JPH0714074B2 - Method for manufacturing photoelectric conversion element - Google Patents

Description

TECHNICAL FIELD The present invention relates to amorphous silicon (hereinafter abbreviated as a-Si: H).
The present invention relates to a photoelectric conversion element, and particularly to a photoelectric conversion element having stable and excellent photoelectric characteristics.

[Prior art and its problems]

Higher efficiency of photoelectric conversion elements, especially amorphous silicon solar cells, has been studied and some results have been achieved at normal film forming speeds, but under high-speed film forming conditions, the improvement of efficiency is still in progress. I just started. That is, the desired high efficiency has not been achieved under the rate film forming conditions in which the formation rate of the photoactive layer (substantially intrinsic thin film) is about 20 Å / S or more. 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. This discloses that, when disilane is used as a raw material, it is in principle essential to perform glow discharge decomposition of disilane under the condition that energy exceeding a certain threshold is supplied (for example, JP-A-58). -1725 and others). The threshold value here is defined as the discharge power at which the thin film formation rate changes mainly depending on the flow rate of disilane rather than the discharge power. Next, the present inventors disclosed a method in which the first conductive thin film was formed by adding an impurity based on disilane (for example, JP-A-58-34407).

On the other hand, in the case of forming a thin film of amorphous silicon by using disilane as described above, the thin film can be formed by a so-called photo-CVD method which has recently attracted attention. It is said that the photo-CVD has a characteristic that the damage of ions is less in principle than the plasma CVD. However, in general, the photo CVD method employs a method of introducing light (usually ultraviolet rays) into the decomposition chamber through a window made of quartz glass, so during the thin film formation operation,
The essential problem that the thin film adheres to the ultraviolet introducing window and the light transmittance gradually decreases, and it is difficult to form the thin film continuously for a long time. That means, to form all the thin films constituting the photoelectric conversion element, that is, the first conductive thin film, the substantially intrinsic thin film, all the thin films such as the second conductive thin film by the photo CVD. However, there was a big problem that the operation had to be interrupted halfway and the thin film adhering to the ultraviolet ray introduction window had to be removed. On the other hand, the first conductive thin film and the second conductive thin film are usually 1/10 to 1 / th compared to the substantially intrinsic thin film.
Since it is as thin as 100, if only this thin film is formed by photo-CVD, the formation is completed in a relatively short time, and there is practically no problem. Therefore, it is a practical method at present that only the first conductive thin film and the second conductive thin film are formed by the photo-CVD method, and the thick substantially intrinsic thin film is formed by the plasma CVD method. Proposed. In that case, it is expected that the first conductive thin film and the second conductive thin film formed by photo CVD are improved in properties such as electrical properties and optical properties. Has been done.

However, as a result of a detailed study by the present inventors,
Surprisingly, the photoelectric conversion element obtained by depositing a substantially intrinsic thin film by the plasma CVD method on the thin film formed by the CVD method has unexpectedly constant performance and characteristics as expected above. However, it was found that the problem of reproducibility that the characteristic value becomes very unstable newly occurs.

In addition, as described above, plasma is formed on the first conductive thin film.
When a substantially intrinsic thin film is formed by the CVD method, the first conductive thin film is damaged by this plasma, its constituent elements are mixed in the intrinsic thin film, or the first conductive thin film is substantially There is also a problem that the interface characteristics with the intrinsic thin film are deteriorated.

[Object of the Invention]

An object of the present invention is to provide a photoelectric conversion element having high photoelectric conversion efficiency, which 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]

In order to solve such a problem, the present inventors have earnestly studied, and as a result, on the first conductive thin film formed by the photo CVD method or the plasma CVD method, a substantially intrinsic thin film is directly deposited by the plasma CVD method. The inventors have found that there is an essential problem in the structure itself of the device, and have completed the present invention.

That is, the present invention provides a first electrode, a first conductive thin film, a thinner first substantially intrinsic thin film, a thinner second substantially intrinsic thin film, and a thicker third electrode on a substrate. Is a photoelectric conversion element formed in the order of a substantially intrinsic thin film, a second conductive thin film, and a second electrode, and is preferably thinner and thinner than the first substantially intrinsic thin film. The gist of the present invention is a photoelectric conversion element in which the total thickness of the second substantially intrinsic thin film is 25 to 500 angstroms.

