Xiaotao Zhang

Abstract Organic semiconducting single crystals (OSSCs) are ideal candidates for the construction of high‐performance optoelectronic devices/circuits and a great platform for fundamental research due to their long‐range order, absence of grain boundaries, and extremely low defect density. Impressive improvements have recently been made in organic optoelectronics: the charge‐carrier mobility is now over 10 cm 2 V −1 s −1 and the fluorescence efficiency reaches 90% for many OSSCs. Moreover, high mobility and strong emission can be integrated into a single OSSC, for example, showing a mobility of up to 34 cm 2 V −1 s −1 and a photoluminescence yield of 41.2%. These achievements are attributed to the rational design and synthesis of organic semiconductors as well as improvements in preparation technology for crystals, which accelerate the application of OSSCs in devices and circuits, such as organic field‐effect transistors, organic photodetectors, organic photovoltaics, organic light‐emitting diodes, organic light‐emitting transistors, and even electrically pumped organic lasers. In this context, an overview of these fantastic advancements in terms of the fundamental insights into developing high‐performance organic semiconductors, efficient strategies for yielding desirable high‐quality OSSCs, and their applications in optoelectronic devices and circuits is presented. Finally, an overview of the development of OSSCs along with current challenges and future research directions is provided.

Flexible electronics have attracted considerable attention recently given their potential to revolutionize human lives. High-performance organic crystalline materials (OCMs) are considered strong candidates for next-generation flexible electronics such as displays, image sensors, and artificial skin. They not only have great advantages in terms of flexibility, molecular diversity, low-cost, solution processability, and inherent compatibility with flexible substrates, but also show less grain boundaries with minimal defects, ensuring excellent and uniform electronic characteristics. Meanwhile, OCMs also serve as a powerful tool to probe the intrinsic electronic and mechanical properties of organics and reveal the flexible device physics for further guidance for flexible materials and device design. While the past decades have witnessed huge advances in OCM-based flexible electronics, this review is intended to provide a timely overview of this fascinating field. First, the crystal packing, charge transport, and assembly protocols of OCMs are introduced. State-of-the-art construction strategies for aligned/patterned OCM on/into flexible substrates are then discussed in detail. Following this, advanced OCM-based flexible devices and their potential applications are highlighted. Finally, future directions and opportunities for this field are proposed, in the hope of providing guidance for future research.

Cocrystal engineering with a noncovalent assembly feature by simple constituent units has inspired great interest and has emerged as an efficient and versatile route to construct functional materials, especially for the fabrication of novel and multifunctional materials, due to the collaborative strategy in the distinct constituent units. Meanwhile, the precise crystal architectures of organic cocrystals, with long-range order as well as free defects, offer the opportunity to unveil the structure-property and charge-transfer-property relationships, which are beneficial to provide some general rules in rational design and choice of functional materials. In this regard, an overview of organic cocrystals in terms of assembly, containing the intermolecular interactions and growth methods, two functionality-related factors including packing structure and charge-transfer nature, and those advanced and novel functionalities, is presented. An outlook of future research directions and challenges for organic cocrystal is also provided.

Because of their advantages, including easy tunability of optical and electrical properties by tailoring the molecular structure, flexibility, and compatibility with a low-temperature fabricating process, the use of organic semiconductors (OSCs) as active layers has shown strong competitiveness as candidates for use in next-generation high-sensitivity organic photodetectors (OPDs). Infrared (IR) OPDs that are sensitive to illumination at wavelengths higher than 780 nm have been rapidly developed in recent years driven by potential applications such as remote control, night vision, and imaging as well as biomedical monitoring. In this review, after a brief illustration of the mechanisms, we summarize the recent advances in high-performance IR organic photodiodes (OPDIs) and organic phototransistors (OPTs). We will highlight the state-of-the-art protocols for constructing qualified IR OPDs, including new OSCs with excellent photoelectric properties, optimization of active-layer-fabrication processes, and novel device architectures. Thereafter, we will discuss the IR organic light detector as a platform for integrated applications, such as health monitoring, spectrometric analysis, and electronic eyes. This review aims to provide readers with a deeper understanding of the design of future IR OPDs and IR-OPD-based integrated practices.