JPH04144290A - Manufacture of crystal silicon solar battery element - Google Patents

Abstract

PURPOSE:To get a solar battery element with high conversion efficiency, wherein the loss by current collecting resistors at the rear of an element is reduced and light shut-in effect is improved, by forming the p-type silicon substrate and the p<+>-layer in the region surrounded by a mesh-shaped electrode in the shape of grooves crossing each other at right angles. CONSTITUTION:By providing grooves 16, which cross each other at right angles, in the region, which is surrounded by the mesh-shaped Ag electrode 10 made at the rear of the element of a p-type semiconductor base layer 12, opportunity increases such as that one part of the light, which has entered the light receiving face of a solar battery 1, reaches the rear and is reflected at the rear, and that one part of the light, which has gone out of the side of the groove, enters the bottom of the groove or the side of other groove again, so the utilization factor of the incident light rises. Moreover, in the p<+>-type semiconductor layer 11 at the rear, the sectional area to the direction of an electrode increases, and the loss by current collecting resistors decreases. Furthermore, in the groove part 16, the depth is approximately 30mum, so the effective thickness of the substrate is approximately 170mum, and the effect of collecting the light generating carriers improves in the region near the junction of the light receiving face without thinning the real thickness of the substrate.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a device backside structure in a -n''/P/p+ type crystalline silicon solar cell device.

[Conventional technology]

Conventionally, attempts have been made to make solar cell elements thinner in order to increase their conversion efficiency. In order to make the device thinner, it is necessary to create a structure in which the light incident inside the device is reflected from the back surface of the device and reflected back into the device without exiting to the outside, that is, a light confinement structure, to improve conversion efficiency. Become.

Furthermore, in the printed electrode forming method using paste, substrate cracks frequently occur during the firing process due to the difference in thermal expansion coefficient between silicon and paste. Therefore, it is also necessary to reduce the electrode area ratio.

Regarding the optical confinement structure, see Reference 1 (James M,
Gee, 20th I E'Potovolt
aic 5peci-alist cont, 198
8, p. 549) reports on the effects of the structure of the front and back surfaces of the groove. In addition, Reference 2 (M, A, Gr
een, et al, Technical D-i
gest of Int'l PVSEC4'5ydn
ey, New Australia, 1989,
p l 59) reports on a solar cell element with a V-groove structure on the light-receiving surface, which aims to reduce series resistance loss in the direction of finger electrodes in the n-th layer of the light-receiving surface and to reduce light reflectance.

[Problem to be solved by the invention]

The above-mentioned conventional technology is a report on a light confinement structure, a reduction in the area ratio of the light-receiving surface electrode (reduction of current collecting resistance loss in the n-soil layer), and a reduction in reflectance. The structure does not take into account both the structure for reducing the Furthermore, in the prior art, (1) the groove structure pattern is very fine, so the device manufacturing method requires a fine patterning process using photolithography, making it a very complicated and expensive process.

An object of the present invention is to provide a solar cell element with high conversion efficiency that reduces current collection resistance loss on the back side of the element and improves the light confinement effect, and a highly economical manufacturing method using a printing method.

[Means to solve the problem]

The above purpose is to form a crystal with an n+ layer formed on the surface of the P-type silicon substrate on the side where light enters, a P+ layer formed on the back surface of the P-type silicon substrate, and a mesh-like electrode formed on the P+ layer. In the silicon solar cell element, this is achieved by forming the P-type silicon substrate and the P+ layer in the region surrounded by the mesh-like electrode into grooves that are orthogonal to each other.

The above object is achieved by forming the P+ layer only at the position where it joins the mesh-like @pole.

The above object is achieved because the mesh-like electrode and the P+ layer are an aluminum-silicon alloy layer, which is an alloy of aluminum and silicon, and a p+ type regrowth layer.

The above object is achieved by setting the area ratio of the mesh electrode to 25% or less.

The above purpose is to form an n+ layer on the surface of a P-type silicon substrate on the side where light is incident, to form a P+ layer on the back surface of the P-type silicon substrate, and to form a mesh-like electrode on the P+ layer. In the method of manufacturing a silicon solar cell element, this is achieved by forming the P type silicon substrate and the P+ layer in the region surrounded by the mesh electrode into mutually orthogonal groove shapes by etching after printing an etching resist.

[Effect]

According to the above configuration, by forming the region surrounded by the mesh-like electrode in the shape of orthogonal grooves, more wall surfaces of the groove are formed than in the case where the P+ layer on the back surface is flat, and the wall surfaces are directed toward the electrode. This results in an increase in the cross-sectional area relative to the current flow rate, which reduces current collection resistance loss.

