JP2735889B2 - Method for forming hydrogenated amorphous silicon film and method for forming photovoltaic device - Google Patents

Description

The present invention relates to a photovoltaic device, a method for forming a hydrogenated amorphous silicon film used as a semiconductor layer such as a thin film transistor, and a photovoltaic device using the film. About.

(B) Conventional technology Plasma chemical vapor deposition (hereinafter referred to as CVD) method and optical C
A hydrogenated amorphous silicon (hereinafter referred to as a-Si: H) film formed by the VD method generally contains 30% to 10% of hydrogen, depending on the substrate temperature.

As is well known, this type of semiconductor has a so-called Staebler-Wronsky effect (hereinafter referred to as SW effect) in which defects increase due to light irradiation or current injection. There is.

It is said that the SW effect is greatly affected by hydrogen existing inside, and researches on the role and stabilization of hydrogen are being conducted. For example, IEEE 14th Photovoltaic S
Pecialist Cont. (1987), pp. 678-683, "M
ATERIAL INVESTIGATIONS FOR HIGH-EFFICIENCY AND HI
GH-RELIABILITYA-SI SOLAR CELLS ".

On the other hand, during the process of forming the a-Si: H film, many attempts have been made to reduce the SW effect and control the amount of hydrogen and the bonding state. However, as an attempt to improve the film quality after film formation, App1. Phys. Lett. 44 (7), 1 April 1984 No. 69
`` Reverse bias and heat trea '' on page 7 to page 699
tment to improve perfomance of a-Si soler cells ''
Is the extent to which the reverse bias annealing shown in FIG.

(C) Problems to be solved by the invention As described above, for stabilization of the a-Si: H film,
First, no effective method has been found, and there have been problems such as a reduction in efficiency of a photovoltaic device or a thin film transistor, or a change in switching voltage.

An object of the present invention is to provide an a-Si: H film in which the localized level does not increase by light irradiation and the efficiency does not decrease.

(D) Means for Solving the Problems According to the formation method of the present invention, a strong light and an electric field are simultaneously applied to a hydrogenated amorphous silicon thin film at a temperature lower than the thin film forming temperature to move a part of hydrogen in the thin film. It is characterized in that the transferred hydrogen is released outside the thin film.

Further, the method for forming a photovoltaic device according to the present invention includes the steps of: forming a transparent conductive film, a hydrogenated amorphous silicon thin film,
And a method of forming a photovoltaic device by sequentially laminating metal electrodes, wherein the metal electrode is formed of a hydrogen-permeable metal or a mesh-like metal, simultaneously applying light and an electric field to the photovoltaic device, A part of the hydrogen in the hydrogenated amorphous silicon thin film is moved, and the transferred hydrogen is released from the metal electrode.

(E) Action Hydrogen in the a-Si: H film is bonded to Si, but the bond is weak and the bond is broken by energy such as light. And the cut hydrogen easily moves, and the original Si and other Si
Again.

Here, when the a-Si: H film is irradiated with strong light, a large amount of hydrogen atoms, electrons, and holes with broken bonds are generated from Si. The hydrogen atoms are positively charged and move to one of the electrodes when an electric field is applied to the film. By releasing the transferred hydrogen atoms to the outside of the film, hydrogen having a weak bond that can be cut by light is released to the outside of the film, and the a-Si: H film can be stabilized.

Further, by using a hydrogen-permeable metal or a mesh-like metal for the metal electrode, the hydrogen atoms transferred to this electrode are easily released to the outside of the film.

(F) Example Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a sectional view of a photovoltaic device using an a-Si: H film according to the present invention.

A transparent conductive film (2) such as ITO is formed on a transparent insulating substrate (1) made of glass or the like. Then, on this transparent conductive film (2), a p-type a-SiC film (3) and an i-type a-Si
A thin film made of hydrogenated amorphous silicon of the film (4) and the n-type a-Si film (5) is laminated by a plasma CVD method, an optical CVD method, or the like.

Subsequently, a back metal electrode (6) is formed on the n-type a-Si film (5) by vacuum evaporation or the like. In the present invention, the metal electrode (6) is made of palladium (Pd), platinum (Pd).
t) or a metal formed from aluminum (Al), silver (Ag) or the like in a mesh shape.

Next, an example of specific conditions for forming the hydrogenated amorphous silicon thin film will be described.

