the first insulating film 7 is formed on the resist mask in the dot region 4 and the exposed surface of the first electrode 2 by sputtering or the like. The first insulating film 7 on the dot region 4 is removed together with the resist mask, and the light absorption layer 3 can be formed as in the first embodiment. The structure shown in FIGS. 9 to 12 is produced by the method described above.

(Third embodiment)
As shown in FIG. 13, the solar cell 102 according to this embodiment includes a substrate 1 and a first electrode 2 on the substrate 1. Between the first electrode 2 and the second electrode 6, the light absorption layer 3 and the n-type layer 5 exist. Further, the light absorption layer 3 exists between the first electrode 1 and the n-type layer 5. A dot region 4 is provided between the first electrode 1 and the light absorption layer 3. A second insulating film 8 exists between the first electrode 2 and the dot region 4. Except for the second insulating film 8, it is common to the solar cell 100 of the first embodiment. Descriptions common to the first embodiment and the third embodiment are omitted. In addition, you may combine the 1st insulating film 7 of 2nd Embodiment, and the 2nd insulating film 8 of this embodiment.

(Second insulating film)
The second insulating film 8 is a surface between the surface of the light absorption layer 3 facing the first electrode 2 and the surface of the first electrode 2 facing the light absorption layer 3 and the surface of the dot region 4 facing the first electrode 2. And an insulating film existing between the first electrode 2 and the surface of the dot region 4 of the first electrode 2 facing the dots. The second insulating film 8 can suppress electrical conduction between the first electrode 2 and the light absorption layer 3, the curvature factor FF is improved, and the conversion efficiency is improved. If the second insulating film 8 is thick, the resistance becomes too high, which is not preferable. It is preferable that the second insulating film 8 is thin, for example, has a thickness of 1 nm or more and 2 nm or less because the second insulating film 8 becomes a tunnel insulating film and suppresses direct conduction between the first electrode 2 and the light absorption layer 3. . The first insulating film 8 is formed by CVD (Chemical Vapor Deposition) or the like.

(Fourth Embodiment) (Multijunction Solar Cell)
The fourth embodiment is a multi-junction solar cell using the solar cell of the first embodiment. FIG. 14 is a schematic cross-sectional view of the multi-junction solar cell 200 of the fourth embodiment. The multi-junction solar cell in FIG. 14 includes a top cell solar cell 201 and a bottom cell solar cell 202. The solar cell 100 of the first embodiment to the solar cell 102 of the third embodiment are used for the top cell 201 of the multi-junction solar cell 200. The battery 202 of the bottom cell includes, for example, a solar battery having a light absorption layer of Si and a solar battery 100 to a third embodiment of the first embodiment having a light absorption layer 3 having a narrower gap than the solar battery 201 of the top cell. The solar cell 102 can also be used. When the solar cell 100 of the first embodiment is used for the top cell, the group I element is preferably Cu, the group III element is Ga, and the group VI element is Se from the viewpoint of the absorption wavelength and the conversion efficiency. Since the light absorption layer of the solar cell of the first embodiment has a wide gap, it is preferably used for the top cell. When the solar cell 100 of the first embodiment is used for the bottom cell, the group I element is preferably Cu, the group III element is In and Ga, and the group VI element is Se from the viewpoint of the absorption wavelength and the conversion efficiency. In the fourth embodiment, the two-stacked other junction solar cell is shown, but three or more solar cells may be stacked.

(Fifth Embodiment) (Solar Cell Module)
The solar cells of the first to fourth embodiments can be used as power generation elements in the solar cell module of the fifth embodiment. The electric power generated by the solar cell of the embodiment is consumed by a load electrically connected to the solar cell, or stored in a storage battery electrically connected to the solar cell.

  Examples of the solar cell module of the embodiment include a structure in which a plurality of cells of solar cells are connected in series, in parallel, in series or in parallel, or a single cell is fixed to a support member such as glass. The solar cell module may be provided with a light collector so that light received in an area larger than the area of the solar cell is converted into electric power. Solar cells include solar cells connected in series, in parallel, or in series and in parallel.

