JP7330015B2 - Solar cells, multi-junction solar cells, solar cell modules and photovoltaic power generation systems - Google Patents

Description

Embodiments relate to solar cells, multi-junction solar cells, solar cell modules, and photovoltaic systems.

There is a multi-junction (tandem) solar cell as a highly efficient solar cell. A tandem solar cell can use a cell with high spectral sensitivity for each wavelength band, and therefore can be more efficient than a single junction. Cuprous oxide compounds, which are inexpensive materials and have a wide bandgap, are also expected as top cells for tandem solar cells.

Sang Woon Lee et al. Advanced Energy Materials., 4 (2014) 1301916

Embodiments provide solar cells, multi-junction solar cells, solar cell modules, and photovoltaic systems with improved properties.

The solar cell of the embodiment comprises a transparent first electrode, a photoelectric conversion layer mainly composed of cuprous oxide on the first electrode, and Zn, Sn and B, or/and Si on the photoelectric conversion layer . It has an n-type layer which is a metal oxide layer containing element M which is one or more elements selected from the group consisting of Zr and Hf, and a transparent second electrode on the n-type layer. The n-type layer is a layer composed of a compound represented by ZnxSnyMzOw, where x, y and z satisfy 0.001≤(z/(x + y ₎ ) _{< 1.00 .} , x satisfies 0.77≦x≦0.8, and y satisfies 0.19≦y≦0.22.

The cross-sectional conceptual diagram of the solar cell of embodiment. The figure explaining the analysis spot of the solar cell of embodiment. 1 is a conceptual cross-sectional view of a multi-junction solar cell according to an embodiment; FIG. The conceptual diagram of the solar cell module of embodiment. 1 is a conceptual cross-sectional view of a solar cell module according to an embodiment; FIG. The conceptual diagram of the solar power generation system of embodiment. 1 is a conceptual diagram of a vehicle according to an embodiment; FIG.

(First embodiment)
A first embodiment relates to a solar cell. FIG. 1 shows a conceptual diagram of a solar cell 100 of the first embodiment. As shown in FIG. 1, the solar cell 100 according to the present embodiment includes a first electrode 1, a photoelectric conversion layer 2 on the first electrode 1, an n-type layer 3 (3A) on the photoelectric conversion layer 2, A second electrode 4 is provided on the n-type layer 3 (3A). An intermediate layer (not shown) may be included between the first electrode 1 and the photoelectric conversion layer 2 and between the n-type layer 3 (3A) and the second electrode 4 . The light may be incident from the first electrode 1 side or from the second electrode 4 side. Light can be incident on the solar cell 100 to generate electricity.

(first electrode)
The first electrode 1 of the embodiment is a transparent conductive layer provided on the photoelectric conversion layer 2 side. In FIG. 1 , the first electrode 1 is in direct contact with the photoelectric conversion layer 2 . The first electrode 1 is preferably a transparent conductive film, or a laminate of a metal film, a transparent conductive film, and a metal film. Transparent conductive films include Indium Tin Oxide (ITO), Al-doped Zinc Oxide (AZO), Boron-doped Zinc Oxide (BZO), and Gallium-doped Zinc Oxide (BZO). -doped Zinc Oxide (GZO), Fluorine-doped Tin Oxide (FTO), Antimony-doped Tin Oxide (ATO), Titanium-doped Indium Oxide (ITiO), Indium Zinc Oxide (IZO), Indium Gallium Zinc Oxide (IGZO), Ta-doped Tin Oxide (SnO ₂ : Ta), Niobium-doped Tin Oxide (Nb-doped Tin Oxide). Oxide; _SnO2 : Nb), tungsten-doped tin oxide (W-doped Tin Oxide; _SnO2 : W), molybdenum-doped tin oxide (Mo-doped Tin Oxide; _SnO2 : Mo), fluorine-doped tin oxide (F-doped Tin Oxide; _SnO2 :F), hydrogen-doped indium oxide (IOH), etc. are not particularly limited. The transparent conductive film may be a laminated film having a plurality of films, and the laminated film may contain a film of tin oxide or the like in addition to the above oxides. As a dopant for a film such as tin oxide, In, Si, Ge, Ti, Cu, Sb, Nb, F, Ta, W, Mo, F, Cl and the like are not particularly limited. The metal film is not particularly limited and may be Mo, Au, Cu, Ag, Al, Ta or W films. Also, the first electrode 1 may be an electrode in which a dot-like, line-like or mesh-like metal is provided on a transparent conductive film. At this time, the dot-shaped, line-shaped or mesh-shaped metal is arranged between the transparent conductive film and the photoelectric conversion layer 2 or on the opposite side of the transparent conductive film from the photoelectric conversion layer 2 . The dot-shaped, line-shaped or mesh-shaped metal preferably has an aperture ratio of 50% or more with respect to the transparent conductive film. The dot-shaped, line-shaped or mesh-shaped metal is not particularly limited and may be Mo, Au, Cu, Ag, Al, Ta or W. When a metal film is used for the first electrode 1, the film thickness is preferably about 5 nm or less from the viewpoint of transparency.

(Photoelectric conversion layer)
The photoelectric conversion layer 2 of the embodiment is a semiconductor layer arranged between the first electrode 1 and the n-type layer 3 . As the photoelectric conversion layer 2, a compound semiconductor layer is preferable. Examples of the photoelectric conversion layer 2 include a semiconductor layer mainly composed of cuprous oxide (90 wt % or more). The photoelectric conversion layer 2 is more specifically a p-type compound semiconductor layer. As the photoelectric conversion layer 2 becomes thicker, the transmittance decreases, and considering film formation by sputtering, a thickness of 10 μm or less is practical, and a semiconductor layer mainly composed of cuprous oxide is preferable as the compound semiconductor layer. The thickness of the photoelectric conversion layer 2 is preferably 800 nm or more and 10 μm or less. As the compound semiconductor layer, a semiconductor layer mainly composed of cuprous oxide or the like may contain an additive. The photoelectric conversion layer 2 as a whole is p-type (including p-type and p+-type). A partial n-type region may be included on the n-type layer 3 side of the photoelectric conversion layer 2 .

