JPH08204217A - Manufacture of solar cell module - Google Patents

Abstract

PURPOSE: To generate laser abrasion phenomenon in patterning a rear electrode through laser irradiation by employing an irregular transparent conductive film having a specified haze rate as a transparent conductive film. CONSTITUTION: An irregular transparent conductive film, having haze rate in the range of 5-30%, is employed. Since the number of times of passing through an amorphous silicon layer is increased, the quantity of laser energy to be absorbed is also increased to cause abrasion easily. In the patterning of a thin film using pulse laser light having high energy density, a part 62 of the laser light 61 is absorbed by the thin film at the time of irradiation thus generating the abrasion phenomenon for imparting energy high enough to crack the molecular bond in the thin film and unbind the molecules thus scattering the film at a breath.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a solar cell module. More specifically, by forming a solar cell on a transparent conductive film having a high haze ratio that facilitates the patterning process, the applicability of the patterning process of the solar cell is broadened and the patterning speed is increased. The present invention relates to a method for manufacturing the solar cell module.

[0002]

2. Description of the Related Art An amorphous silicon solar cell utilizing the photoelectric conversion characteristics of amorphous silicon has an extremely thin amorphous silicon layer required for power generation, which is 1 μm or less, and also sandwiches the amorphous silicon layer. The two-layer electrodes are each 1 μm or less, and
By using inexpensive glass as the substrate, the ratio of the raw material cost is small, and a large cost reduction is expected due to mass production effects. Further, since it is formed by a chemical vapor deposition method using plasma or a film forming method using sputtering or the like, it can be easily formed on a large-area substrate. Furthermore, a solar cell module having a free shape can be formed by selecting the substrate material. However, as global environmental issues have attracted a great deal of attention, amorphous silicon solar cell modules using inexpensive glass substrates can be mass-produced at low cost, so demand for high-power applications is expected. There is.

A module of an amorphous silicon solar cell using a glass substrate is usually constituted by a transparent conductive film formed on a glass substrate, an amorphous silicon layer, and a back electrode. However, as the area of the glass substrate increases, the low conductivity of the transparent conductive film becomes a problem, and the loss of the current flowing in the transparent conductive film cannot be ignored. Therefore, in order to deal with this problem, a method of patterning so that three layers of a transparent conductive film, an amorphous silicon layer, and a back electrode are connected in series is usually taken. As shown in FIG. 1, this method includes transparent conductive films 21 to 24, amorphous silicon layers 31 to 34, and back surface electrodes.
It is formed by forming a groove in each of the layers 41 to 44. For such patterning, methods such as mask evaporation, screen printing and etching removal, and processing by high-density laser irradiation have been used. However, in the mask vapor deposition method, the patterning width required for dividing the unit cell becomes large, so that the power generation area is reduced, resulting in a decrease in generated current.

In addition, the method using screen printing has the drawback that the power generation area is reduced and the number of steps is increased due to the addition of an etching step and the like. Therefore, a patterning method by continuous irradiation with a high-density energy laser has been proposed and developed for manufacturing a solar cell.

In the production of solar cells, a transparent conductive film is first formed on a glass substrate, and a pulsed laser beam processed into a high energy density state by a condenser lens or the like is continuously applied to the substrate to form a transparent laser beam on the substrate. The transparent conductive film is divided into several units. This step is called patterning of the transparent conductive film. Further, an amorphous silicon layer is formed on this, and the pulsed laser light processed into a high energy density state again by a condenser lens is irradiated along the groove formed during the patterning process of the transparent conductive film. Thus, the amorphous silicon layer is selectively removed. This step is called patterning of the amorphous silicon layer.

Then, a back electrode is formed. The formed back electrode makes contact with the back electrode and the transparent conductive film through the groove formed on the amorphous silicon layer to form an electrical conduction state. Here, the rear surface electrode is selectively cut by irradiating the pulsed laser light which is also kept in the high energy density state. This completes all patterning. Thus, a desired solar cell module is completed by forming a state in which current flows only in one direction between adjacent unit cells.

