A new strategy of using forward gradient self-doping to improve the charge separation
efficiency in metal oxide photoelectrodes is proposed. Gradient self-doped CuBi2O4
photocathodes are prepared with forward and reverse gradients in copper vacancies using
a two-step, diffusion-assisted spray pyrolysis process. Decreasing the Cu/Bi ratio of the
CuBi2O4 photocathodes introduces Cu vacancies that increase the carrier (hole)
concentration and lowers the Fermi level, as evidenced by a shift in the flat band toward …