JPH06196738A - Manufacture of solar battery - Google Patents

Abstract

PURPOSE:To increase a reflection efficiency of a rear surface reflection layer to be manufactured, and to improve a conversion efficiency of a solar battery by forming a transparent layer by the sputtering method in which zinc oxide is used in an atmosphere made of at least H2 and an inactive gas. CONSTITUTION:Initially, a metal layer 102 having a high reflection factor is formed on the surface of a conductive substrate 101. A transparent layer 103 having a finely rugged surface is formed on the surface of the metal layer 102. A semiconductor junction 104 is also formed on this transparent layer 103. For example, in the case of a pin-type a-Si solar battery, the semiconductor junction 104 is made up of an n-type a-Si 105, an i-type a-Si 106, and a p-type Si 107. A front surface transparent electrode 108 and a comb-shaped collecting electrode 109 are formed on the semiconductor junction 104. Hence, since the surface of the metal layer 102 is smooth, a reflection factor of light is improved at the metal surface. The surface of the transparent layer 103 has a texture structure, and hence sun light is effectively absorbed by a solar battery, thereby leading to an improved conversion efficiency.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for manufacturing a solar cell,
In particular, the present invention relates to a method of manufacturing a solar cell which has high performance and high reliability and can be mass-produced.

[0002]

2. Description of the Related Art As a future energy source for humanity,
Carbon dioxide generated as a result of its use will be totally dependent on oil and coal, which are said to bring about global warming, and nuclear power, which has no risk of radiation during unexpected accidents and normal operation. Things are problematic. In this respect, the solar cell uses the sun as an energy source and has an extremely small effect on the global environment, and thus is expected to be further popularized. However, at present, there are some problems that prevent its full-scale spread.

Conventionally, single crystal silicon has been often used for solar power generation. However, this type of solar cell requires a large amount of energy and time for crystal growth, and a complicated process is required thereafter, so that it is difficult to increase the mass production effect and it is difficult to provide it at a low price.

On the other hand, amorphous silicon (hereinafter referred to as "a"
-Si ". ), Or CdS / CuInS
So-called thin film semiconductor solar cells using compound semiconductors such as e ₂ have been actively researched and developed. In these solar cells, it suffices to form as many semiconductor layers as necessary on an inexpensive substrate such as glass or stainless steel, the manufacturing process thereof is relatively simple, and there is a possibility of cost reduction. However, this thin-film semiconductor solar cell has not been used in earnest until now because its conversion efficiency is lower than that of crystalline silicon solar cells and there is concern about its reliability for long-term use. Therefore, various measures have been taken in order to improve the performance of the thin film solar cell.

One of them is a back reflection layer for increasing the reflectance of light on the surface of the substrate to return the sunlight not absorbed by the thin film semiconductor layer to the thin film semiconductor layer again and effectively utilize the incident light. . In this case, when sunlight is incident from the substrate side of the transparent substrate, the electrode formed on the surface of the thin film semiconductor is formed of a metal having a high reflectance such as silver (Ag), aluminum (Al), or copper (Cu). Is preferred. When sunlight is incident on the surface of the thin film semiconductor layer, it is preferable to form a similar metal layer on the substrate and then form the semiconductor layer. Further, by interposing a transparent layer having appropriate optical properties between the metal layer and the thin film semiconductor layer, the reflectance can be further enhanced by the multiple interference effect. FIGS. 6 (a) and 6 (b) show the improvement in reflectance with and without zinc oxide (ZnO) as a transparent layer between silicon and various metals (a) and (b). It is the result of the simulation.

The use of such a transparent layer is effective in improving the reliability of the thin film semiconductor solar cell. Further, for example, Japanese Patent Publication No. 60-41878 describes that a semiconductor layer and a metal layer can be prevented from alloying by using a transparent layer. Also, U.S. Pat. Nos. 4,532,372 and 4,59
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 electrodes even if a short circuit portion occurs in the semiconductor layer.

Further, as another device for improving the conversion efficiency of the thin film solar cell, the surface of the solar cell or / and the interface with the back reflection layer is made into fine irregularities (texture structure).
There is a way. With such a configuration, the sunlight is scattered at the front surface of the solar cell or at the interface with the back surface reflection layer,
Furthermore, it is trapped inside the semiconductor (optical trap effect),
It will be effectively absorbed in the semiconductor. When the substrate is transparent, the surface of the transparent electrode such as tin oxide (SnO ₂ ) on the substrate may have a textured structure. When sunlight is incident from the surface of the thin film semiconductor, the surface of the metal layer used for the back surface reflection layer may have a texture structure.
M. Hirasaka, K .; Suzuki, K .; Nak
atani, M .; Asano, M .; Yano, H .; Ok
aniwa has shown that a texture structure for the back reflection layer can be obtained by depositing Al by adjusting the substrate temperature and the deposition rate (Solar Cell Mate).
rials 20 (1990) pp99-11
0). FIG. 7 shows an example of an increase in absorption of incident light due to the use of the back surface reflection layer having such a texture structure. Here, the curve (a) shows the spectral sensitivity when smooth Ag is used as the metal layer, and the curve (b) shows the spectral sensitivity when texture-structured Ag is used.

