JP3270679B2 - Photovoltaic element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a photovoltaic device. More specifically, the present invention relates to a photovoltaic device which has high performance, high reliability for long-term use, and can be mass-produced at low cost.

[0002]

2. Description of the Related Art As a future energy source for humankind,
Oil and coal, which is said to cause global warming due to carbon dioxide generated as a result of its use,
Moreover, it is problematic to rely entirely on nuclear power, which is not without radiation hazard even during normal operation. On the other hand, solar cells, which are one of the photovoltaic elements, are expected to spread because they use sunlight as an energy source and have very little influence on the global environment. However, at present, there are some problems that hinder full-fledged diffusion.

Conventionally, single crystal or polycrystalline silicon has been often used as a material for forming a semiconductor layer which is a power generation layer of a solar cell. However, these solar cells require a large amount of energy and time for crystal growth, 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. In order to solve this problem, so-called thin-film semiconductor solar cells using compounds such as amorphous silicon (hereinafter referred to as a-Si) and CdS.CuInSe ₂ 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 glass or stainless steel, and the manufacturing process is relatively simple.
It has the potential to lower prices. However, thin-film solar cells have not been used in earnest because they have a problem in that their conversion efficiency is lower than that of crystalline silicon solar cells and there is concern about their reliability for long-term use.

[0004] In order to solve the problem of such a thin film solar cell,
In order to improve the performance, the following measures have been taken to increase the conversion efficiency.

The first idea is to increase the reflectivity of light on the surface of the substrate, thereby returning the sunlight not absorbed by the power generation layer made of the thin film semiconductor to the power generation layer again and effectively utilizing the incident light. The use of a back reflection layer that plays the role of Since the short wavelength component of the sunlight spectrum is already absorbed by the power generation layer made of the thin film semiconductor, it is sufficient if the reflectance is higher for light having a longer wavelength. Which wavelength or higher the reflectance should be high depends on the light absorption coefficient and the film thickness of the thin film semiconductor used. When sunlight is incident on the transparent substrate from the substrate side, the electrode formed on the surface of the thin film semiconductor may be formed of a metal having high reflectance such as silver (Ag) or copper (Cu).

FIG. 2 shows the results of examining the reflectivity of each single-layer film made of Ag, Al, Cu and Ni and having a thickness of 200 nm. In the case where sunlight is incident from the surface of the power generation layer made of a thin film semiconductor, it is preferable to form a power generation layer after forming a similar metal layer on a substrate. Further, if a transparent layer having appropriate optical properties is interposed between the metal layer and the power generation layer, the reflectance can be further increased by the multiple interference effect. The use of such a transparent layer is effective in increasing the reliability of the thin-film solar cell. Tokiko Sho 60-41
No. 878 discloses that the use of a transparent layer can prevent alloying between a semiconductor and a metal layer. Nos. 4,532,372 and 4,592.
No. 8,306 describes that by using a transparent layer having an appropriate resistance, it is possible to prevent an excessive current from flowing between the electrodes even if a short circuit occurs in a semiconductor layer.

A second contrivance is to employ a method in which the interface between the front and / or back reflection layers of the solar cell and the power generation layer has a fine uneven structure (texture structure). By adopting such a configuration, sunlight is scattered at the interface between the front surface and / or the back surface reflection layer of the solar cell and the power generation layer,
The sunlight is trapped inside the power generation layer made of a semiconductor (light trapping effect), so that the sunlight is more effectively absorbed in the power generation layer made of a semiconductor. When the substrate is transparent, the surface of a transparent electrode such as tin oxide (SnO ₂ ) on the substrate may be formed into a texture structure. In the case where sunlight enters from the surface of the power generation layer made of a thin film semiconductor, the surface of the metal layer used for the back reflection layer may have a texture structure. Hirasaka et al. Report that by depositing Al by adjusting the substrate temperature and the deposition rate, a texture structure preferable as a back reflection layer can be obtained (M.Hi
rasaka, K. Suzuki, K. Nakatani, M. Asano, M. Yano, HO
kaniwa: Solar Cell Materials 20 (1990) pp99-11
0).

FIG. 3 is a graph showing a state in which the absorption of incident light is increased as a result of employing such a textured back surface reflection layer. FIG. 3A shows the spectral sensitivity of the a-SiGe solar cell when smooth silver is used as the metal layer forming the back reflection layer. FIG. 3B shows the spectral sensitivity when textured silver is used instead of the smooth silver shown in FIG. 3A. In the case of FIG. 3A, the wavelength is 700 nm,
Light near 780 nm and 850 nm is not effectively used in the power generation layer made of the a-SiGe semiconductor. on the other hand,
In the case of FIG. 3B, almost no drop in the conversion efficiency (Q-value) is observed in these wavelength ranges. Therefore, in order to further increase the conversion efficiency, it can be seen that it is effective to use a back reflection layer having a high reflectance for light in these wavelength ranges.

