JP2952121B2 - Photovoltaic element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photovoltaic device such as a solar cell having high performance, high reliability over a long period of time and easy mass production, and an improved metal provided in the photovoltaic device. About layers.

[0002]

2. Description of the Related Art As a future energy source for humankind,
There is no danger of radiation due to the reliance on petroleum or coal, which is said to cause global warming due to the carbon dioxide generated as a result of its use, unexpected accidents, and even during normal operation. It is problematic to rely entirely on nuclear power, which cannot be said to be. Therefore, solar cells, which use the sun as an energy source, have very little influence on the global environment, and have an inexhaustible energy source, are expected to be more widely used. However, at present, there are some problems that hinder full-fledged diffusion.

Conventionally, monocrystalline or polycrystalline silicon has been often used for photovoltaic power generation. However, these solar cells require a large amount of energy and time to grow crystals, and require complicated processes thereafter, so that the mass production effect is hard to increase, and it has been difficult to provide them at low cost. On the other hand, so-called thin-film semiconductor solar cells using compound semiconductors such as amorphous silicon-based (hereinafter referred to as a-Si) and CdS.CuInSe _{2 which} have high mass production effects have been actively researched and developed. In these solar cells,
It is only necessary to form as many semiconductor layers as necessary on an inexpensive substrate such as a glass or stainless steel sheet or plate, and the manufacturing process is relatively simple, and there is a possibility that the price can be reduced. However, thin-film solar cells have not been used in earnest because their conversion efficiency is lower than that of crystalline silicon solar cells, and their reliability for long-term use is uncertain. Therefore, various measures have been taken to improve the performance of the thin-film solar cell.

One of the reasons is to increase the reflectance of light on the substrate surface in order to increase the conversion efficiency, return sunlight not absorbed by the thin film semiconductor layer to the thin film semiconductor layer again, and effectively use the incident light. Is to provide a back reflection layer. For this purpose, when a photoelectric conversion layer is provided on a transparent substrate, sunlight is incident from the substrate side, and electrodes formed on the surface of the thin film semiconductor are formed of silver (Ag), aluminum (Al), copper (C).
It is preferable to use a metal having high reflectivity such as u). In the case where sunlight is incident from the surface of the thin film semiconductor layer, it is preferable to form a photoelectric conversion layer which is a thin film semiconductor after forming a similar metal layer on a substrate. Further, when a transparent layer having appropriate optical properties is interposed between the metal layer and the thin film semiconductor layer, the reflectance can be further increased by the multiple interference effect. FIG. 3 shows a case where zinc oxide (ZnO) is interposed as a transparent layer between silicon and various metals (b), and a case where zinc oxide layer is not interposed (a), a zinc oxide layer is interposed (a). (B) does not involve a zinc oxide layer (b)
It is a result of a simulation showing that the reflectance is more improved.

The use of such a transparent layer is effective in improving the reliability of the thin-film solar cell. Patent notice 60-4
Japanese Patent No. 1878 describes that the use of a transparent layer can prevent alloying between a semiconductor and a metal layer. See also U.S. Patents 4,532,372 and 4,598,306.
Describes that use of a transparent layer having an appropriate resistance can prevent an excessive current from flowing between the electrodes even if a short circuit occurs in the semiconductor layer.

Another method for improving the conversion efficiency of a thin-film solar cell is a method of forming a fine uneven structure at the interface between the solar cell and the front and / or back reflection layers (texture structure). With such a configuration, sunlight is scattered at the interface with the front or back surface reflection layer of the solar cell, further confined in the semiconductor, and can be effectively absorbed in the semiconductor (light trapping effect). Become. When the substrate is transparent, the surface of a transparent electrode such as tin oxide (SnO ₂ ) on the substrate may have an uneven structure. In the case where sunlight enters from the surface of the thin film semiconductor, the surface of the metal layer used for the back reflection layer may have an uneven structure. M. Hiras
aka, K .; Suzuki, K .; Nakatani,
M. Asano, M .; Yano, H .; Okaniwa shows that by depositing Al by adjusting the substrate temperature and the deposition rate, a concavo-convex structure for the back reflection layer can be obtained (S
polar Cell Materials 20 (19
90) pp99-110). FIG. 4 shows an example of an increase in the absorption of incident light due to the use of the back reflection layer having such an uneven structure.
And FIG. Curve (a) in FIG. 4 shows the spectral sensitivity of an a-Si solar cell using smooth Al as a metal layer, and curve (b) shows the spectral sensitivity of an a-Si solar cell using Al having an uneven structure. 5 shows a spectral sensitivity of an a-SiGe solar cell using smooth Cu as a metal layer, and a curve (b) shows a-SiG using Cu having an uneven structure.
e shows the spectral sensitivity of the solar cell.

Further, the concept of the back-surface reflection layer composed of two layers, a metal layer and a transparent layer, can be combined with the concept of the uneven structure. U.S. Pat. No. 4,419,533 discloses a concept of a back reflection layer in which the surface of a metal layer has an uneven structure and a transparent layer is formed thereon.

The use of aluminum or copper as the metal layer of the backside reflection layer is extremely advantageous in reducing the production cost and obtaining a solar cell with high conversion efficiency. However, in the case of using the conventional back reflection layer in which the metal layer or the substrate also serving as the metal layer is aluminum or copper, the reliability for use under severe conditions such as high temperature and high humidity is not always sufficient, and the conversion efficiency is not sufficient. In some cases, it was significantly reduced. For this reason, such a thin-film semiconductor solar cell has not been used in earnest for photovoltaic power generation, although it may be produced at a low price.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and by using an improved back reflection layer, a photovoltaic element having higher conversion efficiency and higher reliability than the conventional one can be manufactured at a low cost. The purpose is to provide at.

[0010]

SUMMARY OF THE INVENTION The present inventors have found the following technical problems to be solved in a back reflection layer using aluminum as a metal having a high reflectance or a back reflection layer using copper. I found something.

(1) Change of transparent layer due to diffusion of aluminum atoms and copper atoms When depositing a thin film semiconductor on the backside reflective layer, usually,
The substrate temperature is set to 00 degrees or higher. At such a temperature, aluminum atoms and copper atoms may diffuse into the transparent layer.
When these aluminum and copper atoms act as dopants, the resistance and chemical resistance of the transparent layer, which is usually a semiconductor itself, change. As a result, if the resistance is too high, a series resistance loss occurs in the circuit, and if the resistance is too low, the current flowing through the short-circuit portion cannot be suppressed. In addition, when a chemical is susceptible to corrosion, a defect occurs due to a chemical such as an etchant used in a subsequent process.

(2) Diffusion of aluminum and copper atoms into the thin film semiconductor layer Further, when aluminum and copper atoms diffuse through the transparent layer to the surface of the transparent layer and the metal comes into direct contact with the thin film semiconductor layer, aluminum In addition, a reaction between copper and the semiconductor occurs, and the function of the semiconductor junction is impaired. In an extreme case, a short circuit occurs with the transparent electrode.

(3) Increase in diffusion due to the uneven structure When the transparent layer, or the transparent layer and the aluminum layer or the transparent layer and the copper layer have an uneven structure, the surface area is increased by forming the uneven structure, so that aluminum atoms or copper atoms are increased. Increase the diffusion of

[0014]

As a result of studying these problems, the present inventors have come up with the following basic concept of the present invention.

