A tandem cell or photoelectrochemical system for the cleavage of water to hydrogen
and oxygen by visible light has two superimposed photocells, both cells being connected
electrically. The photoactive material in the top cell is a semiconducting oxide
placed in contact with an aqueous solution. This semiconducting oxide absorbs the
blue and green part of the solar emission spectrum of a light source or light sources
and generates with the energy collected oxygen and protons from water. The not
absorbed yellow and red light transmits the top cell and enters a second photocell,
the bottom cell, which is mounted, in the direction of the light behind, preferably
directly behind the top cell. The bottom cell includes a dye-sensitized mesoporous
photovoltaic film. The bottom cell converts the yellow, red and near infrared portion
of the sunlight to drive the reduction of the protons, which are produced in the
top cell during the photo catalytic water oxidation process, to hydrogen.