JPH0832094A - Thin film semiconductor solar cell and manufacture thereof - Google Patents

Abstract

PURPOSE:To maintain stably the characteristics, such as a high conversion efficiency, of a solar cell extending over a long period of time by a method wherein a transparent conductive layer is formed into a structure consisting of at least two layers, the one layer out of the two layers is formed into a crystal transparent conductive layer and the other one layer is formed into an amorphous transparent conductive layer. CONSTITUTION:A ZnO transparent conductive layer 103, semiconductive layers 105, 106 and 107 and a transparent electrode layer 108 are formed on a conductive substrate 101. At this time, the layer 103 consists of at least two layers, the one layer out of the two layers is a crystal transparent conductive layer 103 and the other one layer is formed into an amorphous transparent conductive layer 104. Thereby, the adhesive force of the layer 103 to the semiconductor layers is improved, a rise of a series resistance can be reduced, the interface between the transparent conductive layer and the semiconductor layers is formed into a smooth junction and the adhesion of the layer 103 to the semiconductor layers is improved. Accordingly, the characteristics, such as a high conversion efficiency, of a solar cell can be stably maintained extending over a long period of time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin film semiconductor solar cell and a manufacturing method thereof, and more particularly to a highly reliable thin film semiconductor solar cell capable of maintaining high conversion efficiency for a long period of time and a manufacturing method thereof.

[0002]

2. Description of the Related Art The energy consumed by us humans at present depends largely on thermal power generation using fossil fuels such as oil and coal and nuclear power generation. However, due to the fossil fuels that cause global warming due to carbon dioxide generated during use, or to the nuclear power, which can be said to have no danger of radiation even during normal operation as well as accidents,
There are many problems in going on to depend entirely on the future. Therefore, photovoltaic power generation using a solar cell, which has an extremely small effect on the global environment, has attracted attention and is expected to be further spread.

However, in the present situation of solar power generation, there are some problems that prevent the full-scale spread of the power generation.

Conventionally, single crystal or polycrystalline silicon has been often used for solar cells for photovoltaic power generation. However, in these solar cells, much energy and time are required for crystal growth, and a complicated process is required thereafter, so that mass productivity is difficult to increase and it is difficult to provide at low cost. On the other hand, amorphous silicon (hereinafter referred to as a-Si) and C
So-called thin film semiconductor solar cells using compound semiconductors such as dS and CuInSe ₂ have been actively researched and developed. In these solar cells, it suffices to form as many semiconductor layers as necessary on an inexpensive substrate such as glass or stainless steel, the manufacturing process thereof is relatively simple, and there is a possibility of cost reduction. However, thin-film solar cells have not been used in earnest since the conversion efficiency thereof is lower than that of crystalline silicon solar cells and the reliability of long-term use is uncertain. In order to solve this problem and improve the performance of the thin-film solar cell, various measures described below have been made.

One of them is to increase the reflectance of light on the surface of the substrate so that the sunlight not absorbed by the thin film semiconductor layer is returned to the semiconductor layer and the incident light is effectively utilized. A metal layer and a transparent conductive layer are respectively deposited on a flexible substrate). That is, the thin film semiconductor layer may be formed after forming the metal layer having high reflectance on the substrate. As a metal with high reflectance, silver (Ag),
Copper (Cu), aluminum (Al), etc. are known. Among them, Ag has a remarkably high reflectance of 98%,
The effect of improving the solar cell characteristics, especially the photocurrent (J _SC ) is high.
Furthermore, by interposing a transparent conductive layer having appropriate optical properties between the metal layer and the semiconductor layer, the reflectance can be further enhanced by the multiple interference effect.

The use of such a transparent conductive layer is effective in enhancing the reliability of the thin film solar cell. Japanese Patent Examination Sho 60-
Japanese Patent No. 41878 describes that a semiconductor and a metal layer can be prevented from alloying by using a transparent conductive layer. Also, U.S. Pat. Nos. 4,532,372 and 4,4
No. 598,306 describes that by using a transparent conductive layer having an appropriate resistance, it is possible to prevent an excessive current from flowing between electrodes even if a short circuit portion occurs in the semiconductor layer.

