High Carrier Density and High Hole Mobilities of Ion Gel Gated Polymer Thin-Film Transistors

We report the comprehensive characterization of ion gel gated polymer thin-film transistors (IG-PTFTs), in which PQT-12 was used as the active layer and an ion gel comprising a polymer network swollen with an ionic liquid was used as the gate dielectric. The high capacitance of ion gels ($>$10 $\mu $F/cm2) can induce a very large hole density ($\sim $ 2 x 10$^{14}$ charges/cm$^{2})$ in the channel of polymer semiconductor layers in IG-PTFTs, leading to low operation voltages, high hole mobilities of $>$ 1 cm$^{2}$/V·s, and high ON currents. High ionic conductivities of ion gels ($>$ 1 mS/cm) enable fast response time ($\sim $ 1.5 ms at 80 {\%} ON/OFF) of IG-PTFTs. Temperature dependent measurements were carried out with IG-PTFTs. In the high temperature range (310 K $\sim $ 360 K), the device showed faster response time and little hysteresis due to increasing ionic conductivity with the operating temperature. At low temperature (20 K $\sim $ 185 K) where the ions are immobile, high ON currents between source and drain can be maintained with weak temperature dependence. Overall, the results demonstrate that the IG-PTFTs offer opportunities to probe transport of high 2-D charge carrier densities in semiconductors.