JP2002141525A - Substrate for solar cell and thin film solar cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a substrate for a solar cell which can make reduction in the defect density in crystalline silicon films compatible with an optical confinement effect using a roughened surface layer on the substrate for the solar cell, and to provide a thin film solar cell. SOLUTION: A thin film solar cell 20 is constituted by laminating a glass substrate 11a, a roughened surface layer 11b, a P-type crystalline silicon layer 12, an I-type crystalline silicon layer 13, an N-type silicon layer 14, a rear reflective layer 15 and a rear electrode 16 in this order. When a square mean value to show the roughened heights of the layer 11b is used as an index to represent the roughness of the surface of this layer 11b, the square mean value of the roughness of the layer 11b in the form of this embodiment is set in the range of 25 to 600 nm. At the time when the angle of inclination of the roughened surface of the layer 11b to the mean oval of the roughness of the layer 11b is assumed to be Θ the value of tanΘ is set in the range of 0.07 to 0.20.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a substrate for a solar cell and a thin-film solar cell capable of inexpensively manufacturing a solar cell having stable and high photoelectric conversion efficiency.

[0002]

2. Description of the Related Art Fossil fuels such as petroleum are feared for supply and demand in the future, cause global warming, and have a problem of carbon dioxide emission. BACKGROUND ART In recent years, solar cells have attracted attention as an alternative energy source for fossil fuels such as petroleum.

This solar cell has a semiconductor having a pn junction in a photoelectric conversion layer for converting light energy into electric power. In general, silicon is most often used as a semiconductor having this pn junction. From the viewpoint of photoelectric conversion efficiency, it is preferable to use single crystal silicon for this semiconductor. However, a semiconductor using single crystal silicon has a problem of a raw material supply, an increase in area, and a reduction in cost.

On the other hand, a thin-film solar cell using amorphous amorphous silicon as a photoelectric conversion layer has been put to practical use as a material advantageous for realizing a large area and low cost. Furthermore, in order to realize a solar cell that has both high and stable photoelectric conversion efficiency at the level of a single-crystal silicon solar cell and large area and low cost at the level of an amorphous silicon solar cell, the photoelectric conversion of crystalline silicon Use for layers is being considered. In particular, a thin film solar cell (hereinafter, referred to as a crystalline silicon thin film solar cell) in which a crystalline silicon thin film is formed using a thin film forming technique by a chemical vapor deposition method (hereinafter, referred to as a CVD method) similar to that of amorphous silicon. Do) is attracting attention.

[0005] In the following description, unless otherwise specified, the term "crystalline" refers to a state consisting essentially of only crystals, such as "single crystal" and "polycrystal". In addition, the term includes "crystallite" or "microcrystal" in which a crystalline component and an amorphous component are mixed.

Light confinement is one of the technologies that is an important factor in realizing a thin-film solar cell having high photoelectric conversion efficiency. Light confinement means that the surface of a transparent conductive film or a metal layer in contact with the photoelectric conversion layer is made uneven, and light is scattered at the interface to extend the optical path length and increase the amount of light absorbed by the photoelectric conversion layer. Things.

[0007] For example, Japanese Patent Publication No. 16811
No. 83 or Japanese Patent No. 2862174 discloses an example of a solar cell substrate in which the size of the transparent conductive film formed on a glass substrate is defined.

The improvement in photoelectric conversion efficiency due to the light confinement is as follows.
This has the effect of reducing the thickness of the photoelectric conversion layer. Thereby, in the case of an amorphous silicon solar cell, Sta
Light degradation due to the ebller-Wronski effect is suppressed.

Furthermore, crystalline silicon solar cells have been required to have a thickness on the order of several μm, which is several times to ten and several times that of amorphous silicon, due to light absorption characteristics. However, if the photoelectric conversion efficiency is increased by utilizing the light confinement effect, even a crystalline silicon solar cell will result in a drastic reduction in film formation time.

That is, light confinement is an indispensable technique as a means for solving all of high efficiency, stabilization, and cost reduction, which are major issues for practical use of a thin film solar cell.

[0011]

However, the photoelectric conversion efficiency of the conventional crystalline silicon thin-film solar cell as described above has not been improved to date despite vigorous research and development. Compared to the photoelectric conversion efficiency of silicon solar cells, they have reached only the same level.

H. Yamamoto et al, PV
SEC-11, Sapporo, Japan, 1999
The following reports have been made.

On an Asahi-U substrate in which tin oxide having microscopic irregularities is laminated on a glass surface, plasma CVD is performed.
When microcrystalline silicon is formed by the method, silicon crystal grains grow preferentially in a direction perpendicular to the surface of tin oxide.
Then, a large number of defects occur due to the collision of crystal grains having different crystal orientations grown from different uneven surfaces. Such defects become the center of recombination of carriers (electrons and holes) and significantly deteriorate the photoelectric conversion efficiency. Therefore, such defects must be eliminated as much as possible.

H. Yamamoto et al. Also make the following reports at the same time.

When the thickness of the unevenness is reduced by further laminating zinc oxide on the tin oxide having an uneven layer on the surface, the direction perpendicular to the surface of the zinc oxide is the same as in the case of only tin oxide. Silicon crystal grains grow on the surface, and crystal grains grown from different uneven surfaces collide with each other. However, since the misorientation is small, the number of generated defects is reduced.

However, in order to reduce the defects in the crystalline silicon thin film, it is clear that irregularities on the substrate surface should be reduced as much as possible. However, as described above, light confinement is an indispensable technology for thin-film solar cells, and when considering practical use, eliminating or reducing surface irregularities should be avoided.

