JP3022129B2 - Thin film solar cell and manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin-film solar cell having an improved light-transmitting window layer and a method for manufacturing the same.

[0002]

2. Description of the Related Art In the near future, it is expected that energy supply will gradually become more difficult, and high efficiency and low cost of solar cells have become major issues. Above all, thin-film solar cells, which can be easily enlarged, can be significantly reduced in cost, and therefore, there is a strong demand for improvement in energy conversion efficiency. As this thin-film solar cell, a solar cell using a compound semiconductor (II-VI or I-III-VI ₂ ) thin film is being widely developed. The structure of a solar cell using a compound semiconductor thin film is as follows:
And n-type CdS-based semiconductor layer as a window layer that transmits light wide band gap heterojunction formed by laminating a p-type semiconductor layer, such as CdTe-based or CuInSe ₂ system narrow band gap functions as a light absorbing layer Is used.

As a configuration, for example, ITO (Indium T
an N-type CdS layer on a glass substrate provided with
Next, a p-type CdTe layer is formed by vapor deposition, respectively.
Finally, a metal electrode is provided to complete a solar cell. Alternatively, n-type CdS is formed by screen printing and firing on a glass substrate.
The layer is then formed into a p-type CdTe layer by screen printing and firing in the same manner, and finally a metal or carbon electrode layer is provided to form a solar cell. It is known that using a semiconductor having a wider band gap, for example, a CdS-ZnS solid solution thin film instead of CdS is very effective in increasing the amount of transmitted light and increasing the conversion efficiency.

[0004]

As described above, using a window layer of a semiconductor thin film having a wide bandgap and a low resistance is difficult.
Although effective for improving the conversion efficiency, the CdS-ZnS solid solution thin film may have a high resistance if the composition ratio of ZnS is high, and may instead lower the conversion efficiency. It is desired to use a low-resistance n-type semiconductor thin film having a wide band gap. Furthermore, since the window layer and the light absorbing layer generally have different crystal structures and lattice constants, many defects are generated at the interface between the two layers, and these become recombination centers, which cause recombination of photo-generated electrons and holes. They shorten their life and hinder the improvement of the conversion efficiency.

[0005]

According to the structure of the thin-film solar cell of the present invention, a light-absorbing layer made of a p-type semiconductor thin film is provided on a substrate provided with an electrode layer or a metal substrate having electrode properties .
A window layer made of an n-type semiconductor thin film mainly composed of a solid solution CdX-MgX of a chalcogenide CdX of Cd (chalcogen X = S, Se, or Te) and a chalcogenide MgX of Mg on the light absorbing layer , and a transparent conductive layer. sequentially stacked structure of the layers, or on a transparent substrate, set the transparent conductive layer
The Cd chalcogenide CdX is placed on the transparent conductive layer.
Solution CdX-MgX of Mg and chalcogenide MgX
Layer composed mainly of n-type semiconductor thin film , p-type semiconductor
In this configuration, a light absorption layer made of a thin film and an electrode layer are sequentially laminated.

Further, as described above, the solid solution CdX-Mg
Thin having a window layer composed of n-type semiconductor thin film mainly made of X
The method for manufacturing a membrane solar cell is a method for forming the window layer by simultaneously depositing CdX and Mg. Other methods of forming the window layer include Cd, Mg and chalcogen X.
Simultaneously, a method of sputtering and depositing a solid solution of CdX and MgX, a method of simultaneously depositing or sequentially depositing Cd and Mg, and a heat treatment in an atmosphere containing chalcogen X, or a method of simultaneously or simultaneously depositing Cd and Mg. This is a method in which chalcogen X is deposited after the layers are deposited and then heat-treated.

Here, when the chalcogen is Te, CdTe or Cu which is usually used as a light absorbing layer of a p-type semiconductor is used.
Good matching with InSe ₂ -based material is preferable. Further, it is more preferable that the composition ratio of MgTe in the solid solution is 50 mol% or more, since the absorption edge wavelength becomes shorter than that of CdS. Light transmission window layer is CdTe-Mg
When it is a Te solid solution, the light absorbing layer of the p-type semiconductor is Cd
Te is convenient because the lattice constants of each are hardly changed. Particularly, the composition ratio of MgTe is 50 mol%.
When the above is satisfied, the best combination is obtained in terms of matching of the amount of transmitted light and the lattice constant.

[0008]

According to the structure of the solar cell of the present invention, CdX-M
Since the band gap of the gX solid solution is wider than that of CdS, the amount of light transmitted through the window layer increases, and therefore the amount of light absorbed by the light absorbing layer of the p-type semiconductor increases, and as a result, the efficiency of the solar cell improves. In particular, when the chalcogen is Te, the light absorbing layer is formed of CdTe, and the window layer is formed of CdTe-M
When formed of a gTe solid solution, since there is almost no difference in lattice constant between the semiconductors in both layers, the generation of defects that are likely to form recombination centers at the pn junction interface is suppressed, and a remarkable improvement in characteristics, particularly an improvement in open-circuit voltage, is obtained. Can be The C of the present invention
Simultaneous deposition using two sources of dX and Mg, or CdX and M
gX simultaneous deposition, or direct deposition of a solid solution or a mixture of CdX and MgX, or simultaneous treatment of Cd and Mg or laminated deposition followed by heat treatment in an atmosphere containing chalcogen X, or simultaneous deposition of Cd and Mg or laminated deposition of chalcogen X
Can be easily obtained with an inexpensive deposition apparatus using a CdX-MgX solid solution thin film having a wide band gap.

