Uniaxial Alignment of Conjugated Polymer Films for High‐Performance Organic Field‐Effect Transistors

Polymer semiconductors have been experiencing a remarkable improvement in electronic and optoelectronic properties, which are largely related to the recent development of a vast library of high‐performance, donor–acceptor copolymers showing alternation of chemical moieties with different electronic affinities along their backbones. Such steady improvement is making conjugated polymers even more appealing for large‐area and flexible electronic applications, from distributed and portable electronics to healthcare devices, where cost‐effective manufacturing, light weight, and ease of integration represent key benefits. Recently, a strong boost to charge carrier mobility in polymer‐based field‐effect transistors, consistently achieving the range from 1.0 to 10 cm² V^?1 s^?1 for both holes and electrons, has been given by uniaxial backbone alignment of polymers in thin films, inducing strong transport anisotropy and favoring enhanced transport properties along the alignment direction. Herein, an overview on this topic is provided with a focus on the processing–structure–property relationships that enable the controlled and uniform alignment of polymer films over large areas with scalable processes. The key aspects are specific molecular structures, such as planarized backbones with a reduced degree of conformational disorder, solution formulation with controlled aggregation, and deposition techniques inducing suitable directional flow.     

N‐Type 2D Organic Single Crystals for High‐Performance Organic Field‐Effect Transistors and Near‐Infrared Phototransistors

Organic field‐effect transistors and near‐infrared (NIR) organic phototransistors (OPTs) have attracted world's attention in many fields in the past decades. In general, the sensitivity, distinguishing the signal from noise, is the key parameter to evaluate the performance of NIR OPTs, which is decided by responsivity and dark current. 2D single crystal films of organic semiconductors (2DCOS) are promising functional materials due to their long‐range order in spite of only few molecular layers. Herein, for the first time, air‐stable 2DCOS of n‐type organic semiconductors (a furan‐thiophene quinoidal compound, TFT‐CN) with strong absorbance around 830 nm, by the facile drop‐casting method on the surface of water are successfully prepared. Almost millimeter‐sized TFT‐CN 2DCOS are obtained and their thickness is below 5 nm. A competitive field‐effect electron mobility (1.36 cm² V^?1 s^?1) and high on/off ratio (up to 10⁸) are obtained in air. Impressively, the ultrasensitive NIR phototransistors operating at the off‐state exhibit a very low dark current of ≈0.3 pA and an ultrahigh detectivity (D*) exceeding 6 × 10¹⁴ Jones because the devices can operate in full depletion at the off‐state, superior to the majority of the reported organic‐based NIR phototransistors.     

Gas Sensors Based on Nano/Microstructured Organic Field‐Effect Transistors

Benefiting from the advantages of organic field‐effect transistors (OFETs), including synthetic versatility of organic molecular design and environmental sensitivity, gas sensors based on OFETs have drawn much attention in recent years. Potential applications focus on the detection of specific gas species such as explosive, toxic gases, or volatile organic compounds (VOCs) that play vital roles in environmental monitoring, industrial manufacturing, smart health care, food security, and national defense. To achieve high sensitivity, selectivity, and ambient stability with rapid response and recovery speed, the regulation and adjustment of the nano/microstructure of the organic semiconductor (OSC) layer has proven to be an effective strategy. Here, the progress of OFET gas sensors with nano/microstructure is selectively presented. Devices based on OSC films one dimensional (1D) single crystal nanowires, nanorods, and nanofibers are introduced. Then, devices based on two dimensional (2D) and ultrathin OSC films, fabricated by methods such as thermal evaporation, dip‐coating, spin‐coating, and solution‐shearing methods are presented, followed by an introduction of porous OFET sensors. Additionally, the applications of nanostructured receptors in OFET sensors are given. Finally, an outlook in view of the current research state is presented and eight further challenges for gas sensors based on OFETs are suggested.