FIG. 2 shows that silver and copper exhibit high reflectance in the entire wavelength range of 700 to 1000 nm required for the thin film semiconductor used in the present invention, whereas aluminum exhibits a wavelength of 80 nm.
It can be seen that it has a local minimum value near 0 nm and that nickel is low in the entire wavelength range. Therefore, the silver and copper described above are:
It is most suitable as a material for forming the metal layer forming the back reflection layer.

[0010] Furthermore, a second contrivance (two layers of a metal layer and a transparent layer) is used.
It is also possible to combine the first idea (the idea of the texture structure) with the idea of the back reflection layer composed of layers. U.S. Pat. No. 4,419,533 discloses the concept of a backside reflective layer in which the surface of a metal layer has a textured structure and a transparent layer is formed thereon. Further, a transparent layer having a texture structure may be formed on a smooth metal layer. With such a combination, the conversion efficiency of the solar cell has been considerably improved.

However, as the metal of the back reflection layer,
The use of silver or copper having particularly excellent reflectivity is extremely advantageous for obtaining a solar cell with high conversion efficiency, but these metals, particularly silver, are known as metals that cause electrochemical migration.

Electrochemical migration (hereinafter referred to as migration) means that a metal such as a foil, a plating, or a paste comes into contact with a highly hygroscopic or highly hydrophilic insulator under a condition where a DC voltage is applied. When used in an environment with high humidity, this is a phenomenon in which the surface or inside of an insulator grows in a dendritic or stain-like manner by electrolysis to form a conductive path. It has been reported that some metals require other conditions. When migration is experimentally generated, for example, silver (Ag), copper (Cu), and lead (Pb) are generated under the condition of distilled water and an electric field (Ag has a particularly high growth rate of dendritic crystals). , Gold (Au), palladium (Pd) and indium (In)
It is known that, for example, the presence of a halogen ion is necessary in aluminum and the like, and aluminum (Al), nickel (Ni), iron (Fe) and the like do not occur under special conditions other than these.

By the way, even in a solar cell which can be used in various environments, a short circuit between the electrodes due to the above-mentioned migration becomes a problem during long-term use. For example,
Consider a case where a solar cell actually used outdoors is exposed to a high-temperature and high-humidity environment. In general, since the output voltage of a solar cell alone is low, a plurality of submodules (modules of the above-described thin-film semiconductor solar cells) are connected in series and used. When such a solar cell is partially covered by fallen leaves or the like, the output current of the submodule in the covered portion is extremely small as compared with the other submodules, and the internal impedance is substantially increased. As a result, the output voltages of the other sub-modules are applied in the reverse direction. That is,
There is a problem that the condition of occurrence of migration, that is, application of high temperature and high humidity and application of reverse bias, is realized, and a short circuit between the electrodes occurs, leading to destruction of the submodule. In the case where Ag or Cu having a high reflectance suitable for the backside reflection layer is used, this is a technical problem to be particularly improved.

As a solution to this problem, a metal having excellent migration resistance, such as Al or Ni, is replaced with Ag or C.
It may be selected instead of u. However, Al and Ni
In the case of using, for example, migration is improved, but there is a problem that the photoelectric conversion efficiency is reduced because the reflectance is lower than that of Ag or Cu.

[0015]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and uses a photovoltaic device having both excellent migration resistance and high photoelectric conversion efficiency by using an improved back reflection layer. An object is to provide a power element.

[0016]

According to the present invention, there is provided a photovoltaic device comprising a substrate, on which at least a metal layer, a transparent layer, a semiconductor layer and a transparent electrode are sequentially laminated.
The metal layer has an aluminum (Al) concentration of 30 to 50.
at%, the balance being copper-aluminum alloy composed of copper (Cu), and the reflectance of the metal layer is 700 to
It is 85% or more with respect to light of 1000 nm.

[0017]

According to the first aspect of the present invention, in a photovoltaic device in which at least a metal layer, a transparent layer, a semiconductor layer, and a transparent electrode are sequentially laminated on a substrate, the metal layer is made of aluminum (Al). Since it is a copper-aluminum alloy having an Al) concentration of 30 to 50 at% and a balance of copper (Cu), migration of Cu is suppressed. As a result, a photovoltaic element that can prevent a short circuit from occurring inside the solar cell when used in a severe environment is obtained. Also,
Since the reflectance of the metal layer is 85% or more with respect to light having a wavelength of 700 to 1000 nm, incident sunlight can be effectively used. As a result, a photovoltaic element having high photoelectric conversion efficiency can be obtained.

In the invention according to claim 2, the metal layer is
Since the film is formed on the substrate held at a temperature of 120 ° C. or lower by a sputtering method which is a film formation method deviating from thermal equilibrium, a decrease in the reflectance of a metal layer due to high-temperature film formation can be prevented, and photoelectric conversion can be prevented. A highly efficient photovoltaic element can be obtained.

