Organic single crystals: Addressing the fundamentals of organic electronics

Organic optoelectronics is an emerging field that exploits the unique properties of conjugated organic materials to develop new applications that require a combination of performance, low cost, light weight, and processability. For instance, disposable or wearable electronics, light-emitting diodes, smart tags, sensors, and solar cells all fall into this active area of research. Single crystals of conjugated organic molecules are, undoubtedly, the materials with the highest degree of order and purity among the variety of different forms of organic semiconductors. Electronic devices comprising these materials, such as single-crystal transistors and photoconductors developed during the last decade, are by far the best performers in terms of the fundamental parameters such as charge-carrier mobility, exciton diffusivity, concentration of defects, and operational stability. Extremely low density of defects and the resultant remarkable electrical characteristics of some of the organic single-crystal devices allow experimental access to the intrinsic charge transport properties not dominated by charge scattering and trapping. This enables basic studies of the physics of organic semiconductors, including examining the intrinsic structure-property relationship, thus providing a test bed for charge and energy transport theories. The goal of this issue of MRS Bulletin is to provide a broad overview of the state of the art of the field of organic semiconductor single-crystal materials, devices, and theory.