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

The photoelectrochemical response of electrodeposited hematite thin films, whose surface has been sensitized by the adsorption of 5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin (TCPP), was studied. The thin films were obtained by the annealing of an electrodeposited b-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 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 electrodes was followed by means of photovoltammetry and photocurrent-time transient techniques in a solution under white light illumination. The results showed that the photocurrent response exhibited by the TCPP-sensitized hematite films was 70% higher than the unmodified ones.