In the invention according to claim 3, a pair of comb-shaped electrodes made of the metal layer are arranged on the substrate at intervals of 200 μm, and water drops made of pure water are dropped on the comb-shaped electrodes, and the space between the comb-shaped electrodes is formed. When a voltage of 10 V is applied, the time until a short circuit occurs between the pair of comb-shaped electrodes made of the metal layer due to electrochemical migration is 2 minutes or more. Therefore, the photovoltaic voltage using such a metal layer is used. The element has high reliability for long-term use in a harsh environment of high temperature, high humidity, which is a condition for occurrence of migration, and application of a reverse bias.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Photovoltaic Element) The photovoltaic element according to the present invention includes, for example, the one shown in FIG. FIG.
In the figure, 101 is a substrate. As the substrate, a conductive metal substrate is preferable. When a non-conductive substrate is used, a metal layer is preferably deposited by a vacuum evaporation method, a sputtering method, or the like. 102 is a metal layer made of a Cu-Al alloy, 103 is a transparent layer, and these are collectively called a back reflection layer. The transparent layer 103 is transparent to sunlight passing through the power generation layer made of a semiconductor, has an appropriate electric resistance, and has a texture structure on the surface. Reference numeral 104 denotes a power generation layer that forms a thin film semiconductor junction. FIG.
Shows a single cell structure using one set of nip type a-Si based photovoltaic elements as a thin film semiconductor junction, but a tandem cell in which two or more sets of nip type a-Si based photo semiconductor elements are stacked. A structure or a triple cell structure may be used. The power generation layer 104 includes an n-type a-Si layer 105, an i-type a-Si layer 106, and a p-type a-Si layer 107. When the power generation layer 104 forming the thin film semiconductor junction is thin, the power generation layer 104 often has the same texture structure as the transparent layer 103 as shown in FIG. Power generation layer 1
A transparent electrode 108 and a current collecting electrode 109 are provided on 04.

(Substrate and Metal Layer) As the substrate according to the present invention, various metal plates are used. Among them, stainless steel plates, zinc steel plates, aluminum plates, copper plates, and the like are relatively inexpensive and suitable. 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 glass or ceramic plate 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 subjected to a bright annealing treatment.

The sputtering method, which is an example of a film forming method, was used for depositing the metal layer of the present invention.
A vacuum deposition method using resistance heating or an electron beam, a sputtering method, an ion plating method, a CVD method, or the like is used.

(Transparent layer and its texture structure) As the transparent layer according to the present invention, for example, ZnO and In
Oxides such as ₂ O ₃ , SnO ₂ , CdO, CdSnO ₄ and TiO are frequently used. (However, the composition ratio of the compound shown here does not always match the actual state.) In general, the higher the light transmittance of the transparent layer, the better, but the light in the wavelength range absorbed by the thin film semiconductor is better. Need not be transparent. 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 unit area (1
The range of resistance per cm ² ) is preferably 10 ⁻⁶ to 10
Ω, more preferably 10 ^{-5 to} 3 Ω, most preferably 10 Ω
^{−4 to} 1Ω. The thickness of the transparent layer is preferably as small as possible from the viewpoint of transparency, but an average thickness of 100 nm or more is required for the surface to have a texture structure. In some cases, a higher film thickness is required from the viewpoint of reliability. The texture 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. Also in this case, the sputtering apparatus shown in FIG. 3 can be used. Note that 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, or the like) target is used. In the latter case, A
It is necessary to flow oxygen at the same time as r (called a reactive sputtering method).

The reason why the light confinement occurs is considered to be scattering of light in the metal layer due to the texture of the metal layer. In addition, when the surface of the thin film semiconductor has a texture structure similar to that of the transparent layer, light scattering easily occurs due to the phase difference of light, and the effect of the light trap is high.

In order to control the specific resistance of the transparent layer, an appropriate impurity may be added. As the transparent layer of the present invention, the conductive oxide as described above tends to have a too low specific resistance. Therefore, it is preferable that the impurity be appropriately added to increase the resistance. For example, an appropriate amount of an acceptor-type impurity (for example, Cu for ZnO, Al or the like for SnO ₂ ) is added to a transparent layer made of an n-type semiconductor to make the layer intrinsic and increase resistance. Also, the addition of impurities often increases the chemical resistance. To add an impurity to the transparent film, a desired impurity may be added to an evaporation source or a target. In particular, in a sputtering method, a small piece of a material containing an impurity may be placed on a target.

Hereinafter, experiments performed in the course of completing the present invention will be described in detail.

In all the experiments, the DC magnetron sputtering apparatus shown in FIG. 4 was used for depositing the metal layer. In FIG. 4, reference numeral 401 denotes a deposition chamber, which can be evacuated by an exhaust pump (not shown). Inside this, argon (Ar) is supplied by a gas introduction tube 402 connected to a gas cylinder (not shown).
A predetermined flow rate of inert gas such as is introduced, 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 on the surface of an anode 406 provided with a heater 405 inside. Anode 306
, A cathode electrode 408 having a target 407 fixed thereon is provided. Target 40
7 is a block of metal to be deposited, usually of the order of 99.9 to 99.999% pure. Cathode electrode 408
Is connected to a DC power supply 409, applies a DC high voltage by the power supply 409, and generates a plasma 4 between the anode and the cathode.
Raise 10. The metal atoms of the target 407 are deposited on the substrate 404 by the action of the plasma. Also,
By using a magnetron sputtering apparatus in which a magnet is provided inside the cathode 408 to increase the plasma intensity, the deposition rate can be further increased.