The photovoltaic device according to the first aspect of the present invention comprises silicon,
A metal layer formed of aluminum having at least one of copper, zinc, and manganese; a transparent layer provided on the metal layer; and a semiconductor layer having photoelectric conversion provided on the transparent layer. At least one of silicon, copper, zinc, and manganese has a concentration of 1 / e (e = e = 50 ° or more and 500 ° or less) in the thickness direction from the metal layer surface on the transparent layer side.
It is characterized by a monotonically decreasing distribution so as to be the natural logarithm base).

The silicon concentration is 0.5 to 10.0% by weight.

The copper concentration is 0.5 to 10.0% by weight.

The zinc concentration is 0.5 to 10.0% by weight.

Further, at least the surface of the transparent layer has an uneven structure. Further, the second invention provides a metal layer formed of copper containing at least one of silicon, aluminum, zinc, tin, and beryllium, a transparent layer provided on the metal layer, A semiconductor layer having photoelectric conversion provided therein, wherein at least one of silicon, copper, zinc, and manganese has a concentration of 1/50 to 500 ° in the film thickness direction from the metal layer surface on the transparent layer side. It is characterized by a monotonically decreasing distribution such that e (e = base of natural logarithm).

[0020] The silicon concentration is 0.5 to 10.0% by weight.

The aluminum concentration is 0.5 to 10.0.
% By weight.

It is characterized in that the zinc concentration is 0.5 to 10.0% by weight.

[0023] The tin concentration is 0.5 to 10.0% by weight.

The beryllium concentration is 0.1 to 2.0% by weight.

[0025]

At least the surface of the transparent layer has an uneven structure.

FIGS. 1 and 2 show an example of the structure of the thin-film solar cell according to the present invention. 101 is a conductive substrate. An aluminum layer or a copper layer 102 is formed on the surface. Here, the metal layer 10 which is an aluminum layer or a copper layer
2 is doped with appropriate impurities. A transparent layer 103 is formed thereon, and the metal surface and the transparent layer constitute a back reflection layer. The transparent layer may be transparent to sunlight transmitted through the thin film semiconductor layer. FIG. 1 shows a case where the aluminum layer or the copper layer 102 has an uneven structure, and FIG. 2 shows a case where the aluminum layer or the copper layer has a smooth structure and the transparent layer has an uneven structure. . Although an example in which a pin-type a-Si based photovoltaic element is used as the thin film semiconductor junction is shown here, a tandem cell or triple cell structure in which a plurality of pin-type a-Si based photovoltaic elements are stacked may be used. That is, 105 is n-type a-Si, and 106 is i
Types a-Si and 107 are p-type a-Si. When the thin-film semiconductor junction 104 is thin, the entire thin-film semiconductor junction often shows an uneven structure similar to the surface of the transparent layer, as shown in FIGS. 108 is a transparent electrode on the surface. A comb-shaped collecting electrode 109 for collecting electricity is provided thereon. The following effects are obtained by adopting such a structure.

(1) Since aluminum or copper is used for the metal layer 102, the reflectance of sunlight is high.

(2) Since the surface of the transparent layer 103 has a concavo-convex structure, a light trapping effect occurs inside the thin film semiconductor junction 104. Therefore, the incident sunlight is effectively absorbed, and the conversion efficiency of the solar cell is improved.

(3) Since appropriate impurities are contained in the aluminum layer and the copper layer 102, diffusion of aluminum atoms and copper atoms into the transparent layer 103 and the thin film semiconductor junction 104 hardly occurs. Therefore, the resistance and chemical resistance of the transparent layer 103 are stable, and the reliability is high.

Although the details of this are unknown, the appropriate impurity contained in the aluminum layer or the copper layer causes the element layer to suddenly differ from the case where the transparent layer or the semiconductor layer is directly laminated on the aluminum layer or the copper layer. Are not changed because of no change, and it is considered that chemical resistance is stable.

(4) When the area of the concavo-convex structure or the like is substantially increased, the reliability is enhanced particularly by suppressing the diffusion of metal.

The concentration of impurities contained in the aluminum layer and the copper layer can be as much as 40% by weight in the case of zinc, but does not lower the reflectivity of the metal layer, prevents diffusion from the metal layer, and is not useful as an alloy composition. The optimum range is specifically 0.5 to 10.0% by weight when Al contains Si, Cu or Zn, and 0.5 to 10.0% by weight when Al contains Mn. It is in the range of 0.1 to 2.0% by weight. S to Cu
When i, Al, Zn or Sn is contained, 0.5
To 10.0% by weight, and 0.1% when Be is contained.
It is in the range of 1 to 2.0% by weight.

An experiment for demonstrating the effects of the present invention will be described below.

(Experiment 1) A 5 × 5 cm stainless steel plate (S
US430) by DC magnetron sputtering
Of the Al layer by using an Al target containing 10% by weight of
00Å deposited. The substrate temperature at this time was set to 250 degrees.
According to SEM observation, the surface of Al has a diameter of 4000-6.
The protruding portions, which appeared to be crystal grains of about 000 °, were dense and cloudy. On top of that, ZnO was deposited at 700 ° by DC magnetron sputtering. The substrate temperature at this time is set to 10
0 degrees. On the back reflection layer thus formed, the substrate temperature is set to 300 ° C. and the SiH
₄ and PH ₃ as source gases to form an n-type a-Si layer of 200
Å, an i-type a-Si layer SiH ₄ as source gases 400
0 °, a 100 μm p-type microcrystalline (μc) Si layer is deposited using SiH ₄ , BF ₃ , and H ₂ as source gases to form a thin film semiconductor junction (a-S by glow discharge decomposition such as SiH _4).
Since i contains about 10% of hydrogen (H), it is generally referred to as a-Si: H, but is simply referred to as a-Si for simplicity in this description.) An ITO film was formed thereon as a transparent electrode by a resistance heating evaporation method at 650 °.
Deposited. Further, a current collecting electrode having a width of 300 μm was formed on the silver paste by screen printing to obtain a sample 1a.

Next, a sample 1b was obtained in the same manner as the sample 1a, except that an Al layer was formed using an Al target containing 3% by weight of Si.

Next, a sample 1c was obtained in the same manner as the sample 1a, except that an Al layer was formed using an Al target containing 0.5% by weight of Si.

Next, a sample 1d was obtained in the same manner as the sample 1a, except that an Al layer was formed using a target of pure Al.

Next, the substrate temperature during the deposition of Al is set to room temperature,
The deposition temperature of ZnO is 250 degrees and the thickness of ZnO is 400
A sample 1e was obtained in the same manner as the sample 1b, except that the angle was 0 °.

According to the analysis, almost the same concentration of Si as in the target was detected in the deposited Al layer.
The five kinds of samples thus obtained were measured under a solar simulator of AM-1.5, and the conversion efficiency as a solar cell was evaluated. Table 1 shows the results. That is, the conversion efficiency of sample 1d is considerably lower than that of the other samples. This is considered to be a decrease in efficiency due to a short circuit according to a detailed study of solar cell characteristics. The surface of each sample was observed at a magnification of 500 times with a metallographic microscope.
In sample 1d, spot-like discoloration was observed on one surface. When the discolored portion was analyzed by Auger analysis, Al was found on the surface of the Si. Although the sample 1e had the highest efficiency, it is considered that the light reflectance on this surface was the best because the surface of Al was smooth in this sample.

