JP2866982B2 - Solar cell element - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a solar cell element, and more particularly, to a solar cell element having an electrode formed only on the back side of a silicon substrate.

(Prior Art and Problems Thereof) As shown in FIG. 3, a solar cell element has an n ⁺ region 32 formed on one principal surface side in a p-type silicon substrate 31 to form a pn junction. Generally, electrodes 33 and 34 are formed on n ⁺ region 32 on one main surface side of silicon substrate 31 and on the other main surface side, respectively. In FIG. 3, reference numeral 35 denotes an antireflection film.
However, in such a solar cell element, since the electrode 33 is provided on the light receiving surface side, the incident light is blocked by the light receiving surface side electrode 33 and a loss due to shadow occurs, and the light receiving surface side electrode 33 and There is a problem that carrier recombination loss occurs in the high concentration layer 32 on the light receiving surface side.

Therefore, in order to reduce the light shadow area on the light receiving surface side and to suppress the recombination of carriers at the light receiving surface side electrode portion,
A solar cell element as shown in FIG. 4 has also been proposed. That is, only the concave and convex portions 42 and the antireflection film 43 are formed on one main surface side of the p-type silicon substrate 41, and the n ⁺ region 44 and the p ⁺ region 45 are formed on the other main surface side in the silicon substrate 41. Then, electrodes 46 and 47 are formed, which are in point contact with the n ⁺ region 44 and the p ⁺ region 45, respectively. With this configuration, since there is no electrode on the light receiving surface side, the light shadow area becomes zero, and recombination of carriers can be suppressed by reducing the contact area with the electrode. However, this solar cell element has a problem that when the specific resistance of the silicon substrate is large, the series resistance increases when the solar cell element is formed, and when the solar cell element is not a condensing type, the efficiency is greatly reduced.

Further, as shown in FIG. 5, a through hole 52 is formed in the p-type silicon substrate 51, and an n ⁺ region 53 is continuously formed in the light receiving surface side of the silicon substrate 51 and in the through hole 52. A solar cell element has also been proposed in which electrodes 56 and 57 are formed in the p ⁺ region 54 on the back side and the n ⁺ region 55 on the back side of the through hole portion to reduce the light shadow area on the light receiving surface side. (See, for example, JP-A-2-51282). However, in this solar cell element, a high-temperature process of 800 ° C. or more is required to form the n ⁺ region 53 on the surface of the silicon substrate 51 and the through hole 52, and a high concentration layer of n ⁺ is formed on the light receiving surface side. There is a problem that recombination loss of carriers occurs in the high concentration layer on the light receiving surface side due to the formation. In FIG. 5, reference numeral 58 denotes an antireflection film formed on the light receiving surface side of the p-type silicon substrate.

The present invention has been proposed in view of such a problem of the conventional device, and an object of the present invention is to provide a solar cell element that prevents a reduction in efficiency due to a shadow area and prevents a recombination loss of carriers. Things.

(Constitution of the Invention) According to the present invention, a large number of inclined through holes are formed in a p-type silicon substrate having an uneven portion on the light receiving surface side,
An n ⁺ region is formed in the vicinity of the through hole on the back side of the silicon substrate, and an inversion layer is formed continuously from the light receiving surface side of the silicon substrate to the n ⁺ 4 region via the through hole portion. forming a reflection preventing film on the side with the through hole, a p ⁺ region is formed in a portion other than the portion n ⁺ regions are formed in the silicon substrate backside, the electrode on the n ⁺ region and p ⁺ region Is provided, whereby the above object is achieved.

(Operation) As described above, since there is no electrode on the light receiving surface side of the silicon substrate, no light shadow loss and carrier recombination loss occur, and light is received because there is no n ⁺ region on the light receiving surface side. No recombination loss of carriers is caused by the surface side high concentration layer. Furthermore, the surface area of the silicon substrate is increased by forming a concave and convex portion on the light receiving surface side of the silicon substrate and forming a large number of inclined through holes in the silicon substrate.
Therefore, a highly efficient solar cell element can be provided.

