JPH065764B2 - Method for manufacturing amorphous silicon solar cell - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an amorphous silicon solar cell and a method for manufacturing the same,
In particular, it relates to a highly efficient solar cell having a novel amorphous silicon layer obtained by glow discharge decomposition of a compound represented by SinH _{2n + 2} (where n ≧ 2) and a method for producing the same.

Amorphous silicon obtained by glow discharge decomposition of hydride of silicon has a small localized level density in its band gap, and thus it is well known that valence electrons can be controlled. It is possible to form a semiconductor device by glow discharge decomposition of a compound represented by SinH _{2n + 2} (where n ≧ 2).
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The target amorphous silicon film is obtained by glow discharge decomposition at a relatively low pressure of rr or less.

However, since increasing the pressure leads to reducing the performance of the semiconductor device, it is obvious that the semiconductor device can be manufactured at higher speed by increasing the pressure, but a method to achieve this was not found. To be understood.

The inventors of the present invention have made intensive investigations on the above-mentioned difficult problems for the purpose of high-speed production and high efficiency of solar cells, and as a result, have solved this problem, and therefore disclose the technique thereof.

An object of the present invention is to provide a highly efficient solar cell obtained from a compound represented by SinH _{2n + 2} (where n ≧ 2) as a raw material, and a method for producing the same.

Another object of the present invention is to provide a high-speed amorphous silicon film forming technique that enables mass production of solar cells, that is, an efficient production process.

Another object of the present invention is to provide a high quality amorphous silicon film,
That is, it is to provide an amorphous silicon film having a small localized level density in the band gap and an amorphous silicon film in which the Fermi level is located substantially in the center of the band gap.

Another object of the present invention is to provide an amorphous silicon film capable of compensating for defects in the i-type amorphous silicon layer with a very small amount of P-type dopant.

Another object of the present invention is to efficiently form an amorphous silicon layer formed of a compound represented by SinH _{2n + 2} (where n ≧ 2) efficiently.
The purpose of the present invention is to provide a technique for doping a conductivity type of n-type or n-type.

Still another object of the present invention is to provide a method for producing a P-i, n-i junction with a compound represented by SinH _{2n + 2} (where n ≧ 2).

The above-mentioned object of the present invention is to form a P-type amorphous silicon layer by glow discharge of a compound represented by SinH _{2n + 2} (where n ≧ 2) and a substance exhibiting a P-type conductivity type. forming an i-type amorphous silicon layer by glow discharge mixed 3ppm or less relative to the compound represented by sinh a material exhibiting conductivity type _{2n + 2} (where _{n ≧ 2), sinH 2n +} 2 ( where n ≧ 2 )
A method for manufacturing an amorphous silicon solar cell manufactured by a step of forming an n-type amorphous silicon layer by glow discharge of a compound represented by the formula and a material having an n-type conductivity, and including similar steps The amorphous silicon solar cell of the present invention is manufactured by the method.

In the present invention, either a chemically synthesized substance as a compound represented by SinH _{2n + 2} (where n ≧ 2) or a physically synthesized substance such as a silent discharge of monosilane can be effectively used. However, from the viewpoint of industrial production of solar cells, a chemically synthesized substance that can be obtained in large quantities and with stable quality is practically convenient. Further, in order to improve the efficiency of the solar cell, the raw material is preferably highly pure, and in this respect, the preferable raw material in the present invention is 2 in the compound represented by the general formula SinH _{2n + 2} (where n ≧ 2). ≦ n ≦ 5, particularly preferably n =
The second substance, disilane. It does not matter in the present invention that 3 ≦ n ≦ 5 of the substance is mixed in disilane, and hence the mixture is referred to as disilane hereinafter.

However, the content of monosilane is usually 30% by volume or less, preferably 10% by volume or less. If the content of monosilane exceeds 30% by volume, the object of the present invention is no longer achieved. Of course, the presence of a large amount of monosilane lowers the high-speed film forming property, but a further disadvantage is that it is difficult to control the amount of hydrogen in the amorphous silicon film, which influences the performance of the film as a semiconductor device. . That is, it has been confirmed by experiments that disilane forms an amorphous silicon film containing a larger amount of hydrogen than monosilane at the same decomposition temperature. Therefore, the content of hydrogen changes depending on the content of monosilane, and eventually the photoelectric conversion efficiency of the solar cell is lowered. Also in this respect, it can be easily understood that the present invention is a technique different from the conventional glow discharge decomposition of monosilane.

In the present invention, in the step of forming an i-type amorphous silicon layer, a substance exhibiting a P-type conductivity is mixed with disilane in an amount of 3 ppm or less to perform glow discharge to form an i-type amorphous silicon layer. It The i-type amorphous silicon layer formed by disilane seems to have essentially fewer defects,
A substance showing P-type conductivity is added in a very small amount of 3 ppm or less, preferably 0.05 to 3 ppm, more preferably 0.1 to 1 pp.
The addition of m is sufficient. For example, as in Example 1, by introducing a small amount of 0.25 × 10 ⁻⁶ volume of diborane to 1 volume of disilane, defects in the i-type amorphous silicon layer are compensated, and a highly efficient solar cell is obtained.