(Experiment 2) A containing 3% by weight of zinc (Zn)
A sample 2a was obtained in the same manner as the sample 1a of the experiment 1, except that the target 1 was used.

A sample 2b was obtained in the same manner as the sample 1a, except that an Al target containing 3% by weight of copper (Cu) was used.

A sample 2c was obtained in the same manner as the sample 1a except that an Al target containing 1% by weight of manganese (Mn) was used.

According to the analysis, an impurity metal was detected in the deposited Al layer at substantially the same concentration as in the target. The three types of samples thus obtained were measured under a solar simulator of AM-1.5 to evaluate the conversion efficiency as a solar cell. Table 2 shows the results. That is, good conversion efficiency was obtained in each case. Next, the surface of each sample was observed with a metallographic microscope at a magnification of 500 times, and no abnormality was observed.

Further, the back reflection layer (the material deposited up to ZnO) used for each sample was left at a temperature of 300 ° C. for 2 hours. A Cr electrode having an area of 1 cm ² was formed on the surface of ZnO, and the resistance was evaluated using a constant current power supply so that a current of 20 mA flowed. In any of the samples, almost no change in resistance was observed before and after heating.

(Experiment 3) A sample 3a was obtained in the same manner as in the back reflection layer of the sample 1a of the experiment 1.

A sample 3b was prepared in the same manner as the sample 3a, except that an Al layer was deposited using a target of pure Al.

After leaving both samples at 300 ° C. for 2 hours, they were immersed in a 30% iron chloride aqueous solution for 5 minutes. The aqueous iron chloride solution is an etchant used for patterning ITO. Although no particular change was observed in sample 3a, ZnO was significantly corroded in sample 3b. From this,
When the back reflection layer of the sample 3a is used, it is expected that even if a thin film semiconductor has a defect such as a pinhole, the thin film semiconductor is unlikely to be damaged in a later process. According to SIMS analysis, Al was diffused into the transparent layer in Sample 3b immediately after the heat treatment.

(Experiment 4) A 5 × 5 cm stainless steel plate (S
US430) by DC magnetron sputtering
Cu layer by using a Cu target containing 10% by weight of
00Å deposited. The substrate temperature at this time was 300 degrees.
According to SEM observation, the surface of Cu has a diameter of 5000-7.
The protruding portions, which appeared to be crystal grains of about 000 °, were dense and cloudy. On top of that, ZnO was deposited at 700 ° by DC magnetron sputtering. The substrate temperature at this time is set to 10
0 degrees. On the back reflection layer thus formed, the substrate temperature is set to 300 ° C. and the SiH
₄ and PH ₃ as source gases to form an n-type a-Si layer of 200
Å, an i-type a-Si layer SiH ₄ as source gases 400
0 °, a 100 μm p-type microcrystalline (μc) Si layer is deposited using SiH ₄ , BF ₃ , and H ₂ as source gases to form a thin film semiconductor junction (a-S by glow discharge decomposition such as SiH _4).
Since i contains about 10% of hydrogen (H), it is generally referred to as a-Si: H, but is simply referred to as a-Si for simplicity in this description.) An 650 ° ITO film was deposited thereon as a transparent electrode by resistance heating evaporation. Further, a current collecting electrode having a width of 300 μm was formed on the silver paste by screen printing to obtain a sample 5a.

Next, a sample 5b was obtained in the same manner as the sample 5a, except that a Cu layer was formed using a Cu target containing 3% by weight of Si.

Next, a sample 5c was obtained in the same manner as the sample 5a, except that a Cu layer was formed using a Cu target containing 0.5% by weight of Si.

Next, a sample 5d was obtained in the same manner as the sample 5a, except that a Cu layer was formed using a pure Cu target.

Next, the substrate temperature during the deposition of Cu is set to room temperature,
The deposition temperature of ZnO is 250 degrees and the thickness of ZnO is 400
A sample 5e was obtained in the same manner as the sample 5b, except that the angle was set to 0 °.

Next, the substrate temperature at the time of Cu deposition was set to room temperature,
The deposition temperature of ZnO is 250 degrees and the thickness of ZnO is 400
A sample 5f was obtained in the same manner as the sample 5d, except that the angle was set to 0 °.

According to the analysis, Si was detected in the deposited Cu layer at substantially the same concentration as in the target.
The five kinds of samples thus obtained were measured under a solar simulator of AM-1.5 to evaluate the conversion efficiency as a solar cell. Table 5 shows the results. That is, the conversion efficiency of the sample 5d is considerably lower than those of the other samples. This is considered to be a decrease in efficiency due to an extremely high series resistance according to a detailed study of solar cell characteristics. Also in sample 5f, it was recognized that the characteristics were deteriorated and a short circuit occurred. Although the sample 1e had the highest efficiency, it is considered that the reflection on this surface was the best because the Cu surface was smooth in this sample.

(Experiment 5) C containing 3% by weight of aluminum
A sample 6a was obtained in the same manner as the sample 1a of the experiment 4, except that the target of u was used.

Sample 6 was prepared in the same manner as Sample 5a of Experiment 4 except that a Cu target containing 3% by weight of zinc (Zn) was used.
b was obtained.

Sample 6c was obtained in the same manner as Sample 5a, except that a Cu target containing 3% by weight of tin (Sn) was used.

Sample 6d was prepared in the same manner as sample 5a except that a Cu target containing 1% by weight of beryllium (Be) was used.
I got

According to the analysis, an impurity metal having substantially the same concentration as in the target was detected in the deposited Cu layer. The four samples thus obtained were measured under an AM-1.5 solar simulator to evaluate the conversion efficiency as a solar cell. Table 6 shows the results. That is, good conversion efficiency was obtained in each case. Next, the surface of each sample was observed with a metallographic microscope at a magnification of 500 times, and no abnormality was observed.

Further, the back reflection layer (the material deposited up to ZnO) used for each sample was left at a temperature of 300 ° C. for 2 hours. A Cr electrode having an area of 1 cm ² was formed on the surface of ZnO, and the resistance was evaluated using a constant current power supply so that a current of 20 mA flowed. In any of the samples, almost no change in resistance was observed before and after heating.

(Experiment 6) The back reflection layer of Sample 5a was replaced with Sample 7
a.

The back reflection layer of Sample 5d was used as Sample 7b.

The back reflection layer of sample 5f was used as sample 7c.

These samples were heat-treated at 300 ° C. for 2 hours. According to SIMS analysis, Sample 7 after heat treatment
In b, Cu was diffused into the transparent layer, and the characteristic of Sample 5d was low in Experiment 4 because the diffusion of Cu caused the resistance of the transparent layer to be too high. When the surface of the sample 5f after the heat treatment was observed with a metallographic microscope at a magnification of 500, it was found that the ZnO layer was partially peeled off. Furthermore, when the ZnO layer of this sample was etched with acetic acid, it was considered that the Cu surface was rough, and the surface shape changed during the heat treatment to cause peeling of the ZnO layer.

