Varied alkyl chain functionalized organic dyes for efficient dye-sensitized solar cells: Influence of alkyl substituent type on photovoltaic properties

Suppression of dye aggregation and interfacial charge recombination by appropriate structural modification of the sensitizers is crucial to improve the performance of dye-sensitized solar cells (DSSCs). In this article, linear alkyl chains, i.e., hexyl groups, and branched alkyl chains, i.e., 2-ethylhexyl groups, are introduced into a sensitizer with a terthiophene unit as conjugated bridge. The effects of the linear and branched alkyl chains on the photophysical, electrochemical properties and photovoltaic properties are investigated. By comparison, branched alkyl chains are superior to linear alkyl chains in suppression of intermolecular interactions and the electron recombination between the injected electrons and the electron acceptors in the electrolyte. Consequently, a more significant improvement of the open-circuit photovoltage can be achieved by the introduction of branched alkyl chains to the it-conjugated bridge of the organic dye in comparison to the incorporation of linear alkyl chains. Conversely, linear alkyl chains are better than branched alkyl chains in broadening photoresponse and hence photocurrent generation. As a result, a power conversion efficiency of 8.12% was achieved for the DSSC based on FNE29 with linear alkyl chains. (C) 2013 Elsevier B.V. All rights reserved.