Further, as another device for improving the conversion efficiency of the thin film solar cell, the surface of the solar cell or the interface between the semiconductor layer and the back surface reflection layer is formed into a fine unevenness (texture structure).
There is a method. With such a structure, sunlight is scattered at the surface of the solar cell or at the interface between the semiconductor layer and the back surface reflection layer and is further confined inside the semiconductor (optical trap effect), so that the sunlight is effectively absorbed in the semiconductor. Can be absorbed. When sunlight is incident from the surface of the thin film semiconductor, the surface of the metal layer used for the back reflection layer may have a texture structure. M.Hirasaka, K.Suzuki, K.Nakatani,
M.Asano, M.Yano, and H.Okaniwa have shown that a texture structure for the back reflection layer can be obtained by depositing Al by adjusting the substrate temperature and deposition rate (Solar Cell Mate
rials, 20 (1990) pp99-110).

Furthermore, it is possible to combine the idea of the back surface reflecting layer composed of two layers of the metal layer and the transparent conductive layer with the idea of the texture structure. U.S. Pat. No. 4,419,53
No. 3 discloses a back reflection layer in which the surface of a metal layer has a texture structure and a transparent conductive layer is formed on the surface.

An example of the structure of a conventional thin film semiconductor solar cell using such a back reflection layer is shown in FIG. Reference numeral 301 denotes a conductive substrate, on the surface of which a metal layer 302 having a high reflectance and a textured structure is formed.

Further, a transparent conductive layer 303 is formed on it. The transparent conductive layer 303 is transparent to sunlight that has passed through the semiconductor layer 304. The surface also has a texture structure like the metal layer 302. Above this is the semiconductor layer 304. Here, a is used as the semiconductor layer.
An example using a -Si pin junction is shown.

Here, 305 is n-type a-Si, 306 is i-type a-Si, and 307 is p-type a-Si. If the semiconductor layer 304 is thin, as shown in FIG.
4 often has a texture structure similar to that of the transparent conductive layer 303. 308 is a transparent electrode on the surface. A comb-shaped collector electrode 309 is provided thereon. It is expected that the conversion efficiency of the solar cell will be remarkably improved by using the back reflection layer having such a structure, but in actual use, there remains a problem from the viewpoint of reliability.

In the solar cell having the structure shown in FIG. 3, when the solar cell in which the transparent conductive layer 303 is omitted is made, not only the conversion efficiency is lowered but also the resistance between the conductive substrate 301 and the collecting electrode 309 is often low. A condition (shunt) occurs where the specified output is not generated. When a shunted solar cell is examined with a metallurgical microscope, bright spots are often directly visible. This is a pinhole generated in the semiconductor layer 304. Dust that had been on the surface before the semiconductor layer 304 was deposited and a part of the semiconductor layer 304 could be part of the semiconductor layer 30.
It is considered that this is a trace of separation from the surface after deposition of No. 4. When the transparent electrode 308 is laminated in this situation, the transparent electrode 308 is in direct contact with the metal layer 302, so that the resistance between the electrodes is reduced, and the output current of the solar cell is not taken out to the outside and flows through the pinhole 310. It is considered that the conversion efficiency will decrease. However, in the actual production of solar cells, it is difficult to completely prevent dust from being deposited and the semiconductor layer 304 from flaking off from the uneven portions of the substrate during movement between the devices.

By introducing a suitable transparent conductive layer 303, however, the shunt can be greatly improved. As shown in FIG. 4, in the pinhole 310, since the transparent conductive layer 303 is interposed between the transparent electrode 308 and the metal layer 302, the leak current is limited according to the resistance of the transparent conductive layer 303. it is conceivable that.

However, even after such improvements are made,
It turns out that there are still problems depending on how the solar cells are used.

For example, since the output voltage of a single solar cell is generally as low as about 0.6 to 2.5 V, a plurality of sub-modules (the above-mentioned thin film semiconductor solar cells are modularized) are provided as shown in FIG. 501 to 504 are connected in series and used. When actually used outdoors, if a shadow 505 is cast on the sub-modules 502 and 503,
The output currents of the sub-modules 502 and 503 are extremely smaller than those of the other sub-modules, and substantially the internal impedance of the sub-module is large. As a result, the output voltage of the other sub-module is reversely applied (called a partial shade state), that is, a reverse bias is applied, leading to the destruction of the sub-module.