  FIG. 15 shows a conceptual configuration diagram of a solar cell module 300 in which a plurality of solar cells 301 are arranged in the horizontal direction. The solar cell module 300 of FIG. 15 omits connection wiring, but as described above, it is preferable to connect a plurality of solar cells 301 in series, in parallel, or in series and in parallel. The solar cell 301 is preferably the solar cell 100 of the first embodiment or the multi-junction solar cell 200 of the fourth embodiment. Moreover, the solar cell module 300 of the embodiment has a module structure in which a module using the multi-junction solar cell 200 of the fourth embodiment and a module using other solar cells are stacked from the solar cell 100 of the first embodiment. It may be adopted. In addition, it is preferable to employ a structure that increases the conversion efficiency. In the solar cell module 300 of the embodiment, the solar cell 301 has a wide band gap photoelectric conversion layer, and thus is preferably provided on the light receiving surface side.

(Sixth embodiment)
The solar cell module 300 of the embodiment can be used as a generator that generates power in the solar power generation system of the sixth embodiment. The solar power generation system according to the embodiment generates power using a solar cell module. Specifically, the solar cell module that generates power, means for converting the generated electricity, and the generated electricity A storage unit for storing electricity or a load for consuming the generated electricity. FIG. 16 shows a conceptual diagram of the configuration of the photovoltaic power generation system 400 of the embodiment. The solar power generation system of FIG. 16 includes a solar cell module 401 (300), a converter 402, a storage battery 403, and a load 404. Either the storage battery 403 or the load 404 may be omitted. The load 404 may be configured to be able to use electrical energy stored in the storage battery 403. The converter 402 is a device including a circuit or an element that performs power conversion such as transformation or DC / AC conversion, such as a DC-DC converter, a DC-AC converter, and an AC-AC converter. As the configuration of the converter 402, a suitable configuration may be adopted according to the configuration of the generated voltage, the storage battery 403, and the load 404.

  The received photovoltaic cell 301 included in the solar cell module 300 generates electric power, and the electric energy is converted by the converter 402 and stored in the storage battery 403 or consumed by the load 404. The solar cell module 401 is provided with a solar light tracking drive device for always directing the solar cell module 401 toward the sun, a condensing body for concentrating sunlight, a device for improving power generation efficiency, and the like. It is preferable to add.

  The solar power generation system 400 is preferably used for real estate such as a residence, a commercial facility, a factory, or used for movable property such as a vehicle, an aircraft, or an electronic device. By using the photoelectric conversion element excellent in conversion efficiency of the embodiment for the solar cell module 401, an increase in the amount of power generation is expected.

EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example, this invention is not limited to a following example.
Example 1
Two solar cells of top cell and bottom cell are joined to make a multi-junction solar cell, conversion efficiency of multi-junction solar cell, Voc (release voltage) of top cell, Jsc (short-circuit current density), FF (output factor) ), The light transmittance (average from 700 nm to 1150 nm), the aperture ratio and the conversion efficiency, and further the conversion efficiency of the bottom cell. First, a method for manufacturing a top cell will be described. Soda lime glass is used as the substrate. ITO (150 nm) and SnO ₂ (100 nm) are formed by sputtering as the first electrode (back surface transparent electrode). A Pd dispersion (stock solution 4 wt%, average diameter 10 nm) is applied by spin coating and heated in an oxygen stream at 300 ° C. for 30 minutes to blow off organic substances. After UV cleaning, the substrate is heated to 370 ° C. to deposit Ga and Se. Cu and Se are vapor-deposited while heating the substrate temperature to 520 ° C. If an endothermic reaction is observed, the deposition is continued up to 10% of the Cu and Se deposition time, and finally Ga and Se are deposited. When the target Cu / Ga composition is reached, Ga deposition is stopped, annealing is performed for 5 minutes, and then the substrate temperature is lowered. When the substrate temperature falls to 380 ° C., the deposition of Se is stopped.

  A CdS layer is formed as an n-type layer by CBD (Chemical Bath Deposition). Cadmium sulfate is dissolved in an aqueous ammonia solution, thiourea is added, taken out after 300 seconds and washed with water. An organic Zn compound is applied to the substrate by spin coating. Heat at 120 ° C. for 5 minutes to produce a 30 nm ZnO protective layer.