(Experiment 1) In this experiment, the DC shown in FIG.
The metal layer was formed using a magnetron sputtering apparatus while changing the Al concentration in the Cu-Al alloy film. The Al concentration is 15, 30, 45, 5 °, 62, or 85 (at
%).

Hereinafter, description will be given in accordance with an experimental procedure.

(1) On a mirror-polished 5 cm × 5 cm stainless steel plate (SUS304), an Al concentration of 15, 30, 45, 5З, 6 was obtained by DC magnetron sputtering.
2. Deposit 100 nm of 85 at% Cu-Al alloy,
These were designated as samples 1a, 1b, 1c, 1d, 1e, and 1f, respectively.

(2) For comparison, a film made of pure copper or pure aluminum was similarly prepared, and 1 g, 1 g,
h. These samples were 4 nm / sec at room temperature.
, The surface was smooth.

For producing 1 g and 1 h, a target of 99.999% copper or Al was used. Alloy sample 1a has 9
9.999% Al wire was processed into a ring shape and arranged on a Cu target. Samples 1b to 1f are 99.
A 99% copper plate processed into 7 mmφ was prepared on an Al target so as to obtain a desired composition. 1
All samples except g and 1h were analyzed by an X-ray energy dispersive analyzer (XMA) to confirm the composition.

(3) With respect to the above eight kinds of samples, a wavelength of 4
The reflectance with respect to light of 00 to 1200 nm was measured. From the results of FIG. 2, it is known that the reflectance of Al has a minimum value at 800 nm. Therefore, FIG. 5 shows values observed at 800 nm as representative values of the reflectance obtained for each composition.

FIG. 5 shows that the reflectance gradually decreased with the increase in the Al concentration, started to drop sharply at around 50 at%, and showed a minimum at around 60 at%.

Since the refractive index, which is one of the parameters for determining the reflectance, is determined by electron vibration, it is considered that the reflectance is greatly affected by the arrangement of atoms that bind electrons, that is, the crystal structure. Here, Cu-A shown in FIG.
This will be discussed using Binary Alloy Phase Diagrams. The phase diagram shows what phase (crystal structure) appears with respect to temperature in each composition. There is a possibility that the θ phase may appear around the time when the Al concentration at which the reflectance greatly changes exceeds 50 at%. Therefore,
It is considered that the decrease in the reflectance seen in FIG. 5 is related to the θ phase.

(Experiment 2) In this experiment, the substrate temperature was set at 10
0, 120, 140, 160, 200, 300, or 4
At a temperature of 00 ° C., a metal layer made of a Cu—Al alloy was formed.
f and 2 g are different from the sample 1b of the first embodiment. However, the Al concentration showed the high reflectance obtained in Experiment 1 and was 3
The deposition rate was fixed at 0 at%, the deposition rate was fixed at 0.6 nm / sec, and the film thickness was fixed at 900 nm.

The same measurement as in Experiment 1 was performed on these samples, and the results shown in FIG. 7 were obtained. FIG. 7 shows that the reflectance tends to decrease as the substrate temperature increases. In particular, it was determined that the film formation at a temperature of 120 ° C. or lower was preferable, since the amount of decrease increased in a region higher than 120 ° C.

As described above, when the metal layer has a texture structure, light incident on the photovoltaic element can be used more effectively. Generally, in order to deposit a metal layer on a textured structure, film formation may be performed at a high temperature at a low deposition rate. However, the metal layer of the present invention has a low reflectance due to film formation at a high temperature. Therefore, in order to texture the metal layer of the present invention, it is necessary to prepare a texture structure before depositing the metal layer, and to form a film thereon at 120 ° C. or lower.

(Experiment 3) This experiment is characterized in that a comb-shaped electrode mask having a spacing of 200 μm was placed on a 5 cm square alkali-free glass (# 7059) substrate to form a metal layer made of a Cu—Al alloy. Different from the first embodiment.

The Al concentration of the prepared sample was 15, 30,
45, 5 °, 62, or 85 (at%), and the samples were 3a, 3b, 3c, 3d, 3e, and 3f, respectively.
For comparison, samples 3g and 3h of pure Cu and pure Al were similarly prepared. For comparison, a film made of pure copper or pure aluminum was prepared in the same manner, and the films were 3 g and 3 h, respectively.

With respect to these eight kinds of samples,
Pure water droplets were dropped on the electrode gap of 00 μm, a voltage of 10 V was applied, and the growth of dendritic crystals was observed under a microscope. FIG. 8 is a graph in which the vertical axis indicates the time during which the electrodes are short-circuited due to the growth of dendritic crystals, and the horizontal axis indicates the Al concentration in the Cu-Al alloy. From FIG. 8, it was found that as the amount of Al added increased, the time during which the electrodes were short-circuited increased.
It was also found that the frequency of dendritic crystals was reduced. In particular, when the Al concentration exceeded 70 at%, generation of dendritic crystals was not observed.