(Experiment 7) A DC magnetron sputtering apparatus having two independent targets and having a structure in which a substrate sequentially passes through positions facing the respective targets by rotating a substrate holder was prepared.

One target is pure aluminum,
The other target was an aluminum target containing 6% by weight of Si. Using this apparatus, an Al layer was deposited on a 5 × 5 cm stainless plate. At the beginning of the deposition, pure aluminum was deposited by applying a voltage only to the target of pure aluminum. During the deposition, a voltage was applied to the other target and the power (voltage x current) was gradually increased. Finally, when the power of both targets became equal, the application of the voltage was stopped at the same time, and the deposition of the film was stopped. . The rate of increasing the power of the substrate on which Al was deposited only with the target of pure Al and the rate of increasing the power of the other target were changed, and Al films containing Si were deposited near seven types of surfaces in all. The seven samples thus prepared were analyzed for Si concentration from the surface using a secondary ion mass spectrometer (SIMS). The results are shown in FIG. Where the Si concentration from the surface is the peak value

[0068]

[Outside 1] Depth = 1 was calculated. Next, when the substrate temperature was set to 200 ° C. and ZnO was deposited at 4000 ° C. on each Al layer, the ZnO became an uneven structure and the surface became cloudy. Seven types of solar cells (samples 8a to 8g) were produced on the seven types of substrates thus obtained by glow discharge decomposition in the same manner as in Experiment 1. Table 8 shows the results of measuring these conversion efficiencies.
Up to l = 150 °, the conversion efficiency increased and the effect of Si addition was recognized as l became longer. On the other hand, when l was further increased, the conversion efficiency tended to slightly decrease. This is interpreted as follows. According to actual measurements, a slight decrease in reflectance is observed when Si is added to Al. However, when the addition of Si is limited to the vicinity of the surface, the decrease in reflectance is reduced. On the other hand, if the addition of Si is extremely limited near the surface, the effect of suppressing the diffusion of Al is weakened. After all, l = 50
It is considered that about が 500 ° was optimal.

(Experiment 8) The same DC as used in Experiment 7
In a magnetron sputtering apparatus, using a target of pure Al and an aluminum target containing 6% by weight of Zn, in the same manner as in Experiment 7, containing about 3% of Zn near the surface.
And two different Al layers were deposited. In the same manner, two different types of Al layers containing about 1% Mn were deposited near the surface.

Thereafter, a ZnO layer having a concavo-convex structure was deposited on the four types of Al layers in the same manner as in Experiment 7, and a solar cell was further formed, and its characteristics were evaluated. Table 9 shows the results.
Again, by selecting an appropriate value for l, the conversion efficiency could be maximized.

(Experiment 9) In the same manner as in Experiment 7, a pure Cu layer and six types of copper layers containing Si atoms only near the surface were deposited on a stainless steel plate. A ZnO layer having a concavo-convex structure was deposited thereon, and a solar cell was further formed to evaluate the characteristics. Table 10 shows the results. C as in the case of Al
Also in the case of u, the conversion efficiency could be particularly increased by setting l to about 50 ° to 500 °.

(Experiment 10) In the same manner as in Experiment 9, two different layers of Cu containing pure Cu and Zn only near the surface were deposited on a stainless steel plate. In addition, two different types of Cu layers having different l including Sn were deposited only in the vicinity of the surface. or,
Only two different types of Cu layers containing Be were deposited near the surface. A ZnO layer having a concavo-convex structure was deposited on these, and a solar cell was further formed to evaluate characteristics. Table 11 shows the results. By selecting an appropriate value for l, the conversion efficiency could be maximized.

Next, the back surface anti-reflection layer used in the photovoltaic device of the present invention will be described in detail.

(Substrate and Metal Layer) Various metals are used as the substrate. Among them, stainless steel plate, zinc, steel plate, aluminum plate, copper plate and the like are preferable because of their relatively low price. These metal plates may be cut into a certain shape and used, or may be used in a long sheet-like form depending on the plate thickness. In this case, since it can be wound in a coil shape, it is suitable for continuous production, and storage and transportation are easy. Depending on the application, a crystal substrate such as silicon or a sheet or plate of glass, ceramics, resin or the like may be used. The surface of the substrate may be polished, but may be used as it is when the finish is good, such as a stainless steel plate which has been subjected to bright annealing.

Even a substrate having a low light reflectance such as stainless steel or a zinc steel plate can be used by depositing an aluminum layer having a high reflectance on the substrate. In addition, a material having low conductivity as it is, such as glass or ceramics, can be used as a substrate by providing an aluminum layer or a copper layer.

For deposition of the aluminum layer, a vacuum deposition method using resistance heating or an electron beam, a sputtering method, an ion plating method, a CVD method, a plating method, or the like is used. A case of a sputtering method will be described as an example of a film formation method. FIG. 6 shows an example of a sputtering apparatus. 401
Denotes a deposition chamber, which can be evacuated by an exhaust pump (not shown). A predetermined flow rate of an inert gas such as argon (Ar) is introduced into the inside of the chamber from a gas introduction pipe 402 connected to a gas cylinder (not shown), and the opening of the exhaust valve 403 is adjusted. Pressure. The substrate 404 is fixed to the surface of the anode 406 provided with the heater 405 inside. A cathode electrode 408 having a target 407 fixed on the surface thereof is provided opposite to the anode 406. The target 407 is an aluminum block containing an appropriate concentration of impurities. The cathode electrode is connected to a power supply 409. A high voltage such as radio frequency (RF) or direct current (DC) is applied by a power supply 409 to generate plasma 410 between a cathode and an anode. By the action of this plasma, metal atoms of the target 407 are converted to the substrate 4
04. In a magnetron sputtering apparatus in which a magnet is provided inside the cathode 408 to increase the plasma intensity, the deposition rate can be increased.

An example of the deposition conditions will be described. 6 inch diameter S
An Al target containing 5% of i and having a purity of 99.99% was used. A stainless plate (SUS430) having a surface of 5 cm × 5 cm and a thickness of 1 mm having a polished surface was used as a substrate. The distance between the target substrates was 5 cm. When a pressure of 1.5 mTorr was applied and a DC voltage of 500 V was applied while flowing 10 sccm of Ar, plasma was generated and a current of 2 amps flowed. In this state, discharging was continued for one minute. Substrate temperature
Sample 3 at room temperature, 100 degrees, 200 degrees, and 300 degrees
a, 3b, 3c, and 3d. Table 3 summarizes the appearance of these samples and the results of SEM observation. Obviously, when the temperature is increased, the Al surface changes from a smooth surface to an uneven structure. A similar tendency is observed in other film forming methods.

To add an impurity metal to the Al layer, a desired impurity may be added to an evaporation source or a target,
In particular, in the sputtering method, a small piece of a material containing an impurity may be placed on a target.

