JPH0612836B2 - Method for manufacturing photoelectric conversion element - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for manufacturing an amorphous silicon (hereinafter abbreviated as a-Si: H) photoelectric conversion element, and particularly to high efficiency and high speed manufacturing thereof.

[Prior art and its problems]

The photoelectric conversion element, especially the improvement of the efficiency of the amorphous silicon solar cell, has been studied and the results have been achieved, but the improvement of the efficiency has only just begun under the high-speed film forming conditions. That is, high efficiency has not been achieved under the high-speed manufacturing conditions such that the formation rate of the photoactive layer is 20Å / S.

The present inventors have previously disclosed a method for producing an amorphous silicon solar cell using disilane (Si ₂ H ₆ ) as a raw material in order to achieve high speed and high efficiency. That is, it has been disclosed that when disilane is used as a raw material, it is essential to decompose the disilane under the condition that energy exceeding a certain threshold is supplied.

However, it is difficult to control the semiconductor junction interface because disilane has a high film-forming property. This is because this interface has a thickness of 1000 Å or less at most, and when a film is formed at a high speed of 20 Å / S, it must be controlled in a short time of only 50 seconds or less. The present inventors have tried to form this interface with monosilane or to reduce the discharge power to slow the film formation rate, but have not yet obtained sufficient results.

The inventors of the present invention thus create an interface with monosilane and transfer it to disilane, and using disilane to reduce the discharge power to slow down the film deposition rate, even if it is a region of several 100 Å of the interface. It was found to be unfavorable. This is because, in these cases, the short-circuit current is significantly reduced in these cases, and the fill factor (FF) is also reduced.

[Object of the Invention]

An object of the present invention is to provide a method for producing a photoelectric conversion element having high photoelectric conversion efficiency that does not cause a decrease in short circuit current or a decrease in fill factor even under high-speed film forming conditions.

[Disclosure of Invention]

Since the present inventors do not like to use disilane and monosilane in combination, it is possible to study the production of the photoactive layer using only disilane and reduce the deposition rate while providing the required energy to form the interface without degrading the film quality. Focusing attention, the present invention has been completed.

That is, according to the present invention, a first conductive layer, a photoactive layer and a second conductive layer are sequentially formed on a substrate having an electrode by glow discharge decomposition of silicon hydride, and a second electrode is provided. In the method for producing a photoelectric conversion element, at least the photoactive layer is formed by disilane, and the formation rate of the active layer thin film per unit mass of the disilane is mainly dependent on the flow rate of disilane and is substantially dependent on the applied energy amount. Energy is always applied over a minimum energy amount (hereinafter, referred to as a threshold value) that is not affected by, and at least the initial region of the formation of the photoactive layer is at a lower speed and the rest is at a higher speed. Provided is a method for manufacturing a photoelectric conversion element, which is characterized in that the deposition rate is continuously changed.

The present invention will be described in detail below.

The disilane used in the process of the present invention has a monosilane content of less than 10 vol%, preferably less than 5%, more preferably less than 1%, even more preferably less than 0.1%, most preferably almost 0%. The fill factor (FF) of solar cells rapidly deteriorates with increasing monosilane content.

In the method of the present invention, the "threshold value" means the minimum amount of energy per unit mass of disilane that does not substantially affect the rate of formation of the active layer thin film and the amount of applied energy. Although defined, more specifically, as disclosed by the present inventors in Japanese Patent Application No. 58-1726, the a-Si: H film formation rate changes depending on the high frequency power used for glow discharge. It is the glow discharge power value at which it becomes impossible to do so. That is, at glow discharge power exceeding the threshold value, the formation rate is governed by the raw material gas flow rate, so by reducing the raw material gas flow rate,
It can reduce the deposition rate. By using this method, even when forming an a-Si: H film using disilane, the volume velocity can be lowered without lowering the film quality, so that the control of the impurity distribution at the interface and the different film quality can be achieved. The formation of interfaces can be avoided.

On the other hand, the above problems cannot be solved by the method using SiH ₄ or the method using Si ₂ H ₆ to reduce the electric power and the flow rate.

In the present invention, the threshold is the supplied energy (Supplied ene
It is convenient to express it as rgy).

The method of calculating the supplied energy is as follows.