The photoelectric conversion layer 2 is produced by sputtering. The atmosphere during sputtering is preferably a mixed gas atmosphere of an inert gas such as Ar and an oxygen gas. Depending on the type of the substrate holding the solar cell 100, the substrate temperature is heated to 100° C. or more and 600° C. or less, and sputtering is performed using a target containing Cu. For example, a cuprous oxide thin film having a large grain size can be formed on the first electrode 1 by adjusting the sputtering temperature and oxygen partial pressure. As the substrate (substrate holding the first electrode 1) used to fabricate the solar cell 100, acrylic, polyimide, polycarbonate, polyethylene terephthalate (PET), polypropylene (PP), fluorine-based resin (polytetrafluoroethylene (PTFE ), perfluoroethylene propene copolymer (FEP), ethylenetetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), perfluoroalkoxyalkane (PFA), etc.), polyarylate, polysulfone, polyethersulfone and poly Organic substrates such as etherimide and inorganic substrates such as soda lime glass, white plate glass, chemically strengthened glass, and quartz can be used.

95% or more of the photoelectric conversion layer 2 is preferably composed of cuprous oxide. More preferably, 98% or more of the photoelectric conversion layer 2 is composed of cuprous oxide. That is, it is preferable that the photoelectric conversion layer 2 hardly (substantially) contain a different phase such as CuO or Cu. It is preferable that the photoelectric conversion layer 2 is a Cu ₂ O single-phase thin film that does not contain a heterogeneous phase such as CuO or Cu, because the photoelectric conversion layer 2 has a very high translucency. That the photoelectric conversion layer 2 is substantially a single phase of Cu ₂ O can be confirmed by measurement by a photoluminescence method (Photo Luminescence; PL method).

(n-type layer)
The n-type layer 3A is an n-type semiconductor layer arranged between the photoelectric conversion layer 2 and the second electrode 4 . The surface of the n-type layer 3A facing the photoelectric conversion layer 2 is preferably in direct contact with the surface of the photoelectric conversion layer 2 facing the n-type layer 3A. The n-type layer 3A is preferably an amorphous thin film. The n-type layer 3A is preferably a metal oxide layer containing Zn, Sn and one or more elements M selected from the group consisting of Al, Ga, In and B. The element M is a group III element, and by including a group III element in the n-type layer 3A, the n-type layer 3A can be wide-gap, and the electron affinity of the n-type layer 3A can be reduced. A conduction band offset from the photoelectric conversion layer 2 can be reduced. The metal oxide layer (n-type layer _3A ) is preferably a _layer composed of a compound represented by _ZnxSnyMzOw , _where x, y and z are 0.001≦(z/ (x+y))<1.00 is preferably satisfied. If it is out of this range, it is not preferable because the physical properties _are greatly different from those of _ZnxSnyOw , which is _the main constituent element. x, y and z more preferably satisfy 0.001≦(z/(x+y))<0.5, 0.001≦(z/(x+y))<0.25, 0.001≦( It is even more preferred to satisfy z/(x+y))<0.1. The metal oxide layer is preferably _{substantially ZnxSnyMzOw} except _for unavoidable _impurities . This is _{because ZnxSnyMzOw does} not phase-separate into _{ZnxSnyOw and MzOw} by reducing (z/ _{( x} +y)) to widen the gap _. Furthermore, x, y and z more preferably satisfy 0.6≦(x+y+z)/w≦1.4. Element M is more preferably one or more elements selected from the group consisting of Al, Ga and In.

The above composition ratio is obtained by cutting out a cross section in the direction of the schematic diagram of FIG. Scan and find. A boundary (interface) between the photoelectric conversion layer 2 and the n-type layer 3 is also obtained from EDX. The boundary between the photoelectric conversion layer 2 and the n-type layer 3 is obtained as follows. The Cu concentration and Zn concentration are measured by EDX, and the position closest to the second electrode 4 from the n-type layer 3 side where the Cu concentration exceeds the Zn concentration is taken as the boundary. As the measurement positions, nine spots A1 to A9 on the surface of the solar cell 100 viewed from the second electrode 4 side are determined as shown in FIG. Each spot is square and has an area of at least 5 mm ² . As shown in FIG. 2, when the length is D1 and the width is D2 (D1≧D2), the distance D3 (=D1/10) inward from each of the two opposite sides in the width direction of the solar cell 100 , a virtual line is drawn at a distance of D4 (=D2/10) inward from two sides facing each other in the length direction of the solar cell 100, and a width direction passing through the center of the solar cell 100 is drawn. , a virtual line passing through the center of the solar cell 100 and parallel to the longitudinal direction is drawn, and areas centered on nine points of intersection of the virtual lines are defined as observation spots A1 to A9. A cross section observed by SEM or TEM is perpendicular to the plane of FIG. If the shape of the solar cell 100 viewed from the second electrode 4 side is not rectangular, it is preferable to determine the analysis spot based on the inscribed rectangle. The density is the average value of 7 analysis results excluding the maximum and minimum values of the 9 analysis spots.

ZnSnO which is an oxide of Zn and Sn not containing one or more elements M selected from the group consisting of Al, Ga, In and B as the n-type layer 3A provided on the photoelectric conversion layer 2 mainly made of cuprous oxide can be used. ZnSnO that does not contain at least one element M selected from the group consisting of Al, Ga, In and B absorbs a relatively large amount of light in the wavelength band including 350 nm, which is absorbed by the wide bandgap photoelectric conversion layer 2. Therefore, it becomes a factor of lowering the conversion efficiency of the solar cell 100 . For display devices such as monitors, the short wavelength band is partly out of the wavelength band of visible light. is not important. On the other hand, in the solar cell 100 using the photoelectric conversion layer 2 with a wide bandgap, since light in a wavelength band including such a short wavelength band is converted into electricity, a relatively large amount of light in the short wavelength band is absorbed. This is one of the factors that hinder improvement in conversion efficiency.

