JPH0321080A - Manufacturing method for laminated type solar cell - Google Patents

Abstract

PURPOSE:To enable higher efficiency by forming an n-type crystallite silicon (muc-Si) semiconductor layer based on a glow discharge decomposition process where argon gas is added to a reaction system. CONSTITUTION:In the formation of an n-type muc-Si film 5, a slight amount of argon gas is introduced to a reaction system. Specifically, 1 to 10%, preferably 3 to 5% of argon gas is introduced to dilution hydrogen. Introduction of argon gas, if its amount is appropriate, makes it possible to crystallize down to 150Angstrom , although sufficient crystallization less than 250Angstrom is impossible without introducing argon gas. Moreover, when it is fine crystallized, the ohmic performance of pn conjunction can be maintained. It is, therefore, possible to further reduce its thickness of film and minimize photo absorption loss and improve conversion efficiency without the loss of electric conductivity.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention relates to a method for manufacturing a stacked solar cell, and more specifically, it involves stacking unit cells each having a PLN type junction, and reducing the PN between the unit cells. The present invention relates to a stacked solar cell in which an n-type layer forming a junction is made of a microcrystalline silicon semiconductor layer.

[Conventional technology]

Amorphous silicon (A-31) solar cells are rich in resources, have a simple manufacturing process, and require little energy to manufacture, so they are attracting attention as low-cost solar cells and are being actively researched and developed.

However, their conversion efficiency is somewhat lower than that of crystalline silicon solar cells, and efforts are being made to improve this. One of them is that a part of the incident light is absorbed by the doped layer before it reaches the layer where optical carriers are generated, and is not effectively used for power generation. Silicon (μCSi) is used.

Furthermore, a cell sensitive to short wavelength light such as a-SiC or a-SiN is placed on the incident light side of a cell using a normal a-Si cell, and a cell sensitive to short wavelength light such as a-SiGe or aSiSn is placed on the back side. It has been proposed to deploy cells that are sensitive to light to effectively utilize a wide wavelength range of sunlight, thereby significantly improving conversion efficiency.

(1) (2) [Problem to be solved by the invention] When stacking cells as described above to improve conversion efficiency, Jsc (short circuit current) decreases due to light absorption loss at the pn junction between cells. There is a problem. In order to reduce light absorption loss and increase light transmittance, it is effective to reduce the thickness of the p-layer and n-layer. However, in general, as a microcrystalline film is made thinner, microcrystalization ceases, the electrical conductivity rapidly decreases, and it becomes difficult to maintain ohmic properties.

Therefore, the present invention promotes microcrystalization in a thin film to
It is an object of the present invention to provide a method that makes it possible to increase the efficiency of a stacked solar cell by thinning a c-Si layer while maintaining electrical conductivity.

[Means to solve the problem]

In order to achieve the above-mentioned object, the present invention stacks unit cells each having a pin type junction, and the n-type layer forming the pn junction between the unit cells is made of a microcrystalline silicon semiconductor layer. , provides a method for manufacturing a stacked solar cell, characterized in that the n-type microcrystalline silicon semiconductor layer is formed by a glow discharge decomposition method in which argon gas is added to the reaction system.

A stacked solar cell is, for example, a solar cell having a structure in which a plurality of unit cells formed by stacking a p layer, a first layer, and an n layer in this order or in the reverse order are further stacked. A high electromotive force can be obtained by using the light that is not used in the cell in the second and subsequent layers, and the incident energy can be reduced by using a material whose energy bandgap gradually narrows from the light incident side. It is used in such a way as to make effective use of it. The number of stacked cells may be two or more.

In addition to amorphous silicon (a-Si:H), amorphous silicon to which carbon, oxygen, germanium, etc. are appropriately added or alloyed can be used as the cell structure or material of the solar cell.

μc-Si film form or generally S+H as source gas
4. A silicon source such as S121{6 and optionally (3
) (4) Using diluted hydrogen (silicon source: diluted hydrogen = .l: 10~
200) a- by plasma CVD method (glow discharge decomposition method)
Si is deposited at a temperature of 100 to 300°C, a reaction pressure of lQQmtorr to 2 torr, and a power density of 0.01 to 0. 5 W/cut, preferably by adjusting the temperature to a higher temperature, higher power density, and higher hydrogen concentration, and by mixing microcrystals in the a-Si film. For example, the temperature is 250-30
0°C, power density 0. 1 ~ 0. 3 W/cnf is preferred. To impart n-type conductivity to the μc-Si film, it is necessary to
．． 01 to 5 mol % of n-type impurity source, such as phosphine Pll. What is necessary is to mix them and perform plasma CVD.

In the present invention, in the form of such an n-type μc-Sl film, a trace amount of argon gas is added to the reaction system, for example, about 1% to 10%, preferably about 3% to 5%, relative to diluted hydrogen. Features. As a result, although microcrystalization is insufficient when the film thickness is 250 Å or less without the addition of argon gas, the film can be sufficiently crystallized up to a film thickness of about 150 Å.

If it is microcrystalline, the ohmic properties of the pn junction can be maintained, so it is possible to reduce light absorption loss by making the film thinner without losing electrical conductivity.

