JPH09275220A - Semiconductor thin film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve initial conversion factor and the like, by employing as an optical active layer a p-type amorphous silicon germanium hydride semiconductor film containing a specific quantity of chlorine. SOLUTION: A p-type amorphous silicon germanium hydride semiconductor film 6 containing 1-200 atom ppm (p-type a-SiGe:Cl:H) is used for the optical active layer of a injunction amorphous solar cell. This obtains a injunction amorphous thin film solar cell with an initial conversion factor of 10% or above and with a conversion factor after one-year aging test of 9.0% or above.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to high performance solar cells, and more particularly to a technique for improving the quality of a photoactive layer that constitutes the solar cells.

[0002]

2. Description of the Related Art An a-SiGe: H thin film has an optical band gap (hereinafter referred to as an optical gap (Eg); a value determined by Tauc's plot) of 1.0 eV by changing the composition of silicon and germanium in the thin film. It can be controlled over a wide range up to 1.7 eV. Therefore, conventional amorphous silicon thin film containing hydrogen (hereinafter a-Si: H thin film)
(Eg = 1.7 to 1.8eV) is used as a photoactive layer in an amorphous solar cell and this a-SiGe: H thin film is used as a photoactive layer in a tandem cell. It is expected that a wide range of light absorption will be possible with respect to the spectrum contained in, and a highly efficient and photostable amorphous solar cell can be formed. In addition, by using a photoactive layer with an optical gap Eg = 1.5 eV in a single-junction cell, the initial conversion efficiency
10.5% (AM-1.5, measured under 100 mW / cm ² ), there is a possibility that a single junction amorphous solar cell with a conversion efficiency of 9.5% or more after outdoor exposure (1 year) may be obtained. Various methods for forming a-SiGe: H thin films have been tried for practical use.

For example, recently, a single junction for practical use
For a-Si solar cells, an efficiency of η = 8.8% (1 cm ² ) after initial deterioration equivalent to one year of outdoor exposure has been reported (Autumn 1994, Academic Society of Applied Physics (19a-ZK-5, Sanyo Denki)) . However, a single-junction amorphous solar cell having a performance of at least η = 9.5% (1 cm ² ) after initial deterioration equivalent to one year of outdoor exposure, which is a necessary condition for practical use, has not yet been obtained. When this a-SiGe: H thin film is used for the photoactive layer of a single-junction amorphous solar cell,
In order to strengthen the internal electric field on the n-layer side, it is necessary to introduce a p-type dopant, but conventionally, boron was used as this dopant. Since boron also becomes a defect in the a-SiGe: H thin film, it also causes deterioration of the film quality, and there is a limit in improving the characteristics.

[0004]

The present invention aims to improve the quality of a-SiGe: H thin film used for the photoactive layer of a solar cell, and by using this for the photoactive layer, the initial conversion efficiency is improved. The objective is to produce a single-junction amorphous thin-film solar cell with a conversion efficiency of 10.0% or more and a conversion efficiency of 9.0% or more after an outdoor 1-year exposure light deterioration test.

[0005]

That is, the present invention provides:
(1) p-type amorphous hydrogenated silicon germanium (p-type a-SiGe: Cl: H) semiconductor thin film containing 1 to 200 atomic ppm of chlorine, (2) the semiconductor thin film described in (1) as a photoactive layer The present invention relates to an amorphous solar cell used.

Incidentally, FIG. 1 shows the p containing chlorine according to the present invention.
-Type amorphous hydrogenated silicon germanium (p-type a-SiGe: Cl:
H) shows an example of a cell structure when the semiconductor thin film 6 is used as a photoactive layer of an amorphous solar cell.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION A p-type amorphous hydrogenated silicon germanium (p-type a-SiGe: Cl: H) semiconductor thin film containing chlorine is
Silane, germane, and chlorosilane are introduced into the reaction chamber of the capacitively coupled plasma CVD apparatus, and after maintaining a predetermined pressure, they are formed on the substrate by glow discharge. Regarding the optical gap (Eg) of the semiconductor thin film, the target optical gap of Eg = 1.3 to 1.6 eV is obtained by adjusting the gas composition of silane (S) and germane (G). At that time, chlorsilane (C) is added to the gas flow rate ratio γ (= C / (C + S + G)) for the purpose of containing a trace amount of chlorine in the film so that the semiconductor thin film becomes p-type. It is introduced in the range of 0.1-9%.
The chlorine concentration in the film is preferably introduced within the range of about 1 to 200 atomic ppm. In the present invention, these films are applied to the photoactive layer of amorphous solar cells.

As described above, the p-type amorphous hydrogenated silicon germanium (p-type a-SiGe: Cl: H) semiconductor thin film used for the photoactive layer is provided in the reaction chamber of a capacitively coupled plasma CVD apparatus with silane, germane and It is formed on the substrate by introducing chlorosilane and decomposing it by glow discharge. Chlorsilane introduced is used in a minute amount of 0.1 to 1% in the gas flow rate ratio to monosilane and germane gas. When the amount of chlorosilane introduced is too large, defects in the film also increase and the film characteristics deteriorate.

