JPH0936406A - Photoelectric converter and production thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a thin film having irregular surface through low temperature formation by a structure wherein a lower electrode layer comprises an upper layer of high reflectance metal having specified average thickness, and a lower metal layer having specified melting point and irregular upper surface. SOLUTION: ZnO 2 is deposited on the surface of a substrate 1 and a low temperature formation metal layer 3 of Al having irregular surface is formed thereon. The Al layer 3 having irregular surface is formed under conditions of substrate temperature in the range of 225-325 deg.C and the thickness in the range of 75-140nm. Subsequently, a high reflectance metal layer 4 of Ag is formed thereon. Total thickness of the lower electrode layer comprising the metal layers 3, 4 is set at 250nm or less and a photoelectric conversion layer 5 is formed on the lower electrode layer. Since a metal having melting point of 700 deg.C or below is employed in the lower layer, a thin film having irregular surface can be obtained by low temperature formation.

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.
Amorphous silicon (hereinafter referred to as a-Si) formed by decomposing by a CVD method or a thermal CVD method
A photoelectric conversion device using a semiconductor thin film whose main component is
It has the characteristic that it can be easily enlarged, and is expected as a low-cost solar cell. In such a photoelectric conversion device, in addition to light that is directly incident on the photoelectric conversion layer formed of a semiconductor thin film through the transparent electrode layer on the upper surface, the light is reflected on 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 described in JP-A-56-
As disclosed in JP-A-152276, JP-A-58-180069, JP-A-1119074, and the like, a method of making the surface of a substrate supporting an electrode uneven, and JP-A-5-
9-61973, JP-A-3-94173, JP-A-3
-99477, JP-A-3-99478, JP-A-4-9947
There has been a method of forming an electrode having irregularities on a flat substrate as described in JP-A-218977 and JP-A-4-334069.

[0003]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
The method disclosed in Japanese Patent No. 069 has a high reflectance without impairing the uneven shape on the light scattering layer made of an alloy of Si and a metal such as Al formed on the substrate and having an uneven shape on the surface. A metal coating made of Cu or Ag is formed. In this case, the thickness of the metal coating is 200 nm or less in order to prevent the characteristics of the photoelectric conversion structure formed thereon from being deteriorated due to diffusion from the metal coating.

However, in order to form a metal or alloy thin film having a certain grain size as the light-scattering layer, it was necessary to raise the film-forming temperature and increase the film thickness to some extent. In particular, when a flexible substrate such as a plastic film is used as the substrate, when the film forming temperature is increased, the electrode layer is thermally stressed due to the contraction of the substrate. In addition, the stress is increased by increasing the film thickness. Due to these stresses, there has been a problem that characteristic deterioration such as electrode peeling and accompanying short circuit occurs.

An object of the present invention is to solve the above-mentioned problems, to provide a photoelectric conversion device having a thin electrode film which can be formed without increasing the film formation temperature, and which has a lower electrode layer having an uneven surface, and a method for manufacturing the same. To provide.

[0006]

To achieve the above object, the present invention provides a photoelectric conversion device in which a lower electrode layer, a photoelectric conversion layer and a transparent upper electrode layer are sequentially laminated on an insulating substrate, The lower electrode layer has an average thickness of 250 nm or less, an upper layer made of a high-reflectance metal, and a lower layer made of a metal having an uneven shape on the upper surface and having a melting point of 700 ° C. or less. The average distance between the peaks of the irregularities on the upper surface of the lower electrode layer is 150 nm or more and 1000 nm.
The following is preferred. The substrate may be made of a polymer material and flexible, and in that case, the layer portion of the lower electrode layer in contact with the substrate may be made of a conductive oxide.
The lower layer of the lower electrode layer is preferably made of Al, and in that case, the thickness of the lower layer is preferably 150 nm or less. The upper layer of the lower electrode layer is preferably made of Ag. In the method for manufacturing a photoelectric conversion device of the present invention in which the lower layer of the lower electrode layer is made of aluminum, the lower layer has a substrate temperature of 2
It is effective to form the film at 25 ° C. to 325 ° C., and it is preferable to form the upper layer of the lower electrode layer at a substrate temperature of 200 ° C. or less.

