JPH0595126A - Thin film solar battery and manufacturing method thereof - Google Patents

Abstract

PURPOSE:To reduce a light absorption loss through laminated cells and improve conversion efficiency in a thin film solar battery, by using given amorphous silicon oxide as a material for p and n layers, each located on the rear side, opposed to the light incident side, of every pin junction-structured i layer except a pin junction-structured layer at the most distant place from the light incident side. CONSTITUTION:A plurality of pin junction structures mainly made of amorphous silicon oxide are deposited. In this case, amorphous silicon oxide, a-Si(1-x)Ox, where x is less than 0.2, is used as a material for p and n layers 5 and 6, each located on the rear side, opposed to the light incident side, of each pin junction- structured i layer except a pin junction-structured layer at the most distant place from the light incident side. Moreover, the amorphous silicon oxide is formed in a chemical decomposition step, such as a glow discharging decomposition step with the use of a mixed gas of monosilane, carbon dioxide, hydrogen, and doping impurities.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to amorphous silicon.
The present invention relates to a thin-film solar cell in which a plurality of pin-junction structures containing (hereinafter abbreviated as a-Si) as a main material are laminated and a method for manufacturing the same.

[0002]

2. Description of the Related Art An a-Si solar cell formed by a plasma CVD method or a photo CVD method using a silane-based gas is a thin film,
It is expected to be used as a low-cost solar cell because it has the characteristic that it can be easily enlarged. On the other hand, the a-Si solar cell has a so-called "photodegradation phenomenon" in which the characteristics are deteriorated by long-term light irradiation, which is a big problem in practical use. As one method of solving this problem, as shown in FIG.
The joining structure may be a two-layer structure. This solar cell is called a two-layer tandem cell, and photodegradation can be suppressed to about half that of a single cell composed of one ordinary pin junction. The two-layer tandem cell is manufactured as follows.

First, SnO is formed on the glass substrate 1.₂Etc.
The bright electrode 2 is formed, and SiH is formed on it._Four, CH_FourWith the main gas
And H₂The diluent gas, B₂H₆As a doping gas
Amorphous silicon carbide (a-SiC) first p
Form layer 3 to a thickness of 100-150Å. Continued SiH_Four
The main gas, H₂Is used as a diluting gas for the first i-layer 4 of a-Si.
Formed to a thickness of 500 to 800 Å, and further SiH_FourThe main gas,
H₂The diluent gas, PH ₃Is used as a doping gas for a-Si
The first n-layer 5 is formed to a thickness of 100 to 150Å. next,
The second p, i, n layers 6, 7 and 8 are respectively
Formed to a thickness of 0 to 150 Å, 3000 to 5000 Å, 100 to 150 Å
Then, it is manufactured by forming the back surface electrode 12. Well
Also, the n / p junction between the two cells becomes an ohmic junction.
Between the first n layer 5 and the second p layer 6 as necessary.
N or p type micro crystal silicon (μc
-Si) layer is formed.

[0004]

In a-Si solar cells, p
The layers and the n layer are dead layers, and light absorption in these layers leads to power generation loss. Therefore, it is conceivable to increase the optical gap of the p layer corresponding to the window layer to reduce the light absorption. For example, as known from JP-A-56-64476, a-SiC is applied to the p layer, We are trying to reduce light absorption loss. In the case of a two-layer tandem cell, in addition to this, light absorption loss occurs at the n / p junction between cells. This part is different from the n layer on the metal electrode side of the single cell,
Since the intensity of light passing through is about half that of incident light, light absorption has been a major problem. It has been found by simulation that the loss of the short circuit current density Jsc in the n layer is 3 to 5%.

An object of the present invention is to solve the above-mentioned problems and to provide a thin film solar cell in which light absorption loss in the middle of stacked cells is reduced and a manufacturing method thereof.

[0006]

In order to achieve the above object, the present invention provides a thin-film solar cell in which a-Si is used as a main material and a plurality of pin-junction structures are laminated, and the thin-film solar cell is most suitable from the light incident side. Each pin except for the distant pin junction structure
P layer or n-layer on the anti-light incident side of the i layer of the junction structure is represented by the general formula _{a-Si (1-x)} O x, x is assumed to consist of amorphous silicon oxide is less than 0.2. Then, it is effective that the optical gap of the a-SiO layer on the side opposite to the light incident side of the i layer is in the range of 1.9 eV to 2.1 eV, or its photoconductivity is 1 × 10 ⁻⁶ s / cm or more. is there. Further, the present invention is based on pi containing a-Si as a main material.
In a method for manufacturing a thin-film solar cell in which a plurality of n-junction structures are laminated, a p-layer or an n-layer on the anti-light incident side of the i-layer of each pin junction except for the pin junction structure farthest from the light incident side is replaced with SiH ₄ , It is formed of a-SiO generated by decomposing a mixed gas of CO ₂ , H ₂ and a gas containing impurities for doping. Then, it is effective to decompose by glow discharge decomposition.

[0007]

[Function] By increasing the amount of oxygen in the a-Si film, the optical gap Eg becomes larger than 1.9 eV and the absorption loss of the light exiting the i-layer to the next pin junction is reduced. Then
Short circuit current increases. However, the amount of oxygen increases further,
When _{x of} a-Si _(1-x) O _x exceeds 0.16 and becomes close to 0.21, the photoconductivity σ _{ph of the} a-SiO film lowers, the bulk resistance increases, the series resistance component increases, and the fill factor increases. Is reduced. Therefore, it is effective to set σ _ph in the range of 1 × 10 ^-6 s / cm or more, and Eg becomes 2.1 eV in that case. And SiH
_A formed by decomposition of a mixed gas of ₄ , CO ₂ and H ₂
-SiO film, there is no a defect occurs in the film, good quality films are obtained for the violent reaction of SiH ₄ and O ₂ as when forming the a-SiO film by SiH _4, O _2, etc. ..

