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Download fileHigh Charge Carrier Mobility, Low Band Gap Donor–Acceptor Benzothiadiazole-oligothiophene Based Polymeric Semiconductors
journal contribution
posted on 2016-02-20, 06:26 authored by Boyi Fu, Jose Baltazar, Zhaokang Hu, An-Ting Chien, Satish Kumar, Clifford L. Henderson, David M. Collard, Elsa ReichmanisA series of benzothiadiazole oligothiophene and oligo(thienylene
vinylene) donor–acceptor (D–A) copolymers were synthesized
and characterized. These low optical band gap materials (∼1.5
eV) are capable of absorbing photons in the range of 400–800
nm and exhibit good thermal stability. Their hole mobilities, determined
using an organic field-effect transistor (OFET) architecture, vary
over a range of 3 orders of magnitude and strongly correlate with
the molecular ordering and morphology of the respective thin films.
Spin-coated films of the poly(benzothiadiazole-sexithiophene) PBT6, which exhibits a highly crystalline lamellar π–π
stacked edge-on orientation on the OFET substrate, possesses a hole
mobility of ca. 0.2 cm2/V·s. Vinylene-containing analogs PBT6V2 and PBT6V2′ are amorphous and
exhibit very low mobilities. The molecular weight of PBT6 has a strong influence on the electronic properties: a sample with
a lower molecular weight exhibits a mobility approximately 1 order
of magnitude lower than the high molecular weight homologue, and the
absorption maximum is appreciably blue-shifted. The hole mobility
of PBT6 is further enhanced by a factor of ca. 3 through
fabrication of the OFET by drop casting. OFETs fabricated by this
process exhibit mobilities of up to 0.75 cm2/V·s and ION/OFF ratios in the range of 106–107. These results demonstrate the potential of
incorporating benzothiadiazole units into polythiophene derivatives
to develop high-mobility semiconducting polymers.