JPH1093117A - Photoelectric conversion device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain high photoelectric conversion factor by forming a side surface of a collecting electrode of a photoelectric conversion device with a stripe-like collecting electrode at a photosensitive surface of a photoelectric conversion device as a tilting surface which reflects incident light toward a photosensitive surface. SOLUTION: Side surfaces 22a and 22b of a collecting electrode 22 are formed as tilting surface, which reflected incident light toward a photosensitive surface, and a cross sectional contour of the collecting electrode 22 inside a plane at right angles to a stripe direction is made into a trapezoid. A part of incident light is incident on the tilting surfaces 22a, 22b of the trapezoid collecting electrode 22 and reflected by the tilting surfaces 22a, 22b, and proceeds straight toward a photosensitive surface 15c; and reflection light is injected into a photosensitive surface 15c. A part of incident light is incident on the photosensitive surface 15c of a substrate 15 directly, without passing through the collecting electrode 22. Since a high light intensity region 15b, wherein reflection incident light and direct incident light overlap each other is formed in the substrate 15 near a bottom part of the tilting surfaces 22a, 22b of the collecting electrode 22, a high photoelectric conversion factor can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photoelectric conversion device.

[0002]

2. Description of the Related Art As a photoelectric conversion device, for example, Document I (P.
physics of Semiconductor D
devices-2nd Edition 1981, p.
800).
The structure and operation of a conventional solar cell element will be described with reference to FIGS. FIG. 2A is a plan view of the solar cell element, and FIG. 2B is an XX of FIG.
3 shows a cut section at a position cut along the line.

The solar cell element 10 includes a semiconductor substrate 15 having p-type and n-type silicon regions (11 and 12), and a collecting electrode (upper part) for collecting carriers provided on the upper surface of the semiconductor substrate 15, that is, on the light receiving surface 15c. (Electrode) 16, an antireflection film 18, and a back surface electrode 20 provided on the back surface of the substrate 15. A pn junction 14 for generating photovoltaic power is provided in the substrate 15.

Next, the operation principle of the solar cell element 10 will be described below. When light is incident on the light receiving surface (here, the surface of the antireflection film 18) of the solar cell element 10, photocarriers are generated inside the semiconductor substrate 15. Due to the photocarriers, electrons and holes move from the n-type silicon region 12 to the p-type silicon region 11 and a current flows inside the substrate 15. For this reason, the electrons and hole pairs generated by the light drift right and left with respect to each other due to the interface electric field of the pn junction, and the carriers are collected at the upper and lower electrodes to generate photovoltaic power.

[0005]

However, the conventional solar cell element 10 has the following problems. In the conventional solar cell element 10, the shape of the collecting electrode is comb-shaped in order to efficiently collect the photocarriers generated inside the semiconductor substrate 15 on the light receiving surface (FIG. 2A). Moreover,
The cross-sectional shape of the conventional collecting electrode 16 is quadrangular. FIG. 2C is a partially omitted enlarged view showing a part of the cross-sectional shape of the collecting electrode of FIG. 2B in an enlarged manner.

When light is incident on the light-receiving surface of the conventional solar cell element 10 from above, the collecting electrode 16 does not transmit the incident light, so that the shadow region formed by the collecting electrode 16 in the substrate 15 is formed. That is, a shadow region (also referred to as a shadow forming region) 15a shielded by the collecting electrode is formed. Since the shade forming region 15a reduces the light receiving area of the solar cell element, the photoelectric conversion efficiency also decreases, which is not preferable.

[0007] The photoelectric conversion efficiency of the solar cell element 10 (the photoelectric conversion efficiency refers to a value representing the ratio of the input solar radiation energy to the electric output energy output from the terminals of the solar cell in percent). To increase, the collection electrode 16
The distance (L) between the comb teeth 16a of the
It is necessary to reduce the resistance value of the collecting electrode 16 by increasing the comb tooth width (W). However, when the comb tooth width (W) of the collecting electrode of the solar cell element 10 is increased, the light receiving area decreases,
Since the shadow area (shade forming area) 15a formed by the collecting electrode 16 increases, the photoelectric conversion efficiency decreases.

