| Summary: | Optical and photoelectric properties of modern
photosensitive polymers are of great interest due to
their prospects for photovoltaic applications. In particular,
an investigation of absorption and photoconductivity
edge of these materials could provide valuable information.
For these purpose we applied the constant photocurrent
method which has proved its efficiency for inorganic
materials. PCDTBT and PTB7 polymers were used as objects
for the study as well as their blends with a fullerene
derivative PC71BM. The measurements by constant photocurrent
method (CPM) show that formation of bulk heterojunction
(BHJ) in the blends increases photoconductivity
and results in a redshift of the photocurrent edge
in the doped polymers compared with that in the neat
polymers. Obtained from CPM data, spectral dependences
of absorption coefficient were approximated using Gaussian
distribution of density-of-states within HOMO (highest
occupied molecular orbital) and LUMO (lowest unoccupied
molecular orbital) bands. The approximation procedure
allowed us to evaluate rather optical than electrical
bandgaps for the studied materials. Moreover, spectra of
polymer:PC71BM blends were fitted well by the sum of two
Gaussian peaks which reveal both the transitions within
the polymer and the transitions involving charge transfer
states at the donor-acceptor interface in the BHJ.
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