Charge transfer and photogeneration process in device consisting of safranine O dye and TiO2 nano-particles

We have studied the effect of titanium dioxide (TiO2) nano-particles on charge transfer processes in safranine O (SAF) dye photovoltaic device. The photoconductivity is increased by two orders and a sharp saturation is also observed. The device shows a sharp saturation in photocurrent in forward bias which indicates that exciton diffusion and dissociation at the TiO2 interface, due the existence of internal electric field is dominant process for the collection of charge. The value of diode quality factor has been calculated also by fitting the experimental results with modified Shockley equation. The internal electric field is mainly due to the asymmetry between the work functions of the materials. Electron injection from the excited state of dye on illumination, into the conduction band of TiO2 is followed by subsequent hole transfer from the photooxidized dye to the collecting Al electrode, regenerating the dye's original ground state. The charge transfer and photogeneration process in device have been discussed on the basis of current-voltage characteristics and photoaction action spectra of the device. (C) 2002 Elsevier Science B.V. All rights reserved.