As described above, the solar cell module can be manufactured at high speed by performing all the patterning steps including the patterning of the back surface electrode by the continuous irradiation of the high density pulsed laser light. However, it has been conventionally difficult to reproducibly manufacture a solar cell module by patterning the back electrode with continuous irradiation of pulsed laser light. The reason is that the mechanism of the physical phenomenon that occurs when the thin film is irradiated with a pulsed laser beam having a high energy density is not sufficiently understood, and therefore a method for performing good patterning of the back electrode is not available. Because I couldn't find it.

In the patterning process of the back surface electrode by the laser, it is necessary to remove at least the back surface electrode on the laser irradiation surface without damaging the transparent conductive film as the underlayer. In this case, the pulsed laser light emitted has a life of only a few tens of ns, and has an energy amount of 1 × 10 ⁷ J / cm ² or more near the focal point after passing through the condenser lens. As a result, the temperature of the thin film on the irradiated surface rises rapidly. When this temperature rise is extremely rapid and reaches a state of exceeding the boiling point or sublimation point,
A state similar to boiling occurs on the inner surface of the solid thin film, and an instantaneous scattering phenomenon of molecules and cluster-like substances occurs.
This is a phenomenon called laser ablation, and removal of the thin film on the irradiation surface is achieved by effectively utilizing this phenomenon.

However, when the energy of the irradiation laser beam is too weak, the back electrode remains because the removal of the back electrode by laser ablation is incomplete. In such a case, the electrical continuity between the adjacent cells to be disconnected is kept high, and the electrical short circuit state occurs. When the cells are electrically short-circuited in this way, the parallel resistance of the solar cells decreases, causing a decrease in the open-circuit voltage and a decrease in the fill factor, and manufacturing a highly efficient solar cell module. Will not be possible.

On the other hand, when the energy of the irradiation laser beam is too strong, the transparent conductive film as the underlayer is also damaged and the cutting is further effected. The solar cell module thus formed has a series resistance that obstructs the flow of current in the damaged portion of the transparent conductive film, resulting in a decrease in short circuit photocurrent and a decrease in fill factor.

Further complicating the situation is that, according to the study by the present inventors, such insufficient separation and formation in the patterning process does not occur only by the intensity of the laser energy applied. It also depends on the structure and physical properties of the laminated thin film to be irradiated. For example, as a result of the amorphous silicon layer located in the middle being accompanied by a rapid temperature rise due to laser irradiation,
The crystallization causes the resistivity to be remarkably reduced, and an electrical short circuit state may occur. This is because the removal of the thin film by laser ablation is not performed uniformly over the laser-irradiated surface, and the residual silicon layer that has crystallized and becomes conductive causes an electrical short-circuit state. To be

Therefore, according to the knowledge of the present inventors, in order to perform good patterning, the amorphous surface which causes the parallel resistance while causing effective ablation on the irradiation surface of the pulse laser. It is considered necessary to suppress the crystallization of the high-quality silicon layer as much as possible. However, since the physical phenomenon caused by irradiating the thin film with the pulsed laser light having a high energy density was not fully understood, a method for performing good patterning of the back electrode could not be found.

[0013]

SUMMARY OF THE INVENTION In view of the above problems, the present invention is excellent in that a transparent conductive film having a high haze ratio is used to effectively cause a laser ablation phenomenon in patterning by laser irradiation of a back electrode. The present invention is intended to perform selective cutting, and to enable the patterning operation to be performed with good reproducibility. That is, the present inventors
It is intended to provide a method for stabilizing the production of a solar cell module and achieving high speed.

