Operating the stacked photoanode at the thickness of exciton diffusion length enhances the efficiency of photoelectrochemical water splitting

Abstract

In photoelectrochemical water splitting, every impinging photon should not only be absorbed but also be utilized towards reaction. While increasing photoelectrode thickness in photoelectrochemical reactors facilitates photon absorption, it has a debilitating effect on efficiency if the thickness required for complete photon absorption is much more than the exciton diffusion length, which is a property determined by the material and its processing. To address this issue, we demonstrate a general experimental methodology with a stack of cadmium selenide photoanodes wherein the thickness of each photoelectrode is of the order of exciton 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.