The unit of film forming conditions used in the formula [I] is RF power (W) and raw material gas flow rate (standard state flow rate per minute ≡SCCM).
It is a coefficient represented by 44 ≡ 60 (min) 22.4 (/ mol). For example, when disilane 30SCCM and helium gas 270SCCM for dilution, average molecular weight = (30 x 62.2 + 270 x
4) /300=9.82, Then, when RF power (glow discharge power) = 100 W, it is substituted into the formula [I]. To get The threshold value is as defined above. Specifically, for example, in the case of disilane, it is 50 KJ / g-Si.
₂ H _6, when helium dilution 10% disilane least 10 KJ / g-S
i ₂ H ₆ , hydrogen diluted 10% disilane 30KJ / g-Si
_It becomes like ₂ H ₆ .

In the method of the present invention, the formation of the photoactive layer is performed by disilane, and necessary energy above the threshold value for disilane is always applied, and particularly at least the initial region (interface region) of the formation of the photoactive layer is in the range above the threshold value. At a lower speed, the deposition rate is continuously changed so that the remaining most area becomes higher speed.

Here, the interface region means an initial stage of formation of a photoactive layer (for example, a P-i junction interface) or an end point of formation (for example, i-n).
The film thickness part within 1000 Å from the bonding interface), more preferably
It refers to the film thickness portion of 50 to 500Å. In the method of the present invention, the interface region of the photoactive layer must be formed at a deposition rate of 10Å / S or less. If it exceeds 10Å / S, it becomes difficult to control the concentration distribution of cormorant impurities in the depth direction in the region, and the performance of the solar cell deteriorates. In the method of the present invention, the interface region of the photoactive layer is provided with energy below the threshold value as described above, the deposition rate is low at 10 Å / S or less, and the remaining part corresponding to most of the photoactive layer is 20 Å / S. It deposits at a high speed that exceeds

In this case, the deposition rate must be changed continuously. The change of the deposition rate is performed while supplying the supplied energy above the threshold value. Here, the continuous change means a change that is not discontinuous, and the discontinuous change means a change that does not allow the change in the RF power to follow the change in the flow rate so as to satisfy the specified energy supply condition. If the deposition rate is changed abruptly in a discontinuous manner, the solar cell characteristics will deteriorate.

As a practically convenient method, there is a method in which an increase in RF power precedes an increase in flow rate. As long as this method is used, the supplied energy does not fall below the threshold value.

The film deposition rate in the interface region is 10 Å / S or less as described above, but the thickness of this part is as thin as 1000 Å usually 50 to 500 Å, so it should be within the deposition time range of the interface region required from the average deposition rate. For example, a lower film deposition rate is easier to control.

In carrying out the method of the present invention, more preferably, the formation of the photoactive layer is started by transferring the substrate on which the first conductive layer is formed into stable glow discharge.

Discharge is always disturbed when the glow discharge rises. Therefore, in order to avoid this, the substrate is transferred during stable glow discharge. Forming only the interface region in the photoactive layer separately from the remaining portion, which is performed at high speed, is also one of the preferred methods for exerting the effect of the present invention. In order to prevent the discharge from being disturbed during the transfer of the substrate, it is preferable that the substrate and the substrate holder are electrically insulated, or that the substrate and the substrate holder themselves are insulators.

A preferred mode for carrying out the method of the present invention will be described with respect to an example using a glass substrate. A glass substrate on which a transparent conductive film is formed is inserted into the glow discharge reaction chamber. Then under reduced pressure
Keep heating at a temperature of 100-400 ° C. A p-type a-Si: H film is formed with disilane and a p-type doping gas. p
Instead of the type a-Si: H film, a p-type a-Si: H film may be formed from disilane, a p-type doping gas, and a carbon-containing compound by a glow discharge method or a photolysis method. Then, disilane is decomposed in a region where the formation rate of the a-Si: H film does not change depending on the high frequency power used for glow discharge, that is, a region equal to or more than a threshold value to form a photoactive layer. The interface is formed by lowering the flow rate of disilane, and then increasing the flow rate of disilane while increasing the RF power. It is also particularly preferred to transfer the substrate into a glow discharge with a slow deposition rate to begin forming the photoactive layer.

The photoactive layer may be formed by adding a minute amount of diborane of 1 Vppm or less to disilane. Then, an n-type a-Si: H film or an n-type microcrystalline silicon hydride film is formed by using disilane and an n-type doping gas. And second
The electrode is formed to complete the present invention.

The conditions for forming the photoactive layer are a forming temperature of 100 to 400 ° C. and a pressure of 0.0.
It is 5 to 2 Torr. At this time, hydrogen or helium can be used as the diluent gas. By using a diluent gas, the photoconductivity of the photoactive layer can be increased by 2 to 10 times as compared with the case where the diluent gas is not used.