  ZnO: Al is produced by sputtering as the second electrode (upper transparent electrode). The substrate temperature is preferably 60-150 ° C. It is preferable to perform film formation at a relatively low temperature because the open circuit voltage tends to increase.

Ni / Al is deposited as a third electrode (upper electrode). It is desirable to deposit Ni first, so that conductivity can be maintained even if oxidation occurs at the interface with the transparent electrode. Al is vapor-deposited thereon. The film thickness is preferably about 60 nm and 500 nm, respectively.
MgF ₂ is deposited with a thickness of 100 nm as an antireflection film.

Next, a method for manufacturing the bottom cell will be described.
A 0.5 μm thick Si wafer is prepared, and n-type dopant is ion-implanted on the light irradiation side. The n + type is formed immediately below the Ag wiring in order to form a good contact. An antireflection film is formed thereon. A passivation layer (region) is formed on the back side using SiNx. By forming a portion where SiN _x does not exist and conducting only part of it with the back Al electrode, recombination at the crystal interface is reduced and a highly efficient bottom cell can be obtained.

A method for measuring the conversion efficiency is as follows.
A solar simulator simulating an AM1.5G light source is used, and the light quantity is adjusted to 1 sun using a reference Si cell under the light source. The temperature is 25 ° C. Sweep the voltage and measure the current density (current divided by cell area). When the horizontal axis represents voltage and the vertical axis represents current density, the point that intersects the horizontal axis is the open circuit voltage Voc, and the point that intersects the vertical axis is the short-circuit current density Jsc. On the measurement curve, when the voltage and current density are multiplied and the maximum points are Vmpp and Jmpp (maximum power point), respectively, FF = (Vmpp * Jmpp) / (Voc * Jsc)
Efficiency Eff. = Voc * Jsc * FF.
The transmittance is measured by using a spectrophotometer so that the sample surface is perpendicular to the light source and the ratio of the transmitted light to the incident light is measured. The reflectance is obtained by measuring the reflected light of a sample tilted by about 5 degrees from the perpendicular to the incident light. The band gap is obtained from the transmittance / reflectance. In Example 1, the average value of the transmitted light having a wavelength of 700 nm to 1150 nm is calculated from the wavelength range in which the bottom cell can absorb from the wavelength in the region where the transmission is large below the band gap (standard transmission is 50% or more).
The results are summarized in Table 1. The results of other examples and comparative examples are also summarized in Table 1.

(Comparative Example 1)
A top cell solar cell is produced in the same manner as in Example 1 except that the top cell solar cell is produced without spin coating the Pd dispersion, and the multijunction solar cell of Comparative Example 1 is obtained. Then, the solar cell is evaluated by the same method as in Example 1.

(Example 2-8)
A top cell solar cell was produced in the same manner as in Example 1 except that the concentration of the Pd dispersion was changed to produce a top cell solar cell, and the multijunction solar cell of Example 2-8 was produced. obtain. Then, the solar cell is evaluated by the same method as in Example 1. The concentrations of the Pd dispersions in Examples 2 to 8 are 3 wt%, 2 wt%, 1 wt%, 0.75 wt%, 0.5 wt%, 0.25 wt%, and 0.125 wt%.

Example 9
A top cell solar cell was produced in the same manner as in Example 1 except that a Pt dispersion of the same concentration was used instead of the Pd dispersion to produce a top cell solar cell. Type solar cell is obtained. Then, the solar cell is evaluated by the same method as in Example 1.

(Example 10)
Instead of forming dots using the Pd dispersion, a 5 nm thick Mo film and a 25 nm thick Pd were sequentially formed on the first electrode, and using a mask, the dot diameter (diameter) was 8.9 μm, A top cell solar cell was produced in the same manner as in Example 1 except that a circular cell having a pitch (distance between dot centers) of 20 μm was formed to produce a solar cell. Get a solar cell. Then, the solar cell is evaluated by the same method as in Example 1.

(Example 11)
A top cell solar cell was prepared in the same manner as in Example 9 except that dots having a dot diameter (diameter) of 3.5 μm and a pitch (distance between dot centers) of 10 μm were formed to produce a solar cell of the top cell. The multijunction solar cell of Example 11 is obtained. Then, the solar cell is evaluated by the same method as in Example 1.

