Here,
we designed and developed an organic field-effect transistor
(OFET)-based gas sensor by applying solvatochromic dye (Nile red,
NR) with twisted intramolecular charge-transfer (TICT) behavior depending
on the polarity of the surrounding molecules, as an auxiliary NR sensing
medium (aNR-SM). As a polar molecule approaches, intra-charge transfers
from the donor diethylamine group to the ketone group occur in the
NR molecule, resulting in the twisting of the donor functional group
and thereby increasing its dipole moment. Using this characteristic,
NR was applied as an auxiliary sensing medium to the OFET for detecting
ammonia (NH3), a representative toxic gas. The Top-NR case,
where the aNR-SM covers only the top of the organic semiconductor
layer, showed the best gas sensing performance, and its response and
recovery rates were improved by 46 and 94%, respectively, compared
to the pristine case. More importantly, a sensitivity of 0.87 ±
0.045 ppm–1 % was measured, having almost perfect
linearity (0.999) over the range of measured NH3 concentrations,
which is the result of solving the saturation problem in the sensing
characteristics of the OFET-based gas sensor. Our result not only
improved the sensing performance of the OFET-based sensor but also
made an important advance in that the reliability of the sensing performance
was easily secured by applying solvatochromic and TICT behaviors of
an auxiliary sensing medium.
Marangoni flow-driven solidification of a polymer semiconducting film on an aqueous base media can be effectively controlled through spreading coefficient.
Controlling the interfacial properties between the electrode and active layer in organic field‐effect transistors (OFETs) can significantly affect their contact properties, resulting in improvements in device performance. However, it is difficult to apply to top‐contact‐structured OFETs (one of the most useful device structures) because of serious damage to the organic active layer by exposing solvent. Here, a spontaneously controlled approach is explored for optimizing the interface between the top‐contacted source/drain electrode and the polymer active layer to improve the contact resistance (RC). To achieve this goal, a small amount of interface‐functionalizing species is blended with the p‐type polymer semiconductor and functionalized at the interface region at once through a thermal process. The RC values dramatically decrease after introduction of the interfacial functionalization to 15.9 kΩ cm, compared to the 113.4 kΩ cm for the pristine case. In addition, the average field‐effect mobilities of the OFET devices increase more than three times, to a maximum value of 0.25 cm2 V−1 s−1 compared to the pristine case (0.041 cm2 V−1 s−1), and the threshold voltages also converge to zero. This study overcomes all the shortcomings observed in the existing results related to controlling the interface of top‐contact OFETs by solving the discomfort of the interface optimization process.
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