JP2001007365A - Solar cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a high-efficiency and low-cost solar cell by a method wherein a p-type semiconductor layer is formed as a polycrystal thin film and a band gap is set at a specific value. SOLUTION: In an Si-based solar cell, a p-type semiconductor layer is formed as a polycrystal thin film, and a band gap is set at 2.4 eV or higher. As a p-type semiconductor, a calcopyrite compound, a deformed calcopyrite compound or a composite oxide which contains at least Cu is preferable. The calcopyrite compound or the deformed calcopyrite compound comprises a crystal structure which is similar to sphalerite, and it can be regarded as a compound in which, e.g. two pieces of sphalerite are piled up and in which bivalent Zn is substituted alternately for monovalent Cu and trivalent Fe. The compounds may be formed as an epitaxial film, and a thin film which displays p-type conductivity is obtained easily in an amoprphous thin film or a polycrystal thin film. A doping operation is simple. In addition, a change in the electric characteristic of the solar cell clue to electrification or temperature is small, and an electrochemical reaction with an electrode material is not generated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solar cell for converting light energy into electric energy, and more particularly, to improving energy conversion efficiency by improving a window material of a semiconductor layer in a Si-based solar cell. Related to solar cells.

[0002]

2. Description of the Related Art Conventionally, Si-based solar cells, in particular, a-
Si solar cell is an electrode made of metal or transparent conductor,
a-type p-type semiconductor layer (p-layer) made of a-Si, non-doped layer or insulating layer (i-layer) made of a-Si, n-type semiconductor layer (n-layer) made of a-Si, metal or transparent conductor , And a band diagram as shown in FIG. In FIG. 1, Ev is the energy on the valence band term, and Ec is the energy on the bottom of the conduction band. Ef represents the Fermi level, hω ₁ and hω ₂ represent incident photons, and white circles and black circles represent carriers. i
The layers generate photocurrent and transport the generated carriers, and the p and n layers create a built-in potential that promotes carrier drift in the i layer and collect photogenerated carriers. The p-layer is used for a window on the light incident side. Here, the light absorption is small, and a device for effectively transmitting light to the i-layer is devised.

In order to obtain high energy conversion efficiency in such a solar cell, it is necessary to optimize each layer constituting the solar cell and the junction structure.

[0004] Basically, light energy matching that guides light energy into a semiconductor as efficiently as possible. Generation of photocarriers by photoconductive action of semiconductor. Polarization of photogenerated carriers by internal electric field. Collection to the electrode that guides photogenerated carriers to the terminals as effectively as possible. What is necessary is just to make the structure which performs the above efficiently.

[0005] Specifically, the main means for achieving high efficiency are (1) utilizing the light trapping effect using a texture substrate. Example: A method of increasing light absorption by using a concave-convex electrode. (2) A tandem structure combined with a band gap material narrower than a-Si. Example: Adoption of pin-pin-pin structure. (3) A heterojunction window using a wide gap p-layer is employed. Example: Use of a p-type a-SiC window. And the like.
To explain these in more detail,

[0006] (1) is, for example, the 30th Applied Physics-related Lecture Meeting Proceedings 7a-A-10, (1983) 349.
Is stated on the page. This is a method to confine the solar light energy received in the optical matching part to the semiconductor, which is the active layer, as effectively as possible. Specifically, AR (anti-reflection)
This is a method in which light once entering the semiconductor portion is confined by coating, texture surface treatment, or the like so as not to escape to the outside again by reflection from the back electrode or the like.

[0007] (2) is described, for example, by H. Takamura in Jpn.
Appl. Phys. 31 (1992) at page 2394. In order to collect a wider energy spectrum, spectral sensitivities of two or three types of semiconductors are stacked from a light incident side to a wide gap material → a narrow gap material, so as to broaden the spectral sensitivity as a whole.

The present invention pays particular attention to the above (3). The structure in which a-SiC has a wide gap p layer is described by T. Tawada et al. in, for example, Solar Energy Materials, 6, pp. 299 (1982). Also, a-SiC
In addition, the use of p-type a-SiO is also being studied.
In these materials, high efficiency is achieved by reducing the absorption coefficient of the p-layer and improving the IV characteristics presumably due to the wide gap.

As described above, despite the fact that high efficiency can be achieved by using a wide gap p-layer, a wide gap p-layer material studied as a solar cell is a p-type a-SiC.
Or, it was only p-type a-SiO. Since other p-type materials have difficulty in obtaining p-type conductivity in a wide gap in an amorphous or polycrystalline state, there has been no study on a solar cell, and higher efficiency by a p-layer window material is being promoted. Absent.