That is, when the device of the present invention is more specifically defined with reference to the schematic view shown in FIG. 1, the first conductive thin film is formed on the first electrode formed on the substrate. A thinner first substantially intrinsic film is formed on the first conductive thin film, and a thinner first substantially intrinsic film is formed on the thinner first substantially intrinsic film. A second substantially intrinsic thin film is formed, a thicker third substantially intrinsic thin film is formed on the thinner second substantially intrinsic thin film, and the thicker third substantially intrinsic thin film is formed. A photoelectric conversion element in which a second conductive thin film is formed on a third substantially intrinsic thin film, and a second electrode is sequentially formed on the second conductive thin film. Is.

Hereinafter, the present invention will be described in detail.

In the photoelectric conversion element of the present invention, the most characteristic is that the substantially intrinsic thin film is on the thinner first and second substantially intrinsic thin films and the thicker third substantially intrinsic film. It is composed of a thin film of. In other words, of course, such that the thinner first substantially intrinsic film is in contact with the first electrically conductive film, i.e., the first electrically conductive film is thinner first and second substantially In other words, it is in contact with the thicker third substantially intrinsic thin film through the intrinsic thin film.

After the formation of the first conductive thin film, the thinner first substantially intrinsic thin film is treated with a silane compound and a carbon compound, an oxygen compound or a nitrogen compound (hereinafter simply referred to as a carbon compound etc.). It is formed by photolyzing a mixed gas by photo CVD. Here, needless to say, it may contain a diluent gas such as He, Ar, H ₂ and N ₂ .

The sum of the thickness of the thinner first substantially intrinsic thin film and the thickness of the thinner second substantially intrinsic thin film is 25-500.
Å, more preferably 40 to 200 Å. Total film thickness is 25
When it is less than Å, the instability of the characteristics of the obtained photoelectric conversion element cannot be resolved, and the object of the present invention cannot be achieved. The upper limit of the film thickness is not critically limited as long as it is within a range of several thousand Å, but the film formation rate in the photo-CVD method is originally very small, about 1 Å / S or less. However, when the film thickness is unduly increased, it takes an extremely long time to form the film, which is not practical and the total amount is preferably 500 Å or less.

The thinner second substantially intrinsic thin film is formed after the formation of the thinner first substantially intrinsic thin film of impurities such as carbon-containing compounds used to form the first substantially intrinsic film. It is desirable that the supply is stopped and at least the thin film is formed by the photo-CVD method. More preferably, this thinner second substantially intrinsic film is amorphous (amorphous silicon) (a-Si: H).

In the present invention, the silane compound used to form the amorphous silicon thin film has a general formula Si _n H _{2n + 2} (n = 1
~ 3) silicon hydrides represented by the following are preferred. Here, n = 1, 2 and 3 specifically correspond to monosilane (SiH ₄ ), disilane (Si ₂ H ₆ ) and trisilane (Si ₃ H ₈ ), respectively.

As the photo-CVD method used in the present invention, a so-called direct method using light having a wavelength of 190 nm or less and a sensitizing method using a sensitizer such as mercury are particularly used. In the latter, ultraviolet rays of 253.7 nm, which is the resonance absorption line of mercury, are used. The above two methods must be selected in relation to the type of silane compound used as a raw material. That is, in the case of disilane or trisilane corresponding to n = 2 or 3, direct photo CVD method and mercury sensitized CVD
Although any of the methods may be selected, in the case of monosilane corresponding to n = 1, it is necessary to use the mercury-sensitized CVD method. The source of ultraviolet rays is not particularly limited, but specific examples thereof include mercury lamps, rare gas lamps, and deuterium lamps. Among these,
In particular, a low-pressure mercury lamp, which is a kind of mercury lamp, is particularly preferable from the practical viewpoints such as the life of the lamp, the stability, and the ease of handling, as well as the wavelength of the generated ultraviolet rays satisfying the above conditions.