As described above, since the solar cell is used under various temperature and humidity environments, a reverse bias test (hereinafter, abbreviated as HHB test) in a high temperature and high humidity atmosphere is usually the most rigorous test. It's common and needs to be cleared.

However, when such a test is carried out, even in the thin-film solar cell having the transparent conductive layer 303 introduced, the conversion efficiency often deteriorates with the passage of time. In particular, when the surface of the metal layer 302 has a texture structure, the conversion efficiency tends to decrease rapidly.

As described above, the current thin-film solar cell is not sufficiently reliable in a harsh environment, and a more reliable solar cell is desired.

[0019]

In view of the above situation, the present invention aims to provide a highly reliable thin film semiconductor solar cell capable of maintaining a high conversion efficiency for a long period of time and a method for manufacturing the same. And

[0020]

The thin-film semiconductor solar cell of the present invention is a thin-film semiconductor solar cell in which at least a ZnO transparent conductive layer, a semiconductor layer, and a transparent electrode are formed on a conductive substrate. Is composed of at least two layers, of which one layer is a crystalline transparent conductive layer and one layer is an amorphous transparent conductive layer.

In the method for producing a thin film semiconductor solar cell of the present invention, at least a ZnO transparent conductive layer, a semiconductor layer, and a transparent electrode are formed on a conductive substrate, and the transparent conductive layer is composed of at least two layers. A method for manufacturing a thin film semiconductor solar cell, wherein a layer is a crystalline transparent conductive layer and one layer is an amorphous transparent conductive layer, wherein the amorphous transparent conductive layer is at a temperature lower than a film forming temperature of the crystalline transparent conductive layer. Is deposited.

The transparent conductive layer of the crystal is formed at a film forming temperature of 300 ° C.
As described above, it is preferable that the amorphous transparent conductive layer is deposited by the sputtering method and the amorphous transparent conductive layer is deposited by the sputtering method at a film forming temperature of 80 ° C. or less.

Further, in the method for producing a thin film semiconductor solar cell of the present invention, at least a ZnO transparent conductive layer, a semiconductor layer and a transparent electrode are formed on a conductive substrate, and the transparent conductive layer is composed of at least two layers. A method for manufacturing a thin-film semiconductor solar cell, wherein one layer is a crystalline transparent conductive layer and one layer is an amorphous transparent conductive layer, wherein the amorphous film is formed at a film formation rate faster than that of the crystalline transparent conductive layer. Is deposited.

The transparent conductive layer of the crystal is formed at a film forming rate of 9 nm /
deposited by sputtering at a deposition rate lower than s,
The amorphous transparent conductive layer is preferably deposited by a sputtering method at a film forming rate of 9 nm / s or more.

Further, in the method for manufacturing a thin film semiconductor solar cell of the present invention, a crystalline transparent conductive layer and an amorphous transparent conductive layer are formed in different deposition chambers while transporting a flexible long conductive substrate in the longitudinal direction. It is characterized in that the transparent conductive layer is continuously deposited.

[0026]

The function of the present invention will be described below with reference to the embodiments.

On the conductive substrate, a transparent conductive layer, a semiconductor layer,
In a thin film semiconductor solar cell formed with a transparent electrode,
The transparent conductive layer has at least a two-layer structure, one of which is a crystalline transparent conductive layer, and one is an amorphous transparent conductive layer, so that solar cell characteristics such as high conversion efficiency can be stably maintained for a long period of time. A highly reliable solar cell that can be maintained is obtained.

This is because by providing an amorphous transparent conductive layer in addition to the conventional crystalline transparent conductive layer as the transparent conductive layer, the interface between the transparent conductive layer and the semiconductor layer is smoothly joined and the adhesion is improved. it is conceivable that. That is, it is considered that by providing an amorphous transparent conductive layer, the adhesive force is improved and the increase in series resistance can be reduced.
Further, by disposing the amorphous transparent conductive layer, it is considered that the gap of the crystal grains of the crystalline transparent conductive layer is filled and the migration of the metal layer (Ag) is prevented, so that the reduction of the shunt resistance can be suppressed.