[0014]

That is, according to the present invention, patterning of the back electrode of a solar cell module, which comprises a transparent conductive film, an amorphous silicon layer, and a back electrode formed on a transparent insulating substrate, is performed by laser light. In the method for manufacturing a solar cell module according to, the transparent conductive film is 5% or more 3
The method is characterized by using a concave-convex transparent conductive film having a haze ratio of less than 0%, and in the method, the transparent conductive film is one or a combination of ZnO, SnO ₂ and ITO. A method for manufacturing a solar cell module, which is a thin film selected from among the above.

The transparent conductive film in the present invention means a metal oxide having a light transmittance of 70% or more in the visible light region and a conductivity of 10 ³ S / cm or more. Furthermore, it has a thin film structure having a thickness of 100 nm or more and 2000 nm or less formed on a transparent substrate (transparent insulating substrate) typified by glass, and includes zinc oxide (ZnO), tin oxide (SnO ₂ ), Alternatively, it means indium tin oxide (ITO) which is a compound of indium oxide and tin oxide, and has a haze ratio defined below of 5% or more and less than 30%.

The haze ratio (Hz) is defined as follows. That is, in the measured object measured using the A light source,
Let Tp be the transmissivity of light that passes through the object to be measured parallel to the rays of the light source, and let Tp be the transmissivity of the light that is scattered in the object and that is transmitted at an angle different from the straight direction of the light source rays. Assuming Td, the total transmittance Tt is expressed as follows. Tt = Tp + Td At this time, the haze ratio Hz is represented by a value obtained by dividing the diffuse transmittance Td by the total transmittance Tt, that is, Hz = Td / Tt. Therefore, the higher the haze ratio, the higher the diffuse transmittance and the smaller the parallel transmittance.
This suggests that the angle of the concavo-convex portion of the transparent conductive film with respect to the substrate becomes large, or the density of the concavo-convex portion becomes high, so that scattering occurs when passing through the transparent conductive film. . Therefore, as the haze ratio is higher, the irradiated laser light has a reduced proportion of rectilinear light due to scattering, and the passing distance and the number of times of passing through the amorphous silicon layer and the back electrode are increased, and the energy of the irradiated pulse laser is increased. Will be absorbed more. This allows better patterning to be achieved.

A transparent conductive film having a haze ratio of 5% or more and less than 30%, more preferably 10% or more and less than 30% can be easily obtained by forming a film at a relatively high temperature by a low pressure plasma vapor deposition method. It is also possible to select from commercially available products. Usually, those having a haze ratio in this range are used in other fields and are not used in solar cell modules, but in the present invention,
The feature is that this is used for the module.

This effect will be described below. In patterning processing of a thin film using pulsed laser light having a high energy density, when the irradiated laser light is irradiated to the thin film, a part of the energy of the laser light is absorbed by the thin film, and molecules inside the thin film are absorbed. A laser ablation phenomenon occurs in which the bonds are cracked and sufficient energy is given to separate the molecules from each other, causing them to be scattered at once. By the laser ablation, in the process of molecules and clusters in the thin film jumping out, surrounding substances are also involved and scattered.

Now, in the case of an amorphous silicon solar cell having a structure in which an amorphous silicon layer is formed on a transparent conductive film stacked on a transparent insulating substrate and a back electrode is formed, The patterning is generally performed by a method of irradiating a pulsed laser having high density energy from the back electrode side. Laser light in the visible and near-infrared wavelength ranges is mainly used for patterning the back electrode, but an amorphous silicon layer having a high absorption coefficient in the laser range is irradiated. Most of the energy absorption of pulsed lasers. As a result, a laser ablation phenomenon occurs in which molecular bonds inside the thin film are cracked and sufficient energy is given to separate the molecules from each other, causing them to scatter at once. As a result of this ablation, the back surface electrode formed on the amorphous silicon layer is scattered and removed. Therefore, in order to effectively generate laser ablation so as to perform good patterning, it is desirable that the amorphous silicon layer has a structure in which the energy of the pulse laser is sufficiently absorbed.

