An ADMET Route to Low-Band-Gap
Poly(3-hexadecylthienylene
vinylene): A Systematic Study of Molecular Weight on Photovoltaic
Performance
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Abstract
The effect of molecular weight on organic photovoltaic
device performance
is investigated for a series of low-band-gap (ca. 1.65 eV) poly(3-hexadecylthienylene
vinylene)s (C16-PTVs) prepared by acyclic diene metathesis (ADMET)
polymerization. By utilizing monomers of varying cis:trans (<i>Z</i>:<i>E</i>) content, seven C16-PTVs were prepared
with a number-average molecular weight range of 6–30 kg/mol.
Polymers were characterized by size-exclusion chromatography, <sup>1</sup>H NMR spectroscopy, ultraviolet–visible spectroscopy,
thermogravimetric analysis, wide-angle X-ray scattering, and differential
scanning calorimetry. C16-PTVs were integrated into bulk-heterojunction
(BHJ) solar cells with [6,6]-phenyl-C<sub>61</sub>-butyric acid methyl
ester (PCBM), and conversion efficiency was found to increase with
increasing molecular weight. This observation is attributable to an
increase in polymer aggregation in the solid state and a corresponding
increase in hole mobility. Finally, phase behavior and morphology
of the C16-PTV:PCBM active layers were investigated by differential
scanning calorimetry and atomic force microscopy, respectively