(Experiment 4) In this experiment, after ZnO was formed as a transparent layer on a metal layer made of a Cu-Al alloy, a power generation layer consisting of a nip junction of a thin film semiconductor, a transparent electrode, and a current collecting electrode were formed. Were sequentially laminated.

Hereinafter, description will be made in accordance with the manufacturing procedure.

(1) The metal layer was a Cu-Al alloy having an Al concentration of 45 at%, the thickness was 100 nm, and the other points were the same as in the first embodiment.

(2) ZnO having a thickness of 1000 nm was deposited as a transparent layer on the metal layer.

(3) On the transparent layer, a thickness of 20 nm is formed by glow discharge decomposition using SiH ₄ and PH ₃ as source gases.
N-type a-Si layer, the thickness of the SiH ₄ as material gas 4
100 nm i-type a-Si layer, 10 nm thick p-type microcrystal (μc) S using SiH ₄ , BF ₃ and H ₂ as source gases
An i layer was sequentially deposited to form a power generation layer.

(4) On the power generation layer, a resistance heating vapor deposition method is used.
An indium tin oxide film (ITO film) having a thickness of 65 nm was deposited to form a transparent electrode.

(5) On the transparent electrode, a current collecting electrode having a width of 300 μm was formed with an Ag paste to form a solar cell.

The sample obtained by the above steps (1) to (5) was designated as sample 4a.

For comparison, a film made of pure copper or pure aluminum was prepared in the same manner, and samples 4b and 4b were formed respectively.
4c.

For these samples, the photocurrent Jsc was measured under a solar simulator of AM-1.5. While sample 4c was 16.5 mA / cm ^2, the sample 4a is a current value as high as 17.3mA / cm ² was obtained.
For sample 4b, the resistance (Rsh) between the substrate and the current collecting electrode was low, and the specified output was not generated.
Could not be measured.

(Experiment 5) In this experiment, the two kinds of samples obtained in Experiment 4, namely 4a and 4c, were exposed to light at a humidity of 85% and an ambient temperature of 85 ° C. at a reverse voltage of 0.85.
V was applied (high-humidity reverse bias test), and the time change of RshDk (Rsh without light) was measured. Sample 4 having a pure copper metal layer which could not be formed into a cell in Experiment 4
Instead of b, a sample 5b having a metal layer of pure silver Ag having similar migration characteristics was prepared and comparatively evaluated.

FIG. 9 shows the time change of RshDk of each sample.
It is a result. RshDk is 10Ωcm ^TwoDrops below
And the open-circuit voltage is no longer generated under low-light conditions.
It turns out that there is a problem in the characteristics and reliability of
I was Therefore, in the high humidity reverse bias test, RshDk ≧
10kΩcm^TwoWas used as a high humidity reverse bias test passing standard.

From FIG. 9, it was found that the RshDk of the sample 5b suddenly dropped at the same time as the measurement was started, and it fell below 10 kΩcm ² . Sample 4c did not drop below 31 kΩcm ² . Sample 4a has a higher R than sample 4c.
Although shDk is reduced, it is significantly improved and 10k
It did not fall below Ωcm ² .

From the above experimental results, it was found that Cu suitable for the reflective layer
It can be said that it is preferable to form the -Al alloy at an Al concentration of 30 to 50 at% and a substrate temperature of 120C or lower.

[0058]

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

Example 1 In this example, an n-type a-Si-based photovoltaic element in which the power generation layer 104 shown in FIG. 1 was formed was manufactured.

Hereinafter, description will be made in accordance with the manufacturing procedure.

(1) A ZnO target was placed on a sample 1d (a metal layer composed of a Cu—Al alloy film (Al concentration = 5 at%) formed on a stainless steel plate (SUS304) 101) prepared in Experiment 1. Substrate temperature using 350
A 1000 nm ZnO layer 103 was deposited at a temperature of 100 ° C. to obtain a substrate 1001 on which a back reflection layer was formed. Here, ZnO
The surface of the layer had a textured structure.

(2) The substrate 1001 manufactured in the above (1)
And a commercially available capacitively coupled high-frequency CVD shown in FIG.
Using a device (CHJ-3030 manufactured by ULVAC, Inc.), a power generation layer 104 forming a thin film semiconductor junction was formed.

(2-1) Substrate 1 on anode 1002
001 was set, the reaction vessel 1004 was roughly evacuated by an exhaust pump 1009 through an exhaust pipe 1008, and then a high vacuum evacuation operation was performed. At this time, the surface temperature of the substrate 1001 is 3
The temperature was controlled by a temperature control mechanism (not shown) to reach 50 ° C.

(2-2) When exhaust is sufficiently performed,
From a gas supply source 1005 via a gas introduction pipe 1006,
SiH ₄ 300 sccm, SiF _{4 4} sccm, PH ₃ /
55 sccm H ₂ (1% H ₂ dilution) and 40 sccm H ₂
Was introduced into the reaction vessel 1004. The opening of the throttle valve 1008 was adjusted to maintain the internal pressure of the reaction vessel 1004 at 1 Torr, and when the pressure was stabilized, 200 W of electric power was immediately supplied from the high frequency power supply. As a result of maintaining the plasma for 5 minutes, n-type a-S
An i layer 105 was formed.