On the other hand, as disclosed in Japanese Patent No. 1681183 or Japanese Patent No. 2862174,
The cost of a solar cell substrate on which a transparent conductive film having a concavo-convex shape is formed is not sufficiently reduced, and is one of the factors that hinder the spread of thin-film solar cells. As a solution, attention has been paid to using zinc oxide for the transparent conductive film. Zinc oxide is less expensive than tin oxide or ITO, which is widely used as a transparent conductive film. Further, it has an advantage of high plasma resistance, and is suitable as a transparent conductive film material used for a thin film solar cell.

Japanese Patent No. 2974485 discloses an example in which zinc oxide is used as a transparent conductive film material for a thin film solar cell.
Japanese Patent No. 3072832, JP-A-11-23380
No. 0 publication. According to these publications, a thin-film solar cell is provided in which a zinc oxide layer formed by a sputtering method is etched to form an uneven shape. However, these examples are all optimized for amorphous silicon solar cells, and there is room for further improvement for application to crystalline silicon thin film solar cells. In particular, the structure of the irregularities on the substrate surface that exhibits a high light confinement effect without introducing defects in the photoelectric conversion layer has not yet been clarified.

An object of the present invention has been made in view of the above problems, and an object of the present invention is to have a sufficient light confinement effect without increasing a defect density in a crystalline semiconductor layer.
An object of the present invention is to provide a solar cell substrate that can be manufactured at low cost and a thin-film solar cell having stable and high photoelectric conversion efficiency.

[0020]

In order to solve the above-mentioned problems, a substrate for a solar cell according to the present invention has an uneven surface in contact with a photoelectric conversion layer, and the surface opposite to the surface on which the unevenness is formed. And the height of the irregularities is set so that the root-mean-square value is in the range of 25 nm to 600 nm, and the surface of the irregularities with respect to the average line of the irregularities. Ta when the inclination angle is Θ
nΘ is set in the range of 0.07 to 0.20.

According to the above invention, since the unevenness on the surface of the solar cell substrate is provided so as to be in contact with the photoelectric conversion layer, light incident on the unevenness is scattered at the interface. . This scattering of light extends the optical path length, and as a result, the amount of light absorption in the photoelectric conversion layer increases. As described above, by confining the light, the photoelectric conversion efficiency can be improved. With the improvement of the photoelectric conversion efficiency, the thickness of the photoelectric conversion layer is reduced. This makes it possible to significantly reduce the film formation time and the manufacturing cost required for the photoelectric conversion layer.

By the way, in the unevenness of the surface of the solar cell substrate, when the crystal orientation is different, the crystals collide with each other depending on the height, thereby causing a defect. Such a defect becomes a recombination center of carriers and significantly lowers the photoelectric conversion efficiency.

Therefore, according to the above invention, the height of the irregularities is set so that the root-mean-square value is in the range of 25 nm to 600 nm, and the inclination of the irregularities surface with respect to the average line of the irregularities is set. TanΘ when the angle is Θ
Is set in the range of 0.07 to 0.20, so that it is possible to reliably prevent the crystals from colliding with each other. therefore,
Deterioration of photoelectric conversion efficiency due to defects can be reliably prevented.

Preferably, the irregularities are made of a transparent conductive material. In this case, since the incident light is scattered at the interface between the irregularly transparent conductive material and the photoelectric conversion layer, the optical path length of the light is increased, and the light confinement effect can be enhanced.

It is preferable that the transparent conductive material is mainly composed of zinc oxide. In this case, by forming the concavities and convexities with zinc oxide, the structure can be made inexpensively as a whole, and the plasma resistance is high and the quality is hardly changed.

Preferably, the irregularities are formed by etching a material made of the transparent conductive material. In this case, the type of etchant,
By appropriately changing the concentration, the etching time, and the like, the surface shape of the transparent conductive material can be easily controlled, so that desired irregularities can be easily obtained.

In order to solve the above-mentioned problems, another solar cell substrate according to the present invention has a surface in contact with the photoelectric conversion layer which has an uneven surface. Has a substantially hemispherical or conical shape in the range of 200 nm to 2000 nm. More preferably, the diameter of the hole is in the range of 400 nm to 1200 nm. In this case, the height of the unevenness has a root-mean-square value in the range of 25 nm to 600 nm, and the inclination angle of the uneven surface with respect to the average line of the unevenness is ΔΘ.
Is in the range of 0.07 to 0.20, and it is possible to reliably prevent the crystals from colliding with each other. Therefore, it is possible to reliably prevent the photoelectric conversion efficiency from being deteriorated due to the defect.

According to another aspect of the present invention, there is provided a thin-film solar cell including the above-described solar cell substrate, wherein the solar cell substrate is provided with a photoelectric conversion layer including at least one photoelectric conversion element. It is characterized by having.

According to the above invention, the amount of light absorbed by the light confinement effect can be increased without increasing the defects in the photoelectric conversion layer, and the substrate for a solar cell having stable and high photoelectric conversion efficiency can be obtained. Can be provided at low cost.

The surface opposite to the surface in contact with the photoelectric conversion layer is made uneven, and the height of the unevenness is set so that its root mean square is in the range of 15 nm to 600 nm. The tan の when the inclination angle of the uneven surface with respect to the average line of the unevenness is Θ is 0.10 to 0.10.
Preferably, it is set in the range of 0.30.

As a result, suitable irregularities are provided on both surface sides of the photoelectric conversion layer, which is sufficient for a longer wavelength range in addition to the middle wavelength range of 450 to 650 nm in the center of the sunlight spectrum. A large light confinement effect.

[0032] Of the photoelectric conversion layers, the active layer in at least one photoelectric conversion element is more preferably made of crystalline silicon or a silicon alloy.

As a result, light having a wavelength of 700 nm or longer, which cannot be used for photoelectric conversion with amorphous silicon, can be sufficiently used for photoelectric conversion.

