JP3245962B2 - Manufacturing method of thin film solar cell - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a thin-film solar cell having a pin junction mainly composed of amorphous silicon (hereinafter abbreviated as a-Si).

[0002]

2. Description of the Related Art A solar cell mainly composed of a-Si formed by glow discharge decomposition of a source gas or a photo-CVD method has features of being thin and capable of being easily enlarged, and is expected to be a low-cost solar cell. I have. As a structure of this type of solar cell, a pin-type a-Si solar cell having a pin junction is generally used. FIG. 2 shows a structure of such a solar cell, in which a transparent electrode 2, a p-type a-Si layer 31, a p /
It is manufactured by sequentially laminating an i interface layer 4, an i-type a-Si layer 5, an n-type a-Si layer 6, and a metal electrode 7. In this solar cell, power is generated by light incident through the glass substrate 1.

Here, photocarriers contributing to power generation are mainly generated in the i-layer, and the p and n layers are dead layers. Therefore, in a solar cell in which light is incident from the p-layer, it is important to increase the light transmittance of the p-layer corresponding to the window layer so that as much light as possible reaches the i-layer in order to increase the output. . To that end, it is effective to increase the optical gap Eg of the p-layer to reduce the optical absorption loss. For this purpose, a carbon atom may be added to the p-type a-Si layer as known in, for example, JP-A-56-64476, or a nitrogen atom may be added as known in JP-A-57-181176. Or an oxygen atom as known in JP-A-56-142680, or JP-A-58-19.
Attempts have been made to add oxygen atoms and carbon atoms as known in JP-A-6064 or JP-A-61-242085.

[0004]

A large amount of C is formed during the formation of a p-layer.
The optical gap can be increased by alloying by adding N or N. However, at the same time, a large amount of dangling bonds are induced in the film, so that the electric conductivity is reduced. Usually, in an a-Si solar cell, the electric conductivity at 25 ° C. of a film used for a p-layer is limited to 10 ⁻⁸ S / cm or more in order to suppress a decrease in the fill factor. In order to satisfy this condition, the optical gap has to be set to 2 eV or less in the above-mentioned p-type a-SiC: H (B) and p-type a-SiN: H (B). Therefore, the light absorption loss in the p-layer is relatively large, and is 1 to ² mA / cm ² in terms of short-circuit current density.
Loss. Also, according to the description of JP-A-61-242085, undoped a-Si: O: C:
In the H film, the electric conductivity (σ _d ) is 10 when the optical gap is 2.0 eV or more when AMI (simulated sunlight) is irradiated at 100 mW / cm ^2.
It is about ^-12 to 10 ^-13 S / cm, and it is not clear how much a p-layer having an optical gap is obtained when doping is performed.

An object of the present invention is based on the above situation, and uses an a-Si film having an electric conductivity of 0.5 to 1 × 10 ⁻⁶ S / cm and a larger optical gap as a window layer. An object of the present invention is to provide a method for manufacturing a thin film solar cell with higher efficiency.

[0006]

According to the present invention, there is provided a method of manufacturing a thin film solar cell having a pin junction structure comprising amorphous silicon as a main material. The p-layer and the p / i interface layer having a smaller oxygen doping amount than the p-layer on the light incident side of the i-layer are added to a mixed gas in which monosilane and nitrous oxide are diluted with hydrogen and a gas containing impurities for doping is added. Then, it is formed by amorphous silicon oxynitride generated on a substrate heated by decomposition. According to the present invention,
In a thin-film solar cell having a pin junction structure mainly composed of amorphous silicon, a p-layer on the light incident side of the i-layer and a p / i interface layer having a smaller oxygen doping amount than the p-layer are: It is represented by the general formula a-Si _(1-XY) O _X N _Y and 0.05
<X <0.40, 0.03 <Y <0.07, made of an amorphous silicon oxynitride film having an optical gap of 2.0 eV to 2.3 eV at 25 ° C. A method for manufacturing a thin-film solar cell having a conductivity ratio of 5 or less, wherein a monosilane and nitrous oxide are diluted with hydrogen in the p-layer and the p / i interface layer having a smaller oxygen doping amount than the p-layer. It is formed by adding a gas containing impurities for doping to a mixed gas and decomposing the mixed gas. Here, the decomposition of the mixed gas is preferably performed by glow discharge decomposition.

