Synthesis and application of new, pyridine-containing D-p-A organic photosensitizers for DSSCs

Dye-sensitized solar cells (DSSC) have been considered a potential alternative for building-integrated PV devices, but their industrial development has been hampered by their low efficiency and limited lifetime. We synthesized new D-p-A structured DSSC organic sensitizers bearing pyridine-based anchoring groups and we compared effciency and stability with dyes having a traditional cyanoacrylic acceptor (named DF15). Pd-catalyzed cross-coupling reactions were used to build up the common D-p scaffold and to introduce the novel anchoring units . We prepared the target dyes having three regioisomeric carboxypyridines as acceptor groups - Spectroscopic, electrochemical and computational characterization were carried out and compared with DF15 . Test devices prepared with these new sensitizers provided power conversion effìciencies corresponding to 54-63% of those obtained with DF15. More significantly, device stability tests carried out on transparent, larger area cells and determination of desorption pseudo-first order rate constants showed that some of these new compounds were removed from TiO2 more slowly than DF15 suggesting a possible cooperative effect of the two functional groups on semiconductor binding. We increased the electron-withdrawing character of the pyridine rings with N-methylpyridinium derivation. Despite more favorable photophysical properties, the cells built with the cationic sensitizers provided lower efficiencies than their neutral counterparts do.