The transparent conductive layer of the present invention is formed by a film forming method such as a vacuum vapor deposition method and a sputtering method. A sputtering method is particularly preferable, and a crystalline or amorphous structure can be obtained by controlling the film forming temperature and / or the film forming rate.

In particular, the film formation temperature is preferably 300 ° C. or higher in the case of a crystalline transparent conductive layer and 80 ° C. or lower in the case of an amorphous transparent conductive layer. By forming the transparent conductive layer in this temperature range, a solar cell with higher conversion efficiency and higher reliability can be obtained.

For the same reason, in the case of the crystalline transparent conductive layer, it is preferable that the film formation rate is lower than 9 nm / s, and the amorphous transparent conductive layer is formed at 9 nm / s or more.

As the conductive substrate of the present invention, a conductive substrate made of stainless steel, zinc steel or the like is used, but a metal layer having high reflectance such as Ag, Al or Cu is provided to enhance reflectance. preferable. Alternatively, an insulating substrate such as glass having a metal film formed thereon may be used. Further, according to the present invention, continuous film formation can be performed using a roll-to-roll type film forming apparatus using a long substrate.

The method for forming the transparent conductive layer of the present invention will be described below. FIG. 2 shows a roll-to-roll type sputtering apparatus which is preferably used as a transparent conductive film forming apparatus. The apparatus shown in FIG. 2 includes a substrate delivery chamber 204, a substrate winding chamber 205, and a film forming chamber 206. The film forming chamber 206 has a metal layer (A
g) is composed of a reaction chamber 201 and two reaction chambers 202 and 203 capable of independently depositing two transparent conductive layers. A metal layer target (Ag) 210 and ZnO targets 211 and 212 are attached to each reaction chamber. Has been.

Further, heaters 207, 208, 209 and a substrate cooling mechanism 213 are provided to control the film forming temperature. The substrate cooling device is for forming an amorphous transparent conductive layer at a low temperature of 80 ° C. or lower.

Further, 214 is a long substrate, 215 is a sputtering power source, 216 is a sputtering gas supply source (A
r), 217 is a reaction gas supply source (O ₂ ), 218 is a gas flow rate controller, 219 is a rotary pump, 220 is an automatic pressure controller, 221 is a diffusion pump, 222 is a mechanical booster pump and a rotary pump.

While transporting the conductive substrate (long substrate) 214 from the substrate delivery chamber 204 to the substrate winding chamber via the film forming chamber 206, a metal layer (Ag) and a crystalline ZnO transparent conductive layer are formed on the substrate. (ZnO),
Amorphous ZnO layers are successively deposited at each desired temperature.

The experiments conducted in the course of completing the present invention are shown below.

(Experiment 1) In this experiment, the solar cell having the structure shown in FIG. 3 was produced under various conditions, and the relationship between the film forming temperature, the form of the ZnO transparent conductive film and the solar cell characteristics was investigated.

First, a metal layer (Ag) 302 was deposited on a conductive substrate (SUS430) 601 using the sputtering apparatus shown in FIG. A as target 605
g target of 99.99%, Ar gas 24.
Flowing 8 sccm, pressure 2 mTorr, film forming temperature 350
Apply 0.15A current and 380V voltage at
A metal layer having a thickness of 400 nm was deposited on the substrate.

Next, a transparent conductive layer (ZnO) 303 was deposited on the metal layer (Ag) 302. As a target 605, a ZnO 99.99% target is set and Ar
Flowing 24.8 sccm, the pressure is 10 mTorr, and the film forming temperature T _S is 50 ° C., 60 ° C., 70 ° C., 80 ° C., 90
℃, 100 ℃, 150 ℃, 200 ℃, 250 ℃, 300
℃, 350 ℃, various changes to 400 ℃, current 0.15
A, a voltage of 380 V is applied, and the transparent conductive layer (ZnO) is set to 1
000 nm was formed. Here, the film formation rate is 0.2 nm /
s. The crystal structure of the obtained film was examined by X-ray diffraction.

