JP2000277763A - Solar cell and fabrication thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent conversion efficiency from lowering due to micro irregularities incident to the texture structure of a power generating layer by rounding the micro irregularities. SOLUTION: A transparent electrode film 1 is formed by thermal CVD on the surface of a glass substrate opposite to the light incident side and that surface is subjected to conventional texture processing based on etching with acid or alkaline solution to form pointed micro irregularities at first. After a p layer 4 is formed by doping a-Si with boron, a power generation layer 2 of a-SiGe is formed followed by formation of an n layer 5 by doping a-Si with phosphorus. The thin film of the p layer 4, the power generation layer 2 and the n layer 5 forms micro irregularities on the transparent electrode film 1. Consequently, the recessed A and the protrusions B on the power generation layer 2 have curved surfaces and the front ends thereof are rounded.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a solar cell having an amorphous or microcrystalline pin structure and a method for manufacturing the same.

[0002]

2. Description of the Related Art In a conventional solar cell of this type, in order to effectively use light in an i-type thin power generation layer of a semiconductor layer, the light incident side has a textured structure and is formed by minute irregularities of about the wavelength of light. It has been practiced to increase the amount of light absorption in the power generation layer by using light scattering.

Specifically, for example, in the case of a glass substrate type amorphous solar cell, a transparent electrode film such as SnO ₂ is formed on the surface of the glass substrate opposite to the light incident side, and the film is formed at the time of formation. An amorphous pin was formed on the film surface in the form of fine and sharp irregularities (pyramid shape) produced by adjusting the conditions.
A semiconductor layer having a structure is formed, and the i-type power generation layer is formed into a thin film having minute irregularities. Light is confined in the power generation layer by scattering of light in the thin film, and the amount of light absorbed in the power generation layer is increased. I have.

[0004]

In the above-mentioned conventional solar cell, the i-type power generation layer occupying the majority of the semiconductor layer is formed of a thin film having a sharply-pointed micro unevenness. As described, there is a problem that the conversion efficiency is rather lowered.

That is, in the case of the above-mentioned solar cell of the glass substrate type, the schematic structure of the junction between the transparent electrode film and the semiconductor layer is as shown in FIG.
1 'is a transparent electrode film of SnO _{2 and 2} ' is a power generation layer of a semiconductor layer having a pin structure.

[0006] When the transparent electrode film 1 'has a sharply-pointed minute unevenness as shown in FIG. 5, the power generation layer 2' of the semiconductor layer formed on this film surface also has a sharply minute unevenness. .

In FIG. 5, the upper side is the light incident side,
At the time of manufacture, the transparent electrode film 1 'and the semiconductor layer are sequentially laminated on a glass substrate, are formed in a state where the top and bottom of FIG. 5 are inverted, and the "mountains" protruding above the power generation layer 2' in FIG. A part is a concave part A 'having a minute concave-convex shape, and a "valley" concaved downward.
Is a convex portion B '.

In the concave portion A ', a defect is easily generated at the steeply concave end portion, and the steeply protruding end portion of the convex portion B' is thin, so that a leak easily occurs.
The conversion efficiency in is reduced.

Further, the electric field concentrates on the tip portions of the concave portion A 'and the convex portion B', and the electric field intensity in other portions of the power generation layer 2 'is weakened. From this point, the conversion efficiency in the power generation layer 2' is also reduced. descend.
A similar problem occurs in the case of a microcrystalline solar cell.

An object of the present invention is to prevent the above-mentioned decrease in the conversion efficiency due to the film shape of the power generation layer of this type of solar cell, and to improve the conversion efficiency of this type of amorphous or microcrystal. It is an object to provide a solar cell and a method for manufacturing the same.

[0011]

In order to solve the above-mentioned problems, a solar cell according to the present invention is characterized in that the minute irregularities of the power generation layer are curved and round.

Then, as shown in the schematic configuration diagram of the solar cell of the present invention in FIG. 1 corresponding to FIG.
If the concave portion A of the upper power generation layer 2 has a curved surface, a defect is less likely to occur at the tip portion.

Further, if the convex portion B of the power generation layer 2 has a curved surface, the film thickness at the tip end portion is uniform and not thin, so that leakage hardly occurs.

Further, when the concave portions A and the convex portions B have curved surfaces, the electric field concentration at the tip portions thereof is reduced, and the power generation layer 2 is formed.
The electric field strength of other parts does not weaken.

Accordingly, if the unevenness of the power generation layer has a round shape with a curved surface shape, a decrease in conversion efficiency due to the film shape is prevented, and the conversion efficiency is improved as compared with the related art.

The average height of the minute unevenness of the power generation layer is 1
It is preferable that the radius of curvature of the fine irregularities of the curved surface of the power generation layer is 20% or more and 50% or less of its average height.

