C O M M U N I C A T I O N S
ratio after being stored under ambient conditions in the dark for
one month, in sharp contrast to the drastic degradation in perfor-
mance of the regioregular P3HT devices under identical conditions.
In addition, the mobilities for the PQT-12 device extracted from
both the linear (Figure 2b) and saturated regimes were about the
same, and no observable differences were noted with the top- and
bottom-contact device configurations. More importantly, little or
no hysteresis and bias stress effects had been observed with these
devices at and above room temperature (Figures 2b and 2c). All
these data suggest that PQT-12 has exhibited ideal field-effect
transistor behaviors.
In conclusion, we have demonstrated that through structural
design for proper self-assembly ability and controlled π-conjugation,
both oxidative doping stability and excellent TFT performance
characteristics can be built into a polythiophene system. To the
best of our knowledge, PQT is the only conjugated polymer system
that has exhibited the best all-around polymer TFT properties under
ambient fabrication conditions.
Figure 1. XRDs of PQT-12: (a) pressed pellet of precipitated polymer
from polymerization; (b) pressed pellet annealed at ∼140 °C; (c) as-cast
0.2 µm thin film; (d) 0.2 µm thin film annealed at 135 °C; and (e)
transmission electron diffraction pattern of PQT-12 film on carbon grid.
Acknowledgment. The authors wish to thank Ms. Ni Zhao of
McMaster University for obtaining TEM images. Partial financial
support is provided by the National Institute of Standards and
Technology through an Advanced Technology Program Grant
(70NANBOH3033).
Supporting Information Available: Experimental procedures,
thermal analysis, and absorption spectra of PQT-12. This material is
Figure 2. I-V characteristics of exemplary PQT-12 TFT device with 90
µm channel length and 5000 µm channel width: (a) output curves at
different gate voltages; (b) two transfer curves in saturated regime scanned
from positive to negative gate voltages (o (red) and x (blue), VD ) -60 V)
and transfer curve at linear regime (∆, VD ) -6 V); (c) two transfer curves
scanned in different directions between +10 and -20 V.
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