Understanding ionic screening effect in hybrid perovskite transistors based on capacitance and polarizability of the dielectric

The intrinsic mixed ionic-electronic nature of metal halide perovskites has facilitated their dual functionality as prominent semiconductor materials and emerging gate dielectrics applicable to diverse electronic and optoelectronic devices. However, the exploration of various solution-processable polymeric gate dielectrics is limited owing to the inherent ionic defects, interfacial reactions, and limited chemical stability of metal halide perovskite semiconductors. Herein, the charge transport and ionic screening effects occurring in hybrid perovskite transistors are investigated based on the capacitance and polarizability of the gate dielectric. We investigated three categories of polymeric dielectrics, i.e., low-k poly(methyl methacrylate) (PMMA), high-k fluorinated poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP), and high-capacitance ionic P(VDF-HFP), which contains P(VDF-HFP) and an ionic liquid. The gate current modulation of the hybrid perovskite field-effect transistors (FETs) containing a conjugated polymer and formamidinium lead triiodide perovskite blend improved with the increase in the capacitance of the gate dielectric. Therefore, the charge carrier mobilities of the hybrid perovskite FETs increased in the order of PMMA < P(VDF-HFP) < ionic P(VDF-HFP), attributable to the suppressed ionic motion and screening effect, defect passivation, and increasing charge carrier density induced by their respective gate dielectric. These findings improve the understanding of the ionic screening effect, ion migration, and unusual device characteristics of halide perovskite FETs and related devices.