In general, the intensity I ₀ of light passing through a thin film has an absorption coefficient α (λ) with respect to a wavelength λ, and I = I ₀ exp (-α (λ ) * X) The light is attenuated according to the equation (1), and the light intensity after the attenuation becomes I. Therefore, in order to absorb more laser light, the longer the distance the laser light passes, the better.

A comparison between the case where the transparent conductive film has a flat structure and the case where the transparent conductive film has a concavo-convex shape will be described below. The distance becomes longer when the transparent conductive film having an uneven shape is irradiated. The reason will be described with reference to the drawings. First, consider a case where an amorphous silicon layer formed on a transparent conductive film having a flat structure is irradiated with laser light. This is a system having the structure shown in FIG. In this case, the irradiated laser light 62 passes through the amorphous silicon layer 3 and is absorbed. Further, a part of the laser light reaching the interface between the amorphous silicon layer 3 and the transparent conductive film 2 is reflected (shown by a dotted line). Further, the laser light that has passed through this interface reaches the interface with the transparent substrate (transparent insulating substrate) 1, and even at this stage, most of it is transmitted and part of it is reflected. The laser light traveling through the transparent substrate such as glass is reflected at this portion and returns to the thin film side again. In this case, about 10% of the laser light passing through the amorphous silicon layer is reflected at each interface layer, but the reflected light also passes through the same optical path as the incident light, and In the layer, transmission of laser light by only two passes is considered. Therefore, the ratio of laser light absorbed in the amorphous silicon layer is also limited.

On the other hand, a model showing a state in which laser light is vertically incident on the substrate is formed on an amorphous silicon layer formed on a transparent conductive film having an uneven surface. Is [Fig. 3]. At the incident surface of the amorphous silicon layer, the optical path of the laser light is largely changed, and the amorphous silicon layer is irradiated with the laser beam almost vertically. This is because the refractive index of amorphous silicon is as high as about 3.5. Further, the laser light passing through the amorphous silicon layer 3 is reflected at the interface between the amorphous silicon layer and the transparent conductive film 2 (
(Indicated by a dotted line), and again passes through the amorphous silicon layer. Further, the laser light refracted at the interface between the amorphous silicon layer 3 and the back surface electrode 4 is incident on the adjacent convex portion as shown in FIG. On the other hand, the light passing through the transparent conductive film is further partially reflected at the interface with the transparent substrate, passes through another optical path shown in FIG. 3 and enters the amorphous silicon layer. . As a result, due to the influence of refraction and reflection on that surface, it passes through the amorphous silicon layer for a longer time,
It will be absorbed more.

Therefore, as shown in the equation, the passing distance L
Is more likely to pass through the amorphous silicon layer when a transparent conductive film having a concavo-convex structure is used than when a transparent conductive film having a flat structure is used. Since the length becomes longer and the amount of energy of the absorbed laser also becomes larger, it is considered that ablation is more likely to occur.

Further, in FIG. 3, the laser light reflected on the back surface of the transparent insulating substrate and each interface layer is also reflected when it reaches the back side of the back electrode, and has the effect of being confined inside the thin film. Also in this case, the light confinement effect can be exhibited at a higher rate when the uneven transparent conductive film is used. Therefore, by using a transparent conductive film having a high haze ratio that increases the proportion of diffused light, good scribe characteristics can be achieved, and as a result, a higher parallel resistance of the solar cell module can be obtained. It will be. This is because it becomes possible to more easily cause ablation of the irradiated laser light by using a transparent conductive film having a high haze ratio. Therefore, in patterning using a high-density pulsed laser, the concavo-convex shape of the transparent conductive film is an important factor for performing good patterning. It will be the determining factor.

However, in the visible light region, 80
%, There is a limit to increase the haze ratio while maintaining a high transmittance of at least%.
0% is the limit. Therefore, in order to scribe the back electrode satisfactorily, the haze ratio is preferably 5% or more and less than 30%. Furthermore, in order to perform better backside electrode scribing, the haze ratio is 10% or more and 30% or more.
It is desirable to be less than.

