JPS6269408A - Surface roughing of transparent conducting film - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Industrial Application Field The present invention is based on a transparent conductive oxide (TCO) typified by indium tin oxide (ITO), which is SnO, 1nlOs, or a mixture thereof. Regarding the method for roughening a transparent conductive film, the transparent conductive film roughened by this method is used, for example, as a light-receiving surface electrode of a photovoltaic device.

(b) Conventional technology A photovoltaic device in which an amorphous silicon semiconductor layer with a semiconductor junction is used as a photoactive layer is already known. A light-receiving surface electrode layer, a semiconductor photoactive layer, and a back electrode layer are laminated in this order.

In order to improve the photoelectric conversion efficiency of such a photovoltaic device,
Unexamined Japanese Patent Publication No. 58-57756 and the 44th Academic Conference of the Japan Society of Applied Physics (September 25-28, 1980) Proceedings 2
As disclosed in 5P-L-2, page 351, etc., the surface of the light receiving surface M on the light incident side and the pole layer has a thickness of 0.1 μm or more and 2.5 μm.
Attempts have been made to create a rough surface (texture) with the following irregularities to lengthen the optical path length of incident light and to confine it within the photoactive layer.

However, since the surface roughening of the light-receiving surface electrode is carried out during the process of film formation of the light-receiving surface electrode, there is a drawback that it is difficult to provide uniform irregularities.

Further, the surface roughening of the transparent conductive film disclosed in JP-A-59-75678 is carried out by performing etching after forming the transparent conductive film, and this method makes it possible to form uniform irregularities. It is difficult to set up.

(c) Problems to be Solved by the Invention The present invention attempts to solve the above-mentioned problem in which uniform irregularities cannot be easily obtained on the surface of a transparent conductive film.

(2) Means for Solving the Problems The method for roughening the surface of a transparent conductive film of the present invention involves preparing a substrate on which a transparent conductive film of a light-transmitting conductive oxide is disposed on its entire surface, and applying a layer on the transparent conductive film. After scattering island-shaped portions that act as masks during the etching process of the conductive film, and disposing a metal film contributing to the etching operation to a substantially constant thickness on the transparent conductive film including the island-shaped portions, The present invention is characterized in that the transparent conductive film exposed from the island-shaped portion is etched halfway through by causing the metal film to react with an etching solution to roughen the surface.

(e) Operation: Processing of the transparent conductive film as described above; - Prior to the etching process, island-shaped parts that act as masks are scattered on the transparent conductive film, and a metal film that contributes to the etching operation is placed on top of these. By arranging the transparent conductive film at a substantially constant thickness, only the exposed portions of the transparent conductive film exposed from the island-like portions are substantially uniformly etched away.

1 to 4 show the method for roughening the transparent conductive film of the present invention step by step. In the step of FIG. 1, a transparent and insulating substrate (1 ) A transparent conductive film (2) made of TCO such as SnO, Inl's, ITO, etc. is deposited to cover almost the entire main surface of the film by known methods such as electron beam evaporation, sputtering, and thermal CDV. Approximately 1,800 people
About 500 people can be formed.

In the process shown in FIG. 2, a metal oxide such as Cr*Os or TiOs, which acts as a mask during the etching process of the transparent conductive film (2), is etched onto the flat transparent conductive film (2). The island-like portions (3) (3)... are formed in a scattered manner. These island-shaped portions (3) (3)... are formed by reactive vapor deposition or sputtering using a metal body as a source or target in an oxygen atmosphere, and at the early stage of the formation process, the deposited (substrate) Since it is not formed into a film with a constant thickness on the surface but is formed into an island by dissipating in clusters, uniform island-like portions (3), (3), etc. can be easily obtained.

In this example, the island-like portion (3) with a grain size of 200 to 500 people was used as a mask for Cr, O, and Tie.
3)... was produced under the following conditions.

・Cr, O,... Reactive vapor deposition method source 2 Cr atmosphere: O8, 2 X 10-' Torr substrate time 2 300-400°C Vapor deposition time: 2-10 minutes ・TiO*...・Sputtering terquerate: Ti atmosphere: Ar+O, 08 partial pressure 3×10-T
orr or more Substrate temperature - ~200°C Sputtering time: 2 to 10 minutes In the process shown in Fig. 3, the island-like portions (3) (3'')...
The transparent conductive film (2) is coated on the exposed portion of the transparent conductive film (2) containing the transparent conductive film (2).
A metal film (4) contributing to the etching operation of 2) is arranged. For example, the metal film (4) that contributes to the etching operation of the transparent conductive film (2) of the TCO is HCl:H.

Zn reacts with the HCQ of the -1:5 etching solution to generate activated hydrogen for etching, and can be formed to a thickness of approximately several thousand to several micrometers by vapor deposition so that the film thickness is approximately constant.

In the process shown in FIG. 4, the island-shaped portion (3
)<3>... are dotted and a metal film (
An etching solution that contributes to the etching operation of the transparent conductive film (2) by reacting with the metal film (4), such as HCN:H , 0-15, the exposed portions of the transparent conductive film (2) are exposed from the island-like portions (3) (3) and come into direct contact with the metal film (4). is selectively etched and removed by activated hydrogen generated by the reaction between the etching solution and the metal film (4) using the island-shaped portions (3) (3), . . . as an etching-resistant mask.

