The charge-carrier mobility of organic semiconducting polymers is known
to be enhanced when the energetic disorder of the polymer is minimized.
Fused, planar aromatic ring structures contribute to reducing the polymer
conformational disorder, as demonstrated by polymers containing the
indacenodithiophene (IDT) repeat unit, which have both a low Urbach energy
and a high mobility in thin-film-transistor (TFT) devices. Expanding on this
design motif, copolymers containing the dithiopheneindenofluorene repeat unit
are synthesized, which extends the fused aromatic structure with two additional
phenyl rings, further rigidifying the polymer backbone. A range of copolymers
are prepared and their electrical properties and thin-film morphology evaluated,
with the co-benzothiadiazole polymer having a twofold increase in hole mobility
when compared to the IDT analog, reaching values of almost 3 cm2 V−1 s−1 in
bottom-gate top-contact organic field-effect transistors.