JPS59211289A - Manufacture of amorphous silicon solar battery - Google Patents

Abstract

PURPOSE:To readily obtain a desired window layer thickness by previously thickly forming the window layer when forming the layer of the uppermost layer of an a-Si thin film of pin structure, forming two metal electrodes thereon, etching while measuring the resistance between the both electrodes, and obtaining the prescribed window layer thickness. CONSTITUTION:A plurality of cells 20 formed with an a-Si layer and a metal electrode pattern are placed on a susceptor 21 of a plasma etching device, metal electrodes 15, 16 are retained by a terminal 22, high frequency wave is applied to discharge it. The resistance between the electrodes 15 and 16 is gradually increased, and etching is continued until the resistance becomes, for example, 300M. At this time, since the resistance of an I type layer 3 is large, the thickness of the N type layer can be detected from the resistance between the both electrodes. The thickness of the N type layer is irregular at every cell. Accordingly, the resistance between the electrodes of one cell is monitored to control the thickness of the N type layer. In the cell having the layer 4 optimized initially in the thickness is covered with the cell by a substrate of a stainless steel, thereby preventing the etching from developing.

Description

Detailed Description of the Invention [Technical field to which the invention pertains] The present invention forms a pin junction by sequentially stacking amorphous silicon thin films with different properties on a metal substrate, and leaves a region on the top surface where light enters to concentrate the light. The present invention relates to a method of manufacturing an amorphous silicon solar cell provided with an electric metal electrode.

[Prior art and its problems]

Amorphous silicon solar cells are attracting attention as a promising candidate for low-cost solar cells. Because amorphous silicon solar cells form junctions using low-temperature vapor phase growth, they require less energy to create, and the absorption coefficient is more than an order of magnitude higher than that of single-crystal silicon, so the amount of gas consumed during cell formation is low. This is because it has several advantages, such as requiring less. However, since it is still under development, it has several drawbacks compared to single-crystal silicon solar cells, such as low cell efficiency and low yield. It is known that the cell efficiency of this amorphous silicon (hereinafter referred to as a-8i) solar cell depends on the film thickness of the amorphous silicon. FIG. 1 shows the structure of an a-8l solar cell. For example, the conductive substrate 1 using a stainless steel plate is 1 to 10T
A mixed gas of silane gas and diborane gas is placed on an electrode heated to about 200 to 800°C in a vacuum of 100° C., and a high frequency voltage is applied between the electrode and the counter electrode to generate a glow discharge and mix. p by decomposing the gas
Layer-8 Layer 2 is formed to a thickness of about 50 OA. Next, after reducing the degree of vacuum to -10-3 Torr or less, silane gas is introduced under the condition of 1 to 10 Torr, and a non-doped 8-layer layer 8 is deposited to a thickness of about 0.5 .mu.m by glow discharge decomposition. After evacuation to below 1O-3 Torr again, a mixed gas of silane gas and phosphine gas was heated to 1 to 10 Torr.
By introducing at Torr and decomposing by glow discharge, n
Layer-8 Layer 4 is formed to a thickness of approximately 100x. That is, the a Si layer 10 includes a p-type layer 2, a non-doped layer 8, and an n-type layer 2.
It consists of three layers: the shape layer 4.

It is also possible to make 2 an n-type layer and 4 a p-type layer, but
In this case, the thickness of the n-type layer 2 and the p-type layer 4 is approximately 50 mm.
A transparent electrode 5 is formed on the OA-Si layer 10, which needs to have an OA of about 10 OA. The transparent electrode 5 is a transparent conductive film made of indilum tin oxide (ITO), S, n02, etc., and is formed by vapor deposition or the like. The film thickness is set to 700 to 800 A to make the reflectance as low as /J%. Partial collection 1 on this! An electrode 6 is provided, which is a strip metal thin film formed by vacuum deposition, printing, or the like.

FIG. 2 shows the dependence of the output characteristics of this A-8R solar cell on the film thickness of the first layer 4, that is, the A-8 window layer on the side where light 7 is incident. Jsc is a short circuit current, which is maximum when the thickness of one layer is about 100A, giving a value of D, 117M~. Voc is an open circuit voltage, which increases as the thickness of the −1 layer increases, but reaches a maximum when the thickness of one layer is about 10 OA, and thereafter shows a constant value. η is the conversion efficiency, which increases as the 0 layer thickness increases, but reaches its maximum value when the 0 layer thickness is 100A, and 1
It decreases as the layer thickness increases further.

