Chemical Doping Efficiency by Semiconducting Polymer Type in Electrolyte-gated Polymer Transistor

We report the characterization of chemical doping process with electrolyte-gated polymer transistors (EGT), where classical highly crystallined semiconducting polymer - PBTTT or amorphous donor-acceptor (D-A) type semiconducting copolymer -DPP-2T-TT was used as the active layer and an ion gel comprising a polymer network swollen with an ionic liquid was used as the electrolyte. Gate-bias dependent doping concentration that is extracted from the transfer curves reveals that the chemical doping process in disordered DPP-2T-TT copolymer film is more efficient than that of PBTTT film. These results are somewhat contrary to the general observation that neutral molecule doping such as F4-TCNQ was effectively worked in a thiophene-based highly crystalline polymer rather than a D-A type copolymer. However, optical and structural investigations using UV-vis spectroscopy and grazing incident X-ray diffraction (GIXRD) have shown that the structural factors of the polymer semiconductors have a greater influence than the chemical characteristics between the polymer semiconductors and the ionic species in electrolyte.