JPH08125207A - Solar cell and its manufacture - Google Patents

Abstract

PURPOSE: To provide a solar cell with improved conversion efficiency by forming a solar cell with at least three semiconductor layers of a light absorption layer, middle layer, and a window layer. CONSTITUTION: A light absorption layer 2, a middle layer 3, a window layer 4, and a transparent conductive layer 5 are laid out in order on a substrate with an electrode layer or a metal substrate 1 with an electrode property. P-type semiconductor light absorption layer with an electron affinity of χ1 , a work function of Φ1 , and a band gap energy of Eg1 , a semiconductor middle layer with an electron affinity of χ2 , a work function of Φ2 , and a band gap energy of Eg2 , n-type semiconductor window layer with an electron affinity of χ3 , a work function of Φ3 , and a band gap energy of Eg3 , and a transparent conductive layer are successively laminated with conditions of χ1 -χ2 -χ3 , Φ1 >Φ2 >Φ3 and Eg1 <Eg2 <Eg3 .

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a solar cell using a compound and a method for producing the same. More specifically, the present invention relates to a solar cell having a structure in which at least three types of semiconductors are stacked, and a method for manufacturing the same.

[0002]

2. Description of the Related Art Energy supply will become increasingly difficult in the near future
Expected to become, solar cell high efficiency, low cost
Has become a major issue. Above all, increasing the area
Easy-to-use thin-film solar cells can significantly reduce costs.
It is strongly desired to improve the energy conversion efficiency of this
Compound semiconductors (II-VI group and I-III-VI group) are used for thin-film solar cells.
₂Those using thin films are being widely developed. Compound
The structure of a solar cell using a semiconductor thin film is, for example, a band
N-type CdS as a window layer having a wide gap and transmitting light
Since it has a narrow band gap with the system semiconductor layer, it functions as a light absorption layer.
CdTe system or CuInSe that works₂P-type
A heterojunction in which semiconductor layers are stacked is used. Mochiro
, A combination of p-type semiconductor for window layer and n-type semiconductor for light absorption layer
But good. As a configuration, for example, ITO (Indium)
 N-type C on a glass substrate with Tin Oxide)
Form dS layer, then stack p-type CdTe layer by vapor deposition method
A solar cell is formed by finally forming a metal electrode. Also
Is p-type CuInSe on a glass substrate provided with a Mo thin layer.
₂Layer is formed by vapor deposition and then n-type by chemical deposition
Finally, the CdS layer is added to the ZnO or ZnO / ITO transparent electrode.
A polar layer is provided to form a solar cell. 15 with these solar cells
It has become possible to obtain conversion efficiencies as high as 100% or more.

[0003]

As described above, the conversion efficiency is remarkable.
What has improved dramatically is the technological progress of semiconductor thin film formation.
It depends greatly. By the way, the conversion efficiency of the solar cell η
Is η = V_oc(Open voltage) x J_sc(Circuit current) x FF
It is expressed by the relationship of (curve factor). J in this_scHahonton
Although we are getting closer to the theoretical limit,
V_ocAnd the FF that reflects it is less than expected
It's small. This V_ocTo increase conversion efficiency
Is the biggest key for. V_ocLight is generated
Electrons and holes that are carriers are generated in the internal electric field of the pn junction layer.
Therefore, it is separated and generated as an external voltage, but the external voltage is generated.
When it occurs, it cancels the internal electric field and makes it smaller.
This makes it difficult for the photo-generated electrons and holes to separate, and
Combined and died, V_ocWill not contribute to. Actual
This V with solar cells_ocIs difficult to grow in the semiconductor film
In particular, there are many recombination centers that promote recombination at the pn junction interface.
It is difficult to reduce the number of recombination centers
It depends. After all, if these recombination centers are present,
Promotes recombination of generated electrons and holes, and
Shorten, resulting in V _oc, FF doesn't get bigger and changes
This hinders the improvement of conversion efficiency.