Furthermore, it is possible to combine the idea of the backside reflecting layer consisting of two layers of a metal layer and a transparent layer with the idea of the texture 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 a texture structure and a transparent layer is formed on the texture structure. It is expected that such a combination will significantly improve the conversion efficiency of the solar cell.

However, according to the findings of the present inventors,
In many cases, the expected results were not actually obtained. Also, depending on the deposition conditions of the thin film semiconductor,
Despite the provision of the transparent layer, the formed solar cell may not have sufficient reliability for use under high temperature and high humidity. For this reason, thin-film semiconductor solar cells have the potential to be produced at low prices, but have not come into widespread use for solar power generation.

[0010]

The present inventors have found that the conventional backside reflecting layer has the following problems. a) Reduction of reflectance due to texture structure of metal layer When the metal layer has a texture structure, light reflected on the surface is diffusely reflected in various directions. But considering this point,
The textured metal layer tends to have a much lower reflectivity than a smooth metal, even when measured using a reflectometer with an integrating sphere that collects light reflected in all directions. . Especially in the case of Al or Cu, this tendency is remarkable. Therefore, the light passing through the thin film semiconductor cannot be effectively reflected and returned to the thin film semiconductor. As a result, the conversion efficiency of the solar cell is not as high as expected. b) Diffusion of metal to the surface of the transparent layer When depositing a thin film semiconductor on the back surface reflection layer, the substrate temperature is usually 200 ° C. or higher. At such a temperature, metal atoms can penetrate the transparent layer and diffuse to the surface of the transparent layer. When the metal directly contacts the thin film semiconductor layer as described above, the function of the transparent layer is insufficient and the reliability may be deteriorated. c) Problems in the post-process Since there are defects such as pinholes in the thin film semiconductor layer,
The electrode on the surface of the thin film semiconductor and the transparent layer may be in direct contact with each other through such a defective portion. If the transparent layer does not have an appropriate resistance, it is impossible to prevent excessive current from flowing in this portion.

Therefore, it is an object of the present invention to provide an improved method of making a backside reflective layer.

[0012]

As a result of studying these problems, the present inventors have come to recall the basic concept of the present invention described below.

FIG. 1 shows an example of a procedure for manufacturing the solar cell according to the present invention. In FIG. 1A, the conductive substrate 1
A metal layer 102 having a high reflectance is formed on the surface of No. 01. Here, when the substrate 101 itself is made of a material having a sufficiently high reflectance, the metal layer 102 may be omitted. Further, at least the surface of the metal layer 102 is formed so as to be smooth. The DC magnetron sputtering apparatus shown in FIG. 2 is formed thereon to form the transparent layer 103 of FIG.

A DC magnetron sputtering method, which is an example of a method of forming the transparent layer 103, will be described with reference to FIG. The deposition chamber 201 can be evacuated by an exhaust pump (not shown). A predetermined flow rate of an inert gas such as H ₂ and argon (Ar) is introduced into the deposition chamber 201 via gas introduction pipes 202a and 202b connected to a gas cylinder (not shown). In addition, the inside of the deposition chamber 201 is set to a predetermined pressure by adjusting the opening of the exhaust valve 203. A substrate 204 having a smooth metal layer on its surface is fixed inside the surface of an anode 206 provided with a heater 205. A target 207 is fixed to the surface of the anode 206 facing the anode 206, and a cathode electrode 208 having a magnet (not shown) is provided inside. The target 207 is zinc oxide having a purity of 99.9%. The cathode electrode 208 is connected to the power source 209. Then, a high voltage of direct current (DC) is applied by the power source 209 to form plasma 210 between the cathode and the anode. It is considered that due to the action in the plasma, zinc hydroxide in which the zinc oxide of the target 207 is bonded to hydrogen and zinc oxide which has not been bonded to hydrogen are deposited on the substrate 204.

The transparent layer 103 thus obtained is transparent to sunlight that has passed through the semiconductor layer and has an appropriate electric resistance, and its surface has a texture structure. Further above this, there is a semiconductor junction 104, as shown in FIG. Here, p is used as the semiconductor junction.
An example using an in-type a-Si solar cell is shown. That is, the semiconductor junction 104 includes the n-type a-Si 105 and the i-type a-Si1.
06, p-type a-Si 107. When the semiconductor junction 104 is thin, the entire semiconductor junction 104 often exhibits a texture structure similar to that of the transparent layer 103, as shown in FIG. A transparent electrode 108 on the surface is provided on the semiconductor junction 104, and a comb-shaped collector electrode 1 is further provided on the transparent electrode 108.
09 are provided.

