JPH0714075B2 - 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 method for manufacturing a photoelectric conversion element, and more particularly to a method for manufacturing a photoelectric conversion element paste that stably has 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).

Generally, when an intrinsic thin film is formed on the first electroconductive thin film by the plasma CVD method, the formed first electroconductive thin film is plasma-damaged and its constituent elements are included in the intrinsic thin film. There is a problem that they are mixed in, or the interface characteristics between the first conductive thin film and the substantially intrinsic thin film are deteriorated.

Therefore, the present inventors have studied in detail, on the first conductive thin film formed by the plasma CVD method,
The photoelectric conversion device obtained by depositing a substantially intrinsic thin film by the plasma CVD method has inconsistent performance and characteristics,
It was found that the problem of reproducibility that the characteristic value becomes very unstable newly occurs.

[Object of the Invention]

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

[Disclosure of Invention]

In order to solve such a problem, the inventors of the present invention have made extensive studies and found that a structure of an element in which a substantially intrinsic thin film is directly deposited by a plasma CVD method on a first conductive thin film formed by a plasma CVD method. The inventors have found that there is an inherent problem, 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 thicker second substantially intrinsic thin film, and a second conductive film on a substrate. Is a method for manufacturing a photoelectric conversion element in which a conductive thin film and a second electrode are formed in that order, after forming the first conductive thin film by a plasma CVD method, supplying an impurity that imparts the first conductivity. A method for manufacturing a photoelectric conversion element, characterized in that the thinner first substantially intrinsic thin film is formed, preferably, the thickness of the thinner first substantially intrinsic thin film is 25 to The main point is a manufacturing method of 500 Å.

The device manufactured by the method of the present invention will be more specifically defined with reference to the schematic view shown in FIG. 1. The first conductive film is formed on the first electrode formed on the substrate. A thin film is formed, a thinner first substantially intrinsic thin film is formed on the first conductive thin film, and a thinner first substantially intrinsic thin film is formed on the first conductive thin film. A thick second substantially intrinsic thin film is formed, a second conductive thin film is formed on the thicker second substantially intrinsic thin film, and the second conductive thin film is further formed. Is a photoelectric conversion element in which a second electrode is sequentially formed on a conductive thin film.

Hereinafter, the present invention will be described in detail.

In the photoelectric conversion element targeted by the present invention, the most characteristic feature thereof is that the substantially intrinsic thin film has a thinner first substantially intrinsic thin film and a thicker second substantially intrinsic thin film. It is composed of a thin film of. In other words, of course, such that the thinner first substantially intrinsic thin film is in contact with the first conductive thin film, i.e., the first conductive thin film is the thinner first substantially intrinsic thin film. It is in the form of being in contact with the thicker second substantially intrinsic thin film through the thin film.

The thinner first substantially intrinsic thin film is formed by forming a first conductive thin film and then stopping the supply of impurities (dopant) that imparts the first conductive property, and continuously performing the plasma CVD method. It is preferably a formed thin film. More preferably, this thinner first substantially intrinsic thin film is amorphous (amorphous silicon) (a-Si: H) and has a film thickness of 25 Å or more. When the film thickness is less than 25Å, the instability of the characteristics of the obtained photoelectric conversion element cannot be eliminated, 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 liters, but at most about 500 liters is sufficient. From the characteristics and the practical viewpoint, an amorphous silicon film formed by plasma CVD and having a thickness in the range of 40 to 200Å is particularly preferable.

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.

A feature of the present invention is that at least a thinner first substantially intrinsic thin film is formed on the first conductive thin film by a plasma CVD method. After forming the conductive thin film by plasma CVD method, under the condition of forming the first conductive thin film, by stopping the supply of the impurity imparting the first conductive thin film to continue the formation of the thin film. is there. That is, the first conductive thin film is formed by 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 gas by a glow discharge method. It is only necessary to stop the supply of the impurities and keep the other conditions the same to continue the thin film formation.

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 at least the first conductive thin film and the thinner first substantially intrinsic thin film is plasma CVD.
Other thicker second substantially intrinsic thin films, second conductive thin films, etc. are preferably 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.
In the present invention, these forming conditions are not essentially critical conditions and thus are not particularly limited, but for the sake of caution, the preferred conditions for implementation will be described below.

In the present invention, the thicker second 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 unit mass of disilane that is substantially unaffected by the amount of energy applied. 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 may be possible.

