JP2003229587A - Thin film photoelectric conversion element and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the performance of a photoelectric conversion element including a photoconductive conversion unit by improving the interface characteristic between an i-type layer (photoelectric conversion layer) formed with a catalyst CVD method and one conductivity type semiconductor layer. <P>SOLUTION: In the thin film photoconductive conversion element including at least a photoconductive conversion unit wherein a one conductivity type semiconductor layer 3, an active layer 5 and an inverse conductivity type semiconductor layer 6 are sequentially laminated, a diffusion barrier layer 4 which prevents diffusion of a conductivity type determination element to the active layer 5 from the one conductivity type semiconductor layer 3 is formed between the one conductivity type semiconductor layer 3 and the active layer 5. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin film photoelectric conversion element and a manufacturing method thereof, and more particularly to a thin film photoelectric conversion element such as a thin film polycrystalline Si solar cell and an amorphous Si solar cell and a manufacturing method thereof.

[0002]

2. Description of the Related Art Bulk-type crystalline Si solar cells have been put into practical use in the field of solar cells, which are one of photoelectric conversion elements, but the problems of raw material shortages and raw material costs have recently become apparent. It has become apparent. Therefore, it is highly expected that a thin film polycrystalline Si solar cell and an amorphous solar cell that are low in cost and have high conversion efficiency will be put into practical use.

Among these, a central issue is to establish a method for forming a high-quality Si film at a high speed, and the catalytic CVD method has recently received attention as a method for forming this film. Is.

In the catalytic CVD method, a source gas is supplied into a chamber in which a catalyst body (a high melting point metal such as W or Ta) is provided, and the source gas is catalytically decomposed in the catalyst body to deposit a deposition species. It is a kind of film forming method for generating

The catalytic CVD method has features such as a simple apparatus configuration and high gas utilization efficiency, and is capable of high-speed film formation and large-area film formation even when forming a Si film. Further, it has already been proved that a-Si formed by catalytic CVD has a low hydrogen content and a low defect density as compared with a-Si formed by a plasma CVD method or the like.

However, in a pin-structured amorphous Si single cell, after the p-type or n-type amorphous Si layer is formed, the i-type amorphous Si layer (active layer) is applied to the catalyst C.
When a photoelectric conversion unit is manufactured by a method of forming by VD method and further forming an n-type or p-type amorphous Si layer, sufficient diffusion potential is not generated in this unit, resulting in deterioration of device characteristics. There was a problem of doing.

[0007]

As a result of earnest research, the inventors of the present invention have found that when a film is formed by the catalytic CVD method, a large amount of atomic hydrogen is present in the vapor phase, which causes etching conditions, and therefore the lower layer. It has been found that the one-conductivity-type semiconductor layer is damaged by etching, and impurity atoms such as the conductivity-type determinants released into the gas phase by the etching of the one-conductivity-type semiconductor layer are taken in when the i-type layer is formed. It was

Therefore, the thin film photoelectric conversion device according to claim 1 is
A thin-film photoelectric conversion device including at least one photoelectric conversion unit in which a one-conductivity type semiconductor layer, an active layer, and a reverse-conductivity type semiconductor layer are sequentially stacked, wherein the one-conductivity type semiconductor layer and the one-conductivity type are provided between the one-conductivity type semiconductor layer and the active layer. A diffusion barrier layer for preventing diffusion of the conductivity type determining element from the semiconductor layer to the active layer is provided.

At this time, it is preferable that the diffusion barrier layer is made of SiC in terms of light transmission and short-circuit current value, and it is further preferable that the SiC is substantially intrinsic non-single-crystal SiC.

From the viewpoint of throughput, it is desirable that both the diffusion barrier layer and the active layer are made of an amorphous Si layer. From the viewpoint of defect density and photostability, it is preferable that the content of hydrogen in the film of the diffusion barrier layer is 6 to 15 atom%. The thickness of the diffusion barrier layer is 20 to 100.
It is desirable that the thickness of the active layer be 100 to 700 nm.

Further, in order to form a sufficient internal electric field and mainly improve the open circuit voltage and fill factor, the conductivity type determining elements of the one conductivity type semiconductor layer are Al, B, P, Ga and A.
s, and the content concentration is 1 × 1
It is preferably 0 ¹⁸ cm ⁻³ or more.

