Characterization of Safranine O based thin-film sandwich devices by analysing their electrical and photoelectrical behaviour

Safranine O (SAP), chemically known as 3,7-diamino-2,8-dimethyl-5-phenyl-phenazinium chloride, was employed in the form of thin film for the fabrication of In/SAF/ITO and Al/SAF/ITO (ITO is indium-tin oxide) sandwich devices. In these devices, at low voltages, the dark current in forward bias condition corresponds to a positive voltage at ITO, which varies exponentially with applied voltage. The square law dependence at higher voltage region indicates that conduction is limited by a discrete trapping level above the conduction band edge. The analysis of the 1/C2 versus V plots, for low frequencies, reveals that the SAF behaves as a semiconductor. At higher frequencies, the devices exhibit voltage-independent capacitances, which is explained in terms of the extremely slow kinetics of space charges. The photogeneration process in these devices is explained in terms of the exciton dissociation into free carriers at the Schottky barrier (Al/SAF and In/SAF interfaces). Various electrical and photovoltaic parameters are calculated and discussed in detail.