FIG. 5 is a diagram for explaining the relationship between the comb tooth width of the collecting electrode and the conversion loss. As can be understood from FIG. 5, when the comb tooth width W is increased, the cross-sectional area of the collecting electrode is increased, so that the resistance value of the electrode is reduced and the conversion loss is reduced (the solid line of the curve I in FIG. 5).

When the width W of the comb teeth is increased, the shade forming area 15a formed by the collecting electrode 16 increases, so that the conversion loss increases (the dotted line of the curve II in FIG. 5). Therefore, looking at the total (added value) of the resistance value of the collecting electrode and the shadow forming region, as shown by the curve III in FIG. 5, when the comb tooth width is increased, the conversion loss is once affected by the resistance value. However, the conversion loss gradually increases thereafter.

For this reason, conventionally, as a measure for minimizing the conversion loss, the resistance value is reduced by increasing the film thickness of the collecting electrode 16 and increasing the cross-sectional area of the electrode. A method of reducing the comb tooth width W to increase the light receiving area has been adopted.

However, the method of minimizing the comb tooth width W of the collecting electrode 16 or increasing the thickness of the collecting electrode 16 is as follows.
There is naturally a limit, and a solar cell element with sufficiently high photoelectric conversion efficiency could not be obtained conventionally.

Therefore, it has been desired to realize a photoelectric conversion device capable of obtaining high photoelectric conversion efficiency without reducing the light receiving area.

[0013]

Therefore, according to the photoelectric conversion device of the present invention, in a photoelectric conversion device having a stripe-shaped collection electrode on a light receiving surface of the photoelectric conversion device, the side face of the collection electrode is It is characterized in that it is formed as an inclined surface that reflects incident light toward the light receiving surface.

In the present invention, since the inclined surface for reflecting the incident light is formed on the side surface of the collecting electrode, the light incident on the inclined surface from above the light receiving surface is reflected and reflected by the inclined surface. The transmitted light passes through the light receiving surface at a predetermined angle.
Therefore, on the light receiving surface of the photoelectric conversion device, a high light intensity area is formed by overlapping the reflected incident light reflected from the inclined surface and the direct incident light directly incident on the light receiving surface. Therefore, an increase in the light intensity reflected from the inclined surface and incident on the light receiving surface increases the light intensity on the light receiving surface as compared with the related art, so that a photoelectric conversion device employing a conventional collecting electrode having no inclined surface can be used. Compared with this, the photoelectric conversion efficiency increases.

In the present invention, preferably, the cross-sectional shape of the collecting electrode in a plane perpendicular to the stripe direction is trapezoidal or triangular.

As described above, by making the cross-sectional shape of the collecting electrode trapezoidal or triangular, the side surface of the collecting electrode can be an inclined surface, so that the incident light incident on the inclined surface is reflected and received. A high light intensity region can be formed by transmitting through the surface.

In the present invention, the inclination angle between the normal to the light receiving surface of the photoelectric conversion device and the inclined surface is preferably 5 to 5.
Preferably, the angle range is 35 degrees.

By setting the inclination angle to 5 to 35 degrees, the incident light incident on the inclined surface can be efficiently reflected toward the light receiving surface. For this reason, there is an effect of ensuring a shadow forming region formed on the light receiving surface of the photoelectric conversion device by the collecting electrode.

In the present invention, it is preferable that the shape of the collecting electrode is comb-shaped. By making the shape of the comb-shaped collecting electrode, the spacing between the comb teeth can be reduced and the carrier generated in the photoelectric conversion device can be efficiently collected by the collecting electrode.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawings, an embodiment of a photoelectric conversion device of the present invention, in particular, a solar cell element will be described below. FIGS. 1, 2 and 4 merely show the shapes, sizes and arrangements of the components so that the present invention can be understood.