Further, in the method of manufacturing a thin film photoelectric conversion element according to an eighth aspect, at least one photoelectric conversion unit in which one conductive type semiconductor layer, an active layer and an opposite conductive type semiconductor layer are sequentially laminated is provided.
In the method for manufacturing a thin film photoelectric conversion element including the above, the diffusion barrier layer is formed on the one conductivity type semiconductor layer, and then the active layer is formed by a catalytic CVD method.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below by taking a thin film amorphous Si solar cell as an example.

In FIG. 1, 1 is a substrate, 2 is an oxide layer,
Reference numeral 3 is a one conductivity type semiconductor layer, 4 is a diffusion barrier layer, 5 is an active layer, 6 is an opposite conductivity type semiconductor layer, 7 is an oxide layer, 8 is an electrode layer, and 9 is an extraction electrode.

In the thin film photoelectric conversion element shown in FIG. 1, an oxide layer 2 containing at least one of In, Sn and Zn and a p-type or n-type amorphous Si or SiC layer is formed on a glass substrate 1. From one conductivity type semiconductor layer 3, diffusion barrier layer 4 made of substantially intrinsic amorphous SiC, active layer 5 made of substantially intrinsic amorphous Si, n-type or p-type non-single-crystal Si layer The opposite conductivity type semiconductor 6, the oxide layer 7 containing at least one of In, Sn or Zn, and the metal film made of at least one of Ti, Ni, W, Mo, Cu, Ag or Al, or nitriding thereof. The electrode layer 8 is formed of a film or its silicide film. The extraction electrode 9 is formed on the upper surface of the oxide layer 2.
Of these, one photoelectric conversion unit is formed by the one conductivity type semiconductor layer 3, the diffusion barrier layer 4, the active layer 5, and the opposite conductivity type semiconductor 6.

Here, "substantially intrinsic" means a film characteristic that the film is formed under non-doping or very small amount doping conditions and the Fermi level exists near the middle of the band gap.

In manufacturing such a thin film photoelectric conversion element, first, p-type or n-type amorphous Si or S is formed on a glass substrate 1 on which an oxide layer 2 having an uneven structure is formed.
The one-conductivity-type semiconductor layer 3 made of the iC layer is formed by a vacuum film forming method such as a CVD method so as to have a film thickness of about 5 to 50 nm. At this time, the doping concentration of the conductivity determining element of the one conductivity type semiconductor layer 3 formed of the p-type or n-type amorphous Si or SiC layer is set to 1 × 10 ¹⁸ cm ⁻³ or more to increase the diffusion potential difference. The device characteristics can be improved.

The conductivity determining element of the one conductivity type semiconductor layer is preferably any one of Al, B, P, Ga and As. The reason for this is that among the group III or V elements, the solid solubility in Si is relatively high.

Next, a diffusion barrier made of substantially intrinsic amorphous SiC is also formed on the one conductive semiconductor layer 3 made of p-type or n-type amorphous Si or SiC by a vacuum film forming method such as the CVD method. The layer 4 is formed to have a film thickness of about 20 to 30 nm. Since the diffusion barrier layer 4 has a large binding energy between Si and C, it has a good etching resistance against etching species mainly composed of atomic hydrogen, and is made of p-type or n-type amorphous Si or SiC. It has a function of suppressing mutual diffusion of impurities (conductivity determining elements) between the one conductivity type semiconductor layer 3 and the active layer 5 made of substantially intrinsic amorphous Si. In addition, p-type or n-type amorphous Si
Alternatively, it also has an effect of alleviating the discontinuity of the band gap between the one-conductivity-type semiconductor layer 3 made of SiC and the active layer 5 made of substantially intrinsic amorphous Si.

Furthermore, since the diffusion barrier layer 4 made of amorphous SiC has a wide gap material of SiC and has high light transmittance, the so-called window layer can greatly improve the short-circuit current value.

Amorphous SiC among SiC is suitable for the diffusion barrier layer 4 because it is relatively easy to manufacture and has high etching resistance against atomic hydrogen. Among them, the substantially intrinsic one is preferable because the SiC contains almost no impurities, and thus a good electric field junction can be formed at the same interface.

Next, the active layer 5 made of substantially intrinsic amorphous Si is formed by the catalytic CVD method so as to have a film thickness of about 0.3 to 0.5 μm.