(2-3) After the gas is exhausted again, the gas is supplied from the gas supply source 1005 through the gas introduction pipe 1006,
iH ₄ 300 sccm, SiF _{4 4} sccm and H ₂ 40
The sccm was introduced into the reaction vessel 1004. The opening degree of the throttle valve was adjusted to maintain the internal pressure of the reaction vessel 1004 at 1 Torr, and when the pressure was stabilized, 150 W of electric power was immediately supplied from the high frequency power supply. As a result of maintaining the plasma for 60 minutes, an i-type a-Si layer 106 was formed on the n-type a-Si layer 105.

(2-4) After exhausting again, this time from the gas supply source 1005 through the gas introduction pipe 1006, 50 sccm of SiH ₄ , BF ₃ / H ₂ (1% H ₂ dilution)
50 sccm and 500 sccm of H _{2 were} added to the reaction vessel 10.
04. The opening degree of the throttle valve was adjusted to maintain the internal pressure of the reaction vessel 1004 at 1 Torr.
Was turned on. As a result of sustaining the plasma for 2 minutes,
A p-type μc-Si layer 107 was formed on the i-type a-Si layer 106.

(3) ITO is deposited on the sample formed up to the power generation layer 104 in the above (2) using a resistance heating vacuum evaporation apparatus (not shown), and then a paste containing an aqueous solution of iron chloride is printed. A desired transparent electrode 108 was formed.

(4) An Ag paste was screen-printed on the sample formed up to the transparent electrode 108 in the above (3) to form a current collecting electrode 109, thereby completing a thin film semiconductor solar cell.

[0069] Ten thin-film semiconductor solar cells were manufactured by the method shown in the above-mentioned steps (1) to (4), and AM-1.
The Jsc was measured under 5 light.

As a result, the solar cell according to the present example was 6 times smaller than the solar cell having a metal layer made of pure Al separately manufactured.
% More current was obtained.

Further, as a result of performing a high humidity reverse bias test on ten solar cells according to this example, the RshDk value decreased with time, but did not fall below 10 kΩcm ² .

(Embodiment 2) In this embodiment, a tandem solar cell in which the power generation layer shown in FIG. 12 is of nip type and the i-type semiconductor layer is a-Si / a-SiGe using the apparatus shown in FIG. A battery was formed. As the substrate, a belt-like substrate 1102 made of a stainless sheet was used.

Hereinafter, description will be made in accordance with the manufacturing procedure.

(1) A cleaned strip-shaped substrate 1102 (width 350 mm, thickness 0.2 m) is placed in the substrate delivery chamber 1101.
m, a length of 500 m). The strip-shaped substrate 1102 is moved from the substrate delivery chamber 1103 to the metal layer deposition chambers 1104 and 1107 and the transparent layer deposition chamber 1111.
After that, it was sent to the substrate winding chamber 1113. Strip substrate 1
102 is a substrate heater 1105 in each deposition chamber.
1108 or 1110 to the desired temperature.

(2) In a deposition chamber 1104 in which an Al target 1006 having a purity of 99.99% is installed, an Al layer 1202 having a texture structure is formed on a belt-like substrate 1102 having a substrate temperature of 400 ° C. by magnetron sputtering. Deposited.

(3) In a deposition chamber 1107 in which a Cu—Al alloy target 1109 having a purity of 99.99% is installed, a film thickness of 1 is formed on the Al layer 1202 without heating the substrate.
A 00 nm Cu-Al alloy layer 1203 was deposited by DC magnetron sputtering.

(4) In a deposition chamber 1110 in which a ZnO target 1112 having a purity of 99.99% is installed, C
A 1000 nm thick ZnO layer 1204 was deposited on the u-Al alloy layer 1203 by DC magnetron sputtering.

(5) On the ZnO layer 1204, power generation layers 1205 and 1209 made of the thin film semiconductor shown in FIG.
Was formed. Here, 1205 is a bottom cell, 1209
Is the top cell. Furthermore, 1206 and 1210 are n
Type a-Si layers, 1208 and 1212 are p-type μc-S
i, 1207 is an i-type a-SiGe layer, and 1211 is an i-type a-SiGe layer.
-Si layer.

The power generation layer 120 made of these thin film semiconductors
Nos. 5 and 1209 were continuously manufactured using a roll-to-roll type film forming apparatus as described in U.S. Pat. No. 4,492,181.

(6) The transparent electrode 12 is formed on the power generation layer 1209 by using a sputtering apparatus similar to the apparatus shown in FIG.
13 was formed.

(7) A current collecting electrode 1214 was formed on the transparent electrode 1213.

(8) After patterning the transparent electrode 1213 and forming the current collecting electrode 1214, the belt-like substrate 11
02 was cut.

By using such a continuous thin film forming apparatus, the effect of mass production could be improved.

By the method shown in the above-mentioned steps (1) to (8), 100 thin-film semiconductor solar cells were manufactured and
The Jsc was measured under 1.5 light.

