JPH08288529A - Photoelectric conversion device and manufacture thereof - Google Patents

Abstract

PURPOSE: To prevent electrodes from being separated by a method wherein a roughened surface is formed on the form of the surface of the lower electrode layer of a photoelectric conversion device of a structure, wherein the lower electrode layer, a photoelectic conversion semiconductor layer and a transparent upper electrode layer are laminated in order on a flexible and insulative substrate, and the mean thickness of the roughened surface and the mean interval between the roughened mountaines of the roughened surface are formed within a prescribed value. CONSTITUTION: Ag is subjected to DC sputtering in Ar gas on an insulative and flexible substrate 1 to form a lower electrode layer 2. A substrate temperature at the time of the sputtering of the Ag is controlled at 200 to 400 deg.C to form a roughened surface 8, which has a mean film-forming thickness of 250μm or thinner, the mean interval of 150 to 1000nm between roughened mountains and a difference of altitude of 50 to 150nm. After an N-type a-Si layer 3, an I-type a-Si layer 4, an I-type u-SiO layer 5 and a P-type u-SiO later 6 are deposited in order on the layer 2 by a chemical vapor deposition method, the layer 6 is subjected to RF sputtering to deposit an indium-tin oxide on the layer 6 and a transparent upper electrode layer 7 is formed. Thereby, separation of the electrodes and a short-circuit between the electrodes are prevented from being generated and the characteristics of a photoelectric conversion device are improved by a light scattering effect.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photoelectric conversion device using a semiconductor thin film as a photoelectric conversion layer and a method for manufacturing the same.

[0002]

2. Description of the Related Art A raw material gas is a plasma CVD method or an optical CVD method.
A photoelectric conversion device using a semiconductor thin film containing amorphous silicon (hereinafter referred to as a-Si) or the like as a main component formed by decomposing by a CVD method or a thermal CVD method has a feature that a large area can be easily achieved, Expected as a cost solar cell. In such a photoelectric conversion device, in addition to the light directly incident on the photoelectric conversion layer made of a semiconductor thin film through the transparent electrode layer on the upper surface, the light is reflected by the surface of the lower electrode layer provided on the substrate side of the semiconductor thin film and photoelectrically converted. Light incident on the conversion layer also contributes to power generation. It is known that if the surface of the electrode layer is not flat and has an uneven surface shape, light scattering is caused thereby and the optical path length is increased, so that the photoelectric conversion efficiency is improved. A method for forming an electrode having such a surface shape on a substrate is disclosed in Japanese Patent Laid-Open No. 56-1.
52276, JP-A-58-180069, JP-A-1
No. 119,074, etc., a method for making the surface of a substrate supporting an electrode uneven, and JP-A-59-59.
-61973, JP-A-3-94173, and JP-A-3-94173.
99477, JP-A-3-99478, JP-A4-2.
There is a method of forming an electrode having irregularities on a flat substrate as described in Japanese Patent Application Laid-Open No. 18977 and Japanese Patent Application Laid-Open No. 4-334069. As a method for forming the uneven electrode, a method using a polycrystalline metal (Japanese Patent Laid-Open No. 3-99477)
No.), a method of vapor-depositing and heat-treating a metal electrode (JP-A-3-99478), a method of using a metal two-layer structure (JP-A-4-218977), a metal alloy such as Al or Ag, or Si with these. Method of using alloy
(JP-A-4-334069) and the like are disclosed.

[0003]

The former method of making the surface of the base body uneven has the following problems. Primarily,
Depending on the substrate material, it may be difficult to obtain unevenness of an appropriate size for light scattering. For example, in a polymer material, the size of the structure formed by molecules is smaller than the size of the unevenness required to enhance photoelectric conversion, and it is difficult to form appropriate unevenness. Secondly, when the step of making the surface of the base body uneven includes a mechanical process or a wet process, defects are caused by shavings and moisture when the step of forming a photoelectric conversion element thereon is performed. Thirdly, the process of manufacturing the photoelectric conversion device is complicated due to the addition of the process of processing the substrate.

In the latter method of forming the uneven electrode on the flat substrate, the conventional uneven electrode is premised on a hard and thick substrate such as a glass plate, a stainless steel plate or a semiconductor wafer. For this reason, detailed studies have been conducted on the size of the unevenness, that is, the height difference of the ridges and valleys, the distance between the ridges and valleys, but the thickness of the electrode is practically the thickness required to obtain the appropriate ridges and valleys. Most of them were just described. When these concavo-convex electrodes are applied to the flexible substrate, the flexible substrate has a large coefficient of thermal expansion, so that the characteristics of the photoelectric conversion device are deteriorated such as electrode peeling caused by thermal stress during element formation and accompanying short circuit. . Further, when a polymer material is used as the flexible substrate, electrode peeling may occur due to water contained in the polymer material.

The present invention solves the above-mentioned problems, and provides a photoelectric conversion device having a surface shape optimal for light scattering and in which electrode separation does not occur even when a flexible substrate is used, and a manufacturing method thereof. is there.

