Single-crystal field-effect transistors of new Cl2-NDI polymorph processed by sublimation in air

Physical properties of active materials built up from small molecules are dictated by their molecular packing in the solid state. Here we demonstrate for the first time the growth of n-channel single-crystal field-effect transistors and organic thin-film transistors by sublimation of 2,6-dichloro-naphthalene diimide in air. Under these conditions, a new polymorph with two-dimensional brick-wall packing mode (β-phase) is obtained that is distinguished from the previously reported herringbone packing motif obtained from solution (α-phase). We are able to fabricate single-crystal field-effect transistors with electron mobilities in air of up to 8.6 cm2 V−1 s−1 (α-phase) and up to 3.5 cm2 V−1 s−1 (β-phase) on n-octadecyltriethoxysilane-modified substrates. On silicon dioxide, thin-film devices based on β-phase can be manufactured in air giving rise to electron mobilities of 0.37 cm2 V−1 s−1. The simple crystal and thin-film growth procedures by sublimation under ambient conditions avoid elaborate substrate modifications and costly vacuum equipment-based fabrication steps.