In the embodiment, by adding one or more elements M selected from the group consisting of Al, Ga, In and B to the n-type layer 3A, the n-type layer 3A that does not interfere with light absorption in the photoelectric conversion layer 2 is formed. As a result, the transmittance of n-type layer 3A and solar cell 100 was improved. In addition, by adding one or more elements M selected from the group consisting of Al, Ga, In and B, the lower end of the conduction band of the photoelectric conversion layer 2 and the n-type layer are more improved than when ZnSnO is used for the n-type layer 3 . By reducing the difference between the 3A conduction band bottoms, the Voc was improved, and in addition to the improvement of the transmittance, the conduction discontinuity was eliminated and the conversion efficiency was improved. The transmittance at a wavelength of 350 nm of the n-type layer _3A made of _a compound represented by _ZnxSnyMzOw containing one or more elements M selected from _the group consisting of Al, Ga, In and B is , is preferably 90% or more. The n-type layer 3A made of _a compound represented by _ZnxSnyMzOw containing one or more elements M selected from the group consisting of Al, Ga, In and _B is the absorption of _the photoelectric conversion layer 2. Excellent transmittance in the wavelength band. That is, the n-type layer 3A of the embodiment can increase the amount of light reaching the photoelectric conversion layer 2 more than ZnSnO, and can improve both the power generation amount of the solar cell 100 and the transparency of the solar cell 100.

The thickness of the n-type layer 3 is typically preferably 3 nm or more and 50 nm or less. If the thickness of the n-type layer 3 is less than 3 nm, a leakage current may occur when the coverage of the n-type layer 3 is poor, resulting in deterioration of the characteristics. If the coverage is good, the film thickness is not limited to the above. If the thickness of the n-type layer 3 exceeds 50 nm, the resistance of the n-type layer 3 becomes excessively high, which may lead to deterioration in characteristics, or a decrease in short-circuit current due to a decrease in transmittance. Therefore, the thickness of the n-type layer 3 is more preferably 5 nm or more and 50 nm or less, and even more preferably 5 nm or more and 10 nm or less. Further, the surface roughness of the n-type layer 3 is preferably 5 nm or less in order to realize a film with good coverage.

The n-type layer 3 can be formed by, for example, an atomic layer deposition (ALD) method, a sputtering method, or the like.

Conduction band offset (ΔE= Ecp−Ecn) is preferably −0.2 eV or more and 0.6 eV or less (−0.2 eV≦ΔE≦+0.6 eV). If the conduction band offset is greater than 0, the conduction band at the pn junction interface becomes discontinuous and spikes occur. If the conduction band offset is less than 0, the conduction band at the pn junction interface becomes discontinuous and a cliff occurs. Since both spikes and cliffs act as barriers to photogenerated electrons, smaller ones are preferable. Therefore, the conduction band offset is more preferably 0.0 eV or more and 0.4 eV or less (0.0 eV≦ΔE≦+0.4 eV). However, this is not the case when the in-gap level is used for conduction. The location of the CBM can be estimated using the following technique. The valence band maximum (VBM) is actually measured by photoelectron spectroscopy, which is an evaluation method for electron occupied levels, and then the CBM is calculated assuming the bandgap of the material to be measured. However, since an actual pn junction interface does not maintain an ideal interface due to interdiffusion and generation of cation vacancies, there is a high possibility that the bandgap will change. Therefore, it is preferable to evaluate CBM by reverse photoelectron spectroscopy that directly utilizes the reverse process of photoelectron emission. Specifically, the electronic state of the pn junction interface can be evaluated by repeating low-energy ion etching and forward/reverse photoelectron spectroscopy on the surface of the solar cell. Since one or more elements M selected from the group consisting of B, Al, In and Ga are included in the n-type layer 3 in addition to Zn and Sn, the electron affinity is reduced, and the photoelectric conversion layer 2 and the n-type layer 3 are separated. difference in CBM becomes smaller.

As for the second electrode 4, it is preferable to use a transparent electrode similar to the electrode mentioned for the first electrode 1. As shown in FIG. As the second electrode 4, other transparent electrodes such as multilayer graphene provided with extraction electrodes containing metal wires can also be employed.

(Anti-reflection film)
The antireflection film of the embodiment is a film for facilitating the introduction of light into the photoelectric conversion layer 2, and is formed on the first electrode 1 or the second electrode 4 on the side opposite to the photoelectric conversion layer 2 side. preferably. As the antireflection film, it is desirable to use, for example, MgF ₂ or SiO ₂ . Note that the antireflection film can be omitted in the embodiment. Although it is necessary to adjust the film thickness according to the refractive index of each layer, it is preferable to deposit a thin film having a thickness of about 70 to 130 nm (preferably 80 to 120 nm).

(Second embodiment)
A second embodiment relates to a solar cell. FIG. 1 shows a conceptual diagram of a solar cell 101 of the second embodiment. As shown in FIG. 1, the solar cell 101 according to the present embodiment includes a first electrode 1, a photoelectric conversion layer 2 on the first electrode 1, an n-type layer 3 (3B) on the photoelectric conversion layer 2, A second electrode 4 is provided on the n-type layer 3 (3B). An intermediate layer (not shown) may be included between the first electrode 1 and the photoelectric conversion layer 2 and between the n-type layer 3 ( 3 B) and the second electrode 4 . The light may be incident from the first electrode 1 side or from the second electrode 4 side. Light can be incident on the solar cell 101 to generate electricity. The elements other than the element M of the n-type layer 3B of the second embodiment are common to the solar cell 101 of the first embodiment. Contents described in the first embodiment but not described in the second embodiment are common to the first embodiment.