(Example 12)
Instead of forming dots using the Pd dispersion, dots are formed by imprinting. The dot shape is circular. The dot diameter is 230 nm. The pitch (the distance between dot centers) is 460 nm. It is a laminated dot of Mo having a thickness of 5 nm and Pd having a thickness of 25 nm. Except for these, a top cell solar cell is produced in the same manner as in Example 9, and the multijunction solar cell of Example 12 is obtained. Then, the solar cell is evaluated by the same method as in Example 1.

(Example 13)
A top cell solar cell was prepared in the same manner as in Example 1 except that a 1 nm thick SiN _x film was formed on the first electrode by CVD before applying the Pd dispersion. Type solar cell is obtained. Then, the solar cell is evaluated by the same method as in Example 1.

(Example 14-21)
In Example 14-21, Mo is used for the dots, the dot shape is circular, the dot height is 40 nm, and a dot region is produced as in Example 10. The dot diameters of Examples 14-22 are 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, and 10 μm in order, and the dot pitch is adjusted so that the aperture ratios shown in Table 1 are obtained. Except for these, a top cell solar cell is produced in the same manner as in Example 10 to obtain a multi-junction solar cell in Examples 14-21. Then, the solar cell is evaluated by the same method as in Example 1.

(Examples 22-30)
In Examples 22-30, a dot region is prepared in the same manner as in Example 10, using Mo for the dots, setting the dot shape to a circle, setting the dot height to 50 nm, and setting the dot diameter to 6 μm. The dot pitch is adjusted so that the aperture ratio shown in Table 1 is obtained. Except for these, a top cell solar cell is produced in the same manner as in the example, and the multi-junction solar cell of Example 22-30 is obtained. Then, the solar cell is evaluated by the same method as in Example 1.

(Examples 31-33)
In Examples 31-33, a dot region is prepared in the same manner as in Example 10 using Mo for dots, a dot shape of a hexagonal nut shape, a dot height of 50 nm, and a dot diameter of 6 μm. The dot pitch is adjusted so that the aperture ratio shown in Table 1 is obtained. Furthermore, the dots are hollow and have a circular cavity. If the dot is not hollow, the aperture ratio of Examples 31-33 is 80%. The diameters of the hollow circles in the dots of Examples 31-33 are 2 μm, 3 μm, and 4 μm in order. Except for these, a top cell solar cell is produced in the same manner as in Example 10 to obtain the multi-junction solar cell of Examples 31-33. Then, the solar cell is evaluated by the same method as in Example 1.

(Examples 34-38)
In Examples 34-38, AlO _x or SiN _x is formed as a first insulating film on the first electrode to form a dot region. The first insulating film of Example 34-38 in turn, the thickness of the 5NmAlO _x, the thickness of the 15nmAlO _x, 5nmSiN _x thickness, thickness 10NmSiN _x, a 20NmSiN _x thickness. A dot region is produced in the same manner as in Example 10 with a dot shape of a circle (hollow), a dot height of 80 nm, and a dot diameter of 6 μm. Except for these, a top cell solar cell is produced in the same manner as in Example 10 to obtain a multi-junction solar cell of Examples 34-38. Then, the solar cell is evaluated by the same method as in Example 1.

(Examples 39-41)
Examples 39-41 are examples except that a dot region is prepared by applying a dispersion containing metal particles having an average diameter of 6 μm (Example 39: Mo, Example 40: Ru, Example 41: Pd). A top cell solar cell is produced by the same method as in Example 1 to obtain a multi-junction solar cell of Examples 39-41. Then, the solar cell is evaluated by the same method as in Example 1.

(Example 42)
In Example 42, Mo is uniformly formed on a transparent conductive film, and a copolymer that is phase-separated by self-assembly is formed thereon, and a layer separation film having an average diameter of 50 nm and a pitch (distance between dot centers) of 150 nm. Form. After removing the non-existing Mo by dry etching or wet etching, SiN _x is deposited on the entire surface. The copolymer and the SiN _x deposited thereon are also removed at the same time. Except for these, a top cell solar cell is produced in the same manner as in Example 10, and the multijunction solar cell of Example 42 is obtained. Then, the solar cell is evaluated by the same method as in Example 1.
Furthermore, the power generation efficiency can be improved by making the average diameter in the in-plane direction of the dots in the dot region smaller than the average crystal grain size in the in-plane direction of the interface on the first electrode side of the light absorption layer.

