Cyano or o-nitrophenyl? Which is the optimal electron-withdrawing group for the acrylic acid acceptor of D-π-A sensitizers in DSSCs? A density functional evaluation

We report a DFT, TDDFT and DFTB investigation of the performance of two donor-π-acceptor (D-π-A)-type organic dyes bearing different electron-withdrawing groups (EWG) for dye-sensitized solar cells (DSSCs) to evaluate which EWG is better for an acrylic acid acceptor, i.e., Cyano (-CN) or o-nitrophenyl (o-NO-Ph). A series of theoretical criteria applied successfully in our previous work to explain the different performance of organic dyes related to open-circuit photovoltage (V) and short-circuit current density (J) were used to evaluate the performance of the dyes with just different EWG. Our calculated results reveal that dye 2 with o-NO-Ph has a larger vertical dipole moment, more electrons transferred from the dye to the semiconductor and a lower degree of charge recombination, which could lead to larger V ; while the larger driving force and comparable light harvesting efficiency could lead to higher J, highlighting the potential of o-NO-Ph as an EWG in an acrylic acid acceptor. © 2012 Springer-Verlag Berlin Heidelberg.