[0010]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for forming a p-type semiconductor in a polycrystalline film, such as a chalcopyrite compound or a modified chalcopyrite compound or an oxide material such as CuAlO ₂ or SrCu ₂ O _2. An object of the present invention is to provide a highly efficient and inexpensive solar cell by using a layer made of a composite oxide containing the same as a p-layer window material of the solar cell.

[0011]

This object is achieved by any one of the following constitutions (1) to (5). (1) An Si-based solar cell, wherein the p-type semiconductor layer is a polycrystalline thin film and has a band gap of 2.4 eV or more. (2) The solar cell according to (1), wherein the p-type semiconductor layer is a chalcopyrite compound or a modified chalcopyrite compound. (3) The solar cell according to (1), wherein the p-type semiconductor layer is a composite oxide containing at least Cu. (4) The solar cell according to (3), wherein the composite oxide containing Cu is a delafossite compound. (5) The main component of the composite oxide containing Cu is SrCu
The solar cell of (3) above, which is ₂ O ₂ .

[0012]

The present inventors have found that a thin film having a wide gap and a p-type conductivity in a polycrystalline film state is extremely effective as a solar cell p-layer.

The present invention provides a p-type semiconductor in a polycrystalline film state.
Chalcopyrite or modified chalcopyrite
CuAlO which is a compound or oxide material_Two, SrCu
_TwoO_Two A layer made of a composite oxide containing Cu such as a solar cell
And a conventional a-SiCp type window
Higher efficiency with wider band gap material instead of material
Inexpensive solar cells can be realized.

It is necessary that a p-layer for a solar cell can be formed in a polycrystalline state on a glass substrate or the like. Therefore, thin film formation and physical property evaluation of thin films of various semiconductor materials, and a-
The bonding characteristics with Si were evaluated and examined.

In this study, the present inventors found that p-type a-
Instead of the SiC type semiconductor thin film, attention was paid to a layer made of a chalcopyrite compound, a modified chalcopyrite compound, or a composite oxide containing Cu, which is a p-type semiconductor having a large band gap.

That is, the present invention provides a conventional p-type a-Si
As a result of using a p-type semiconductor layer made of a chalcopyrite compound or a modified chalcopyrite compound, which is a p-type semiconductor having a larger band gap, or a composite oxide containing Cu, instead of the C semiconductor, it is effective in increasing the efficiency. I understood. Incidentally, the band gap of a-SiC is about 2.0 eV or less.

FIG. 2 shows a band structure when a p-type wide gap window material is used. Here, in a normal a-Si solar cell, the light absorption of the p-type layer on the window side is large, but in the present invention, light absorption is small by using a wide-gap p-layer window, and light of short wavelength is also effectively used. Light can be guided to the i-layer. Note that the reference numerals in the figure are the same as those in FIG.

At the interface between the p-layer and the i-layer, an electric field is generated due to the Fermi level difference as shown in FIG. 2, so that the minority carriers generated in the i-layer are directed toward the electrode on the p-layer side. Things are reflected. Therefore, recombination does not occur in the vicinity of the electrode on the p-layer side, and the number of components toward the n-layer side increases, so that the efficiency increases.

Further, by using the Fermi levels of the p-layer and the n-layer, an internal electric field for effectively extracting carriers can be increased, thereby increasing the open-circuit voltage.

The delafossite compound and the SrCu ₂ O ₂ compound which are monovalent Cu-containing composite oxides are described in, for example, New GLASS Vol.
(1998) p. 43, Hiroshi Kawasoe, Hideo Hosono "Search for p-type conductive transparent oxides", Nature No. 389
(1988) p. 941; KAWAZOE, M.A. Y
ASKAWA, H .; HYODO, M.A. KURITA,
H. YANAGI, H .; HOSONO "P-type elect
rical conduction in transparent thin films of CuAlO
2 ", Applied Physics Letters No. 73 (1998) 22
Page 0, A. KUDO, H .; YANAGI, H .; HO
SONO, H .; KAWAZOE ”SrCu ₂ O ₂ : Ap-type con
ductive oxide with wide band gap ".