In order to solve the above conventional problems, the present invention drastically reduces the recombination of generated electrons and holes by extremely reducing one carrier at a semiconductor junction where carrier recombination is active. It is an object of the present invention to provide a solar cell that suppresses an increase in open circuit voltage and has high conversion efficiency, and a method for manufacturing the same.

[0005]

In order to achieve the above object, the first solar cell of the present invention comprises a p-type semiconductor 1 on a substrate provided with an electrode layer or a metal substrate having an electrode property.
Of the light absorption layer, the intermediate layer of the semiconductor 2, the window layer of the n-type semiconductor 3, and the transparent conductive layer are sequentially stacked, and the electron affinity of the light absorption layer of the p-type semiconductor 1 is Is χ ₁ , the work function is Φ ₁ , and the bandgap energy is E
_g1 , the electron affinity of the intermediate layer of the semiconductor 2 is χ ₂ , the work function is Φ ₂ , and the bandgap energy is E _g2, and the electron affinity of the window layer of the n-type semiconductor 3 is χ ₃ and the work function is When Φ ₃ and the bandgap energy are E _g3 , χ ₁ , χ ₂ and χ ₃ are almost equal, and Φ ₁ > Φ ₂ >
It is characterized by satisfying the relation of Φ ₃ and E _g1 <E _g2 <E _g3 .

Next, the second solar cell of the present invention comprises a transparent conductive layer, a window layer of the n-type semiconductor 3, and a transparent conductive layer on a transparent substrate.
A solar cell in which an intermediate layer of a semiconductor 2, a light absorption layer of a p-type semiconductor 1, and an electrode layer are sequentially stacked, and the electron affinity of the window layer of the n-type semiconductor 3 is χ ₃ , and the work function is Φ ₃ , the bandgap energy is E _g3 , the electron affinity of the intermediate layer of the semiconductor 2 is χ ₂ , the work function is Φ ₂ , the bandgap energy is E _g2, and the electrons of the light absorption layer of the p-type semiconductor 1 are When the affinity is χ ₁ , the work function is Φ ₁ , and the bandgap energy is E _g1 , χ ₁ , χ ₂ and χ ₃ are almost equal, and Φ ₁ > Φ ₂ > Φ ₃ and E _g1 <E _g2 <E _g3
It is characterized by satisfying the following relationship.

In the first to second solar cell structures, the p-type semiconductor 1 is made of CuInSe ₂ , CuGaS.
It is preferably at least one compound selected from e ₂ , CuInS ₂ and CdTe.

In the above structure, the p-type semiconductor 1 is used.
Is a solid solution of CuInSe ₂ —CuGaSe ₂ , CuI
_{nS 2 -CuGaS 2, CuInSe 2 -CuInS} 2
And at least one compound selected from CuGaSe ₂ —CuGaS ₂ is preferable.

In the above structure, the semiconductor 2 is C
It is preferably at least one compound selected from dSe and solid solution CdTe-MgTe. Further, in the above structure, the n-type semiconductor 3 is preferably at least one compound selected from CdS, ZnSe, and ZnO.

In the above structure, the n-type semiconductor 3
Is a solid solution CdS-ZnS, CdS-MnS, CdSe
-MnSe, ZnSe-MnSe and CdTe-MgT
It is preferably at least one compound selected from e.

Next, in the first manufacturing method of the present invention, an electron affinity is χ ₁ , a work function is Φ ₁ , and a bandgap energy is on a substrate provided with an electrode layer or a metal substrate having an electrode property. A light-absorbing layer of p-type semiconductor 1 having E _g1 is formed, on which electron affinity is χ ₂ , work function is Φ ₂ , bandgap energy is E _g2 , and χ ₂ ~
An intermediate layer of a semiconductor 2 having χ ₁ , Φ ₂ <Φ ₁ and E _g2 > E _g1 is formed, and an electron affinity χ ₃ , a work function Φ ₃ , and a bandgap energy E _g3 are formed on the intermediate layer. , And χ _{3 to} χ ₂ , Φ ₃ <Φ ₂ and E _g3 > E _g2.
A window layer of the semiconductor 3 of the mold is formed, and a transparent conductive layer is further formed thereon.

