JPH0243776A - Manufacture of thin film solar cell - Google Patents

Abstract

PURPOSE:To dispense with a patterning process of an amorphous semiconductor layer, which is to be performed between the formation of the amorphous layer and a second electrode, and to make the connection resistance between units adjacent to each other lower by a method wherein the output and the sweep rate of laser rays used for boring a through-hole are so set as to be within a specified range of values. CONSTITUTION:Two or more first electrodes 21-23 are formed so as to be arranged in a line on an insulating substrate 1, and an amorphous semiconductor layer 3 and a second electrode layer 4 are laminated covering the electrodes 21-23, and then not only two or more through-holes 71-73 are bored in the second electrode layer 4 and the amorphous semiconductor layer 3 reaching above the vicinity of the edges of the first electrodes 21-23 respectively but also the amorphous semiconductor layer 3 and others around the through-holes 71-73 are made excellent in conductivity by irradiation with laser rays 6, and only the second electrode layer 4 is divided by cutting if off at the points above the inside of the first electrodes 21-23 and separate from the through-holes 71-73. In the manufacture of a series-connected type thin film solar cell as mentioned above, a YAG laser is used for obtaining the above laser rays 6, whose optical output and sweep rate of the laser beam is made to be 400-450mW and 90-100mm/sec respectively.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention provides a unit cell comprising an amorphous semiconductor layer on an insulating substrate and having a first electrode on the substrate side and a second electrode on the opposite side of the substrate. , relates to a method for manufacturing thin film solar cells connected in series by connecting a first electrode layer to a second electrode layer of an adjacent cell.

[Conventional technology]

Since amorphous semiconductor films formed by glow discharge decomposition of raw material gas or photo-CVD are grown in a vapor phase, they can be easily grown to a large area and are expected to be used as photoelectric conversion films for low-cost solar cells. In order to efficiently extract power from such large-area amorphous solar cells, a well-known method is to use series-connected solar cells as shown in Figure 2. A first electrode 21 made of a transparent conductive thin film such as tin oxide or ITO is placed on the substrate.
．． 22, 23... are formed in a strip shape, and amorphous semiconductor layer regions 31, 32, which are photovoltaic force generating parts are formed thereon.
33..., and then second electrodes 41, 42, 43, etc. made of a metal thin film or a transparent conductive thin film were formed.

First electrode 21. Combination of three amorphous semiconductor layers and second electrode 41, first electrode 22. A combination of the amorphous semiconductor layer 32 and the second electrode 42 constitutes each unit cell. Then, a pattern of the picture electrode and the amorphous semiconductor layer is formed so that the first electrode layer of one unit cell is in partial contact with the second electrode layer of the adjacent unit cell, and each unit cell is connected in series. connected to.

In order to obtain good performance in such a series-connected solar cell, the resistance between the first electrode layer and the second electrode layer of the adjacent unit cell that is in contact with it must be small, and the resistance of the first electrode layer in one unit cell must be small. There is good contact between the electrode layer and the amorphous semiconductor layer and between the amorphous semiconductor layer and the second electrode layer, and in particular, if a part of the amorphous semiconductor layer is missing due to scratches or the like, a part of the first electrode layer and a part of the second electrode layer are It is important to eliminate direct contact and so-called short circuits.

Typically, the formation of a series contact solar cell involves the following steps: depositing a first electrode layer on the entire surface, patterning the first electrode layer, depositing the amorphous semiconductor layer on the entire surface, patterning the amorphous semiconductor layer, depositing the second electrode layer on the entire surface, and depositing the second electrode layer on the entire surface. The patterning is performed in the order of patterning the two electrode layers, and a process technique such as a laser scribing method, a mechanical scribing method, or a photoetching method is used for turning each layer.

However, when the amorphous semiconductor layer patterning process is performed between the formation of the amorphous semiconductor layer and the second electrode layer, minute fragments and dust in the atmosphere are generated during the patterning process of the amorphous semiconductor layer. As a result, the amorphous semiconductor layer may be scratched, causing a short circuit, or the surface may be contaminated, preventing good contact with the second electrode layer. In order to remove surface contamination, it is necessary to clean the surface before forming the second electrode layer, but adding this cleaning step will further damage the amorphous semiconductor layer and increase the probability of short circuits. Another disadvantage is that the number of man-hours required to manufacture the solar cell increases.

In order to create a series-connected solar cell that does not have the problems caused by the patterning process of the amorphous semiconductor layer, the first electrode and the second electrode are formed separately, but the amorphous semiconductor layer is not divided, and its high sheet resistance is Taking advantage of this fact, the connection between each unit cell is made by contacting the extended portions of the first electrode layer and the second electrode layer, which are pulled out laterally when viewed in the arrangement direction of the unit cells. There is a method to do this. However, this method
There is a drawback that the area occupied by the solar cell becomes large due to the extensions of the first and second electrode layers, and the power generation capacity per area becomes small.

