PHOTOELECTROCHEMICAL CELL AND ENERGY SYSTEM USING SAME

A photoelectrochemical cell (100) includes: a semiconductor electrode (120) including a conductor (121), a first n-type semiconductor layer (122) having a nanotube array structure, and a second n-type semiconductor layer (123); a counter electrode (130) connected to the conductor (121); an electrolyte (140) in contact with the second n-type semiconductor layer (123) and the counter electrode (130); and a container (110) accommodating the semiconductor electrode (120), the counter electrode (130) and the electrolyte (140). Relative to a vacuum level, (I) band edge levels of a conduction band and a valence band in the second n-type semiconductor layer (123), respectively, are higher than band edge levels of a conduction band and a valence band in the first n-type semiconductor layer(122), (II) a Fermi level of the first n-type semiconductor layer (122) is higher than a Fermi level of the second n-type semiconductor layer (123), and (III) a Fermi level of the conductor (121) is higher than the Fermi level of the first n-type semiconductor layer (122).