However, if the haze ratio is less than 5%, the parallel transmittance of light rays is high, and it is not possible to effectively utilize such as scattering and reflecting sufficiently irradiated laser light. As a result, it becomes difficult to cause laser ablation to obtain good scribe characteristics, and thus it becomes impossible to scribe the back electrode satisfactorily. Therefore, the parallel resistance of the obtained solar cell module is low, and it becomes impossible to manufacture a highly efficient solar cell.

[0027]

EXAMPLES The present invention will be described below based on examples.
In the examples, a glass substrate that is a transparent insulating substrate is used.
An example using a plate will be described with reference to FIG. Glass base
A transparent conductive film 2 made of tin oxide is formed on the plate 1 under reduced pressure plasma.
1 having a film thickness of 1 μm formed by the vapor deposition method
Cut out to a size of 0 cm x 10 cm and wash the substrate surface with a brush.
Clean by cleaning to remove foreign matter attached. In this example
The transparent conductive film has a haze ratio of 1%, 5%, 10%,
The thing of 15% was used. After this, with a cleaned transparent conductive film
Use a glass substrate on a stage that can move in the horizontal XY axes.
Let Oscillation of pulsed laser with high energy density
At the same time, do not move the movable stage linearly.
Laser is continuously irradiated to separate and divide the transparent conductive film.
Form transparent conductive film units 21, 22, 23, 24 by
I made it. Most of the lasers used at this time are for the substrate 1.
Select one with a wavelength that does not absorb. Selected wavelength
The range should be 350 nm to 2000 nm.
Is desirable. In the example, the wavelength is 1064 nm
Nd: YAG laser with Q switch was used. Irradiation
Energy per laser pulse is about 3 × 10⁸J
/cm ²And form an image on the transparent conductive film with the long focus lens.
Position, and the irradiation width is 40 on the substrate surface.
Was set to 50 μm. Q switch frequency is
5 kHz, the moving speed of the movable stage is 100 mm / s
However, nothing is limited to this condition.

Further, the glass substrate on which the transparent conductive film is divided and formed in this manner is subjected to plasma chemical vapor deposition to form an amorphous silicon layer in a vacuum using a silicon hydride-based gas such as silane. It was formed to have a thickness of 200 to 1000 nm. After formation, the transparent conductive film was placed on a movable stage using a laser device similar to that used for divisional formation, and a pulse laser also having a high energy density was placed at a position slightly shifted in the divisional formation groove of the transparent conductive film. By continuously irradiating and forming new dividing grooves 31a, 32a, and 33a, the units are separated and divided into units like 31, 32, 33, and 34. At this time, the laser wavelength used was 532 nm, which has a large absorption in the amorphous silicon layer and a small absorption in the transparent conductive film and the glass substrate. In this embodiment, the Q switch frequency is 3 kHz and the moving speed of the movable stage is 60 mm / s, but the present invention is not limited to this condition. Then, a Ag thin film of 3000 A was formed by a sputter deposition method using Ag as a target, and further 1000 A of Al was similarly formed by a sputter deposition method to form a back electrode.

After forming the back electrode, patterning was performed by irradiation with pulsed laser light having high density energy. The pulse laser is used to cause an electrical disconnection between adjacent unit cells by linearly connecting the irradiation pulses as in the case of cutting the transparent conductive film. The irradiation position of this pulse laser was 100 μm or more away from the irradiation position of the transparent conductive film. The laser wavelength used was 532 nm, which has a high absorption in the amorphous silicon layer and a low absorption in the transparent conductive film and the glass substrate. In this embodiment, the Q switch frequency is set to 2 kHz and the moving speed of the movable stage is set to 60 mm / s, but the present invention is not limited to this condition. Thus, by continuously irradiating a pulsed laser having a high energy density 41a,
The dividing grooves shown in 42a and 43a can be formed.