In order to solve these problems, after the step of laminating the amorphous semiconductor layer and the second electrode layer over the first electrode layer, the second electrode layer and the amorphous semiconductor layer are laminated by laser beam irradiation. A plurality of through holes reaching near the edge of the first electrode are formed, and the amorphous semiconductor layer around the through holes is made to have good conductivity, or a second electrode is formed around the through holes.

A method has been proposed that includes a step of making an amorphous semiconductor and a first electrode highly conductive, and a step of cutting and dividing only the second electrode layer from the through hole above the inside of the first electrode (
(Refer to the specification and book of Japanese Patent Application No. 62-211798).

[Problem to be solved by the invention]

However, in the above-mentioned technology, if the output of the laser beam is too low, the second electrode and amorphous semiconductor layer cannot be removed successfully, leading to an increase in contact resistance, and if the output is too high, the second electrode and the amorphous semiconductor layer may be removed. The strong laser light may be irradiated and even the first electrode layer may be removed. Furthermore, although there are multiple through holes, the density of the through holes changes depending on the sweep speed or number of sweeps of the laser beam when forming the multiple through holes, and if the density is low, contact may occur. There was a problem that resistance increased and output characteristics deteriorated.

[Means to solve the problem]

In order to solve the above-mentioned problems, the method of the present invention forms a plurality of first electrodes arranged in a line on an insulating substrate, and laminates an amorphous semiconductor layer and a second electrode layer to cover the first electrodes. After the process, a plurality of through holes reaching near the edges of each first electrode are formed in the second electrode layer and the amorphous semiconductor layer by irradiation with laser light, and the amorphous semiconductor layer around the through holes is made to have good conductivity. a step of converting or making the second electrode, amorphous semiconductor, and the first electrode around the through hole conductive; and a step of cutting only the second electrode layer above the inside of the first electrode from the through hole and decomposing it. Among the
It is assumed that the output of the laser beam is 150 to 450 mW and the sweep speed is 90 to 100 mm/sec.

[Effect]

When the laser beam output and sweep speed are defined as described above, energy sufficient to remove the second electrode and the amorphous semiconductor layer, but not sufficient to remove the first electrode, is applied.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. 1, in which parts common to those in FIG. 2 are given the same reference numerals.

FIG. 1(a) is a diagram showing the state of a solar cell immediately before electrical connection between unit cells is made using a laser beam according to the present invention. This state can be obtained as follows. First, a first electrode layer consisting of a 5n02 film is placed on a glass substrate l.
The first electrodes 21, 22, 23, . . . are patterned by a laser scribing method. Next, an amorphous semiconductor layer 3 with a thickness of 400 mm is applied on top of this.
The second electrode layer 4 made of an aluminum thin film is subsequently formed to a thickness of 3,000 to 5,000 wafers without buttering the amorphous semiconductor layer. The second electrode layer 4 may be formed not only from an aluminum thin film but also from a silver thin film.

However, in the case of a thin Ag film, it is somewhat difficult to make a through hole with a laser beam due to its high reflectance, so the thickness should be approximately 2000, and the electrical connection of the second electrode layer should be made with a thickness greater than that. It is a cross-sectional view showing the state in which the
C) is a second electrode layer (Ag
FIG. 4 is a diagram showing a cross section of a final series-connected thin film solar cell obtained by patterning the thin film 4 in a conventional manner. However, the electrical connection shown in Figure 1(b) and the electrical connection shown in Figure 1(b)
The order of patterning the second electrode layer shown in C) can also be reversed.

A YAG laser with a wavelength of 0.53 μm is used as a laser light source for making the above-mentioned electrical connection, and enters from the aluminum thin film, that is, the second electrode 4 side. Here, based on FIG. 3, the relationship between laser power and contact resistance will be described. In this case, when the excitation lamp current of the laser is gradually increased from 0, evaporation of the aluminum thin film does not occur in the first region where the lamp current is low, and as the lamp current is increased, the aluminum thin film and the amorphous semiconductor layer evaporate. At the periphery of the amorphous semiconductor layer removed at the same time, a portion where the amorphous semiconductor layer and aluminum melt or crystallize and become highly conductive is generated. At this time, the first electrode layer made of SnG is hardly damaged except for a slight change in surface quality. The optimum value in this second region of laser power is 400 to 450 mW.

Further, in the third region where the lamp current is large (laser power of 500 mv or more), not only the aluminum thin film and the amorphous semiconductor layer but also the first electrode layer are evaporated and removed, so this must be avoided.

Next is the fourth. Based on FIG. 5, the relationship between laser sweep speed and contact resistance will be described. As can be seen from FIG. 4, at an output of 400 to 450 mW, which is the optimum value of the laser power, the optimum value is when the beam sweep speed is 90 to 100 marks/sec (second region). That is, when the sweep speed is faster than that (110 mm/sec: third region), the density of the formed through holes is low (Fig. 5 (a)), and the electrical connection between unit cells is insufficient. becomes. Also, when the sweep speed is slow (80 mIII/sec or less: region -)
In this case, the through-holes are formed overlapping each other (Fig. 5 (C)), and the degree of laser light irradiation to the first electrode increases, resulting in deterioration or evaporation of the first electrode, resulting in contact failure. resistance increases.