[0006]

In order to achieve the above object, the present invention comprises a lower electrode layer, a photoelectric conversion semiconductor layer and a transparent upper electrode layer which are sequentially laminated on a flexible and insulating substrate. In the photoelectric conversion device, the surface shape of the lower electrode layer is uneven, and the average thickness thereof is 250 μm or less. When the photoelectric conversion layer is made of an a-Si-based material, it is preferable that the average interval of the uneven peaks of the lower electrode layer surface layer is 150 nm or more and 1000 nm or less, and the height difference between the uneven peaks is 50 nm or more and 150 nm or less. Is good. It is preferable that the substrate-side layer of the lower electrode layer is made of a conductive oxide thin film and the surface layer is made of a metal thin film. In that case, the thickness of the conductive oxide thin film is preferably 30 nm or less. Then, it is effective that the unevenness of the surface shape of the lower electrode layer is the unevenness obtained by the metal thin film. The present invention also provides the above-mentioned method for manufacturing a photoelectric conversion device, which comprises a step of sequentially laminating a lower electrode layer, a photoelectric conversion layer made of an a-Si-based material, and a transparent upper electrode layer on an insulating substrate. A substrate temperature of 30 to form at least the surface layer of the lower electrode layer.
A step of forming a metal thin film at 0 ° C. or higher and 450 ° C. or lower is included.

[0007]

The magnitude of the thermal stress, which is a factor of the characteristic deterioration of the photoelectric conversion device using the flexible substrate, depends on the thermal expansion coefficient and the film thickness of the material used. By lowering the average thickness of the lower electrode having a concavo-convex surface shape, which has been conventionally several hundreds nm or several μm, to 250 nm or less, stress is relieved and deterioration of characteristics of the photoelectric conversion device using the flexible substrate is suppressed. . The average interval of the uneven peaks on the surface of the lower electrode layer is 1 of the wavelength of the incident light.
It is known that // 2 effectively works for light scattering. Therefore, when the photoelectric conversion layer is made of an a-Si material, the a-Si material absorbs 300 nm to 200 nm.
It is effective to adjust the average spacing of the peaks to 150 nm or more and 1000 nm or less, which is ½ of the wavelength of 0 nm. Also,
It is also known that the unevenness of the unevenness on the surface of the lower electrode layer regulates the lower limit of the wavelength of light that can scatter light. Therefore, when the photoelectric conversion layer is made of an a-Si-based material, the peak-valley height difference is adjusted to 150 nm or less, which is 1/2 of 300 nm. However, if the thickness is less than 50 nm, the effect of light scattering is lost, so the thickness is set to 50 nm or more. Such surface shapes can be obtained by forming at least the surface layer from a metal thin film formed at a substrate temperature of 300 ° C. or higher and 450 ° C. or lower. When a polymer material is used as the flexible substrate, the presence of the conductive oxide thin film on the substrate has an effect of absorbing moisture contained in the polymer material and preventing the metal thin film from being affected. However, if this conductive oxide becomes thick, the flexibility of the substrate may be impaired, stress may be generated between the substrate and the film, and the film may be separated from the metal thin film. Therefore, it is set to 30 nm or less.

[0008]

EXAMPLE FIG. 1 is a sectional view of a solar cell according to an example of the present invention. Insulating and flexible substrate 1 having a thickness of 5
A 0 μm polyimide sheet was used. The base may be any as long as it has similar insulating properties and flexibility, and other insulating plastic films such as PES, PEN, PET, and aramid can be considered. On this board 2.
A conductive layer was formed by DC sputtering of Ag in an Ar gas of 0 × 10 ⁻³ Torr to form an electrode layer 2. Electrode layer 2
ZnO on the surface of the substrate 1 before the sputtering of the substrate temperature 200 ℃
It is also possible to deposit water to a thickness of about 30 nm by the RF sputtering method and absorb moisture from the plastic film. This electrode layer 2 is used as a lower electrode, and R is formed on the lower electrode.
Using a plasma CVD method (chemical vapor deposition method) with F glow discharge, SiH ₄ , H ₂ , and PH ₄ are used as reaction gases, and the n-type a-Si layer 3, SiH ₄ , and H ₂ are used as reaction gases, and i-type a -Si layer 4, SiH ₄ , CO ₂ , H ₂ as reaction gas, i-quality microcrystalline SiO (hereinafter referred to as μ-SiO)) layer 5, SiH ₄ , CO ₂ , H ₂ , B ₂ H ₆ as reaction gas After that, a p-type μ-SiO layer 6 was sequentially deposited, and then ITO (indium tin oxide) was deposited by RF sputtering to form a transparent upper electrode layer 7.

