Characterization of photoelectric polymeric material by using capacitive transducers

Electrical properties of polymeric materials, in which a transition metal complex [tris(2,2'-bipyridyl)Ru(II)]Cl-2 is dispersed, are investigated, under light irradiation conditions, as a function of the complex concentration and of the light intensity and pulse duration. This idea is based on the fact that light absorption produces, as result of the electronic excitation, a temporary change in the electrical dipole moment of the metal complex and this in turn results in changes induced, under light stimulus, in capacitances, whose dielectric is mainly made by the polymeric compound. The material characterization system is therefore based on interdigitated planar capacitors over which the polymeric compound is deposited. The light action induces changes in the dielectric properties of the polymer and these changes reflect into the capacitance value and are in turn converted into an output voltage by suitable capacitance-to-voltage signal conditioning circuits. A differential configuration is adopted in these circuits, based on a dummy interdigitated transducers coated with the same polymer but shielded from the light stimulus, in order to filter out unwanted spurious signals.