For the deposition of the copper layer, a vacuum deposition method using resistance heating or an electron beam, a sputtering method, an ion plating method, a CVD method, a plating method, or the like is used. A case of a sputtering method will be described as an example of a film formation method. FIG. 6 shows an example of a sputtering apparatus. Reference numeral 401 denotes a deposition chamber, which can be evacuated by an exhaust pump (not shown). Inside this, a gas introduction pipe 402 connected to a gas cylinder (not shown) is provided.
As a result, an inert gas such as argon (Ar) is introduced at a predetermined flow rate, the opening of the exhaust valve 403 is adjusted, and the inside of the deposition chamber 401 is set to a predetermined pressure. The substrate 404 is fixed to the surface of the anode 406 provided with the heater 405 inside. A target 4 is provided on the surface facing the anode 406.
A cathode electrode 408 to which the reference numeral 07 is fixed is provided. The target 407 is a copper block containing an appropriate concentration of impurities. The cathode electrode is connected to a power supply 409. A high voltage such as radio frequency (RF) or direct current (DC) is applied by a power supply 409 to generate plasma 410 between a cathode and an anode. The metal atoms of the target 407 are deposited on the substrate 404 by the action of the plasma. In a magnetron sputtering apparatus in which a magnet is provided inside the cathode 408 to increase the plasma intensity, the deposition rate can be increased.

An example of the deposition conditions will be described. 6 inch diameter S
A Cu target containing 5% i and having a purity of 99.99% was used. A stainless plate (SUS430) having a surface of 5 cm × 5 cm and a thickness of 1 mm having a polished surface was used as a substrate. The distance between the target substrates was 5 cm. When a pressure of 1.5 mTorr was applied and a DC voltage of 500 V was applied while flowing 10 sccm of Ar, plasma was generated and a current of 2 amps flowed. In this state, discharging was continued for one minute. Substrate temperature
Sample 7 at room temperature, 100 degrees, 200 degrees, and 300 degrees
a, 7b, 7c and 7d. Table 7 summarizes the appearance of these samples and the results of SEM observation. Obviously, when the temperature is increased, the surface of Cu changes from a smooth surface to an uneven structure. A similar tendency is observed in other film forming methods.

To add an impurity metal to the Cu layer, a desired impurity may be added to the evaporation source or the target. In particular, a small piece of a material containing the impurity may be placed on the target in the sputtering method. .

(Transparent Layer and its Uneven Structure) The transparent layer is made of ZnO, In ₂ O ₃ , SnO ₂ , CdO, C
Oxides such as dSnO ₄ and TiO are often used (however, the composition ratios of the compounds shown here do not always match the actual conditions). In general, the higher the light transmittance of the transparent layer, the better, but it is not necessary to be transparent for light in the wavelength range absorbed by the thin film semiconductor. It is preferable that the transparent layer has a resistance in order to suppress a current caused by a pinhole or the like. On the other hand, the effect of the series resistance loss due to this resistance on the conversion efficiency of the solar cell must be within a negligible range. From such a viewpoint, the range of the resistance per unit area (1 cm ² ) is preferably 10 ^{-6 to} 10 Ω, more preferably 10 ^{-5 to 3} Ω, and most preferably 10 ^{-4 to 1} Ω. The thickness of the transparent layer is preferably as small as possible from the viewpoint of transparency.
0 ° or more is required. In some cases, a higher film thickness is required from the viewpoint of reliability. The uneven structure will be described later in detail.

For deposition of the transparent layer, a vacuum deposition method using resistance heating or an electron beam, a sputtering method, an ion plating method, a CVD method, a spray coating method, or the like is used. A sputtering method will be described as an example of a film formation method.
Also in this case, the sputtering apparatus shown in FIG. 6 can be used. However, in the case of an oxide, there are a case where the oxide itself is used as a target and a case where a metal (Zn, Sn, etc.) target is used. In the latter case, it is necessary to flow oxygen into the deposition chamber simultaneously with Ar (this is called a reactive sputtering method).

An example of the deposition conditions will be described. 5cm x 5cm 1mm thick stainless steel plate with polished surface (SUS43
0) was used as a substrate. 6 inch diameter 99.9% pure Zn
Using O target, distance between target substrates is 5cm
The pressure was 1.5 m while flowing Ar at 10 sccm.
When the voltage was maintained at Torr and a DC voltage was applied, plasma was generated and a current of 1 amp flowed. In this state, discharging was continued for 5 minutes. Substrate temperature, room temperature, 100 degrees, 200 degrees,
Samples 4a, 4b, 4c, and 4d were used instead of 300 degrees.
Table 4 summarizes the appearance of these samples and the results of SEM observation. Increasing the temperature changes the surface morphology of ZnO. In the samples 4c and 4d where turbidity occurred, crater-like concave portions were observed on the surface, and this is considered to be the cause of turbidity (FIG. 7).

As a reason why light trapping occurs due to the uneven structure, when the metal layer has an uneven structure (FIG. 1), scattering of light in the metal layer can be considered. When an uneven structure is adopted (FIG. 2), scattering due to the phase shift of the incident light between the concave portion and the convex portion at the surface of the thin film semiconductor and / or the interface with the transparent layer may be considered. The pitch is preferably about 3000 to 20000 °, more preferably 4000 to 15000 °, or the difference in height is preferably 500 to 20000 °, more preferably 700 to 10000 °. In addition, when the surface of the thin film semiconductor has a concavo-convex structure similar to the surface of the transparent layer, light scattering easily occurs due to the phase difference of light, and the effect of the light trap is high.

[0086]

【Example】

(Example 1) In this example, a pin-type a-Si thin film semiconductor solar cell having the structure shown in the schematic sectional view of FIG. 1 was manufactured. Average thickness of a 5 × 5 cm 1 mm thick stainless steel plate 101 whose surface has been polished with an Al target containing 2% of Si by using the apparatus shown in FIG. Deposited a 4000 ° aluminum layer 102. Then, using a ZnO target, Z at an average thickness of 700 ° at a substrate temperature of 100 ° C.
An nO layer 103 was deposited.

Subsequently, the substrate on which the back reflection layer was formed was set in a commercially available capacitively coupled high-frequency CVD apparatus (CHJ-3030 manufactured by ULVAC, Inc.). Rough evacuation and high vacuum evacuation operations were performed by an evacuation pump through the evacuation pipe of the reaction vessel. At this time, the surface temperature of the substrate becomes 250 ° C.
Controlled by a temperature control mechanism. At the time when the exhaust was sufficiently performed, SiH ₄ , 300 sccm, S
iF ₄ , 4 sccm, PH ₃ / H ₂ (1% H ₂ dilution) 5
5 sccm and H ₂ 40 sccm were introduced, the opening of the throttle valve was adjusted, the internal pressure of the reaction vessel was maintained at 1 Torr, and when the pressure was stabilized, 200 W of power was immediately supplied from the high frequency power supply. The plasma was maintained for 5 minutes. Thereby, the n-type a-Si layer 105 becomes transparent layer 10
3 was formed. After evacuating again, this time, 300 sccm of SiH ₄ and ₄ sccc of SiF ₄
m, 40 sccm of H ₂ were introduced, the opening of the throttle valve was adjusted, and the internal pressure of the reaction vessel was maintained at 1 Torr.
Immediately after the pressure becomes stable,
The power of W was applied and the plasma was maintained for 40 minutes. As a result, the i-type a-Si layer 106 becomes the n-type a-Si layer 105.
Formed on After evacuating again, this time, 50 sccm of SiH ₄ and BF ₃ / H ₂ (1% H ₂
(Dilution) 50 sccm and H ₂ 500 sccm were introduced, and the opening degree of the throttle valve was adjusted to adjust the internal pressure of the reaction vessel to 1
When the pressure was stabilized and the pressure was stabilized, 300 W of power was immediately supplied from the high frequency power supply. Plasma is 2
Lasted for minutes. As a result, a p-type μc-Si layer 107 was formed on the i-type a-Si layer 106. Next, the sample was taken out from the high-frequency CVD apparatus, ITO was deposited by a resistance heating vacuum evaporation apparatus, and then a paste containing an aqueous solution of iron chloride was printed to form a desired pattern of the transparent electrode 108. Further, an Ag paste was screen-printed to form a current collecting electrode 109, thereby completing a thin-film semiconductor solar cell. In this way 10
AM1.5 (100 mW / cm ² )
When the characteristics were evaluated under light irradiation, an excellent conversion efficiency of 8.1 ± 0.3% in photoelectric conversion efficiency was obtained with good reproducibility. Further, these solar cells were allowed to stand for 1000 hours in an environment of a temperature of 50 ° C. and a humidity of 90%.
A decrease of 0.5% was hardly observed.