[0034]

[Embodiment] One embodiment of the thin-film solar cell of the present invention will be described below with reference to FIG.

As shown in FIG. 1, the thin-film solar cell 20 of the present invention comprises a glass substrate 11a, an uneven surface layer 11b, a p-type crystalline silicon layer 12, an i-type crystalline silicon layer 13, an n-type silicon layer 14, The back reflection layer 15 and the back electrode 16 are stacked in this order.

The thin-film solar cell 20 is a thin-film solar cell called a super straight type in which light is incident from the glass substrate 11a side.

The solar cell substrate 11 includes a glass substrate 11a and an uneven surface layer 11b.

The glass substrate 11a is a solar cell substrate 11
Is a transparent substrate. The thickness of the substrate is not particularly limited, but may be, for example, about 0.1 to 30 mm so as to have appropriate strength and weight to support the structure.

In this embodiment, glass is used as the material of the transparent substrate. Alternatively, various materials such as polyimide or polyvinyl resin having a heat resistance of about 200 ° C., and those in which they are laminated are used. it can.
Further, those surfaces may be covered with a metal film, a transparent conductive film, an insulating film, or the like.

The uneven surface layer 11b is made of a transparent conductive material, and is formed by etching zinc oxide, which is a transparent conductive material.

In the case where a transparent conductive film is formed on the surface of the solar cell substrate 11 by forming irregularities by etching, the type, concentration, etching time, etc. of the etchant are appropriately changed to obtain a transparent conductive film. The surface shape can be easily controlled, and it is easy to form irregularities in which the mean square value indicating the height of the irregularities and tanΘ are within a predetermined range.

By using an acid or alkali solution as an etchant, the solar cell substrate 11 can be manufactured at a lower cost than in a conventional manufacturing method. At this time, examples of the acid solution that can be used include one or a mixture of two or more of hydrochloric acid, sulfuric acid, nitric acid, hydrofluoric acid, acetic acid, formic acid, and perchloric acid. Among them, hydrochloric acid and acetic acid are used. Is particularly preferred. These acid solutions can be used at a concentration of, for example, about 0.05 to 5.0% by weight, but in the case of a relatively weak acid such as acetic acid, 0.1 to 5.0% by weight.
It may be used at a concentration of about 0% by weight. Examples of the alkaline solution include sodium hydroxide, ammonia, potassium hydroxide, calcium hydroxide, and aluminum hydroxide.
Species or a mixture of two or more species can be mentioned. Among them, it is particularly preferable to use sodium hydroxide. These alkaline solutions are preferably used at a concentration of about 1 to 10% by weight.

Further, by using a transparent conductive material for the uneven surface layer 11b, light incident into the thin-film solar cell 20 is scattered at the interface with the photoelectric conversion layer 21. Therefore, the optical path length of light becomes longer, and the light confinement effect can be enhanced. As a result, the photoelectric conversion efficiency increases, and the thickness of the photoelectric conversion layer 21 can be reduced.

As a result, the thin-film solar cell 20 made of crystalline silicon can be made thinner, and the film-forming time can be greatly reduced. Furthermore, when the photoelectric conversion layer 21 is formed, it is possible to prevent impurities contained in the solar cell substrate 11 from being taken into the photoelectric conversion layer 21.

Further, zinc oxide, which is a transparent conductive material for forming the uneven surface layer 11b, is inexpensive, has high plasma resistance, and is hardly deteriorated. Thereby, a material such as tin oxide, indium oxide, or ITO, which is widely used for the transparent conductive film, is used.
The solar cell substrate 11 which is inexpensive and has high plasma resistance can be obtained.

Incidentally, a trace amount of impurities may be added to the transparent conductive material. For example, when zinc oxide is a main component, a group IIIB element such as gallium or aluminum of about 5 × 10 ^{20 to} 5 × 10 ²¹ cm ⁻³ ,
Alternatively, since the resistivity is reduced by containing a Group IB element such as copper, it is suitable for use as an electrode.

If the thickness of the transparent conductive film is too small, the characteristics as a solar cell may not be uniform. On the other hand, if the transparent conductive film is too thick, the photoelectric conversion efficiency decreases due to a decrease in transmittance, and the cost increases due to an increase in the film formation time, so that the thickness is about 0.1 to 2.0 μm. Is preferred.

The transparent conductive film can be formed, for example, by sputtering, normal pressure CVD, low pressure CVD, electron beam evaporation,
It can be produced by a known method such as a sol-gel method and an electrodeposition method.
Among them, in particular, by manufacturing by a sputtering method, it becomes easy to control the light transmittance and the resistivity of the uneven surface layer 11b to those suitable for the thin-film solar cell 20.

Here, as an index representing the unevenness of the surface of the uneven surface layer 11b, a root mean square value indicating the height of the unevenness and tan と き when an inclination angle of the uneven surface with respect to an average line of the unevenness is Θ are used. The uneven surface layer 11 of the present embodiment
The mean square value of b is set in the range of 25 to 600 nm, and tan Θ is set in the range of 0.07 to 0.20.

By forming the uneven surface layer 11 b set in the above range, the unevenness on the surface of the solar cell substrate 11 is provided so as to be in contact with the photoelectric conversion layer 21. Light is scattered. This light scattering prolongs the optical path length, and as a result, the amount of light absorbed by the photoelectric conversion layer 21 increases. As described above, by confining the light, the photoelectric conversion efficiency can be improved. By improving the photoelectric conversion efficiency, the thickness of the photoelectric conversion layer 21 is reduced. Thereby, it is possible to significantly reduce the film formation time and the manufacturing cost required for the photoelectric conversion layer 21.

