Semiconductor Electrodes: LVI . Principles of Multijunction Electrodes and Photoelectrosynthesis at Texas Instruments' p/n‐Si Solar Arrays

In photoelectrochemical (PEC) cells based on single junctions of semiconductors with solutions or metals, photopotentials are rarely above 0.6–0.8V. The higher photovoltages needed to drive more energetic reactions require multijunction cells involving multilayer electrodes or series connection of PEC cells. Such PEC cells are considered, and their behavior is shown to be predicted from the current‐potential (i‐V) behavior at each interface; the sum of the voltage drops at a given current yields the i‐V characteristic of the overall PEC cell. These principles are illustrated with the Texas Instruments arrays based on silicon spheres and Si p/n junctions contacting a solution via a noble metal layer. Reactions considered include generation of with reduction of or the generation of , the photobromination of phenol, and the photochlorination of cyclohexene in acetonitrile.