[0009] chlorosilane of the general formula _{Si n H m Cl 2n + 2} -m (n is a natural number, m <2n + 2) represented by the monochrome silanes, dichlorosilane, monochlorobenzene disilane, compounds such as di-chloro disilane using To be

As germane gas, compounds such as monogermane and digermane represented by the general formula Ge _n H _{2n + 2} (n is a natural number) are used.

[0011] The silane gas, the general formula Si _n H _{2n + 2 (n} is a natural number) represented by, monosilane, disilane, compounds such as trisilane is used.

Needless to say, even if a diluent gas such as H ₂ or He is used in combination with these gases, the present invention is not particularly hindered. With these gases, the optical gap 1.3-1.
A 6-eV a-SiGe: H thin film is formed. This a-SiGe: H thin film is applied to the photoactive layer of a crystalline solar cell or an amorphous solar cell.

The high frequency power source used in the plasma CVD method is mainly industrially used at 13.56MHz, 100MHz, 2.45MHz.
The frequency of GHz is used, but the frequency is appropriately selected according to the purpose of film formation. The raw material gas is supplied to the reaction chamber through the mass flow controller, and after being controlled to a predetermined pressure, high frequency power is applied to the RF electrode to discharge for a predetermined time and deposit a thin film on the substrate. In addition, a-SiGe: H
The amount of chlorine contained in the thin film is in the range of about 0.1 to 200 ppm when trace element quantitative measurement is performed by SIMS.
The value was considerably smaller than the corresponding gas flow rate ratio.

When the semiconductor thin film of the present invention is formed by the plasma CVD method, the forming temperature is 100 to 250 ° C., preferably 120 to 220 ° C., and the forming pressure is 0.01 to 1 Torr, preferably 0.05 to 0.15 Torr. Done. The applied RF power density is 1 mW / cm ² to 1 W / cm ² , preferably ² mW / cm ² to 30 mW /
Deposition is carried out at an RF power density of cm ² . The deposition rate at this time is 0.1 to 10 Å / s, preferably 0.2 to 0.6 Å / s.
Do with. p-type amorphous hydrogenated silicon germanium (p
(Type a-SiGe: Cl: H) as the flow rate ratio of the gas used to form the semiconductor thin film, when SiH ₄ , GeH ₄ , and SiH ₂ Cl ₂ are used, SiH ₄ : GeH ₄ : SiH ₂ Cl ₂ = 10: (0-20) :( 0.01-1) is preferable. The chlorine concentration in the film is preferably 1 to 200 ppm, more preferably 10 to 100 ppm.

In the photoactive layer of an amorphous solar cell, p
-Type amorphous hydrogenated silicon germanium (p-type a-SiGe: C
(l: H) When applying a semiconductor thin film, p-type or
Forms an n-type semiconductor thin film with a thickness of 1 to 100 nm, and then p-type
Alternatively, the n-type dopant is 10^Fifteen~Ten¹⁸cm^-3,contains
Weakly-doped a-Si: H thin film or a-SiC: H thin film formed 5 to 30 nm
In addition, the intrinsic a-Si: H with an optical gap of about 1.70 to 1.86 eV
After forming a thin film of 5 to 30 nm, the Ge composition y gradually changes.
A-Si_1-yGe_y: H thin film 10 to 30 nm thick, p-type amorphous
Hydrogenated silicon germanium (p-type a-SiGe: Cl: H) half
A conductor thin film is formed with a film thickness of 10 to 500 nm. And the composition y
Gradually changes a-Si_1-yGe_y: H thin film 10 to 30 nm type
After the formation, the optical gap of about 1.70 ~ 1.86 eV
An intrinsic a-Si: H thin film is formed with a thickness of 5 to 30 nm, and an n-type or
 p-type dopant 10^Fifteen~Ten¹⁸cm ^-3, Containing weak dope
Form an a-Si: H thin film or a-SiC: H thin film with a thickness of 5 to 30 nm, and further
Form an n-type or p-type semiconductor thin film and electrode on the
Form a crystalline solar cell. For thin film forming substrate,
There is no particular limitation. As a thin film forming substrate,
ITO, SnO_TwoPlate with transparent conductive film made of ZnO and ZnO
Conventionally used for glass, borosilicate glass, quartz glass, etc.
Useful glass substrate materials with transparent conductive film
However, metal and conductive plastics are thin.
It can be used as a film forming substrate material.

