Organic field-effect transistors processed by an environmentally friendly non-halogenated solvent blend

Abstract

Chlorinated solvents exhibit excellent solubility characteristics for common conjugated molecules and superior physical properties such as adequate viscosity, surface tension and high boiling point, so they are the preferred processing solvent option for realizing high-performance organic devices by cost-effective graphic art printing, despite their known adverse environmental impact. Based on Hansen solubility parameter analysis, this study employed a non-halogenated binary solvent blend of mesitylene and acetophenone to closely mimic the efficiency of dichlorobenzene, a well-known chlorinated solvent for widely used conjugated polymers used in organic field-effect transistors (OFETs) such as poly{[N,N′-bis(2-octyldodecyl)-1,4,5,8-naphthalenediimide-2,6-diyl]-alt-5,5′-(2,2′-bithiophene)} (P(NDI2OD-T2)), 3,6-bis-(5bromo-thiophen-2-yl)-N,N-bis(2-octyl-1-dodecyl)-1,4-dioxo pyrrolo[3,4-c]pyrrole (DPPT-TT) and indacenodithiophene-co-benzothiadiazole (IDT-BT). We tuned the solvent quality of the non-halogenated binary blend in various ratios and studied their effect on polymer pre-aggregation in the solution state, polymer microstructure, and morphological evolution of polymer thin films cast from the solvent blends. High-performance top-gate/bottom-contact OFETs were demonstrated with field-effect mobility values of up to ∼0.574, ∼0.634 and ∼0.785 cm² V⁻¹ s⁻¹ for P(NDI2OD-T2), DPPT-TT, and IDT-BT polymers, respectively, employing a mesitylene and acetophenone blend (95 : 5 vol%) as a processing solvent.