Since the solar cell element 10 of the present invention has the same structure as the above-described conventional structure except for the structure of the collecting electrode, the structure of the present invention will be described in detail focusing on the collecting electrode. .

[First Embodiment] A first embodiment of the collecting electrode of the present invention will be described with reference to FIG. FIG. 1A shows a cross-sectional view of a position cut along a plane orthogonal to the direction of the comb teeth of the collecting electrode formed on the light receiving surface of the solar cell element.

In the present invention, the side surface 22a of the collecting electrode 22
And 22b are formed as inclined surfaces for reflecting the incident light toward the light receiving surface. In the first embodiment, the cross-sectional shape of the collector electrode 22 in a plane perpendicular to the stripe direction is a trapezoid (FIG. 1A). Here, a trapezoidal collector electrode having a trapezoidal cross section is referred to as a trapezoidal collector electrode 22.

Next, with reference to FIG. 1A, the behavior of light when the light receiving surface of the solar cell element is irradiated with incident light will be described.

When light is incident from above the light receiving surface of a solar cell having a trapezoidal collecting electrode 22, the substrate 15 below the collecting electrode 22 has a shadow forming region 15a formed by the collecting electrode 22 as in the prior art. It is formed.

A part of the incident light is incident on the inclined surfaces 22a and 22b of the trapezoidal collecting electrode 22, and the inclined surface 22a
a and 22b, and go straight toward the light receiving surface 15c. Thereafter, the reflected light enters the light receiving surface 15c.
Here, the light receiving surface 1 is reflected by the inclined surfaces 22a and 22b.
The incident light that has entered the inside 5c is referred to as reflected incident light.

On the other hand, a part of the incident light that has entered the structure shown in FIG. 1A directly enters the light receiving surface 15 c of the substrate 15 without passing through the trapezoidal collecting electrode 22. Here, the light receiving surface 1
The incident light directly incident on 5c is referred to as direct incident light. For this reason, a high light intensity region 15b in which the reflected incident light and the direct incident light overlap each other is formed in the substrate 15 near the skirts of the inclined surfaces 22a and 22b of the collecting electrodes (FIG. 1A). .

Next, with reference to FIGS. 3A and 3B, a description will be given of the dependency of the reflection coefficient of the optical power when light is incident on a flat surface and the angle of the incident light is changed. I do. FIG. 3A is a diagram in which the relationship between the incident angle and the reflection coefficient of optical power is calculated and plotted using a calculation formula. The horizontal axis represents the angle (degree) of the incident light, and the vertical axis represents the light. The power reflection coefficient (arbitrary constant) is shown. Also, (B) in FIG. 3, the electric field of the incident light is a diagram for the incident angle theta _i, electric field of refracted light, and the relationship between the refractive angle theta _t be described.

In the present invention, in order to create FIG. 3A, first, the light reflection coefficient is obtained from a calculation formula with reference to FIG. 3B.

[0030] As can be understood from FIG. 3 (B), a substrate of refractive index n ₂ (for example, GaAs substrate), when is incident at an angle theta _i field E _i of the incident light to the normal NN ' ,
Electric field E _i of the incident light is reflected on the surface of the GaAs substrate, divided into an electric field E _t transmitted light straight passes through the electric field E _r and the GaAs substrate of the reflected light.

At this time, the light reflection coefficient γ _E is expressed by equation (1).

Γ _E = E _r / E _i = (n ₁ cos θ _i −n ₂ cos θ _t ) / (n ₁ cos θ _i + n ₂ cos θ _t ) (1) where E _i is the electric field of the incident light. , _Er is the electric field of the reflected light, n
₁ is the refractive index of air (n ₁ = 1), n ₂ is the refractive index of the GaAs substrate, θ _i is the incident angle of incident light, and θ _t is the refraction angle of transmitted light.