First, the p-type a-SiC film (3) is set at a substrate temperature of 100 to 200.
C. and the pressure is maintained at 0.1 to 1 Torr. And, as decomposition energy, set high frequency output 13.56MHz, output 20W,
As a reaction gas, SiH _{4 at} a flow rate of 5 sccm, CH _{4 at} a flow rate of 5 sccm,
Using B ₂ H ₆ with a flow rate of 0.05 sccm, by plasma CVD method,
A 450 ° -thick p-type a-SiC film (3) is formed.

Next, the i-type a-Si film (4) is set to a substrate temperature of 150 to 300.
C. and the pressure is maintained at 0.1 to 0.5 Torr. Then, an i-type a-Si film (4) having a film thickness of 8000 Å was formed by plasma CVD using SiH ₄ having a flow rate of 30 sccm as a reactive gas, with a high frequency output of 13.56 MHz and an output of 10 W as the decomposition energy. I do.

The n-type a-Si film (5) maintains the substrate temperature at 150 to 300 ° C. and the pressure at 0.1 to 0.5 Torr. Then, the decomposition energy was set to a high frequency output of 13.56 MHz and an output of 10 W, and SiH _{4 at} a flow rate of 5 sccm and PH ₃ at a flow rate of 0.015 sccm were used as the reaction gas. An Si film (3) is formed.

As described above, the metal electrode (6) is made of a hydrogen-permeable metal such as Pd or Pt by a vacuum evaporation method or the like to have a thickness of 500 μm.
Form a thin film or use a metal such as Al, Ag, etc.
What is necessary is just to form in a mesh-like metal film of 0.1 to 10 μm and a line interval of 1 to 100 μm.

In the present invention, as shown in FIG. 1, a strong electric field of 10 ⁵ V / cm or more is applied so that the back metal electrode (6) side of the photovoltaic device becomes negative. In this embodiment, the transparent conductive film (2)
And a metal electrode (6), a power source (7) is connected, and a forward bias of +10 V is applied so that the metal electrode (6) becomes negative. And 10 ¹⁹ Photon by halogen lamp (8)
The photovoltaic device (10) is irradiated with light at an irradiation intensity of s / cm ² · sec.

FIG. 2 shows a photovoltaic device (a) according to the present invention formed by holding the above-mentioned state for one hour, and a photovoltaic device (b) before applying a process, that is, before applying light and an electric field. ,
The result of measuring the amount of hydrogen in the film by SIMS or the like is shown. As shown in FIG. 2, in the photovoltaic device of the present invention,
The amount of hydrogen decreased from 15% to 8%, indicating that unstable hydrogen was released outside the film.

FIG. 3 is a measurement diagram showing the deterioration characteristics of the photovoltaic device formed according to the present invention, which has been subjected to the above-described processing, and (a), and the conventional photovoltaic device, which has not been subjected to the processing (b). Third
As is clear from the figure, in the conventional apparatus, the sunlight 50
Although it decreased by 25% after irradiation for 0 hours, the device of the present invention
% Has been improved.

(G) Effects of the Invention As described above, according to the present invention, unstable hydrogen in the hydrogenated amorphous silicon film is released outside the film, so that deterioration due to the SW effect is significantly reduced, It is possible to improve the efficiency of the photovoltaic device, the thin film transistor, and the like and to suppress the fluctuation of the switching voltage.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a photovoltaic device using an a-Si: H film according to the present invention, and FIG. 2 is a photovoltaic device according to the present invention and hydrogen in the film of the photovoltaic device before being subjected to processing. FIG. 3 is a measurement diagram showing the deterioration characteristics of the photovoltaic device according to the present invention and the conventional photovoltaic device.

Continuation of the front page (56) References JP-A-62-259423 (JP, A) JP-A-62-69608 (JP, A) JP-A-61-226919 (JP, A) Applied Physics Letters, vol. 44, no. 7, I April 1984, p. 697-699, G.A. A. Swartz, "Reverse bias and heat treatment to improve Perfomance of a -Si; solv cells"

Claims (2)

(57) [Claims] An intense light and an electric field are simultaneously applied to a hydrogenated amorphous silicon thin film formed by a chemical vapor deposition method at a temperature lower than a thin film forming temperature to move a part of hydrogen in the thin film. A method for forming a hydrogenated amorphous silicon film, wherein hydrogen is released outside the thin film. 2. A method of forming a photovoltaic device comprising a transparent conductive film, a hydrogenated amorphous silicon thin film, and a metal electrode sequentially stacked on a substrate, wherein the metal electrode is formed of a hydrogen-permeable metal or a mesh. It is formed of a metal, and simultaneously applying light and an electric field to the photovoltaic device to move a part of hydrogen in the hydrogenated amorphous silicon thin film, and to release the transferred hydrogen from the metal electrode. Of forming a photovoltaic device.