[0009]

Embodiments of the present invention will be described below. 1 and 2 show examples of the configuration of a solar cell according to the present invention. FIG.
A light absorbing layer 2 made of a p-type semiconductor and a solid solution CdX on a metal substrate having electrode properties or a substrate 1 provided with an electrode layer.
-A solar cell having a configuration in which a window layer 3 made of an n-type semiconductor mainly composed of MgX and a transparent conductive layer 4 are sequentially formed.

In the solar cell shown in FIG. 2, a window layer 7 made of an n-type semiconductor mainly composed of a thin film of CdX and MgX is formed on a light-transmitting substrate 5 provided with a transparent conductive layer 6. To p
A light absorption layer 8 made of a mold semiconductor, and an electrode layer 9 is further formed thereon.

[Example 1] On a glass substrate provided with a Pt electrode layer, a light absorbing layer made of a p-type semiconductor mainly composed of CdTe and having a thickness of 5 μm was formed by vapor deposition.
0 angstrom is removed by an etching method, and CdTe and MgTe are further deposited thereon by co-evaporation of CdTe and Mg.
Is 1: 1 and the total thickness is 0.5 μm.
An e-MgTe solid solution film Cd _0.5 Mg _0.5 Te is formed.
Next, In is added to this film. That is, Cd _0.5 M
On the g _0.5 Te film, 1% of the whole In is vapor-deposited and heated in N ₂ gas at 400 ° C. for 30 minutes to be diffused and effective addition of In is performed. A transparent electrode layer ITO is formed on the window layer made of the n-type semiconductor thus formed. Thus, a solar cell having a configuration as shown in FIG. 1 is manufactured.

Example 2 A solar cell is formed in the same manner as in Example 1 except that a solid solution film Cd _0.2 Mg _0.8 Te having a molar ratio of CdTe and MgTe of 2: 8 is used. Comparative Example 1 A solar cell is manufactured in the same manner as in Example 1 except that the window layer is made of ordinary CdS, that is, 1% of In is added to a CdS vapor-deposited film.

Example 3 A solid solution film having a molar ratio of CdTe and MgTe of 1: 1 and a total thickness of 0.5 μm on a glass substrate provided with a transparent conductive layer ITO by simultaneous vapor deposition of CdTe and Mg. Cd _0.5
Mg _0.5 Te is formed. Next, In is added to this film. That is, the entire 1d layer is formed on the Cd _0.5 Mg _0.5 Te film.
% Of In is vapor-deposited and heated at 400 ° C. for 30 minutes in N ₂ gas to be diffused and effectively added to In. On the window layer made of n-type semiconductor which forms the shape, the light-absorbing layer made of p-type semiconductor consisting mainly of a 5μm thick CdTe is vapor deposited to form an Au electrode thereon. Thus, a solar cell having a configuration as shown in FIG. 2 is manufactured.

Example 4 A solar cell is formed in the same manner as in Example 3 except that a solid solution film Cd _0.2 Mg _0.8 Te having a molar ratio of CdTe to MgTe of 2: 8 is used. [Comparative Example 2]
A window layer is formed by adding 1% of In to a conventional CdS vapor-deposited film,
Otherwise, a solar cell is manufactured in the same manner as in Example 3.

A of the solar cells of each of the above Examples and Comparative Examples
Tables 1 and 2 show the characteristics with respect to the irradiation light of M1 (100 mW / cm ² ). Incidentally, Voc (V) is a voltage discharge opening,
Jsc (mA / cm ² ) is the closing current, η (%) is the conversion efficiency, F. Represents a fill factor.

[0016]

[Table 1]

[0017]

[Table 2]

As can be seen from Tables 1 and 2, the characteristics of the solar cell obtained with the structure of the present invention are far superior to those of the solar cell obtained with the conventional structure. This is because the CdTe-MgTe solid solution film of the solar cell of the present invention has a higher spectral transmittance than the CdS film of the conventional solar cell. Further, the remarkable improvement of the open circuit voltage (Voc) is due to the above-mentioned semiconductor layers CdTe and CdT constituting both pn layers.
It is considered that the difference of the lattice constant of the e-MgTe solid solution is extremely small. A solar cell including a CdTe-MgTe solid solution film obtained by co-evaporation of CdTe and Mg has excellent characteristics. Addition of In increases light transmittance and electric conductivity.

