JPH02298078A - Manufacture of solar battery - Google Patents

Abstract

PURPOSE:To process a fine dot by a simple method and to acquire a structure of highly efficient electrode by applying short wavelength laser light to a surface of a reflection preventing film formed on a photosensitive surface, by forming the fine dot and by forming a surface electrode by printing and firing an electrode material to a predetermined position for forming an electrode including the section. CONSTITUTION:An n<+>-diffusion layer 11 is formed to a surface of a p-type silicon substrate 10 to form a p-n junction. Then, an SiO2 oxide film 3 which becomes a passivation layer is formed, a TiO2 film 2 is formed thereon as a first reflection preventing film, and an SnO2 film 1 is further formed thereon as a second reflection preventing film. An n<+>-diffusion layer which remains on a rear is removed through etching to form a p<+>-layer 12 and a rear electrode 4 as a BSF layer. It is held to an X-Y stage, and short wavelength laser light is applied to a predetermined region for forming of a dot-like surface electrode. After such fine process is carried out, surface electrodes 6, 6... are printed and fired at a predetermined position of a surface electrode including holes 5, 5....

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a solar cell, and particularly to a method for manufacturing an electrode thereof.

(Prior art) As a ninth method to improve the efficiency of solar cells,
One example of this is to reduce the contact area of the electrode on the light-receiving surface.

Generally, the surface of the diffusion layer on the light-receiving side of a solar cell is roughly divided into a light-receiving portion and a portion directly below the electrode. Of these, the surface of the light receiving part is 1ks i02
A so-called basibasin treatment is performed to reduce the recombination of minority carriers in this part and improve the characteristics by covering it with an oxide film such as oxide film. On the other hand, in the area under the electrode, the recombination of minority carriers at the contact area between the electrode and the diffusion layer on the surface of the silicon substrate is infinite. It is necessary to increase the bearing area.

In order to reduce the contact area between the electrode and diffusion 1, it is possible to reduce the electrode area as an I-contact method, but if you simply reduce the electrode area, the influence of the single-row resistance will increase. , resulting in a decrease in characteristics due to a decrease in fill factor (FF). The commonly used printed and fired electrodes are characterized by their low cost, but when using these electrodes, the electrode occupancy rate of 3 to 4% is the limit with conventional technology.

In order to exceed this limit value, it is possible to reduce the contact area between the electrode and the diffusion layer by creating an electrode structure in which the contact area between the diffusion layer and the electrode is shaped like a metal dot, thereby improving the surface passivation effect by 11%. . FIGS. 2(a) and 2) are schematic cross-sectional views showing the manufacturing process of a product having such a dot electrode by printing and firing. Usually solar cells are
An n+ diffusion layer 11 is formed on the front surface of a p-type silicon substrate 10, a p+ diffusion layer 12 is formed on the back surface, and the surface of the n+ diffusion layer 11 is 1ks.
Covered with an oxide film 3 for bathibasilin such as io2,
Furthermore, the surface is covered with an anti-reflection film. In this figure, 'ri
It is composed of a double layer of an o2 film 2 and a 5n02 film l. The antireflection film may be one layer. P+ diffusion layer 12 on the back side
On the 0 surface, almost the entire surface is covered with Niwa-Kushi, AI! The back electrode 4 is formed by covering with other appropriate metal. Silver paste is printed in dots on the surface of the anti-reflection film, and surface electrodes 6-1.6-1. The upper part of ... is formed. This is 8
When fired at a temperature of 50° C. or higher, as shown in the second factor (b), the silver paste penetrates through the antireflection film and the oxide film 3 and forms the surface electrode 6- which contacts the n+ diffusion layer 11 in a dot shape.
1°6-1°... is formed. Thereafter, connecting electrodes connecting the dot-shaped surface electrodes 6-1, 6-1°, . . . are formed using metal paste. The connecting electrodes are also formed by printing and firing.

Note that there is also a method of removing the antireflection film and passivation film on the surface of the silicon substrate into fine dots using photoetching technology, and then depositing metal to form the electrodes.

(Problems to be Solved by the Invention) In the printing and baking method described above, due to technical limitations of screen printing, the area occupation rate of the dot electrodes is limited to 1.5%.

Furthermore, when applying the photoetching method to polycrystalline silicon substrates aimed at lowering costs, it is not practical due to the effects of the surface level difference of several tens of microns that occurs during the texture treatment of the substrate surface. do not have.

(Means for Solving Problem 11) In the present invention, the surface of an antireflection film formed on the light-receiving surface of a silicon substrate of a solar cell is irradiated with short wavelength laser light to form fine dots, An electrode material such as Ag paste is printed and fired at the planned position where the electrode will be formed, including the dot portion, to form a surface electrode.

(Function) The short wavelength laser beam has a spot size of 1μ by the optical system.
Since it is possible to set the size from 100% to any size, it is possible to achieve sufficient accuracy with photoetching.
A pattern of many dots can be drawn directly on the surface of the antireflection film.

