Photoelectrochemistry of Hematite Thin Films

Optical investigation indicated that both nanorod and pyrolysis hematite thin films show direct and indirect band gap transitions. Nanorod film shows a direct band gap of 2.14 eV and an indirect band gap of 2.04 eV. Pyrolysis film gives a direct gap of 2.15 eV and an indirect gap of 2.08 eV. Pyrolysis film has much higher IPCEs than the nanorod film. IPCE measurements give band gaps of 1.94 and 2.00 eV for nanorod film and pyrolysis film, respectively. Photocurrent onsets in 1M NaOH solution were -0.44 V for nanorod film and -0.14 V for pyrolysis film. For nanorod film, linear (photocurrent)^0.5 ∼ light intensity relationship means a high charge carriers' recombination. Linear photocurrent ∼ light intensity relationship with pyrolysis film indicates a fast charge transfer. Adopting pyrolysis film in the dual photoelectrode assembly resulted in zero short circuit photocurrent, due to the mis-match of the CBM of the pyrolysis film with the VBM of the p-GaInP₂. It is expected that combining the advantages of the two films should form an efficient electrode for photoelectrochemical water splitting with efficient charge transfer and a large surface area.