JP3331268B2 - Solar cell element and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solar cell element, and more particularly to a structure of a solar cell element constituting a solar cell module and a method of manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, as a power generation element used for photovoltaic power generation, a solar cell element having a pn junction on a silicon substrate has been generally used. The structure of the most commonly used solar cell element is as shown in FIG. 5, and a pn junction is formed by providing an n-type diffusion layer near the sunlight receiving surface of a p-type silicon substrate. I have.

[0005] The structure shown in FIG. 5 shows the most basic principle. An n ⁺ layer 101 is laminated on a p-type silicon substrate 100, a surface grid electrode 102 is formed on the upper surface, and a back electrode 103 is formed on the lower surface. Is provided. An antireflection film 104 is provided on the upper surface of the grid electrode 102.

In such a structure, light 105 incident from the light receiving surface enters the inside of the silicon substrate 100 and is absorbed in the substrate. At this time, light having energy larger than the band gap of silicon is applied to the silicon substrate 10.
An electron-hole pair is generated in the photovoltaic element and the current is taken out as an electric current 106 through an electrode provided in the solar cell element.

Since this solar cell element is manufactured using a silicon substrate as described above, the size of only one element is limited, and the required power cannot be compensated. Generally, for example, as shown in FIG. As described above, the solar cell module is used as a solar cell module in which a plurality of elements 107 are connected in series and parallel by a connection line 108.

[0006]

The solar cell module as shown in FIG. 6 has the following problems. That is, this is a case where a part of the solar cell module is covered with the light shielding material 109.

Hereinafter, description will be made with reference to FIG. Now, assume that the both ends of the module are short-circuited to simplify the problem. The output of the solar cell element covered with the shade 109 decreases with the size of the shadow, and when completely covered by the shadow,
The output of this element alone is almost zero. At this time, this solar cell element 107 ′ can be considered as a load on a module in which other solar cell elements 107 are connected in series. Here, the solar cell element 107 that is generating power is represented as a parallel output of the current source 110 and the diode 111, and the solar cell element 107 ′ that is shaded and does not generate power is represented as only the diode. In this state, the voltage and current that are shaded and applied to the solar cell element are determined as follows.

The output voltage-current characteristics of the solar cell module excluding the solar cell element covered by the shadow are shown by A in FIG. On the other hand, the solar cell element covered by the shadow operates as a simple diode, and its characteristics are shown by B in FIG. As shown in FIG. 7, a constant current flows through the circuit, and the terminal voltage of the module generating power is equal to the applied voltage of the shaded cell. Therefore, the curve B shown in FIG. The intersection P of the curves C and A gives the operating point of the module, i.e. the applied voltage and current of the shaded solar cell element. Here, the solar cell element 107 ′ covered with a shadow
, A reverse voltage is applied and a reverse current flows, and the product (I
_OP × V _OP ) is consumed as electric power. This power consumption is specifically converted to heat, and raises the element temperature.

When the generated heat is large, the device temperature continues to rise, and there is a possibility that the device will eventually be destroyed by heat.
Whether an element is actually destroyed depends on the number of series-parallel modules, ambient temperature, load condition, shadow generation mode, etc., but as described above, only series connection, short-circuit load, and only one element Shaded situations are the most problematic. At this time,
Whether a shadowed element is destroyed depends on the reverse characteristics of the element.

[0010] When a part of the solar cell element is shaded, it is considered as shown in FIG. in this case,
Since the remaining part of the solar cell element, in which a part has been shaded, generates power, its characteristic is that the curves B and C in FIG. 8A are translated along the current axis in accordance with the generated current. 8 (b) are shown as curves B 'and C'. The module operating point in this case is determined in the same manner as in FIG. 8A, and is the intersection P 'of the curve A and the curve C' in FIG. 8B. At this time, the power consumption of the solar cell element covered by the shadow is significantly larger than that of FIG. 8A due to the addition of the photovoltaic current, and the possibility of destruction of the element increases.

By the way, among the conventional solar cell elements,
Silicon solar cells used for artificial satellites have relatively good reverse characteristics and low reverse current,
When a part of the device is covered with a shadow, a high reverse bias voltage is applied and a photovoltaic current flows, so that the amount of heat generated is large, and there is a high possibility of thermal destruction.