A feature of the present invention is that two thinner first and second substantially intrinsic thin films are formed on the first conductive thin film. Is like.

After the formation of the first conductive thin film, the light irradiation and the supply of the raw material gas are stopped, and the raw material gas in the system is sufficiently exhausted. CVD
Forming a thinner first substantially intrinsic film. Subsequently, the source gas of the thinner first substantially intrinsic thin film in the system is similarly exhausted sufficiently, and then the second thinner substantially intrinsic thin film is formed.

Alternatively, after forming the first conductive thin film, under the condition of forming the first conductive thin film, by stopping the supply of the impurities imparting the first conductive thin film and continuing the formation of the thin film. is there. That is, the first conductive thin film, a silane compound, an impurity gas that imparts the first conductivity, a mixed gas such as a diluent gas and a carbon-containing compound, is preferably formed by photo-CVD that decomposes by ultraviolet rays. , The supply of the impurity imparting the first conductivity is stopped and the other conditions are the same, and the formation of the thin film is continued to form a thinner first substantially intrinsic thin film, and further, This is a method of forming a second thinner substantially intrinsic thin film by stopping the supply of impurities such as the carbon compound without stopping the light irradiation.

The temperature of the substrate and the atmospheric pressure when the thin film is formed are sufficient in the ranges of 100 to 400 ° C. and 0.01 to 10 Torr, respectively.

In the present invention, the formation of the thinner first and second substantially intrinsic thin films is preferably performed by photo-CVD, while the other first conductive thin film, the thicker third substantially intrinsic thin film. For the formation of the second conductive thin film,
The first conductive thin film is preferably photo CVD or plasma C
Preferably, the VD and the thicker second substantially intrinsic thin film, second conductive thin film, etc. are formed by plasma CVD. Since the second conductive thin film is originally not so thick, it is of course a preferable embodiment to be formed by the photo CVD method. These forming conditions are not essentially critical conditions in the present invention, and thus are not particularly limited,
As a reminder, the preferred conditions for implementation will be described below.

In the present invention, the thicker third substantially intrinsic thin film (hereinafter abbreviated as i film) is preferably formed by the plasma CVD method of the silane compound as described above. The i
In order to form a film at a high speed, it is desirable that the plasma CVD is performed using disilane and supplying discharge energy equal to or higher than a threshold value, as already proposed by the present inventors. The threshold value here means that the formation rate of the i film changes mainly depending only on the disilane flow rate,
It is defined as the lowest amount of energy per disilane site mass that is substantially unaffected by the amount of applied energy. Regarding the threshold value, more specifically, as disclosed by the present inventors in Japanese Patent Laid-Open No. 58-1726, the formation rate of the a-Si: H film depends on the high frequency power used for glow discharge. It is the value of the glow discharge power where it does not change.

It is convenient to express such a threshold value as the supplied energy as proposed by the present inventors.

The supply energy is calculated by the following formula.

The unit of the film forming conditions used in the formula [I] is RF power (W), raw material gas flow rate (standard state flow rate per minute = SCCM), and is represented by 1344 = 60 (min) × 22.4 (/ mol) Is a coefficient that is For example, in the case of disilane 30SCCM and helium gas 270SCCM for dilution, the average molecular weight = (30 x 62.2 + 270
X4 / 300 = 98.2, disilane weight fraction = (30 x 62.2) / (3
00 x 9.82) = 0.633, RF power (glow discharge power)
= 100W, substitute in the formula [I], To get

The threshold value is as defined above, but it goes without saying that the threshold value varies depending on the reaction apparatus and reaction conditions used. With respect to such a threshold value, for example, when an actual specific numerical value based on the result of the study conducted by the present inventors for a parallel plate type plasma CVD apparatus is illustrated, disilane alone is 40
(KJ / g-Si ₂ H ₆ ), 1 for helium diluted 10% disilane
0 (KJ / g-Si ₂ H ₆ ), 30 for hydrogen diluted 10% disilane
(KJ / g-Si ₂ H ₆ ), with diluted disilane showing a lower threshold.