[0007]

[Function] Generally, SiH_Four, O_TwoThe film formed by
SiH in the gas phase_FourAnd O_TwoReacts violently with SiO_TwoIs generated
Therefore, this is taken into the film, resulting in a film with many defects.
I will. a-Si: O: N film is SiH_Four, N_TwoO and
H_TwoCan be formed by glow discharge decomposition of a mixed gas of
SiH_FourAnd N_TwoSince O does not react in the air, SiO _TwoIs raw
A good film with few defects is not formed. Sa
In addition, the optical gap is set in the range of 2.0 to 2.3 eV,
Electric power σ_phAnd dark conductivity σ_dRatio σ_ph/ Σ_dIs 5 or less
With an optical gap of 2.0 eV or more,
^-8Pin having a p layer or n layer of S / cm or more as a window layer
A bonded thin-film solar cell is obtained.

[0008]

FIG. 1 shows a cross-sectional structure of an a-Si solar cell according to one embodiment of the present invention. The same reference numerals as in FIG. 2 denote the same parts. This solar cell is manufactured as follows. First, SnO ₂ was used as a transparent electrode 2 on a glass substrate 1.
Is formed to a thickness of 5000 to 10000 mm. This substrate was mounted on a plasma CVD apparatus, and SiH ₄ (monosilane),
A p-type a-SiO film 3 is formed by a glow discharge decomposition method using CO ₂ as a main gas, H ₂ as a diluent gas, and B ₂ H ₆ as a doping gas.
Is formed to a thickness of 100 to 200 mm. Here, the addition amount as _{B 2 H 6 / SiH 4 =} 0.2 ~1% are of B ₂ H _6, the substrate temperature during film formation 140 to 250 DEG ° C., hydrogen dilution (H ₂ / Si
H ₄ ) is in the range of 10 to 50. Subsequently, SiH ₄ , CH
_{Using 4} as a main gas and H ₂ as a diluent gas, ap / i interface layer 4 of a-SiC is formed to a thickness of 50 to 200 °. No boron is added to the p / i interface layer 4 and the optical gap is equal to that of the p layer 3 and i.
The film formation conditions were selected so that the values were intermediate between the layers (1.8 to 2.0 eV). Further, after the substrate temperature was raised to 200 to 250 ° C., an i-type a-Si layer 5 was formed to a thickness of 2000 to 5000 ° using SiH ₄ as a main gas and H ₂ as a diluent gas, and a Si
An n-type a-Si layer 6 is formed to a thickness of 150 to 300 ° using H ₄ as a main gas, H ₂ as a diluent gas, and PH ₃ as a doping gas. Finally, the metal electrode 7 is formed by vapor deposition of Ag or Al or by sputtering and patterning.

FIG. 3 shows N ₂ O when an a-Si: O: N film is formed.
Shows a Si was determined by the gas flow rate ratio of _{SiH 4 (N 2 O / SiH} 4) and X-ray photoelectron spectroscopy (XPS), O, the relationship between the composition ratio of N. In FIG. 4, the relationship between the electrical conductivity of the a-Si: O: N film and the optical gap is shown by a solid line 41 when the film was formed under the following conditions. Gas used: SiH ₄ , N ₂ O, H ₂ , B ₂ H ₆ Gas flow rate ratio: H ₂ / SiH ₄ = 20 B ₂ H ₆ / SiH ₄ = 0.006 N ₂ O / SiH ₄ = 0.125 １1 Substrate temperature ℃ 170 ° C. Pressure も の 0.5 Torr In FIG. 4, the dotted line 42 indicates that CO ₂ is used instead of N ₂ O.
Is a relationship between the electrical conductivity and the optical gap of an a-SiO film formed under the following optimum conditions using the above formula.

Gas used: SiH ₄ , CO ₂ , H ₂ , B ₂ H ₆ Gas flow ratio: H ₂ / SiH ₄ = 20 B ₂ H ₆ / SiH ₄ = 0.006 CO ₂ / SiH ₄ = 2.52 Substrate temperature: 170 ° C. Pressure: 0.5 Torr From the results shown in FIG. 4, the film characteristic when N ₂ O is used is C
It can be said that the characteristics are almost the same as those when O ₂ is used. Electrical conductivity of 10 ^-6 S / cm or more has an optical gap of 2.08 eV
Which is obtained from a-Si using CO ₂ indicated by a dotted line 42.
Although slightly inferior to the case of the O film, the value is about 0.1 eV higher than that of the conventional a-SiC film or a-SiN film, which indicates that the characteristics are excellent.

The a-Si: O: N film formed under the above conditions
Table 1 shows the photoconductivity and dark conductivity at 25 ° C.

[0012]

[Table 1] From Table 1, it was found that when σph / σd is 5 or less, an electric conductivity of 10 ⁻⁸ S / cm or more can be obtained.