(Example) Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a perspective view showing one embodiment of a solar cell element according to the present invention, wherein 1 shows a p-type silicon substrate as a whole.

The silicon substrate 1 has a thickness of 50 to 2 having a specific resistance of about 0.4 Ωcm containing a p-type impurity such as boron.
It is composed of a silicon substrate of about 00 μm. This silicon substrate 1 may be a single crystal silicon substrate formed by a pulling method or the like, or may be a polycrystalline silicon substrate formed by a casting method or the like.

A large number of through holes 1a are formed in the silicon substrate 1. This through-hole 1a increases the surface area (light receiving area) of the silicon substrate 1 and the inversion layer 7 described later.
Is formed to guide to the back side of the silicon substrate 1. This through hole 1a is formed to have a diameter of about 50 μm. It is preferable that the through-hole 1a is formed to be inclined in order to efficiently take incident light into the silicon substrate 1.

On the light receiving surface side of the silicon substrate 1, a pyramid-shaped uneven portion 1b is formed by texture processing. The pyramid-shaped uneven portion 1b is formed to reduce the reflection loss of irradiation light on the surface of the silicon substrate 1. In addition,
Not only the pyramid-shaped uneven portion but also a large number of V-shaped grooves may be formed. When a V-shaped groove is formed on the surface of the silicon substrate 1, it is formed by a photolithography technique using a sodium hydroxide solution or the like.

In FIG. 1, reference numeral 3 denotes an electrode in an n ⁺ region, and reference numeral 4 denotes an electrode in a p ⁺ region.

FIG. 2 is a partial sectional view of the solar cell element according to the present invention.

In the silicon substrate 1, a through hole 1a is formed to be inclined.

In the vicinity of the through hole 1a on the back side of the silicon substrate 1,
An n ⁺ region 5 is selectively formed. This n ⁺ region 5 is
It contains a high concentration of impurities such as P.

In a portion other than the portion where the n ⁺ region 5 is formed on the back surface side of the silicon substrate 1, ap ⁺ region 6 serving as a BSF (back surface electric field) layer is formed at an appropriate distance from the n ⁺ region 5 portion. ing. The p ⁺ region 6 is configured to contain a high concentration of an aluminum element or the like.

On the light receiving surface side of the silicon substrate 1 and on the surface side in the through hole 1a, an inversion layer 7 containing ions such as Ce at a low concentration is provided.
Are formed so as to be connected to n ⁺ region 5 formed on the back surface side. The inversion layer 7 is formed to separate electrons and holes generated near the surface by an electric field formed in the inversion layer, and to guide electrons guided to the surface to the n ⁺ region 5.

A passivation film 2 made of a silicon oxide (SiO _x ) film or the like is formed on the surface of the silicon substrate 1 including the inside of the through hole 1a.
Is formed to a thickness of about 50 mm.

The light receiving surface side of this passivation film 2 and through hole 1a
Are a silicon nitride film (Si _x N _y ) film 8 having a refractive index n of about 2.4 containing ions such as Ce and magnesium fluoride (MgF ₂ ) having a refractive index n of about 1.4 not containing ions such as Ce.
A multilayer antireflection film made of a film 9 and the like is formed. The multilayer antireflection films 8 and 9 are formed to have a thickness of about 600 ° and 1000 °, respectively.

Further, an n ⁺ region 5 formed on the back side of the silicon substrate 1 is formed.
An electrode 3 made of Al or the like in contact with the n ⁺ region 5 in a point-like manner and an electrode 4 made of Al or the like in contact with the p ⁺ region 6 in a point-like manner are formed thereon. The n ⁺ region 5, the electrode 3, and the electrode 4 of the p ⁺ region 6 may be formed in a comb-tooth shape so as to merge at the opposing portions on the back surface side of the silicon substrate 1. The electrode 3 in the n ⁺ region 5 and the electrode 4 in the p ⁺ region 6 also serve as a BSR (backside antireflection layer).

