JP2815688B2 - Manufacturing method of thin film solar cell - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a photoelectric conversion layer whose main material is amorphous silicon (hereinafter abbreviated as a-Si). The present invention relates to a method for manufacturing a thin-film solar cell that generates an electromotive force.

[Conventional technology]

An amorphous silicon thin film formed by glow discharge decomposition or photolysis of monosilane gas or the like can be easily formed into a large area because it is obtained by a vapor phase growth method, and is used for a photoelectric conversion layer of a low-cost solar cell. In order to improve the efficiency of such a solar cell, it is desirable that the amount of light incident on the photoelectric conversion layer be large. For this purpose, a back electrode provided on the side opposite to the light incident side of the photoelectric conversion layer is formed of a metal having a high reflectance, and the reflection on the electrode surface is used.
However, when a metal used for the back electrode, for example, an alloy of silver and silicon is formed at the interface between the a-Si layer and the back electrode, the reflection characteristics are deteriorated because the alloy layer has low transparency. FIG. 2 shows an a-Si solar cell described in Japanese Patent Application Laid-Open No. 55-108780, in which an a-Si solar cell is formed on a glass substrate 1 via a transparent electrode 2 provided with a collecting electrode 3 at the edge. The alloying is suppressed by interposing the transparent conductive layer 6 between the Si photoelectric conversion layer 4 and the silver electrode 5 and separating the a-Si layer and the silver electrode sufficiently. The a-Si layer 4 and the silver electrode 5 are separated to such an extent that alloying does not occur. However, in order to make the light reflected by the silver electrode incident on the a-Si layer and not to increase the series resistance component of the solar cell, an intervening layer is formed. No. 6 needed to be transparent and conductive.

[Problems to be solved by the invention]

Forming the transparent conductive layer 6 not only on the light incident side of the s-Si layer but also on the opposite side requires an increase in material costs and the addition of expensive equipment such as a vapor deposition apparatus or a sputtering apparatus. There was a problem that the manufacturing cost of the battery was increased. Further, in order to prevent the a-Si layer 4 from being deteriorated by heat, the transparent conductive layer 6 must be formed at a relatively low temperature of 200 ° C. or less, and it is difficult to form a high-quality film with high transparency. there were.

An object of the present invention is to provide a method of manufacturing a thin-film solar cell which addresses the above-mentioned problem and prevents alloying of a-Si and a metal of a back electrode without interposing a transparent conductive layer.

[Means for solving the problem]

In order to achieve the above object, according to the present invention, a photoelectric conversion layer containing amorphous silicon as a main material is laminated on a transparent insulating substrate via a transparent electrode made of a transparent conductive film, and then oxidized. Heat treatment at a temperature of 100 to 200 ° C. in a neutral atmosphere to form a silicon oxide layer having a thickness of 10 to 30 ° on the surface of the photoelectric conversion layer, and further provide a back electrode made of metal thereon. Alternatively, a photoelectric conversion layer mainly composed of amorphous silicon is laminated on a transparent insulating substrate via a transparent electrode made of a transparent conductive film, and then the discharge is generated in an oxidizing atmosphere to form the photoelectric conversion layer. A silicon oxide layer having a thickness of 10 to 30 mm is formed on the surface of the substrate, and a back electrode made of metal is further provided thereon.

[Action]

Since the silicon oxide film is interposed between the photoelectric conversion layer and the back surface electrode, the alloy of the metal of the back surface electrode and a-Si does not occur, and the reflection characteristics are improved. The silicon oxide film is translucent and insulative, but has a very thin thickness of 10 to 30 °, so that the series resistance component does not increase. Further 100-200
Since the a-Si layer can be formed by heat treatment at a low temperature of ° C. or only by generation of electric discharge, the a-Si layer does not deteriorate by heat.