In the equation (1), n ₁ (the refractive index of air is 1) and n ₂ (the refractive index of GaAs) are known, and if the incident angle θ _i is known, the refraction angle θ is obtained according to Snell's law of refraction. _t is found. N ₁ , n ₂ ,
By substituting cos θ _i and cos θ _t into the terms on the right side of equation (1), the light reflection coefficient γ _E is obtained.

Further, power is proportional to the square of the electric field, the reflection coefficient R _E of the optical power is expressed by equation (2).

R _E = γ _E ² (2) The reflection coefficient of the optical power when the incident angle θ _i is changed using the above equations (1) and (2) is calculated and plotted. It is (A) of FIG.

As can be understood from FIG. 3A, the reflection coefficient of the optical power is about 0.1 to 0.2 when the incident angle (θ _i ) is 0 to 70 degrees, but the incident angle (θ _{When i} ) exceeds 70 degrees, the reflection coefficient of the optical power sharply increases. Therefore, since an increase in the reflection coefficient causes conversion loss, the incident angle needs to be 70 degrees or less.

Next, the relationship between the trapezoidal collecting electrode 22 and the incident angle of light reflected on the inclined surface will be described with reference to FIG. FIG. 4 is a diagram for explaining the relationship between the inclination angle of the trapezoidal collecting electrode and the incident angle reflected on the inclined surface. Here, the side surfaces 22a and 22b of the trapezoidal collecting electrode 22, that is, the inclined surfaces are denoted by the symbol AB. Further, the angle between the inclined surface AB and the normal BH of the light receiving surface 15c is θ _g
And

When the incident light MO enters the inclined surface AB of the trapezoidal collecting electrode 22, it is reflected by the inclined surface AB and travels straight in the ON direction. At this time, the normal BH and the incident light M
Since O is parallel, ∠HBO and ∠MOA are equal.

Since the incident angle θ _i is equal to the reflection angle θ _r , ∠MOA and ∠BON are equal. Therefore,
If the intersection of the reflected light ON and the normal HB is S, then ∠HBO
The angle (2θ _g ) obtained by adding ∠BON is equal to ∠HSO.

If the normal on the light receiving surface where the reflected light ON is incident is H'N, then ∠H'NO is equal to ∠HSO.

As is clear from the above description, the inclination angle {the double angle of HBO (θ _g ) is the angle between the reflected light and the normal line}
It can be seen that H′NO (2θ _g ) is obtained.

As already described with reference to FIG. 3A, when the incident angle is set to 70 degrees or more, the reflection coefficient of the optical power increases. Therefore, the incident angle must be set to 70 degrees or less. Therefore, the inclination angle ∠HBO of the trapezoidal collecting electrode 22 is set to the incident angle ∠H ′ in order not to increase the reflection coefficient of the optical power.
It is necessary to make it within 1/2 of NO, that is, within 35 degrees.

If the inclination angle of the trapezoidal collecting electrode 22 is made close to 0 degrees, the effect of reflecting incident light is lost.
It is preferable that the inclination angle is 5 degrees or more. Therefore, in the first embodiment of the present invention, the inclination angle is 5 to 5.
The angle range is preferably 35 degrees.

As described above, in the first embodiment,
By making the collecting electrode a trapezoidal cross section and making the side surface of the collecting electrode an inclined surface, the incident light is reflected on the inclined surface, goes straight toward the light receiving surface, and is reflected incident light transmitted through the light receiving surface, and directly on the light receiving surface Is superimposed on the direct incident light incident on the
A high light intensity region 15b is formed near the collecting electrode 22 of FIG. For this reason, in the present invention, the light intensity on the light receiving surface of the solar cell element becomes larger than before, so that the shadow forming region formed on the substrate 15 by the collecting electrode is substantially guaranteed, and the conversion efficiency is improved.

[Second Embodiment] Next, FIG.
The second embodiment of the present invention will be described with reference to FIG. FIG. 1B shows a cross section when the cross-sectional shape of the comb-shaped collecting electrode is triangular.