Next, the method for manufacturing a solar cell according to the present invention comprises:
The transparent electrode film or the metal film is subjected to at least one of a chemical etching process of dipping in an acid or alkali solution and a plasma process of exposing it to the plasma to expose the micro-rough surface of the transparent electrode film or the metal film. Then, the semiconductor layer was formed on the transparent electrode film or the back electrode and the semiconductor layer were formed on the metal film, and the i-type power generation layer of the semiconductor layer was rounded in a curved shape. It is formed on a thin film with minute irregularities.

Therefore, the power generation layer is formed so as to have minute irregularities, and the irregularities are curved and rounded,
A reduction in conversion efficiency due to the thin film shape of the power generation layer due to the texture structuring is prevented, and an amorphous or microcrystalline glass substrate type or metal substrate type solar cell with improved conversion efficiency can be manufactured.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIGS. (1) One embodiment of the present invention applied to a glass substrate type amorphous solar cell and a method for manufacturing the same will be described with reference to FIGS. FIG. 2 shows the configuration of the main part of the solar cell with the light incident side facing upward, and is formed with the upside down of FIG.

In the figure, reference numeral 1 denotes a transparent electrode film of SnO ₂ having a film thickness of 8000 ° formed on a glass substrate, and 3 denotes an amorphous silicon (a-Si) having a pin structure formed on the transparent electrode film 1. A semiconductor layer having a thickness of 100
Type a-SiC p-layer 4, a-SiGe with a thickness of 3000 °
And an n-type a-Si n-layer 5 having a thickness of 2000 °.

Reference numeral 6 denotes a film thickness 400 formed on the semiconductor layer 3.
It is a back electrode film of 0 ° and has a two-layer structure of ZnO / Ag.

The solar cell shown in FIG. 2 has a concave portion A shown in FIG.
5A, a convex portion B corresponding to the convex portion B 'in FIG.
Are all curved and rounded.

Next, a method of manufacturing the solar cell of FIG. 2 will be described. First, the transparent electrode film 1 is formed on the surface of the glass substrate opposite to the surface on the light incident side by a thermal CVD method, and the surface (the back surface as viewed from the light incident side) is etched with an acid or alkali solution. The same texture processing as in the prior art is performed, and the surface is first formed into a steep fine irregular shape having an average height of about 2000 ° with a sharp tip.

Next, on the film surface of the transparent electrode film 1 having the steep fine irregularities, a hydrochloric acid treatment is performed by immersing the film surface in a hydrochloric acid solution for about 0.5 to 5 minutes so that the tip of the convex portion B is mainly curved. A chemical etching process) and a plasma process of exposing the concave portion A to a curved surface mainly by exposing it to argon plasma for about 1 to 10 minutes are performed in the order of hydrochloric acid process and plasma process, or vice versa.

Further, the transparent electrode film 1
After the formation of the fine irregularities on the film surface becomes an appropriate curved surface, the process shifts to the formation of the semiconductor layer 3 by the plasma CVD method.

Then, a-Si is doped with boron to
After forming the layer 4, the power generation layer 2 of a-SiGe is formed,
Thereafter, n-layer 5 is formed by doping a-Si with phosphorus.

At this time, the thin films of the p layer 4, the power generation layer 2, and the n layer 5 have minute irregularities of the transparent electrode film 1.

Therefore, the power generation layer 2 has a concave portion A and a convex portion B having a curved surface shape, and their tip portions are rounded.

After the formation of the n-layer 5, a ZnO / Ag back electrode film 6 is formed on the layer 5 by a sputtering method to manufacture a glass substrate type solar cell having the structure shown in FIG.

Next, the relationship between the minute uneven shape of the power generation layer 2 and the conversion efficiency of the solar cell will be described. First, the radius of curvature and the average height of the minute unevenness of the power generation layer 2 will be described. FIG.
As shown in the figure, the radiuses r _A , r _B of the circles a, b (two-dimensional) or spheres (three-dimensional) conforming to the curved shape of the tip of the concave portion A, the convex portion B of the formed power generation layer 2 are minute irregularities. Radius of curvature.

In order to objectively grasp the height of the minute unevenness of the power generation layer 2 by using the original height before forming the curved surface shape, circles a and b in FIG. and two points p in contact with a curved surface p', seeking q and q', their tangent intersection _t a, obtains the _{t B,} the intersection point _t a, high Satoshi original uneven the distance h _{t B,} the The average of the height is defined as the average height of the minute unevenness of the power generation layer 2.

The extrapolation of the circles a and b and the measurement of the distance h are performed as follows.
For example, the power generation layer 2 is observed with an electron microscope, and the processing is performed from the drawing of FIG. 3 on the monitor screen.