The semiconductor solar cell manufactured by the above procedure has the following effects. a) Since the surface of the metal layer 102 (or the substrate 101 itself) is smooth, the reflectance of light on the metal surface is increased. Moreover, since the surface of the transparent layer 103 (and the semiconductor junction 104) has a texture structure, an optical trap effect occurs inside the semiconductor junction 104. Therefore, the incident sunlight is effectively absorbed, and the conversion efficiency of the solar cell is improved. b) Since the surface of the metal layer 102 (or the substrate 101 itself) is smooth, the contact area with the transparent layer 103 is reduced, and reactions such as diffusion of metal atoms into the transparent layer 103 are less likely to occur. c) Since the transparent layer 103 has an appropriate resistance, an excessive current does not flow even if a defect occurs in the semiconductor layer.

Generally, the higher the light transmittance of the transparent layer having a fine uneven surface obtained by the method of the present invention, the better. However, for the light in the wavelength range absorbed by the semiconductor,
It need not be transparent. The transparent layer should have resistance in order to suppress the current due to pinholes.
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 range that can be ignored. From this point of view, the range of resistance per unit area (1 cm ²⁾ is preferably 10 ⁻⁶ to 10 Ω, and more preferably 10
^{-5 to 3} Ω, most preferably 10 ^{-4 to 1} Ω.

The thickness of the transparent layer is preferably as thin as possible in terms of transparency, but in order to have a texture structure on the surface,
An average film thickness of 1000 Å or more is required. Further, from the viewpoint of reliability, a film thickness larger than this may be required.

The reason why light is confined by the texture structure is considered to be light scattering in the metal layer when the metal layer itself has a texture structure. When the metal layer is smooth and the transparent layer has a texture structure, scattering may occur due to the phase shift of the incident light between the concave portion and the convex portion at the surface of the semiconductor and / or the interface with the transparent layer. The pitch is preferably 3000 to 20000
About angstrom, more preferably 4000-15
000 angstroms. The height difference is preferably 500 to 20,000 angstroms, more preferably 700 to 10,000 angstroms.
Alternatively, when the surface of the semiconductor has a texture structure similar to that of the transparent layer, light scattering is likely to occur due to the phase difference of light, and the effect of optical trapping is high.

[0020]

The back reflective layer produced according to the present invention has a high reflection efficiency, and by using this, incident sunlight can be effectively utilized, and thus a high conversion efficiency can be obtained. Further, leakage current can be prevented even in direct contact between the semiconductor layer and the metal layer or a defective portion, and thus a highly reliable thin film solar cell can be provided at low cost.

[0021]

EXAMPLES Experiments for showing the effects of the present invention will be described below.

(Experiment 1) 5 × 5 cm stainless steel plate (S
US430) on the Al by DC magnetron sputtering method
Was deposited to 1500 angstroms. The substrate temperature at this time was room temperature. A transparent layer of 5000 angstrom was deposited thereon by a DC magnetron sputtering method using a target of zinc oxide in an atmosphere of H ₂ and Ar gas. The substrate temperature at this time was 150 ° C. In appearance, the surface of Al was smooth and glossy. The surface of the transparent layer has a pitch of 5000-80 according to SEM observation.
Unevenness of about 00 angstrom was observed, and the appearance was cloudy.

On the back reflection layer thus formed, the gloss
-By discharge decomposition method, SiH_Four, PH ₃As source gas
n-type a-Si layer is 200 angstrom, SiH_FourTo
4000 angstrom of i-type a-Si layer as source gas
Dome, SiH_Four, BF₃, H ₂With p-type as a source gas
Deposit 100 Å of crystalline (μc) Si layer
Conductor connection was used. SiH_FourGlow discharge decomposition method such as
A-Si contains about 10% hydrogen (H).
Therefore, it is generally written as a-Si: H, but this description
For simplicity, it is simply referred to as a-Si. Transparent on this
650 an ITO film as a bright electrode by resistance heating vapor deposition
Angstrom deposited. Further on it with silver paste
A collector electrode having a width of 300 μm was formed and used as a sample 1a.

Next, except that H ₂ was not introduced, sample 1a was used.
Sample 1b was obtained in the same manner as in.

A sample 1c was obtained in the same manner as the sample 1a except that the substrate temperature during Al deposition was 300 ° C.

A sample 1d was obtained in the same manner as the sample 1a except that an Al substrate having the same size as the stainless steel substrate and having a polished surface was used and Al was not deposited.

