JPS63220581A - Manufacture of photoelectric conversion element - Google Patents

Abstract

PURPOSE:To obtain an element of high efficiency by a method wherein a first p-type semiconductor thin film is doped with two to five times as much impuri ties as a second p-type semiconductor thin film. CONSTITUTION:A first p-type semiconductor thin film which has been doped with high-concentration p-type impurities is formed, with 5-50 Angstrom , on an elec trode composed of a translucent conductive oxide by a glow discharge; after that, while the concentration of the p-type impurities is reduced to 1/2-1/5 and other conductions are kept to be the same, a second p-type semiconductor thin film having the required characteristics for an ordinary amorphous photoe lectric conversion element is formed with a prescribed thickness. That is to say, a p-type semiconductor thin film (a p-layer) is formed after it has been divided into a first p-layer and a second p-layer; the first p-layer is doped with two to five times as much high-concentration impurities as the second p-layer. It is preferable that the supply amount of impurities to a silane compound ranges from 1 to 20% when the first p-type semiconductor thin film of high p-concentration is formed and that the film thickness ranges from 5 to 50 Angstrom . By this setup, it is possible to obtain the photoelectric conversion element whose efficiency of photoelectric conversion is excellent.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a method for manufacturing an amorphous silicon (hereinafter also abbreviated as a-3tsH) photoelectric conversion element, and in particular, to a method for manufacturing the highly efficient element.

[Prior art and its problems] Investigations into improving the efficiency of photoelectric conversion elements, particularly amorphous silicon solar cells, have been focused on improving the characteristics of semiconductor thin films and forming methods for p+t+n semiconductor thin film junctions. On the other hand, the light-transmitting conductive oxide such as tin oxide or ITO used as the light-incidence side electrode is electrically n-type, and normal photoelectric conversion is performed by laminating a p-type semiconductor thin film thereon. In the case of devices, it is important to improve the electrical properties of the interface between the transparent conductive oxide and the P-type semiconductor thin film, and this study has been conducted using an example in which platinum silicide is provided at the interface. To a certain extent (for example, Hanaki et al. "Improvement of interface properties in a-3+ solar cells", Proceedings of the 46th Annual Conference of the Japan Society of Applied Physics, p. 711, 2p-ZA-13, 19)
October 1, 1985 to October 4, 1985). However, platinum is an expensive noble metal, and since a process for forming the thin film is added, it has poor industrial practicality.

Therefore, the present inventors have intensively studied the method of forming a p-type semiconductor thin film in a photoelectric conversion element, and have improved the electrical properties of the interface between the transparent conductive oxide and the p-type semiconductor thin film without sacrificing industrial practicality. They discovered that it can be improved and completed the present invention.

[Disclosure of the Invention] As shown in the schematic diagram of FIG. 1, the method for manufacturing the photoelectric conversion element of the present invention basically involves forming an electrode made of a light-transmitting conductive oxide on a light-transmitting and insulating substrate. , an n-type semiconductor thin film, a substantially intrinsic thin film (i-type semiconductor thin film), an n-type semiconductor thin film, and a back metal electrode, which are formed in this order, and are particularly characterized by the method for forming the n-type semiconductor thin film. It is. That is, a high concentration of n is applied on an electrode made of a transparent conductive oxide.
After forming a first n-type semiconductor thin film doped with a type impurity of 5 to 50 A by glow discharge, the concentration of the n-type impurity was set to 172 to 115, and other conditions were the same, and a normal amorphous silicon photoconductor was deposited. A second P-type semiconductor thin film having characteristics used in a conversion element is formed to a predetermined thickness.

That is, the n-type semiconductor thin film (p layer) is divided into the first p layer and the second pN layer in this way, and the first p layer is 2 to 5 times larger than the second p layer. This is done by doping impurities to a high concentration of .

When forming the first high p-concentration n-type semiconductor thin film, the impurity supply amount is 1 to 20% with respect to the silane compound, and the film thickness is 5 to 5%.
A range of 0 angstroms is preferred. If the supply amount and film thickness are larger than this, the loss of light in the thin film will increase, and the characteristics of the photoelectric conversion element will deteriorate on the contrary.

In the present invention, these semiconductor thin films are amorphous (a-Si:H or a-3iC:H), and the silane compound used for their formation is of the general formula S
i, lHz. . The hydrogenated silicon and carbon-containing compounds represented by z (n=1 to 3) have the general formula St (Cl
unsaturated hydrocarbons such as methylsilane, ethylene, acetylene, etc., represented by ls)-)14-M (m□1-3);
Saturated hydrocarbons such as methane, ethane, propane, butane are preferably used.

Furthermore, as the impurity imparting n-type conductivity, diporane is preferably used, and as the diluent gas, hydrogen or helium is preferably used.