From these results, it is important to reproduce the single layer thickness to around 100A with good controllability in order to improve cell efficiency and yield. However, as the a-8 film production device becomes larger, the degree to which it becomes difficult to control the a-St film thickness increases. Also, with current generation equipment,
When forming the window layer, the growth rate of the a-8i film was kept constant1
The film thickness is determined by adjusting the growth time. For example, when four 10-lot A-8I film layers of 1000 A were deposited near a dormitory, the film thickness varied within the range of 900 to 1100 A when controlled by growth time. This means that the controllability of the film thickness is ±10 inches. In other words, even if a thickness of 100 A, which is the maximum value in FIG. 2, is obtained, a film having a single layer thickness of about 90 layers is produced, and the characteristics deteriorate accordingly. In this state a
When a window layer is formed on the light incident side of a -8i solar cell, if the cell has a large area, there will be variations in efficiency over the entire surface, and the efficiency will be low as a whole.

[Purpose of the invention]

The present invention aims to improve the film thickness control of the window layer of a solar cell having an A-8+ thin film made of PIM, and to improve the efficiency of an A-8+ solar cell, especially a large-area A-8I solar cell. do.

[Key points of the invention]

In the present invention, when forming the window layer which is the top layer of the A-8I thin film with the pin structure, after forming a layer thicker than a predetermined window layer thickness in advance, two metal electrodes that can be used as current collecting electrodes are provided thereon.
The above object is achieved by etching the uppermost layer while detecting the film thickness by measuring the resistance between both electrodes to obtain a predetermined window layer thickness.

[Embodiments of the invention]

In FIG. 8, parts common to those in FIG. 1 are given the same reference numerals. 7 (Heating the stainless steel substrate 1 of FIIIX70+1 to 200 to 800°C, and forming the p-type layer −8iJi 2 t about 50OA in a vacuum state of 1 to 10 Torr,
/ 7 F 7 ) (ila-8 layer layer 8 about 0.5 μm
are deposited to a thickness of . Next, an n-8 layer 14 is grown to a thickness of about 2ooK, which is twice the desired window layer thickness of 1ooX. Next, metal electrodes 15 and 16 made of titanium or aluminum films are formed by vacuum evaporation.
The film thickness of this metal electrode is 2000 to 500X and is deposited using a mask in the same pattern as the current collecting electrode to be formed.

The metal electrodes 15, 16 need to be in two separate patterns as shown in FIG. This a-8
Four cells 20 each having one layer and a metal electrode pattern formed thereon are placed on a susceptor 21 of a plasma etching apparatus in the form shown in FIG.
Hold down the metal electrodes 15 and 16. This terminal 22 is insulated from the susceptor with an insulator 28 such as an insulator. Lead wires are drawn out from these terminals 22, respectively, so that the resistance of both terminals can be measured outside the reaction chamber of the apparatus. At this time, the vacuum chamber is shielded from light to prevent light from entering the alt layer. When the resistance was measured in this way, the resistance value was 1 from 170.
It varied to 30MΩ.

After evacuating this reaction tank to below 1O-3 Torr, 8t
F4 gas was introduced and high frequency was applied under conditions of 0.2 to 0.8 Torr to cause discharge. The discharge power at this time is 2
00W, which is about four times the discharge power in the case of 8iH4 gas. During discharge, the lead wire drawn out from the terminal 22 was short-circuited to maintain the same potential as the susceptor 21. 1
After every 0 seconds of discharge, the discharge is stopped and a dark state is created, and this electrode 15.
When the resistance was measured between 16 and 16, the resistance gradually increased.

Etching was continued until this resistance reached 800. It was confirmed that the n-type layer was etched at almost the same speed on the same susceptor. This seems to be because the gas pressure is set to 718 for forming the a''Si layer, and the uniformity of the discharge is good.The resistance between the two electrodes, 800M11, corresponds to the thickness of one layer of 100A. At this time, the thickness of one layer 8 is 0.5 μm, but the resistance is large as 1 is 1Ω or more, so the thickness of the first layer can be detected from the resistance between both electrodes.Thickness of the first layer of the cell Since the resistance varies from cell to cell, it is necessary to monitor the interelectrode resistance of each cell and control the film thickness of one layer to 100λ.
For cells having 100% oxidation, the cells were covered with a stainless steel substrate prepared in advance in the tank. In this way, it was possible to prevent the progress of etching. The vacuum is broken only after the thickness of one layer in all cells has been optimized.