Further, according to the above configuration, the height of the unevenness is set so that the root-mean-square value is in the range of 15 nm to 600 nm, and tan ０．１ is 0.1.
It is set in the range of 0 to 0.30. Thereby, it is possible to reliably prevent the crystals forming the photoelectric conversion layer 21 from colliding with each other. Therefore, it is possible to reliably prevent the photoelectric conversion efficiency from being deteriorated due to the defect.

In other words, at least one uneven surface layer 11b is formed on the solar cell substrate 11, and the mean square value of the unevenness is 25 nm or more and tanΘ
Is set to 0.07 or more, it is possible to form the uneven surface layer 11b having a sufficient light confinement effect. Further, the mean square value is 600 nm or less, and ta
By setting nΘ to 0.20 or less, even if the silicon crystal grains formed on the uneven surface layer 11b collide, the increase in the number of generated defects is suppressed because the height and orientation difference of the unevenness are appropriate. it can.

In order to obtain the effect of the present invention more effectively, the mean square value of the height of the unevenness is 25 to 400 nm.
And tanΘ is more preferably in the range of 0.07 to 0.15. By forming the unevenness that satisfies the conditions of the mean square value and tan Θ, the uneven surface layer 11b having a small number of defects and a large light confinement effect can be obtained more reliably.

Further, a hole which is a part of the unevenness on the surface of the solar cell substrate 11 and has a more gentle unevenness than the above unevenness is
It has a substantially hemispherical or conical shape with a diameter in the range of 200 to 2000 nm.

As a result, it is possible to form the uneven surface layer 11b having the unevenness in the above-described preferred range with good reproducibility with respect to the mean square value of the unevenness height and tan Θ. Therefore, since a good light confinement effect is obtained, the solar cell substrate 11 with high photoelectric conversion efficiency can be obtained.

The diameter of the hole is 400 to 1200.
Within the range of nm, a more favorable light confinement effect can be obtained, and the uneven surface layer 11b with less defects can be formed, so that the present invention can be implemented more effectively.

In this embodiment, etching is used as a means for forming the uneven surface layer 11b. However, the present invention is not limited to the etching. For example, a film may be formed on the glass substrate 11a having a smooth surface, at the same time as depositing the film, the surface of which may be uneven. The film forming the uneven surface layer 11b may be the same material as the solar cell substrate 11, or may be a different material. Further, it can also be formed by performing machining such as sandblasting on the surface of the solar cell substrate 11.

Further, a photoelectric conversion layer 21 that converts incident light into electricity, that is, performs so-called photoelectric conversion, is formed by the p-type crystalline silicon layer 12, the i-type crystalline silicon layer 13, and the n-type silicon layer 14. ing.

The surface of the photoelectric conversion layer 21 has an irregular shape, and irregularities made of an i-type crystalline silicon layer 13 are formed under the following conditions, and an n-type silicon layer 14 is laminated thereon. ing. Since the n-type silicon layer 14 is thin, it may be considered that the uneven shape of the i-type crystalline silicon layer 13 is projected as it is. The above conditions are that the root mean square value indicating the height of the unevenness is set in a range of 15 to 600 nm, and tan Θ is set in a range of 0.10 to 0.30.

As a result, suitable irregularities are provided on both surfaces of the photoelectric conversion layer 21.
By adding irregularities under conditions different from 1b, a sufficient light confinement effect is produced in any of a middle wavelength region and a longer wavelength region in a wavelength range of 450 to 650 nm at the center of the solar spectrum. Can be.

Means for forming the irregularities under the above conditions on the surface of the i-type crystalline silicon layer 13 include, for example, each semiconductor film (the p-type crystalline silicon layer 1) constituting the photoelectric conversion layer 21.
2, i-type crystalline silicon layer 13, n-type silicon layer 14)
The photoelectric conversion layer 21 may be formed at the same time as the deposition, so that irregularities are formed on the surface. At this time, the forming conditions may be determined in consideration of the fact that the shape of the unevenness on the surface of the photoelectric conversion layer 21 is affected by the shape of the uneven surface layer 11b provided on the solar cell substrate 11. In addition, the photoelectric conversion layer 21
Even if it is a machining process such as sandblasting or a chemical processing process such as etching,
The irregularities can be formed.

The back reflection layer 15 is a thin film electrode made of zinc oxide having a thickness of 50 nm and formed by magnetron sputtering.

The back electrode 16 is formed by depositing silver to a thickness of 500 nm by electron beam evaporation. The electrodes 17 are respectively drawn out from the back electrode 16 and the uneven surface layer 11b to form a super straight type. A thin-film solar cell 20 is configured.

With the above configuration, the photoelectric conversion layer 21 having a high photoelectric conversion rate by utilizing the light confinement effect and having few defects can be formed on the unevenness of the uneven surface layer 11b provided for increasing the photoelectric conversion rate. The solar cell substrate 11 can be obtained. Furthermore, by using this solar cell substrate 11,
An inexpensive thin film solar cell 20 having a high photoelectric conversion rate can be obtained.

In this embodiment, the photoelectric conversion layer 21
Has described an example including one photoelectric conversion element.
However, the photoelectric conversion layer 21 may be formed of a plurality of photoelectric conversion elements, and among them, the active layer (I-type layer) in at least one photoelectric conversion element is formed of crystalline silicon or a silicon alloy. I just need. Then, long-wavelength light having a wavelength of 700 nm or more, which cannot be used for photoelectric conversion with amorphous silicon, can be sufficiently used.

The above-mentioned silicon alloy is, for example, silicon
Si with tin added to silicon_xSn _1-x, And germana
Si doped with N_xGe_1-xAnd other materials.

Further, in order to make the effect of the present invention concrete, Examples 1 to 3, Comparative Examples and Conventional Examples will be described below.