As a result, in comparison with the solar cell having a metal layer made of pure Al which was separately manufactured, the solar cell of the present example obtained an average of 5.4% more current.

Further, as a result of performing a high humidity reverse bias test on ten solar cells according to this example, the RshDk value decreased with time, but did not fall below 10 kΩcm ² .

(Embodiment 3) In this embodiment, a strip-shaped substrate made of a stainless steel sheet having a textured surface is used as the substrate, and the power generation layer is a nip type and the i-type semiconductor layer is a-Si / a-. Example 3 is different from Example 2 in that a triple solar cell of SiGe / a-Si was formed. In the deposition chamber 1104, no Al metal layer was formed.

A metal layer made of a Cu—Al alloy and a transparent layer were deposited using the apparatus shown in FIG. Thereafter, a solar cell was formed using the roll-to-roll apparatus shown in FIG. 13 and under the manufacturing conditions shown in Table 1.

[0089]

[Table 1]

Hereinafter, the manufacturing procedure will be described in detail with reference to Table 1.

(1) Strip-shaped substrate (width 35 cm) 5401
Was set in a load chamber 5010 for introducing a belt-like substrate.
The strip-shaped substrate 5401 is passed through all the deposition chambers and all the gas gates, and the sheet winding jig 5 in the unloading chamber 5150 is used.
Connected to 402.

(2) The inside of each deposition chamber was evacuated to 10 ⁻³ Torr or less using an exhaust device (not shown).

(3) Mixing device 50 for forming a deposited film
24, 5034, 5044, 5054, 5064, 50
74, 5084, 5094, 5104, 5114, 51
24, 5134, and 5144, hydrogen gas was supplied to each deposition chamber.

(4) Each gas gate 5201, 5202,
5203, 5204, 5205, 5206, 5207,
5208, 5209, 5210, 5211, 5212,
At 5213 and 5214, hydrogen gas was supplied to each gas gate from each gate gas supply device. In this example, since the distance between the strip-shaped substrate and the gas gate in the gas gate was 1 mm, the hydrogen gas flowed at 1000 sccm.

(5) The belt-shaped substrate 5401 was heated to a predetermined temperature shown in Table 1 by using the substrate heating heater of each deposition apparatus.

(6) After the substrate temperature was stabilized, the hydrogen gas supplied to each deposition chamber was switched to a predetermined source gas used for deposition in each deposition chamber shown in Table 1.

(7) After switching the source gas, the degree of opening and closing of the exhaust valve of each exhaust device was adjusted to adjust the degree of vacuum of each deposition chamber shown in Table 1.

(8) After the step (7), the belt-like substrate 5
Transport of 401 was started. After the degree of vacuum was stabilized, RF power and MW power for plasma generation shown in Table 1 were supplied to each deposition chamber.

100 thin-film semiconductor solar cells were manufactured by the method shown in the above steps (1) to (8), and
The Jsc was measured under 1.5 light.

As a result, compared to the solar cell having a metal layer made of pure Al, which was separately manufactured, the solar cell of this example obtained an average of 5.7% more current.

As a result of performing a high humidity reverse bias test on the ten solar cells according to this example, the RshDk value decreased with time, but did not fall below 10 kΩcm ² .

[0102]

As described above, according to the present invention,
Since a back reflection layer having high reflectivity and improved migration resistance can be formed, a photovoltaic element having high reliability and high photoelectric conversion efficiency can be obtained. In addition, copper and aluminum, which are materials for the back reflection layer, are inexpensive,
A photovoltaic element that can be mass-produced at low cost is obtained.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a photovoltaic device according to Example 1 of the present invention.

FIG. 2 shows Ag, A studied as a metal layer according to the present invention.
4 is a graph showing the reflectance of an l, Cu or Ni film.

FIG. 3 is a graph showing a result of an increase in incident light absorptivity when a back reflection layer having a texture structure according to the present invention is used.

FIG. 4 shows D used for forming a metal layer according to Experiment 1 of the present invention.
It is a schematic diagram of a C magnetron sputtering apparatus.

FIG. 5 is a graph showing the relationship between the Al content in the Cu—Al alloy film and the reflectance of each sample with respect to light having a wavelength of 800 nm according to Experiment 1 of the present invention.

FIG. 6 is a phase diagram of a Cu—Al alloy according to the present invention.

FIG. 7 is a graph showing the relationship between the temperature of the substrate forming each sample and the reflectance according to Experiment 2 of the present invention.

FIG. 8 is a graph showing the relationship between the time when electrodes were short-circuited due to the growth of dendritic crystals and Cu—Al in each sample according to Experiment 3 of the present invention.
4 is a graph showing a relationship with an Al concentration in an alloy.

FIG. 9 is a graph showing the relationship between RshDk and elapsed time of each sample according to Experiment 5 of the present invention.

FIG. 10 shows a capacitively coupled high-frequency plasma C according to the present invention.
It is a schematic diagram of a VD device.

FIG. 11 is a schematic view of a forming apparatus used for continuously forming a back reflection layer according to the present invention.

FIG. 12 is a schematic sectional view of a tandem solar cell according to Example 2 of the present invention.