Transparent electrodes 17 were deposited on the four cells thus obtained, as shown in FIG. The solar cell thus completed has a metal substrate 1 and a transparent electrode 1 directly above the metal electrode 16.
Photovoltaic force can be taken out from 7, and the metal electrode 16 used for resistance measurement also serves as a current collecting electrode. When the characteristics of the completed solar cell were measured, there was almost no variation in cell characteristics, and an efficiency of over 7.5% was achieved. It is easy to understand that this result is extremely superior to the efficiency of 10 lots of solar cells produced using the conventional method, which varied in the range of 6.5 to 7.5 inches. .

FIG. 7 shows a second embodiment. When the n-layer 14 is etched after providing the metal electrodes 15 and 16, the lower part of the electrode remains as it is, and the other part becomes about 100A.

In this case, if the step between the electrode 15.16 and the etched 0 layer 4 becomes large, the transparent electrode 17 may be interrupted at the step, so the film thickness of the electrode 15.16 is set to about 200A. Ru. Since such thin electrodes have a large sheet resistance, in particular in large-area solar cells, printed electrodes are placed on the trunks 24 and 25 of the metal electrodes 15 and 16 shown in FIG. 4 via a transparent electrode layer 17. It is effective to reduce the series resistance of the cell by adding 18. Branches 26, 2 of metal electrodes 15, 16
In case 7, the current is small, so providing an additional electrode has almost no effect.

When forming the n-layer, introduce silane gas, phosphine gas, and hydrogen gas at a ratio of 1:0.01:20, approximately 200
When decomposed by glow discharge with the power of W, the n-layer has a power of about 10OA.
It has a microcrystalline structure with a collection of crystal grains. This layer wire specific resistance has a value of about 1Ω. Therefore, the resistance between the left and right metal electrodes 15 and 16 shown in FIG. 8 had a value of 18KQ-17KO after 20 layers of zero layer were formed. In this case 100
It has been found that in order to obtain the n-layer of A, it is best to etch the n-layer until the resistance of both becomes 80 KO.

In the above embodiment, the case where the n-layer is the top layer has been described, but the top layer can also be formed when the n-layer, i-layer, and p-layer of the a-8i thin film are laminated in order from the substrate side to form a pin junction. The invention can be applied to obtain the optimum thickness of the p-layer.

〔Effect of the invention〕

As described above, the present invention provides a-81 with a pin structure.
In order to optimize the thickness of the thin window layer, a thick top layer is formed in advance, and the resistance between two metal electrodes placed on top of it is measured while being etched. It is extremely effective as a method for manufacturing amorphous silicon solar cells with good characteristics, as it is possible to easily obtain a window layer thickness of

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of a conventional A-8i solar cell, Figure 2 is a
-1# showing the dependence of the output characteristics of the -8i solar cell on the thickness of one layer
! Figure 3 is a sectional view at an intermediate stage in the production of a large-area A-81 solar cell according to an embodiment of the present invention, Figure 4 is a plan view at the same stage as Figure 8, and Figure 5 is an embodiment thereof. FIG. 6 is a cross-sectional view of a solar cell according to this embodiment, and FIG. 7 is a plan view showing a plasma etching operation according to another embodiment.
FIG. 2 is a cross-sectional view of a solar cell. 1... Metal substrate, 2... a-8ip layer, 8... a
-8ii layer, 4-a-8in layer (window layer), 14-a-8
in layer, 15.16...metal electrode. O 1 Figure? 24 a -so R'k '# , Figure 1121 O 3 Seki de 4 Figure 1121

Claims (1)

[Claims] 1) In a method in which amorphous silicon thin films with different properties are sequentially laminated on a metal substrate to form a pin junction and a current collecting metal electrode is provided leaving a light incident area on the top surface, the uppermost layer of the amorphous silicon thin film is predetermined. After forming a window layer thicker than the window layer, a metal electrode separated into two parts that can be used as a current collecting electrode is placed on top of the window layer, and the thickness of the top layer is detected by measuring the resistance between the two metals. 1. A method for producing an amorphous silicon solar cell, the method comprising: obtaining a predetermined window layer thickness.