In general, a solar battery device includes a configuration shown in FIG. 1. In FIG. 1, the reference numeral 1 represents a p-type semiconductor substrate formed in a plate-like shape, and having a size ranging from 100 to 150 mm square and a thickness ranging from 0.1 to 0.3 mm. The p-type semiconductor substrate herein includes a polycrystalline or monocrystalline silicon and the like and is doped with a p-type impurity such as boron and the like. A manufacturing method for the solar battery device will be hereinafter described. First, this substrate is doped with an n-type impurity such as phosphorus and the like to form an n-type diffusion layer 2. Next, an antireflection film 3 such as silicon nitride (SiN) and the like is provided. Then, a conductive aluminum paste is printed on a backside of the substrate by a screen printing method. Thereafter, by drying and firing the conductive aluminum paste, a backside electrode 6 and a BSF (Back Surface Field) layer 4 are formed simultaneously. Successively, a conductive silver paste is printed on a front-side of the substrate. Then, the conductive silver paste is dried and fired to form front-side electrodes 5. With regard to the solar battery device manufactured in such a manner, the front-side electrodes 5 include busbar electrodes and current-collecting finger electrodes. The busbar electrodes are for taking out light-generating current generated by the solar battery device to the outside thereof. The current-collecting finger electrodes are connected to these busbar electrodes. Hereinafter, while a surface of the substrate which is to be a light receiving surface side of the solar battery is referred to as a front-side, a surface of the substrate which is to be the opposite side of the light receiving surface is referred to as a backside.
With regard to the solar battery device manufactured in such a manner, the electrodes are generally formed by the screen printing method and firing as mentioned above. In the screen printing method, in order to form the finger electrodes and the busbar electrodes on the light receiving surface of the solar battery cell, for example, a conductive paste containing a silver powder, an organic vehicle, and a glass frit is generally used. Solids of various types of inorganic oxides or conductive materials and the like may be added to this conductive paste to improve performance thereof. When applying this conductive paste to a predetermined position of the semiconductor substrate by the screen printing method and firing the paste, the silver powder sinters each other under high-temperature to form silver electrodes. At the same time, the glass frit is softened to melt the antireflection film and reach the n-type diffusion layer, and the silver electrodes are electrically connected to the n-type diffusion layer. In general, such a method is called Fire Through, which is adopted as a method for forming electrodes of various solar battery cells.
With regard to the aforementioned method for forming electrodes, in order to fire the electrodes, the semiconductor substrate should be subjected to high-temperature treatment at 600° C. or more. Due to this high-temperature treatment, the semiconductor substrate is damaged by heat. Alternately, a contaminant which is a lifetime killer gettering upon the diffusion layer may be released inside the semiconductor substrate, which decreases a lifetime of the semiconductor substrate. Furthermore, the electrodes formed by Fire Through are obtained by sintering the conductive particle for a short time. Therefore, the following electrodes may be easily formed, which is a problem. That is, electrodes which have small density compared to electrodes formed by plating and have plenty cavities in front-sides or insides of the electrodes, and each area of those electrodes connected to the semiconductor substrate is not uniform and is easily peeled off, for example. Such a decrease in the lifetime and abnormality in the electrodes may cause problems in performance or long-term reliability of the solar battery cell so that solutions to these problems are demanded.
In order to solve the problems, for example, Patent Document 1 discloses a method where a solar battery cell formed by firing electrodes is subjected to heat treatment under an atmosphere including at least hydrogen gas to improve contact resistance of the electrodes. However, in the method disclosed in Patent Document 1, a process is added after firing, which leads to increase costs. Furthermore, there is a problem in safety of the process since hydrogen gas, which is difficult to handle, is used. Therefore, a much simpler method to solve the problems is demanded.