The n-type layer 3B is preferably a metal oxide layer containing one or more elements M selected from the group consisting of Zn, Sn and Si, Ge, Zr and Hf. Element M in the second embodiment is an element of group IVA (group 4 element) and group IVB (group 14 element). In the same manner as the group III element (group 13 element) of the morphology, the n-type layer 3B can be wide-gap, and the electron affinity of the n-type layer 3 can be reduced, thereby reducing the conduction band offset with the photoelectric conversion layer 2. can be made smaller. The element M may further include one or more group III elements selected from the group consisting of Al, Ga, In and B, and one or more selected from the group consisting of Al, Ga, In and B. Group III elements of The metal oxide layer (n-type layer _{3B )} is preferably a layer composed of a compound represented by _ZnxSnyMzOw , where x, y _and z are 0.001≦(z/ (x+y))<1.00 is preferably satisfied. If it is out of this range, it is not preferable because the physical properties _are greatly different from those of _ZnxSnyOw , which is _the main constituent element. x, y and z more preferably satisfy 0.001≦(z/(x+y))<0.5, 0.001≦(z/(x+y))<0.25 or 0.001≦( It is even more preferred to satisfy z/(x+y))<0.1. The metal oxide layer is preferably _{substantially ZnxSnyMzOw} except _for unavoidable _impurities . This is _{because ZnxSnyMzOw does} not phase-separate into _{ZnxSnyOw and MzOw} by reducing (z/ _{( x} +y)) to widen the gap _. Furthermore, x, y and z more preferably satisfy 0.6≦(x+y+z)/w≦1.4.

As the element M of the n-type layer 3B, it has been found that the group III elements consisting of Al, Ga, In and B and the group IVA and IVB elements Si, Ge, Zr and Hf are all suitable. Ta. Compared with solar cell characteristics, the latter group of IV group elements tends to improve characteristics and is more preferable. Specifically, both the elements of the IV group and the III group can reduce the electron affinity of the n-type layer 3, thereby improving Voc to the same extent. Furthermore, when an element belonging to Group IV is used, FF (Fill Factor) is improved in addition to Voc. The difference between the FFs of the IV group and the III group is that when either the IV group element or the III group element is added, the electron affinity of the n-type layer 3 is about the same, but the electronic physical properties of the n-type layer 3 (electron It is presumed that the difference in FF appeared due to the difference in concentration and electron mobility). In the n-type layer 3B, the addition of the group IV element improves the transmittance of the absorption band wavelength of the photoelectric conversion layer 2 . From the viewpoint of improving FF, when the element M contains both a group IV element and a group III element, the concentration of the group IV element is preferably higher than that of the group III element.

(Third Embodiment)
A third embodiment relates to a multi-junction solar cell. FIG. 3 shows a conceptual cross-sectional view of a multi-junction solar cell 200 of the third embodiment. The multi-junction solar cell 200 of FIG. 3 has the solar cell (first solar cell) 100 (101) of the first embodiment or the second embodiment and the second solar cell 201 on the light incident side. The bandgap of the photoelectric conversion layer of the second solar cell 201 is smaller than that of the photoelectric conversion layer 2 of the solar cell 100 (101) of the first embodiment or the second embodiment. Note that the multi-junction solar cell of the embodiment also includes a solar cell in which three or more solar cells are joined.

Since the bandgap of the photoelectric conversion layer 2 of the solar cell 100 (101) of the first embodiment or the second embodiment is about 2 eV, the bandgap of the photoelectric conversion layer of the second solar cell 201 is 1.0 eV or more. It is preferably 0.4 eV or less. The photoelectric conversion layer of the second solar cell 201 is preferably a compound semiconductor layer of one or more of CIGS, CIT, CdTe, and copper oxide-based compounds having a high In content, or crystalline silicon. .

By using the solar cell 100 (101) according to the first embodiment or the second embodiment as the first solar cell, the bottom cell (second Since it is possible to prevent the conversion efficiency of the solar cell from being lowered, an efficient multi-junction solar cell can be obtained.

(Fourth embodiment)
The fourth embodiment relates to a solar cell module. FIG. 4 shows a conceptual perspective view of a solar cell module 300 of the fourth embodiment. A solar cell module 300 in FIG. 4 is a solar cell module in which a first solar cell module 301 and a second solar cell module 302 are stacked. The first solar cell module 301 is on the light incident side and uses the solar cell 100 of the first embodiment. Second solar cell 201 is preferably used for second solar cell module 302 .

FIG. 5 shows a conceptual cross-sectional view of the solar cell module 300. As shown in FIG. In FIG. 5, the structure of the first solar cell module 301 is shown in detail, and the structure of the second solar cell module 302 is not shown. In the second solar cell module 302, the structure of the solar cell module is appropriately selected according to the photoelectric conversion layer of the solar cell used. The solar cell module of FIG. 5 includes a plurality of sub-modules 303 surrounded by dashed lines in which a plurality of solar cells 100 (solar cells) are horizontally arranged and electrically connected in series. They are electrically connected in parallel or in series.

The solar cells 100 are scribed, and adjacent solar cells 100 have the second electrode 4 on the upper side and the first electrode 1 on the lower side connected. As with the solar cell 100 (101) of the first or second embodiment, the solar cell 100 of the fourth embodiment also includes a substrate 10, a first electrode 1, a photoelectric conversion layer 2, an n-type layer 3, and a second electrode. 4.

If the output voltage is different for each module, the current may flow backward to the part with the lower voltage, or excessive heat may be generated, leading to a decrease in the output of the module.

In addition, by using the solar cell of the present application, it is possible to use a solar cell suitable for each wavelength band. is desirable because it increases the overall output of the

If the conversion efficiency of the entire module is high, it is possible to reduce the proportion of energy that becomes heat in the irradiated light energy. Therefore, it is possible to suppress a decrease in efficiency due to an increase in the temperature of the entire module.

