JPH0480548B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for manufacturing a carbon film for a sintered film type CdS/CdTe solar cell.

Prior Art A sintered film type CdS/CdTe solar cell has a Cds film 53, a CdTe film 54, a carbon film 55, a Cds film 53, a CdTe film 54, a carbon film 55,
The Ag film 56 is sequentially formed, and Ag+ is formed on the CdS film 53.
It has a structure in which the In film 57 is provided in a comb-teeth shape. 51 is incident sunlight, and sunlight is made to enter from the side of the glass substrate that does not have a film surface such as CdS.

A method for manufacturing a sintered film type CdS/CdTe solar cell having such a structure is described, for example, in Japanese Patent Application Laid-Open No. 11570/1983. Among these, the part related to the firing method of the carbon film is that the glass substrate coated with carbon paste, which is the raw material of the carbon film, on the CdTe film is placed in a firing boat, and then placed on the belt conveyor of a belt conveyor type continuous firing furnace. It is disclosed that they are fired side by side and sequentially. FIG. 6 shows a conventional method in which carbon paste is applied and placed in a firing boat, and FIG. 7 shows the structure of a belt furnace used for firing carbon films.

As shown in FIG. 6, a carbon paste 64 is applied by printing to a CdS/CdTe film 63 formed on a glass substrate 62, and then applied to a stainless steel firing boat 61 for firing the carbon film. It can be paid to The carbon film is fired by passing the firing boat thus prepared through a belt furnace shown in FIG. 7 in Figure 7
1 is a furnace cover, 72 is a belt, 73 is a firing boat arranged closely on the belt 72, 74 is a heat generating heater, 75 is an N ₂ gas pipe for spouting N ₂ gas into the furnace, and 76 is an exhaust pipe. be.

Problems to be Solved by the Invention As already mentioned in part, the CdS/
The method for manufacturing a solar cell with a CdTe structure is to form an n-type CdS sintered film on a glass substrate, form a CdTe sintered film on top of it, then screen print carbon paste for electrodes on the CdTe sintered film, and then use a baking boat. A sintered carbon film is formed by placing the carbon in a belt conveyor type continuous firing furnace and firing it at a maximum temperature of 450°C in an inert gas atmosphere.

In the above manufacturing method, the necessary conditions for the carbon electrode material for screen printing include low electrical resistance, high adhesive strength of the sintered film, and the ability to be screen printed. It will be done. Conventionally, Everyohm (manufactured by Nippon Graphite Industries, Ltd.) has been used as a material that satisfies these requirements. Everyohm is widely used as a carbon material for electrodes because it has low electrical resistance, a strong sintered film, and can be screen printed. Resin (phenol type) and dispersant (vinyl type) contained in this carbon material
In addition to improving screen printability,
It works to increase the adhesive strength with the CdTe fired film, but
In the firing of the present invention, the carbon film is once hardened as the temperature rises during firing, and then gradually decomposed and evaporated to form a carbon film.

As mentioned above, as a firing method in which the resin gradually evaporates in an inert gas atmosphere and almost no resin is present at the end of firing, conventional methods have been to increase the firing time to satisfy the above conditions. was. For example, if the total length is 4000mm and the maximum temperature setting is 450℃, the belt conveyor speed of the kiln will be set for 1 minute.
Fire at 30mm. In this method, the resin gradually evaporates, there are no bubbles in the carbon film, there is sufficient time, and an element with good reproducibility is obtained. However, at a firing belt speed of 30 mm per minute, the required time is approximately 130 minutes, and it is necessary to improve mass productivity.
As a solution to this problem, an attempt was made to increase the belt speed, but the desired characteristic values could not be obtained, and the belt speed was limited to 30 mm per minute for firing in this belt furnace.

Therefore, the present invention provides a carbon film firing method that does not adversely affect the performance of solar cells, has excellent mass productivity, and is reproducible.

Means for Solving the Problems The technical means of the present invention for solving the above problems is a method of stacking two solar cell substrates coated with the carbon paste, one facing upward and the other facing downward, with the sunlight incident sides back to back. It is fired in

Effect The effect of this technical means is as follows.

