Effect of bulk doping and surface-trapped states on water splitting with hematite photoanodes

Abstract

Hematite (α-Fe2O3) is an intensively studied photoanode for water splitting. However, the solar-hydrogen efficiency of an α-Fe2O3 photoanode remains limited because of its low conductivity and high surface recombination rate that limit its photocurrent output. In this work, hematite (α-Fe2O3) photoanodes prepared by electroplating were investigated for their majority and minority carrier concentration and surface-trapped states. The results show that the photocurrent generation strongly depends both on the bulk doping and the interface density of states (Dit). A high electron concentration (over 1.2 × 1020 cm−3) with high Dit (1.4 × 1016 cm−2 eV−1) may jeopardize the water splitting, with negligible photocurrent output under AM1.5 illumination. In contrast, a photocurrent is detected when the electron concentration and Dit is lower than 6.1 × 1019 cm−3 and 8.8 × 1014 cm−2 eV−1. This result has also been interpreted with the variation of the α-Fe2O3–electrolyte band diagram with the bias potential.