Next, the second manufacturing method of the present invention is transparent.
The electron affinity is χ on the transparent substrate with the conductive layer.₃In
The function is Φ₃And the band gap energy is E_g3so
A window layer of a certain n-type semiconductor 3 is formed, and an electron affinity is formed on the window layer.
Power is χ₂And the work function is Φ₂And bandgap energy
Gee is E_g2And χ₂~ Χ₃, Φ₂> Φ₃Big
One E_g2<E_g3Forming an intermediate layer of the semiconductor 2, which is
Has electron affinity χ₁And the work function is Φ₁And
Energy is E_g1And χ₁~ Χ ₂, Φ₁
> Φ₂And E_g1<E_g2Absorption of p-type semiconductor 1 which is
A layer is formed, and an electrode layer is further formed on the layer.
To collect.

The structure of the solar cell of the present invention is as shown in FIG.
A substrate provided with an electrode layer or a metal substrate having an electrode property
Above, the electron affinity is χ₁And the work function is Φ₁Big and band
Gap energy is E_g1Of the p-type semiconductor 1 which is
Convergence, electron affinity is χ₂And the work function is Φ₂Big and band
Gap energy is E_g2Which is the intermediate layer of the semiconductor 2,
Has an electron affinity χ₃And the work function is Φ₃Big and band
Gap energy is E _g3Window of n-type semiconductor 3 which is
Layer and transparent conductive layer are laminated in sequence, and χ₁
~ Χ₂~ Χ₃, Φ₁> Φ₂> Φ₃And E_g1<E_g2<E
_g3Or on a translucent substrate, as shown in FIG.
Transparent conductive layer, electron affinity is χ₃And the work function is Φ₃And
Bandgap energy is E_g3N-type semiconductor 3
Window layer, electron affinity is χ₂And the work function is Φ₂Big and van
The gap energy is E_g2An intermediate layer of the semiconductor 2, which is
Electron affinity is χ₁And the work function is Φ₁Big and band
Energy is E_g1A p-type semiconductor 1 light absorbing layer,
It consists of a structure in which electrode layers are sequentially stacked, and₁~ Χ₂~
χ₃, Φ₁> Φ₂> Φ₃And E_g1<E_g2<E_g3And
You.

FIG. 3 shows the energy band structure of these solar cells. In the figure, χ ₁ , χ ₂ , and χ ₃ have almost the same energy values, and the difference between them ((χ ₃ −χ ₂ )
It is preferable that (χ ₂ −χ ₁ ) be about the value of the kinetic energy of the carrier (about 0.025 eV). (Φ ₃ −Φ ₁ ) gives the diffusion potential. (E _g2 −
It is preferable that E _g1 ) be at least about twice the kinetic energy value of the carrier (described above), and preferably 0.1 eV or more.

As a method of manufacturing these solar cells, electrodes are used.
On a layered substrate or a metal substrate with electrode properties,
Child affinity is χ₁And the work function is Φ₁And band gap
Energy is E_g1The light absorption layer of the p-type semiconductor 1 that is
Electron affinity is χ₂And the work function is Φ₂Big
The band gap energy is E_g2And χ₂~
χ₁, Φ₂<Φ₁And E_g2> E_g1In semiconductor 2 which is
Interlayer is formed, and electron affinity is χ on it.₃And the work function is
Φ₃And the band gap energy is E_g3And then
Maybe χ₃~ Χ₂, Φ₃<Φ₂And E_g3> E_g2Is n
-Type semiconductor 3 window layer, and further forming a transparent conductive layer thereon
Or on a transparent substrate with a transparent conductive layer,
Child affinity is χ₃And the work function is Φ₃And band gap
Energy is E_g3Forming a window layer of n-type semiconductor 3 which is
And the electron affinity is χ₂And the work function is Φ₂And
Bandgap energy is E_g2And χ₂~ Χ
₃, Φ₂> Φ₃And E_g2<E_g3The middle of semiconductor 2 which is
Layer, on top of which electron affinity is χ ₁And the work function is Φ₁And
Bandgap energy is E_g1And χ₁~ Χ
₂, Φ₁> Φ₂And E_g1<E_g2P-type semiconductor 1
Two types of light absorption layer and the electrode layer formed on it
There is.