[0016]

EXAMPLES The effects of the present invention will be described with reference to the following examples. Example 1 An amorphous solar cell was formed using a plasma CVD apparatus. The composition is SnO ₂ transparent conductive glass substrate / p ^{+. A} -SiC: H film (10 nm) / p- ^{. A} -SiC: H film (6 nm) / a-Si: H
Film (10 nm) / Ge Graded a-Si _1-y Ge _y : H film (Eg = 1.77
→ 1.50eV, 15nm) / p-type amorphous hydrogenated silicon germanium (p-type a-SiGe: Cl: H) semiconductor thin film (Eg = 1.48eV, 150nm) / G
e Graded a-Si _1-y Ge _y : H film (Eg = 1.50 → 1.77eV,
15 nm) / a-Si: H film (10 nm) / n- ^{. A} -Si: H film (4 nm) / n ^{+. A} -Si: H film
(10 nm) / ITO (20 nm) / Ag (200 nm). The frequency of the RF power supply was 13.56 MHz. A film was formed by using monosilane, monogermane, and dichlorosilane as source gases for a p-type amorphous hydrogenated silicon germanium (p-type a-SiGe: Cl: H) semiconductor thin film. The gas flow rate ratio at the time of forming the p-type amorphous hydrogenated silicon germanium (p-type a-SiGe: Cl: H) semiconductor thin film was SiH ₄ : GeH ₄ : SiH ₂ Cl ₂ = 10: 1: 0.05. The predicted optical gap is 1.48 eV. P-type amorphous hydrogenated silicon germanium (p
The film thickness of the type a-SiGe: Cl: H) semiconductor thin film was set to 150 nm. As a result of quantitative elemental analysis of chlorine concentration in this film, 13 atoms
It was ppm.

The formation temperature of the photoactive layer was 180 ° C.
The forming pressure was 100 mTorr, and the RF power density was 6 mW / cm ² . The size of the RF electrode is φ10 cm. The average deposition rate at this time was 0.2 A / s. As a result, the initial conversion efficiency η = 1
0.5%, outdoor exposure equivalent to 1 year, efficiency after initial deterioration, η =
A single junction amorphous solar cell with a high value of 9.20% was obtained.

Comparative Example 1 In the single-junction amorphous solar cell shown in Example 1, a p-type amorphous hydrogenated silicon germanium (p-type a-SiGe: Cl: H) semiconductor thin film containing a small amount of chlorine was used. Instead of p, it contains a trace amount of boron as a dopant.
-Type amorphous hydrogenated silicon germanium (p-type a-SiGe: B:
H) A semiconductor thin film was applied to the photoactive layer. As a manufacturing condition, the gas flow rate ratio is SiH ₄ : GeH ₄ : B ₂ H ₆ (0.5 ppm / H ₂ dilution) = 1
It was set to 0: 1: 1. As a result, a single-junction amorphous solar cell having η = 8.50% as an efficiency after initial deterioration equivalent to one year of outdoor exposure was obtained.

[0019]

INDUSTRIAL APPLICABILITY The present invention applies a p-type amorphous hydrogenated silicon germanium (p-type a-SiGe: Cl: H) semiconductor thin film to the photoactive layer of a single-junction amorphous solar cell, and thus can be used outdoors. A high value of η = 9.20% was obtained as the efficiency after 1 year of exposure and after initial deterioration.

[Brief description of drawings]

FIG. 1 p-type amorphous hydrogenated silicon germanium (p-type a
-SiGe: Cl: H) semiconductor thin film applied to the photoactive layer of an amorphous solar cell

[Explanation of symbols]

1 Substrate with transparent conductive film 2 p-type or n-type semiconductor thin film 3 p-type or n-type dopant 10 ¹⁵ to 10 ¹⁸ cm ^-3
Contains a weakly doped a-Si: H thin film or a-SiC: H thin film 4 Intrinsic a-Si: H thin film 5 Ge Composition y gradually changes a-Si _1-y Ge _y : H thin film 6 Chlorine 1 ~ P-type amorphous hydrogenated silicon germanium (p-type a-SiGe: Cl: H) semiconductor thin film containing 200 atom ppm 7 Ge composition y gradually changes a-Si _1-y Ge _y : H thin film 8 Intrinsic a-Si: H thin film 9 n-type or p-type dopant 10 ¹⁵ to 10 ¹⁸ cm ^-3 ,
Weakly doped a-Si: H thin film or a-SiC: H thin film containing 10 n-type or p-type semiconductor thin film 11 Electrode

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kimihiko Saito 1190 Kasama-cho, Sakae-ku, Yokohama-shi, Kanagawa Mitsui Toatsu Chemical Co., Ltd. (72) Mitsuru Sadamoto 1190 Kasama-cho, Sakae-ku, Yokohama, Kanagawa Mitsui Toatsu Chemical Incorporated (72) Inventor Shin Fukuda 1190 Kasama-cho, Sakae-ku, Yokohama-shi, Kanagawa Mitsui Toatsu Chemical Co., Ltd.

Claims (2)

[Claims] 1. A p-type amorphous hydrogenated silicon germanium (p-type a-SiGe: Cl: H) semiconductor thin film containing 1 to 200 atomic ppm of chlorine. 2. An amorphous solar cell using the semiconductor thin film according to claim 1 for a photoactive layer.