X-ray diffraction is a widely used method for studying the crystal structure.
Diffraction occurs in the direction of θ, and a sharp peak appears. On the other hand, the peak does not appear in the amorphous structure. From this difference, it is possible to know the crystal structure of the material by X-ray diffraction.

FIG. 8 shows an example of the result of X-ray diffraction of crystalline ZnO. In this sample, a metal layer (Ag) was deposited on a conductive substrate, and a conventional transparent conductive layer was further deposited, so that a peak of Ag also appeared. If it is an amorphous transparent conductive layer, the diffraction pattern as shown in FIG. 8 does not appear.

Table 1 shows the results of examining the X-ray diffraction of the transparent conductive layer formed at various film forming temperatures Ts. As shown in Table 1, it was found that the transparent conductive layer formed at 80 ° C. or lower has an amorphous structure.

Then, the RF plasma CVD shown in FIG.
The thin film semiconductor layer 304 was deposited as follows using the apparatus according to the method. In the apparatus of FIG. 7, a metal layer 302 is deposited on a conductive substrate 301, and a transparent conductive layer 303 is further deposited (herein, generically referred to as a substrate 701), which is set as shown in FIG. Exhausted. The gas is supplied by the gas supply unit 705, the RF power source 707 is applied to the RF electrode 703, and the substrate 7 is connected to the electrode 703 and the ground.
A discharge is generated between the substrate 701 and the source gas to decompose the substrate gas 701.
N-type a-Si layer 305, i-type a-Si layer 306, p
Type microcrystal (μc) -Si layer 307 of 10 nm,
A film having a thickness of 300 nm and a thickness of 10 nm was formed. The film forming temperature is 35
At 0 ° C., SiH ₄ , PH ₃ (n-type a-
Si layer), SiH ₄ (i-type a-Si layer), SiH ₄ , BF
₃ , H ₂ (p-type μc-Si layer) was used (note that SiH ₄
Since about 10% of hydrogen (H) is contained in a-Si by the iso-glow discharge decomposition method, it is generally expressed as a-Si: H, but in the present description, it is simply referred to as a-Si. Notation).

A transparent electrode layer 308 having a thickness of 80 nm is deposited on the thin film semiconductor layer 304 by a resistance heating vapor deposition method, and a collector electrode 309 having a thickness of 1 μm is formed by an EB vapor deposition method. A battery was made.

This thin-film semiconductor solar cell was placed at a temperature of 80 ° C.
The durability test was carried out by introducing into a HHB test with a humidity of 80% and a bias voltage of -0.8V. Table 1 shows the results.

[0047] In Table 1, the item of the series resistance (R _S) R _S
(240h) / R _S (0h) means 2 after the HHB test is input.
Set the value of series resistance Rs (240h) for 40 hours to HHB
It is a value divided by the value of the series resistance R _S (0 h) before the test is input. That is, it can be said that the lower this value is, the less the series resistance increases and the more reliable the sample. The shunt resistance (R _Sh ) item, on the contrary, can be said to be a highly reliable sample with a smaller decrease in shunt resistance as the value increases.

As shown in Table 1, amorphous ZnO
_Shows that the photocurrent J _SC tends to be low, but the reliability is excellent. Further, although crystalline ZnO has poor reliability, it has a high effect of increasing J _SC . As described above, it was found that each of them has excellent characteristics, but does not satisfy reliability and high current.

(Experiment 2) Using the sputtering apparatus shown in FIG. 6, in the same manner as in Experiment 1, a metal layer (Ag) was deposited on a conductive substrate, and the power (W) of the sputtering power source was changed. 1000 times the transparent conductive layer at various deposition rates.
nm was deposited and the X-ray diffraction was measured. The film forming rate of the transparent conductive layer is 0.1 nm / s, 0.2 nm / s,
0.5 nm / s, 1 nm / s, 2 nm / s, 3 nm /
s, 5 nm / s, 6 nm / s, 7 nm / s, 8 nm /
s, 9 nm / s, and 10 nm / s. The film forming temperature was 300 ° C. The results of the X-ray diffraction measurement are shown in Table 2.

