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.     

25th Anniversary Article: Organic Field‐Effect Transistors: The Path Beyond Amorphous Silicon

Over the past 25 years, organic field‐effect transistors (OFETs) have witnessed impressive improvements in materials performance by 3–4 orders of magnitude, and many of the key materials discoveries have been published in Advanced Materials. This includes some of the most recent demonstrations of organic field‐effect transistors with performance that clearly exceeds that of benchmark amorphous silicon‐based devices. In this article, state‐of‐the‐art in OFETs are reviewed in light of requirements for demanding future applications, in particular active‐matrix addressing for flexible organic light‐emitting diode (OLED) displays. An overview is provided over both small molecule and conjugated polymer materials for which field‐effect mobilities exceeding > 1 cm² V^–1 s^–1 have been reported. Current understanding is also reviewed of their charge transport physics that allows reaching such unexpectedly high mobilities in these weakly van der Waals bonded and structurally comparatively disordered materials with a view towards understanding the potential for further improvement in performance in the future.     

Exploiting Ionic Coupling in Electronic Devices: Electrolyte‐Gated Organic Field‐Effect Transistors

Currently there is great interest in using organic semiconductors to develop novel flexible electronic applications. An emerging strategy in organic semiconductor materials research involves development of composite or layered materials in which electronic and ionic conductivity is combined to create enhanced functionality in devices. For example, we and other groups have employed ionic motion to modulate electronic transport in organic field‐effect transistors using solid electrolytes. Not only do these transistors operate at low voltages as a result of greatly enhanced capacitive coupling, but they also display intriguing transport phenomena such as negative differential transconductance. Here, we discuss differences in operation between traditional (e.g., SiO₂) and electrolyte‐based dielectrics, suggest further improvements to currently used electrolyte materials, and propose several possibilities for exploiting electrolytes in future applications with both organic and inorganic semiconductors.     

Free‐Standing 2D Hexagonal Aluminum Nitride Dielectric Crystals for High‐Performance Organic Field‐Effect Transistors

The existence of defects and traps in a transistor plays an adverse role on efficient charge transport. In response to this challenge, extensive research has been conducted on semiconductor crystalline materials in the past decades. However, the development of dielectric crystals for transistors is still in its infancy due to the lack of appropriate dielectric crystalline materials and, most importantly, the crystal morphology required by the gate dielectric layer, which is also crucial for the construction of high‐performance transistor as it can greatly improve the interfacial quality of carrier transport path. Here, a new type of dielectric crystal of hexagonal aluminum nitride (AlN) with the desired 2D morphology of combing thin thickness with large lateral dimension is synthesized. Such a suitable morphology in combination with the outstanding dielectric properties of AlN makes it promising as a gate dielectric for transistors. Furthermore, ultrathin 2,6‐diphenylanthracene molecular crystals with only a few molecular layers can be prepared on AlN crystal via van der Waals epitaxy. As a result, this all‐crystalline system incorporating dielectric and semiconductor crystals greatly enhances the overall performance of a transistor, indicating the importance of minimizing defects and preparing high‐quality semiconductor/dielectric interface in a transistor configuration.