WO2006087786A1

WO2006087786A1 - Solar cell manufacturing method

Info

Publication number: WO2006087786A1
Application number: PCT/JP2005/002456
Authority: WO
Inventors: Takaaki Iwata; Hisashi Tominaga; Kimikazu Hazumi
Original assignee: Mitsubishi Denki Kabushiki Kaisha
Priority date: 2005-02-17
Filing date: 2005-02-17
Publication date: 2006-08-24
Also published as: JPWO2006087786A1

Abstract

A solar cell manufacturing method wherein manufacturing equipment whose maintenance is easy can be used and a solar cell which does not easily generate electrical leakage is generated. In the solar cell manufacturing method, a pulse laser beam having a pulse width of 100nsec or less is used to electrically insulate a P-type electrode forming region from an N-type electrode forming region in the crystalline silicon based solar cell, and PN isolation is realized. The solar cell can be manufactured by using the laser equipment, which is low price, can be easily maintained and does not take much installation space, by obtaining the pulse laser beam by using YAG laser or YVO4 laser equipment.

Description

Manufacturing method of solar cell

Technical field

The present invention relates to a method for manufacturing a solar cell, and more particularly to a method for electrically insulating a p-type electrode and an n-type electrode of a crystalline silicon solar cell.

Background art

[0002] In a method of manufacturing a silicon solar cell using silicon, a method using wet etching or plasma etching as a step of electrically insulating a p-type electrode and an n-type electrode (PN separation) Is well known. However, since the above method takes a long time or the silicon wafer is easily broken in the transfer process before and after the process of stacking the silicon wafers for the etching process, a method using a laser as an alternative to the etching has been proposed. . As a laser used for PN separation, one using an excimer laser (for example, refer to Patent Document 1) or one using a Q-switch YAG laser (for example, refer to Patent Document 2) has been reported.

[0003] Patent Document 1: US Pat. No. 4989059 (page 6, Figl)

Patent Document 2: JP-A-5-75148 (Page 2-3, Fig. 1)

Disclosure of the invention

Problems to be solved by the invention

[0004] When using a laser for PN separation, if the excimer laser shown in Patent Document 1 is used as the above laser, a harmful gas is used, so maintenance is easy and the device becomes large and takes up space. There was a point. In addition, if the Q-switch YAG laser (wavelength 1.06 [m], nores width 200 [sec], energy density 10 ⁸ [WZcm ² ]) shown in Patent Document 2 is used as the laser, it is inexpensive but pulsed. There was a problem that it was easy to heat-process with a long width. Further, in this case, there is a problem that the electrical insulation is insufficient as compared with the case where a conventional etching method or excimer laser is used.

[0005] The present invention has been made to solve the above-described problems, and it is possible to use a manufacturing apparatus that can be easily maintained, and at the same time, it is difficult to cause electrical leakage. A battery manufacturing method is provided.

Means for solving the problem

[0006] A method for manufacturing a solar cell according to the present invention electrically connects a p-type electrode formation region and an n-type electrode formation region of a crystalline silicon solar cell using a pulsed laser beam having a pulse width of 100 [nsec] or less. Insulating process is performed and PN is separated.

The invention's effect

[0007] According to the present invention, by shortening the pulse width of the laser, it is possible to effectively check even if a short wavelength one such as an excimer laser is not selected. In other words, the short pulse makes it difficult for heat to occur, that is, the silicon around the processed part where heat does not accumulate at the processing point does not melt, so the p-type electrode formation region and the n-type electrode formation region are separated. There is a remarkable effect that electrical insulation can be performed more reliably.

Brief Description of Drawings

FIG. 1 is a process diagram showing a manufacturing process of a solar cell according to Embodiment 1 of the present invention.

FIG. 2 is a diagram showing a processing example of PN separation by a laser according to Embodiment 1 of the present invention.

FIG. 3 is a diagram showing the waveform of a laser used in the method for manufacturing a solar cell according to Embodiment 1 of the present invention in comparison with a conventional laser waveform.

FIG. 4 is a circuit configuration diagram showing an equivalent circuit of the solar battery cell according to the first embodiment of the present invention.

FIG. 5 is a diagram showing a relationship between a pulse width and a diode current of a laser in which PN separation laser power according to the first embodiment of the present invention is implemented.