However, the thin film materials discussed in the above literature relate to transparent conductors,
No application has been considered for mold window materials.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION The solar cell of the present invention is characterized in that, in a Si-based solar cell, the p-type semiconductor layer is a polycrystalline thin film and has a band gap of 2.4 eV or more. p
As the type semiconductor, a chalcopyrite compound or a modified chalcopyrite compound, or a composite oxide containing at least Cu is preferable.

The chalcopyrite compound or the modified chalcopyrite type compound has a crystal structure similar to zincite, for example, by stacking two zincite and alternately adding divalent Zn to monovalent Cu. And trivalent Fe. The chalcopyrite compound or the modified chalcopyrite compound may be an epitaxial film, but a thin film having p-type conductivity can be easily obtained even from an amorphous or polycrystalline thin film. Doping is also easy. In addition, there is little change in electrical characteristics due to energization or temperature, and there is no electrochemical reaction with the electrode material. Furthermore, it is excellent in translucency.

The chalcopyrite compound or the modified chalcopyrite compound used in the present invention is a chalcopyrite compound, which is I-III-V represented by CuAlS _2.
II-IV-V ₂ represented by I ₂ or ZnSnAs _2,
II-III ₂ -VI ₄ typified by ZnAl ₂ Se ₄ (here, Cu, Ag, etc. as Group I elements, Al, Ga, In, Tl, etc. as Group III elements, S, V, etc. as Group VI elements)
Group II elements such as Se and Te include Zn and Cd.
Compounds such as Si, Ge, and Sn as Group IV elements, and compounds such as P, As, and Sb as Group V elements, and mixed crystal compounds of combinations of a plurality of components using these compounds are preferable.

Examples of the modified chalcopyrite compound include C
I-III-IV-VI ₄ represented by uAlGeS ₄ (I, I
II, IV, defect chalcopyrite compound of VI is similar to the above), typified by _{Cu 5 AlSe 4 I 5 -III-} VI
₄ (I, III, and VI are the same as described above) and a mixed crystal compound of a combination of a plurality of components using these compounds are preferable.

The composition ratios of these compounds do not exactly take the values described above, but each compound has a certain solid solubility limit. Therefore, the composition ratio may be within the range.

Among the above compounds, CuAlS
₂ , CuAlSe ₂ , CuGaS ₂ , CuGaSe ₂ ,
AgAlS ₂ , AgAlSe ₂ , AgGaS ₂ , AgG
aSe ₂ and their mixed crystal compounds are particularly preferable because they can be easily controlled in composition and become a wide-gap semiconductor.

Among the composite oxides containing monovalent Cu, delafossite compounds, for example, CuAlO ₂ compounds
A monovalent Cu, Cu ⁺ by trivalent Al, AlO ₂ ^- to form a two-dimensional plane perpendicular to the c-axis, respectively, are alternately laminated. In SrCu ₂ O ₂ , units having a dumbbell structure of O—Cu—O are connected in a zigzag manner to form a one-dimensional chain in a crystal structure. The delafossite compound or SrCu ₂ O ₂ may be an epitaxial film,
A thin film having p-type conductivity can be easily obtained even in an amorphous or polycrystalline thin film. Doping is also possible. In addition, there is little change in electrical characteristics due to energization or temperature, and there is not much electrochemical reaction with the electrode material. Furthermore, it is excellent in translucency.

Composite oxidation containing monovalent Cu used in the present invention
The material is delafossite compound CuAlO._Two
I-III-VI represented by_TwoOr ZnAl_TwoO_FourNiyo
II-III represented_Two−VI_Four(Where the group I element is C
Group III elements such as u and Ag include Al, Ga, In,
Group VI elements such as Tl include O, S, Se, and Te.
Group II elements include group IV elements such as Zn and Cd.
Si, Ge, Sn, etc.
Pr, As, Sb, etc.) or SrCu2O
_TwoOr SrCu_TwoO_Two, Instead of Sr
Other alkaline earth metals or Sc, Y and other metals
For example, BaCu using rukari metal_TwoO_TwoAC such as
u_TwoO_Two(A: alkaline earth metal or rare earth metal)
Is preferably represented by In addition, and their conversion
A mixed crystal compound of a combination of a plurality of components using a compound is preferred.
New

The composition ratio of these compounds does not exactly take the above-mentioned values, but has a certain solid solubility limit for each element. Therefore, CuAlO ₂ , SrC
An oxide such as u ₂ O ₂ may have a composition ratio within the range.

Among the above compounds, CuAlO
₂ , CuGaO ₂ , ACu ₂ O ₂ (A: alkaline earth metal or rare earth metal, preferably Sr, Ba)
And these mixed crystal compounds are particularly preferable because composition control is easy and a wide gap semiconductor can be obtained.

