In photoelectrochemical water splitting, every impinging photon should not only be absorbed butalso be utilized towards reaction. While increasing photoelectrode thickness in photoelectrochemical reactorsfacilitates photon absorption, it has a debilitating effect on efficiency if the thickness required for completephoton absorption is much more than the exciton diffusion length, which is a property determined by thematerial and its processing. To address this issue, we demonstrate a general experimental methodology with astack of cadmium selenide photoanodes wherein the thickness of each photoelectrode is of the order ofexciton diffusion length and which improves overall photocurrent by about 50%.

Stacked-photo anodes for photoelectrochemical water splitting reaction with each anode having thickness ~ exciton diffusion length. The fraction of light transmitted from the previous anode oxidizes water into O₂ and H⁺. The sum of the thickness of photoanodes is sufficient to absorb all incident light.