Trans-A2B2 Zn(II) porphyrin dyes with various donor groups and their Co-sensitization for highly efficient dye-sensitized solar cells

We have designed and synthesized four donor-acceptor based trans-A2B2 Zn(II) porphyrin dyes with various donor moieties and phenylcarboxy as acceptor group in three steps. Two strong electron-donating groups (carbazole, phenothiazine, pyrene and bisthiophene) were attached to porphyrin core to enhance the light absorption of dye molecules and phenylcarboxy acted as acceptor group on TiO2 surface. The alkyl chains present in KP-Zn-CBZ and KP-Zn-PTZ dyes are helpful to suppress the aggregation of dyes at the semiconductor surface. The synthetic route of these dyes was facile, high yield and three steps procedure which involved MacDonald condensation followed by hydrolysis and Zn insertion. The absorption and emission bands of all four dyes were broadened and red shifted due to the charge transfer from donor groups to porphyrin moiety. A wide range of power conversion efficiency was shown by dyes and the order of ƞ was as followed KP-Zn-PTZ (5.48%) > KP-Zn-PYR (3.38%) > KP-Zn-CBZ (2.64%) > KP-Zn-BTP (1.71%). Co-sensitization of porphyrin dyes with N719 dye promoted the complementary absorption in the visible region and put a restriction on dye aggregation also which improved the cell performance. Co-sensitized KP-Zn-PTZ with N719 dye showed the highest PCE efficiency up to 8.80% with a Jsc = 17.4 mA cm−2, Voc = 0.73 V and FF = 70% which was superior to individual co-sensitized Zn(II) porphyrin dyes and N719 dye alone (ƞ = 7.3%).