On the other hand, a solar cell element used for terrestrial use has a larger reverse current than a solar cell element for an artificial satellite. However, since a current does not flow enough to alleviate the reverse bias voltage, a reverse bias is applied. In this case, since both the voltage and the current increase, the power consumption increases and a large amount of heat is generated.

Therefore, conventionally, when a reverse voltage is applied, a bypass diode for flowing a current in the reverse direction is often provided. However, when a bypass diode is provided, the manufacturing process and the element structure are much more complicated than a normal solar cell element, or when a bypass diode is incorporated in a semiconductor substrate, the photoelectric conversion unit is formed by the bypass diode. There is a problem that the output power is reduced due to a decrease in the power consumption.

Therefore, an object of the present invention is to provide a case where a part of a solar cell module is covered with a shadow, a reverse current flows as in the case where a bypass diode is provided, and element breakdown can be prevented. SUMMARY OF THE INVENTION An object of the present invention is to provide a highly reliable solar cell device which has solved the above-mentioned drawbacks, that is, a large number of manufacturing steps, a complicated device structure, a reduction in output power, and the like, and a method for manufacturing the same.

[0015]

In order to achieve the above object, a solar cell element according to the present invention has a pn junction formed near the surface of a semiconductor substrate, and a comb-shaped electrode and the comb-shaped electrode formed on the surface of the semiconductor substrate. A wide current collecting electrode commonly connected to the electrodes is formed, and only under the current collecting electrode , a junction surface of the pn junction is formed to be a V-shaped groove toward the back surface of the semiconductor substrate, In the V-shaped groove forming portion, when a reverse bias voltage is applied, junction breakdown occurs at a lower voltage than other portions.

A solar cell element having a pn junction formed near the surface of a semiconductor substrate, and a comb-shaped electrode and a wide current collecting electrode commonly connected to the comb-shaped electrode formed on the surface of the semiconductor substrate. in, only under the collector electrode, only at least a portion of the joint surface of the pn junction, characterized by comprising formed so as to be V-shaped groove toward the back surface of the semiconductor substrate.

Further, the method for manufacturing the solar cell element includes a step of covering the surface of the semiconductor substrate other than a region where the V-shaped groove is to be formed with a protective film, and a step of covering the region where the V-shaped groove is to be formed. Forming a V-shaped groove by performing anisotropic etching; and forming a pn junction on the semiconductor substrate including the V-shaped groove.

Here, the plane orientation of the surface of the semiconductor substrate before the etching is (100) plane, and the axial directions of the long side and the short side of the region where the V-shaped groove is to be formed are <100>. And

Further, as another manufacturing method, a step of forming a V-shaped cut groove by a dicing blade in a region where a V-shaped groove is to be formed in the surface of the semiconductor substrate; Forming a pn junction on the formed semiconductor substrate.

[0020]

As described above, since the solar cell element of the present invention has a V-shaped groove formed in the substrate, when a reverse bias is externally applied to the solar cell element, the solar cell element will When a part of a solar cell module in which a plurality of battery elements are connected is covered with a shadow, an electric field concentrates on a pn junction formed along a V-shaped groove of the solar cell element alone, and a V-shaped part is formed. Since the distance between the front and back double-sided electrodes at the location where the groove is formed is shorter than at other locations, junction breakdown is likely to occur. Therefore, a reverse current flows at a voltage lower than that of the conventional solar cell element.

In other words, the solar cell element according to the present invention can flow the same amount of reverse current at a lower reverse bias voltage than the conventional one, so that the power consumption due to the reverse bias, that is, the heat generation is reduced, and the destruction of the element due to heat is reduced. Can be avoided.

The solar cell element according to the present invention has a structure in which only a V-groove is formed in a part of a pn junction surface formed on a semiconductor substrate. Can be simplified.

In particular, in a solar cell element in which a comb-shaped electrode and a wide current collecting electrode commonly connected to the comb-shaped electrode are formed on the surface of a semiconductor substrate, a V-shaped groove is formed under the current collecting electrode. Since it is formed, a portion which is not originally a photoelectric conversion portion is used, so that the area of the photoelectric conversion portion is not reduced at all even in comparison with a structure having no V-shaped groove.