Further, in the present invention, it is preferable that the amorphous silicon layer is formed in the presence of entrained gas. Conventionally, when a monosilane gas was used as a raw material, an entrained gas was not necessarily required, and it was rather preferable to use 100% pure monosilane. However, when forming an amorphous silicon layer with disilane, it is preferable to carry out in the presence of an entrained gas. In the present invention, the accompanying gas also means a carrier gas, and specifically, hydrogen or helium is used as the accompanying gas. Good results are obtained when the amount of the accompanying gas used is 1 to 1,000 volumes with respect to 1 volume of disilane. One of the advantages of using the entrained gas is that the formation rate of the amorphous silicon layer can be easily controlled. However, another notable advantage is that the amorphous silicon layer is protected against harmful impurities. Appears to be insensitive, and is highly practical because a highly efficient solar cell can be stably obtained. Another advantage is that a stable glow discharge region can be formed only with the accompanying gas. The film formation rate with disilane is very high. As a concrete example,
When manufacturing a pin structure amorphous silicon solar cell, P
The formation of the n-type or n-type amorphous silicon layer is completed within about 20 seconds. Therefore, after inserting the substrate into the reaction chamber to form a P-type or n-type amorphous silicon layer, the matching of the Goro discharge is performed by the entrained gas first, and then the disilane and P
A substance exhibiting conductivity type or n-type conductivity can be introduced. This advantage arises from the properties of disilane,
It can be seen that the characteristics of conventional monosilane are completely different. When forming an amorphous silicon layer in a continuous process, an accompanying gas or an accompanying gas and P
The substrate can be inserted into the glow discharge region of disilane that optionally contains a substance exhibiting a conductivity type or an n-type conductivity without breaking discharge. Also at this time, after inserting the substrate under the discharge of the accompanying gas, by introducing disilane,
The disilane loss can be reduced resulting in economic benefits.

As described above, the process problem caused by the high-speed film forming property of disilane can be solved by using an entrained gas in the batch process. However, this problem is alleviated in the continuous process as described above.
That is, it is shown that the process for producing an amorphous silicon solar cell using disilane is more suitable for a continuous process than a batch process, and at this time, the use of entrained gas has an economic effect.

As described above, the amorphous silicon solar cell using disilane as a raw material and the method for manufacturing the same are significantly superior to those using monosilane as a raw material.

Next, an embodiment of the present invention will be described. The manufacturing process of the present invention proceeds in one or a plurality of reaction chambers equipped with glow discharge equipment, raw material gas introduction equipment, vacuum exhaust equipment, substrate heating equipment and, if necessary, a vacuum preliminary chamber for substrate insertion, removal, or transfer. To be Using hydrogen or helium as an entrained gas, disilane and _a substance having a P-type conductivity of Group IIIa are introduced into the reaction chamber, the vacuum exhaust amount is adjusted, and the reaction chamber pressure is adjusted to 0.
It is controlled to 1 to 5 torr, and DC or RF power of 1 to 100 W is applied to perform glow discharge.

For III _a group substance having a P-type conductivity, such as disilane and B ₂ H ₆ as described above is, of course be capable of introducing them into the glow discharge by carrier gas after insertion of the substrate into the reaction chamber .

Then, the substrate on which the first electrode heated to 250 to 400 ° C was formed was transferred to the reaction chamber in the vacuum prechamber with no entrained gas of 0.1 to 5 torr without breaking the glow discharge of the reaction chamber. To be done. A P-type amorphous silicon layer is formed within about 20 seconds. There is no particular limitation on the substrate that can be used in the present invention. Then, a substance having a P-type conductivity is added to the reaction chamber at a volume ratio of 3 ppm or less with respect to disilane to introduce into the reaction chamber to form an i-type (intrinsic) amorphous silicon layer. The formation of the i-type amorphous silicon layer is completed within about 6 minutes. Next, PH _{3, A s} H V _a group materials and disilane shows n-type conductivity such as ₃ was introduced into the reaction chamber, the n-type amorphous silicon layer is formed. The formation of the n-type amorphous silicon layer is completed within about 20 seconds like the P-type amorphous silicon layer. Next, the second electrode is formed to obtain the solar cell of the present invention.

The material used for the first or second electrode in the present invention is an electrode material useful for an amorphous silicon solar cell, such as aluminum, molybdenum, chromium, ITO (indium tin oxide), a thin film of tin oxide, or stainless steel, It is a thin plate of molybdenum.

As described above, the present invention is extremely useful as a novel photoelectric energy conversion device and is a useful manufacturing method.

Hereinafter, the present invention will be described more specifically with reference to Examples.