On the other hand, according to an experiment, if the hydrochloric acid treatment and the plasma treatment were not performed on the transparent electrode film 1 at all, the interface between the p layer 4 and the power generation layer 2 and the interface between the power generation layer 2 and the n layer 5 were steep and minute. The average height of the irregularities was 2000 °.

When the transparent electrode film 1 of this solar cell is immersed in a hydrochloric acid solution for about 0.5 to 5 minutes, the concave portion A of the power generation layer 2 has a curved surface shape, and then is exposed to argon plasma for about 1 to 10 minutes. It was confirmed that the convex portion B of the power generation layer 2 also had a curved surface shape.

The shape of the curved surfaces of the concave portions A and the convex portions B changes depending on the time of the hydrochloric acid treatment and the plasma treatment, and the time (total time) of both treatments is variously changed from 0 to 12 minutes to manufacture a solar cell. When the conversion efficiency (%) was measured, the relationship between the ratio (%) of the radius of curvature of the minute unevenness of the power generation layer 2 to the average height and the conversion efficiency (%) of the solar cell was as follows.
The results are shown in Table 1 below.

[0036]

[Table 1]

As is apparent from Table 1, the radius of curvature of the minute irregularities of the power generation layer 2 is 2 times the average height (2000 °).
When it is 0% or more and 50% or less, the conversion efficiency of the solar cell is improved.

Further, while maintaining the radius of curvature of the fine irregularities of the power generation layer 2 at 30% of its average height, the average height of the fine irregularities of the power generation layer 2 is changed in the range of 300 to 5000 ° to manufacture a solar cell. These solar cells (the solar cells of the present invention),
The conversion efficiency was measured and compared with a conventional battery having the same average height and steep fine irregularities. The results were as shown in Table 2 below.

[0039]

[Table 2]

As is clear from Table 2, when the average height of the fine irregularities is 1000 ° or more and 3000 ° or less, the conversion efficiency of the solar cell is improved by forming the concave portions A and the convex portions B into curved surfaces.

That is, when the plasma treatment is performed, the tip of the concave portion A of the power generation layer 2 mainly has a rounded shape, and the crystallinity in the concave portion A and the bonding state between the films are improved. And the occurrence of defects is reduced.

Further, when the hydrochloric acid treatment is performed, the tip of the convex portion B of the minute unevenness of the power generation layer 2 becomes rounded by dropping the corner, and the occurrence of the leak at the convex portion B is prevented. Is done.

Further, when the tip portions of the concave portions A and the convex portions B are rounded, the concentration of the electric field on those portions is reduced,
The electric field intensity in other parts of the power generation layer 2 does not become weak.

Therefore, when the minute irregularities of the power generation layer 2 are formed into a curved surface, and the tip portions of the concave portions A and the convex portions B are both rounded, the occurrence of defects in the concave portions A is prevented, and at the same time, the convex portions are formed. B is prevented from occurring, and the concentration of the electric field at the tips of the concave portions A and the convex portions B is alleviated. As a result, the shape factor (FF) of the power generation layer 2 is improved and the solar cell Conversion efficiency is improved.

It was confirmed by experiments that the concave portion A and the convex portion B were effective when the average height of the fine irregularities of the power generation layer 2 was 1000 ° or more and 4000 ° or less.

In order not to impair the effect of light confinement in the thin film of the power generation layer 2 due to the minute unevenness, the radius of curvature of the minute unevenness is desirably 20% or more and 50% or less of its average height. .

This is also evident from the fact that the power generation efficiency is reduced when the radius of curvature of the fine unevenness is larger than 50% in Table 1, and when the radius of curvature of the fine unevenness of the power generation layer 2 is larger than 50%. This is because the surface is almost flat and the light scattering effect is reduced.

Incidentally, it goes without saying that the time of the chemical etching treatment and the plasma treatment varies depending on various conditions such as the type and amount of the solution or gas.

The acid solution for chemical etching may be a solution of sulfuric acid or hydrofluoric acid other than hydrochloric acid, and the gas for plasma treatment may be a rare gas other than argon gas such as krypton or canon. .

In the first embodiment, both the chemical etching process and the plasma process are performed. However, either one of the processes is performed to form one of the concave portion A and the convex portion B into a curved surface shape, and the roundness is obtained. Of course, the effect can be obtained even if it is attached.

(Other Embodiment) Next, another embodiment of the present invention applied to a microcrystalline solar cell of a metal substrate type and a method of manufacturing the same will be described with reference to FIG. FIG. 4 is a configuration diagram of a solar cell in which the upper side is the light incident side similarly to FIG. 1, and 7 is a 1 μm-thick aluminum metal film formed by vapor deposition on a stainless steel substrate as a metal substrate.

Reference numeral 8 denotes a back electrode film having a thickness of 2000 .ANG. Formed on the metal film 7 by sputtering.
/ ZnO three-layer structure.