The inorganic layer of the present invention preferably has a band gap of at least 2.5 eV, more preferably at least 2.7 eV, further preferably at least 3.0 eV, particularly preferably at least 3.2 eV. The upper limit is not particularly limited, but is usually about 4 eV. 2.5 eV band gap
With the above, an element having transparency with visible light can be obtained.
The material used for the inorganic layer having a band gap of 2.5 eV or more may be appropriately selected from the above-described composite oxides containing monovalent Cu.

Some of the materials used for the p-type semiconductor layer show the properties of a p-type semiconductor as they are, but when these compounds are produced, a known doping substance or gas is added to make the p-type semiconductor. Is preferred. It is particularly preferable to perform p-type conversion by shifting the composition without doping. Whether a semiconductor is a p-type semiconductor can be determined by Hall measurement or the Seebeck effect.

Examples of the form of the p-type semiconductor layer include an amorphous thin film, a microcrystalline thin film, a polycrystalline thin film, an epitaxial thin film, a single crystal thin film, a mixed thin film thereof, a laminated thin film thereof and an artificial lattice thin film. Is used. In particular, a solar cell often uses an amorphous substrate such as a glass substrate, and a polycrystalline thin film is preferable. Since the polycrystalline thin film can be formed over a large area and is crystalline, the semiconductor characteristics of the p-type semiconductor layer can be effectively used.

The thickness of the p-type semiconductor layer is not particularly limited, but is about 1 nm to 3 μm. The p-type low-resistivity p-type semiconductor layer may be relatively thick, and preferably 100 nm to 2 μm in order to provide a large-area, pinhole-free and high crystallinity.

As a method for manufacturing the above p-type semiconductor layer,
Various physical or chemical thin film forming methods such as a sputtering method, a vapor deposition method, an MBE method, and a CVD method are used. In order to improve characteristics, a post reduction annealing method, a selenization method, a sulfuration method, and the like are used. Post-treatment may be used after thin film formation.

In the present invention, as a substrate for forming a solar cell structure, an amorphous substrate such as an organic film, an organic plate, glass, quartz, etc., and a crystalline substrate such as Si, Ga
As, ZnSe, ZnS, GaP, InP and the like.
A substrate on which an amorphous or metal buffer layer is formed can also be used. Al, Sb,
Ti, V, Cr, Mn, Fe, Co, Ni, Y, Zr,
Nb, Mo, Pd, La, Hf, Ta, W, Re, I
One or more of r, Pt and Au can be used. Further, ceramic substrates such as alumina and zirconia, and organic substrates such as plastics are also preferable.
Among these, a glass substrate is particularly preferable.

On the other hand, the i-layer (intrinsic semiconductor) made of a Si-based thin film in the present invention is a semiconductor having a lower impurity concentration than the thermally generated electron / hole density. The density of thermally generated electrons and holes is the density of electrons and holes generated at the finite band at the finite temperature by thermal disturbance when electrons are excited from the valence band to the conductor. Means

As the i-layer, the above-mentioned a-Si
Besides, all conventionally known materials are applied. For example, a
-SiCH, a-SiF, a-SiHF, a-SiGe
H, a-SiGeF, a-SiGeHF, a-SiC
H, a-SiCF, a-SiCHF and the like can be mentioned. i
Although the thickness of the layer depends on the material used, it is usually 5
It is about nm to 5 μm.

An n-layer (negative semic) made of a Si-based thin film
Onductor) is, for example, a semiconductor obtained by adding phosphorus or the like as an impurity to silicon. An element having five valence electrons, such as phosphorus, has one extra electron and becomes a free electron. Examples of the electron control agent for obtaining the n layer include Group V elements, for example, P, N, As, Sb, and the like. The thickness of the n-layer is usually about 10 nm to 200 nm, although it depends on the material used.

As the electrode material, ITO is generally used. ITO usually contains In ₂ O ₃ and SnO in a stoichiometric composition, but the amount of O may slightly deviate from this. The mixing ratio of SnO ₂ to In ₂ O ₃ is 1-2.
0 wt%, more preferably 5 to 12 wt%. Also, IZ
The mixing ratio of ZnO to In ₂ O _{3 in} O is usually 1
It is about 2 to 32% by weight. In addition, a low-resistance semiconductor such as ZnO or GaN is transparent and is preferable. Further, as the electrode material other than these, a conductive oxide is preferable, and particularly, a material containing the following conductive oxide is preferable.

