Polymerized ionic
liquids (PILs) are a potential solution to the
large-scale production of low-power consuming organic thin-film transistors
(OTFTs). When used as the device gating medium in OTFTs, PILs experience
a double-layer capacitance that enables thickness independent, low-voltage
operation. PIL microstructure, polymer composition, and choice of
anion have all been reported to have an effect on device performance,
but a better structure property relationship is still required. A
library of 27 well-defined, poly(styrene)
-b-
poly(1-(4-vinylbenzyl)-3-butylimidazolium-
random
-poly(ethylene glycol) methyl ether methacrylate)
(poly(S)-
b
-poly(VBBI
+
[X]-
r
-PEGMA)) block copolymers, with varying PEGMA/VBBI
+
ratios
and three different mobile anions (where X = TFSI
–
, PF
6
–
or BF
4
–
), were synthesized, characterized and integrated into OTFTs. The
fraction of VBBI
+
in the poly(VBBI
+
[X]-
r
-PEGMA) block ranged from to 100 mol % and led to glass
transition temperatures (
T
g
) between −7
and 55 °C for that block. When VBBI
+
composition was
equal or above 50 mol %, the block copolymer self-assembled into well-ordered
domains with sizes between 22 and 52 nm, depending on the composition
and choice of anion. The block copolymers double-layer capacitance
(
C
DL
) and ionic conductivity (σ)
were found to correlate to the polymer self-assembly and the
T
g
of the poly(VBBI
+
[X]-
r
-PEGMA) block. Finally, the block copolymers were integrated into
OTFTs as the gating medium that led to n-type devices with threshold
voltages of 0.5–1.5 V while maintaining good electron mobilities.
We also found that the greater the σ of the PIL, the greater
the OTFT operating frequency could reach. However, we also found that
C
DL
is not strictly proportional to OTFT output
currents.