From Table 2, it was found that the transparent conductive layer formed at a film forming rate of 9 nm / s or more has an amorphous structure and becomes crystalline at a film forming rate lower than that.

Further, in the same manner as in Experiment 1, the semiconductor layer,
A transparent electrode and a collecting electrode were formed to manufacture a solar cell having the structure shown in FIG. Table 2 shows the results of the HHB test performed on the manufactured solar cells in the same manner as in Experiment 1.

It can be seen from Table 2 that amorphous ZnO has excellent reliability and crystalline ZnO has a high effect of increasing Jsc.

[0053]

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

Example 1 A solar cell having the two-layer structure of the transparent conductive layer shown in FIG. 1 was produced.

Using the roll-to-roll type sputtering apparatus shown in FIG. 2, a metal layer Ag is formed on a long conductive substrate.
(400 nm) and two transparent conductive layers (10 nm and 1000 nm, respectively) were continuously formed at the film forming temperatures shown in Table 3. The film formation rate of the transparent conductive layer was 0.2 nm / s for both crystalline and amorphous.

Next, the long substrate was cut, and in the same manner as in Experiment 1, a semiconductor layer was formed by using the apparatus shown in FIG. 7, and then a transparent electrode and a collecting electrode were formed to form a thin film semiconductor solar cell. It was made. The manufactured solar cell was subjected to the HHB test in the same manner as in Experiment 1 to evaluate the characteristics. Table 2 shows the results.

In Table 2, the characteristics of the solar cell J _SC , R _S
The good ones and R _Sh are all good, the practically usable ones are good, and the practically problematic ones are bad.

As shown in Table 2, it is understood that when the transparent conductive layer has a two-layer structure, one of which has a crystal structure and the other has an amorphous structure, excellent reliability and current characteristics are exhibited. In particular, it was optimal to form the crystalline transparent conductive layer at 300 ° C. or higher and the amorphous transparent conductive layer at 80 ° C. or lower.

Example 2 The same as Example 1 except that the amorphous transparent conductive layer was formed on the crystalline transparent conductive layer at different film forming rates based on the result of the experiment 2. A thin film semiconductor solar cell was produced and an HHB test was conducted. The film forming temperature of the transparent conductive layer was 300 ° C. in all cases.
The results are shown in Table 4.

From Table 4, by setting the film forming rate of one of the transparent conductive layers at 9 nm / s or more and depositing the other at a film forming rate lower than 9 nm / s, the amorphous transparent conductive layer and the transparent crystal can be obtained. A two-layer structure consisting of conductive layers is obtained,
It was found that a thin film solar cell excellent in photocurrent and reliability can be obtained.

Example 3 Using the DC sputtering apparatus shown in FIG. 6, a metal Ag film was formed to a thickness of 400 nm, and then a crystalline transparent conductive layer ZnO was formed to a thickness of 1000 nm (film formation rate: 0.2).
nm / s, film formation temperature 350 ° C.) and amorphous transparent conductive film ZnO were deposited to a thickness of 10 nm (film formation rate 0.2 nm / s, film formation temperature 80 ° C.).

On this, in the same manner as in Experiment 1, a thin film semiconductor layer, a transparent electrode, and a current collecting electrode were deposited. This is sample 1.

A sample 2 was prepared in the same manner as the sample 1 except that the stacking order of the crystalline and amorphous transparent conductive films was reversed.

On the other hand, for comparison, one transparent conductive layer was used, 1000 nm of crystalline ZnO was formed at a film forming temperature of 300 ° C. and a film forming rate of 0.2 nm / s. It was made.

An HHB test and a durability test were performed on the above samples. In the HHB test, the temperature was 8
Bias voltage -0.8V in an atmosphere of 0 ° C and 80% humidity
Was applied. For each solar cell, the solar cell conversion characteristics, the shunt resistance Rsh, and the time change of the series resistance were traced. The results are shown in FIGS.

As shown in the figure, in the conventional solar cell (comparative sample), the conversion efficiency of the solar cell and the shunt resistance (R _Sh ) were lowered and the series resistance (R
_S ) also rose sharply, whereas sample 1 of this example
It can be seen that the characteristics of Nos. 2 and 2 are stable and maintain high characteristics.

