Spectral sensitization of a sprayed ZnO thin film electrode by a new synthetic dye (2-imidazolin-5-one) in acetonitrile medium

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Abstract
A new tailor-made organic dye, namely 4-m-methoxy-p-hydroxybenzylidene-2-m-methoxy-p-hydroxystyryl-1-phenyl-2-imidazolin-5-one (subsequently referred to as 2-imidazolin-5-one) has been studied as a photosensitizer for its application in a photoelectrochemical cell. Highly n-doped polycrystalline thin ZnO films prepared by the spray pyrolysis method were used as photoelectrodes and hydroquinone as the supersensitizer for such investigations. The absorption spectrum of the adsorbed dye on a dry ZnO electrode was found to be drastically modified compared with that of dye in solution and this has been attributed to the strong interaction between dye and ZnO surface and the formation of J-aggregates due to intermolecular hydrogen bonding. The cyclic voltammogram of the dye at the platinum electrode exhibited a quasi-reversible anodic peak with formal redox potential EDD+/0=1.24 V versus SSCE. The flat band potential of the ZnO electrode in dye containing acetonitrile solution, Vfb=-0.62 V versus SSCE, was determined from the Mott-Schottky plots. The transient technique was used to monitor the response of a dye-coated ZnO electrode to monochromatic light. The photocurrent response of a dye-coated ZnO electrode was found to be extended well into the visible region. The incident photon to current conversion efficiency (IPCE) was found to be 3.4% at the excitation wavelength (480 nm) of the dye.

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