That is, when the solar cell substrates coated with carbon are fired in a stacked manner with their sunlight incident sides aligned with each other, the bottom side of the firing boat is fired using a net-like or open bottom side. As a result, the resin (phenol type) and dispersant (vinyl type) generated from the lower (downward) side substrate can be smoothly evaporated and dissipated. Due to this effect, properties that are completely the same as those of the fired carbon film on the upper (upward) side can be obtained on the lower side, and the production speed is doubled.

Example Hereinafter, an example of the present invention will be described along with a comparative example based on the attached drawings.

Comparative Example 1 Figure 7 shows a belt conveyor type continuous firing furnace used in the present invention and comparative examples, in which a substrate with a carbon film printed on a CdTe sintered film is placed in a firing boat in the state shown in Figure 6, and the boat is placed on the belt. This is a diagram when they are lined up. In the drawing, the furnace body is partially connected to the furnace cover 7.
1, and is set to about 500°C in the center by a heater 74. N ₂ gas to create the main active atmosphere is introduced through a gas pipe 75 with gas inlet holes, and a gas exhaust pipe 76 with suction holes at several locations is installed at the top of the furnace.

Comparative Example 2 In a firing boat 73 placed on a belt conveyor 72 that moves through the furnace, substrates with a CdS film coated with CdTe and carbon coated thereon are placed facing upward and arranged on the belt 72. Fire.

As the firing conditions, the firing temperature, firing belt speed, _N2 gas inflow amount, forced exhaust amount of _N2 gas, etc. are set. The firing temperature is approximately 500℃ at the center of the furnace, the firing belt speed is 30mm/min, the forced exhaust rate of inert gas is 30/min, the total flow rate of _N2 gas is 25/min, and the oxygen concentration in the furnace is 1000PPM to 8000PPM. I did this. After that, as is well known, on the carbon film
Ag and In films were formed on the Ag film and CdS film, and a solar cell was completed by performing the prescribed firing treatment for each, and the energy conversion efficiency of the solar cell was measured.

In FIG. 4a, the efficiency of the individual solar cells is plotted in the order in which they were fired. In this case, uniformly high efficiency was obtained as before.

Comparative Example 3 The implementation method of this example is shown in FIG. The difference between this method and Comparative Example 1 is that the CdS film is coated with CdTe.
A device with a carbon film formed on top of the film,
This is a method of stacking both sheets facing upward in a firing boat and firing them. As mentioned earlier, carbon-containing resins (phenol-based) and dispersants (vinyl-based) improve screen printability and
It works to increase the adhesive strength with the CdTe film, but it hardens once as the temperature rises during firing, and gradually decomposes and evaporates within a certain oxygen concentration in the furnace, and by the time firing is finished, almost no resin exists. is desirable. In this sense, when stacking two layers and firing them using the method of this comparative example, if the lower carbon film side is brought into close contact with the light incident side of the upper glass substrate and fired, the dispersant in the lower carbon film will not evaporate. The dispersant remains in the carbon film even at the end of firing, increasing the electrical resistance, as shown in Figure 4b.
As shown in , the characteristics of the lower fired element were approximately 30% worse than those of the upper fired element.

