Cyclopentadithiophene-functionalized Ru(II)-bipyridine sensitizers for dye-sensitized solar cells

Two ruthenium sensitizers TT-230 and TT-232 based on cyclopenta[2,1-b:3,4-b']dithiophene (CDT) were tested in dye-sensitized solar cells (DSSCs) using,a tri-iodide/iodide redox couple, and their performances compared to the benchmark Z907. Both dyes of general formula Ru(LL')(NCS)(2) feature the same 4.4'-dicarboxylic acid 2,2'-bipyridine moiety acting as the anchoring group (L) to attach the dye on the TiO2 surface, and two CDT subunits as ancillary groups (L' either directly-linked (11-230) or vinylene-linked (TT-232) to the bipyridine moiety. In comparison with TT-230, the it-extended conjugation in TT-232 caused significant redshift and broadening of the absorption bands. However, despite better light-harvesting properties, the DSSC device sensitized with TT-232 strikingly underperformed compared to TT-230 under same conditions (PCE = 3.2% and 6.1%, respectively). The use of co-adsorbent (CHENO) or surfactants did not help to improve the photovoltaic properties of TT-230, and resulted in a degradation of the overall efficiency of the cell. (C) 2014 Elsevier Ltd. All rights reserved.