[0007]

When the lower layer of the lower electrode layer is formed by using a pure metal such as Al having a melting point of 700 ° C. or lower, an uneven shape can be formed on the upper surface with a thin film thickness, and an alloying element that lowers the conductivity is used. No need to add. If an upper layer made of a high-reflectance metal such as Ag is formed thereon, a lower electrode layer having an uneven surface is obtained even if the thickness of the layer is uniform, and the light is incident from the transparent upper electrode layer. Since light is reflected and scattered with high reflectance, photoelectric conversion efficiency is improved. And, the average thickness of the lower electrode layer having the uneven surface shape is 250 n
When the thickness is m or less, the stress is relieved, and in particular, the characteristic deterioration of the photoelectric conversion device using the flexible substrate made of a polymer material is suppressed. It is known that when the average spacing of the peaks of the uneven shape on the surface of the lower electrode layer is 1/2 of the wavelength of incident light, it works effectively for light scattering. Therefore, when the photoelectric conversion layer is made of an a-Si based material, it is 15 which is 1/2 of the wavelength of 300 nm to 2000 nm absorbed by the a-Si based material.
It is effective to adjust the average spacing of the peaks to 0 nm or more and 1000 nm or less. When a polymer material is used for 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. When the lower layer of the lower electrode layer is formed of Al, stable photoelectric conversion characteristics can be obtained when the thickness is 150 nm or less. Then, the substrate temperature during film formation 22
An Al layer having a surface irregular shape is obtained at 5 ° C. or higher. In the conventional method of forming an electrode film at a substrate temperature of 350 ° C. or higher,
Although about 1% of the heat shrinkage of the flexible substrate is observed, in the film formation at the substrate temperature of 325 ° C. or less, the heat shrinkage of the substrate becomes 0.3% or less, which is an unmeasurable level. If the upper layer of Ag or the like is formed at a substrate temperature higher than 200 ° C. after the lower layer of Al is formed, recrystallization of Al occurs and the unevenness of the surface of the Al layer does not remain on the upper layer. Layer formation is 2
It is performed at 00 ° C or lower.

[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. This substrate may be anything 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 the surface of the substrate 1, the substrate temperature is 200 ° C. and the Ar pressure is 1 × 10 ⁻³ Tor.
Approximately 30 nm of ZnO thin film 2 by RF sputtering method at r
Formed to a thickness of ZnO has a function of absorbing moisture from the plastic film. A low temperature forming metal layer 3 having an uneven surface was formed of Al on the ZnO thin film 2, and the following experiment was conducted to determine the film forming conditions.

A SnO ₂ thin film was formed on a glass plate, and four kinds of substrates were deposited by changing the film pressure. A lower electrode was formed of Ag on the substrate, and the i layer had a thickness of 400 nm.
The a-Si photoelectric conversion layer and the transparent electrode layer were laminated to prepare a photoelectric conversion cell. The Ag electrode layer is formed by sputtering (S
P), electron beam evaporation (EB) at 250 ° C. and room temperature (RT). FIG. 2 shows the short circuit current value of each cell thus manufactured. Lines 21, 22, 23, 24
Indicates the type of substrate. As a result, it was found that the cell using the substrate 23 has the best characteristics. The distance between the peaks of the uneven surface of the substrate is about 150 nm.
To about 500 nm with an average spacing of about 200 nm
It is. An Al film having such an uneven shape is formed with a substrate temperature of 225 ° C. to 325 ° C. and a film thickness of 75 nm to 140 n.
It was formed by the film forming condition of m. Next, the high reflectance metal layer 4 made of Ag is laminated. The high reflectance layer 4 needs to have a thickness of about 100 nm or more in order to satisfactorily cover the uneven shape of the lower layer surface, but the total film of the lower electrode layer including the metal layer 3 and the metal layer 4 is required. The thickness is 250 nm or less. The photoelectric conversion layer 5 is formed on this lower electrode layer. In this example, the n-type, i-type, and p-type a-Si layers were sequentially formed by RF glow discharge to form a photoelectric conversion layer. Finally by sputtering, I _n2 O _3: to form a transparent electrode layer 6 of ITO is SnO _2. The reflection on the surface of the transparent electrode layer 6 can be prevented by controlling the film thickness as is well known. FIG. 3 shows the relationship between the manufacturing yield of the photoelectric conversion device manufactured in this manner and the Al film thickness of the low-temperature formed metal layer 3. The Ag film thickness of the highly reflective metal layer 4 was fixed to 100 nm. Defects are mainly caused by short circuits. As shown in the figure, the film thickness of Al was found to be 150 nm or less, preferably 100 nm or less.