The four types of samples thus obtained were used as AM-1.
It measured under the solar simulator of 5 and evaluated the conversion efficiency as a solar cell. The results are shown in Table 1.

[0028]

[Table 1] The following can be seen from Table 1. a) When the backside reflecting layer having a transparent layer deposited by introducing H ₂ is used, the conversion efficiency is improved in any case as compared with the case where a transparent layer without H ₂ is used. b) The most effective back reflection layer is an Al layer with a smooth surface, and H
_This was the case when a transparent layer deposited by introducing ₂ was used. c) Even if polished Al is used as the substrate, smooth A
The same effect as forming the 1-layer was obtained.

(Experiment 2) In Experiment 1, except that Ag was used instead of Al and the current collecting electrode was not formed, Sample 1 was used.
Sample 2a was obtained in the same manner as a.

A sample 2b was obtained in the same manner as the sample 2a except that the substrate temperature at the time of Ag deposition was 250 degrees instead of room temperature.

In the sample 2a, the surface of Ag was smooth.
However, since the surface of the transparent layer deposited by introducing H ₂ has a texture structure, the entire back surface reflection layer is slightly yellowish and has no gloss. On the other hand, in Sample 2b, the surface of Ag showed a texture structure. Table 2 shows AM of both samples
The measurement result of the conversion efficiency in -1.5 is shown.

[0032]

[Table 2] From Table 2, Sample 2b had a remarkably low conversion efficiency, which was considered to be due to a short circuit due to the current-voltage characteristics.
Further, when both samples were observed by SEM, spot-like defects were observed at various places in the sample 2b, and it was found from the results of Auger analysis that Ag diffused to the surface at these places.

(Experiment 3) A sample 3a was obtained in the same manner as the sample 2a except that O ₂ was introduced at the time of depositing the transparent layer. Sample 3a
The conversion efficiency of AM-1.5 was 10.1%, which was almost the same as that of sample 2a.

(Experiment 4) 5 × 5 cm stainless steel plate (S
US430) and Ag by DC magnetron sputtering method
Was deposited to 1500 angstroms. The substrate temperature at this time was room temperature. A transparent layer of 4000 angstroms was deposited thereon by a DC magnetron sputtering method in an atmosphere of H ₂ and O ₂ and Ar gas using a zinc target. The substrate temperature at this time was 200 ° C.

From the appearance, the surface of Ag was smooth and glossy. According to SEM observation, the surface of the transparent layer was found to have irregularities with a pitch of about 6000 to 10000 angstroms, and was slightly yellowish in appearance and was not glossy.
Sample 4a was obtained on the back reflective layer thus formed in the same manner as in Example 1.

Next, except that H ₂ was not introduced, sample 4a was used.
Sample 4b was obtained in the same manner as in.

Both the samples thus obtained were measured under a solar simulator of AM-1.5 to evaluate the conversion efficiency as a solar cell. The results are shown in Table 3.

[0038]

[Table 3] From Table 3, in the case of using the back reflector layer having a transparent layer deposited by introducing of H ₂ it can be seen that the conversion efficiency is improved as compared with the case of using the transparent layer was not introduced and H _2.

Next, the back surface reflection layer in the semiconductor solar cell manufactured according to 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 before use, or may be used in the form of a long sheet depending on the plate thickness. In the case of a sheet, it can be wound into a coil, which makes it suitable for continuous production and easy to store and transport. Further, depending on the application, a glass or ceramic plate based on crystals such as silicon can be used. Although the surface of the substrate may be polished, it may be used as it is if it has a good finish, such as a bright annealed stainless steel plate.

On a substrate such as stainless steel or zinc steel plate which has a low light reflectance as it is, or on an insulating substrate such as glass, a metal layer having a high reflectance such as silver or aluminum is deposited on the substrate. To use. However, when it is used as the back surface reflection layer, the short wavelength component of the sunlight spectrum is already absorbed by the semiconductor, so that it is sufficient if the reflectance for light of a longer wavelength is higher. . Which wavelength or higher wavelength should have high reflectance depends on the light absorption coefficient and the film thickness of the semiconductor used. For example, in the case of a 4000 nm thick a-Si, this wavelength is about 6000.
It becomes Angstrom, and copper can be used preferably (Fig. 6).
reference). Further, even a material having a low conductivity as it is, such as glass or ceramics, can be used as a substrate by providing a metal layer.