Thus, finally, 41, 42, 43, 44
It is possible to form an integrated solar cell element constituted by the units divided as described above. At this time, the current generated when the solar cell is irradiated with light flows in the order of 33 → 23 → 42a → 42 → 32 → 22 → 41a → 41 if one part is observed, and [Fig. 1 With respect to the integrated solar cell element shown in the above], the current-voltage characteristic can be evaluated by connecting a current-voltage measuring device to the terminals where the electrode 41 corresponds to the anode and the electrode 44 corresponds to the negative electrode. 1 produced in this way
The performance of the 0 cm square sub-module was evaluated with an AM1.5 solar simulator.

When a transparent conductive film having a haze ratio of 1% was used, the conversion efficiency of the obtained 10 cm square solar cell submodule was 5.2%. Moreover, when the parallel resistance of each unit cell was evaluated, it was in the range of 10Ω or more and less than 200Ω.

On the other hand, when a transparent conductive film having a haze ratio of 5% was used, the conversion efficiency of the obtained 10 cm square solar cell submodule was 7.1%. Further, when the parallel resistance of each unit cell was evaluated, it was in the range of 50Ω or more and less than 300Ω. Furthermore, when a transparent conductive film having a haze ratio of 10% was used, the conversion efficiency of the obtained 10 cm square solar cell submodule was 9.2%. Moreover, when the parallel resistance of each unit cell was evaluated, it was in the range of 300Ω or more. Furthermore, when a transparent conductive film having a haze ratio of 15% was used, the conversion efficiency of the obtained 10 cm square solar cell submodule was 9.7%. Further, when the parallel resistance of each unit cell was evaluated, it was in the range of 400Ω or more.
The current-voltage characteristics of this solar cell are shown in FIG. That is, in order to manufacture a highly efficient solar cell module, it is more preferable to use a transparent conductive film having a haze ratio of 5%, and further 10% or more.

[0033]

EFFECT OF THE INVENTION By using a substrate having a transparent conductive film having a high haze ratio in manufacturing a solar cell module, a patterning method by irradiation with a pulsed laser having a high energy density can be facilitated and a high efficiency solar cell can be obtained. Batteries can be formed.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a solar cell module manufactured by the method of the present invention.

FIG. 2 is a diagram showing an optical path when an amorphous silicon layer formed on a transparent conductive film having a flat structure and a back electrode are irradiated with a laser.

FIG. 3 is a diagram showing an optical path when an amorphous silicon layer formed on an uneven transparent conductive film and a back electrode are irradiated with a laser.

FIG. 4 is a diagram showing current-voltage characteristics of an amorphous solar cell module manufactured by the method of the present invention during light irradiation.

[Explanation of symbols]

 1 transparent insulating substrate such as glass 2 transparent conductive film 21 transparent conductive film unit cell 22 transparent conductive film unit cell 23 transparent conductive film unit cell 24 transparent conductive film unit cell 3 amorphous silicon layer 31 amorphous silicon layer unit cell 32 Amorphous silicon layer unit cell 33 Amorphous silicon layer unit cell 34 Amorphous silicon layer unit cell 4 Back metal electrode 41 Back metal electrode unit cell 42 Back metal electrode unit cell 43 Back metal electrode unit cell 44 Back metal electrode unit Cell 61 Laser incident light 62 Laser reflected light

Claims (2)

[Claims] 1. A method of manufacturing a solar cell module, wherein a transparent conductive film, an amorphous silicon layer, and a back electrode are formed on a transparent insulating substrate by patterning the back electrode with a laser beam. The method as described above, wherein an uneven transparent conductive film having a haze ratio of 5% or more and less than 30% is used as the transparent conductive film. 2. The transparent conductive film is ZnO, SnO ₂ and I.
The method of manufacturing a solar cell module according to claim 1, wherein the thin film is a thin film selected from one or a combination of TOs.