The SEM of the surface of the electrode layer 2 when the substrate temperature during Ag sputtering for forming the electrode layer 2 was changed in the range of 200 to 400 ° C. and the average film thickness was changed in the range of 100 to 600 μm ( A photograph taken by a scanning electron microscope) is shown in FIG. As described above, it was found that the surface shape can be controlled by the formation temperature and the film thickness, and that the electrode having the uneven surface 8 as schematically shown in FIG. 1 can be formed even at an average film thickness of 100 nm at 300 ° C. to 400 ° C. Therefore, the film formation temperature of the electrode layer 2 is fixed at 400 ° C., and the average film thickness is 100 nm to 600 n.
By changing to m, 20 solar cells each having the structure shown in FIG. 1 were manufactured by the following method. FIG. 2 shows the proportion of the solar cells that were not short-circuited. Thus, it was found that the average film thickness is 250 nm or less, preferably about 100 nm in order to obtain a high yield. In addition, the spectral sensitivity (100 mW / cm ² , AM of a solar cell using a flat electrode having an average film thickness of 100 nm and a small unevenness formed at a substrate temperature of 200 ° C. and an uneven electrode formed at a temperature of 400 ° C. (100 mW / cm ² , AM
(1.5) is shown in FIG. 4 by a dotted line 41 and a solid line 42, respectively. In the case of using the uneven electrode, the spectral sensitivity is increased in the wavelength range of 600 to 750 nm, and the solar cell characteristics are improved as shown in Table 1 due to the increase in the short-circuit current.

[0010]

[Table 1] Since the unevenness of the electrode surface has an average interval of peaks that is about ½ of the wavelength of incident light, which is effective for light scattering, for example, the wavelength 55 at which the collection efficiency of a-Si is the highest.
It can be seen from FIG. 3 that the average spacing of peaks near 275 nm, which is 1/2 of 0 nm, is obtained when the substrate temperature is 300 ° C. or higher even when the average film thickness is 250 μm or less. However, due to the heat resistance of the flexible substrate, the maximum substrate temperature can be suppressed to 450 ° C.

[0011]

According to the present invention, by setting the average thickness of the lower electrode having the uneven surface shape on the substrate of the photoelectric conversion device to be 250 nm or less, which is thinner than the conventional one, the thermal stress can be obtained even on the flexible substrate. It has been possible to realize a photoelectric conversion device exhibiting improved characteristics due to the light scattering effect without causing characteristic deterioration such as electrode peeling or short circuit caused thereby. In addition, a metal thin film is formed on a flexible substrate at a base temperature of 300 ° C. or higher and 450 ° C. or lower, which is an industrially realistic and simple method.
It has become possible to actually form a concavo-convex electrode having a light scattering effect even when the average thickness is 250 nm or less. That is, a photoelectric conversion device having an uneven electrode on a flexible substrate has been put into practical use.

[Brief description of drawings]

FIG. 1 is a sectional view of a solar cell according to an embodiment of the present invention.

FIG. 2 is a relationship diagram between the yield of solar cells and the average film thickness of the lower electrode.

FIG. 3 is a photograph showing the surface metallographic structure of an electrode formed by changing the substrate temperature and the film thickness.

FIG. 4 is a spectral sensitivity characteristic diagram of solar cells of Examples and Comparative Examples of the present invention.

[Explanation of symbols]

 1 substrate 2 lower electrode layer 3 n-type a-Si layer 4 i-type a-Si layer 5 i-type μ-SiO layer 6 p-type μ-SiO layer 7 transparent electrode layer 8 uneven surface

Claims (7)

[Claims] 1. A photoelectric conversion device in which a lower electrode layer, a photoelectric conversion semiconductor layer, and a transparent upper electrode layer are sequentially laminated on a flexible and insulating substrate, and the surface shape of the lower electrode layer is uneven. A photoelectric conversion device having an average thickness of 250 μm or less. 2. The photoelectric conversion layer is made of an amorphous silicon-based material, and the average interval of the uneven peaks on the surface of the lower electrode layer is 15.
The photoelectric conversion device according to claim 1, which is 0 nm or more and 1000 nm or less. 3. The photoelectric conversion layer is made of an amorphous silicon material, and the height difference between the peaks and valleys of the irregularities on the surface of the lower electrode layer is 50.
The photoelectric conversion device according to claim 1 or 2, wherein the photoelectric conversion device has a wavelength of not less than 150 nm and not more than 150 nm. 4. The photoelectric conversion device according to claim 1, wherein the layer of the lower electrode layer on the substrate side is made of a conductive oxide thin film, and the surface layer is made of a metal thin film. 5. The photoelectric conversion device according to claim 4, wherein the conductive oxide thin film has a thickness of 30 nm or less. 6. The photoelectric conversion device according to claim 4, wherein the unevenness of the surface shape of the lower electrode layer is unevenness obtained by a metal thin film. 7. The method according to claim 1, further comprising a step of sequentially laminating a lower electrode layer, a photoelectric conversion layer made of an amorphous silicon material and a transparent upper electrode layer on a flexible and insulating substrate. In the method for manufacturing a photoelectric conversion device described, in order to form at least the surface layer of the lower electrode layer,
A method of manufacturing a photoelectric conversion device, comprising a step of forming a metal thin film at a substrate temperature of 300 ° C. or higher and 450 ° C. or lower.