FIG. 6 is a diagram showing a laser groove machining shape according to the first embodiment of the present invention.

Explanation of symbols

[0009] 1 silicon weno, 2 N + layer, 3 antireflection film, 4 A1 electrode, 5, 6 Ag electrode, 7 P + layer, 8 laser processing groove, 9a, 9b corner cut off part, 11 photovoltaic current source, 12 Diode, 13 series resistance, 14 parallel resistance.

BEST MODE FOR CARRYING OUT THE INVENTION Embodiment 1.

FIGS. 1A to 1F are process diagrams showing a method for manufacturing a solar cell according to the first embodiment of the present invention, and show a cross section of a silicon wafer in each process.

First, a p-type crystalline silicon ingot is sliced to a predetermined thickness (about 300 [m]) to form wafer 1 (FIG. 1 (a)).

Next, damage etching (up to about 20 [m]) is performed on the damaged layer on the wafer surface, and pyramidal texture etching is performed to reduce reflectivity for the purpose of increasing photocurrent. Further, phosphorus is diffused on the surface of the wafer using phosphorus oxychloride to form an N + layer 2. In order to reduce the reflectance, an antireflection film 3 is formed on the upper surface of the wafer (FIG. 1 (b)).

Next, a p-type electrode is formed on the lower surface of the wafer, which also has the A1 electrode 4 and the Ag electrode 5 and force. To make a p-type electrode, A1 paste and Ag paste are used, and each is screen printed in a predetermined pattern and dried (Fig. 1 (c) (d)).

Similarly, in order to form an n-type electrode composed of Ag electrode 6 on the upper surface of wafer 1, Ag paste is screen-printed in a predetermined pattern and dried (FIG. 1 (d)).

After the paste on both sides of wafer 1 is dried, each A1 atom diffused from the A1 paste on the lower surface of the wafer into the p-type silicon wafer by offsetting the N + layer 2 into the p-type silicon wafer 1 P + layer 7 is formed. As a result, an N + PP + junction is formed, and a p-type electrode force composed of A1 electrode 4 and Ag electrode 5 is formed on the lower surface of the wafer, and an n-type electrode composed of Ag electrode 6 is formed on the upper surface (Fig. L). (e)).

Next, using a short-pulse LD-pumped solid laser (wavelength 1064 [nm] -355 [nm]) with a pulse width of 100 [nsec] or less (for example, 10-40 [nsec]) A laser beam is irradiated along the periphery of the electrode (repetition frequency 10 [kHz] —100 [kHz]), groove (width 20—40 [/ ζ πι], depth number [m] —50 [m]) 8 Form. As a result, the n-type electrode formation region on the upper surface of the wafer and the p-type electrode formation region on the lower surface of the wafer are electrically insulated, and PN separation is realized (Fig. L (f)).

The solar battery cell is completed through the above steps. Based on this, a plurality of solar cells are arranged side by side and modularized to complete a solar cell module. [0011] In the above-described embodiment, the above-described laser processing is performed by groove-causing the periphery of the p-type electrode on the lower surface of the wafer, as shown in FIGS. 1 (f) and 2 (f-1). As shown in Fig. 2 (f-2), the periphery of the n-type electrode on the upper surface of the wafer may be grooved. Further, as shown in FIGS. 2 (f-3) and (f-4), the corners of the wafer 1 may be cut off. 9a and 9b are the corner cut-out portions by the laser.

[0012] In the above embodiment, a laser beam from a short-pulse LD-pumped solid-state laser is used. However, if the pulse width is 100 [nsec] or less, the laser to be used is an LD-pumped solid-state laser. Not only a laser but another laser device may be used.

In this embodiment, the fundamental wave of Nd: YAG (YAG laser added with neodymium as an active atom) or Nd: YVO (YVO laser added with neodymium as an active atom),

4 4

Or Nd: YAG or Nd: YVO 3rd harmonic is used for actual machining

Four

As a result, it was confirmed that electrical insulation was good.

FIG. 3 is a diagram showing a laser waveform A used in the method for manufacturing a solar cell of the present invention in comparison with a conventional laser waveform B. The pulse width of the conventional laser waveform B is larger than 100 [nsec], and the waveform is used, whereas the laser waveform A according to the present invention has a pulse width of 100 [nsec] or less. Therefore, the peak power is about 10 [kw] or more, which is larger than before.