The thickness of the i film is usually about 2000Å to 1μ, but the forming temperature and the forming pressure are usually 100 to 400 ° C. and 0.01 to 10 Torr, respectively, and disilane gas such as hydrogen or helium is used. It is also preferable to dilute the compound with these diluting gases for use in order to improve the performance of the photoelectric conversion element.

In the present invention, the first conductive thin film and the second conductive thin film have different conductivity types. For example, if the first conductivity type is p-type, the second conductivity type is n-type.

Hereinafter, the case where the first conductivity type is the p-type will be described, but it goes without saying that the opposite case is also possible.

The first conductive thin film, that is, the p film, is formed by photo-CVD or plasma-CVD that decomposes a mixed gas such as a silane compound, an impurity gas that imparts the first conductivity, a diluent gas and a carbon-containing compound with ultraviolet rays. When disilane is used to form the i film, it is preferable to use disilane also to form the p film. And, more specifically, in this case, the thinner first substantially intrinsic thin film, which is a feature of the present invention, is also preferably formed from disilane. As described above, when disilane is used, both the direct method and the mercury sensitizing method can be selected as the photo-CVD method, but the mercury sensitizing method is not selected for monosilane. I won't.

In the present invention, a compound of Group III of the periodic table is used as the impurity gas that imparts p-type conductivity, and diborane gas is particularly preferable. Also, as the diluent gas,
As mentioned above, hydrogen and helium are preferable. Further, as the carbon-containing compound, alkyl silanes such as monomethylsilane, dimethylsilane, trimethylsilane, tetramethylsilane, monoethylsilane, diethylsilane, triethylsilane, tetraethylsilane; unsaturated hydrocarbons such as ethylene and acetylene; methane, ethane ,propane,
A saturated hydrocarbon such as butane is preferably used. Among these, it is particularly preferable to use alkylsilane or acetylene for improving the characteristics of the photoelectric conversion element. The amount of the carbon-containing compound added is usually about 0.001 to 100 in the atomic ratio of carbon to silane in the raw material. For example, when alkylsilane is used, the range is about 0.01 <C / Si <5; acetylene. In the case of unsaturated hydrocarbon such as ethylene, the range of 0.001 ≦ C / Si ≦ 1 may be used.

On the other hand, what is used as the oxygen-containing compound gas is O ₂
Alternatively, nitrogen-oxygen compounds such as O ₃ and N ₂ O, NO, and NO ₂ can be mentioned, but O ₂ is particularly preferable. Further, as the nitrogen compound, NH ₃ and N ₂ H ₄ are mentioned as preferable ones, and among them, NH ₃ is most preferable.

The thickness of the p film is usually about 100Å to 500Å, but its forming temperature and forming pressure are usually 100 to 400 ° C, preferably 120 to 250 ° C; and 0.01 to 10 Torr, preferably 0.
05 to 2 Torr.

On the other hand, the second conductive thin film is an n-type film in this case. (Hereinafter, the thin film is abbreviated as n film). The n film is formed by plasma CVD or photo CVD of a mixed gas such as a silane compound, an impurity gas imparting the second conductivity, and a diluent gas. Therefore, both monosilane and disilane are effectively used as the silane compound. As an impurity gas that imparts n-type conductivity, there are V
Although a compound of the group is used, phosphine gas is particularly preferable. Note that it is preferable that the n film is microcrystallized in order to improve the conductivity. It is preferable to use hydrogen as a diluent gas for the microcrystallization.

The thickness of the n film is usually about 100Å to 500Å, but its forming temperature and forming pressure are usually 100 to 400 ° C a, preferably 120 to 250 ° C; and 0.01 to 10 Torr, preferably 0.
05 to 2 Torr. The preferable hydrogen dilution amount is about 5 to 100 in terms of the ratio of hydrogen flow rate / silane compound flow rate.

