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

Abstract

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.