(9) If ultraviolet light with a wavelength of 350 μm or less is selected, it will hardly pass through commonly used antireflection coating materials and will evaporate due to heat generation due to absorption of irradiation energy.

Further, the degree of processing can also be controlled by the irradiation energy intensity or the number of irradiations. Therefore, it is possible to process fine dots using a very simple method and realize a highly efficient electrode structure.

(9! Example) FIGS. 1(a), 1(b) and 1(C) are schematic cross-sectional views showing each step of electrode formation according to the present invention.

In FIG. 3111(a), the surface of the p-type silicon substrate 10 that has been cleaned is diffused with POCff3 gas to form an n+ diffusion layer 11, thereby forming a pn junction. At this time, an n+ diffusion layer is also formed on the back surface, but it will be removed in a later step. Subsequently, 5io2 with a thickness of 150A is deposited on the surface of the n+ diffusion layer 11 in an oxygen atmosphere to form a base layer.
An oxide film 3 is formed.

Next, on this oxide film 3, a TiO layer is applied to form the first anti-reflection film.
sli12 is formed to a thickness of 350A (D thickness L, and a 5n02 film 1t-150A is formed on top of the s2 film to a thickness of 1t-150A. Next, the n+ diffusion 11 remaining on the back side is
is removed by etching, and AI! By printing and firing the paste, the p+112 and back electrode 4, which will become the BSF skin, are formed. The nine p-type silicon substrate 10 processed in this way is held on an X-Y stage and exposed to short wavelength laser light (
For example, a region where a dot-shaped surface electrode is to be formed is irradiated with XeC (wavelength: aosnm). In this example, the laser beam dimensions are 150 x 50μ,
Dot pitch! The energy intensity was varied from 1 to 5 rays and the machining process was carried out as -50 to 500μ. Regarding the surface state after processing, the Snug film 1, which is the second antireflection film, is removed at an energy intensity of up to 2 intensities, and the first antireflection film is removed at an energy intensity of aJ/i of 1. TiO
2 membrane 2 is removed. Hole made by laser beam irradiation 5.5...
* may be a depth that reaches a part of the TiO2 film 20, or may be a depth that includes the 5io2 oxide film 3. In addition, when irradiated with an energy intensity of 5 J/, 4 or more, n
+ Melting and evaporation of the surface of the diffusion layer 11 occur.

Figure 1(b) shows the hole 5 after this = Rina micromachining.
．． The figure shows a state in which surface electrodes 6, 6, .

FIG. 1(c) shows the fired state after the above steps.

Generally, Ag paste has unique temperature characteristics depending on the type of glass frit contained therein. The Ag paste used here is 5% for the TiO2 film.
Buy at a temperature of 80℃ or higher, and for 5n02 membrane, 8
It has the property of penetrating at a temperature of 50°C or higher. Therefore, if irradiation processing is performed within the energy intensity range of 2 to 4 J, Q among the above processing conditions, A
g paste is T)02 film 2f: penetrates n+ diffusion layer 11
The surface electrode 6.6... is completed. The Ag paste on the 5n02 film 1, which is not microfabricated except for the dot portions, does not penetrate through the 5n02 film 1t at a temperature around 600°C. The 5n02 film 1 acts as a barrier to the Ag paste. In this way, good dot-shaped surface electrodes 6, 6°, . . . are formed in the center.

In addition, in the present invention, when the dot pitch is 50 μm,
Surface electrode 6.6. The occupation rate of the contact area between ... and n+ diffusion/111 is 1.27%, and when the dot pitch is 500 μm, it is 0.13%, which is much lower than the conventional method (1).

(Effects of the Invention) According to the present invention, electric current. Although both voltage showed an improving trend,
In particular, the open-circuit voltage showed a significant increase of 5 to 10 v compared to the value of the device using the conventional method. Also, F
Regarding F, a value equivalent to that of the conventional element was obtained despite the small electrode contact area.

The anti-reflection coating on the surface of the silicon substrate is coated with short wavelength laser light.
Since the Ag paste is printed with dots in a fine pattern and then fired, there is no need for two types of electrode materials, one for penetrating the anti-reflection film and one for not penetrating the anti-reflection film, as in the past. There is also no need for a tumbler.

Furthermore, since the processing ability is on the same level as photoetching, the electrode contact area can be significantly reduced, greatly contributing to making solar cells more efficient. Furthermore, processing is easy to control and processing speed is fast, resulting in high productivity.

[Brief explanation of the drawing]

FIGS. 1(a), (b), and (c) are schematic sectional views of each process according to an embodiment of the present invention, and FIGS. 2(a) and (b) are schematic sectional views of each process of a conventional example. be.

Claims (1)

[Claims] 1. The surface of the antireflection film formed on the surface of the light-receiving surface is irradiated with short wavelength laser light to form fine dots, and electrode material is printed at the planned positions where electrodes will be formed, including the dots. A method for manufacturing a solar cell characterized by firing to form a surface electrode