JPH0128512B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing photovoltaic elements such as solar cells. Photovoltaic elements using various semiconductor and oxide-based transparent conductive films have conventionally existed. In recent years, amorphous silicon ( _hereinafter referred to as
It was revealed that valence electrons (referred to as a-Si) can be controlled, which was previously thought to be impossible.
Since then, it has been considered that photovoltaic elements can be constructed from thin films and that it is easy to increase the area, and applications such as solar cells have been considered. A-Si films, which are used in solar cells and other devices and can control valence electrons, contain large amounts of hydrogen and fluorine. In addition, the optimum value of the substrate temperature when creating a-Si is approximately
The temperature is 250℃. An oxide-based transparent conductive film is formed on this a-Si film to create a photovoltaic device, but the necessary characteristics of the transparent conductive film are high light transmittance and low sheet resistance. It is said that It is desirable that the transmittance is 85% or more and the sheet resistance is 100Ω/□ or less. For oxide-based transparent conductive films such as indium oxide and tin oxide, the thickness is preferably 1 μm or less in order to obtain a transmittance of 85% or more, and the thickness is preferably 1 μm or less in order to obtain a sheet resistance of 100 Ω/□ or less.
Since a thickness of 1000 Å or more is preferable, a transparent conductive film with a thickness of about 3000 Å is often used. A transparent conductive film with good light transmittance and low resistance cannot be obtained unless the substrate temperature is 300° C. or higher when forming an oxide-based transparent conductive film by means such as vacuum evaporation. However, after forming the a-Si film, if the a-Si is heated above the temperature at which it was formed (250°C), the hydrogen and fluorine contained in the a-Si will be released, causing the a-Si to deteriorate. It had the disadvantage that the characteristics, that is, the characteristics of the solar cell deteriorated. The present invention provides a photovoltaic device consisting of at least an oxide-based transparent conductive film and a semiconductor, by forming the transparent conductive film on the semiconductor through a plasma state, thereby lowering the substrate temperature during formation and achieving good characteristics. In other words, the present invention provides a photovoltaic element with high photoelectric conversion efficiency. Examples will be described in detail below. FIG. 1 is a cross-sectional view showing the structure of a photovoltaic device using an a-Si semiconductor, in which 1 is a stainless steel substrate, 2 is an a-Si semiconductor layer, and 3 is an indium oxide substrate.
A transparent conductive film of tin (5 to 10 wt% tin oxide), 4 represents sunlight. The a-Si semiconductor layer 2 is composed of a p-type a-Si layer doped with boron B, an i-type a-Si layer not doped with impurities, and an n-type a-Si layer doped with phosphorus P. Created using the plasma CVD method (glow discharge decomposition method). An indium tin oxide transparent conductive film 3 was formed on a stainless steel substrate 1 with an a-Si layer 2 formed thereon by the conventional method and the method of the present invention. Conventional method Indium oxide/tin transparent conductive film is deposited at a substrate temperature of 150
It was formed by vacuum evaporation method at ℃. Vacuum level is 10 ^-6 Torr
The growth rate of the film is approximately 1 Å/sec. Conventional method A transparent conductive film was formed by vacuum evaporation in an oxygen atmosphere of 10 ^-4 Torr at a substrate temperature of 150°C. The film growth rate is approximately 1 Å/sec. Conventional method A transparent conductive film was formed by vacuum evaporation in an oxygen atmosphere of 10 ^-4 Torr at a substrate temperature of 350°C. The film growth rate is approximately 1 Å/sec. Example An indium oxide/tin transparent conductive film was formed using the ion plating method described below at a substrate temperature of 150°C. The ion plating method is a method of forming a film by ionizing evaporated particles and/or atmospheric gas using an ionization electrode that applies a high frequency or DC voltage between an evaporation source and a substrate. In this method, since the evaporated substance and the atmospheric gas are ionized and activated, reactive deposition of the evaporated substance and the atmospheric gas is possible. Furthermore, by applying a negative voltage to the substrate, it is possible to cause ionized particles to adhere to the substrate with greater kinetic energy than in normal vapor deposition, thereby forming a film with good adhesion. In this example, the evaporation source was indium tin oxide (5 to 10 wt% tin oxide), and 200 W of 13.56 MHz high frequency power was applied to the ionization electrode.
The oxygen atmosphere was 10 ^-4 Torr. The oxygen partial pressure is preferably 10 ^-2 to 10 ^-5 Torr in order to stabilize ionization. Further, no negative DC voltage was applied to the substrate. In the conventional method and the embodiment of the present invention explained above, the thickness of the transparent conductive film is 3000 Å, and the area is 9
^mm2 . In addition, the manufacturing method and structure other than the transparent conductive film were all the same. The solar light (AM-1,
Table 1 shows the output characteristics during irradiation (100mW/cm ² ). Jsc is the short-circuit photocurrent, Voc is the frequency edge voltage, FF is the curve foil factor, and _Eff is the photoelectric conversion efficiency.

[Table] As shown in Table 1, in the conventional method, the light transmittance of the transparent conductive film is low, so the short-circuit photocurrent value is low. In the conventional method, the light transmittance of the transparent conductive film is slightly improved and the short-circuit photocurrent is increased compared to the conventional method, but this is not sufficient. In the conventional method, the light transmittance of the transparent conductive film is improved, but the temperature of the substrate on which the a-Si film is formed is raised to 350°C during the formation of the transparent conductive film. The characteristics deteriorate and the short-circuit photocurrent also stops increasing.
The other properties are also poor, and the photoelectric conversion rate is also poor. On the other hand, in the embodiments of the present invention, since the substrate temperature is low and the transparent conductive film has good light transmittance, it exhibits very excellent characteristics and therefore has good photoelectric conversion efficiency. Although there is a method of ionizing oxygen by electron beam irradiation as a method for creating plasma, the above-mentioned method of ionizing oxygen using a high frequency electric field or a direct current electric field is preferable for obtaining a transparent conductive film with high light transmittance and low resistance. Also, in this example, the case where indium tin oxide was used as the evaporation source was described;
A similar effect can be obtained by using metal indium or tin as the evaporation source and performing reactive evaporation. Although the case of using an indium oxide-based transparent conductive film such as indium oxide and tin has been described, the same effect can be obtained with a tin oxide-based transparent conductive film such as tin oxide or tin oxide added with antimony oxide. Although there are other oxides that have translucency and conductivity, tin oxide-based and indium oxide-based transparent conductive films are excellent. Further, although the case of a-Si as the semiconductor has been described, the same effect can be obtained in the case of a semiconductor whose characteristics deteriorate when exposed to high temperatures of 250° C. or higher. As explained in detail above, according to the present invention, a photovoltaic element with high photoelectric conversion efficiency can be obtained.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing the structure of a photovoltaic element. 1: stainless steel substrate, 2: a-Si semiconductor layer,
3: Transparent conductive film, 4: Sunlight.

Claims (1)

[Claims] 1. In a method for manufacturing a photovoltaic device in which a transparent conductive film is formed on an amorphous silicon semiconductor substrate by a PVD method, the transparent conductive film is an indium oxide-based or tin oxide-based thin film, and the transparent conductive film is The conditions for forming the evaporation source include applying a high frequency electric field or a direct current electric field between the evaporation source and the substrate while maintaining the substrate temperature below 250°C in an oxygen partial pressure atmosphere of 10 ^-2 to ^{10 -5} Torr, A method for producing a photovoltaic element, characterized in that a film is formed by PVD that undergoes a plasma state by ionizing evaporated particles or atmospheric gas by this electric field.