Cathodic electrodeposition of ZnO/EosinY hybrid thin films from dye added zinc nitrate bath and their photoelectrochemical characterizations

Abstract

A comprehensive study has been conducted on the cathodic electrodeposition of ZnO/eosinY hybrid thin films from aqueous mixed solutions containing Zn(NO3)2 and eosinY, as well as their photoelectrochemical characteristics. Adsorption of eosinY molecules on the growing surface of ZnO leads to the automatic formation of a nano-porous hybrid structure consisting of interconnected nano-sized ZnO crystals. The dye molecules are loaded into the film at a very high amount as orderly packed layer, being chemically attached to the internal surface of ZnO through their carboxylic acid group, and a major part of them could be desorbed by alkaline treatment without dissolving ZnO. Under the conditions of film preparation, electrochemical reduction of an eosinY molecule coupled with stable complex formation with a Zn2+ ion has been observed and is supposed to play a key role in the process of "self-assembly" of the three dimensional ZnO/eosinY hybrid structures. The electrodeposited ZnO/eosinY hybrid thin films exhibit a high performance as sensitized photoelectrodes. Intensity modulated photocurrent and photovoltage spectroscopies have shown a fast diffusion and a long lifetime of electrons injected from photoexcited eosinY into the conduction band of ZnO, indicating an almost barrier-free transport in the porous network of ZnO grown from solution. A high incident photon to current conversion efficiency of 47% was obtained in the absorption maximum of the loaded dye following a mild heat treatment of the film at 150°C, making the present material applicable to conductive plastic substrates for realization of flexible dye-sensitized solar cells.