Next, a-Si: O: N is applied to the p-layer of the single cell.
The characteristics when the film was applied were compared with those when an a-SiO film manufactured using CO ₂ was applied. Here, the thicknesses of the p layer 3, the i layer 5, and the n layer 6 of the single cell are respectively
100 mm, 4000 mm, and 200 mm. P-type a used for cell
The conditions for forming the -Si: O: N film are as follows. Gas used: SiH ₄ , N ₂ O, H ₂ , B ₂ H ₆ Gas flow rate ratio: H ₂ / SiH ₄ = 20 B ₂ H ₆ / SiH ₄ = 0.006 N ₂ O / SiH ₄ = 0 ... 0.5 Substrate temperature... 170 ° C. Pressure... 0.5 Torr a-SiO film formation conditions are the same as above.

The characteristics of the obtained p-type a-Si: O: N film and a-SiO film are as follows. a-Si: O: N film Optical gap: 2.07 eV Photoconductivity: 2.69 × 10 ^-6 S / cm Electrical conductivity: 1.12 × 10 ^-6 S / cm a- SiO film Optical gap: 2.16 eV Photoconductivity: 1.1 x ^10-6 S / cm Electrical conductivity: 0.5 x ^10-6 S / cm In these prototype cells, p / I interface layer 4
In each cell of the p-layer having the a-Si: O: N film and the a-SiO film, the oxygen doping amount is smaller than that of the p-layer.
-Si: O: N film and a-SiO film are used. Table 2 shows the results of measuring the conversion efficiency of the fabricated cell under irradiation with light of AM 1.5 and 100 mW / cm ² . Incidentally, Table 2 also shows, for comparison, those using the a-SiC film for the p layer and the p / i interface layer.

[0015]

[Table 2] From this table, it can be seen that Jsc using the a-Si: O: N film for the p layer and the p / i interface layer has a larger Jsc than that using the a-SiC film for the p layer and the p / i interface layer. Obtained, and the efficiency is increased. It can be seen that, as compared with those using the a-SiO film for the p layer and the p / i interface layer, the optical gap is small, the Jsc and the efficiency are inferior, but similar high ones are obtained.

[0016]

According to the method of manufacturing a thin-film solar cell of the present invention, as a result of adopting the above configuration, the electric conductivity is 10 ^-8 S.
/ Cm or more, a film having an optical gap of 2.1 eV or more can be formed. Thereby, the light absorption loss can be reduced and the short-circuit current density can be improved as compared with the case where a conventional p layer having an optical gap of 2.0 eV or less is used.
Further, while having a high optical gap, σ _ph is about 10 ^−6.
, The series resistance component can be kept low, cells with a fill factor of 0.7 or more can be formed, and cells with a conversion efficiency of 12% or more can be formed.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a single cell of an a-Si solar cell according to one embodiment of the present invention.

FIG. 2 is a cross-sectional view of a single cell of a conventional a-Si solar cell.

FIG. 3 is a graph showing a relationship between a gas flow rate ratio and a film composition ratio when an a-Si: O: N film is formed.

FIG. 4 is a diagram showing the relationship between the electrical conductivity of an a-Si: O: N film and an optical gap.

[Explanation of symbols]

 Reference Signs List 1 glass substrate 2 transparent electrode 3 p-type a-Si: O: N layer 4 p / i interface layer 5 i-type a-Si layer 6 n-type a-Si layer 7 metal electrode

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-60-262470 (JP, A) JP-A-59-108370 (JP, A) JP-A-63-224223 (JP, A) JP-A-58-108 209171 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 31/04-31/078

Claims (3)

(57) [Claims] 1. A pin comprising amorphous silicon as a main material.
In a method for manufacturing a thin film solar cell having a junction structure,
The p-layer and the p / i interface layer having a smaller oxygen doping amount than the p-layer on the light incident side of the layer are formed by adding a gas containing doping impurities to a mixed gas in which monosilane and nitrous oxide are diluted with hydrogen. And a method of manufacturing a thin-film solar cell, comprising amorphous silicon oxynitride generated on a substrate heated by decomposition. 2. A pin using amorphous silicon as a main material.
In a thin-film solar cell having a junction structure, a p-layer on the light-incident side of the i-layer and p-p with a smaller oxygen doping amount than the p-layer
/ I interface layer is represented by the general formula a-Si _(1-XY) O _X N _Y , where 0.05 <X <0.40, 0.03 <Y <0.07
Consisting of an amorphous silicon oxynitride film,
And the optical gap is 2.0 eV to 2.3 eV,
A method for producing a thin-film solar cell wherein the ratio of photoconductivity to dark conductivity at 25 ° C. is 5 or less, wherein the p-layer and the p / i interface layer having a smaller oxygen doping amount than the p-layer are made of monosilane and A method for manufacturing a thin-film solar cell, comprising: adding a gas containing impurities for doping to a mixed gas in which nitrogen oxide is diluted with hydrogen; and decomposing the mixed gas. 3. The method according to claim 1, wherein the decomposition of the mixed gas is performed by glow discharge decomposition.