For depositing the metal layer, a resistance heating method, an electron beam vacuum vapor deposition method, a sputtering method, an ion plating method, a CVD method, a plating method, or the like is used. The case of the sputtering method will be described as an example of the film forming method. Figure 3
Shows an example of a sputtering apparatus. The deposition chamber 501 can be evacuated by an exhaust pump (not shown). This deposition chamber 50
A predetermined flow rate of an inert gas such as argon (Ar) is introduced into the inside of 1 through a gas introduction pipe 502 connected to a gas cylinder (not shown), and the opening of an exhaust valve 503 is adjusted to thereby form a deposition chamber. The inside of 501 is set to a predetermined pressure. Board 5
04 is an anode 50 having a heater 505 provided therein
It is fixed on the surface of 6. A cathode electrode 5 facing the anode 506 and having a target 507 fixed on the surface thereof.
08 is provided. The target 507 is a block of a metal to be deposited and is usually a pure metal having a purity of about 99.9% to 99.999%, but a specific impurity may be introduced depending on the case. The cathode electrode 508 is connected to the power source 509. Then, a radio frequency (RF) or direct current (DC) high voltage is applied by the power source 509 to form plasma 510 between the cathode and the anode. By the action of this plasma 510, the target 50
7 metal atoms are deposited on the substrate 504. Further, in a magnetron sputtering apparatus in which a magnet is provided inside the cathode 508 to enhance plasma intensity, the deposition rate can be increased.

An example of deposition conditions will be given below. That is, an Al target having a diameter of 6 inches and a purity of 99.99% was used, and a stainless steel plate (sus430) having a surface of 5 cm × 5 cm and a thickness of 1 mm was used as a substrate. The distance between the target substrates was 5 cm. And Ar 10 scc
The pressure was kept at 1.5 mTorr while flowing m, and the Al target with a diameter of 6 inches and a purity of 99.99% was used.
When a DC voltage of 00V was applied, plasma started and 2
Ampere current flowed. In this state, discharging was continued for 1 minute. The substrate temperature is room temperature, 100 degrees, 200 degrees, 3
Samples 5a, 5b, 5c and 5d were changed to 00 degrees. Table 4 summarizes the appearance of these samples and the results of SEM observation.

[0043]

[Table 4] As is clear from Table 4, it is recognized that the Al surface changes from a smooth surface to a texture structure when the substrate temperature is increased. Similar tendencies are observed in other metals and other film forming methods. (Transparent Layer and Rexture Structure Thereof) A sputtering method, which is a film forming method of a transparent layer having a fine uneven surface, will be described with reference to FIG. However, zinc oxide may be used as the target or a zinc target may be used. In both cases, the amount of power to be input, the flow rate of O _{2 to be} introduced, the pressure of the deposition chamber, etc. are RF or DC as the power source, the presence or absence of a magnet on the back of the target, the strength of the magnetic field when the magnet is installed, or the substrate and the target. There are some differences depending on the distance and so on. However, in general, in the former case, the amount of input power 0.5~5W / cm ² per unit area of the target, preferably 0.5 to 4 W / cm ^2, more preferably 0.7~3W
/ Cm ² . The O ₂ flow rate to be introduced is 0 to 10, preferably 0 to 100 for the inert gas flow rate to be introduced.
5, more preferably 0-2. The pressure in the deposition chamber during film formation is 0.5 to 50 mTorr, preferably 1 to
It is 30 mTorr, more preferably 2 to 20 mTorr.

[0044] Similarly, in the latter case, the amount of input power 1~30W / cm ² per unit area of the target, preferably 1.5~20W / cm ^2, more preferably 2~15W
/ Cm ² . The O ₂ flow rate to be introduced is 1 to 1500, preferably 5 to 1000, and more preferably 10 to 800 with respect to 100 to the introduced inert gas flow rate.
The preferable range of the pressure in the deposition chamber during film formation is the same as in the case where the former target is zinc oxide.

In the case of using either of the targets, the H ₂ flow rate to be introduced is 0.1 to 200, preferably 0.3 to 150, relative to 100 flow rate of the inert gas to be introduced in the former case. More preferably, it is 0.5 to 100. In the latter case, a stable and reproducible transparent layer can be obtained when the O ₂ flow rate is 100 to 200, preferably 0.3 to 150, and more preferably 0.5 to 100. .

Here, the DC magnetron sputtering method is taken as an example. As described above, in FIG.
01 can be evacuated by an exhaust pump (not shown). In addition, an inert gas such as H ₂ and argon (Ar) is introduced into the deposition chamber 201 from gas introduction pipes 202a and 202b connected to a gas cylinder (not shown) at a predetermined flow rate so as to have a desired mixing ratio. The inside of the deposition chamber 201 is set to a predetermined pressure by adjusting the opening degree of the exhaust valve 203. The substrate 204 having a smooth metal layer on its surface is fixed to the surface of an anode 206 having a heater 205 provided therein. Anode 2
Cathode electrode 2 having a target 207 fixed to the surface thereof facing to 06 and having a magnet (not shown) inside thereof.
08 is provided. The cathode electrode is connected to the power source 209. Then, a direct current (DC) is generated by the power source 209.
High voltage is applied and plasma 21 is applied between the cathode and the anode.
Set 0. It is considered that due to the action in the plasma, zinc hydroxide in which the zinc oxide of the target 207 is bound to hydrogen and zinc oxide which has not been bound to hydrogen are deposited on the substrate 204.