When the cross-sectional shape of the collecting electrode 24 is triangular, a high light intensity region 15b similar to that of the trapezoidal cross-section is formed on the light receiving surface (FIG. 1B). For this reason, when light is vertically incident on the light-receiving surface of the solar cell element, the shadow-forming region 15a formed by the collecting electrode 24 is secured by the high-light-intensity region 15b. Has the effect of increasing the photoelectric conversion efficiency.

Further, according to the present invention, the triangular collector electrode 24 is used, so that the trapezoidal collector electrode 22 can be used.
Since the cross-sectional area of the collecting electrode 24 can be increased,
There is an advantage that the resistance value of the collecting electrode is reduced and the conversion loss can be reduced.

In the first and second embodiments described above,
Although an example using a solar cell element as a photoelectric conversion device has been described, a light-receiving element that converts light into an electric signal, such as a photodiode, an image sensor, a phototransistor, and a photoconductive cell, or a photoconductor element whose resistance value changes with light. It can also be applied as a collecting electrode.

[0049]

As is apparent from the above description, according to the photoelectric conversion device of the present invention, the side surface of the collecting electrode is formed as an inclined surface for reflecting the incident light toward the light receiving surface. An area (high light intensity area) where light reflected on the surface and incident on the light receiving surface (reflected incident light) and light directly incident on the light receiving surface (direct incident light) overlaps is formed on the light receiving surface. For this reason, the shadow-forming region formed by the collecting electrode is ensured, and the photoelectric conversion efficiency can be increased as compared with the related art. In addition, when the photoelectric conversion device is a solar cell element, higher electromotive force can be expected as compared with the related art.

[Brief description of the drawings]

FIGS. 1A and 1B are cross-sectional views for explaining the cross-sectional shapes of trapezoidal and triangular collector electrodes of the present invention.

2A is a plan view for explaining the structure of a conventional solar cell element, FIG. 2B is a cross-sectional view taken along line XX of FIG. 2A, and FIG. () Is an enlarged view showing a part of the collecting electrode portion of (B) in an enlarged manner.

3A is a diagram for explaining a relationship between an incident angle and a reflection coefficient of optical power, and FIG. 3B is a diagram illustrating various angles of an electric field of incident light, an electric field of reflected light, and an electric field of transmitted light. It is a figure for explaining the relation with.

FIG. 4 is a diagram for explaining a relationship between an incident angle and an inclination angle when incident light is incident on an inclined surface of a trapezoidal collecting electrode.

FIG. 5 is a diagram for explaining a relationship between a comb tooth width of a collecting electrode and a conversion loss.

[Explanation of symbols]

 15: Semiconductor substrate 15a: Shadow forming region 15b: High light intensity region 15c: Light receiving surface 22: Trapezoidal collecting electrode 24: Triangular collecting electrode 22a, 22b, 24a, 24b: Inclined surface

Claims (6)

[Claims] 1. A photoelectric conversion device comprising a collection electrode in the form of a stripe on a light-receiving surface of the photoelectric conversion device, wherein a side surface of the collection electrode is formed as an inclined surface for reflecting incident light toward the light-receiving surface. A photoelectric conversion device, comprising: 2. The photoelectric conversion device according to claim 1, wherein a cross-sectional shape of the collecting electrode in a plane orthogonal to a stripe direction is trapezoidal. 3. The photoelectric conversion device according to claim 1, wherein a cross-sectional shape of the collection electrode in a plane orthogonal to a stripe direction is triangular. 4. The photoelectric conversion device according to claim 1, wherein an inclination angle between a normal to the light receiving surface and the inclined surface is 5 degrees.
A photoelectric conversion device having an angle range of up to 35 degrees. 5. The photoelectric conversion device according to claim 1, wherein said collecting electrode has a comb-like shape. 6. The photoelectric conversion device according to claim 1, wherein the photoelectric conversion device is a solar cell element.