FIG. 13 is a schematic view of a roll-to-roll type forming apparatus used for manufacturing a photovoltaic device according to the present invention.

[Explanation of symbols]

101 substrate, 102 metal layer made of Cu-Al alloy, 103 transparent layer, 104 power generation layer forming a thin film semiconductor junction, 105 n-type a-Si layer, 106 i-type a-Si layer, 107 p-type a-Si layer, 108 transparent electrode, 109 current collecting electrode, 401 deposition chamber, 402 gas introduction pipe, 403 exhaust valve, 404 substrate, 405 heater, 406 anode, 407 target, 408 cathode electrode, 409 DC power supply, 410 plasma, 1001 substrate, 1002 anode , 1003 cathode, 1004 reaction vessel, 1005 gas supply source, 1006 gas introduction pipe, 1007 high frequency power supply, 1008 throttle valve, 1009 exhaust device, 1101 substrate delivery chamber, 1102 belt-like substrate, 1103 roll of belt-like substrate 1102, 1104 Al layer Deposition chamber 1105, 1108, 1111 heater, 1106 Al target, 1107 Cu-Al layer deposition chamber, 1109 Cu-Al alloy target, 1110 ZnO layer deposition chamber, 1112 ZnO target, 1113 substrate winding chamber, 1201 strip substrate, 1202 Al Metal layer, 1203 Cu-Al alloy layer, 1204 ZnO layer, 1205 bottom cell, 1206, 1210 n-type a-Si layer, 1207 i-type a-SiGe layer, 1208, 1212 p-type μc-Si, 1209 top cell, 1211 i Type a-Si layer, 1213 Transparent electrode, 1214 Current collecting electrode, 5010 Load chamber for introducing sheet-like substrate, 5020 First n-type layer deposition chamber, 5030 First RF-i layer (n / i) deposition chamber 5050 first MW-i layer deposition chamber, 5050 first RF-i layer (p / i) deposition chamber, 5060 first p-type layer deposition chamber, 5070 second n-type layer deposition chamber, 5080 second RF-i (n / i) deposition chamber, 5090 second MW-i layer deposition chamber, 5100 second RF-i layer (p / i) deposition chamber, 5110 second p-type layer deposition chamber, 5120 third n-type layer deposition chamber, 5130 RF-i layer deposition chamber Chamber, 5140 third p-type layer deposition chamber, 5150 unload chamber, 5011, 5021, 5031, 5041, 5051,
5061, 5071, 5081, 5091, 5101,
5111, 5121, 5131, 5141, 5151
Exhaust pipe, 5012, 5022, 5032, 5052, 5062,
5072, 5082, 5102, 5112, 5122,
5132, 5142, 5152 exhaust pump, 5201, 5202, 5203, 5204, 5205,
5206, 5207, 5208, 5209, 5210,
5211, 5212, 5213, 5214 gas gate, 5301, 5302, 5303, 5304, 5305,
5306, 5307, 5308, 5309, 5310,
5311, 5312, 5313, 5314 Gas supply pipe to gas gate, 5023, 5033, 5053, 5063, 5073,
5083, 5103, 5113, 5123, 5133,
5143 RF supply coaxial cable, 5024, 5034, 5054, 5064, 5074,
5084, 5104, 5114, 5124, 5134,
5144 RF power supply, 5025, 5035, 5045, 5055, 5065,
5075, 5085, 5095, 5105, 5115,
5125, 5135, 5145 source gas supply pipes, 5026, 5036, 5046, 5056, 5066,
5076, 5086, 5096, 5106, 5116,
5126, 5136, 5146 Mixing device, 5042, 5092 Exhaust pump (with diffusion pump), 5043, 5093 MW introduction waveguide, 5044, 5094 MW power supply, 5400 Sheet feeding jig, 5401 Sheet substrate, 5402 Sheet winding jig.

Continuation of front page (56) References JP-A-8-18084 (JP, A) JP-A-7-263729 (JP, A) JP-A-6-204533 (JP, A) JP-A-62-203369 (JP) JP-A-57-103370 (JP, A) JP-A-55-108780 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 31/04-31/078

Claims (3)

(57) [Claims] 1. A method according to claim 1, wherein at least a metal layer, a transparent layer,
In a photovoltaic device in which a semiconductor layer and a transparent electrode are sequentially laminated, the metal layer has an aluminum (Al) concentration of 30 to 50.
at%, the balance being copper-aluminum alloy composed of copper (Cu), and the reflectance of the metal layer is 700 to
A photovoltaic element characterized by being at least 85% with respect to light of 1000 nm. 2. The photovoltaic device according to claim 1, wherein the metal layer is formed on the substrate maintained at a temperature of 120 ° C. or lower by a sputtering method. 3. A pair of comb electrodes made of the metal layer are arranged on the substrate at an interval of 200 μm, a drop of pure water is dropped on the comb electrodes, and a voltage of 10 V is applied between the comb electrodes. 3. The photovoltaic device according to claim 1, wherein the time required for a short circuit between the pair of comb electrodes made of the metal layer by electrochemical migration is 2 minutes or more.