Next, an example of deposition conditions will be described. Polished surface 5 cm x 5 cm 1 mm thick stainless steel plate (su
s430) was used as the substrate. Diameter 6 inches Purity 99.9%
With a zinc oxide target of 5 cm, the distance between the target substrates is 5 cm, H ₂ is ₂ sccm, and Ar is 15 sccc.
When the pressure was kept at 3.5 mTorr and a DC voltage was applied while flowing m, plasma stood up and a current of 1 ampere flowed. In this state, discharge was continued for 5 minutes. Then, the substrate temperature was changed to room temperature, 100 ° C., 200 ° C. and 300 ° C. to obtain samples 6a, 6b, 6c and 6d. Table 5 shows the appearance of these samples and the results of SEM observation. When the temperature is raised, the surface morphology of the transparent layer changes.

[0048]

[Table 5] (Embodiment 1) In this embodiment, a pin type a-Si having the structure shown in the schematic sectional view of FIG.
A photovoltaic element was prepared.

That is, the surface is polished 5 × 5 cm and the thickness is 1 m.
2 using a zinc oxide target in the apparatus shown in FIG. 2, a substrate temperature of 180 degrees, and an H ₂ flow rate of ₂ sccc.
m, the flow rate of Ar used as an inert gas is 10 sccm,
The transparent layer 103 having an average thickness of 6000 angstrom was deposited at a pressure of 3.3 mTorr in the deposition chamber and an input power amount of 1.8 W / cm ² per unit area of the target. According to SEM observation, the surface of the transparent layer 103 is 50
Unevenness of about 00 to 9000 angstroms is seen,
It was cloudy in appearance.

Subsequently, the substrate on which the lower electrode was formed was marketed.
Capacitive coupling type high frequency CVD equipment for sale (CH made by ULVAC, Inc.
J-3030). Exhaust pump, reaction volume
Roughing and high vacuuming operations are performed sequentially through the exhaust pipe of the vessel.
It was. At this time, the surface temperature of the substrate becomes 250 ° C.
It was controlled by a temperature control mechanism. When exhaust is sufficient
At the point, SiH_Four300 sccm, Si
F_Four4 sccm, PH ₃/ H₂(1% H₂Dilution) 55
sccm, H₂Introduce 40 sccm, throttle again
Adjust the opening of the valve to adjust the internal pressure of the reaction vessel to 1 Torr.
To a high frequency immediately after the pressure is stabilized.
Power of 200 W was applied from the power source. Plasma for 5 minutes
Lasted.

By the above operation, the n-type a-Si layer 105
Was formed on the transparent layer 103. After exhausting again,
This time, SiH ₄ 300sccm, SiF
Introducing ₄ sccm and 40 sccm of H ₂ and adjusting the opening of the slot valve to adjust the internal pressure of the reaction vessel to 1 Torr.
When the pressure was maintained at r and the pressure was further stabilized, an electric power of 150 W was immediately applied from the high frequency power source, and the plasma was maintained for 40 minutes. As a result, the i-type a-Si layer 106 is n
It was formed on the mold a-Si layer 105.

After exhausting again, this time introducing gas
SiH from tube_Four50 sccm, BF ₃/ H₂(1% rare
Release) 50 sccm, H₂Introduce 500 sccm,
Adjust the opening of the slot valve to reduce the internal pressure of the reaction vessel to 1
Hold at Torr, and when the pressure becomes stable, immediately
Then, a power of 300 W was turned on from the high frequency power source. plasma
Lasted 2 minutes. Thereby, the p-type μc-Si layer 10
7 was formed on the i-type a-Si layer 106.

Next, the sample is taken out from the high frequency CVD apparatus, ITO is deposited by a resistance heating vacuum vapor deposition apparatus, and then a paste containing an aqueous solution of iron chloride is printed to obtain a desired transparent electrode 1.
No. 08 pattern was formed. Further, Ag paste was screen-printed to form a collector electrode 109, and a thin film semiconductor solar cell was completed. 10 samples are made by this method,
When characteristics were evaluated under irradiation with AM1.5 (100 mW / cm ² ) light, excellent conversion efficiency of 9.8 ± 0.2% in photoelectric conversion efficiency was obtained with good reproducibility. In addition, these solar cells should be installed in an environment of temperature of 50 degrees and humidity of 90%.
After being left for a period of time, the conversion efficiency was 9.7 ± 0.5%, which was hardly observed.

