  Electroabsorption (EA) measurements can be used to identify the type of
excitons contributing to the absorption spectra of semiconductors which have
applications in optoelectronics. However, the inferences from the EA
measurement greatly depend on the method of fitting and extraction of
parameters from the measured spectra. We deconstruct the absorption spectrum by
fitting multiple Gaussians and obtain the relative contribution of first and
second derivative of each absorption band in EA spectrum, which gives
indication of the Frenkel, charge transfer or mixed nature of the excitons
involved. We check the applicability of the method for pentacene which is
widely used and well studied organic semiconductor. We report EA measurements
of
poly[(2,5-bis(2-hexyldecyloxy)-phenylene)-alt-(5,6-difluoro-4,7-di(thiophen-2-yl)benzo[c]-[1,2,5]-thiadiazole)]
(PPDT2FBT). Our analysis shows that besides the feature around 3.07 eV, which
is strongly Frenkel-like, most of the absorption bands for PPDT2FBT are mixed
states, having relatively high charge transfer contributions. Since charge
transfer excitons have higher dissociation efficiencies, we infer PPDT2FBT to
be a promising candidate for photovoltaic applications.