Further, as a method for manufacturing this solar cell element, the surface of the semiconductor substrate other than the region where the V-shaped groove is to be formed is covered with a protective film, and then the V-shaped groove is to be formed anisotropically. Since the V-shaped groove can be formed only by performing the reactive etching, the manufacturing method is extremely simple. According to this manufacturing method, the angle of the V-shaped groove is 70.
5 °. At this time, by setting the plane orientation of the surface of the semiconductor substrate before the etching to the (100) plane, the etching is easily performed, and the (111) plane which becomes the slope of the V-shaped groove appears. In addition, by setting the axial direction of the long side and the short side of the V-shaped groove forming region to <100>,
For example, a straight V-shaped groove can be formed below the wide electrode in a direction along the electrode.

In addition to the above-described manufacturing method, when forming a V-shaped groove having a further acute angle, the V-shaped groove may be formed in the semiconductor substrate by a dicing blade. If a dicing blade is used, a V-shaped groove having a minimum angle of 45 ° can be obtained.

In the above-described method of manufacturing a solar cell element, it is not necessary to add a new process from the conventional process, and therefore, a highly reliable solar cell element can be provided without increasing the cost.

[0027]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A feature of the present invention is that, when light to a solar cell element is blocked and a reverse bias voltage is applied to the solar cell element, a portion where junction breakdown occurs at a lower voltage than other portions is provided in the element. As a result, the power consumption (generated heat) can be reduced by the amount corresponding to the reduction of the reverse bias voltage applied to the element, thereby preventing the element from being destroyed and improving the reliability.

The details will be described below with reference to the drawings. 1A and 1B are a cross-sectional view and a top view, respectively, of a solar cell device according to an embodiment of the present invention.

As shown in FIG. 1, an n-type diffusion layer 2 is laminated on a p-type silicon substrate 1, and a pn junction layer 3 is formed. Then, on the n-type diffusion layer 2, an n-type electrode 6 including a comb-shaped electrode portion 4 and a wide current collecting electrode 5 commonly connected to the comb-shaped electrode portion 4, and a p-type silicon substrate 1. A p-type electrode 7 is formed on the back side of the.

The current collecting electrode 5 of the pn junction layer 3
Is formed so as to be a V-shaped groove 8 directed toward the back surface of the p-type silicon substrate.

In this embodiment, as described above, since the V-shaped groove 8 is provided, light to the solar cell element is blocked, and when a reverse bias is applied to the light-shielded portion, the following operation is performed. Do.

That is, when a reverse bias is applied, an electric field is concentrated on the pn junction 3 formed along the V-shaped groove 8, particularly at the tip, and the n-type current collecting electrode 5 and the p-type electrode 7 Since the distance between them is shorter than that of the other portions, junction breakdown is likely to occur at this portion. Therefore, a current flows in a reverse direction at a voltage much lower than the reverse bias voltage applied without the structure of the present embodiment. As a result, heat generation due to the reverse bias voltage is reduced, and element destruction due to heat can be avoided.

By the way, if it is a conventional solar cell element,
Although the above operation was performed by providing a bypass diode, for example, when a bypass diode externally connected to the solar cell element is provided, the entire structure becomes very complicated, and the shape is also increased. There was a problem of being larger.

Further, when the bypass diode is incorporated in the semiconductor substrate, there is a problem that the forward characteristic is deteriorated because the photoelectric conversion unit is reduced by the bypass diode.

In this respect, according to the solar cell element of the present embodiment, since the V-shaped groove 8 is formed only in a part of the pn junction surface 3 formed in the p-type silicon substrate 1, Can be greatly simplified. Moreover, since the V-shaped groove 8 is formed under the current collecting electrode 5 at a position which is not originally a photoelectric conversion portion, the area of the photoelectric conversion portion is reduced even in comparison with a structure without the V-shaped groove. Nothing.

In this embodiment, the V-shaped groove 8 is provided below the current collecting electrode 5. However, as another embodiment, the V-shaped groove 8 may be provided at a place other than below the electrode. However, when provided at a location other than under the electrode, if provided over substantially the entire light receiving surface, such as a textured cell, the absorption of infrared light increases. The output is expected to decrease due to the rise. Also,
When formed in a part of a limited area of the light receiving surface, a voltage drop occurs due to a series resistance component according to a distance from the current collecting electrode, and thus an applied voltage required for junction breakdown increases. Therefore, it is desirable to provide it below the electrode as in the embodiment of FIG.

