Modulating Poly(methyl methacrylate) Gate Dielectric Behavior with Cosolvent and Low-Temperature Processing for Low-Threshold-Voltage Flexible Organic Field-Effect Transistors

Low-power flexible electronic and bioelectronic applications are in substantial demand of low-threshold-voltage organic field-effect transistors (OFETs). Detailed studies on surface and interfacial properties have shown that the annealing temperature, dipole moment, and dielectric constant of the processing solvents impact various device parameters such as the capacitance density, threshold voltage, stability, and density of charge trapping states. In this work, we achieved low-threshold-voltage operation in OFETs by employing a mixture of solvents comprising low and high dipole moments to process poly(methyl methacrylate) (PMMA). A blend with an optimized ratio of t-butyl alcohol and acetonitrile solvents was used to prepare the PMMA gate dielectric layer. Both t-butyl alcohol and acetonitrile have a boiling point of 82 °C, which implies a very low annealing temperature to treat the PMMA films. This helps in realizing flexible devices on unconventional substrates requiring low-temperature processing. The devices fabricated on glass and flexible substrates yielded good electrical performance, exhibiting a low threshold voltage of −3.5 ± 0.02 V, good bias stress stability, and mechanical flexibility. Through a combination of experimental studies, we aim to provide insights into how solvent choice influences the dielectric layer properties and the operation of OFETs. Therefore, our work demonstrates the efficacy and potential of a solvent engineering approach utilizing mixed solvents to treat PMMA as a gate dielectric layer, facilitating low-temperature and low-threshold-voltage flexible OFET devices.