(Example 1) A procedure for producing the solar cell substrate 11 and the thin-film solar cell 20 will be described with reference to FIG.
Note that, for convenience of description, members having the same functions as those in the drawings described in the above embodiment are denoted by the same reference numerals, and description thereof will be omitted.

On one principal surface of the glass substrate 11a having a smooth surface, a substrate temperature of 15% was applied by magnetron sputtering.
At 0 ° C., zinc oxide was formed to a thickness of 500 nm. Gallium of about 1 × 10 ²¹ cm ⁻³ is added to the zinc oxide. As a result, the sheet resistance of the obtained zinc oxide was 10 Ω / □, and the transmittance for light having a wavelength of 800 nm was 80%.

Subsequently, the zinc oxide surface was etched. After immersing the glass substrate 11a coated with zinc oxide in a 0.5% by weight hydrochloric acid aqueous solution at a liquid temperature of 25 ° C. for 30 seconds, the surface is sufficiently washed with pure water, and a solar cell substrate having an uneven surface layer 11b is provided. 11 was obtained. Observation of the surface shape of the uneven surface layer 11b with a scanning electron microscope revealed that a large number of substantially hemispherical holes having a diameter of about 200 to 1400 nm were formed on the surface.

In order to examine the surface shape of the uneven surface layer 11b in detail, the surface shape was measured with an atomic force microscope. From the shape of the hole in the depth direction, it was found that the shape of the hole was substantially hemispherical or conical. Then, in order to express the characteristics of the surface shape by numerical values, the root mean square value (RMS) of the height of the unevenness was used as an index of the unevenness height. Further, assuming that the most frequent wavelength W of the sinusoidal curve obtained when the surface shape waveform curve is Fourier-transformed is used as an index of the unevenness pitch, and the inclination of the uneven surface with respect to the average line of the surface unevenness is Θ,
Θ = 2RMS / (W / 2) = 4RMS / W, RM
The values of S and tanΘ were used as indices of the uneven shape. The mean square value of the height of the unevenness at this time was 28 nm, and tan ０．０ was 0.08.

On the solar cell substrate 11 thus obtained, 1
The p-type crystalline silicon layer 12 and the i-type crystalline silicon layer 1 are formed by a plasma CVD method using a high frequency of 3.56 MHz.
3. An n-type silicon layer 14 was sequentially stacked.

The p-type crystalline silicon layer 12 is made of ₃ SCCM of SiH ₄ gas, 600 SCCM of H ₂ gas, and 1 SCC of B ₂ H ₆ gas adjusted to 5000 ppm by H ₂ gas.
M, a film forming chamber pressure of 200 Pa, a discharge power of 25 W, and a substrate temperature of 140 ° C. were formed to have a thickness of 30 nm. The i-type crystalline silicon layer 13 is made of SiH ₄ gas 11 SCCM,
The film was formed under the conditions of 350 SCCM of H ₂ gas, a film forming chamber pressure of 200 Pa, a discharge power of 20 W, and a substrate temperature of 140 ° C.
The thickness was set to 0 nm. The n-type silicon layer 14 is made of SiH ₄
10 SCCM of gas, 100 SCCM of PH ₃ gas adjusted to 1000 ppm by H ₂ gas, and 27 P of film forming chamber pressure
a, a discharge power of 30 W and a substrate temperature of 180 ° C. were formed into a film having a thickness of 30 nm.

After taking out from the plasma CVD apparatus (not shown), the shape of the surface of the n-type silicon layer 14 was measured with an atomic force microscope.
8 nm, and tan ０．０ was 0.06.

Further, the surface of the n-type silicon layer 14
When the X-ray diffraction method was performed using (220) X-ray diffraction peak
Integrated intensity I₂₂₀And integral intensity of (111) X-ray diffraction peak
Degree I_{1 11}Ratio I₂₂₀/ I₁₁₁Was 3.0. Where the actual
The X-ray diffraction peak obtained in FIG.
Although it is not information of a single substance, it is compared with the i-type crystalline silicon layer 13.
In all, a p-type crystalline silicon layer 12 and an n-type silicon layer
14 is very thin. Therefore, the result of the X-ray diffraction method
Reflects the crystal orientation of the i-type crystalline silicon layer 13
It does not matter.

Thereafter, zinc oxide was formed to a thickness of 50 nm as the back surface reflection layer 15 by magnetron sputtering. Further, the back electrode 16 is formed by electron beam evaporation.
Is formed with a thickness of 500 nm as a glass substrate 11a.
A super straight type thin-film solar cell 20 to which light is incident from the side was obtained.

The AM1.5 (1)
00mW / cm ²⁾ current under the irradiation condition - was measured voltage characteristic, short circuit current is 25.0mA / cm ^2,
The open circuit voltage was 0.524 V, the form factor was 0.700, and the photoelectric conversion efficiency was 9.17%.

From these results, it can be seen that the irregularity shape of the irregularity height of the irregularity surface layer 11b of root mean square = 28 nm and tanｔ = 0.08 has a higher photoelectric conversion rate than the comparative example and the conventional example shown below. Was obtained. Also,
As in this example, when the diameter of the holes on the surface of the uneven surface layer 11b was 200 to 1400 nm, it was found that the uneven surface layer 11b having the unevenness under the above conditions could be formed.

Further, it is determined whether or not the shape of the unevenness where the mean square value of the unevenness height of the surface of the n-type silicon layer 14 is 18 nm and tanΘ = 0.06 is appropriate for obtaining the light confinement effect. This is determined from the results of Example 3 in which the conditions for forming the irregularities on the silicon layer surface described below were changed.

Embodiment 2 Another embodiment of the thin-film solar cell of the present invention will be described below.