The temperature of the substrate and the atmospheric pressure when the thin film is formed are 100 to 400°C and 0.01 to 1, respectively.
A range of 0 Torr is sufficient.

Further, in the present invention, the means for forming these semiconductor thin films is not limited to the plasma CVD method, but is also a preferred embodiment even if other CVD methods such as optical CVD and thermal CVD are used.

The conditions for forming thin films other than the conditions for forming the first and second n-type semiconductor thin films are not essentially critical conditions for the present invention, and therefore are not particularly limited, but the following are preferred just in case: The conditions for implementation will be explained.

In the present invention, the i-film is preferably formed by a disilane plasma CVD method, as already proposed by the present inventors, in order to further enhance the above-mentioned industrial practicality. This is because disilane has a growth rate that is several times faster than monosilane and has excellent mass productivity. Particularly preferably, as already proposed by the inventors, the plasma CVD is carried out under the supply of a discharge energy above a threshold value for disilane. More specifically, the present inventors have already proposed this in Japanese Patent Laid-Open No. 1726/1983.

The thickness of the i-film is usually about 2000A to 1μ,
The forming temperature and forming pressure are usually 100~
A temperature of 400°C and a temperature in the range of 0.01 to 10 Torr is sufficient, and it is also preferable to use it diluted with a diluent gas such as hydrogen or helium in order to improve the performance of the photoelectric conversion element.

On the other hand, an n-type semiconductor thin film is produced by plasma CVD using a silane compound, an impurity gas that imparts n-type conductivity, and a diluent gas.
Formed by law. Therefore, both monosilane and disilane can be effectively used as the silane compound. n
Phosphine is preferred as the impurity gas that imparts conductivity to the mold, and hydrogen is preferred as the diluent gas. Note that since it is preferable to microcrystallize the n-type semiconductor thin film to improve its conductivity, the flow rate ratio of hydrogen and silane compound is important.

The thickness of an n-type semiconductor thin film is usually about 100 to 800 A, and the forming temperature and pressure are usually 100 to 400'C and 0.01 to 10 Torr, respectively.
Preferably it is 0.05 to 3 Torr. Further, the preferred flow rate ratio of hydrogen and silane compound is about 5 to 100.

[Preferred form for carrying out the invention] In order to carry out the invention, a film forming apparatus capable of continuously carrying out plasma CVD is suitably used.

That is, it is a film forming apparatus that is at least basically equipped with each of the following means: a substrate introduction means, a substrate heating means, a substrate holding means, a gas introduction means, a vacuum evacuation means, a plasma discharge electrode, and a plasma discharge power supply. Preferably, the apparatuses are connected to each other via a substrate transfer means, and are separated by a gate valve or the like as necessary. Second
The figure schematically shows an example of such a film forming apparatus suitable for carrying out the present invention.

First, a substrate provided with an electrode made of a transparent conductive oxide is placed in the plasma CVD apparatus as described above, and a first p-type semiconductor thin film and a second p-type semiconductor thin film are formed under the conditions described above. do.

Next, the substrate on which this thin film has been formed is transferred by a substrate transfer means to a plasma CVD apparatus for forming a J-type semiconductor thin film. After the i-film is formed in the i-type semiconductor thin film forming chamber, it is further transferred to the n-type semiconductor thin film forming chamber by the substrate transfer means. After forming the n-type semiconductor thin film, it is transferred to the back metal electrode forming apparatus by the substrate transfer means, and after the back metal electrode is thus formed, it is taken out of the forming apparatus as a photoelectric conversion element.

Of course, in the above embodiment, an electrode made of a transparent conductive oxide on a substrate is divided to form a plurality of photoelectric conversion elements, such as solar cells, and these are connected in series with a back metal electrode. It is also useful in the formation of integrated solar cells.

The material of the substrate used in the present invention may be any material as long as it has insulating and translucent properties. Basically, film or plate-shaped materials made of glass, heat-resistant polymers, or other substances can be effectively used. As for the electrode material, a transparent or transparent material must of course be used on the light incident side, and a translucent conductive oxide such as TO1 tin oxide is used. Further, as the back metal electrode, a thin film of metal such as aluminum, molybdenum, nickel, or chromium can be effectively used.

Hereinafter, embodiments of the present invention will be explained in more detail with reference to Examples.

[Example] The film forming apparatus schematically shown in FIG. 2 was used. The substrate 6 heated under vacuum in the substrate loading chamber 1 was transferred to the p-type semiconductor thin film forming chamber 2.