NaCl type oxide: TiO, VO, Nb
O, RO _1-x (where, R: one or more rare earth elements (Sc
And Y), 0 ≦ x <1), LiVO _{2 and the} like.

Spinel oxide: LiTi ₂ O ₄ , Li
M _x Ti _2-x O ₄ (where M = Li, Al, Cr, 0 <
_{x <2), Li 1-} x M x Ti 2 O 4 ( where, M = Mg,
Mn, 0 <x <1), LiV ₂ O ₄ , Fe ₃ O _{4 and the} like.

Perovskite oxide: ReO_Three, WO
_Three, MxReO_Three(Where M metal, 0 <x <0.
5), MxWO_Three(Where M = metal, 0 <x <0.
5), A_TwoP₈W₃₂O₁₁₂(Where A = K, Rb, T
l), Na_xTa_yW_1-yO_Three(Where 0 ≦ x <1,0
<Y <1), RNbO_Three(Where R: one or more rare
Earth (including Sc and Y)), Na_1-xSr_xNbO_Three
(Where 0 ≦ x ≦ 1), RTiO_Three(Where R: one
Or more rare earths (including Sc and Y)), Ca_{n + 1}
Ti_nO_{3n + 1-y}(Where n = 2, 3,..., Y>
0), CaVO_Three, SrVO_Three, R_1-xSr_xVO_Three(here
R: one or more rare earths (including Sc and Y);
0 ≦ x ≦ 1), R_1-xBa_xVO_Three(Where R: one type
The above rare earths (including Sc and Y), 0 ≦ x ≦ 1),
Sr_{n + 1}V_nO_{3n + 1-y}(Where n = 1, 2,
3. . . . , Y> 0), Ba_{n + 1}V_nO_{3n + 1-y}(here,
n = 1, 2, 3,. . . . , Y> 0), R_FourBaCu_FiveO
_13-y(Where R: one or more rare earth elements (Sc and Y
), 0 ≦ y), R_FiveSrCu₆O_Fifteen(Where R:
One or more rare earths (including Sc and Y)), R_TwoS
rCu_TwoO₆._Two(Where R: one or more rare earths (S
c and Y)), R_1-xSr_xVO_Three(here,
R: one or more rare earth elements (including Sc and Y)), C
aCrO_Three, SrCrO_Three, RMnO_Three(Where R: one
Or more rare earths (including Sc and Y)), R_1-xS
r_xMnO_Three(Where R: one or more rare earth elements (Sc
And Y), 0 ≦ x ≦ 1), R_{1- x}Ba_xMnO_Three
(Where R: one or more rare earth elements (including Sc and Y)
M), 0 ≦ x ≦ 1), Ca_1-xR_xMnO_3-y(here,
R: one or more rare earth elements (including Sc and Y), 0 ≦
x ≦ 1, 0 ≦ y), CaFeO_Three, SrFeO_Three, Ba
FeO_Three, SrCoO_Three, BaCoO_Three, RCoO
_Three(Where R: one or more rare earths (Sc and Y
Including)), R_1-xSr_xCoO_Three(Where R: one or more
Rare earths (including Sc and Y), 0 ≦ x ≦ 1), R
_1-xBa_xCoO_Three(Where R: one or more rare earth elements
(Including Sc and Y), 0 ≦ x ≦ 1), RNiO
_Three(Where R: one or more rare earth elements (Sc and Y
Including)), RCuO_Three(Where R: one or more rare earths
(Including Sc and Y)), RNbO_Three(here,
R: one or more rare earth elements (including Sc and Y)), N
b₁₂O₂₉, CaRuO_Three, Ca_1-xR_xRu_1-yMn_yO_Three
(Where R: one or more rare earth elements (including Sc and Y)
M), 0 ≦ x ≦ 1, 0 ≦ y ≦ 1), SrRuO_Three, Ca
_1-xMg_xRuO_Three(Where 0 ≦ x ≦ 1), Ca_1-xS
r_xRuO_Three(Where 0 <x <1), BaRuO_Three, C
a_1-xBa_xRuO_Three(Where 0 <x <1), (Ba,
Sr) RuO_Three, Ba_1-xK_xRuO_Three(Where 0 <x
≦ 1), (R, Na) RuO_Three(Where R: one or more
Rare earths (including Sc and Y)), (R, M) R
hO_Three(Where R: one or more rare earths (Sc and
Y), M = Ca, Sr, Ba), SrIrO_Three,
BaPbO_Three, (Ba, Sr) PbO_3-y( here,
0 ≦ y <1), BaPb_1-xBi_xO_Three(Where 0 <x
≦ 1), Ba_1-xK _xBiO_Three(Where 0 <x ≦ 1),
Sr (Pb, Sb) O_3-y(Where 0 ≦ y <1), S
r (Pb, Bi) O_3-y(Where 0 ≦ y <1), Ba
(Pb, Sb) O_3-y(Where 0 ≦ y <1), Ba
(Pb, Bi) O_3-y(Where 0 ≦ y <1), MMo
O_Three(Where M = Ca, Sr, Ba), (Ba, C
a, Sr) TiO_3-x(Where 0 ≦ x) and the like.