Example 2 When depositing a transparent layer, O ₂
Was introduced in the same manner as in Example 1 except that 0.1 sccm was introduced.
Ten samples were prepared. AM1.5 (100
mW / cm ² ) When the characteristics were evaluated under light irradiation,
The photoelectric conversion efficiency was 9.4 ± 0.3%, which was excellent in reproducibility.

(Embodiment 3) In this embodiment, FIG.
The pin type a-SiGe having the configuration shown in the schematic sectional view of FIG.
A photovoltaic element was produced.

That is, the surface is polished 5 × 5 cm and the thickness is 1 m.
A stainless steel plate 101 with a thickness of 1500 is plated by a plating method.
An Ag layer 102 having a smooth angstrom surface was formed. Then, using a DC magnetron sputtering method, using a zinc target, the substrate temperature is 200 ° C., and the H ₂ flow rate is ₂ sccc.
m, O ₂ flow rate 10 sccm, A used as an inert gas
Flow rate of r is 10 sccm, pressure in deposition chamber is 4.0 mTorr
r, input power amount 6.0 W per unit area of target
/ Cm ² , a transparent layer 103 having an average thickness of 5000 angstrom was deposited.

Next, as an i layer, Si ₂ H ₆ of 50 scc is formed.
m, GeH ₄ was introduced at 10 sccmH ₂ at 300 sccm, and the internal pressure of the reaction vessel was maintained at 1 Torr.
Ten samples were prepared in the same manner as in Example 1 except that a-SiGe was used in which a power of 00 W was applied and the plasma was maintained for 10 minutes to be deposited. AM1.5 (1
When the characteristics were evaluated under irradiation with light of 00 mW / cm ² ), excellent conversion efficiency of 8.7 ± 0.3% in photoelectric conversion efficiency was obtained with good reproducibility.

Example 4 A back surface reflection layer was continuously formed using the apparatus shown in FIG. In this apparatus, the substrate delivery chamber 603 has a cleaned stainless sheet roll 6 having a width of 350 mm, a thickness of 0.2 mm and a length of 500 m.
01 is set. From here stainless sheet 6
02 is sent to the substrate winding chamber 606 through the metal layer deposition chamber 604 and the transparent layer deposition chamber 605. Seat 60
No. 2 can be heated to a desired temperature by the substrate heaters 607 and 608 in each deposition chamber. Deposition chamber 60
The target 609 of No. 4 is Al having a purity of 99.99%,
Sheet 602 by DC magnetron sputtering method
Deposit an Al layer on top. The target 610 in the deposition chamber 605 is zinc oxide having a purity of 99.5%, and a transparent layer is subsequently deposited by the DC magnetron sputtering method.
Depending on the deposition rate and the desired film thickness, the target 610 is 4
It consists of pieces.

A back reflection layer was formed using this apparatus. That is, the sheet feeding speed is set to 20 cm / min, and the substrate temperature during the transparent layer deposition is set to 1 by using only the substrate heater 608.
It was adjusted to be 00 degrees. Also, H ₂ / Ar = 3/20
Each gas is flowed so that the pressure becomes 3.0
DC voltage of 500 V was applied to each cathode. A current of 6 amps flowed to the target 709 and a current of 4 amps flowed to the target 710. When the wound sheet was examined, the thickness of the Al layer was 1600 Å, the average thickness of the transparent layer was 3800 Å, and the surface of the transparent layer was cloudy.

On top of this, a-Si / a- of the structure shown in FIG.
A SiGe tandem solar cell was formed. This solar cell has a substrate 701, a metal layer 702, a transparent layer 703,
It is composed of a bottom cell 704 and a top cell 708.
Furthermore, n-type a-Si layers 705 and 709, and p-type μc-Si7
07, 711, i-type a-SiGe layer 706, i-type a-S
It is composed of an i layer 710. These thin film semiconductor layers are
The roll-to-roll type film forming apparatus as described in US Pat. No. 4,492,181 was used for continuous production. The transparent electrode 712 was deposited by a sputtering device similar to the device of FIG. After patterning the transparent electrode 712 and forming the collector electrode 713, the sheet 602 was cut. Since all the processes can be continuously processed in this way, mass production effects can be achieved.

100 samples were prepared by this method, and the AM
When characteristics were evaluated under irradiation with light of 1.5 (100 mW / cm ² ), excellent conversion efficiency of 11.5 ± 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 10.9 ± 0.6%, which showed almost no deterioration.