[0008]

EXAMPLE A thin-film solar cell of an example of the present invention having the structure of FIG. 1 was manufactured as follows. On a glass substrate 1 First, a transparent electrode 2 of SnO ₂ or the like, a-Si thereon
The first p-layer 3 made of C, the first i-layer 4 made of a-Si, and the first n-layer 5 made of a-SiO are respectively 120 Å, 700
Å, formed to a thickness of 100 Å. Then, a second p layer 6 made of a-SiC, a second i layer 7 made of a-Si and a second n layer.
Layer 8 was formed to a thickness of 120Å, 3000Å and 150Å respectively, and a metal electrode 12 of Ag or the like was formed. Of these, the first n-layer 5 according to the present invention is formed by the following method.

Silane (SiH ₄ ), carbon dioxide (CO ₂ ), hydrogen as raw material gas is placed in a film forming chamber containing a glass substrate 1 on which a transparent electrode 2, a first p layer 3 and a first i layer 4 are already formed.
(H ₂ ) and phosphine (P
H ₃ ) is introduced. The flow rate of each gas is H ₂ / SiH ₄ =
20, CO ₂ / SiH ₄ = 0.1 to 4, PH ₃ / SiH ₄ = 0.01
And the total gas pressure is 0.5 Torr. The substrate temperature is kept at 150 ° C., high frequency power is applied between the electrodes, and an a-SiO film is formed by glow discharge decomposition. a
The composition of the —SiO film can be changed by changing the gas ratio of SiH ₄ and CO ₂ . Where a-Si
The optical gap Eg and the electrical conductivity σ _ph when the film composition x of the n layer represented by _(1-x) O _x was changed, and the solar cell characteristics of the two-layer tandem cell produced by applying the film were shown. It shows in Table 1. The film composition of the n-layer is the value analyzed by X-ray photoelectron spectroscopy (XPS), and the solar cell characteristics are AM1.5, 100mW.
It is a value measured under simulated sunlight of / cm ² .

[0010]

[Table 1]

As can be seen from Table 1, the optical gap Eg is increased by increasing the amount of oxygen in the film, and the short circuit current density Jsc is improved accordingly. The maximum improvement in Jsc is about 3%, which shows good correspondence with the simulation results. On the other hand, focusing on the fill factor FF, it is found that it is almost constant in the range of X ≦ 0.16, but it decreases when it becomes larger than that. this is,
This is because the decrease in photoconductivity σ _ph increases the bulk resistance of the n layer and increases the series resistance component. Therefore, σ _ph
When an a-SiO film in the range of ≧ 1 × 10 ⁻⁶ s / cm is used for the n layer, Jsc is improved without lowering FF and the conversion efficiency η
Was found to improve.

FIG. 2 shows a three-layer tandem cell of another embodiment of the present invention, and the same parts as those in FIG. 1 are designated by the same reference numerals. In this case, the second n layer 8 forming the second n / p junction is also formed of a-SiO satisfying the condition of σ _ph ≧ 1 × 10 ⁶ s / cm, and the same effect as the two-layer tandem cell is obtained. It was The third p layer 9 is made of a-SiC and the third n layer 11 is made of a-Si.
However, amorphous silicon germanium is applied to the third i layer 10 to improve the long wavelength sensitivity.

[0013]

According to the present invention, by applying a-SiO whose oxygen content is adjusted to the layer on the light incident side of the n / p or p / n junction between the cells of the tandem cell, the i-layer is formed. The light absorption loss in the n-layer or p-layer behind the
An improvement in short circuit current density can be achieved. As a result, it was possible to obtain a thin-film solar cell exhibiting higher conversion efficiency than the tandem cell manufactured by the conventional method.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a two-layer tandem cell embodying the present invention.

FIG. 2 is a cross-sectional view of a three-layer tandem cell embodying the present invention.

[Explanation of symbols]

 1 glass substrate 2 transparent electrode 3 first p layer 4 first i layer 5 first n layer 6 second p layer 7 second i layer 8 second n layer 9 third p layer 10 third i layer 11 third n Layer 12 Metal electrode

Claims (5)

[Claims] 1. Amorphous silicon as a main material
In a structure in which a plurality of n-junction structures are laminated, each pi except the pin-junction structure farthest from the light incident side.
p layer or n-layer on the anti-light incident side of the i layer of the n junction structure is represented by the general formula _{a-Si (1-x)} O x, characterized in that x is made of amorphous silicon oxide is less than 0.2 Thin film solar cell. 2. The optical gap of the amorphous silicon oxide layer on the anti-incidence side of the i layer is 1.9 eV to 2.1 eV.
The thin film solar cell according to claim 1, which is in the range of. 3. The thin film solar cell according to claim 1, wherein the amorphous silicon oxide layer on the side of the i layer opposite to the light incident side has a photoconductivity of 1 × 10 ⁻⁶ s / cm or more. 4. A pi containing amorphous silicon as a main material.
In a method for manufacturing a thin-film solar cell in which a plurality of n-junction structures are stacked, a p-layer or an n-layer on the anti-light incident side of the i-layer of each pin junction structure except for the pin junction structure farthest from the light incident side is replaced with monosilane A method for manufacturing a thin-film solar cell, which comprises forming with amorphous silicon oxide generated by decomposing a mixed gas of carbon dioxide, hydrogen and a gas containing impurities for doping. 5. The method for manufacturing a thin film solar cell according to claim 4, wherein the decomposition is performed by glow discharge decomposition.