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Bilayer p-n heterojunctions are promising structures to construct ambipolar organic field-effect transistors (aOFETs) for organic integrated circuits. However, due to the lack of effective strategies for high-quality p-n heterojunctions with clear interfaces, the performance of aOFETs is commonly and substantially lower than that of their unipolar counterparts, which hinders the development of aOFETs toward practical applications. Herein, a one-step solution crystallization strategy was proposed for the preparation of high-quality bilayer p-n heterojunctions. A mixed solution of a p- and an n-type organic semiconductor was dropped on a liquid substrate, and vertical phase separation occurred spontaneously during crystallization to produce bilayer p-n heterojunctions composed of molecularly thin two-dimensional molecular crystals. Due to the clear interface of the bilayer p-n heterojunctions, the maximum mobility (average mobility) reached 1.96 cm2 V−1 s−1 (1.12 cm2 V−1 s−1) for holes and 1.27 cm2 V−1 s−1 (0.61 cm2 V−1 s−1) for electrons in ambient air. So far as we know, these values were the highest among double-channel aOFETs measured in ambient air. This work provides a simple yet efficient strategy to construct high-quality bilayer p-n heterojunctions, which lays a foundation for their application in high-performance optoelectronic devices. [ABSTRACT FROM AUTHOR]

From 2,5-di(trimethylsilanyl)dithieno[2,3-b:3′,2′- d ]thiophene ((TMS) 2 - DTT) and (TMS) 2 -diseleno[2,3- b :3′,2′- d ]thiophene ((TMS) 2 - DST), asymmetric organic semiconductor materials (E)− 2-(4-octylstyryl)− 5-phenyl-DTT (PEP - DTT) and (E)− 2-(4-octylstyryl)− 5-phenyl-DST (PEP - DST) were synthesized via bromination, Suzuki coupling, deprotection, formylation and Wittig reactions, with the yields of 48% and 28%, respectively. Apart from the synthetic work, two-dimensional molecular crystals (2DMCs) with a growth size of few hundreds of micrometers of PEP - DTT and PEP - DST were successfully realized for organic field-effect transistors (OFETs) devices through "layer-defining strategy". Bottom-gate/top-contact OFETs on the basis of PEP - DTT and PEP - DST 2DMCs as active layers displayed p-channel features with maximum mobility of 2.04 and 1.36 cm2 V−1 s−1, respectively. • In this study, two kinds of asymmetric fused thiophene/selenophene-based organic small molecule materials PEP - DTT/DST were synthesized and their hundreds of micrometers 2DMCs were obtained through "layer-defining strategy". Bottom-gate/top-contact organic field-effect transistors based on 2DMCs of PEP - DTT / DST as active layers showed the highest hole mobility as 2.04 and 1.36 cm2 V−1 s−1, respectively. Hundreds of micrometers of 2DMCs growth of asymmetric organic small molecules is realized, which provides a basis for studying the intrinsic optoelectronic properties of asymmetric organic small molecules materials in the 2D flatland. [ABSTRACT FROM AUTHOR]

A novel strategy for the growth of molecularly thin two-dimensional molecular crystals (2DMCs) of organic semiconductors with poor solubility was developed. Large-area bilayer 2DMCs were grown on a liquid surface at elevated temperatures, with record mobility and superior photoresponse. [ABSTRACT FROM AUTHOR]

Two‐dimensional molecular crystals (2DMCs) open a new door for the controllable growth of 2D materials by molecular design with a energy gap and solution processability. However, the growth of 2DMCs with defined molecular layers remains full of challenges. Herein, we report a novel method to produce various 2DMCs with a defined number of molecular layers. When the surface tension and viscosity are tuned to control the spreading of the solution on the liquid surface, large‐area quasi‐freestanding 2DMCs from bulk size down to the monolayer limit are obtained, which makes it possible to probe the intrinsic layer‐dependent optoelectronic properties of organic semiconductors down to the physical limit, and paves the way for the application of 2DMCs in new optoelectronic devices and technologies. [ABSTRACT FROM AUTHOR]

Innenrücktitelbild: Layer-Defining Strategy to Grow Two-Dimensional Molecular Crystals on a Liquid Surface down to the Monolayer Limit (Angew. Chem. 45/2019) Keywords: Grenzflächen; Organische Elektronik; Organische Halbleiter; Organische Kristalle; Photodetektoren. [Extracted from the article]