In addition, the light incident on the n+ layer of the solar cell element is transmitted to the n+ layer, P
Although the light is absorbed by the silicon substrate and the P+ layer, some of the light reaches the back surface. The light reaching the back surface is reflected at the bottom of the groove as seen from the back surface side, and since the junction of the light-receiving surface, that is, the junction between the n+ layer and the P-type silicon substrate is close, absorption loss is small and the light utilization rate is high.

A part of the light that is reflected by the P+ layer on the back surface, refracted from the wall surface of the groove, and jumped out has a high probability of entering the bottom of the groove or the wall surface of another groove again, so the light confinement effect reduces the amount of incident light. Utilization rate increases.

Furthermore, by forming the grooves, the thickness of the solar cell element is optically reduced, so the conversion efficiency is increased, and the convex portions other than the grooves function as reinforcing materials, increasing the mechanical strength.

〔Example〕

Hereinafter, one embodiment of the present invention will be described based on the drawings.

As shown in FIG. 1, the solar cell 1 of the first embodiment has a P+ semiconductor layer 11 on the back surface of the element of a P-type semiconductor base layer 12, a mesh-like Ag electrode 10 on top of the P+ semiconductor layer 11, and a region surrounded by this electrode. groove perpendicular to] 6, n+ type half body layer 1 on the light receiving surface
3 Thick oxide film 14 that also serves as an antireflection film, light-receiving surface electrode 15
has.

In solar cell 1, P-type semiconductor base layer 12 has a thickness of approximately 200 μm. As shown in FIG. 2, the mesh-like Ag electrodes 10 on the back side of the device have a pitch of 2 mm,
1+am, line width approximately 200μm, thickness approximately 45μm (
It has a buried structure with an electrode area ratio of approximately 25%.

The orthogonal grooves 16 in the area surrounded by the electrodes have a width of about 100 μm, a pitch of 200 μm, and a depth of about 30 μm. p+ type half body layer 11, depth is approximately 0.2μ
m.

Sheet resistance is approximately 70Ω/mouth. N+ type half body layer 13, depth is approximately 1.0 μm, sheet resistance is approximately 100
Ω/mouth. Thick oxide film 1 that also serves as an anti-reflection film
No. 4 has a thickness of approximately 0.1 μm.

In such a structure, the conversion efficiency increases for the following reasons. By providing orthogonal grooves 16 in the area surrounded by the electrodes of the mesh-like Ag electrode 10 formed on the back surface of the element of the P-type semiconductor base layer 12, a portion of the light incident on the light-receiving surface of the solar cell 1 is transmitted to the back surface. A portion of the light that reaches the groove, reflects on the back surface, and exits from the side surface of the groove has a higher chance of re-entering the bottom of the groove or the side surface of another groove, increasing the utilization rate of the incident light. Further, in the back P+ type semiconductor layer 11, the cross-sectional area with respect to the electrode direction increases, and current collection resistance loss is reduced. Furthermore, since the depth of the groove 16 is about 30 μm, the effective thickness of the substrate is about 170 μm, and the bonding of the light-receiving surface (n-type semiconductor layer 13 and P The current collection effect of photogenerated carriers in the region close to the junction of the type semiconductor base layer 12 is improved.

Here, the groove width, depth, and pitch of the mesh-like Ag electrode 10 on the back surface of the element and the orthogonal grooves 16 are an example of the manufacturing method described later, and improve printing technology and solar cell manufacturing method. etc., and is not limited to this example.

Next, a method for manufacturing the solar cell of this example will be described.

The P-type semiconductor base layer 12 has an initial thickness of about 260 μm.
, the specific resistance is about 1Ω・Cl11, and the minority carrier diffusion length is
It is approximately 170 μm. On the back side of the element, a pitch of 2 mm for forming grooves for buried electrodes, and a line width of 1 mm and approximately 20
An etching resist having a mesh pattern of 0 .mu.m and an orthogonal pattern with a pitch of 200 .mu.m and a line width of about 100 .mu.m for forming grooves perpendicular to the region is applied by a printing method. Next, when the etching resist is removed after etching for 1 minute using an HF/HNO etching solution, the aforementioned pattern having a depth of about 30 μm is simultaneously formed.

Next, alkali etching is performed as an uneven treatment to make the surface non-reflective. After this etching, the thickness of the P-type semiconductor base layer 12 is approximately 200 μm. Next, due to phosphorus diffusion, the depth is approximately 0.25 μm and the sheet resistance is approximately 150 μm.
An n-type semiconductor layer 13 of Ω/hole is formed. After that, the thick oxide film 14, which also serves as an anti-reflection film, is thermally oxidized to approximately 0.1
μm formation and processing of the light-receiving surface is completed. Next, before processing the back surface, an etching resist is applied to the entire surface by a printing method in order to protect the light-receiving surface. Next, the oxide film formed on the back surface in the previous step is removed using HF/H2O solution, and the n++ semiconductor layer formed on the back surface is removed using HF/HNO and etchant. When the etching resist is removed, a P-type etchant is formed. Semiconductor base layer 12 is exposed. Next, a p-type semiconductor layer 11 having a depth of about 0.2 μm and a sheet resistance of about 70 Ω/hole is formed in the P-type semiconductor base layer 12 on the back surface by boron diffusion.