(Comparative Example 2)
Instead of forming dots using the Pd dispersion, a top layer is formed in the same manner as in Example 1 except that a 5 nm thick gold thin film is formed and the light absorption layer 3 is formed on the gold thin film. A solar cell of the cell is produced, and the multijunction solar cell of Comparative Example 2 is obtained. The gold thin film is atomized by the heat treatment during the formation of the light absorption layer 3.

(Comparative Example 3)
A top-cell solar cell is produced in the same manner as in Example 15 except that Ni is used for the dots, and the multi-junction solar cell of Comparative Example 3 is obtained.

By introducing metal dots, it becomes difficult to form an oxide layer at the contact interface with the light absorption layer, a good contact is formed, and Voc is increased. Although it should be possible to form a good contact with a transparent electrode by reviewing the heat treatment and the process, the light absorption layer is oxidized at a high temperature, so the process must be at a low temperature, and the mobility of the light absorption layer increases. It is considered difficult.
If only dots are present, conduction from the transparent electrode is also present. Therefore, in order to eliminate the conductive path between the transparent electrode and the light absorption layer, the region other than the dots can be further improved by introducing an insulating layer. In addition, the FF is higher when the area ratio of the metal dot region is higher, and the FF is higher overall when there is a metal dot and an insulating film. The aperture ratio is important for increasing the power generation of the bottom cell and middle cell below, but the FF of the top cell gets worse as the aperture ratio approaches 100%. This is because the contribution of conduction between the transparent electrode and the light absorption layer is increased. When Ni is used for the dot, a dot pattern can be formed in the same manner when Mo is used. However, when the element concentration analysis in the film is performed by SIMS (Secondary Ion Mass Spectrometry) after forming the light absorption layer. It can be seen that Ni is segregated on the front and back surfaces of the film. As a result, a leak path is formed in the light absorption layer, and the conversion efficiency is extremely deteriorated.
In the specification, some elements are represented only by element symbols.

  The embodiment of the present invention has been described above. However, the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying constituent elements without departing from the scope of the invention in the implementation stage. Moreover, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, you may combine suitably the component covering different embodiment like a modification.

DESCRIPTION OF SYMBOLS 100, 101, 102 ... Solar cell, 1 ... Board | substrate, 2 ... 1st electrode, 3 ... Light absorption layer, 4 ... Dot area | region, 5 ... N-type layer, 6 ... 3rd electrode, 7 ... 1st insulating film, 8 DESCRIPTION OF SYMBOLS 2nd insulating film, 200 ... Multijunction type solar cell, 201 ... Top cell solar cell, 202 ... Bottom cell solar cell, 300 ... Solar cell module, 301 ... Solar cell, 400 ... Solar cell system, 401 ... Solar Battery module 402 ... Converter 403 Storage battery 404 Load

Claims (9)

A first electrode;
A second electrode;
A light absorption layer between the first electrode and the second electrode;
The solar cell which has a dot area | region containing a dot between the said 1st electrode and the said light absorption layer.   The solar cell according to claim 1, wherein an aperture ratio of the dot region is 50% or more and 99.95% or less.   The dot of the said dot area | region is a solar cell of Claim 1 or 2 containing any 1 or more types in a metal, an alloy, a conductive oxide, and a conductive nitride.   4. The solar cell according to claim 1, wherein a first insulating film is present between the dots in the dot region.   The solar cell according to any one of claims 1 to 4, wherein a second insulating film is present between the dot region and the first electrode.   6. The solar cell according to claim 1, wherein an average diameter in an in-plane direction of the dots is smaller than an average crystal grain size in an in-plane direction of an interface of the light absorption layer on the first electrode side. .   A multi-junction solar cell using the solar cell according to claim 1.   A solar cell module using the solar cell according to any one of claims 1 to 6 or the multi-junction solar cell according to claim 7.   A solar power generation system using the solar cell module according to claim 8.