Example 2 In this example, a pin-type a-SiGe thin film semiconductor solar cell having the structure shown in the schematic sectional view of FIG. 2 was produced. A 5 × 5 cm 1 mm thick stainless steel plate 101 having a polished surface was subjected to an ion plating method at a substrate temperature of room temperature and Al containing 1% by weight of Cu.
And an Al layer having a thickness of 1500 ° and a smooth surface was deposited. Then, Sn was blown again in an oxygen atmosphere at a substrate temperature of 350 ° C. by ion plating,
An SnO ₂ layer having an average thickness of 1 micron and a textured surface was deposited.

For the i layer, 50 scc of Si ₂ H ₆ was used.
m, 10 sccm of GeH ₄ and 300 sccm of H ₂ were introduced, the internal pressure of the reaction vessel was maintained at 1 Torr, and 100 W
Except that a-SiGe deposited by applying power and maintaining plasma for 10 minutes was used in the same manner as in Example 1.
One sample was prepared. AM1.5 (100mW
/ Cm ² ) When the characteristics were evaluated under light irradiation, an excellent conversion efficiency of 8.4 ± 0.4% in photoelectric conversion efficiency was obtained with good reproducibility. In the case of this example, it is considered that the reflection of light on this surface was particularly good because the Al surface was smooth.

(Example 3) Using a device shown in FIG. 8, a back reflection layer was continuously formed. Here, the substrate delivery chamber 603 has a cleaned width of 350 mm, a thickness of 0.2 mm,
A stainless steel sheet roll 601 having a length of 500 m is set. From here, the stainless sheet 602 passes through the metal layer deposition chamber 604 and the transparent layer deposition chamber 605 and is sent to the substrate winding chamber 606. The sheet 602 can be heated to a desired temperature by the substrate heaters 607 and 608 in each deposition chamber. Target 6 of deposition chamber 604
09 is A having a purity of 99.99% (2.0% is Zn).
1, sheet 6 by DC magnetron sputtering
An Al layer is deposited on the substrate 02. The target 610 in the deposition chamber 605 is made of ZnO having a purity of 99.9%, and a ZnO layer is continuously deposited by DC magnetron sputtering. There are two targets 609 in relation to the deposition rate and the desired film thickness.

The back reflection layer was formed using this apparatus. The sheet feeding speed was set to 20 cm / min, and the substrate temperature during Al deposition was adjusted to 250 ° C. using only the substrate heater 607. Ar flow and pressure 1.5 mTorr
r, and a DC voltage of 500 V was applied to each cathode. Currents of 6 amps each flowed through the target 609, and 4 amps flowed through the target 610. Examination of the wound sheet revealed that the average thickness of the Al layer was 3000 °
The average thickness of the nO layer was 800 °, and the surface of the Al layer was cloudy.

Further, a-Si / a- of the structure shown in FIG.
A SiGe tandem solar cell was formed. Here, 701 is a substrate, 702 is an aluminum layer, 703 is a ZnO layer, 7
04 is a bottom cell and 708 is a top cell. Further, 705 and 709 are n-type a-Si layers, and 707 and 711 are p-type a-Si layers.
Type μc-Si, 706 is an i-type a-SiGe layer, and 710 is an i-type a-Si layer. These thin film semiconductor layers may be rolled as described in U.S. Pat. No. 4,492,181.
It was manufactured continuously using a two-roll type film forming apparatus. A transparent electrode 712 is deposited by a sputtering apparatus similar to the apparatus shown in FIG. 713 is a current collecting electrode. After patterning the transparent electrode and forming the current collecting electrode, the sheet 602 was cut. In this way, all the processes were continuously processed, and a mass production effect was obtained.

In this way, 100 samples were prepared, and the AM
When the characteristics were evaluated under irradiation of 1.5 (100 mW / cm ² ) light, an excellent conversion efficiency of 10.4 ± 0.2% in photoelectric conversion efficiency was obtained with good reproducibility. These solar cells were left for 1000 hours in an environment of a temperature of 50 ° C. and a humidity of 90%, but the conversion efficiency was 10.0 ± 0.5%, and almost no deterioration was observed. Another 100 created by this method
When the sheet was irradiated with light equivalent to AM 1.5 for 600 hours in an open state, the deterioration by light was small at 9.8 ± 0.3%. This is because, by adopting a random configuration, light having a longer wavelength is effectively absorbed, and the output voltage can be increased. This is also because deterioration of the thin film semiconductor layer under light irradiation can be reduced. Thus, a highly reliable thin-film solar cell having high conversion efficiency combined with the effect of the back reflection layer of the present invention was obtained.

Example 4 A back reflection layer was formed in the same manner as in Sample 1a of Experiment 1, except that an Al layer containing 2% by weight of Mn was used. On this substrate, the substrate on which the Al layer and the ZnO layer were not deposited, Cu was deposited by 0.2 μm and Indium (In) was deposited by 0.4 μm by sputtering. Next, the sample was transferred to a quartz glass bell jar and heated to 400 ° C., and hydrogen selenide (H ₂ Se) diluted to 10% with hydrogen was passed through the bell jar, and CuInS
A thin film of e ₂ (CIS) was formed. A CdS layer was again deposited thereon by 0.1 μm by a sputtering method and then annealed at 250 ° C. to form a p / n junction. A transparent electrode and a current collecting electrode were formed thereon in the same manner as in Example 1.

This solar cell was manufactured using AM1.5 (100 mW /
cm ² ) Characteristic evaluation was performed under light irradiation.
The solar cell with the Al layer and ZnO layer had an excellent conversion efficiency of 8.9%, while the solar cell without the Al layer and ZnO had an inferior characteristic of 7.3%. It has been found that the invention is also effective for thin film semiconductors other than a-Si.

Example 5 In this example, a pin-type a-Si thin-film semiconductor solar cell having the structure shown in the schematic sectional view of FIG. 1 was produced. 5 × 5cm thickness 1 with polished surface
6 mm on a stainless steel plate 101 mm.
Substrate temperature of 220 using a Cu target with 3%
The average thickness of the surface is 4,000 as a degree
A layer 102 of Cu was deposited. Then, at a substrate temperature of 100 ° C., the average thickness is 700 using a ZnO target.
Ｚｎ ZnO layer 103 was deposited.