Another 100 sheets prepared by this method are
When irradiated with light equivalent to AM1.5 for 600 hours in the open state, the deterioration due to the light was small at 10.6 ± 0.4%. This is because by adopting the tandem structure, light having a longer wavelength can be effectively absorbed, and as a result, the output voltage can be made higher, and the deterioration of the semiconductor layer under light irradiation can be reduced. Then, combined with the effect of the back surface reflection layer manufactured by the manufacturing method of the present invention, a solar cell having high conversion efficiency and high reliability was obtained. (Example 5) A back reflection layer was formed in the same manner as in Example 1 except that a Cu plate having a polished surface was used as the substrate.
Cu was deposited by 0.2 μm and indium (In) was deposited by 0.4 μm on the substrate by the sputtering method. Then, the sample was transferred to a quartz glass bell jar, and hydrogen selenide (H ₂ Se) diluted to 10% with hydrogen was poured into the bell jar while heating at 400 ° C.
A thin film of CuInSe ₂ (CIS) was formed. A CdS layer was again deposited thereon to a thickness of 0.1 micron by the sputtering method and then annealed at 250 ° C. to form a p / n junction. Then, a transparent electrode and a current collecting electrode were formed thereon in the same manner as in Example 1.

This solar cell is AM1.5 (100 mW /
cm ² ) When the characteristics are evaluated under light irradiation, excellent conversion efficiency of 9.3% is obtained, and the production method of the present invention is effective for thin film semiconductors other than a-Si. all right.

[0064]

As described above, by using the back surface reflecting layer produced by the present invention, the reflectance of light is increased and the light is effectively confined in the semiconductor. Therefore, absorption of light into the semiconductor is increased, and a solar cell with high conversion efficiency can be obtained.

Further, metal atoms are less likely to diffuse into the semiconductor film, and even if there is a partial short circuit in the semiconductor, the leak current is suppressed by an appropriate electric resistance, so that a highly reliable solar cell can be obtained. .

Further, such a back reflection layer is roll-to-roll.
Since it can be manufactured as a part of a mass-production method such as a roll method, it can be manufactured at low cost and contributes greatly to the spread of solar power generation.

[Brief description of drawings]

FIG. 1 is a sectional view showing a structure of an embodiment of a thin film semiconductor solar cell of the present invention.

FIG. 2 is an explanatory view showing the structure of an example of a sputtering apparatus suitable for manufacturing the back surface reflection layer of the present invention.

FIG. 3 is an explanatory view showing the structure of another example of a sputtering apparatus suitable for producing the back surface reflection layer of the present invention.

FIG. 4 is an explanatory view showing the structure of another example of a sputtering apparatus suitable for producing the back surface reflection layer of the present invention.

FIG. 5 is a cross-sectional view showing the structure of another embodiment of the thin film semiconductor solar cell of the present invention.

FIG. 6 Zn vs. reflectance at the interface between silicon and metal
In the graph showing the effect of O, (a) shows the case where ZnO is absent,
(B) is when ZnO is present.

FIG. 7 is a graph showing an improvement in spectral sensitivity of a solar cell due to a texture structure.

[Explanation of symbols]

 204, 504, 702, 101, 701 Substrate 102, 702 Metal layer 103, 703 Transparent layer 105, 705, 709 n-type a-Si 106, 710 i-type a-Si 706 i-type a-SiGe 107, 707, 711 p Type μc-Si 108,712 Transparent electrode 109,713 Current collecting electrode 604 Metal layer deposition chamber 605 Transparent layer deposition chamber 201,501 Deposition chamber 202a, 202b, 502 Gas inlet pipe 203, 503 Exhaust valve 206, 506 Anode 208, 508 Cathode electrode 601 Substrate roll 207, 507, 609, 610 Target 205, 505, 607, 608 Substrate heating target 209, 509 Power supply 210, 510 Plasma

Claims (3)

[Claims] 1. A semiconductor is formed on a back reflection layer formed by forming a transparent layer having fine irregularities on a substrate at least the surface of which is made of a metal layer having a high reflectance for light, and further thereon. A method of manufacturing a solar cell in which a transparent electrode is formed on the transparent layer, wherein the transparent layer is formed by a sputtering method using zinc oxide as a target in an atmosphere containing at least H ₂ and an inert gas. How to make solar cells. 2. The method for manufacturing a solar cell according to claim 1, wherein O ₂ is contained in the atmosphere. 3. A fine concavo-convex transparent layer is formed on a substrate, at least the surface of which is made of a metal layer having a high reflectance for light, and a semiconductor is formed on the back surface reflecting layer. A method of manufacturing a solar cell in which a transparent electrode is formed on the transparent layer, wherein the transparent layer is formed by a sputtering method using zinc as a target in an atmosphere containing at least H ₂ and O ₂ and an inert gas. The manufacturing method of the solar cell.