Layered perovskite oxide (K ₂ NiF)
Type ₄ ): R _{n + 1} Ni _n O _{3n + 1} (where R: Ba,
Sr, rare earth (including Sc and Y) one or more of, n = 1 to 5 _{integer), R n + 1 Cu n} O 3n + 1 ( here,
R: Ba, Sr, one or more of rare earths (including Sc and Y), n = 1 to 5), Sr ₂ RuO ₄ , S
r ₂ RhO ₄ , Ba ₂ RuO ₄ , Ba ₂ RhO _{4 and the} like.

Pyrochlore type oxide: R_TwoV_TwoO_7-y(This
Here, R: one or more rare earth elements (including Sc and Y)
M), 0 ≦ y <1), Tl_TwoMn_TwoO_7-y(Where 0 ≦
y <1), R_TwoMo_TwoO_7-y(Where R: one or more
Rare earth (including Sc and Y), 0 ≦ y <1), R_TwoR
u_TwoO_7-y(Where R: Tl, Pb, Bi, rare earth
(Including Sc and Y), 0 ≦ y <
1), Bi_2-xPb_xPt_2-xRu _xO_7-y(Where 0
≦ x ≦ 2, 0 ≦ y <1), Pb_Two(Ru, Pb) O_7-y
(Where 0 ≦ y <1), R_TwoRh_TwoO_7-y(here,
R: Tl, Pb, Bi, Cd, rare earth (Sc and Y
), 0 ≦ y <1), R_TwoPd_TwoO_7-
y(Where R: Tl, Pb, Bi, Cd, rare earth (S
c and Y), 0 ≦ y <1),
R_TwoRe_TwoO_7-y(Where R: Tl, Pb, Bi, C
d, one or more of rare earths (including Sc and Y),
0 ≦ y <1), R_TwoOs_TwoO₇−_y(Where R: Tl,
Pb, Bi, Cd, rare earth (including Sc and Y)
At least one kind, 0 ≦ y <1), R_TwoIr_TwoO_7-y(here
And R: Tl, Pb, Bi, Cd, rare earth (Sc and
Y), 0 ≦ y <1), R_TwoPt_Two
O_7-y(Where R: Tl, Pb, Bi, Cd, rare earth
(Including Sc and Y), 0 ≦ y <
1) etc.

Other oxides: R_FourRe₆O₁₉(here,
R: one or more rare earth elements (including Sc and Y)), R
_FourRu₆O₁₉(Where R: one or more rare earth elements (Sc
And Y)), Bi_ThreeRu_ThreeO₁₁, V_TwoO_Three, Ti_TwoO
_Three, Rh_TwoO_Three, VO_Two, CrO_Two, NbO_Two, MoO
_Two, WO_Two, ReO_Two, RuO_Two, RhO_Two, Os
O _Two, IrO_Two, PtO_Two, PdO_Two, V_ThreeO_Five, V_nO
_2n-1(N = integer from 4 to 9), SnO_2-x(Where 0
≦ x <1), La_TwoMo_TwoO₇,, (M, Mo) O (here
Where M = Na, K, Rb, Tl), Mo_nO_3n-1(N =
4, 8, 9, 10), Mo₁₇O₄₇, Pd_1-xLi_xO (this
Here, x ≦ 0.1) and the like. An oxide containing In.

[0048] In particular among these, oxides or conductive perovskite oxide containing In are preferred, particularly In ₂
O ₃ , In ₂ O ₃ (Sn doped), RCoO ₃ , RMn
O ₃ , RNiO ₃ , R ₂ CuO ₄ , (R, Sr) CoO
₃ , (R, Sr, Ca) RuO ₃ , (R, Sr) RuO
₃ , SrRuO ₃ , (R, Sr) MnO ₃ (R is a rare earth containing Y and Sc), and their related compounds are preferred. Generally, a conductive oxide has a large work function, and it is particularly preferable to use it as an anode.

