Soft template-assisted self-assembly: a general strategy toward two-dimensional molecular crystals for high-performance organic field-effect transistors

Abstract

Two-dimensional molecular crystals (2DMCs) are highly desirable to probe the intrinsic properties of organic semiconductors and are promising candidates for constructing high-performance optoelectronic devices. Liquids such as water are favorable substrates to produce high-quality 2DMCs because of the elimination of the ubiquitous coffee ring effect (CRE) of solid substrates. However, crystal growth on a water surface relies on solvents with high surface tension for good spreading, which severely limits the choice of solvents and thus the optimization of crystal growth. Herein, we reported a soft template-assisted self-assembly (STAS) strategy to grow large-area high-quality 2DMCs on a water surface irrespective of the surface tension of the solvents. The as-grown quasi-freestanding 2DMCs on the water surface could be transferred layer by layer to construct molecularly thin bilayer p–n heterojunctions. Organic field-effect transistors (OFETs) based on these p–n heterojunctions exhibited ambipolar charge transport characteristics with a hole mobility of up to 1.50 cm⁻² V⁻¹ s⁻¹ and an electron mobility of up to 0.79 cm⁻² V⁻¹ s⁻¹ under ambient air. The STAS strategy is applicable to solvents with both high and low surface tensions and organic semiconductors of various structures, and opens a new avenue for the construction of high-performance organic optoelectronic devices.