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 (D_it). A high electron concentration (over 1.2 × 10²⁰ cm⁻³) with high D_it (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 D_it 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.