Synthesis, Characterization, and Transistor and Solar Cell Applications of a Naphthobisthiadiazole-Based Semiconducting Polymer

We report the synthesis and characterization of a novel
donor–acceptor
semiconducting polymer bearing naphthobisthiadiazole (NTz), a doubly
benzothiadiazole (BTz)-fused ring, and its applications to organic
field-effect transistors and bulk heterojunction solar cells. With
NTz’s highly π-extended structure and strong electron
affinity, the NTz-based polymer (PNTz4T) affords a smaller bandgap
and a deeper HOMO level than the BTz-based polymer (PBTz4T). PNTz4T
exhibits not only high field-effect mobilities of ∼0.56 cm2/(V s) but also high photovoltaic properties with power
conversion efficiencies of ∼6.3%, both of which are significantly
high compared to those for PBTz4T. This is most likely due to the
more suitable electronic properties and, importantly, the more highly
ordered structure of PNTz4T in the thin film than that of PBTz4T,
which might originate in the different symmetry between the cores.
NTz, with centrosymmetry, can lead to a more linear backbone in the
present polymer system than BTz with axisymmetry, which might be favorable
for better molecular ordering. These results demonstrate great promise
for using NTz as a bulding unit for high-performance semiconducting
polymers for both transistors and solar cells.