Even if a solid solution CdTe-MgTe having another composition ratio of CdTe and MgTe is used, A may be used instead of In.
Similar effects can be obtained by using 1 or Ga. This solid solution thin film can also be obtained by the following method. That is, a method of simultaneously depositing Cd, Te and Mg, CdT
a method of evaporating MgTe by an electron beam method by co-evaporation of e and MgTe, a method of evaporating a solid solution or a mixture of CdTe-MgTe by a sputtering method, and a heat treatment in an atmosphere containing Te after evaporating Cd and Mg simultaneously or laminated. Or a method of simultaneously depositing or depositing Cd and Mg and depositing Te after vapor deposition, followed by heat treatment. Alternatively, the same effect can be obtained by using another chalcogenide (CdS or CdSe) or chalcogen (S or Se) instead of Te compound or Te.

[0020]

According to the present invention, an excellent solar cell having a very high conversion efficiency can be easily obtained. Since this solar cell has a thin-film configuration, a significant cost reduction can be achieved.

[Brief description of the drawings]

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

FIG. 2 is a longitudinal sectional view showing a configuration of a solar cell according to another embodiment of the present invention.

[Explanation of symbols]

Reference Signs List 1 substrate provided with electrode layer or metal substrate provided with electrode properties 2 light absorption layer made of p-type semiconductor 3 window layer made of n-type semiconductor mainly composed of CdX-MgX solid solution 4 transparent conductive layer 5 translucent substrate 6 Transparent conductive layer 7 Window layer made of n-type semiconductor mainly composed of CdX-MgX solid solution 8 Light absorbing layer made of p-type semiconductor 9 Electrode layer

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takahiro Wada 1006 Kazuma Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) References JP-A-4-74481 (JP, A) JP-A-4-4- 83379 (JP, A) JP-A-3-64974 (JP, A) JP-B-51-26366 (JP, B2) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 31/04-31 / 078 C01G 11/00-11/02

Claims (10)

(57) [Claims] To 1. A electrode layer provided substrate or metal substrate having an electrode of the light-absorbing layer made of p-type semiconductor thin film
Cd chalcogenide CdX on the light absorbing layer.
(Chalcogen X = S, Se, or Te) and a chalcogenide of Mg, a window layer composed of an n-type semiconductor thin film mainly composed of a solid solution CdX-MgX of MgX, and a transparent conductive layer in this order.
A thin-film solar cell having the following laminated structure. 2. A transparent conductive layer is provided on a translucent substrate.
A window layer made of an n-type semiconductor thin film mainly composed of a solid solution CdX-MgX of Cd chalcogenide CdX (chalcogen X = S, Se, or Te) and magnesium chalcogenide MgX on the transparent conductive layer, p-type semiconductor A thin-film solar cell having a configuration in which a light absorption layer made of a material and an electrode layer are sequentially laminated. 3. The thin-film solar cell according to claim 1, wherein the chalcogen is Te, and the composition ratio of MgTe in the solid solution is 50% by mole or more. 4. The thin-film solar cell according to claim 3, wherein the p-type semiconductor thin film of the light absorbing layer is CdTe. 5. A thin-film solar cell having a window layer comprising an n-type semiconductor thin film mainly composed of a solid solution CdX-MgX of a chalcogenide CdX of Cd (chalcogen X = S, Se or Te) and a chalcogenide MgX of Mg. A method of manufacturing a thin-film solar cell, wherein the window layer is formed by simultaneously depositing CdX and Mg. 6. A thin-film solar cell having a window layer comprising an n-type semiconductor thin film mainly composed of a solid solution CdX-MgX of a chalcogenide CdX (chalcogen X = S, Se, or Te) and a chalcogenide MgX of Mg. A method for producing a thin-film solar cell, wherein the window layer is formed by simultaneously depositing Cd, Mg, and chalcogen X. 7. A thin-film solar cell having a window layer comprising an n-type semiconductor thin film mainly composed of a solid solution CdX-MgX of a chalcogenide CdX of Cd (chalcogen X = S, Se or Te) and a chalcogenide MgX of Mg. a manufacturing method, a thin, characterized by forming the window layer by sputtering deposition of solid solution of CdX and MgX
Manufacturing method of membrane solar cell. 8. A thin-film solar cell having a window layer comprising an n-type semiconductor thin film mainly composed of a solid solution CdX-MgX of a chalcogenide CdX of Cd (chalcogen X = S, Se or Te) and a chalcogenide MgX of Mg. A method for producing a thin-film solar cell, wherein the window layer is formed by performing a heat treatment in an atmosphere containing chalcogen X simultaneously or after depositing Cd and Mg in a laminated manner. 9. A thin-film solar cell having a window layer comprising an n-type semiconductor thin film mainly composed of a solid solution CdX-MgX of a chalcogenide CdX of Cd (chalcogen X = S, Se or Te) and a chalcogenide MgX of Mg. A method for manufacturing a thin-film solar cell, comprising: forming a window layer by depositing chalcogen X and performing heat treatment simultaneously or after laminating Cd and Mg. 10. The method according to claim 5, wherein the chalcogen is Te.
The method for producing a thin-film solar cell according to any one of the above.