For convenience of explanation, members having the same functions as those in the drawings described in the above embodiment are given the same reference numerals, and explanations thereof are omitted.

In this embodiment, the thin-film solar cell was manufactured in the same manner as in Example 1 except that the time for immersing the solar cell substrate 11 in the hydrochloric acid aqueous solution was 45 seconds when the surface of the solar cell substrate 11 was etched. Was prepared. Thereby, the uneven surface layer 1
It is expected that the height of the unevenness of 1b will be larger than in Example 1.

Before the formation of the photoelectric conversion layer 21, the uneven surface layer 1
Observation of the shape of 1b with a scanning electron microscope revealed that a large number of substantially hemispherical holes having a diameter of about 400 to 1000 nm on the surface were formed.

To examine the shape of the uneven surface layer 11b in detail, the surface shape was measured by an atomic force microscope. The shape of the hole formed in the uneven surface layer 11b of the present example was substantially hemispherical or conical as in the case of Example 1, but the mean square value of the uneven height in this example was 40 nm. And tanΘ was 0.13.

After the formation of the photoelectric conversion layer 21 composed of a silicon layer, the surface shape of the n-type silicon layer 14 was measured by an atomic force microscope.
And tan ０．０ was 0.06.

Further, after the formation of the photoelectric conversion layer 21, the X-ray
When the folding method was performed, the integration of the (220) X-ray diffraction peak was performed.
Strength I₂₂₀And (111) X-ray diffraction peak integrated intensity I₁₁₁of
Ratio I_{Two 20}/ I₁₁₁Is 2.8, which is almost the same as in the first embodiment.
Value.

The AM1.5 (100 m)
(W / cm ² ) When the current-voltage characteristics under the irradiation conditions were measured, the short-circuit current was 25.4 mA / cm ² , the open-circuit voltage was 0.527 V, the form factor was 0.701, and the photoelectric conversion efficiency was 9.38%. Met.

From the results, in the present embodiment in which the conditions for forming the concavo-convex surface layer 11b were changed, the mean square value of the concavo-convex height was 40 nm and the shape of the concavo-convex surface layer 11b was tanΘ = 0.23. It was found that a photoelectric conversion rate higher than that of the uneven shape of No. 1 was obtained.

The mean square value of the height of the irregularities = 20 nm,
Whether or not the irregular shape of the n-type silicon layer 14 of tan Θ = 0.06 is appropriate for obtaining a good light confinement effect is determined by the following results of Example 3 as in Example 1. to decide.

(Embodiment 3) Still another embodiment of the thin-film solar cell of the present invention will be described below.
Note that, for convenience of description, members having the same functions as those in the drawings described in the above embodiment are denoted by the same reference numerals, and description thereof will be omitted.

In this embodiment, the i-type crystalline silicon layer 13
A thin-film solar cell 20 was produced in the same manner as in Example 2, except that the SiH ₄ gas was changed to 250 SCCM during the formation. This is expected to increase the height of the irregularities on the surface of i-type crystalline silicon layer 13.

After the photoelectric conversion layer 21 made of a silicon layer was formed, the shape of the surface of the n-type silicon layer 14 projecting the unevenness of the surface of the i-type crystalline silicon layer 13 was measured by an atomic force microscope. Mean square value of 26 nm
And tanΘ was 0.09.

Further, when the X-ray diffraction method was performed, (22
0) The ratio I ₂₂₀ / I ₁₁₁ of the integrated intensity I ₂₂₀ of the X-ray diffraction peak to the integrated intensity I ₁₁₁ of the (111) X-ray diffraction peak is 3.2, which is almost the same value as in Examples 1 and 2. Was.

The AM1.5 (100 m
(W / cm ² ) The current-voltage characteristics under the irradiation conditions were measured. The short-circuit current was 26.8 mA / cm ² , the open-circuit voltage was 0.525 V, the form factor was 0.702, and the photoelectric conversion efficiency was 9.88%. Met.

When the results are compared with those of Examples 1 and 2, it can be seen that there is almost no difference between the open circuit voltage and the form factor. On the other hand, it can be seen that the photoelectric conversion efficiency is improved by the increase in the short-circuit current. It is considered that this is because the shape of the surface of the n-type silicon layer 14 is suitable for confinement of long-wavelength light.

From the results, the root-mean-square value of the height of the unevenness on the surface of the n-type silicon layer = 26 and tan Θ = 0.0
It has been found that a photoelectric conversion efficiency higher than that of Examples 1 and 2 can be obtained with the formation condition of the unevenness on the surface of the n-type silicon layer 14 of 9.

Comparative Example A comparative example of the thin-film solar cell of the present invention will be described below.

In this comparative example, a thin-film solar cell was produced in the same manner as in Example 1 except that the time of immersing the substrate in an aqueous hydrochloric acid solution during etching of the substrate surface was changed to 15 seconds. Accordingly, it is expected that the height of the unevenness of the uneven surface layer will be smaller than in each of the above examples.

Before the formation of the photoelectric conversion layer composed of a silicon layer, the shape of the uneven surface layer was observed with a scanning electron microscope. As a result, a substantially hemispherical hole having a diameter of about 50 to 200 nm was formed on the surface. I understood that. However,
The number of holes that can be clearly discriminated as a hole is determined in Example 1.
And less than in 2.

In order to examine the shape of the uneven surface layer in detail, the surface shape was measured with an atomic force microscope. The shape of the hole formed in the uneven surface layer of the present example was substantially hemispherical or conical as in the case of Example 1, but the mean square value of the uneven height in the present example was 12 nm. Yes, tan
Θ was 0.05.