A single compound Cu is used as the p-type semiconductor 1.
InSe₂, CuGaSe₂, CuInS₂Or Cd
Te and solid solution CuInSe₂-CuGaSe₂, CuI
nS ₂-CuGaS₂, CuInSe₂-CuInS₂
Or CuGaSe₂-CuGaS₂Of light absorption
It is preferable in terms. As the semiconductor 2, the compound CdSe or
The solid solution CdTe-MgTe is preferred. n-type semiconductor 3
As a compound CdS, ZnSe or ZnO or a solid solution
CdS-ZnS, CdS-MnS, CdSe-MnS
e, ZnSe-MnSe or CdTe-MgTe
It is preferable in terms of permeability. Regarding semiconductor 1, 2 or 3
Is electron affinity, work function and band gap energy
Is limited to the compounds described above as long as the necessary conditions are satisfied.
There is no.

[0017]

According to the structure of the solar cell of the present invention, a semiconductor heterojunction having three layers having an energy band structure as shown in FIG. 3 is formed. The function of this is compared with that of a normal semiconductor heterojunction composed of two layers having an energy band structure as shown in FIG. As shown in FIG. 4, in the conventional two-layer heterojunction, two kinds of semiconductors shown in (D) are joined,
A pn junction as shown in (E) is formed. When this is irradiated with light, electrons and holes generated in the light absorption layer are separated according to the internal electric field, resulting in separation of photogenerated carriers as shown in (F). There is a recombination center R at the hetero interface, through which electrons and holes are recombined to enter a steady state. At the time of recombination at this interface, the degree of recombination is determined by the smaller carrier and its lifetime τ in this part. In a normal two-layer heterojunction, the electron and hole concentrations n and p are almost the same, so the degree of recombination can be expressed by n / τ when considering the electrons.

On the other hand, as shown in FIG. 3, in the three-layer heterojunction of the present invention, three kinds of semiconductors shown in FIG.
A kind of pin junction as shown in (B) is formed. When this is irradiated with light, electrons and holes generated in the light absorption layer are separated according to the internal electric field (in this case, only the electrons mainly move).
The separation of photo-generated carriers as shown in (C) occurs. In this case, the interface where recombination occurs has moved to the right, indicating a recombination different from the case of FIG. That is, the distribution of photogenerated electrons and holes is high at the interface as shown in the upper part of (C), but the electron concentration is much smaller than in the case of FIG. Therefore, the degree of recombination n / τ becomes small. The electron lifetime τ is somewhat influenced by the hole concentration p, but is not inversely proportional. Since recombination is reduced, the photogenerated electrons and holes are more effectively separated from each other, resulting in an increase in open circuit voltage V _oc . As a result, the FF is also increased and the conversion efficiency can be greatly improved.

The thickness of the intermediate layer 2 is preferably about 0.01 to 1 μm. This is because if the intermediate layer is too thin, the concentration of photogenerated carriers (electrons in this case) at the interface with the recombination center R shown in FIG. The thickness of the portion of the light absorption layer to which an electric field is applied (indicated by a symbol above the valence band in the band diagram of FIG. 3) decreases, and J _sc decreases. Because.

