Synthesis and characterization of dianchoring organic dyes containing 2,7-diaminofluorene donors as efficient sensitizers for dye-sensitized solar cells

New metal free dianchoring organic dyes featuring A-pi-D-pi-D-pi-A (acceptor -pi bridge - donor - pi bridge - donor - pi bridge - acceptor) configuration have been designed incorporating fluorene and oligothiophene units and successfully synthesized. Elongating the conjugation pathway between the donor and acceptor units altered the distance between the anchoring sites besides the absorption and redox properties. These dyes exhibited broad and intense absorption when compared to the corresponding monoanchoring donor-pi-acceptor congeners. Though the dye containing bithiophene unit exhibited comparatively low V-oc due to low electron life time and facile back electron transfer, showed high power conversion efficiency arising from the good light-harvesting capability attributable to the intense absorption peak in the visible region and enhanced interfacial electron transfer rate. This work demonstrates that the smaller distance of separation between the anchoring units increases the insulating capacity of the molecular layer which retards the back electron transfer. (C) 2013 Elsevier B.V. All rights reserved.