1. Field of the Invention
The invention relates to a method for measuring current-voltage “I-V” characteristics of a solar cell, and a solar cell.
2. Description of Related Art
Solar cells have been expected to be a new energy source, since the solar cells can directly convert clean and inexhaustibly supplied solar energy into electric energy.
In a manufacturing process of a solar cell, I-V characteristics of the solar cell are measured by the so-called four terminal measurement method (for example, see Japanese Patent Application Publication No. 2006-118983). Here, the four terminal measurement method is a measurement method using a plurality of probe pins for current measurement and one probe pin for voltage measurement, which contact with a collecting electrode, in each of a light receiving surface and a rear surface of the solar cell. Specifically, a relationship between current and voltage, when the voltage applied to the solar cell is swept is measured while the light receiving surface is irradiated with artificial sunlight. Thereby, the I-V characteristics of the solar cell are measured.
Here, the solar cell includes a plurality of fine line-shaped electrodes and a connection electrode intersecting the plurality of fine line-shaped electrodes as the collecting electrode on the light receiving surface. The connection electrode is an electrode for connecting a wiring member that connects solar cells to each other, and is formed wide. In such a solar cell, when the I-V characteristics are measured by the four terminal measurement method, what has to be done for performing the measurement is only to connect the plurality of probe pins for current measurement and the one probe pin for voltage measurement with the connection electrode.
Note that, the surface of the connection electrode becomes an equipotential surface by a voltage applied by the one probe pin for voltage measurement, and the probe pins for current measurement contacting the surface of the connection electrode are short-circuited to each other.
Conventionally, a proposal has been made of a first solar cell having only a plurality of fine line-shaped electrodes formed on a light receiving surface as a collecting electrode, and a second solar cell having a plurality of fine line-shaped electrodes and a coupling line formed on a light receiving surface, the coupling line having a thin line form and configured to couple the fine line-shaped electrodes to each other (see Internal Patent Application Publication No. WO 2008/023795). With such a solar cell, manufacturing cost of the solar cell can be reduced, because it is not necessary to form a wide connection electrode.
However, in the first solar cell, the fine line-shaped electrodes are not electrically connected to each other. Accordingly, even if one probe pin for voltage measurement applies the voltage to one fine line-shaped electrode, the surfaces of all of the fine line-shaped electrodes do not become equipotential surfaces.
Moreover, in a second solar cell, the coupling line has a thin line form, and electric resistance is large. For that reason, a potential difference is generated between the probe pin for voltage measurement and each of the probe pins for current measurement. As a result, there has been a problem that accuracy in measurement of the I-V characteristics of the solar cell is reduced.
The invention has been made in consideration of the circumstances mentioned above. An object of the invention is to provide a method for measuring I-V characteristics of a solar cell and a solar cell that can improve accuracy of measurement.