Photoelectric Conversion Properties of Nanocrystalline TiO2 Electrodes Sensitized with Hemicyanine Derivatives

Four hemicyanine derivatives, (E)-N-(3-sulfopropyl-4-[2-(4-dimethylaminophenyl)ethenyl]pyridinium (PS), (E)-N-(3-sulfopropyl-4-[2-(4-dimethylaminophenyl)ethenyl]quinolinium (QS), (E)-N-(3-sulfopropyl-4-[2-(4-N-methyl-N-hexadecylaminophenyl)ethenyl]pyridinium (LPS), and (E)-N-(3-sulfopropyl-4-[2-(4-N-methyl-N-hexadecylaminophenyl)ethenyl]quinolinium (LQS), have been synthesized and characterized with regard to their absorption and electrochemical properties. Photoelectrochemical experiments show that these hemicyanine dyes with D-π-A systems can yield efficient charge separation under illumination of simulated solar light. Alkyl chain has a remarkable effect on dye adsorbance, incident photon-to-electron conversion efficiency, and overall energy conversion yield. The overall yield is approximately doubled when the methyl group replaces the long alkyl chain. Action spectrum of QS displayed a broad feature with 33.8% of maximum monochromatic incident photon-to-electron conversion efficiency (IPCE), and a thin-layer sandwich-type solar cell based on nanocrystalline TiO2 film modified with QS produced about 2% of overall yield. For the first time, a photovoltaic liquid-junction solar cell based on nanostructured TiO2 electrode sensitized by hemicyanine dyes is reported.