Method of producing zinc oxide thin film, method of producing photovoltaic device and method of producing semiconductor device

Abstract

The present invention provides a method of producing a zinc oxide thin film in which a current is passed between a conductive substrate immersed in an aqueous solution containing at least zinc ions, ammonium ions and zinc ammonia complex ions, and an electrode as an anode immersed in the aqueous solution to form a zinc oxide thin film on the conductive substrate. This method stabilizes formation of the zinc oxide thin film and improves adhesion between the thin film and the substrate.

Description

BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to a method of producing a zinc oxide thin film, a method of producing a photovoltaic device, and a method of producing a semiconductor device substrate. [0003] 2. Description of the Related Art [0004] In a conventional photovoltaic device comprising amorphous silicon hydride, amorphous silicon germanium hydride, amorphous silicon carbide hydride, microcrystalline silicon or polycrystalline silicon, a reflecting layer formed on the back thereof is utilized for improving a collection efficient at long wavelengths. Such a reflecting layer preferably exhibits effective reflection properties at a wavelength near the band ends of a semiconductor material at which absorption is low, i.e., a wavelength of 800 to 1200 nm. Materials satisfying this condition include metals such as gold, silver, copper and aluminum. [0005] Also, an uneven layer optically transparent in the predetermined wavelengt...

AI Technical Summary

Benefits of technology

The present invention provides a method for producing a high-quality zinc oxide thin film by electrodeposition, which can be used in photovoltaic devices. The method allows for stable formation of a zinc oxide layer with an uneven surface that can effectively exhibit light confinement or scattering for light at wavelengths of 600 to 1000 nm. The method is cost-effective and can be carried out using existing equipment. The resulting zinc oxide thin film has excellent adhesion to the substrate and can be easily produced on a conductive substrate with a transparent conductive layer. The method can be controlled to control the hydrogen ion concentration of the aqueous solution and the conductive substrate. The resulting photovoltaic device has high quality and low power cost.

Problems solved by technology

Although conventional known methods of producing a zinc oxide thin film include a vacuum deposition method, a sputtering method, an ion plating method, and a CVD method, all methods require an expensive vacuum apparatus, and an expensive vaporization source.

Also the light confinement effect at wavelengths of 600 to 1000 nm is insufficient.

However, in these wet methods, a substrate must be heated to about 300 to 800° C., and thus substrates which can be used are limited.

Also, zinc hydroxide is contained in the thin film together with zinc oxide, and it is thus difficult to form a pure zinc oxide thin film.

In these methods, since an expensive vacuum apparatus and expensive target are unnecessary, the production cost of a zinc oxide thin film can significantly be decreased.

However, the electrochemical deposition methods have the following problems:

(1) Particularly, an increase in current density or concentration of the solution causes the problem of easily producing abnormal growth of a needle-like, spherical, resin-like shape of the micron order or more on the deposited thin film.

The use of such a zinc oxide thin film as a part of a photovoltaic device possibly causes the abnormal growth to induce a shunt path in the photovoltaic device.

(2) In the zinc oxide thin film formed by one of the above methods, unevenness easily occurs in the grain sizes of zinc oxide crystals, and particularly, the problem of unevenness occurs in the case of a large area.

Conventionally, only smooth thin films are formed by the electrochemical deposition methods, and a method of electrochemically depositing a zinc oxide thin film having unevenness for the light confinement effect has not been established yet.

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