〔Example〕

FIG. 1 shows a cross-sectional structure of a thin-film solar cell manufactured by a method for manufacturing a thin-film solar cell according to one embodiment of the present invention.
Parts common to the drawings are denoted by the same reference numerals. This solar cell was manufactured as follows. First, the glass substrate 1
A transparent conductive film was deposited or sputter-formed thereon to form a transparent electrode 2, and a photoelectric conversion layer 4 having a pin junction was formed thereon using an a-Si or a-SiC thin film. Next, it was placed in an oven and heat-treated in air. The substrate temperature during the heat treatment was 100 to 200 ° C., and the processing time was 5 to 100 hours. Then, the current collecting electrode 3 on the edge of the silver back electrode 5 and the transparent electrode 2 was formed. This a-Si
The short-circuit current density of the solar cell changes as shown in FIG. 3 depending on the heat treatment time in air. The parameter is the substrate temperature. At a substrate temperature of 100 to 200 ° C., the short-circuit current density increases as the heat treatment time increases. The increase in short circuit current density is at most 1.6 mA / cm ² . When the same heat treatment was performed in a nitrogen atmosphere, no increase in short-circuit current density was observed. From the above, it is considered that the increase in the short-circuit current density when the heat treatment is performed in the air is due to the formation of the silicon oxide layer 7 on the surface of the photoelectric conversion layer 4.

FIG. 4 shows the current / voltage characteristics of the a-Si solar cell having the oxide layer 7 formed thereon and the a-Si solar cell having no oxide layer formed thereon by heat treatment at 150 ° C. for 100 hours. Show. The conversion efficiency when the silicon oxide layer was not formed was 11.6%, whereas the conversion efficiency was improved to 12.4% by forming the silicon oxide layer 7.

The silicon oxide layer 7 formed according to the present invention is an insulator. Therefore, the film thickness is limited to a range that does not increase the series resistance of the solar cell, that is, about 10 to 30 ° at which current flows by tunneling. As shown in FIG. 2, this film thickness is much thinner than the transparent conductive layer 6 conventionally provided to prevent alloying of a-Si and Ag. As described above, the silicon oxide layer used in the present invention is completely different in conductivity and film thickness from the conventional transparent conductive layer.

Next, another embodiment for forming the silicon oxide layer 7 will be described. The substrate formed up to the a-Si layer 4 in FIG. 1 is mounted on one electrode of a capacitively coupled vacuum reaction chamber.
After evacuation, oxygen gas is introduced and the pressure is maintained at 0.2-1 torr. Thereafter, a discharge is generated by applying a voltage between the electrodes to form an oxide film with a thickness of 10 to 30 mm. FIG. 5 shows current / voltage characteristics of the a-Si solar cell with and without the oxide film formed by this method by lines 51 and 52, respectively. The formation of the oxide film improved the short-circuit current by 1.6 mA / cm ² . As a result, the conversion efficiency is 11.6%
From 12.1%.

〔The invention's effect〕

According to the present invention, it is possible to improve the reflectance of the back electrode without using a special material such as SnO ₂ or ITO by merely changing the surface after forming a photoelectric conversion layer containing a-Si as a main material. That is, the current of the thin-film solar cell can be increased. Further, according to the present invention, the amount of light incident on the photoelectric conversion layer of the thin-film solar cell can be increased without using an expensive device such as a vapor deposition device or a sputtering device, and the characteristics can be improved.

For the above reasons, according to the present invention, a thin-film solar cell with high efficiency can be manufactured at lower cost than the conventional method.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an a-Si solar cell manufactured by a method of manufacturing a thin-film solar cell according to one embodiment of the present invention, FIG. 2 is a cross-sectional view of a known a-Si solar cell, and FIG. FIG. 4 is a graph showing the relationship between the substrate heat treatment time and the short-circuit current density during the manufacturing process according to the present invention, using the substrate temperature as a parameter. 5 is a current-voltage characteristic diagram of an a-Si solar cell, and FIG. 5 is a current-voltage characteristic diagram of an a-Si solar cell with and without a silicon oxide layer according to another embodiment of the present invention. is there. 1: glass substrate, 2: transparent electrode, 4: photoelectric conversion layer, 5: back electrode, 7: silicon oxide layer.

Claims (2)

(57) [Claims] 1. A photoelectric conversion layer mainly composed of amorphous silicon is laminated on a transparent insulating substrate via a transparent electrode made of a transparent conductive film, and then a temperature of 100 to 200 ° C. in an oxidizing atmosphere. Forming a silicon oxide layer having a thickness of 10 to 30 mm on the surface of the photoelectric conversion layer, and further providing a back electrode made of a metal on the silicon oxide layer. 2. A photoelectric conversion layer mainly composed of amorphous silicon is laminated on a transparent insulating substrate via a transparent electrode made of a transparent conductive film, and then a discharge is generated in an oxidizing atmosphere. A method for manufacturing a thin-film solar cell, comprising: forming a silicon oxide layer having a thickness of 10 to 30 mm on a surface of a photoelectric conversion layer, and further providing a back electrode made of metal thereon.