Abstract:
Studies on Dye-Sensitized devices (DSDs) were initiated around late 1960s. DSDs are studied as a
low cost alternative for photovoltaic optoelectronic devices, notably as solar cells. Their performance
depends on the photon absorption and carrier injection properties of the sensitizer (dye). In general, the
charge transfer in the molecule is based on the Donor-π-bridge-Acceptor (D-π-A) mechanism. Additionally,
the orientation of the dye molecule affects the photon-absorption-cross-section, the injection efficiency of
the carriers from the sensitizer to the semiconductor-electrode. Three variants of cyanine dyes were
identified to have different orientations with respect to the TiO2 surface. The current-voltage variations of
the three dyes as sensitizers were studied experimentally on an n-TiO2/Dye/p-CuSCN configuration. The
TiO2 films were prepared on fluorine-doped tin oxide (FTO) glass plates (1×1.5 cm2) by hydrolyzing titanium
isopropoxide slurry mixed with Degussa P25 TiO2 powder. The TiO2 film thickness was ~10 μm. The I-V
characteristics of the cells were recorded using a calibrated halogen lamp and a KEITHELY 2400 source
meter; the photocurrent action spectra was measured using a SP-DK480 monochromator and a SR-850
lock-in-amplifier set-up calibrated with a standard silicon photodiode. The absorption spectra were
obtained using Ocean Optics USB2000 UV-VIS spectrometer. Additionally, a theoretical study was
conducted, using the inbuilt functions in ChemDraw®, to calculate the MM2 energy minimization, identify
the molecule’s orientation and the HOMO and LUMO positions. The results have shown a correlation
between the orientation of the dye molecule and the photocurrent of the device. Furthermore, the
orientation of the dye molecule appears to be influencing the photon-harvesting efficiency and the
penetration of the hole-conductor into the device. Additionally, the photocurrent results imply the MO‘s
positions affecting the carrier transport properties of the device