[0020]

EXAMPLES The present invention will be described in more detail below with reference to examples. (1) On a glass substrate provided with a Pt electrode layer, a 5 μm thick p-type semiconductor light-absorbing layer mainly composed of CdTe is formed by vapor deposition, and CdTe and Mg are simultaneously vapor-deposited on the glass substrate to form CdTe.
And MgTe molar ratio is 8: 2, total thickness 0.5 μm
CdTe-MgTe solid solution film Cd _0.8 Mg _0.2 Te of was formed. Further, an n-type semiconductor window layer mainly composed of CdS was formed thereon to a thickness of 0.05 μm by a chemical deposition method, and a transparent electrode layer ZnO / ITO was formed thereon. For comparison, without providing an intermediate Cd _0.8 Mg _0.2 Te layer,
The other characteristics of the solar cell which were the same as those described above were also examined. (2) On a glass substrate provided with a transparent conductive layer ITO / ZnO, an n-type semiconductor window layer mainly composed of CdS was formed to a thickness of 0.1 μm by a chemical deposition method, and a thickness of 0. A 5 μm CdSe film was formed by vapor deposition. Further, a 5 μm-thick p-type semiconductor light-absorbing layer mainly containing CdTe was vapor-deposited thereon, and an Au electrode was formed thereon. For comparison, the characteristics of a solar cell similar to the above except that no intermediate CdSe layer was provided were also examined. The characteristics of these solar cells with respect to irradiation light of AM1 (100 mW / cm ² ) are shown in Table 1 (solar cell of (1) above) and Table 2 (solar cell of (2) above). V _OC (V) is an open circuit voltage, J _SC (mA / cm ² ) is a closed circuit current, η (%) is a conversion efficiency, FF is a fill factor, and A is a diode factor.

[0021]

[Table 1]

[0022]

[Table 2]

As can be seen from Tables 1 and 2, the characteristics of the solar cell of this example are far superior to those of the solar cell obtained by the conventional constitution. The remarkable increase in the open circuit voltage (V _oc ) in the solar cell of this example is because the intermediate layer is present between the pn layers to suppress recombination of photogenerated electrons and holes. Increasing V _oc also increases _fill factor FF, resulting in a significant improvement in conversion efficiency. A decrease in the diode factor A indicates a decrease in recombination at the junction (especially at the interface).

[0024]

As described above, according to the present invention, at least three layers, that is, the light absorption layer of the semiconductor 1, the intermediate layer of the semiconductor 2, and the window layer of the semiconductor 3 are formed, so that the recombination of carriers is active. One carrier is extremely reduced in the semiconductor junction, recombination of generated electrons and holes is significantly suppressed, the open circuit voltage is increased, and the conversion efficiency of the solar cell is improved.

Further, according to the manufacturing method of the present invention, it becomes possible to efficiently and rationally manufacture an excellent solar cell having a high conversion efficiency. Further, since this solar cell is formed of a thin film, the cost can be significantly reduced.

[Brief description of drawings]

FIG. 1 is a sectional view showing the configuration of a solar cell according to an embodiment of the present invention.

FIG. 2 is a sectional view showing the structure of a solar cell according to an embodiment of the present invention.

FIG. 3 is an energy band configuration diagram of a solar cell according to an embodiment of the present invention.

FIG. 4 is an energy band configuration diagram of a conventional solar cell.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate provided with an electrode layer or a metal substrate having an electrode property 2 Light absorption layer of semiconductor 1 3 Intermediate layer of semiconductor 2 4 Window layer of semiconductor 3 5 Transparent conductive layer 6 Transparent substrate 7 Transparent conductive layer 8 Semiconductor 3 Window layer 9 Intermediate layer 10 of semiconductor 2 Light absorbing layer 11 of semiconductor 1 Electrode layer

Claims (9)