FIG. 2 is a diagram comparing characteristics between the embodiment of FIG. 1 and the solar cell element without the V-shaped groove 8 of FIG. The horizontal axis represents reverse voltage (reverse bias), and the vertical axis represents reverse current. In the drawing, a curve D represents the present embodiment, and a curve E represents the case where no V-shaped groove is formed. As is clear from FIG. 2, by providing the V-shaped groove 8 as in the present embodiment, the reverse current starts to flow rapidly when the reverse voltage is about 2 V or more. In other words, the current flows in the reverse direction at the stage where the reverse voltage is not applied so much that the reverse voltage is not applied any more. That is, the heat generated by the reverse voltage can be suppressed low, and the device can be prevented from being destroyed.

FIGS. 3A to 3C are views showing a method of manufacturing the solar cell of FIG. As shown in FIG. 3A, the method for manufacturing a solar cell element according to this embodiment
After the surface of the mold silicon substrate 1 is covered with a protective film having an etching resistance, for example, a silicon oxide film 9, the silicon oxide film 2 at the edge of the substrate is removed by photoetching to provide a rectangular exposed portion 10. . The size of the exposed portion 10 is, for example, about 40 to 50 μm (width) × about 40 mm (length).

Here, by setting the plane orientation of the surface of the silicon substrate 1 to the (100) plane, etching described later is easily performed, and the (111) plane which becomes the slope of the V-shaped groove 8 appears. . In addition, by setting the axial direction of the long side and the short side of the V-shaped groove forming region to be <100>, for example, the V-shaped groove may be straight under the wide current collecting electrode 5 in the direction along the electrode. 8 can be formed.

Next, the exposed portion 10 is subjected to anisotropic etching using a low-concentration solution of KOH or NaOH, as shown in FIG. A (111) plane, which is a slope, appears, and a V-shaped groove 8 is formed. The angle formed by the bottom of the V-shaped groove 8 is determined by the crystal structure.
5 degrees. The width of the exposed portion 10 is about 4 as described above.
When the thickness is 0 to 50 μm, the depth of the V groove is about 30 to 35 μm.

Next, on the light receiving surface side of the p-type silicon substrate 1,
An impurity imparting a conductivity type opposite to that of the silicon substrate 1 is diffused, and an n-type diffusion layer 2 is formed to form a pn junction surface 3. Next, as an electrode for extracting a photocurrent from the solar cell element, an n-type surface electrode 6 composed of a comb-shaped electrode 4 and a current collecting electrode 5 connected to the comb-shaped electrode 4 is provided on the front surface side, and a back surface. A p-type back electrode 7 is formed on each side. Here, the wide current collecting electrode 5 is formed on the upper surface of the V-shaped groove 8. As described above, the solar cell element of this example is obtained.

A diffusion layer for providing a back surface field effect may be provided on the back surface of the substrate, and an antireflection film may be provided on the front surface. In addition, a layer that provides the other conductivity type of the substrate is formed on part of the back surface of the silicon substrate, and electrodes of both one conductivity type and the other conductivity type are provided on the back surface, and no electrode exists on the front surface. It may have a structure.

According to the above manufacturing method, the V-shaped groove can be formed only by performing anisotropic etching on the region where the V-shaped groove is to be formed, so that the manufacturing method is extremely simple. Moreover, the method for manufacturing the solar cell element is different from the conventional process,
Since there is no need to add a new device, a highly reliable solar cell element can be provided without increasing the cost. Separately from the above-described manufacturing method, when an acute V-shaped groove is formed, a V-shaped groove is formed on the semiconductor substrate by a dicing blade.
A method of forming a groove can be adopted. Hereinafter, description will be made with reference to the drawings.

FIGS. 4 (a) to 4 (c) are manufacturing process diagrams of a solar cell device according to another embodiment of the present invention. The same functional portions as those in FIG. 3 are denoted by the same reference numerals. First, FIG.
As shown in FIG. 4A, a dicing blade 11 having an acute end face is prepared, and the dicing blade 11 forms a cut in the surface of the silicon substrate as shown in FIG. 4B. The angle of the cut groove in this case is
As a matter of course, the angle substantially matches the end face angle of the dicing blade 11. With the current dicing blade 11, an angle up to about 45 degrees can be obtained.

