Charge Separation at Pd−Porphyrin/TiO2 Interfaces

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.