(Fifth embodiment)
The fifth embodiment relates to a photovoltaic power generation system. The solar cell module 300 of the fourth embodiment can be used as a generator for generating power in the solar power generation system of the fifth embodiment. A solar power generation system according to an embodiment generates power using a solar cell module. It has a storage means for storing electricity or a load for consuming the generated electricity. FIG. 6 shows a configuration conceptual diagram of a photovoltaic power generation system 400 of the embodiment. The photovoltaic power generation system of FIG. 6 has a photovoltaic module 401 (300), a power conversion device 402, a storage battery 403, and a load 404. Either one of the storage battery 403 and the load 404 may be omitted. The load 404 may be configured to use the electrical energy stored in the storage battery 403 . The power conversion device 402 is a device including a circuit or element that performs power conversion such as transformation and DC/AC conversion. As for the configuration of the power conversion device 402 , a suitable configuration may be adopted according to the generated voltage, the configuration of the storage battery 403 and the load 404 .

Photovoltaic cells included in sub-module 303 included in photovoltaic module 300 generate electric power, and the electrical energy is converted by converter 402 and stored in storage battery 403 or consumed by load 404 . The solar cell module 401 is provided with a sunlight tracking drive device for always directing the solar cell module 401 toward the sun, a light collector for collecting sunlight, a device for improving power generation efficiency, and the like. Adding is preferred.

The photovoltaic power generation system 400 is preferably used in real estate such as residences, commercial facilities, and factories, and in movable properties such as vehicles, aircraft, and electronic equipment. By using the solar cell with excellent conversion efficiency of the embodiment for the solar cell module 401, an increase in power generation is expected.

A vehicle is shown as an example of use of the photovoltaic power generation system 400 . FIG. 7 shows a structural conceptual diagram of the vehicle 500. As shown in FIG. A vehicle 500 in FIG. 7 has a vehicle body 501 , a solar cell module 502 , a power conversion device 503 , a storage battery 504 , a motor 505 and tires (wheels) 506 . The power generated by the solar cell module 501 provided on the upper part of the vehicle body 501 is converted by the power conversion device 503 and charged by the storage battery 504 or consumed by the load such as the motor 505 . Vehicle 500 can be moved by rotating tires (wheels) 506 with motor 505 using power supplied from solar cell module 501 or storage battery 504 . The solar cell module 501 may be composed only of the first solar cell module provided with the solar cell 100 of the first embodiment instead of the multi-junction type. When adopting a transparent solar cell module 501, it is also preferable to use the solar cell module 501 as a power-generating window on the side surface of the vehicle body 501 in addition to the upper portion of the vehicle body 501.

EXAMPLES The present invention will be more specifically described below based on examples, but the present invention is not limited to the following examples.

(Example 1)
On a white plate glass substrate, an ITO transparent conductive film is deposited as a first electrode on the back side, and an Sb-doped SnO ₂ transparent conductive film is deposited thereon. A cuprous oxide compound is formed on the transparent first electrode by heating the substrate at 450° C. by sputtering in a mixed gas atmosphere of oxygen and argon gas. Thereafter, n-type Zn _0.78 Sn _0.21 Al _0.02 O ₁ (z/(x+y)=0.02, (x+y+z)/w=1) was deposited on the p-cuprous oxide layer by atomic layer deposition. .01) is deposited to a thickness of 10 nm. After that, an AZO transparent conductive film is deposited as a second electrode on the surface side. A solar cell is obtained by depositing _MgF2 as an antireflection film thereon.

A solar simulator simulating an AM1.5G light source is used, and the amount of light is adjusted to 1 sun using a reference Si cell under the light source. The air temperature shall be 25°C. The voltage is swept and the current density (current divided by cell area) is measured. When the horizontal axis is the voltage and the vertical axis is the current density, the point at which the horizontal axis intersects is the open circuit voltage Voc, and the point at which the vertical axis intersects is the short circuit current density Jsc. On the measurement curve, multiply the voltage by the current density, and let Vmpp and Jmpp (maximum power point) be the maximum points, respectively, then FF (=(Vmpp*Jmpp)/(Voc*Jsc)) and efficiency Eff. (=Voc*Jsc*FF) is obtained.

(Example 2)
Example 1 except that Zn _0.78 Sn _0.21 Ga _0.05 O ₁ (z/(x+y)=0.05, (x+y+z)/w=1.04) is deposited to 10 nm as the n-type layer. A solar cell is fabricated in the same manner as in , and its characteristics are evaluated.

(Example 3)
Example 1 except that Zn _0.78 Sn _0.21 In _0.10 O ₁ (z/(x+y)=0.1, (x+y+z)/w=1.09) is deposited to 10 nm as the n-type layer. A solar cell is fabricated in the same manner as in , and its characteristics are evaluated.

(Example 4)
Example 1 except that Zn _0.78 Sn _0.21 B _0.05 O ₁ (z/(x+y)=0.051, (x+y+z)/w=1.04) is deposited to a thickness of 10 nm as the n-type layer. A solar cell is fabricated in the same manner as in , and its characteristics are evaluated.

(Example 5)
Example 1 except that Zn _0.78 Sn _0.21 Al _0.001 O ₁ (z/(x+y)=0.001, (x+y+z)/w=0.99) is deposited to a thickness of 10 nm as the n-type layer. A solar cell is fabricated in the same manner as in , and its characteristics are evaluated.

(Example 6)
Example 1 except that Zn _0.78 Sn _0.21 Al _0.98 O ₂ (z/(x+y)=0.99, (x+y+z)/w=0.99) is deposited to a thickness of 10 nm as the n-type layer. A solar cell is fabricated in the same manner as in , and its characteristics are evaluated.

(Example 7)
Example 1 except that Zn _0.78 Sn _0.21 Al _0.01 O ₁ (z/(x+y)=0.01, (x+y+z)/w=1.00) is deposited to a thickness of 10 nm as the n-type layer. A solar cell is fabricated in the same manner as in , and its characteristics are evaluated.

(Example 8)
Example 1 except that Zn _0.78 Sn _0.21 Al _0.1 O ₁ (z/(x+y)=0.1, (x+y+z)/w=1.09) is deposited to a thickness of 10 nm as the n-type layer. A solar cell is fabricated in the same manner as in , and its characteristics are evaluated.

(Example 9)
Example 1 except that Zn _0.78 Sn _0.20 Al _0.02 O ₁ (z/(x+y)=0.02, (x+y+z)/w=1.00) is deposited to a thickness of 10 nm as the n-type layer. A solar cell is fabricated in the same manner as in , and its characteristics are evaluated.