That is, in the present invention, the amorphous transparent conductive layer may be provided either before or after the crystalline transparent conductive layer, and it is understood that this structure has higher reliability than the conventional example.

Next, an adhesion test was conducted to examine the adhesive force at the transparent conductive layer / semiconductor layer interface. The adhesion test is a test in which a sample is cut into a grid pattern with a cutter knife, and a tape is attached onto the sample to remove the film with an even force.

As a result of the test, in the conventional solar cell, peeling occurred in 25 out of 25, but no peeling was observed in the sample of this example. As a result of XMA analysis of the peeled-off comparative sample, it was found that the peeled-off comparative sample was peeled at the interface between the transparent conductive layer and the semiconductor layer.

(Example 4) In this example, a solar cell having a transparent conductive layer having a three-layer structure and a four-layer structure was produced. The structure of the three-layer structure is as follows: crystal 1000 nm / amorphous 10 nm / crystal 1000 nm from the substrate side.
000 nm / amorphous 10 nm / crystal 1000 nm
/ Amorphous 10 nm. These solar cells,
Let them be Sample 3 and Sample 4, respectively.

This sample was placed in an environmental test box for HHB test for 240 hours, and the time change of solar cell conversion efficiency was examined. The results are shown in Fig. 9. As shown in the figure, it can be seen that the stability is further improved by forming the multiple transparent conductive layers.

[0072]

[Table 1]

[0073]

[Table 2]

[0074]

[Table 3]

[0075]

[Table 4]

[0076]

As described above, according to the present invention, the following effects can be obtained. The present invention is a thin-film semiconductor solar cell in which a transparent conductive layer, a semiconductor layer, and a transparent electrode are formed on a conductive substrate, and the transparent conductive layer has at least a two-layer structure,
By providing one of them as a crystalline transparent conductive layer and one as an amorphous transparent conductive layer, a highly reliable solar cell capable of stably maintaining solar cell characteristics such as high conversion efficiency for a long period of time is obtained. To be

The transparent conductive layer of the present invention is formed by a film forming method such as a vacuum vapor deposition method and a sputtering method. A sputtering method is particularly preferable, and a crystalline or amorphous structure can be obtained by controlling the film forming temperature and / or the film forming rate.

In the transparent conductive layer of the present invention, the film forming temperature is preferably 300 ° C. or higher in the case of a crystalline transparent conductive layer,
In the case of an amorphous transparent conductive layer, it is preferably 80 ° C or lower. By forming the transparent conductive layer in this temperature range,
A solar cell with higher conversion efficiency and higher reliability can be obtained.

In the transparent conductive layer of the present invention, the film formation rate is preferably lower than 9 nm / s in the case of a crystalline transparent conductive layer, and the amorphous transparent conductive layer is preferably formed in a rate of 9 nm / s or more. . By forming the transparent conductive layer at this film formation rate, a solar cell with higher conversion efficiency and higher reliability can be obtained.

As the conductive substrate of the present invention, a conductive substrate made of stainless steel, zinc steel or the like is used, but a metal layer having high reflectance such as Ag, Al or Cu is provided to enhance reflectance. preferable. Alternatively, an insulating substrate such as glass having a metal film formed thereon may be used. Further, according to the present invention, continuous film formation can be performed using a roll-to-roll type film forming apparatus using a long substrate.

Therefore, according to the present invention, it is possible to provide a highly reliable thin film semiconductor solar cell capable of maintaining a high conversion efficiency for a long period of time and a method for manufacturing the same.

[Brief description of drawings]

FIG. 1 is a schematic view showing an example of a thin film semiconductor solar cell of the present invention.

FIG. 2 is a schematic view showing a roll-to-roll type sputtering apparatus suitable for the present invention.

FIG. 3 is a schematic view showing a conventional thin film semiconductor solar cell.

FIG. 4 is a schematic diagram illustrating a pinhole of a conventional thin film semiconductor solar cell.

FIG. 5 is a schematic view showing a partial shade state by the solar cell module.

FIG. 6 is a schematic view showing an RF plasma CVD apparatus used for forming a semiconductor layer.