Further, when the X-ray diffraction method was performed after the formation of the photoelectric conversion layer, the integrated intensity of the (220) X-ray diffraction peak was determined.
The ratio I of the integrated intensity I ₁₁₁ of the I ₂₂₀ to the (111) X-ray diffraction peak I
₂₂₀ / _I111 is 3.2, which is almost the same value as in the first to third embodiments.

The AM1.5 (100 m
(W / cm ² ) When the current-voltage characteristics under the irradiation conditions were measured, the short-circuit current was 22.9 mA / cm ² , the open-circuit voltage was 0.520 V, the form factor was 0.699, and the photoelectric conversion efficiency was 8.32%. Met.

As compared with the cases of Examples 1 to 3, it can be seen that the values of the open circuit voltage and the form factor hardly change, but the value of the short circuit current decreases. That is, it means that the uneven structure on the surface of the solar cell substrate is insufficient for producing the light confinement effect due to insufficient etching time.

From these results, it is found that the uneven surface layer having a good light confinement effect cannot be obtained under the uneven surface forming conditions of the mean square value of the uneven surface height of the uneven surface layer = 12 nm and tanΘ = 0.05. Was. It was also found that when the diameter of the holes on the surface of the uneven surface layer was 50 to 200 nm, the uneven surface layer having a good light confinement effect could not be obtained, as in the case described above.

(Conventional Example) In order to clarify the effect of the thin-film solar cell of the present invention, a conventional thin-film solar cell will be described as follows.

On a substrate (Trade name: Asahi-U) in which tin oxide having surface irregularities was formed by a normal pressure CVD method on a glass substrate having a smooth surface, a back electrode was formed at a substrate temperature of 150 ° C. by an electron beam evaporation method. Was formed to have a thickness of 500 nm. Further, zinc oxide was deposited at a substrate temperature of 150 ° C. to a thickness of 50 n by magnetron sputtering.
m to prepare a thin-film solar cell having an uneven surface layer.

Note that zinc oxide is provided to prevent a reduction reaction of tin oxide caused by hydrogen plasma during formation of the crystalline silicon layer.

In order to examine the shape of the uneven surface layer of the solar cell substrate in detail, the surface shape was measured with an atomic force microscope. The shape of the concavo-convex surface layer of this conventional example was a well-known pyramid type, the mean square value of the concavo-convex height was 42 nm, and tan ０．３ was 0.31.

When the X-ray diffraction method was performed after forming the photoelectric conversion layer composed of the silicon layer, the integrated intensity I _{220 of} the (220) X-ray diffraction peak and the integrated intensity I of the (111) X-ray diffraction peak were obtained.
The ratio I ₂₂₀ / I ₁₁₁ of the I ₁₁₁ was 1.5.

The AM1.5 (100 m)
(W / cm ² ) When the current-voltage characteristics under the irradiation conditions were measured, the short-circuit current was 24.7 mA / cm ² , the open-circuit voltage was 0.517 V, the form factor was 0.692, and the photoelectric conversion efficiency was 8.84%. Met.

Compared with the cases of Examples 1 to 3, it can be seen that the values of all of the short-circuit current, open-circuit voltage and form factor are reduced.

When considered in conjunction with the results of the X-ray diffraction method, a large number of defects are introduced during the formation of the crystalline silicon layer in the conventional structure of the substrate surface irregularities, and therefore, it is suitable for a crystalline silicon thin film solar cell. Not mean.
Therefore, in the unevenness of the uneven surface layer formed by the conventional method (root mean square = 42 nm, tanΘ = 0.31),
It was found that a good light confinement effect was not obtained and a thin-film solar cell with high photoelectric conversion efficiency could not be obtained.

In order to reduce the defects of the uneven surface layer and to obtain an uneven surface layer having a good light confinement effect, it is preferable to make the height or azimuth difference of the unevenness smaller than the result of the conventional example. I think that the.

From the results of Examples 1 to 3, the comparative example, and the conventional example, the root-mean-square value of the uneven height of the uneven surface layer 11b is in the range of 25 to 600 nm, and tan 、 is
It was found that irregularities having a good light confinement effect can be formed in the range of 0.07 to 0.20.

Further, it was found that if the diameter of the hole, which is a part of the unevenness of the uneven surface layer 11b, is 200 to 2000 nm, unevenness suitable for the above-mentioned uneven shape condition can be formed.

Further, if the mean square value of the height of the unevenness on the surface of the n-type silicon layer 14 is in the range of 15 to 600 nm and tan 、 is in the range of 0.10 to 0.30, more favorable light It has been found that the thin-film solar cell 20 having the concavo-convex effect having the confinement effect can be provided.

Therefore, with the structure of the surface irregularities of the solar cell substrate 11 of the present invention, a large number of defects are not introduced during the formation of the photoelectric conversion layer 21 and the thin-film solar cell 20 having high photoelectric conversion efficiency can be obtained. It became clear that it could be provided.

[0118]

As described above, the substrate for a solar cell of the present invention has a roughened surface in contact with the photoelectric conversion layer, and receives light from the opposite side of the surface on which the unevenness is formed. Substrate, the height of the irregularities is set so that the root-mean-square value is in the range of 25 nm to 600 nm, and the angle of inclination of the irregular surface relative to the average line of the irregularities is represented by Θ. Is set in the range of 0.07 to 0.20.

According to the present invention, the light confinement effect is enhanced,
There is an effect that a solar cell substrate with improved photoelectric conversion efficiency can be obtained. With the improvement of the photoelectric conversion efficiency, the thickness of the photoelectric conversion layer is reduced. This makes it possible to significantly reduce the film formation time and the manufacturing cost required for the photoelectric conversion layer. Further, it is possible to reliably prevent the photoelectric conversion efficiency from deteriorating due to defects.