The first conductive thin film, that is, the p film is formed by plasma CVD in which a mixed gas such as a silane compound, an impurity gas imparting the first conductivity, a diluent gas and a carbon-containing compound gas is decomposed by glow discharge. 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. 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. Further, hydrogen or helium is preferable as the diluent gas. Further, as the carbon-containing compound gas, alkyl silanes such as monomethylsilane, dimethylsilane, trimethylsilane, tetramethylsilane, monoethylsilane, diethylsilane, triethylsilane and tetraethylsilane; unsaturated hydrocarbons such as ethylene and acetylene; methane, Saturated hydrocarbons such as ethane, propane and butane are preferably used. Among these, it is preferable to use alkylsilane or acetylene for improving the characteristics of the photoelectric conversion element.

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 method of the present invention, a film forming apparatus capable of continuously performing plasma CVD is preferably used. That is, the film forming apparatus is basically equipped with at least each of the substrate introducing means, the substrate heating means, the substrate holding means, the gas introducing means, the vacuum exhausting means, the plasma discharge electrode, and the plasma discharge power source, and these are preferable. It is preferable that the above-mentioned devices are connected to each other through a basic transfer means, and if necessary, are partitioned by a gate valve or the like. FIG. 2 schematically shows an example of such a film forming apparatus suitable for carrying out the present invention. First, plasma CV as above
The substrate provided with the first electrode is installed in the D device, and the substrate is heated to 100 to 400 ° C. under vacuum evacuation. Then, while introducing the raw material gas, the inside of the p film forming chamber is evacuated by the vacuum evacuation means, the pressure inside the film forming apparatus is maintained in the range of 0.01 to 10 Torr, and plasma CVD is performed to form the p film. After the p film is formed to the required thickness, the supply of the dopant such as diborane is stopped and further 25
Form a thin film of ~ 500Å (ie, a thinner first substantially intrinsic film).

Then, the substrate on which the thin film is formed is transferred to the plasma CVD apparatus for forming the i film (that is, the thicker second 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 second electrodes are 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
It was formed to a thickness of about 200Å by glow discharge with Torr.
Then, the supply of acetylene and diborane was stopped and a first substantially intrinsic thin film was continuously formed to a thickness shown in Table 1. 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, plasma CV of disilane is formed under the condition that the forming temperature is 100 to 400 ° C, the pressure is 0.05 to 2 Torr, and the discharge energy is above the threshold
An i film was formed by D. 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
It was / 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 4.

Table 1 also shows, as a comparative example, a thinner first substantially intrinsic thin film having a thickness of 20Å (Comparative Example 1) and an example in which the thin film is not formed at all (Comparative Example 2). ) Is also shown.

Needless to say, compared with these comparative examples, in the examples of the present invention, the FF (fill factor) and the short-circuit current were significantly improved, and as a result, the photoelectric conversion element efficiency was extremely excellent. It is clear that the device is obtained.

[Effects of the Invention] As described above, according to the present invention, the first substantially thin film having a specific thickness between the first conductive thin film and the second substantially intrinsic thin film formed by the plasma CVD method. According to the method of forming and interposing an intrinsic thin film in the plasma CVD method, characteristic values such as FF (fill factor) and short-circuit current are significantly improved, as a result, as a result, Since a method for manufacturing a photoelectric conversion element having extremely excellent photoelectric conversion element efficiency is provided, it must be said that its industrial applicability is extremely large.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing an example of the configuration of a photoelectric conversion element obtained by the present invention. FIG. 2 is a schematic view showing an example of a preferable apparatus for forming the element of the present invention.
In the figure, 1 ... Substrate insertion chamber, 2 ... P film formation chamber, 3
…… i film forming chamber, 4 …… n film forming chamber, 5 …… second electrode forming chamber and substrate extraction chamber, 6 …… substrate, 9 …… discharge power application electrode, 10 …… installed electrode, 11 …… Substrate heating heater, 12 ...
… Electrode material heater, 13 …… Metal mask, 14 and 20
...... Vacuum exhaust line, 15 …… Source 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 thicker second substantially intrinsic thin film, and a second conductive material on a substrate. A method of manufacturing a photoelectric conversion element in which a thin film and a second electrode are sequentially formed,
After forming the first conductive thin film by the plasma CVD method, the supply of the impurities imparting the first conductivity is stopped to continuously and without stopping the plasma, the first substantially thinner intrinsic thin film. 2. A method for manufacturing a photoelectric conversion element, which comprises forming a thin film of. 2. The method of claim 1 wherein the thickness of the thinner first substantially intrinsic film is 25 to 500 angstroms.