Crystallization Control of Organic Semiconductors during Meniscus-Guided Coating by Blending with Polymer Binder

Small molecule organic semiconductors (OSCs) suffer from their uncontrolled nucleation and growth during solution processing limiting their functionality in electronic devices. In this work, a new method is presented based on dip-coating a blend consisting of OSC and insulating polymer to control the crystallization of the active film for organic field-effect transistors. A small fraction of amorphous poly(methyl methacrylate) (PMMA) efficiently improves the crystallization of dip-coated small molecule OSCs, α,ω-dihexylquaterthiophene (DH4T) and diketopyrrolopyrrole-sexithiophene (DPP6T). The maximum charge carrier mobilities of dip-coated OSC:PMMA films are significantly higher than drop-cast blend ones and comparable with OSC single crystals. The high charge carrier mobility originates from a continuous alignment of the crystalline films and stratified OSC and PMMA layers. The improved crystallization is attributed to two mechanisms: first, the polymer binder leads to a viscosity gradient at the meniscus during dip-coating, facilitating the draw of solute and thus mass transport. Second, the polymer binder solidifies at the bottom layer, reducing the nucleation barrier height of small molecule OSC. The findings demonstrate that a small fraction of a polymer binder during dip-coating efficiently improves the crystallization as well as the electronic properties of small molecule OSC films.