9 is plasma CVD on the back electrode film 8.
A microcrystalline semiconductor layer having a pin structure formed by the method,
An n-type microcrystalline silicon n-layer 10 formed by doping phosphorus with a thickness of 500 ° in order from the bottom, a power generation layer (i-layer) 11 of microcrystalline silicon with a thickness of 1 μm, and a 100 ° -thick boron dope And a p-type microcrystalline silicon p-layer 12.

Reference numeral 13 denotes a surface electrode film made of an ITO film having a thickness of 700 ° formed on the p-layer 12 by sputtering.

Then, when manufacturing this solar cell,
The surface of the metal film 7 is immersed in a solution of potassium hydroxide for 5 minutes and subjected to a chemical etching treatment. And each layer 10, 11, 1 of the semiconductor layer 9
2 are formed in order.

At this time, both the convex portion C and the concave portion D of the thin film of the power generation layer 11 have a curved shape, and their tip portions are rounded, and the same effect as in the first embodiment can be obtained.

When the metal film 7 is formed without being immersed in a solution of potassium hydroxide, the power generation layer 11 has a steep unevenness in the concave portion D based on the minute unevenness in the texture processing of the film surface.

A solar cell (the solar cell of the present invention) formed by gradually changing the immersion time in a potassium hydroxide solution between 0.3 minutes and 5 minutes, and a conventional solar cell formed without immersion in this solution The following Table 3 was obtained by comparing the relationship between the average height of the fine irregularities of the power generation layer 11 and the conversion efficiency with respect to the battery.

[0059]

[Table 3]

As is clear from Table 3, the power generation layer 1
When the average height of the fine irregularities is 1000 ° or more and 3000 ° or less, the conversion efficiency is improved by forming a curved surface.

The present invention can be applied to various types of amorphous or non-crystalline solar cells of a glass substrate type or a metal substrate type and a method of manufacturing the same. The type and amount of the solution and the plasma processing gas, the processing time, and the like may be appropriately set according to the conditions.

[0062]

The present invention has the following effects. First, in the solar cell of the present invention, since the unevenness of the power generation layers 2 and 11 formed of the thin film with minute unevenness is curved and rounded, defects at the tip of the recess are small. In addition, the leakage at the tips of the projections is small, and the concentration of the electric field at those tips is prevented, so that the power generation layers 2, 11
The electric field strength of other parts does not decrease.

Therefore, it is possible to provide an amorphous or microcrystalline solar cell in which the conversion efficiency is prevented from lowering due to the minute irregularities due to the texture structuring of the power generation layers 2 and 11, and the conversion efficiency is improved. .

Next, according to the method of manufacturing a solar cell of the present invention, the power generation layers 2 and 11 are formed to have fine irregularities, and the irregularities are formed into a round shape with a curved surface. A reduction in conversion efficiency due to the thin film shapes 2 and 11 is prevented, and an amorphous or microcrystalline solar cell with improved conversion efficiency can be manufactured.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a part of a solar cell of the present invention.

FIG. 2 is a configuration diagram of a solar cell according to one embodiment of the present invention.

3 is an explanatory diagram of an average curvature and an average height of minute unevenness of the solar cell of FIG. 2;

FIG. 4 is a configuration diagram of a solar cell according to another embodiment of the present invention.

FIG. 5 is a schematic configuration diagram of a part of a conventional battery.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Transparent electrode film 2, 11 Power generation layer (i layer) 3, 9 Semiconductor layer 6, 8 Back electrode film 7 Metal film

Claims (4)

[Claims] 1. An amorphous or microcrystalline solar cell in which a power generation layer is formed of a thin film having minute irregularities, wherein the minute irregularities of the power generation layer are curved and rounded. battery. 2. An average height of minute irregularities of a power generation layer is 1000.
2. The method according to claim 1, wherein the angle is not less than {3,000}.
The solar cell as described. 3. The solar cell according to claim 1, wherein a radius of curvature of the minute unevenness of the power generation layer is 20% to 50% of an average height of the minute unevenness of the power generation layer. . 4. An amorphous material is formed on the surface of the fine electrode of the transparent electrode film formed on the glass substrate or on the surface of the back electrode film formed on the metal substrate via the metal film of the small unevenness. In a method for manufacturing a solar cell for forming a semiconductor layer having a crystalline or amorphous pin structure, a chemical etching process in which an acid or alkali solution is immersed in a finely uneven film surface of the transparent electrode film or the metal film, plasma After performing at least one of plasma treatments for exposing the transparent electrode film or the metal film to a curved surface with minute irregularities on the film surface, forming the semiconductor layer on the film surface of the transparent electrode film or the metal film Forming the back electrode and the semiconductor layer on the film surface of (i), and forming the i-type power generation layer of the semiconductor layer into a thin film having a curved surface and a rounded fine irregularity. Solar cell manufacturing method.