The role of ethanol-water solvent mixtures in N719 sensitization of electrodeposited ZnO nanorods
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Water plays an important role in N719 sensitization of ZnO films for application as photoanodes in DSC devices. The role of water content in ethanolic N719 sensitization solutions was examined resorting to N719-solvent interaction studies based on Kamlet-Taft solvatochromic parameters. Results show that as the water content increases, solvent’s HBA ability decreases, hindering dye aggregation in solution and increasing the fraction of dye carboxylic groups available for anchorage onto the charged ZnO surface. The impact of dye-dye-solvent equilibria in solution on ZnO nanorod films sensitization and device behavior was evaluated. Devices assembled with films sensitized in N719 solutions containing equal parts of ethanol and water showed a twofold increase in short-circuit current densities when compared to those sensitized in ethanol only, despite exhibiting significantly less stained films. Data indicate that the presence of water in the sensitization solution reduces the amount of dye aggregates in solution and on the ZnO surface.
KeywordsZnO nanorods ZnO-based photoanodes sensitization Kamlet-Taft solvent parameters Solvent effect on N719 dye aggregation
Financial support from Fundação para a Ciência e a Tecnologia (Portugal), through projects PEst-OE/QUI/UI0612/2013, UID/MULTI/00612/2013, and UID/GEO/50019/2013, are greatly appreciated. The authors wish to thank Prof. S. Sério for the sputtering work, Prof. N. Nunes, and Prof. R. Elvas-Leitão for enlightening discussions and Dr. M. J. Brites for aiding with device preparation and access to solar simulator facilities.
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