Example 1 A parallel plate electrode type RF capacitive coupling type reaction chamber provided with a vacuum preliminary chamber having a substrate heating means was used. From raw gas introduction equipment
The raw material gas was introduced at a volume ratio of B ₂ H ₆ / Si ₂ H ₆ /He=0.1/10/90. The evacuation amount of the vacuum evacuation system was adjusted to maintain the reaction chamber pressure at 1 torr. On the other hand, insert a glass substrate with ITO film into the vacuum preliminary chamber and heat it to 350 ° C in He zero atmosphere.
The pressure was reduced to 1 torr. Glow discharge was started by applying 8W power from 13.56MHz RF power supply. When discharge matching was obtained, the substrate was transferred from the preliminary chamber to the reaction chamber, and a P-type amorphous silicon layer was deposited on the ITO film for 20 seconds. Then B ₂
H ₆ / Si ₂ H ₆ /He=2.5×10 ^-6 / 10/10/90 The source gas is switched to the source gas described above, glow discharge is performed for 5 minutes, and an i-type amorphous silicon layer is deposited and formed. did. Next, in the same manner, the raw material having a capacity ratio of PH ₃ / Si ₂ H ₆ /He=0.05/10/90 was switched to, and glow discharge was continued for 20 seconds to deposit and form an n-type amorphous silicon layer. Then, an ITO film was formed on the n-type amorphous silicon layer by an electron beam vapor deposition method to form a second electrode. Lead wires for extracting photoelectric output were connected to the first and second electrodes. A schematic diagram of the amorphous silicon solar cell thus obtained is shown in FIG. In this solar cell, when the AMI light is irradiated by the solar simulator, the incident direction of the light is 10 in FIG.
In any of the 20 directions, the fill factor was 0.6 or more and the photoelectric conversion efficiency was 6% or more in the irradiation area of 2 mm square. FIG. 2 illustrates a photoelectric conversion characteristic diagram of the solar cell obtained by this method.

Example 2 B ₂ as a source gas when forming i-type amorphous silicon
Using _{H 6 / Si 2 H 6 /He=2.5×10} -6 / 10 / Instead of using 90 of the gas _{B 2 H 6 / Si 2 H} 6 /He=0.5×10 -6 / 10/90 gas Then, a solar cell was formed in the same manner as in Example 1. The fill factor was 0.6 to 0.66, and the photoelectric conversion efficiency was good at 6.3%.

Comparative Example 1 B ₂ as a source gas when forming i-type amorphous silicon
The same experiment as in Example 2 was performed except that the gas source gas of H ₆ / Si ₂ H ₆ / He = 2 × 10 ⁻⁴ / 10/90 (B ₂ H ₆ 20 ppm relative to disilane) was used. Phil Fatter is 0.45-0.50,
The photoelectric conversion efficiency was only 3.6%, which was very low.

Comparative Example 2 The same experiment as in Example 1 was performed except that the p-type amorphous silicon layer was formed by using monosilane (SiH ₄ ) instead of disilane (Si ₂ H ₆ ) in Example 1. . The obtained solar cell had a low open-end voltage, a large fill factor of 0.45, and a low photoelectric conversion efficiency of 4.3%. In Example 1,
Considering that the fill factor is 0.6 or more and the photoelectric conversion efficiency is 6% or more, only the monosilane is used in place of disilane to form the p-type amorphous silicon layer, and the obtained solar cell is obtained. It has become clear that the fill factor and photoelectric conversion efficiency drop as much as expected, and it ends up. That is, it has been shown that monosilane and disilane are similar materials that cannot be treated equivalently as raw materials for forming this amorphous silicon solar cell.

Comparative Example 3 Example 1 was repeated except that in Example 1, the amount of diborane added to disilane when forming the i-type amorphous silicon layer was changed to 10 ppm instead of 0.25 ppm per disilane.
The same experiment was performed. The fill factor is 0.42
Then, the photoelectric conversion efficiency dropped to 4.0%. Thus, when diborane is added in an amount more than the specified amount of disilane, the defects in the i layer are not compensated,
On the contrary, it seems that new defects will occur.

[Brief description of drawings]

FIG. 1 shows a schematic vertical sectional view of an amorphous silicon solar cell of the present invention. FIG. 2 is a photoelectric conversion characteristic diagram of the amorphous silicon solar cell of the present invention. In the drawing, 1 ... Substrate, 2 ... First electrode, 3 ...
P-type amorphous silicon layer, 4 ... i-type amorphous silicon layer,
5 ... n-type amorphous silicon layer, 6 ... second electrode, 7 ...
… Output terminal, 10, 20 …… Incident light, 30 …… Maximum power

Claims (1)

[Claims] 1. A step of forming a p-type amorphous silicon layer by glow discharge of disilane, an entrained gas, and a substance having a p-type conductivity type, and a substance having a p-type conductivity type with respect to disilane.
Forming an i-type amorphous silicon layer by glow discharge of disilane and entrained gas mixed with 05 to 0.25 ppm, n-type amorphous silicon layer by glow discharge of disilane, entrained gas and a substance showing n-type conductivity To form an amorphous silicon layer using essentially only disilane as a raw material.
A method for producing a pin-type amorphous silicon solar cell having a photoelectric conversion efficiency of 6% or more and 6% or more.