Attached
In dye sensitized (DS) devices, the excited dye molecules inject carriers to the energy bands of the
attached semiconductor material, thereby separating the charges and driving a current in an external
circuit. Although many initially encountered technical hurdles are overcome, the efficiency of DS solar
cells remains low due to the narrower spectral response. Therefore, investigation of methods to
broaden the spectral response of a DS solar cell is very important. In general, long carbonic chains
are known to absorb infrared radiation. Alterations of a cyanine dye molecules with carbon chains
can be used to extend the response spectra of the DS solar cell and other DS devices. The results of
such an investigation are presented here. The investigation was carried out with four cyanine dye
derivatives. These dyes were coated on TiO2 electrodes. The TiO2 electrodes were prepared by
hydrolysis of titanium isopropoxide and depositing the slurry on fluorine doped conducting tin oxide
(FTO) glass plates (1× 1.5 cm2
). CuSCN dissolved in propyl sulfide was used as the hole collecting (ptype) material, and was deposited on the dye coating, by keeping the dye coated electrode on a hot
plate (~120 °C). The result shows broadening in the absorption and response spectra of the DS device
as the length of the carbon chains in the dye molecules increases. The cyanine dyewith the longest
central polymethine chain, has the largest red shift in the response spectra threshold, which
extended into the near infrared region (~900nm). Additionally, the lengths of the other carbon
ligands in the dye molecules also contributed to the broadening of the spectral response of DS
devices. For the other three dyes, consisting of the same center polymethine chain length but with
the CH3-, the CH3CH2- and the (CH3)2N(CH2)3- ligands attached to pyrrolidinium ring had their
response thresholds red shifted in the same consecutive order as the ligand length, implying a
correlation among the chain length and the extension in the response threshold.