Example 1 In this example, stainless steel was used as the firing boat.
A steel mesh boat was used. The external appearance of this reticulated firing boat is shown in Figure 1a. In FIG. 1a, the net 11 is made of thin stainless steel wires with a diameter of 0.3 mm arranged vertically and horizontally at intervals of 3 mm, and the periphery is supported by a stainless steel frame 12. FIG. 1b shows a state in which a carbon film is fired using this mesh firing boat. Glass substrate 13
A, CdS/CdTe printed and configured on 13B
As shown in the figure, the solar cell elements consisting of the films 14A, 14B and the carbon pastes 15A, 15B coated thereon are stacked upward and downward, and the carbon paste film 15B of the downward facing elements is placed in a reticulated boat net. 11, and further placed on the belt conveyor 16 of the belt furnace for firing. Although only one baking boat is shown in FIG. 1b, in reality, a plurality of baking boats are arranged adjacently on the conveyor. Firing conditions are Comparative Examples 1 and 2
is the same as In the case of such a net-shaped firing boat, there was a concern that the carbon film 15B would come into contact with the stainless steel net 11, causing negative effects such as peeling.
The dispersant and dispersant (vinyl type) pass through the mesh of the baking boat and belt conveyor and evaporate without any hindrance as the temperature rises during baking, forming carbon. There was no difference in properties between the two, and it was possible to obtain properties that were completely the same as those of the conventional one-stage firing method (Comparative Example 1).

Example 2 In this example, a stainless steel boat with an open bottom and a frame supporting the glass substrate only at the periphery was used as the firing boat. FIG. 2a shows the appearance of this boat, and FIG. 2b schematically shows the state in which a carbon film is fired using this boat.

CdS/CdTe films 23A, 23B applied and fired on glass substrates 22A, 22B, and carbon paste 24A, coated thereon.
24B are stacked one on top of the other in an upward and downward direction as shown in the figure, and the periphery of the glass substrate 22B of the downward facing element is placed on an open-bottom firing boat 21. In this case, the substrate support frame of the firing boat should be dimensioned so that it does not come into contact with the carbon paste coating surface. These open firing boats were arranged adjacent to each other on the belt conveyor 25, and Comparative Examples 1 and 2
The carbon film is fired under the same firing conditions. In this case as well, the resin and dispersant contained in the carbon paste evaporate smoothly through the opening of the frame and the mesh of the belt conveyor even when the substrate is facing downward, and there is no difference in characteristics between the firing elements facing upward and downward. , 4th
Results almost similar to those in Figure c were obtained.

Effects of the Invention As detailed above, the carbon film firing method according to the present invention, that is, the bottom side of the firing boat uses a net-like or open type, and the glass substrates are stacked with the sunlight incident side aligned with each other. Therefore, conventional 1
The same characteristics can be obtained under exactly the same conditions as stage firing. The firing speed is twice that of the conventional method, which can greatly contribute to improving mass productivity.

[Brief explanation of the drawing]

Figure 1a is an external view of a stainless steel net-like firing boat used for firing the carbon membrane of the present invention, and Figure 1b is a state in which elements are arranged on the stainless steel net-like boat for firing the carbon membrane of the present invention. Figure 2a is an external view of a firing boat made of stainless steel with an open bottom used for firing the carbon membrane of the present invention, and Figure 2b is a firing boat made of stainless steel with an open bottom. Figure 3 is a cross-sectional view showing the state in which two elements are stacked upward on a firing boat, and Figure 4 shows the firing method of the present invention and the conventional one-stage firing method. Figure 5 is a cross-sectional view of a sintered film type CdS/CdTe solar cell, and Figure 6 is a comparison diagram of the characteristics when two elements are fired by stacking them facing upwards. FIG. 7 is a cross-sectional view showing a state in which elements are arranged in a row, and FIG. 7 is a schematic diagram of a belt furnace used for firing the carbon film of the present invention. 11...Stainless steel net, 12...Stainless steel frame, 13A, 13B...Glass substrate, 14A, 14B...CdS/CdTe film, 1
5A, 15B...Carbon paste, 16...Belt conveyor, 21...Open bottom firing boat,
22A, 22B...Glass substrate.

Claims (1)

[Claims] 1. When manufacturing a solar cell element by laminating sintered films of CdS, CdTe, carbon, Ag and In, and Ag on a transparent glass substrate, applying the carbon base on the CdTe sintered film, In the method of placing the glass substrate in a firing boat and firing it using a continuous firing furnace, the sunlight incident side of the glass substrate is
A method for firing a carbon film for a solar cell, characterized in that the bottom of a firing boat used for combining and firing the sheets is net-like or open, and only a portion has a stand that supports the glass substrate.