First, in the first p-type semiconductor thin film, the flow rate ratio of the raw material gas is
Diporane/disilane-10/100 to 6/100, dimethylsilane/disilane-271, disilane/hydrogen = 1/
No. 20 was formed to a thickness of 5 to 15 A by glow discharge at a formation temperature of 250° C. and a pressure of 0.2 Torr.

Next, a second p-type semiconductor thin film was formed by setting the flow rate of diborane to 115 to 1/3 of the above and the flow rate of dimethylsilane to 172A.

Further, the gate valve 19 was opened, and the substrate was transferred to the i-type semiconductor thin film forming chamber 3 by the substrate transfer means 16. In the i-type semiconductor thin film formation chamber, the formation temperature is 300°C and the pressure is 0.0.
An i-film was formed by plasma CVD of disilane under conditions of 5 Torr and discharge energy equal to or higher than the dark value.

Next, it was transferred to the n-type semiconductor thin film forming chamber 4, and a microcrystallized n-type semiconductor thin film was formed from monosilane and hydrogen-diluted phosphine by plasma CVD. The raw material gas flow ratio was phosphine/monosilane = 2/100 and monosilane/hydrogen - 1740. Then, it was transferred to the back metal electrode forming chamber 5 and an aluminum ram electrode was formed by vacuum evaporation.

The photoelectric conversion characteristics of the photovoltaic conversion element thus obtained are AM
The results are shown in Table 1. In Example 1.2, the thickness of the first and second p-type semiconductor thin films was changed; 3 shows Example 2 in which the gas composition ratio was changed.

Table 1 [Comparative Example] Comparative Example 1 is an example in which the experiment was conducted in exactly the same manner except that the first p-type semiconductor thin film was not formed at all.
As shown in Table 1.

As is clear from Table 1, by providing a thin first p-type semiconductor thin film doped with impurities at a higher concentration than the second p-type semiconductor thin film on an electrode made of a transparent conductive oxide, A photoelectric conversion element having extremely high photoelectric conversion efficiency exceeding 11χ has been obtained. This is presumed to be because the short circuit current increased significantly and carriers began to flow smoothly between the transparent conductive oxide electrode and the p-type semiconductor thin film.

[Effect of the invention 1 As described above, according to the present invention, the electrical characteristics of the interface between the transparent conductive oxide electrode and the p-type semiconductor thin film can be significantly improved without using expensive precious metals, etc., and with a simple process. We were able to. As a result, a method for manufacturing a photoelectric conversion element with extremely excellent photoelectric conversion efficiency is provided, and it must be said that its industrial applicability is extremely large.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view showing an example of the configuration of a photoelectric conversion element obtained by the Munagi invention. FIG. 2 is a schematic diagram showing an example of a preferred apparatus for forming the element of the present invention. In the figure, 1...substrate loading chamber, 2...
・N film formation chamber, 3...J film formation chamber, 4...
...N film formation chamber, 5...Second electrode formation chamber and substrate removal chamber, 6...Substrate, 9...Discharge power application electrode, 10... ...Installed electrode, 11...
... Substrate heating heater, 12 ... Electrode material heating heater, 13 ... Metal mask, 14 and 20 ... Vacuum exhaust line, 15 ... Raw material Gas introduction line, 16...Substrate transfer means, 1
7... Insulating material, 18... Discharge power application power source, 19... Gate valve patent applicant
Mitsui Toatsu Chemical Co., Ltd. Engraving of Drawings 1st Drawing Metal Electrode Type Semiconductor Thin Film 2nd P-type Semiconductor Thin Film - P-type Semiconductor Thin Film Electrode Laser Substrate Made of Photoconductive Oxide Procedural Amendment (Method) June 1986 ! 7th Director General of the Patent Office Kuro 1) Mr. Akio 1, Indication of the case Patent Application No. 53059 of 1988 2, Name of the invention Method for manufacturing photoelectric conversion elements 3, Person making the amendment ゛Relationship to the case Patent applicant address 3-2-5-4 Kasumigaseki, Chiyoda-ku, Tokyo Number of inventions to be increased by the amendment 0 5 Date of amendment order May 26, 1985 (shipped) 6 Subject of amendment

Claims (2)

[Claims] (1) On a transparent and insulating substrate, an electrode made of a transparent conductive oxide, a first p-type semiconductor thin film, a second p-type semiconductor thin film, a substantially intrinsic thin film, and an n-type semiconductor A method for manufacturing a photoelectric conversion element in which a thin film and a back metal electrode are formed in this order, the first p-type semiconductor thin film being doped with 2 to 5 times as much p-type impurity as the second p-type semiconductor thin film. 1. A method for manufacturing a photoelectric conversion element, characterized by: (2) The manufacturing method according to claim 1, wherein the first p-type semiconductor thin film has a thickness of 5 to 50 angstroms.