Charge separation has been investigated at Pd−porphyrin (Pd−P)/TiO2 interfaces by surface photovoltage spectroscopy in the Kelvin-probe arrangement. Ultrathin nanoporous TiO2 layers were covered with Pd−P molecules from highly diluted organic solution starting from the submonolayer range. Mechanisms of charge separation including charge separation in TiO2 nanoparticles, an ionic transport component, and injection of electrons into TiO2 from states of solitary Pd−P molecules not interacting with each other on the surface and from Pd−P molecules interacting with each other and with TiO2 were identified. A developed model for the simulation of surface photovoltage spectra considered mechanisms of charge separation and respective recombination paths. Characteristic charge separation lengths and recombination coefficients were obtained for the different components of separated charge.

Time-resolved surface photovoltage (SPV) is an important method for studying charge separation, for example, in nanostructured semiconductors. High precision differential measurement of SPV transients was realized with two identical measurement capacitors and high-impedance buffers. In addition, logarithmic readout and averaging procedures were implemented for single transients over eight magnitudes in time. As a model system ultrathin CdS layers were investigated. The thickness dependencies of the SPV amplitudes and that of the dominating relaxation mechanisms are demonstrated and discussed.

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Molecules of Pd(II) 5‐(4‐carboxyphenyl)‐10,15,20‐tris(4‐methylphenyl) porphyrin were adsorbed from highly diluted dichloromethane solution on ultra‐thin layers of nanoporous TiO2 and investigated by modulated surface photovoltage (SPV) spectroscopy. An additional transition with a maximum at 2.03 eV appeared in the SPV spectra after moderate annealing in vacuum irrespective to the amount of adsorbed molecules. The new transition has been ascribed to the formation of a charge transfer complex due to an interaction between the Pd centred porphyrin and Ti surface atoms. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)