(Example 10)
Example 1 except that Zn _0.78 Sn _0.22 Al _0.03 O ₁ (z/(x+y)=0.03, (x+y+z)/w=1.03) is deposited to a thickness of 10 nm as the n-type layer. A solar cell is fabricated in the same manner as in , and its characteristics are evaluated.

(Example 11)
Except for _{depositing Zn0.78Sn0.21Al0.015Ga0.015O1} (z/(x+y)=0.03, (x+y+z) _/w=1.02 ) to 10 nm as the n _- type layer _. A solar cell is produced in the same manner as in Example 1, and its characteristics are evaluated.

(Example 12)
except that _{Zn0.77Sn0.19Al0.02O0.8} (z/( _x +y)=0.02, (x+y+z)/w=1.23) is deposited _to 10 nm as the n-type layer _. A solar cell is produced in the same manner as in Example 1, and its characteristics are evaluated.

(Example 13)
Zn _0.77 Sn _0.19 Al _0.02 O _1.3 (z/(x+y)=0.02, (x+y+z)/w=0.75) was deposited to a thickness of 10 nm as the n-type layer. A solar cell is produced in the same manner as in Example 1, and its characteristics are evaluated.

(Example 14)
Example 1 except that Zn _0.8 Sn _0.21 Al _0.02 O ₁ (z/(x+y)=0.02, (x+y+z)/w=1.03) is deposited to 3 nm as the n-type layer. A solar cell is fabricated in the same manner as in , and its characteristics are evaluated.

(Example 15)
except that _{Zn0.78Sn0.21Al0.02O1.6} (z/ ₍ x+y)=0.02, (x+y+z)/w=0.63) _is deposited to 50 nm as the n-type layer _. A solar cell is produced in the same manner as in Example 1, and its characteristics are evaluated.

(Example 16)
Example 1 except that Zn _0.78 Sn _0.21 Al _0.0008 O ₁ (z/(x+y)=0.0008, (x+y+z)/w=0.99) is deposited to a thickness of 10 nm as the n-type layer. A solar cell is fabricated in the same manner as in , and its characteristics are evaluated.

(Example 17)
Example 1 except that Zn _0.78 Sn _0.21 Al _1.1 O ₂ (z/(x+y)=1.1, (x+y+z)/w=1.05) is deposited to 10 nm as the n-type layer. A solar cell is fabricated in the same manner as in , and its characteristics are evaluated.

(Example 18)
Example 1 except that Zn _0.78 Sn _0.21 Al _0.6 O ₁ (z/(x+y)=0.6, (x+y+z)/w=1.59) is deposited to a thickness of 10 nm as the n-type layer. A solar cell is fabricated in the same manner as in , and its characteristics are evaluated.

(Example 19)
Example 1 except that Zn _0.78 Sn _0.21 Al _0.49 O ₁ (z/(x+y)=0.50, (x+y+z)/w=1.48) is deposited to 10 nm as the n-type layer. A solar cell is fabricated in the same manner as in , and its characteristics are evaluated.

(Example 20)
Example 1 except that Zn _0.78 Sn _0.21 Al _0.40 O ₁ (z/(x+y)=0.40, (x+y+z)/w=1.39) is deposited to a thickness of 10 nm as the n-type layer. A solar cell is fabricated in the same manner as in , and its characteristics are evaluated.

(Example 21)
Example 1 except that Zn _0.78 Sn _0.21 Al _0.25 O ₁ (z/(x+y)=0.25, (x+y+z)/w=1.24) is deposited to a thickness of 10 nm as the n-type layer. A solar cell is fabricated in the same manner as in , and its characteristics are evaluated.

(Example 22)
Example 1 except that Zn _0.78 Sn _0.21 Al _0.20 O ₁ (z/(x+y)=0.20, (x+y+z)/w=1.19) is deposited to a thickness of 10 nm as the n-type layer. A solar cell is fabricated in the same manner as in , and its characteristics are evaluated.

(Example 23)
Example 1 except that Zn _0.78 Sn _0.21 Al _0.0004 O ₁ (z/(x+y)=0.0004, (x+y+z)/w=0.99) is deposited to a thickness of 10 nm as the n-type layer. A solar cell is fabricated in the same manner as in , and its characteristics are evaluated.

(Example 24)
Example 1 except that Zn _0.78 Sn _0.21 Al _1.5 O ₂ (z/(x+y)=1.52, (x+y+z)/w=1.25) is deposited to 10 nm as the n-type layer. A solar cell is fabricated in the same manner as in , and its characteristics are evaluated.

(Example 25)
Zn _0.78 Sn _0.21 Al _0.016 In _0.016 Ga _0.016 O ₂ (z/(x+y)=0.048, (x+y+z)/w=1.04) with a thickness of 10 nm as the n-type layer A solar cell is produced in the same manner as in Example 1 except for the deposition, and the characteristics are evaluated.

(Example 26)
except that _{Zn0.78Sn0.21Al0.002O2.5} (z/(x+y)= _0.002 , (x+y+z)/w=0.40) is deposited to 10 nm as _the n-type layer _. A solar cell is produced in the same manner as in Example 1, and its characteristics are evaluated.

(Example 27)
Example 1 except that Zn _0.78 Sn _0.21 Si _0.01 O ₁ (z/(x+y)=0.01, (x+y+z)/w=1.00) is deposited to a thickness of 10 nm as the n-type layer. A solar cell is fabricated in the same manner as in , and its characteristics are evaluated.

(Example 28)
Example 1 except that Zn _0.78 Sn _0.21 Ge _0.04 O ₁ (z/(x+y)=0.04, (x+y+z)/w=1.03) is deposited to a thickness of 10 nm as the n-type layer. A solar cell is fabricated in the same manner as in , and its characteristics are evaluated.