Subsequently, the substrate on which the back reflection layer is formed
To a commercially available capacitively coupled high-frequency CVD device (manufactured by ULVAC
CHJ-3030). With the exhaust pump,
Rough evacuation and high vacuum evacuation operations are performed through the exhaust pipe of the reaction vessel.
Was. At this time, the surface temperature of the substrate becomes 250 ° C.
Controlled by a temperature control mechanism. When exhaust has been sufficiently exhausted
From the point of view of the gas introduction pipe,_Four 300sccm, Si
F_Four 4sccm, PH _Three / H_Two (1% H_Two Dilution) 55s
ccm, H_Two Introduce 40sccm, throttle valve
Adjust the degree of opening to maintain the internal pressure of the reaction vessel at 1 Torr
When the pressure stabilizes, immediately 2
The power of 00W was turned on. The plasma lasts for 5 minutes
Was. As a result, the n-type a-Si layer 105 becomes transparent layer 103
Formed on After exhausting again, this time introduce gas
SiH from pipe_Four 300 sccm, SiF_Four 4sccm,
H_Two Introduce 40sccm and adjust the throttle valve opening
Adjust to maintain the internal pressure of the reaction vessel at 1 Torr.
Is stable, 150W from the high frequency power supply immediately
Power was turned on and the plasma was maintained for 40 minutes. to this
Thus, the i-type a-Si layer 106 is formed on the n-type a-Si layer 105.
Been formed. After exhausting again, this time it's a gas introduction pipe
SiH_Four 50sccm, BF_Three / H_Two (1% H_Two Rare
A) 50 sccm, H_Two Introduce 500sccm
Adjust the opening of the throttle valve to adjust the internal pressure of the reaction vessel to 1T.
orr, and when the pressure stabilizes, immediately
300 W of power was supplied from the wave power supply. Plasma is 2 minutes
Lasted for a while. Thereby, the p-type μc-Si layer 107 becomes i
Formed on the mold a-Si layer 106. Next, the sample is
Take out from the CVD device, and I
After depositing TO, print paste containing iron chloride aqueous solution
Then, a desired pattern of the transparent electrode 108 was formed. Further
Ag paste is screen printed to form the collecting electrode 109
Thus, a thin-film semiconductor solar cell was completed. 10 pieces in this way
A sample of AM1.5 (100 mW / cm^Two )light
When the characteristics were evaluated under irradiation, the photoelectric conversion efficiency was
Excellent conversion efficiency of 8.4 ± 0.4% with good reproducibility
Was. In addition, these solar cells are operated at a temperature of 50 degrees and a humidity of 90%.
It was left in the environment for 1000 hours, but the change efficiency was 8.1 ±
Almost no reduction was observed at 0.4%.

Example 6 In this example, a pin-type a-SiGe thin film semiconductor solar cell having the structure shown in the schematic sectional view of FIG. 2 was produced. A 5 × 5 cm 1 mm thick stainless steel plate 101 having a polished surface is coated with Cu containing 1% by weight of Zn at a substrate temperature of room temperature by an ion plating method.
Was formed, and a Cu layer having a thickness of 1500 ° and a smooth surface was deposited. Then, Sn was blown again in an oxygen atmosphere at a substrate temperature of 350 ° C. by ion plating,
S having an average thickness of 1 micron and an uneven surface
An nO ₂ layer was deposited.

For the i-layer, 50 scc of Si ₂ H ₆ was used.
m, 10 sccm of GeH ₄ and 300 sccm of H ₂ were introduced, the internal pressure of the reaction vessel was maintained at 1 Torr, and 100 W
Except that a-SiGe deposited while maintaining the plasma for 10 minutes by applying power was used in the same manner as in Example 5.
One sample was prepared. AM1.5 (100mW
/ Cm ² ) When the characteristics were evaluated under light irradiation, an excellent conversion efficiency of 8 to 9 ± 0.4% in photoelectric conversion efficiency was obtained with good reproducibility. Since the optical band gap of a-SiGe is narrower at about 1.45 eV than the optical band gap of a-Si (about 1.7 eV), the sensitivity to long-wavelength light is high, and the reflectance is high at long wavelengths. The Cu back reflection layer was extremely effective. In addition, it is considered that the reflection of light on this surface was particularly good because the surface of Cu was smooth.

(Example 7) Using the apparatus shown in FIG. 8, a back reflection layer was continuously formed. Here, the substrate delivery chamber 603 has a cleaned width of 350 mm, a thickness of 0.2 mm,
A stainless steel sheet roll 601 having a length of 500 m is set. From here, the stainless sheet 602 passes through the metal layer deposition chamber 604 and the transparent layer deposition chamber 605 and is sent to the substrate winding chamber 606. The sheet 602 can be heated to a desired temperature by the substrate heaters 607 and 608 in each deposition chamber. Target 6 of deposition chamber 604
09 is C having a purity of 99.99% (however, 2.0% is Sn).
u, sheet 6 by DC magnetron sputtering
On top of this, a Cu layer is deposited. The target 610 in the deposition chamber 605 is made of ZnO having a purity of 99.9%, and a ZnO layer is continuously deposited by DC magnetron sputtering. There are two targets 609 in relation to the deposition rate and the desired film thickness.

Using this apparatus, a back reflection layer was formed. The sheet feeding speed was set to 20 cm / min, and the substrate temperature during Cu deposition was adjusted to 220 ° C. using only the substrate heater 607. Ar flow and pressure 1.5 mTorr
r, and a DC voltage of 500 V was applied to each cathode. Currents of 6 amps each flowed through the target 609, and 4 amps flowed through the target 610. Examination of the wound sheet revealed that the average thickness of the Cu layer was 2800 °
The thickness of the nO layer was 800 ° on average, and the surface of the Cu layer was cloudy.

On top of this, a-Si / a- of the structure shown in FIG.
A SiGe tandem solar cell was formed. Here, 701 is a substrate, 702 is a Cu layer, 703 is a ZnO layer, 704 is a bottom cell, and 708 is a top cell. Further 705,
709 is an n-type a-Si layer, 707 and 711 are p-type μc-
Si, 706 is an i-type a-SiGe layer, and 710 is an i-type a-SiGe layer.
It is a Si layer. These thin film semiconductor layers are described in U.S. Pat.
It was manufactured continuously using a roll-to-roll type film forming apparatus as described in 492,181. 712
Is a transparent electrode and was deposited by a sputtering apparatus similar to the apparatus of FIG. 713 is a current collecting electrode. After patterning the transparent electrode and forming the current collecting electrode, the sheet 602
Was cut. In this way, all the processes were continuously processed, and a mass production effect was obtained.