FIG. 7 is a schematic view showing a DC sputtering device used for forming a transparent conductive layer.

FIG. 8 is an example of an X-ray diffraction pattern of a crystalline ZnO layer.

FIG. 9 is a graph showing the change over time in conversion efficiency in the HHB test.

FIG. 10 is a graph showing a time change of series resistance Rs in an HHB test.

FIG. 11: Shunt resistance RshDK in HHB test
It is a graph which shows the time change of.

[Explanation of symbols]

101 substrate, 102, 302 metal layer, 103 crystalline ZnO layer, 104 amorphous ZnO layer, 105, 305 n-type a-Si, 106, 306 i-type a-Si, 107, 307 p-type a-Si, 108, 308 transparent Electrode, 109, 309 Current collecting electrode, 201 Metal layer (Ag) deposition reaction chamber, 202, 203 Transparent conductive layer deposition reaction chamber, 204 Substrate feeding chamber, 205 Substrate winding chamber, 206 Deposition chamber, 207, 208, 209 Heater, 210 metal layer target (Ag), 211, 212 ZnO target, 213 substrate cooling mechanism, 214 long substrate, 215 sputtering power source, 216 sputtering gas supply source (Ar), 217 reaction gas supply source (O ₂ ), 218 gas flow controller, 219 rotary pump, 2 0 automatic pressure regulator, 221 diffusion pump, 222 mechanical booster pump and rotary pump, 301 conductive substrate, 303 transparent conductive layer, 304 semiconductor layer, 310 pinhole, 501-504 submodule, 505 shadow, 601, 701 substrate, 602 substrate holder, 604, 704 chamber (vacuum container), 605-607 target, 608-610 DC power supply, 611, 706 automatic gas flow control device, 612, 705 gas supply means, 613, 708 automatic gas pressure control device, 614 , 709 Exhaust pump, 703, 707 RF electrode.

Claims (6)

[Claims] 1. A thin-film semiconductor solar cell comprising a conductive substrate and at least a ZnO transparent conductive layer, a semiconductor layer, and a transparent electrode formed thereon, wherein the transparent conductive layer comprises at least two layers, one of which is crystalline. Is a transparent conductive layer, and one layer is an amorphous transparent conductive layer. 2. A ZnO transparent conductive layer, a semiconductor layer, and a transparent electrode are formed on a conductive substrate, the transparent conductive layer is composed of at least two layers, and one of them is a crystalline transparent conductive layer, A method of manufacturing a thin film semiconductor solar cell, wherein one layer is an amorphous transparent conductive layer, characterized in that the amorphous transparent conductive layer is deposited at a temperature lower than a film forming temperature of the crystalline transparent conductive layer. Method for manufacturing solar cell. 3. A film forming temperature of the transparent conductive layer of the crystal is 300.
The method for producing a thin-film semiconductor solar cell according to claim 2, wherein the amorphous transparent conductive layer is deposited at a temperature of 80 ° C. or less by sputtering, and the amorphous transparent conductive layer is deposited at a temperature of 80 ° C. or less. 4. A ZnO transparent conductive layer, a semiconductor layer, and a transparent electrode are formed on a conductive substrate, the transparent conductive layer is composed of at least two layers, one of which is a crystalline transparent conductive layer, A method of manufacturing a thin-film semiconductor solar cell in which one layer is an amorphous transparent conductive layer, characterized in that the amorphous transparent conductive layer is deposited at a film formation rate higher than the film formation rate of the crystalline transparent conductive layer. Method for manufacturing thin film semiconductor solar cell. 5. The crystalline transparent conductive layer is deposited by a sputtering method at a deposition rate lower than 9 nm / s, and the amorphous transparent conductive layer is deposited by a sputtering method at a deposition rate of 9 nm / s or more. The method for manufacturing a thin film semiconductor solar cell according to claim 4. 6. The crystalline transparent conductive layer and the amorphous transparent conductive layer are continuously deposited in different deposition chambers while transporting a flexible long conductive substrate in the longitudinal direction. The method for manufacturing a thin film semiconductor solar cell according to claim 2, wherein