Investigation of the role of TiO2 underlayer in the anodic potential shift of the onset potential in hematite photoanode

Abstract

We fabricated hematite (α-Fe₂O₃)-based photoanodes with TiO₂ underlayer to reveal the origin of the unexpected anodic shift of the onset potential. We demonstrated that, particularly at the relatively low applied bias voltage, the TiO₂ underlayer played a significant role in Fermi level pinning, resulting in the reduction of the photovoltage. The back recombination between the long-lived holes surviving at the surface of α-Fe₂O₃ and the free electrons in the conductive substrate was retarded in the presence of the TiO₂ underlayer, implying that it acted as a blocking layer, but the trap-mediated recombination could be accelerated, resulting in the reduction of the photocurrent at the low applied bias condition.