In this way, 100 samples were prepared, and the AM
When the characteristics were evaluated under irradiation of 1.5 (100 mW / cm ² ) light, an excellent conversion efficiency of 10.8 ± 0.3% in photoelectric conversion efficiency was obtained with good reproducibility. Further, these solar cells were left for 1000 hours in an environment of a temperature of 50 ° C. and a humidity of 90%, but the conversion efficiency was 10.6 ± 0.5%, and almost no deterioration was observed. Another 100 created by this method
When the sheet was irradiated with light equivalent to AM 1.5 for 600 hours in an open state, the deterioration due to light was small at 10.0 ± 0.3%. This is because the tandem configuration effectively absorbs light having a longer wavelength, thereby increasing the output voltage. This is also because deterioration of the thin film semiconductor layer under light irradiation can be reduced. Thus, a highly reliable thin-film solar cell having high conversion efficiency combined with the effect of the back reflection layer of the present invention was obtained.

Example 8 A back reflection layer was formed in the same manner as in Sample 4a of Experiment 4 except that a Cu layer containing 2% by weight of Be was used. On this substrate, the substrate on which the Cu layer and the ZnO layer were not deposited, Cu was deposited by 0.2 μm and Indium (In) was deposited by 0.4 μm by sputtering. Next, the sample was transferred to a quartz glass bell jar and heated to 400 ° C., and hydrogen selenide (H ₂ Se) diluted to 10% with hydrogen was passed through the bell jar, and CuInS
A thin film of e ₂ (CIS) was formed. A CdS layer was again deposited thereon by 0.1 μm by a sputtering method and then annealed at 250 ° C. to form a p / n junction. A transparent electrode and a current collecting electrode were formed thereon in the same manner as in Example 5.

This solar cell was manufactured using AM1.5 (100 mW /
cm ² ) When the characteristics were evaluated under light irradiation, Cu
The solar cell with the layer and the ZnO layer had an excellent conversion efficiency of 9.8%, while the solar cell without the Cu layer and ZnO had a poor characteristic of 7.3%. It has been found that the invention is also effective for thin film semiconductors other than a-Si.

[0106]

By using the back reflection layer of the present invention,
Since the light reflectance is increased and the light is effectively confined in the thin-film semiconductor, the absorption of light into the thin-film semiconductor increases, and a photovoltaic device with high conversion efficiency can be obtained. Further, metal atoms are less likely to diffuse into the transparent layer and further into the semiconductor film, and a highly reliable photovoltaic element can be obtained. When the area of the concavo-convex structure or the like is substantially expanded, a more reliable photovoltaic element can be obtained by suppressing the diffusion of metal in particular.
Further, such a back reflection layer can be manufactured as a part of a method having high productivity such as a roll-to-roll method. Thus, the present invention greatly contributes to the spread of photovoltaic power generation.

[0107]

[Table 1]

[0108]

[Table 2]

[0109]

[Table 3]

[0110]

[Table 4]

[0111]

[Table 5]

[0112]

[Table 6]

[0113]

[Table 7]

[0114]

[Table 8]

[0115]

[Table 9]

[0116]

[Table 10]

[0117]

[Table 11]

[Brief description of the drawings]

FIG. 1 is a diagram showing a cross-sectional structure in which a metal layer of a photovoltaic element of the present invention has an uneven structure.

FIG. 2 is a diagram showing a cross-sectional structure of a photovoltaic element of the present invention in which a metal layer is smooth and a transparent layer has an uneven structure.

FIG. 3 shows Zn versus reflectance at the interface between silicon and metal.
The figure which shows the effect of O. (A) In the absence of ZnO, (b) Z
When there is nO.

FIG. 4 is a diagram showing an improvement in spectral sensitivity of a solar cell due to an uneven structure when Al is used as a metal layer.

FIG. 5 is a diagram showing an improvement in spectral sensitivity of a solar cell due to an uneven structure when Cu is used as a metal layer.

FIG. 6 is a view showing a structure of a sputtering apparatus suitable for manufacturing the back reflection layer of the present invention.

FIG. 7 is an SEM photograph of a transparent layer having an uneven structure.

FIG. 8 is a view showing the structure of another sputtering apparatus suitable for producing the back reflection layer of the present invention.

FIG. 9 is a diagram showing a cross-sectional structure of another embodiment of the thin-film semiconductor solar cell of the present invention.

FIG. 10 is a diagram showing a distribution of Si concentration from the surface of a metal layer by a secondary ionic substance analyzer (SIMS).

[Explanation of symbols]

 101, 701 Substrate 102, 702 Metal layer 103, 703 Transparent layer 105, 705, 709 n-type a-Si 106, 710 i-type a-Si 107, 707, 711 p-type μc-Si 108, 712 Transparent electrode 109, 713 Collector electrode 401 Deposition chamber 402 Gas conduit 403 Exhaust valve 404, 602 Substrate 405, 607, 608 Substrate heater 406 Anode 407, 609, 610 Target 408 Cathode electrode 409 Power supply 410 Plasma 603 Substrate delivery chamber 604 Metal layer deposition chamber 605 Transparent Layer deposition chamber 606 Substrate winding chamber 601 Roll of substrate 706 i-type a-SiGe

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-3-99477 (JP, A) JP-A-60-231372 (JP, A) JP-A-62-203369 (JP, A) JP-A-59-1984 150485 (JP, A) JP-A-59-25218 (JP, A) JP-A-3-120820 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01L 31/04

Claims (13)

(57) [Claims] Claims: 1. A small amount of silicon, copper, zinc and manganese.
A metal layer formed of aluminum having one Kutomo, a transparent layer provided on the metal layer, set on the transparent layer
And a semiconductor layer having a vignetting photoelectric conversion, the silicone
At least one of copper, zinc, manganese is transparent
50 ° or more and 500 ° or more from the metal layer surface on the layer side in the film thickness direction.
Below, the concentration is simply 1 / e (e = base of natural logarithm).
A photovoltaic element characterized by a gradual decreasing distribution . 2. The photovoltaic device according to claim 1, wherein said silicon concentration is 0.5 to 10.0% by weight. 3. The photovoltaic device according to claim 1, wherein said copper concentration is 0.5 to 10.0% by weight. 4. The method according to claim 1, wherein the zinc concentration is 0.5 to 10.0% by weight.
The photovoltaic device according to claim 1, wherein 5. The photovoltaic device according to claim 1, wherein said manganese concentration is 0.1 to 2.0% by weight. 6. At least a photovoltaic element according to claim 1, wherein the surface of the transparent layer is characterized by a concave-convex structure. 7. Silicon, aluminum, zinc, tin, bery
A metal layer formed of copper containing at least one of lithium, a transparent layer provided on the metal layer,
And a semiconductor layer having provided photoelectric conversion, the serial
At least one of copper, zinc, manganese,
50 ° or more and 500 °
So that the concentration becomes 1 / e (e = base of natural logarithm) below
A photovoltaic element characterized by a monotonically decreasing distribution . 8. The photovoltaic device according to claim 7, wherein said silicon concentration is 0.5 to 10.0% by weight. 9. The photovoltaic device according to claim 7, wherein said copper concentration is 0.5 to 10.0% by weight. 10. The photovoltaic device according to claim 7, wherein said zinc concentration is 0.5 to 10.0% by weight. 11. The tin concentration is 0.5 to 10.0% by weight.
The photovoltaic device according to claim 7, wherein 12. The beryllium concentration of 0.1 to 2.0.
The photovoltaic device according to claim 7, wherein the content is% by weight. 13. The photovoltaic device according to claim 7, wherein at least the surface of the transparent layer has an uneven structure.