(Example 29)
Example 1 except that Zn _0.78 Sn _0.21 Zr _0.08 O ₁ (z/(x+y)=0.08, (x+y+z)/w=1.07) is deposited as an n-type layer to a thickness of 10 nm. A solar cell is fabricated in the same manner as in , and its characteristics are evaluated.

(Example 30)
Example 1 except that Zn _0.78 Sn _0.21 Hf _0.08 O ₁ (z/(x+y)=0.08, (x+y+z)/w=1.07) is deposited to 10 nm as the n-type layer. A solar cell is fabricated in the same manner as in , and its characteristics are evaluated.

(Example 31)
Example 1 except that Zn _0.78 Sn _0.21 Si _0.002 O ₁ (z/(x+y)=0.002, (x+y+z)/w=0.99) is deposited to a thickness of 10 nm as the n-type layer. A solar cell is fabricated in the same manner as in , and its characteristics are evaluated.

(Example 32)
Example 1 except that Zn _0.78 Sn _0.21 Si _0.77 O ₂ (z/(x+y)=0.78, (x+y+z)/w=0.88) is deposited to a thickness of 10 nm as the n-type layer. A solar cell is fabricated in the same manner as in , and its characteristics are evaluated.

(Example 33)
Example 1 except that Zn _0.78 Sn _0.21 Si _0.02 O ₁ (z/(x+y)=0.02, (x+y+z)/w=1.01) is deposited to a thickness of 10 nm as the n-type layer. A solar cell is fabricated in the same manner as in , and its characteristics are evaluated.

(Example 34)
Example 1 except that Zn _0.78 Sn _0.21 Si _0.17 O ₁ (z/(x+y)=0.17, (x+y+z)/w=1.16) is deposited to a thickness of 10 nm as the n-type layer. A solar cell is fabricated in the same manner as in , and its characteristics are evaluated.

(Example 35)
Example 1 except that Zn _0.78 Sn _0.20 Si _0.04 O ₁ (z/(x+y)=0.04, (x+y+z)/w=1.02) is deposited to a thickness of 10 nm as the n-type layer. A solar cell is fabricated in the same manner as in , and its characteristics are evaluated.

(Example 36)
Example 1 except that Zn _0.78 Sn _0.22 Si _0.05 O ₁ (z/(x+y)=0.05, (x+y+z)/w=1.05) is deposited to a thickness of 10 nm as the n-type layer. A solar cell is fabricated in the same manner as in , and its characteristics are evaluated.

(Example 37)
Except for _{depositing Zn0.78Sn0.21Si0.025Hf0.025O1} (z/(x+y)=0.05, ₍ x+y+z)/w=1.04) to 10 nm as _{the n} -type layer A solar cell is produced in the same manner as in Example 1, and its characteristics are evaluated.

(Example 38)
Zn _0.77 Sn _0.19 Si _0.01 O _0.8 (z/(x+y)=0.01, (x+y+z)/w=1.23) was deposited to 10 nm as the n-type layer. A solar cell is produced in the same manner as in Example 1, and its characteristics are evaluated.

(Example 39)
Zn _0.77 Sn _0.19 Si _0.01 O _1.3 (z/(x+y)=0.01, (x+y+z)/w=0.75) was deposited to 10 nm as the n-type layer. A solar cell is produced in the same manner as in Example 1, and its characteristics are evaluated.

(Example 40)
Example 1 except that Zn _0.78 Sn _0.21 Si _0.008 O ₁ (z/(x+y)=0.008, (x+y+z)/w=1.00) is deposited to a thickness of 10 nm as the n-type layer. A solar cell is fabricated in the same manner as in , and its characteristics are evaluated.

(Example 41)
Zn _0.78 Sn _0.21 Si _0.01 O _1.6 (z/(x+y)=0.01, (x+y+z)/w=0.63) was deposited to 10 nm as the n-type layer. A solar cell is produced in the same manner as in Example 1, and its characteristics are evaluated.

(Example 42)
Zn _0.78 Sn _0.21 Si _0.002 O _0.7 (z/(x+y)=0.002, (x+y+z)/w=1.42) was deposited to 10 nm as the n-type layer. A solar cell is produced in the same manner as in Example 1, and its characteristics are evaluated.

(Example 43)
Example 1 except that Zn _0.78 Sn _0.21 Si _1.2 O ₂ (z/(x+y)=1.21, (x+y+z)/w=1.10) is deposited as an n-type layer to a thickness of 10 nm. A solar cell is fabricated in the same manner as in , and its characteristics are evaluated.

(Example 44)
Except _{for depositing Zn0.78Sn0.21Si0.032Al0.016O1} (z/(x+y)= _0.048 , (x+y+z)/w=1.04) to 10 nm as _the n-type layer. A solar cell is produced in the same manner as in Example 1, and its characteristics are evaluated.

(Example 45)
Example 1 except that Zn _0.78 Sn _0.21 Si _0.5 O ₁ (z/(x+y)=0.51, (x+y+z)/w=1.49) is deposited to a thickness of 10 nm as the n-type layer. A solar cell is fabricated in the same manner as in , and its characteristics are evaluated.

(Example 46)
Example 1 except that Zn _0.78 Sn _0.21 Si _0.6 O ₁ (z/(x+y)=0.61, (x+y+z)/w=1.59) is deposited to a thickness of 10 nm as the n-type layer. A solar cell is fabricated in the same manner as in , and its characteristics are evaluated.

(Example 47)
Example 1 except that Zn _0.78 Sn _0.21 Si _0.4 O ₁ (z/(x+y)=0.40, (x+y+z)/w=1.39) is deposited to a thickness of 10 nm as the n-type layer. A solar cell is fabricated in the same manner as in , and its characteristics are evaluated.

(Example 48)
Example 1 except that Zn _0.78 Sn _0.21 Si _0.3 O ₁ (z/(x+y)=0.30, (x+y+z)/w=1.29) is deposited to a thickness of 10 nm as the n-type layer. A solar cell is fabricated in the same manner as in , and its characteristics are evaluated.

