Low-voltage, high-performance polymeric field-effect transistors based on self-assembled monolayer-passivated HfO_x dielectrics: Correlation between trap density, carrier mobility, and operation voltage

We report on high-performance polymeric field-effect transistors (PFETs) operating at low voltages (V_op) using a self-assembled monolayer (SAM)-passivated HfO_x dielectric layer. A diketopyrrolopyrrole and quaterthiophene-based copolymer (PDPP2DT-T2) was spin-coated in air as an active channel material on top of a HfO_x gate dielectric that was passivated with n-octyltrichlorosilane (OTS), n-octadecyltrichlorosilane (ODTS), and n-dodecylphosphonic acid (PAC12) SAMs. The high capacitance and low leakage current of the SAM-passivated HfO_x dielectrics enabled the devices to operate at |V_op| of less than 4 V. In particular, the PFETs using ODTS-passivated HfO_x demonstrated a high hole mobility (μ_eff ^h) of 1.98 cm² V⁻¹ s⁻¹, a current on/off ratio of 1.4 × 10⁴, and a threshold voltage of −0.8 V despite the fact that the device fabrication and all measurements were conducted under ambient conditions without encapsulation. Moreover, the μ_eff ^h value observed in this study is the best for high-k-dielectric-based low-voltage PFETs reported to date. This work demonstrates that our facile modification of high-k dielectrics with SAMs is a highly effective method for realizing high-performance semiconducting copolymer-based transistors working at a low V_op regime with low power consumption.