[Preferred modes for carrying out the invention]

In order to carry out the present invention, a film forming apparatus capable of continuously performing optical CVD and plasma CVD is preferably used. That is, the optical CVD device is a film forming device basically equipped with at least each means of an ultraviolet insertion window, a substrate introducing means, a substrate heating means, a substrate holding means, a gas introducing means, a vacuum exhausting means,
The plasma CVD apparatus is a film forming apparatus basically provided with a plasma discharge electrode and a plasma discharge power source instead of the ultraviolet introduction window, but preferably both are connected to each other via a basic transfer means. Moreover, it is preferable that the film forming apparatus is partitioned by a gate valve or the like as necessary so that photo CVD and plasma CVD can be continuously performed. FIG. 2 schematically shows an example of such a film forming apparatus suitable for carrying out the present invention.

First, a substrate provided with the first electrode is placed on the photo-CVD apparatus as described above, and the substrate is heated to 100 to 400 ° C. under vacuum exhaust. Then, while introducing the source gas, the inside of the p-film formation chamber is evacuated by the vacuum evacuation means, and the pressure inside the film formation apparatus is adjusted to 0.01
The p-film is formed by maintaining the temperature within the range of up to 10 Torr and performing photo-CVD while radiating ultraviolet rays. After the p film is formed to the required thickness, the supply of the dopant such as diborane is stopped and the silane compound and the carbon-containing compound are allowed to flow to form a thin film of 10 to 200Å (that is, a thinner first substantially intrinsic thin film). Form. Subsequently, the supply of carbon-containing compounds, etc. was stopped and further 25-500
It forms a thin film with a thickness of Å (ie, a second, thinner, substantially authentic film).

Alternatively, as an alternative method, after the p-film is formed, the emission of ultraviolet rays and the supply of all the raw material gases are once stopped, and then 10 ⁻⁶ To
Evacuate to a high vacuum of about rr or less, and supply the silane compound and carbon-containing compound again, while performing the same optical CV as above.
First, a thin film of 10 to 200Å is formed by D. Further, the light irradiation and the supply of raw materials were stopped, the system was evacuated to a high vacuum, and then only the silane compound was supplied again.
It is sufficient to form a thin film of 25 to 500 Å by D.

Next, the substrate on which this thin film is formed is transferred to the plasma CVD apparatus for forming the i film (that is, the thicker third substantially intrinsic thin film) by the basic transfer means. After the i film is formed in the i film forming chamber, it is further transferred to the n film forming chamber by the substrate transfer means. The n film is formed by either plasma CVD or photo CVD. After the n film is formed, it is transferred to the second electrode forming device by the substrate transferring means, and after the second electrode is formed, it is taken out to the forming device as a photoelectric conversion element.

Of course, in the above embodiment, the first electrode is divided to form a plurality of photoelectric conversion elements, for example, solar cells, and the third electrode is connected in series to form an integrated solar cell. Is also useful in.

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

For example, the substrate may be one having an insulating property, a conductive property, a transparent property, or an opaque property. 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 the substrate. As the electrode material, of course, a transparent or transparent material must be used on the light incident side, but there is no other practical limitation. Thin films or thin plates of aluminum, molybdenum, nichrome, ITO, tin oxide, stainless steel, etc. are effectively used as the electrode material.

Hereinafter, embodiments of the present invention will be described more specifically with reference to Examples. In the following examples, the thickness of the thin film was measured with a stylus type film thickness meter and a multiple interferometer. The actual film thickness was controlled by a method in which the film thickness was divided by the actual film formation time as an average film formation rate, and the film formation time required to obtain the required film thickness was controlled using the average film formation rate. .

〔Example〕

As the film forming apparatus, the film forming apparatus shown in the schematic view of FIG. 2 was used.