The p-type or n-type doping gas is diborane (B ₂
H ₆₎ and phosphine (PH ₃₎ is used diluted with hydrogen or helium.

In addition to the above-described embodiment, the method for forming a solar cell is (i) a method of stacking n-type-i-type-p-type from the substrate side, (ii) disassembling the electrodes to form a plurality of solar cells A method for producing an integrated solar cell, which is obtained by a series connection of these, (ii) after uniformly forming an electrode and an a-Si: H film, decomposing it by heating means such as laser light, and then integrating. There are various methods, and any of these methods can be used. Further, the p, i, n-type a-Si: H film can be formed in a single reaction chamber or in separate reaction chambers.

In the present invention, the p-type, i-type and n-type a-Si: H layers have film thicknesses of 50 to 500Å, 2000 to 8000Å and 50 to 500Å, respectively.

The materials of the substrate and electrodes used in the present invention are not particularly limited, and conventionally used substances are effectively used.

For example, the substrate may have any of insulating or conductive properties and transparent or opaque properties. Basically, a film or plate-like material formed of a substance such as glass, alumina, silicon, stainless steel, aluminum, molybdenum, and heat resistant polymer can be effectively used as a substrate. As the electrode material, of course, a transparent or translucent material must be used on the light incident side, but there is no other limitation. A thin film or thin plate of aluminum, molybdenum, nichrome, ITO, tin oxide, stainless steel, etc. is effectively used as an electrode material.

[Preferred modes for carrying out the invention]

 The present invention will be described below with reference to examples.

(Example) The method of the present invention was carried out in a plasma CVD apparatus including a substrate insertion chamber, a p-layer, a photoactive layer, an n-layer forming chamber, and a substrate unloading chamber. The p layer is B ₂ H ₆ / Si ₂ H ₆ = 0.1vol%,
Si ₂ H ₆ / H ₂ = 50 vol%, pressure 0.1 Torr, supply energy 8.2 KJ / g-Si ₂ H ₆ , temperature 200 ° C., and a film thickness of about 100 Å was formed. Next, it was moved to the photoactive layer forming chamber and the temperature was adjusted to 300
A photoactive layer was formed with the supply energy of 60 KJ / g-Si ₂ H _{6 at} a forming pressure of 0.08 to 0.3 Torr. The photoactive layer is formed by transferring the substrate to an interface forming part having a deposition rate of 2Å / S, retaining it for 50 seconds, and then changing the RF power and flow rate so that the deposition rate is 30Å / S.
It was performed by setting the film thickness to Å. The average deposition rate at this time is higher than 23Å / S. Then, it was transferred to the n-layer forming chamber.

PH ₃ / Si ₂ H ₆ = 1vol%, S ₂ H ₆ / H ₂ ＝ 10vol%, n layer is about 30
0 Å formed. It was taken out through the substrate taking-out chamber and an Al electrode was formed by vacuum vapor deposition. Irradiation with light of 100 mW / cm ² of AMI resulted in a short-circuit current of 13 to 14 mÅ, despite the high-speed manufacturing conditions where the average deposition rate of the photoactive layer exceeded 23 Å / S.
/ Cm ² , the fill factor is maintained at 0.65 to 0.7,
It was found that the photoelectric conversion efficiency did not decrease.

〔The invention's effect〕

As described above, for example, as shown in the above Examples, according to the method of the present invention, the photoelectric conversion efficiency can be improved even under the high-speed manufacturing conditions without causing the deterioration of the solar cell characteristics such as the decrease of the short circuit current and the decrease of the fill factor. It is possible to achieve high efficiency.

Claims (1)

[Claims] 1. A photoelectric conversion element in which a first conductive layer, a photoactive layer and a second conductive layer are sequentially formed on a substrate having electrodes by glow discharge decomposition of silicon hydride, and a second electrode is provided. In the method for producing the same, at least the formation of the photoactive layer is performed with disilane, and the formation rate of the active layer thin film per unit mass of the disilane is mainly dependent on the disilane flow rate and is substantially affected by the applied energy amount. The minimum amount of energy (hereinafter referred to as the threshold value) is constantly applied to transfer the substrate on which the first conductive layer is formed during the stable glow discharge that has been previously formed, and the light is emitted without disturbing the glow discharge. The formation of the active layer is started and at least the initial 100 of the formation of the photoactive layer.
The region below 0 Å has a deposition rate lower than 10 Å / sec, and the remaining photoactive layer is deposited by continuously changing the deposition rate without stopping the glow discharge so that the deposition rate becomes higher. Method for manufacturing conversion element.