The solar cell element according to the above-mentioned invention is characterized in that:
A p-layer / n-layer or a substrate / electrode / n-layer / p-layer /
The structure may be reverse to that of the electrode. These are appropriately selected and used, for example, depending on the battery manufacturing process. In particular, when an opaque material is used for the anode, the reverse structure of the substrate / cathode / layer exhibiting a light emitting function / anode is preferable.

The device of the present invention has a multi-layer structure of electrode layer / layer exhibiting light emitting function / electrode layer / layer exhibiting light emitting function / electrode layer / layer exhibiting light emitting function / electrode layer. It may be a tandem structure. With such an element structure, the efficiency can be further improved.

[0051]

EXAMPLES Specific examples of the present invention will be described below to explain the present invention in further detail. Example 1 In FIG. 2, a solar cell using a CuGaS ₂ thin film which is a chalcopyrite compound as a p-type semiconductor layer was manufactured. .

As a glass substrate, 7059 manufactured by Corning Incorporated
The substrate was scrubbed with a neutral detergent.

A Nesa film was formed on this substrate by RF magnetron sputtering at a substrate temperature of 250 ° C. and a film thickness of 20 nm.
An ITO transparent electrode layer of 0 nm was formed.

Next, the substrate temperature was set to 250 ° C., and Cu: Ga: S = 1.26: 0.74: 2 in atomic ratio.
Using a target prepared with the composition of
200 nm thick Cu by F magnetron sputtering
A GaS ₂ thin film was formed.

As a result of composition analysis of the CuGaS ₂ thin film by X-ray fluorescence analysis, the atomic ratio of Cu: Ga: S = 1.14:
0.98: 1.88. According to X-ray diffraction, it is a polycrystalline thin film having a chalcopyrite type crystal structure,
It was found that the thin film was oriented to (112). The resistivity of the CuGaS ₂ thin film was 640 Ωcm, and it was found from the measurement of the Seebeck coefficient that it was a p-type semiconductor film. The light transmission characteristics revealed that the band gap was 2.5 eV.

Here, the CuGaS ₂ thin film was taken out for evaluation, but in actual device fabrication, after the CuGaS ₂ thin film was formed, the i-layer and the n-layer of a-Si were formed by CVD.

Further, a SiH layer having a thickness of 400 nm
Formed. At this time, the film was formed by introducing a SiH ₄ at a flow rate of 50 SCCM by a plasma CVD method.

As an n layer, a microcrystalline Si layer was formed to a thickness of 30 nm. The film formation conditions at this time were as follows: SiH ₄ was introduced at a flow rate of 10 SCCM by plasma CVD, and at this time, 1000 ppm hydrogen diluted PH ₃ was introduced at 200 SCCM in addition to this.

Further, the electrodes were formed by sputtering.
An ITO transparent electrode film was formed to a thickness of 200 nm. Electrode area is 1cm
^{And 2} .

From the obtained solar cell element structure in a vacuum,
Using a probe electrode, the electrode was pulled out from the anode and the cathode, and an electric field was applied. The VI characteristics showed diode characteristics.

Further, when the open circuit voltage of the solar cell was measured using a solar simulator, a value larger than 0.95 V was obtained as compared with 0.85 V of the conventional a-Si solar cell.

The efficiency of the solar cell of the present invention was 8.0%, which was also higher than that of the simultaneously manufactured α-Si solar cell of 7.5%.

The reason why excellent efficiency was obtained by this embodiment is that the use of a chalcopyrite compound as a p-type semiconductor layer as a wide-gap p-layer window results in less light absorption and shorter wavelength light. The light can be effectively guided to the i-layer, and the generated carriers do not recombine in the vicinity of the electrode on the p-layer side. it is conceivable that. Also, it is considered that the open voltage was increased because the internal electric field was large.

Example 2 A solar cell using a SrCu ₂ O ₂ thin film for the p-type semiconductor layer in FIG. 2 was produced.

In the same manner as in Example 1, SrCu was formed on a substrate with a Nesa film electrode by using a multiple reactive evaporation method according to the following procedure.
_{A 2} O ₂ thin film was formed as a wide gap p-layer window.

