Preparation and photoelectrochemical characterization of porphyrin-sensitized α -Fe₂ O₃ thin films

The photoelectrochemical response of electrodeposited hematite (α -Fe₂ O₃) thin films, whose surface has been sensitized by the adsorption of 5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin (TCPP), was studied. The α -Fe₂ O₃ thin films were obtained by the annealing of an electrodeposited Β -FeOOH precursor layer. The structural and morphological characteristics of the resulting hematite films were studied by X-ray diffraction, scanning electron microscopy, and atomic force microscopy techniques. The semiconducting characteristics of unmodified and sensitized TCPP hematite films were determined by electrochemical impedance measurements and by Mott-Schottky analysis. The hematite films exhibited an n-type behavior and a donor carrier concentration (N_D =3× 10¹⁷ cm^-3) for both unmodified and TCPP-sensitized ones. However, it was observed that the presence of TCPP shifts the energy of the surface states to higher values. The photoelectrochemical response of the unmodified and sensitized α -Fe₂ O₃ electrodes was followed by means of photovoltammetry and photocurrent-time transient techniques in a 0.1 M NaOHK⁺0.1 M KI solution under 25 mW/ cm² white light illumination. The results showed that the photocurrent response exhibited by the TCPP-sensitized hematite films was 70% higher than the unmodified ones.