For example, as a source gas, SiH ₄ / H ₂ = 30
/ 15 sccm, substrate temperature 340 ° C. to 350 ° C., W
(Tungsten) catalyst body temperature is 1600 to 1800 ° C.,
The distance between the catalyst body and the substrate is 4 to 6 cm, and the film forming pressure is 0.5 to
It is about 5 Pa.

The amorphous Si layer obtained under the above conditions has a low spin density of about 1 × 10 ¹⁸ cm ^-3 and a low defect density, and the amount of hydrogen in the film is relatively small at around 4%. The deposition rate is 2 nm / sec or more, and high-speed film formation is easy.

Next, n is formed on the active layer 5 made of amorphous Si.
A reverse conductivity type semiconductor layer 6 made of non-single-crystal Si of p-type or p-type is formed by a vacuum film forming method such as a CVD method so as to have a film thickness of about 5 to 100 nm.

Further, an oxide layer 7 such as ITO or ZnO is formed on the reverse conductivity type semiconductor 6 made of non-single crystal Si by a sputtering method or a MOCVD method, and then an electrode layer 8 made of a metal such as Ag or Al. Are formed by a sputtering method or a vapor deposition method.

Finally, the extraction electrode 9 made of a metal such as Ag or Al is formed on the oxide layer 2.

FIG. 2 shows the light characteristics of the amorphous Si solar cell element manufactured by the above method, and B (boron) in the depth direction is shown.
The concentration measurement results are shown in FIG. For comparison, FIG. 4 shows the light characteristics of the element in which the diffusion barrier layer 4 made of the amorphous SiC layer is not formed, and FIG. 5 shows the measurement result of the B (boron) concentration in the depth direction. The B (boron) concentration in the depth direction is measured by SIMS (secondary ion mass spectrometry: Se).
conductivity Ion Mass Spectros
copy) device.

As shown in FIGS. 2 and 4, in the conventional thin film photoelectric conversion element, the short-circuit current (J _ph ) is 7 mA / cm ^2.
While the open circuit voltage (V) was 0.5 V, it is substantially intrinsic to the one conductivity type semiconductor layer 3 made of a p-type or n-type amorphous Si or SiC layer as in the present invention. Amorphous S
The semiconductor amorphous SiC layer 4 is formed between the i-layer and the active layer 5.
, The short-circuit current (J _ph ) is 15 mA / cm ²
Then, it is found that the open current (V) becomes 0.68 V and the device characteristics are dramatically improved.

Further, as shown in FIGS. 3 and 5, in the conventional thin film photoelectric conversion element, B is diffused from the underlayer to the active layer at the p-i junction existing at a depth of about 0.3 μm. Is observed, and the B concentration is 1 × 10 ¹⁸ cm in the active layer.
^It is a very high concentration of ^-3 . For this reason, a sufficient diffusion potential difference is not obtained at the p-i junction, which deteriorates the device characteristics. On the other hand, in the thin film photoelectric conversion element of the present invention, the B concentration profile at the pi junction existing at a depth of about 0.2 μm changes sharply, and a good junction is formed. From the above, amorphous SiC
It was demonstrated that the layer has a diffusion barrier effect on the conductivity determining element (boron).

The one conductivity type semiconductor layer 3 is formed on the catalyst CV.
It may be formed by the D method. In that case, it is desirable to provide a thin film layer having excellent reduction resistance between the oxide layer 2 and the one conductivity type semiconductor layer 3. For example, the thin film layer may be Zn
O or the like may be formed by sputtering.

Further, the diffusion barrier layer 4 may be made of amorphous Si formed by a plasma CVD method in addition to the above-mentioned SiC. In this case, the diffusion barrier layer 4 has a function of preventing diffusion of the conductivity type determining element and also has photoactivity. In the present invention,
Even if the diffusion barrier layer 4 has photoactivity, it is not the active layer but the diffusion barrier layer 4 that has the function of preventing the diffusion of the conductivity type determining element.

Below, the diffusion barrier layer 4 is plasma C
An embodiment in the case of using amorphous Si formed by the VD method will be described.

