Understanding Effects of Ion Diffusion on Charge Carrier Mobility of Electrolyte-Gated Organic Transistor Using Ionic Liquid-Embedded Poly(3-hexylthiophene)

In electrolyte-gated organic electronics, including electrochromic devices, organic field-effect transistors, and organic electrochemical transistors, the underlying working principle is determined by the permeability of the electrochemically active ions within the electrolyte dielectric into the organic semiconductor layer; as such, the carrier mobility of organic semiconductors in electrolyte-gated devices remains unclear because of the different degrees of ion penetration depending on the fabrication process and device architecture. Here, ion-embedded organic semiconductors are developed by precisely incorporating ionic liquid (IL) in poly(3-hexylthiophene) (P3HT), and then the effects on the charge carrier mobility in organic transistors using poly(methyl methacrylate) (PMMA), poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP)) and electrolyte dielectrics are systematically investigated. Neat P3HT transistors show saturation mobility of 0.080 ± 0.003, 0.287 ± 0.025, and 5.04 ± 0.16 cm² V⁻¹ s⁻¹ using PMMA, P(VDF-HFP), and polymer electrolyte dielectrics, respectively. Compared with control neat P3HT devices, nonproportional normalized saturation mobilities of 0.46 (0.30), 1.65 (1.35), and 0.74 (0.89) are observed for P3HT:IL of 99.5:0.5(98:2) v/v% devices using PMMA, P(VDF-HFP), and polymer electrolyte dielectrics, respectively. In addition, it is found that the ion penetration into P3HT can influence the metal/semiconductor contact and interfacial charge trapping at the dielectric/semiconductor, which can disrupt the efficient charge carrier transport.