After that, after printing and drying Ag paste on the back side and light receiving side, 6
The mesh-like Ag electrode 10 is formed by heating at 00° C. for 1 minute in a nitrogen atmosphere and cooling, thereby obtaining the solar cell of this example. The characteristics of this device are particularly improved in short-circuit current density and fill factor compared to a conventional device that does not have the groove 16 perpendicular to the area surrounded by the mesh-like Ag electrode 1o on the back surface of the device (the mesh-like electrode area ratio is the same). The above-mentioned effect was confirmed through experiments.

Furthermore, FIG. 3 shows a second embodiment of the present invention.

This solar cell 2 has a mesh-like Ag-AQ electrode 17. A groove 16 perpendicular to the area surrounded by this electrode, a thick oxide film 14, a P+ type semiconductor layer 11 provided only at the position where it joins with this electrode, an n+ type semiconductor M13 on the light receiving surface, and a thick oxide film that also serves as an antireflection film. oxide film] 4 and a light-receiving surface electrode 15.

This solar cell 2 has the following features in the solar cell 1 of the first embodiment:
While the P+ type semiconductor layer 11 is formed on the entire back surface, it is formed only on the electrode part, and the area surrounded by the electrode is replaced by the BSF structure of the P+ type semiconductor layer 11 for back surface passivation. An oxide film 14 is formed. This back oxide film 14 is formed at the same time as an oxide film that also serves as a light-receiving surface antireflection film.
- The AQ electrode 17 and the p-senju conductor layer 11 of the electrode part are made of Ag
- An aluminum-silicon alloy layer and a P+ type regrowth layer formed by an alloy reaction between aluminum and silicon by using AQ paste. Therefore, in the manufacturing method of this embodiment, the boron diffusion step for forming the p-sensitivity conductor layer can be omitted, which simplifies the manufacturing process and saves cost and time.

〔Effect of the invention〕

According to the present invention, by forming the region surrounded by the mesh-like electrode in the shape of orthogonal grooves, many wall surfaces of the groove are formed, and the cross-sectional area of the wall surfaces increases in the direction of the electrode. Since the current collection resistance loss is reduced and the utilization rate of incident light is increased due to the light confinement effect, the effect of increasing the efficiency of converting light into electric power of the crystalline silicon solar cell element can be obtained.

Furthermore, the printing method has the effect of increasing the economic efficiency of the manufacturing method 2

[Brief explanation of the drawing]

FIG. 1 is a rear perspective view of a crystalline silicon solar cell element according to a first embodiment of the present invention, FIG. 2 is a plan view showing the entire pattern of the mesh-like electrode shown in FIG. 1, and FIG. FIG. 2 is a rear perspective view of a crystalline silicon solar cell element according to a second example. 1... Solar cell element, 2... Solar cell element, 10.
...Mesh-like Ag electrode, 11...P ten-type semiconductor layer,
12... P-type semiconductor base layer, 13... n-type semiconductor layer, 14... oxide film, 15... light-receiving surface Ag electrode, 16
...Orthogonal grooves, 17...Mesh-like Ag-AQ electrode.

Claims (1)

[Claims] 1. n^+ on the surface of the P-type silicon substrate on the side where light enters.
A layer is formed on the back surface of the P-type silicon substrate.
In a crystalline silicon solar cell element in which a + layer is formed and a mesh-like electrode is formed on the p^+ layer, the P-type silicon substrate and the p^+ layer in a region surrounded by the mesh-like electrode are mutually orthogonal. A crystalline silicon solar cell element characterized by being formed in a groove shape. 2. The crystalline silicon solar cell element according to claim 1, wherein the p^+ layer is formed only at a position where it is bonded to the mesh electrode. 3. The crystalline silicon solar cell according to claim 2, wherein the mesh electrode and the p^+ layer are an aluminum-silicon alloy layer that is an alloy of aluminum and silicon, and a p^+ type regrowth layer. element. 4. The crystalline silicon solar cell element according to any one of claims 1 to 3, wherein the area ratio of the mesh electrode is 25% or less. 5. n^+ on the surface of the P-type silicon substrate on the side where light enters.
A layer is formed on the back surface of the P-type silicon substrate.
In a method for manufacturing a crystalline silicon solar cell element in which a + layer is formed and a mesh-like electrode is formed on the p^+ layer, the P-type silicon substrate and the p^+ layer in a region surrounded by the mesh-like electrode are 1. A method for producing a crystalline silicon solar cell element, which comprises printing an etching resist and then etching it to form grooves that are perpendicular to each other.