[Claims] 1. A light absorption layer of a p-type semiconductor 1, an intermediate layer of a semiconductor 2, and a window layer of an n-type semiconductor 3 on a substrate provided with an electrode layer or a metal substrate having an electrode property. A solar cell in which a transparent conductive layer is sequentially laminated, wherein the electron affinity of the light absorption layer of the p-type semiconductor 1 is χ ₁ , the work function is Φ ₁ , and the bandgap energy is E _g1 .
The electron affinity of the intermediate layer of the semiconductor 2 is χ ₂ , the work function is Φ ₂ , and the bandgap energy is E _g2. The electron affinity of the window layer of the n-type semiconductor 3 is χ ₃ , the work function is Φ ₃ , When the bandgap energy is Eg ₃ , χ ₁ and χ ₂ and χ ₃ are almost equal, and the relationship is Φ ₁ > Φ ₂ > Φ ₃ and E _g1 <E _g2 <E _g3. battery. 2. A transparent conductive layer, a window layer of an n-type semiconductor 3, an intermediate layer of a semiconductor 2, a light absorption layer of a p-type semiconductor 1, and an electrode layer are sequentially formed on a transparent substrate. In the laminated solar cell, the electron affinity of the window layer of the n-type semiconductor 3 is χ ₃ , the work function is Φ ₃ , the band gap energy is E _g3, and the electron affinity of the intermediate layer of the semiconductor 2 is χ _2. , Work function is Φ ₂ , bandgap energy is E _g2 , electron affinity of the light absorption layer of the p-type semiconductor 1 is χ ₁ , work function is Φ ₁ , and bandgap energy is E _g1 , χ ₁ And χ ₂ and χ ₃ are substantially equal to each other, and satisfy the relations of Φ ₁ > Φ ₂ > Φ ₃ and E _g1 <E _g2 <E _g3 . 3. The p-type semiconductor 1 is CuInSe ₂ , C
The solar cell according to claim 1, which is at least one compound selected from uGaSe ₂ , CuInS _2, and CdTe. 4. The p-type semiconductor 1 is CuInS in a solid solution.
_{e 2 -CuGaSe 2, CuInS 2 -CuGaS} 2,
CuInSe ₂ —CuInS ₂ and CuGaSe ₂ —C
The solar cell according to claim 1 or 2, which is at least one compound selected from uGaS ₂ . 5. The semiconductor 2 comprises CdSe and solid solution CdT.
The solar cell according to claim 1, which is at least one compound selected from e-MgTe. 6. The solar cell according to claim 1, wherein the n-type semiconductor 3 is at least one compound selected from CdS, ZnSe and ZnO. 7. The n-type semiconductor 3 is a solid solution CdS-Zn.
S, CdS-MnS, CdSe-MnSe, ZnSe-
The solar cell according to claim 1, which is at least one compound selected from MnSe and CdTe-MgTe. 8. A substrate provided with an electrode layer or having an electrode property
On a metal substrate with an electron affinity of χ₁And the work function is Φ₁so
And the band gap energy is E_g1Is a p-type semiconductor
The light absorption layer of body 1 is formed, and the electron affinity is χ on it.₂so
Work function is Φ₂And the band gap energy is E_g2
And χ₂~ Χ₁, Φ₂<Φ₁And E_g2> E_g1
The intermediate layer of the semiconductor 2 is formed, and the electron affinity is formed on the intermediate layer.
Is χ₃And the work function is Φ₃And bandgap energy
Is E_g3And χ₃~ Χ ₂, Φ₃<Φ₂And
E_g3> E_g2Forming a window layer of the n-type semiconductor 3 which is
The sun is characterized in that a transparent conductive layer is formed on it.
Battery manufacturing method. 9. A window layer of an n-type semiconductor 3 having an electron affinity of χ ₃ , a work function of Φ ₃ and a bandgap energy of E _g3 is formed on a transparent substrate provided with a transparent conductive layer. , The electron affinity is χ ₂ , the work function is Φ ₂ , the bandgap energy is E _g2 , and χ ₂ ~
forming an intermediate layer of the semiconductor 2 in which χ ₃ , Φ ₂ > Φ ₃ and E _g2 <E _g3 , on which electron affinity is χ ₁ , work function is Φ ₁ , and bandgap energy is E _g1 , And χ _{1 to} χ ₂ , Φ ₁ > Φ ₂ and E _g1 <E _g2 p
Forming a light absorption layer of the semiconductor 1 of the mold, and further forming an electrode layer thereon.