FIG. 4 shows a quantum efficiency spectral characteristic of the photoelectric conversion device of the embodiment of the present invention as a dotted line 41 and a quantum efficiency spectral characteristic of the conventional photoelectric conversion device as a solid line 42. A conventional photoelectric conversion device is one in which a lower electrode is formed of Ag only on a flexible substrate via a ZnO thin film, and the film formation temperature of the Ag film is 350 ° C. The other upper structure is the same as that of FIG. As you can see from the comparison of these two curves,
The difference in the spectral sensitivity characteristics in the vicinity of 00 nm to 700 nm is remarkable. The short-circuit current is 16.3 in the conventional photoelectric conversion device.
whereas a mA / cm ^2, in the photoelectric conversion device of Example was 17.65mA / cm ^2.

In the above embodiment, the low temperature forming metal layer 3 is made of A.
1 was used, but a metal having a melting point lower than that of Al, for example, Zn or I
n and the like can also be used. In addition, the high reflectance metal layer 4
Cu can be used in place of Ag.

[0012]

According to the present invention, when the lower electrode layer is divided into an upper layer made of a metal having a high reflectance and a lower layer having an uneven surface, a metal having a melting point of 700 ° C. or less is used for the lower layer. As a result, it was possible to form the surface at a low temperature and obtain an uneven surface with a thin film thickness. As a result, it is not necessary to go through a high temperature process, and it is possible to avoid the factor of yield reduction such as thermal stress. Further, it is not necessary to use an alloy for the lower layer, and it is possible to avoid a decrease in conductivity of the electrode layer. As a result, in particular, it has become possible to simultaneously improve the stability and increase the efficiency of a photoelectric conversion device using a polymer film substrate.

[Brief description of drawings]

FIG. 1 is a sectional view showing a structure of a photoelectric conversion device according to an embodiment of the present invention.

FIG. 2 is a relationship diagram of a short-circuit current of a photoelectric conversion device in which an Ag electrode is formed as a lower electrode on a different glass substrate, the type of substrate, and a film forming method.

FIG. 3 is a relationship diagram of the manufacturing yield of the photoelectric conversion device according to the example of the present invention and the film thickness of an Al lower layer.

FIG. 4 is a quantum efficiency spectral characteristic diagram of photoelectric conversion devices of Examples and Comparative Examples of the present invention.

[Explanation of symbols]

 1 Substrate 2 ZnO Thin Film 3 Low Temperature Forming Metal Layer 4 High Reflectance Metal Layer 5 Photoelectric Conversion Layer 6 Transparent Electrode Layer

Claims (9)

[Claims] 1. A photoelectric conversion device in which a lower electrode layer, a photoelectric conversion layer and a transparent upper electrode layer are sequentially laminated on an insulating substrate, wherein the lower electrode layer has an average thickness of 250 nm or less and high reflectance. A photoelectric conversion device comprising an upper layer made of a metal and a lower layer made of a metal having an uneven shape on the upper surface and having a melting point of 700 ° C. or less. 2. The photoelectric conversion device according to claim 1, wherein the average spacing between peaks of irregularities on the upper surface of the lower layer of the lower electrode layer is 150 nm or more and 1000 nm or less. 3. The photoelectric conversion device according to claim 1, wherein the substrate is made of a polymer material and has flexibility. 4. The photoelectric conversion device according to claim 3, wherein a layer portion of the lower electrode layer in contact with the substrate is made of a conductive oxide. 5. The photoelectric conversion device according to claim 1, wherein the lower layer of the lower electrode layer is made of aluminum. 6. The photoelectric conversion device according to claim 5, wherein the thickness of the lower layer of the lower electrode layer is 150 nm or less. 7. The upper layer of the lower electrode layer is made of silver.
7. The photoelectric conversion device according to any one of 1 to 6. 8. The method for manufacturing a photoelectric conversion device according to claim 5, wherein the lower layer of the lower electrode layer is formed at a substrate temperature of 225 ° C. to 325 ° C. 9. The method for manufacturing a photoelectric conversion device according to claim 8, wherein the upper layer of the lower electrode layer is formed at a substrate temperature of 200 ° C. or lower.