[For production]

Addition of argon increases the amount of ions in the plasma,
It is thought that the grain size of the microcrystals that are formed becomes smaller, and even a thin film becomes microcrystalline. According to the present invention, since the grain size of the microcrystals can be reduced to 150A or less, a good n-type μC-31 film can be obtained with a thin film of about 150 people.

[Example] An n-type Si film was formed on Corning glass by plasma CVD, and the relationship between the film thickness and electrical conductivity was investigated. n
The film forming conditions for type S1 film were: temperature 270°C, pressure, 1. O.T.
orr, power density 0. 3 W/cut, and raw material gas is 1% PH3/SiH4, SiH4/H
2 = (5) (6) Using 1/120, the film thickness was adjusted by changing the film forming time.

The electrical conductivity of the obtained n-type S1 film on glass was evaluated using a normal coplanar type. The results are summarized in FIG. 2 as a broken line. When the film thickness became 250A or less, the electrical conductivity decreased rapidly, indicating that microcrystalization was insufficient.

Next, under the same conditions as above, except that Corning glass/a-3i was used together with Corning glass as the substrate, argon gas was added to the reaction system (raw material gas) at a ratio of 3 to H2.
% was added, and similar film formation and electrical conductivity measurements were performed.

The results are summarized as a solid line in Figure 2, and the film thickness is 15
It is shown that it is sufficiently crystallized to about 0A. Corning Glass Top and Corning Glass/a-
The electrical conductivity on Si was comparable.

Under conventional conditions without the addition of argon, there are cases where crystallization occurs on glass but not on a-Si, that is, on actual devices, but by adding argon, this problem is eliminated. , a thin microcrystalline film was stably obtained.

Next, the film forming method of the present invention was applied to a stacked solar cell, and the effect of thinning the n-type layer was investigated.

Referring to FIG. 1, first, a transparent electrode 2 is formed on a transparent glass substrate 1, and then a p-type a-Si film (thickness 100 A) 3 and a type 1 film of a first cell are formed using a plasma CVD method. a-Si
A film (1000 thick) 4 was deposited.

Thereafter, the film was air-broken and divided into several pieces, and an n-type μc-Si film (1% phosphorus doping) 5 was deposited by plasma CVD under various conditions and film thicknesses. Above them, the p-type a of the second cell
-Si film (thickness 100 people) 6, type 1 a-Si film (thickness,
1500A) 7, n-type a-Si film thickness 25OA) 8
was deposited. Further, an aluminum electrode 9 was formed thereon.

The film forming conditions for the n-type μC-S1 film are a temperature of 270°C and a pressure of I
TOrrS power density 0. 3 W/ant, and the following three types of films were formed.

■) Hydrogen dilution only, film thickness 300 people, 2> Hydrogen dilution only, film thickness 150 people, 3) Argon addition, film thickness 150.

The VI characteristics and device parameters (7) (8) of the obtained device were evaluated under AM-1 illumination. The results are shown in the table below in Figure 3.

Surface film thickness balance: IOOOA/1500A sample n-layer production method Voc (V) Jsc (mA/c++f)
FP1> Hydrogen dilution only 1.66 2
．． 96 0.816 (300A) 2) Hydrogen dilution only 1.60 3.13
0.741 (150A) 3) 72q crystal zr addition ■・663・140・81
5 Comparing samples 1) and 2), in 2), the amount of light incident on the second layer increases due to the effect of thinning the μc-n layer, and the short circuit current (
Jsc) is increasing, but the n/p ohmic property is impaired and a king appears near the open circuit voltage (Voc), and both the form factor (FF value) and Voc are decreasing. On the other hand, in the case of 3), the JSC is comparable to that of 2), and the FF value and Vo
c is also good, and both optical absorption loss reduction and n/p ohmic junction are realized.

Furthermore, with these technologies, 1.75eV/1.7
When a three-layer tandem cell of 58V/L50eV was fabricated, a conversion efficiency η=10.27% (1c%) was achieved.

〔Effect of the invention〕

By adding a small amount of Ar to the reaction gas during the formation of an a-Si film by glow discharge decomposition, it is possible to obtain a μc-Si film that exhibits good ohmic properties even at a film thickness of 150 mm, and this can be used for stacked solar cells. A pn junction can be applied to a certain n-type layer to improve conversion efficiency.

[Brief explanation of drawings]

Figure 1 is a schematic cross-sectional view of a stacked solar cell, Figure 2 is a graph showing the dependence of electrical conductivity on the thickness of a microcrystalline thin film, and Figure 3
The figure is an I-V characteristic diagram of a two-layer Kundem device. 1... Substrate, 2... Transparent electrode, 3
．． 4.5...first cell, 3...p layer, 4...1
Layer, 5...n layer, 6.7.8...second cell, 6...p layer, 7...1 layer, (9) (10) 8...n layer, 9. ··electrode.

Claims (1)

[Claims] 1. In the production of a stacked solar cell, which is formed by stacking unit cells with pin-type junctions, and in which the n-type layer forming the p-n junction between the unit cells is made of a microcrystalline silicon semiconductor layer.
A method for manufacturing a stacked solar cell, characterized in that the n-type microcrystalline silicon semiconductor layer is formed by a glow discharge decomposition method in which argon gas is added to the reaction system.