1. Field of the Invention
The present invention relates to a photoelectric conversion device that converts optical energy to electric energy and has a multiterminal structure.
2. Description of the Related Art
A photoelectric conversion device with the use of a semiconductor junction, such as a solar cell can be classified into a single junction type which has one semiconductor junction and a multi junction type which has a plurality of semiconductor junctions. A multi-junction photoelectric conversion device in which a plurality of semiconductor junctions whose band gaps are different from each other are arranged so as to overlap with each other in a direction of travel of light can convert sunlight including light with a wide wavelength range from ultraviolet rays to infrared rays into electrical energy with higher conversion efficiency without waste.
Note that when a multi-junction photoelectric conversion device has a two-terminal structure where stacked photoelectric conversion elements are connected in series, current flowing through all of the photoelectric conversion elements is determined in accordance with the photoelectric conversion element with the lowest short-circuit current. Thus, in the case where the photoelectric conversion elements have voltage-current characteristics different from each other, it is difficult to drive all of the photoelectric conversion elements at the respective maximum output points, at which the maximum output voltages can be output. On the other hand, even in the case of using a multi-junction photoelectric conversion device, when the multi-junction photoelectric conversion device has a multiterminal structure in which electric power is taken out from each of the photoelectric conversion elements that are not connected in series, each of the photoelectric conversion elements can be driven at the maximum output points. Accordingly, the multiterminal structure can achieve high photoelectric conversion efficiency of the whole photoelectric conversion device in comparison with the two-terminal structure.
Patent Document 1 discloses a power supply device in which a plurality of photoelectric conversion elements with different output characteristics from each other are stacked and the plurality of photoelectric conversion elements are connected in parallel through respective voltage regulator circuits.