Probing electron transfer dynamics of phenosafranine with iodide

In dye sensitized solar cells (DSCs), the excited state deactivation of the dye typically occurs by either electron injection to the conduction band of the semiconductor or quenching by iodide ions present in the electrolyte. Complete understanding of latter process in DSCs is not encountered fully on small molecules (i.e. dyes). In this paper, we have employed time resolved techniques to probe the excited state deactivation of the dye by iodide ions. For this reason, we have chosen phenosafranine (PSF, electron acceptor in the excited state) and lithium iodide (electron donor) in acetonitrile medium. Results show that there is an efficient quenching between excited states of PSF with iodide ions. The obtained bimolecular quenching rate constants (kq) were in diffusion controlled limit. Time resolved absorption studies reveals that the observed quenching is due to electron transfer from iodide to excited state of PSF, as evidenced by the observation of iodide anion radical at 440 nm. This fundamental work may provide hint to improve the power conversion efficiency of small molecules based devices.