Next is the 6th. Based on FIG. 7, the number of steps (hereinafter referred to as cutting) of forming through holes and forming highly conductive parts (hereinafter referred to as cutting) and contact resistance will be described. As shown in FIG. 6, it is better to cut twice than once, but if it is cut three times, the contact resistance increases. The reason why it is better to do it twice than once is because the area of the good conductive part increases (Fig. 7 (a), (b)), but after the third time, the resistance increases. It can be explained as follows. That is, when a through hole is formed using a laser beam, the surface of the first electrode layer is slightly altered in quality.

The influence of this portion on the contact resistance is irrelevant when the density of the through holes is low, but as the density increases, the influence gradually becomes apparent (FIG. 7(C)).

In other words, the contact resistance is determined by the competition between the highly conductive part and the deteriorated part of the first electrode layer, so when the number of cuttings is 1, there is insufficient conductive part, and after 3 times, the deteriorated part of the first electrode layer is insufficient. An increase in both causes an increase in contact resistance. However, the number of times of cutting is not always two, and it changes depending on the thickness of the first electrode layer. In FIG. 8, the first electrode layer is made of Sn.
The relationship between the contact resistance and the number of cuttings using film thickness as a parameter when using O□ is shown. At this time, the laser power was 400 mW, and the sweep speed was 1 (10 mm/sec). It can be seen that if the SnO2 layer is relatively thin, the number of cutting is sufficient, and if it is thick, it is better to cut 2 to 3 times.

This is because when the film thickness of SnO is thin, the sheet resistance of SnO2 itself increases, so it is better to have fewer altered parts in the first electrode layer, and when it is thick, the sheet resistance of SnO2 decreases, so the sheet resistance of the first electrode layer This is because the altered part is not affected even if it increases to a certain extent.

〔Effect of the invention〕

According to the present invention, electrical connections between a plurality of unit cells formed on an insulating substrate, each consisting of a first electrode layer, an amorphous semiconductor layer, and a second electrode layer, are established by irradiating laser light from the second electrode layer side. When the second electrode layer and the amorphous semiconductor layer are removed to form a through hole, the amorphous semiconductor layer and the second electrode layer are melted or crystallized around the through hole, resulting in a highly conductive portion with a sufficient area. Since the laser power and sweep speed of the laser beam were optimized when performing this process, there is no need to include a patterning process for the amorphous semiconductor layer between the formation of the amorphous semiconductor layer and the formation of the second electrode layer. It becomes possible to connect between the two with a lower resistance, and a series-connected thin film solar cell with low cost and high reliability can be obtained.

[Brief explanation of the drawing]

1(a), 1), and 1(C) are cross-sectional views showing step by step an embodiment of the manufacturing method to which the present invention is applied; FIG. 2 is a cross-sectional view of a conventional series-connected thin film solar cell; Figure 3 is a diagram showing the relationship between laser power and contact resistance, Figure 4 is a diagram showing the relationship between laser beam sweep speed and contact resistance, Figure 5 (a),
(b), (C) are plan views of the area around the through hole when the laser beam sweep speed is changed, Figure 6 is a diagram showing the relationship between the number of cuttings and contact resistance, and Figures 7 (a) and (b). ),
(C) is a plan view of the area around the through hole when the number of cuttings is changed, and FIG. 8 is a diagram showing the relationship between the number of cuttings and the contact resistance when SnO and thin film are used as parameters. 1 glass substrate, 21.22.23 first electrode, 3 amorphous semiconductor layer, 31.32.33 amorphous semiconductor layer region, 4 second electrode layer, 41.42.43 second electrode, 51.52.53 good conductivity Sexual part, 6 Laser light,? 1.72.73 Through holes. Figure: Beam sweep speed (mm/5ec) Figure: (a) (b) (C) Figure: Razor power (mW) Figure: Cutting frequency (a) (b) (C) Figure:

Claims (1)

[Claims] 1) When manufacturing a device in which a plurality of unit cells made of an amorphous semiconductor layer are connected in series on an insulating substrate and have a first electrode on the substrate side and a second electrode on the opposite side, a process of forming a plurality of first electrodes arranged in a line; covering the first electrodes with an amorphous semiconductor layer;
After the step of laminating the second electrode layer, the second electrode layer and the amorphous semiconductor layer are irradiated with laser light to form a plurality of through holes reaching above the vicinity of the edge of each first electrode, and to form a plurality of through holes around the through holes. The amorphous semiconductor layer has good conductivity or the second electrode around the through hole, the amorphous semiconductor layer,
In the method for manufacturing a thin film solar cell, the method includes the step of making the first electrode conductive and cutting only the second electrode layer on the inside of the first electrode from the through hole to divide the YAG layer. Using a laser, the laser light output is 400~4
50 mW, and the sweep speed of the laser beam was 90-100 mW.
A method for manufacturing a thin-film solar cell, characterized in that the solar cell is manufactured at a rate of mm/sec.