When the irregularities are made of a transparent conductive material, the incident light is scattered at the interface between the transparent conductive material having the irregularities and the photoelectric conversion layer, so that the optical path length of the light becomes longer and the light is closed. The effect that it becomes possible to raise the incorporation effect is produced.

The transparent conductive material is mainly made of zinc oxide, so that the unevenness is made of zinc oxide, so that it can be made inexpensively as a whole, and has high plasma resistance and is hardly deteriorated. To play.

The irregularities are formed by etching the transparent conductive material, and the transparent conductive material is appropriately changed by changing the type, concentration, etching time, etc. of the etchant. Since the surface shape of the conductive material can be easily controlled, an effect that desired irregularities can be easily obtained is exerted.

As described above, another substrate for a solar cell according to the present invention has a surface in contact with the photoelectric conversion layer which is uneven, and the hole has a diameter of 200 nm to 2000 nm.
And a substantially hemispherical or conical shape in the range of

According to the present invention, the height of the unevenness has a root-mean-square value in the range of 25 nm to 600 nm, and the inclination angle of the uneven surface with respect to the average line of the unevenness is ΔΘ.
Tan の is in the range of 0.07 to 0.20, and the collision of crystals can be reliably avoided. Therefore, it is possible to reliably prevent the photoelectric conversion efficiency from being deteriorated due to the defect.

The diameter of the hole is 400 nm to 12 nm.
When the thickness is within the range of 00 nm, the same effect as described above can be obtained more reliably.

As described above, the thin-film solar cell according to the present invention comprises the above-mentioned solar cell substrate, and the solar cell substrate is provided with a photoelectric conversion layer comprising at least one photoelectric conversion element. is there.

According to the present invention, the amount of light absorbed by the light confinement effect can be increased without increasing the defects in the photoelectric conversion layer, and a solar cell substrate having stable and high photoelectric conversion efficiency can be obtained. An effect that it can be provided at low cost is achieved.

The surface opposite to the surface in contact with the photoelectric conversion layer is made uneven, and the height of the unevenness is set so that the root-mean-square value is in the range of 15 nm to 600 nm. TanΘ when the inclination angle of the uneven surface with respect to the average line of the unevenness is ０．１ is 0.10 to 0.10.
Preferably, it is set in the range of 0.30.

As a result, suitable irregularities are provided on both surfaces of the photoelectric conversion layer, and are sufficient for a longer wavelength range in addition to a middle wavelength range of 450 to 650 nm in the center of the sunlight spectrum. There is an effect that a light confinement effect can be generated.

The active layer of at least one of the photoelectric conversion layers is made of crystalline silicon or a silicon alloy.
An effect is obtained that light having a long wavelength of m or more can be sufficiently used for photoelectric conversion.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a structure of a thin-film solar cell of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 11 solar cell substrate 11 a glass substrate 11 b uneven surface layer 12 p-type crystalline silicon layer 13 i-type crystalline silicon layer 14 n-type silicon layer 15 back reflection layer 16 back electrode 17 electrode 20 thin film solar cell 21 photoelectric conversion layer

 ──────────────────────────────────────────────────続 き Continuing from the front page (71) Applicant 500132649 Michio Kondo 1-1-1 Umezono, Tsukuba City, Ibaraki Pref., National Institute of Advanced Industrial Science and Technology (74) The above three agents 100080034 Patent Attorney Kenzo Hara (72) Inventor Kenji Wada 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Co., Ltd. (72) Inventor Yoshiyuki Nasuno 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka Sharp Co., Ltd. (72) Invention Person Michio Kondo 1-1-4 Umezono, Tsukuba, Ibaraki Pref., Within the Institute of Technology, Electronic Technology Research Institute (72) Inventor Akihisa Matsuda 1-4-1 Umezono, Umezono, Tsukuba, Ibaraki, Japan F-term (Reference) 5F051 AA02 CB12 CB15 DA04 FA02 FA19 FA23 GA03 GA16

Claims (9)

[Claims] 1. A solar cell substrate in which a surface in contact with a photoelectric conversion layer is uneven, and light is incident from a side opposite to a surface on which the unevenness is formed. Mean square value is 25 nm to 600
nm, and the tan と き when the inclination angle of the uneven surface with respect to the average line of the unevenness is Θ is set in the range of 0.07 to 0.20. Substrate for a solar cell. 2. The solar cell substrate according to claim 1, wherein said irregularities are made of a transparent conductive material. 3. The solar cell substrate according to claim 2, wherein said transparent conductive material is mainly made of zinc oxide. 4. The solar cell substrate according to claim 3, wherein the irregularities are formed by etching a material made of the transparent conductive material. 5. A solar cell substrate in which the surface in contact with the photoelectric conversion layer is made uneven, wherein the hole that is a part of the unevenness of the solar cell substrate has a diameter of 2.
A solar cell substrate having a substantially hemispherical or conical shape in the range of 00 nm to 2000 nm. 6. The hole has a diameter of 400 nm to 1200 n.
6. The solar cell substrate according to claim 5, wherein the substrate has a substantially hemispherical or conical shape in the range of m. 7. A thin-film solar cell comprising the solar cell substrate according to claim 1, wherein the solar cell substrate is provided with a photoelectric conversion layer comprising at least one photoelectric conversion element. . 8. A surface opposite to the surface in contact with the photoelectric conversion layer is made uneven, and the height of the unevenness has a root-mean-square value of 15 nm to 600 nm.
nm, and tan 角 when the inclination angle of the uneven surface with respect to the average line of the unevenness is Θ is set in the range of 0.10 to 0.30. The thin-film solar cell according to claim 7, wherein 9. The active layer in at least one of the photoelectric conversion layers is made of crystalline silicon or a silicon alloy.
2. The thin-film solar cell according to 1.