A substantially intrinsic amorphous Si layer is formed on the one conductivity type semiconductor layer 3 by a plasma CVD method, preferably with a thickness of 20 to 100 nm, and a diffusion barrier layer 4 is provided. Subsequently, another amorphous Si layer is formed by a catalytic CVD method, preferably with a thickness of 100 to 700 nm, and the active layer 5 is provided. When both the diffusion barrier layer 4 and the active layer 5 are made of amorphous Si as described above, high throughput can be realized because the manufacturing gas is the same and only the film forming method is changed.

In this embodiment, when the diffusion barrier layer 4 made of amorphous Si is formed by the plasma CVD method,
In the plasma CVD method, the atomic hydrogen density in the gas phase is low,
The etching action is also weak. Therefore, when providing the diffusion barrier layer 4, it is difficult to diffuse the conductivity determining element of the one conductivity type semiconductor layer 3. In addition, the diffusion barrier layer 4 is etched by itself when the active layer 5 is provided by the catalytic CVD method, but prevents diffusion of the conductivity determining element of the one conductivity type semiconductor layer 3.

At this time, the thickness of the diffusion barrier layer 4 is 2
If it is less than 0 nm, the diffusion preventing effect may be insufficient, and if it exceeds 100 nm, photodeterioration in the diffusion barrier layer 4 may be large, resulting in a decrease in device efficiency after stabilization. There is. On the other hand, the thickness of the active layer 5 is 1
If it is less than 00 nm, light absorption in the active layer becomes insufficient, and the short-circuit current value may decrease. On the other hand, 700n
If it is more than m, the resistance value of the active layer 5 increases, so that the characteristics such as fill factor may deteriorate.

In order to make the diffusion barrier layer 4 and the active layer 5 made of amorphous Si have low defect density and high photostability, the amount of hydrogen in the diffusion barrier layer 4 is 6 to 15 atomic%. It is preferable that the amount of hydrogen in the film of the active layer 5 be 1 to 5 atom%. If it is less than each range, the defect density may increase, and if it exceeds each range, the photostability may decrease.

Next, other materials for the diffusion barrier layer 4 and / or the active layer 5 include amorphous SiGe and β.
There are -FeSi _2, but not limited thereto. The diffusion barrier layer 4 can be made of any material as long as it prevents diffusion of the conductivity type determining element.

In the above example, the superstrate type element using glass as the substrate has been described, but it may be a substrate type element using a SUS substrate or the like, or a tandem structure element in which a plurality of photoelectric conversion units are laminated. The same effect can be obtained when applied.

[0040]

As described above, according to the invention of claim 1, the diffusion of the conductivity determining element from the one conductivity type semiconductor layer to the active layer is performed between the one conductivity type semiconductor layer and the active layer. By providing the diffusion barrier layer for preventing the above, favorable electric field junction formation can be realized, and the device characteristics are improved.

According to the second aspect of the present invention, since the diffusion barrier layer is made of SiC which is a wide gap material, the light transmittance and the short circuit current value can be further improved.

According to the third aspect of the present invention, since the SiC is substantially non-single crystalline SiC, the diffusion barrier layer contains almost no impurities. The current value can be further improved.

Further, according to the invention of claim 4, since both the diffusion barrier layer and the active layer are made of amorphous Si, the gas forming process is changed by using the same gas when these layers are provided. Therefore, high throughput can be achieved.

Further, according to the invention of claim 5, in the thin film photoelectric conversion element of claim 4, since the hydrogen content in the film of the diffusion barrier layer is 6 to 15 atom%, the diffusion barrier layer has It is possible to suppress the defect density to a low level and maintain a high light stability.

Further, according to the invention of claim 6, in the thin film photoelectric conversion element of claim 4, the diffusion barrier layer has a film thickness of 20 to 100 nm, so that the diffusion preventing effect is sufficient. In addition, the light stability can be maintained high, and the thickness of the active layer can be 100 to
Since the thickness is 700 nm, it is possible to suppress a decrease in the short-circuit current value, and it is possible to suppress the resistance value of the active layer to be low and prevent the characteristics such as the fill factor from being deteriorated.

According to the invention of claim 7, the conductivity determining element of the one conductivity type semiconductor layer is Al, B, P or G.
Since it is either a or As and its content concentration is set to a high concentration of 1 × 10 ¹⁸ cm ⁻³ or more, a sufficient internal electric field is formed, and mainly the open-circuit voltage and fill factor are improved. be able to.