The substrate 6 vacuum-heated in the substrate insertion chamber 1 is the p-film forming chamber 2
Was transferred to. The p film has a source gas flow rate ratio of diborane /
Disilane = 2/100, acetylene / disilane = 1/10, disilane / hydrogen = 1/20; formation temperature 100-300 ° C; pressure 0.1-1
The light of 184.9 nm of the low-pressure mercury lamp 7 was introduced from the ultraviolet ray introduction window 8 by Torr, and it was formed to a thickness of about 200 Å by photo-CVD. After turning off the low-pressure mercury lamp, the introduction of the raw material gas was stopped, and 10 ^-6 To
Exhausted below rr. Then, acetylene / disilane = 1 /
Introduce acetylene and disilane in a ratio of 20, pressure 0.05 ~
A thinner first substantially intrinsic film was formed at 0.5 Torr. This condition is shown in Table 1. Next, the introduction of acetylene was stopped, disilane was introduced, and the mercury lamp was turned on again at a pressure of 0.05 to 0.5 Torr to form a thinner second substantially intrinsic thin film with a thickness of 50Å. Then, the gate valve 19 was opened, and the substrate was transferred to the i-film forming chamber 3 by the substrate transfer means 16. In the i-film forming chamber, the forming temperature is 100 to 400 ° C and the pressure is 0.05.
In the condition that the discharge energy is above the threshold value at ~ 2 Torr,
An i film was formed by plasma CVD of disilane. Next, it was transferred to the n-film forming chamber 4 and a microcrystallized n-film was formed by plasma CVD from monosilane and hydrogen-diluted phosphine. Source gas flow rate is phosphine / disilane = 1/100,
Disilane / hydrogen = 1/50. Then, it was transferred to the electrode forming chamber 5 and an aluminum electrode was formed by vacuum evaporation.

The photoelectric conversion characteristics of the photoelectric conversion element thus obtained are AM1, 1
It was measured while irradiating with light of 00mW / cm ² . The results are shown in Table 1 as Examples 1 to 5.

Table 1 also shows, as an example for comparison, an example in which a thinner substantially non-intrinsic thin film is formed (Comparative Example 1).
Is also shown.

Not to mention comparison with these comparative examples, in the examples of the present invention, the improvements in FF (fill factor) and short circuit current are remarkable, and As a result, it is clear that the photoelectric conversion element is extremely excellent in photoelectric conversion element efficiency.

〔The invention's effect〕

As described above, according to the present invention, the first and second substantially intrinsic thin films having a specific thickness are interposed between the first conductive thin film and the third substantially intrinsic thin film. According to the configuration, for example, as shown in the above embodiments, characteristic values such as FF (fill factor) and short-circuit current are significantly improved, and as a result, a photoelectric conversion element having extremely excellent photoelectric conversion element efficiency is provided. It must be said that its industrial availability is extremely high.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing an example of the configuration of the photoelectric conversion element of the present invention. FIG. 3 is a schematic view showing an example of a preferable apparatus for forming the element of the present invention in FIG. In the figure,
1 ... Substrate insertion chamber, 2 ... p film formation chamber, 3 ... i film formation chamber, 4 ... n film formation chamber, 5 ... Second electrode formation chamber / substrate extraction chamber, 6 ... Substrate, 7 ...... Low-pressure mercury lamp, 8 …… UV light introduction window, 9 …… Discharge power application electrode, 10 …… Installed electrode,
11 …… Base material heater, 12 …… Electrode material heater,
13 …… Metal mask, 14 and 20 …… Vacuum exhaust line, 15
...... Raw material gas introduction line, 16 …… Substrate transfer means, 17 ……
Insulating material, 18 …… Discharge power application power source, 19 …… Gate valve

Claims (2)

[Claims] 1. A first electrode, a first conductive thin film, a thinner first substantially intrinsic thin film, a thinner second substantially intrinsic thin film, and a thicker third third substrate on a substrate. A method for manufacturing a photoelectric conversion element, wherein a substantially intrinsic thin film, a second conductive thin film and a second electrode are formed in this order, wherein the thinner first substantially intrinsic thin film is a silane compound. And a gas mixture of a carbon compound, an oxygen compound or a nitrogen compound is formed by a photo CVD method, and a thinner second substantially intrinsic thin film is formed by stopping the supply of the carbon compound, the oxygen compound or the nitrogen compound, and the photo CVD method. Forming a thicker third substantially intrinsic thin film by plasma CVD at a higher rate than the thinner first substantially intrinsic thin film and the thinner second substantially intrinsic thin film. A method for manufacturing a photoelectric conversion element, comprising: 2. The total thickness of the thinner first substantially intrinsic thin film and the thinner second substantially intrinsic thin film is 25.
The method of claim 1, wherein the method is from 500 to 500 Angstroms.