Numerical modeling investigations of the impact of a thin p-type cocatalyst modifier on an n-type photon absorber for unbiased overall solar water splitting

Abstract

Surface modifications of semiconductor photoelectrodes are often introduced to enhance charge separation and reaction kinetics during solar-driven water splitting. Examples include the formation of n–n heterojunctions and the deposition of electrocatalyst layers. The internal electric field in a p–n junction is expected to be stronger than that in an n–n junction, and several studies have used p-type semiconducting electrocatalyst decoration to improve the overall performance of water splitting. However, a design guideline for the p-type modification layer has not been clearly reported. Therefore, we numerically investigated the impact of a thin p-type modification layer on the photoelectrochemical performance of an n-type photoanode. The key parameters were varied in simulations, including the band position, dopant densities, thickness of the p-type layer, and the dopant densities in the n-type region. Our numerical simulations show that the depletion depths in the p-type modification layer and n-type photon absorber are the key characteristics that need to be tuned, which is mainly achieved by controlling the dopant densities. This work also discusses the critical distinction of a p–n heterojunction compared to an n–n heterojunction photoanode.