Preparation and Photoelectrochemical Characterization of Porphyrin-Sensitized α-Fe2O3 Thin Films

The photoelectrochemical response of electrodeposited hematite (alpha-Fe2O3) thin films, whose surface has been sensitized by the adsorption of 5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin (TCPP), was studied. The alpha-Fe2O3 thin films were obtained by the annealing of an electrodeposited beta-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=3x10(17) 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 alpha-Fe2O3 electrodes was followed by means of photovoltammetry and photocurrent-time transient techniques in a 0.1 M NaOH+0.1 M KI solution under 25 mW/cm(2) white light illumination. The results showed that the photocurrent response exhibited by the TCPP-sensitized hematite films was 70% higher than the unmodified ones.