The photovoltaic properties and structure of palladium tetraphenylporphyrin on tin oxide photoelectrochemical cells

The photovoltaic properties of palladium tetraphenylporphyrin films on n-doped SnO 2 transparent electrode in contact with a solution of quinone/hydroquinone are discussed as a function of the preparation of the film and history of its treatment with heat, H 2 , or O 2 /H 2 O. Magnetic circular dichroism (MCD) spectra of the electrodes provide guidance on film structure. There are three important results. First, MCD spectra show that photovoltaic behaviour is independent of crystallinity of the film. Second, the evolution of film behaviour as "doping" by O 2 /H 2 O occurs shows that photoprocesses occur at both the interface of the film with SnO 2 and the electrolyte, leading to both photoanodic and photocathodic processes. Third, MCD spectra show that "doping" is not a surface or trace phenomenon but affects the axial ligand sensitive region of the spectra of molecules throughout the film. Transport of charge through the film by successive "redox" reactions appears to provide the simplest qualitative explanation of the results. That is, conduction is by hopping in a non-stoichiometrically oxidized film.