Furthermore, since the metal film (4) is deposited to a constant thickness by vapor deposition or the like, activated hydrogen can be generated evenly on the contact surface, and uniform surface roughening can be achieved.

By etching the transparent conductive film (2) halfway through its thickness, only the exposed portion of the transparent conductive film (2) is etched away, as shown in FIG. 2) to island-like portions (3) (3)...
The exposed surface is roughened and the height difference is approximately 200 to 2000.
A human textured surface (5) is provided.

On the other hand, in the etching process for a tin-based transparent conductive film (2) such as Snow, the tin cannot be removed by etching using the etching solution for the indium-based transparent conductive film (2). The etching process of the system includes
Zn, which reacts with HCl of the etching solution to generate activated hydrogen, is deposited on the surface to be etched in advance. Therefore, when etching this tin-based transparent conductive film (2), after the step shown in Fig. 2 to form the island-like portions (3) (3)...
Approximately several thousand to several micrometers can be deposited in advance so that the film thickness is almost uniform. With such a deposited Zn film having a substantially constant thickness, active hydrogen can be generated evenly, and the surface can be uniformly roughened.

Note that etching using such a deposited Zn film can also be applied to the indium-based transparent conductive M(2).

FIG. 5 shows the basic structure of a photovoltaic device in which a light-receiving surface electrode is a transparent conductive film (2) provided with an uneven surface (5) by the surface roughening method of the present invention. That is, (1) to (3), (
5) is the already explained substrate ~ uneven surface, and on the back side of the uneven surface (5), there are pins parallel to the film surface inside,
An amorphous silicon-based semiconductor photoactive layer (6) having semiconductor junctions such as pn, pi, pinpin, etc., and an Affi
,Ag,TCO/Aj! .

Pole the back side of a single calendar or laminated structure such as TCO/Ag (7)
and are stacked in this order.

Therefore, the Cr that acted as a mask during the etching process
, O, or Tie, the light-receiving surface side is in contact with the TCO transparent conductive film (2), and the back side is in contact with the amorphous silicon-based semiconductor photoactive layer (6). What should be kept in mind in a photovoltaic device is to guide a large amount of the light necessary for photoelectric conversion operation to the semiconductor photoactive layer (6) that performs photoelectric conversion operation, in other words, to suppress the amount of light reflection on the light receiving surface side. That's true. Looking at the refractive index of a photovoltaic device having the configuration described above, the refractive index of blue plate glass, which is a typical material for the substrate (1), is 1.45 to 1.6, followed by TC.
That of the O transparent conductive film (2) is about 2.0, and the Cr and O3 constituting the island portions (3) (3)...
or Tie, the refractive index of each is approximately 2.5 and approximately 2.6.
It is. On the other hand, the refractive index of the amorphous silicon-based semiconductor photoactive layer (6) that performs photoelectric conversion is approximately 3.4 to 4.0, and therefore, the island-shaped portion acts as a mask during the etching process of the transparent conductive film (2). (3) (3)...A material with a refractive index higher than that of the transparent conductor g(2), that is, TC
Cr*Os or 7 i 0 for O! By selecting , interface reflection caused by a large change in refractive index at the interface can be made extremely small.

(G) Effects of the Invention As is clear from the above explanation, the method for roughening the surface of a transparent conductive film of the present invention is such that the island-shaped portions dotted on the transparent conductive film serve as etching-resistant masks during the etching process of the conductive film. (2) Coupled with the presence of a metal film that contributes to the etching operation and is deposited to a certain thickness, by limiting such etching to the middle of the transparent conductive film,
Only the exposed portions of the transparent conductive film exposed from the island portions are etched away, so that a uniform uneven surface can be easily formed. Furthermore, if a material with a refractive index higher than that of the transparent conductive film is selected for the island-shaped portion, as in the case of a semiconductor photoactive layer of a photovoltaic device, even larger changes can be alleviated and interface reflections can be suppressed. In photovoltaic devices such as the above, the photoelectric conversion efficiency is increased.

[Brief explanation of drawings]

Figures 1 to 4 are enlarged cross-sectional views of main parts showing each step of the surface roughening method of the present invention, and Figure 5 is a photovoltaic device incorporating a transparent conductive film roughened by the surface roughening method of the present invention. FIG. 2 is an enlarged cross-sectional view of the main parts of the device. (1)...Substrate, (2)...Transparent conductive film, (3)...
... Island-shaped portion, (4) ... Metal film, (5) ... Uneven surface.

Claims (4)

[Claims] (1) preparing a substrate on which a transparent conductive film of a light-transmitting conductive oxide is disposed on one principal surface, dotting island-shaped portions on the transparent conductive film to act as a mask during the etching process of the conductive film; After disposing a metal film that contributes to the etching operation to a substantially constant thickness on the transparent conductive film including the island-like portions, the metal film and the etching solution are reacted to remove the transparent conductive film exposed from the island-like portions. A method for roughening a transparent conductive film, characterized in that the conductive film is roughened by etching partway through the conductive film. (2) The method for roughening the surface of a transparent conductive film according to claim 1, wherein the refractive index of the island-shaped portion is larger than the refractive index of the transparent conductive film. (3) The transparent conductive film is Cr_2O_3 or SnO
_2. The method for roughening a transparent conductive film according to claim 2, characterized in that: _2. (4) The method according to claim 1, 2, or 3, wherein the transparent conductive film is a SnO_2-based light-transmitting conductive oxide, and the metal film is a Zn film. Method for roughening transparent conductive film.