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

Hematite (alpha-Fe2O3) is an intensively studied photoanode for water splitting. However, the solar-hydrogen efficiency of an alpha-Fe2O3 photoanode remains limited because of its low conductivity and high surface recombination rate that limit its photocurrent output. In this work, hematite (alpha-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 x 10(20) cm(-3)) with high D-it (1.4 x 10(16) 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 x 10(19) cm(-3) and 8.8 x 10(14) cm(-2) eV(-1). This result has also been interpreted with the variation of the alpha-Fe2O3-electrolyte band diagram with the bias potential.