The following steps are the same as in FIG. 2 and will not be described.

In this embodiment, the structure obtained is the same as that of the embodiment shown in FIG. 1, so that the same effect can be obtained.

[0047]

As described above, according to the solar cell element of the present invention, a plurality of solar cell modules are connected to each other and used as a solar cell module, and even if a part of the solar cell module is shielded from light, the solar cell module can be used. The reverse bias voltage in the part is lower than before, so the power consumption is lower, the calorific value is also lower,
A situation such as breakage of the element can be avoided.

Further, the solar cell element having this structure does not require any special device or the like, and can be realized by adding only a few steps to the conventional process, so that the solar cell element is very practical.

[Brief description of the drawings]

FIGS. 1A and 1B are a cross-sectional view and a top view, respectively, of a solar cell device according to an embodiment of the present invention.

FIG. 2 is a characteristic comparison diagram of the embodiment of FIG. 1 and an example without a V-shaped groove of FIG. 1;

FIGS. 3A to 3C are manufacturing process diagrams of the solar cell of FIG.

4 (a) to 4 (c) are views showing a manufacturing process of a solar cell according to another embodiment of the present invention.

FIG. 5 is a perspective view of a conventional solar cell element.

FIG. 6 is a side view of a conventional solar cell module.

FIG. 7 is a diagram for explaining a problem of a conventional solar cell module.

FIGS. 8 (a) and (b) are drawings for explaining a problem of a conventional solar cell element.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Semiconductor substrate 3 pn junction surface 4 Comb-shaped electrode 5 Current collecting electrode 8 V-shaped groove 9 Protective film 10 V-shaped groove planned area (exposed part)

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-3-79086 (JP, A) JP-A-3-71677 (JP, A) JP-A-5-243592 (JP, A) JP-A-5-243592 136444 (JP, A) JP-A-56-2625 (JP, A) JP-A-56-148876 (JP, A) JP-A-3-34583 (JP, A) Japanese Utility Model Publication No. 57-125551 (JP, U) (58) Field surveyed (Int. Cl. ⁷ , DB name) H01L 31/04-31/078

Claims (5)

(57) [Claims] 1. A solar cell element comprising: a pn junction formed near a surface of a semiconductor substrate; and a comb-shaped electrode and a wide current collecting electrode commonly connected to the comb-shaped electrode formed on the surface of the semiconductor substrate. In the above , the junction surface of the pn junction is formed so as to form a V-shaped groove toward the back surface of the semiconductor substrate only under the current collecting electrode. In the V-shaped groove forming portion, a reverse bias voltage is reduced. A solar cell element characterized in that when it is applied, junction breakdown occurs at a lower voltage than other parts. 2. A solar cell element comprising: a pn junction formed near a surface of a semiconductor substrate; and a comb-shaped electrode and a wide current collecting electrode commonly connected to the comb-shaped electrode formed on the surface of the semiconductor substrate. in, only under the collector electrode, only at least a portion of the joint surface of the pn junction, the solar cell element characterized by comprising formed so as to be V-shaped groove toward the back surface of the semiconductor substrate . 3. The method for manufacturing a solar cell element according to claim 1, wherein a step of covering a surface of the semiconductor substrate other than a region where a V-shaped groove is to be formed with a protective film. Forming a V-shaped groove by performing anisotropic etching on a region where the V-shaped groove is to be formed, and forming a pn junction on the semiconductor substrate including the V-shaped groove. And a method for manufacturing a solar cell element. 4. The method for manufacturing a solar cell element according to claim 3, wherein the plane orientation of the surface of the semiconductor substrate before the etching is a (100) plane, the long side of the region where the V-shaped groove is to be formed, and A method for manufacturing a solar cell element, wherein the axial direction of the short side is <100>. 5. The method for manufacturing a solar cell device according to claim 1, wherein a region where a V-shaped groove is to be formed in the surface of the semiconductor substrate is formed in a V-shape with a dicing blade. A method for manufacturing a solar cell element, comprising: a step of forming a cut groove; and a step of forming a pn junction on a semiconductor substrate on which the V-shaped cut groove is formed.