One might imagine a monolithic dual-purpose self-regulating photoelectrochemical device comprised of a multijunction tandem solar cell, electrolytic cell, and power sharing circuitry. The tandem cell structure at illumination will be efficient inherently by using several different gaps. Its series structure will give an open-circuit voltage larger than that necessary to decompose water. The excess photovoltage with respect to water splitting can be diverted to an external load. The cell will generate primarily electric power under heavy load (small load resistance) and will generate primarily hydrogen gas at light load (high load resistance). The structure might be built up as a CIGS cell on aluminum foil, with, for example, a tungsten trioxide blue light cell deposited on top. The upper surface of the tungsten trioxide cell could be metallized with a transparent electrode, and fed through a load resistor to a second aluminum foil below the original aluminum foil, the interspace between the two foils being filled with water to be electrolyzed.
9.4