(Example 49)
Example 1 except that Zn _0.78 Sn _0.21 Si _0.00002 O ₁ (z/(x+y)=0.00002, (x+y+z)/w=0.99) is deposited to a thickness of 10 nm as the n-type layer. A solar cell is fabricated in the same manner as in , and its characteristics are evaluated.

(Example 50)
Example 1 except that Zn _0.78 Sn _0.21 Si _0.0002 O ₁ (z/(x+y)=0.0002, (x+y+z)/w=0.99) is deposited to a thickness of 10 nm as the n-type layer. A solar cell is fabricated in the same manner as in , and its characteristics are evaluated.

(Example 51)
Example 1 except that Zn _0.78 Sn _0.21 Si _1.5 O ₂ (z/(x+y)=1.52, (x+y+z)/w=1.25) is deposited to 10 nm as the n-type layer. A solar cell is fabricated in the same manner as in , and its characteristics are evaluated.

(Example 52)
_{Zn0.78Sn0.21Si0.024Ge0.012Zr0.012O2} (z/(x+y)= _0.048 , (x+y ₊ z)/w=1.04) _with a thickness of _{10 nm} as the n-type layer A solar cell is produced in the same manner as in Example 1 except for the deposition, and the characteristics are evaluated.

(Example 53)
except that _{Zn0.78Sn0.21Si0.002O2.5} (z/(x+y)= _0.002 , (x+y+z)/w=0.40) is deposited to 10 nm as _the n-type layer _. A solar cell is produced in the same manner as in Example 1, and its characteristics are evaluated.

(Comparative example 1)
A solar cell was fabricated in the same manner as in Example 1, except that Zn _0.78 Sn _0.21 O ₁ (z/(x+y)=0, (x+y+z)/w=0.99) was deposited to a thickness of 10 nm as the n-type layer. Fabricate and evaluate properties.

Tables 1 and 2 show the results of Examples and Comparative Examples. An improvement of 0.2 V or more compared to Voc of Comparative Example 1 is evaluated as A. If the Voc is the same as the Voc of Comparative Example 1 or is improved by less than 0.2 V with respect to the Voc of Comparative Example 1 (including the case where the Voc is lowered), it is evaluated as B. A case where the Voc is lower than that of Comparative Example 1 is evaluated as C. If the transmittance is higher than the transmittance at 350 nm of Comparative Example 1 and is 50% or more, it is evaluated as A, otherwise it is evaluated as B. When the FF of the example is higher than the FF of Comparative Example 1 by 10% or more, it is evaluated as A +. degree) is evaluated as B. The composition of the n-type layer in Examples and Comparative Examples is obtained from the conditions during film formation.

All of the solar cells of Examples are excellent in transmittance and improved in Voc as compared with Comparative Example 1 in which no Group III element is added. An increase in Voc by 0.2 V increases Voc by about 20% or more, which greatly contributes to the improvement of conversion efficiency. Solar cells with high transmittance and Voc are similarly obtained in the examples in which the Group III element is changed. The amount of element III added may be large to some extent, but if the amount added is too large, the characteristics tend to deteriorate. Also, when the amount of the Group III element added is small, the characteristics approach those of Comparative Example 1, but are superior to those when no addition is made. Moreover, all the solar cells of the examples had higher FF than the comparative example. It is presumed that this was influenced by the Voc being higher than that of the comparative example. Furthermore, Examples 27-53 had higher FF than Examples 1-26. It is presumed that this is because the n-type layer containing the IV group element has better electronic physical properties (electron concentration and electron mobility) and the electric resistance of the n-layer becomes smaller. The solar cells of the examples are excellent not only in short wavelength transmittance but also in long wavelength transmittance. contributes to the improvement of total power generation.
In the specification, some elements are represented only by element symbols.

Although the embodiments of the present invention have been described above, the present invention is not to be construed as being limited to the above-described embodiments, and can be embodied by modifying constituent elements without departing from the gist of the present invention. Also, various inventions can be formed by appropriate combinations of the plurality of constituent elements disclosed in the above embodiments. For example, like modifications, constituent elements of different embodiments may be appropriately combined.

DESCRIPTION OF SYMBOLS 100, 101... Solar cell (1st solar cell, top cell), 1... 1st electrode, 2... Photoelectric conversion layer, 3 (3A, 3B)... n-type layer, 4... 2nd electrode, 200... Multijunction type Solar cell 201 Second solar cell (bottom cell) 300 Solar cell module 301 First solar cell module 302 Second solar cell module 10 Substrate 303 Submodule 400 Photovoltaic system DESCRIPTION OF SYMBOLS 401... Solar cell module, 402... Power converter, 403... Storage battery, 404... Load, 500... Vehicle, 501... Vehicle body, 502... Solar cell module, 503... Power converter, 504... Storage battery, 505... Motor, 506... tire (wheel)

Claims (7)

a transparent first electrode;
a photoelectric conversion layer mainly composed of cuprous oxide on the first electrode;
An n-type layer which is a metal oxide layer containing an element M which is one or more elements selected from the group consisting of Zn, Sn and B and/or Si , Zr and Hf on the photoelectric conversion layer. and,
a transparent second electrode on the n-type layer ;
The n- type layer _{is a} layer composed of a compound represented _by ZnxSnyMzOw _,
x, y and z satisfy 0.001≦(z/(x+y))<1.00,
x satisfies 0.77≦x≦0.8,
y is a solar cell satisfying 0.19≦y≦0.22 . 2. The solar cell according to claim 1 , wherein x, y and z satisfy 0.001≤(z/(x+y))<0.5. x, y and z satisfy 0.001≦(z/(x+y))<1.00,
3. The solar cell according to claim 1, wherein x, y, z and w satisfy 0.6≤(x+y+z)/w≤1.4. 4. The solar cell according to claim 1, wherein the n-type layer has a thickness of 3 nm or more and 50 nm or less. A multi-junction solar cell using the solar cell according to any one of claims 1 to 4 . A solar cell module using the solar cell according to any one of claims 1 to 4 . A photovoltaic power generation system that generates power using the photovoltaic module according to claim 6 .