Two
novel porphyrin–porphyrin dyads, the symmetrical Zn[Porph]–Zn[Porph]
(2) and unsymmetrical Zn[Porph]–H2[Porph]
(4), where Zn[Porph] and H2[Porph] are the
metalated and free-base forms of 5-(4-aminophenyl)-10,15,20-triphenylporphyrin,
respectively, in which two porphyrin units are covalently bridged
by 1,3,5-triazine, have been synthesized via the stepwise amination
of cyanuric chloride. The dyads are also functionalized by a terminal
carboxylic acid group of a glycine moiety attached to the triazine
group. Photophysical measurements of 2 and 4 showed broaden and strengthened absorptions in their visible spectra,
while electrochemistry experiments and density functional theory calculations
revealed negligible interaction between the two porphyrin units in
their ground states but appropriate frontier orbital energy levels
for use in dye-sensitized solar cells (DSSCs). The 2-
and 4-based solar cells have been fabricated and found
to exhibit power conversion efficiencies (PCEs) of 3.61% and 4.46%,
respectively (under an illumination intensity of 100 mW/cm2 with TiO2 films of 10 μm thickness). The higher
PCE value of the 4-based DSSC, as revealed by photovoltaic
measurements (J–V curves)
and incident photon-to-current conversion efficiency (IPCE) spectra
of the two cells, is attributed to its enhanced short-circuit current
(Jsc) under illumination, high open-circuit
voltage (Voc), and fill factor (FF) values.
Electrochemical impedance spectra demonstrated shorter electron-transport
time (τd), longer electron lifetime (τe), and high charge recombination resistance for the 4-based cell, as well as larger dye loading onto TiO2