The solar cell element as described above is formed by the following steps.

 First, the p-type silicon substrate 1 is cleaned with HCl or the like.

Next, a large number of through-holes 1a are formed to be inclined using a laser such as YAG narrowed to about 10 μm.

Next, in order to remove the damaged layer, the surface of the silicon substrate 1 is lightly etched using a mixed solution of hydrofluoric acid and nitric acid.

Next, a pyramid-shaped uneven portion 1b is formed on the light receiving surface side of the silicon substrate 1. The pyramid-shaped uneven portion 1b is formed by a texturing process using a sodium hydroxide solution.

Next, a passivation film 2 made of a silicon oxide film or the like is formed by a plasma CVD method, and a predetermined portion (a portion where an n ⁺ region and a p ⁺ region are formed) on the back surface is etched away.

Next, an n ⁺ region 5 and a p ⁺ region 6 are formed on the back side of the silicon substrate 1.
Are formed by ion implantation or thermal diffusion.

Next, a silicon nitride film 8 containing Ce ions or the like is formed on the light receiving surface side of the silicon substrate 1 and the passivation film 2 in the through hole 1a by a plasma CVD method or the like.

The inversion layer 7 is formed into an n layer by etching after forming an n ⁺ layer.

Next, electrodes 3 and 4 made of Al or the like are formed on n ⁺ region 5 and p ⁺ region 6 by screen printing or vapor deposition.

Finally, the magnesium fluoride film 9 of the silicon nitride film 8
Is formed by a plasma CVD method or the like to form a multilayer antireflection film, thereby completing the process.

(Effects of the Invention) As described above, in the solar cell element according to the present invention, a large number of inclined through holes are formed in the p-type silicon substrate having the concave and convex portions on the light receiving surface side, and the through holes on the back side of the silicon substrate are formed. An n ⁺ region is formed in the vicinity of the hole, an inversion layer is formed from the light-receiving surface side of the silicon substrate to the n ⁺ region via the through-hole portion, and reflected on the light-receiving surface side of the silicon substrate and in the through-hole. forming a barrier layer, a p ⁺ region is formed in a portion other than the portion n ⁺ regions are formed in the silicon substrate backside, and the n ⁺ region
Since the electrode is formed on the p ⁺ region and there is no electrode on the light receiving surface, the shadowing loss becomes zero and the recombination loss of carriers near the electrode is eliminated.

Further, since there is no n ⁺ layer on the light receiving surface side of the silicon substrate, recombination loss of carriers due to n ⁺ is eliminated.

Further, the presence of the inversion layer (n layer) enables effective current collection.

As described above, the voltage / current characteristics are improved as compared with the conventional configuration.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an embodiment of a solar cell element according to the present invention, FIG. 2 is a sectional view of FIG. 2 similarly, FIG. 3 is a view showing a conventional solar cell element, and FIG. FIG. 5 is a view showing another conventional solar cell element, and FIG. 5 is a view showing another conventional solar cell element. 1: p-type silicon substrate 1a: through-hole 1b: uneven portion, 2: antireflection film 3: electrode in n ⁺ region 4: electrode in p ⁺ region 5: n ⁺ region 6: p ⁺ region 8, 9: antireflection film

Claims (1)

(57) [Claims] 1. A semiconductor device comprising ^{: a} plurality of inclined through holes formed in a p-type silicon substrate having an uneven portion on a light receiving surface side; and an n ⁺ region formed near a through hole on a back surface side of the silicon substrate. Forming an inversion layer continuous from the light receiving surface side of the silicon substrate to the n ⁺ region via the through hole portion, forming an antireflection film on the light receiving surface side of the silicon substrate and in the through hole, and forming the n ⁺ region and p ⁺ region formed in a portion other than the formed portion, the solar cell element obtained by forming an electrode on the n ⁺ region and p ⁺ region.