Further, in the method of manufacturing a thin film photoelectric conversion element according to the present invention, the thin film photoelectric conversion element includes at least one photoelectric conversion unit in which one conductive type semiconductor layer, an active layer and an opposite conductive type semiconductor layer are sequentially stacked. Forming a diffusion barrier layer on the one conductivity type semiconductor layer to prevent diffusion of a conductivity type determining element from the one conductivity type semiconductor layer to the active layer, and then forming the active layer by a catalytic CVD method. As a result, excellent electric field junction formation is realized, and the device characteristics are improved.

[Brief description of drawings]

FIG. 1 is a schematic view showing an embodiment of a thin film photoelectric conversion element according to the present invention.

FIG. 2 is a diagram showing light characteristics of a thin film photoelectric conversion element according to the present invention.

FIG. 3 is a SIMS (Secondary Ion Mass Sp) of boron concentration of the thin film photoelectric conversion device according to the present invention.
It is a figure which shows the analysis result.

FIG. 4 is a diagram showing a light characteristic of a conventional thin film photoelectric conversion element.

FIG. 5: SIM of boron concentration in a conventional thin film photoelectric conversion element
It is a figure which shows S analysis result.

[Explanation of symbols]

1 substrate 2 Oxide layer 3 One conductivity type semiconductor layer 4 Diffusion barrier layer 5 Active layer 6 Reverse conductivity type semiconductor layer 7 Oxide layer 8 electrode layers 9 Extraction electrode

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Hideki Shirama             6 at 1166 Haseno, Jamizo-cho, Yokaichi-shi, Shiga               Kyocera Corporation Shiga Yokaichi Factory (72) Inventor Hirofumi Senda             6 at 1166 Haseno, Jamizo-cho, Yokaichi-shi, Shiga               Kyocera Corporation Shiga Yokaichi Factory (72) Inventor Hideki Matsumura             93, 43, Minami, 43, Kanazawa, Ishikawa Prefecture (72) Inventor Jun Masuda             1 of 2-56 Mamagai, Kanazawa, Ishikawa Prefecture (72) Inventor Makoto Konagai             3- 3-3, Higashiyaguchi, Ota-ku, Tokyo             801 F term (reference) 5F051 AA05 CA05 CA14 CA34 CB15                       DA04 FA02 FA19 GA03

Claims (8)

[Claims] 1. A thin-film photoelectric conversion device including at least one photoelectric conversion unit in which a semiconductor layer of one conductivity type, an active layer, and a semiconductor layer of opposite conductivity type are sequentially stacked, and between the semiconductor layer of one conductivity type and the active layer. A thin film photoelectric conversion element, further comprising a diffusion barrier layer for preventing diffusion of a conductivity type determining element from the one conductivity type semiconductor layer to the active layer. 2. The thin film photoelectric conversion element according to claim 1, wherein the diffusion barrier layer is made of SiC. 3. The non-single crystal S in which the SiC is substantially intrinsic
The thin film photoelectric conversion element according to claim 2, wherein the thin film photoelectric conversion element is iC. 4. The thin film photoelectric conversion element according to claim 1, wherein both the diffusion barrier layer and the active layer are made of amorphous Si. 5. The hydrogen content in the film of the diffusion barrier layer is 6 to 6.
The thin film photoelectric conversion element according to claim 4, wherein the content is 15 atomic%. 6. The film thickness of the diffusion barrier layer is 20 to 100.
5. The thin film photoelectric conversion element according to claim 4, wherein the thickness of the active layer is 100 to 700 nm. 7. The conductivity determining element of the one conductivity type semiconductor layer is any one of Al, B, P, Ga and As, and the content concentration thereof is 1 × 10 ¹⁸ cm ⁻³ or more. 7. The thin film photoelectric conversion element according to claim 1, wherein 8. A method of manufacturing a thin film photoelectric conversion element, comprising at least one photoelectric conversion unit in which a semiconductor layer of one conductivity type, an active layer, and a semiconductor layer of opposite conductivity type are sequentially stacked, wherein the semiconductor layer is formed on the one conductivity type semiconductor layer. A method for manufacturing a thin film photoelectric conversion element, comprising forming a diffusion barrier layer for preventing diffusion of a conductivity type determining element from one conductivity type semiconductor layer to the active layer, and then forming the active layer by a catalytic CVD method. .