The substrate was fixed to a substrate holder provided in a vacuum chamber and provided with a rotation and heating mechanism, and the vacuum evaporation chamber was evacuated to 10 ^-6 Torr by a pump. Oxygen was introduced into the chamber at a rate of 25 cc / min from the nozzle, and the substrate was heated to 350 ° C. and rotated. The rotation speed was 20 rpm.

Thereafter, the metal Sr and Cu were simultaneously supplied from independent evaporation sources while controlling the Sr / Cu molar ratio to 0.5. At this time, the oxygen pressure in the chamber is
At 1 × 10 ⁻⁴ Torr, Sr and Cu metal were reacted with oxygen to form an SrCu ₂ O ₂ thin film having a thickness of about 300 nm.

When the composition of this thin film was examined by X-ray fluorescence analysis, the molar ratio was Sr: Cu = 3.2: 6.8.

For the obtained SrCu ₂ O ₂ thin film, X
Evaluation by RD was performed. From the XRD pattern, it was confirmed that the formed SrCu ₂ O ₂ thin film was a polycrystalline thin film.

The obtained SrCu ₂ O ₂ thin film was measured for light transmission characteristics, and it was confirmed that the thin film was transparent in a visible region and an infrared region. The calculated band gap was about 3.3 eV.

The SrCu ₂ O ₂ thin film had a sheet resistance of 0.11 MΩ / □ and a resistivity of 3.3 Ωcm at room temperature. In addition, p-type conductivity was confirmed from the polarity of the Seebeck constant.

Here, the SrCu ₂ O ₂ thin film was taken out for evaluation, but in actual device fabrication, SrCu ₂ O 2 was used.
After the formation of the _two thin films, an i-layer and an n-layer of a-Si were formed by CVD in the same manner as in Example 1.

Further, as the i layer, a SiH layer was formed at a thickness of 400 nm.
Formed. At this time, the film was formed by introducing a SiH ₄ at a flow rate of 50 SCCM by a plasma CVD method.

As an n layer, a microcrystalline Si layer was formed to a thickness of 30 nm. The film formation conditions at this time were as follows: SiH ₄ was introduced at a flow rate of 10 SCCM by plasma CVD, and at this time, 1000 ppm hydrogen diluted PH ₃ was introduced at 200 SCCM in addition to this.

Further, the electrodes were formed by sputtering.
An ITO transparent electrode film was formed to a thickness of 200 nm. Electrode area is 1cm
^{And 2} .

From the obtained solar cell element structure in a vacuum,
Using a probe electrode, the electrode was pulled out from the anode and the cathode, and an electric field was applied. The VI characteristics showed diode characteristics.

Further, when the open-circuit voltage of the solar cell was measured using a solar simulator, a value larger than 0.93 V was obtained as compared with 0.85 V of the conventional a-Si solar cell.

The efficiency was 7.7%, and the α
The efficiency was also improved compared to 7.5% of the -Si solar cell.

The reason why excellent efficiency was obtained by this embodiment is that the use of SrCu ₂ O ₂ as a p-type semiconductor layer as a wide-gap p-layer window reduces light absorption and shortens the wavelength of light. Can effectively guide light to the i-layer, and the generated carriers do not recombine in the vicinity of the electrode on the p-layer side. it is conceivable that. Also, it is considered that the open voltage was increased because the internal electric field was large.

[0080]

As described above, according to the present invention, C is a chalcopyrite compound or a modified chalcopyrite compound or an oxide material which becomes a p-type semiconductor in a polycrystalline film state.
By using a layer made of a composite oxide containing Cu such as uAlO ₂ or SrCu ₂ O ₂ as a p-layer window material of a solar cell,
A highly efficient and inexpensive solar cell can be provided.

[Brief description of the drawings]

FIG. 1 is a diagram showing a structure of a conventional a-Si solar cell.

FIG. 2 is a diagram showing a structure of an a-Si solar cell of the present invention.

Claims (5)

[Claims] 1. A Si-based solar cell, wherein the p-type semiconductor layer is a polycrystalline thin film and has a band gap of 2.4 eV or more. 2. The p-type semiconductor layer is a chalcopyrite compound or a modified chalcopyrite compound.
Solar cell. 3. The solar cell according to claim 1, wherein said p-type semiconductor layer is a composite oxide containing at least Cu. 4. The solar cell according to claim 3, wherein the composite oxide containing Cu is a delafossite compound. 5. The main component of the composite oxide containing Cu is S
The solar cell of claim 3 is a RCU ₂ O _2.