The relationship between the electrical characteristics of the solar battery cell and the pulse width of the laser beam used for processing will be described below.

The electrical characteristics of solar cells can be explained by the equivalent circuit shown in FIG. The equivalent circuit consists of a photovoltaic current source 11 (1), a diode 12, a series resistor 13 ( _r ), a parallel resistor 14 (r) and s sh, and the series resistor 13 (r) is the ohmic loss of the solar cell surface, the parallel resistor 14 (r) represents the loss due to the res s sh cage current (I). Whether the PN separation is done well sh

Can calculate the leakage current (I) when reverse bias is applied. The smaller the leakage current (I) when reverse bias is applied, the lower the sh

It is possible to judge whether or not electrical insulation has been achieved. Therefore,

The electrical characteristics were compared by changing the pulse width of the laser used in the groove cleaning process for PN separation (Fig. 1 (f)). [0014] Figure 5 shows the leakage current (I) when the laser pulse width and reverse bias (1 1 [V]) are applied.

Indicates the relationship with sh.

In order to obtain good electrical insulation, the leakage current (I) must be less than 0.1 [A].

sh

Figure 5 shows that the electrical insulation is good when the pulse width is 100 [nsec] or less. On the other hand, when the pulse width is longer than 100 sec, the leakage current (I) is 0.6 [A].

sh

Thus, electrical insulation is deteriorated.

As a result of observing the laser-processed wafer, it was found that melting occurred in the vicinity of the processed part when processed under these conditions, which is presumed to deteriorate the electrical insulation.

[0015] Based on the above examination, in order to prevent thermal processing and perform PN separation with good electrical insulation, in addition to the conventional method using an excimer laser, that is, the method of shortening the laser wavelength, a laser pulse For the first time in the present invention, it has been clarified that it is effective to set the width to 100 [nsec] or less.

[0016] Note that Fig. 5 shows that the pulse width is 100 [nsec] or less and the leakage current (I) is 0. 1 [A]

sh

Thus, it was confirmed that the electrical insulation was performed well. Harmonics increase energy, which has the advantage of expanding the range of available processing materials. In addition, since the beam can be narrowed down, there is an advantage that fine processing is possible. Use of the fundamental wave has the effect of simplifying the device configuration.

[0017] Irradiation energy is another parameter that determines the quality of electrical insulation. If the irradiation energy is low, it will be insufficient. On the other hand, if the energy is too high, melting will occur and electrical insulation will not be improved. Whether the laser wavelength is 1064 [nm] (fundamental wave) or 355 [nm] (third harmonic wave), the processing conditions for good electrical insulation are per pulse and per unit area. The irradiation energy was 10-30 (Pulse 'cm ² )].

[0018] From the above, it is necessary that the laser beam to be used is a pulsed laser beam having a pulse width of 100 [nsec] or less and an irradiation energy density in a range where melting does not occur. If these conditions are met, processing can be performed using the fundamental wave or can be checked using the nth harmonic (n ≥ 2)! [0019] Further, the processing rate is good so that the overlapping rate of the spots when the irradiation spots are overlapped and the groove force is applied is 60% or more.

[0020] In addition, the processing trajectory of the groove force due to the laser is, for example, a shape combining straight lines such as a "well" shape and a "mouth" shape as shown in FIGS. 6 (a) and 6 (b). Thus, the drive system of the laser processing apparatus can be made simple.

Claims

The scope of the claims

[1] Using a pulsed laser beam with a pulse width of lOOnsec or less, the P-type electrode formation region and the N-type electrode formation region of the crystalline silicon solar cell are electrically insulated and PN separated A method for manufacturing a solar cell.

2. The method for manufacturing a solar cell according to claim 1, wherein the pulsed laser beam is obtained using a fixed laser device.

[3] The solid-state laser device is a YAG laser or YVO laser and is insulated using a fundamental wave.

Four

The method for producing a solar cell according to claim 2, wherein:

[4] The solid-state laser device is a YAG laser or YVO laser, and the nth harmonic (n≥ 2)

Four

3. The method for manufacturing a solar cell according to claim 2, wherein the insulating process is performed using the solar cell.