π-σ-Phosphonic acid organic monolayer–amorphous sol–gel hafnium oxide hybrid dielectric for low-voltage organic transistors on plastic

Abstract

A vacuum-free solution processed hybrid dielectric composed of an anthryl-alkyl-phosphonic acid (π-σ-PA) self-assembled monolayer on an amorphous sol–gel processed hafnium oxide (HfO_x) is demonstrated for low-voltage organic thin film transistors (OTFTs) on plastic substrates. The π-σ-PA/HfO_x hybrid dielectric provides high capacitance (0.54 µF cm⁻²) and low leakage current (2 × 10⁻⁸ A cm⁻²), and has a chemically and electrically compatible dielectric interface for evaporated and solution processed acene semiconductors. The utility of this dielectric is demonstrated by fabricating pentacene and 6,13-bis(triisopropyl-silylethynyl) pentacene (TIPS-PEN) based OTFTs with operating voltages under 2 V, subthreshold slopes as low as 100 mV dec⁻¹, and average mobilities of 0.32 cm² V⁻¹ s⁻¹ and 0.38 cm² V⁻¹ s⁻¹, for pentacene and TIPS-PEN, respectively.