Ambipolar Transport in Organic Conjugated Materials

The relative mobility of holes versus electrons in π‐conjugated materials is a long‐standing issue in the field of organic electronics. In this Progress Report, we first argue on the basis of theoretical considerations that in general organic semiconductors are intrinsically as good electron transporters as they are hole transporters. Then, in the light of selected experimental works, we discuss the origin of the features that prevent the observation of intrinsic electron transport, and the strategies that have been developed to promote ambipolar transport in field‐effect transistors.     

Controlling Electronic States and Transport Properties at the Level of Single Molecules

Since molecular electronics has been rapidly growing as a promising alternative to conventional electronics towards the ultimate miniaturization of electronic devices through the bottom‐up strategy, it has become a long‐term desire to understand and control the transport properties at the level of single molecules. In this Research News article it is shown that one may modify the electronic states of single molecules and thus control their transport properties through designing and fabrication of functional molecules or manipulating molecules with scanning tunneling microscopy. The rectifying effect of single molecules can be realized by designing a donor–barrier–acceptor architecture of Pyridine–σ–C₆₀ molecules to achieve the Aviram–Ratner rectifier and by modifying electronic states through azafullerene C₅₉N molecules. The effect of the negative differential resistances can be realized by appropriately matching the molecular orbital symmetries between a cobalt phthalocyanine (CoPc) molecule and a Ni electrode. The electronic states and transport properties of single molecules, such as CoPc and melamine molecules, can be altered through manipulation or modifying molecular structures, leading to functionalized molecular devices.     

电子传输材料及其在有机光导体中的应用

电子传输材料按其结构可分为多硝基化合物,氰基化合物,醌类化合物和萘的酸酐衍生物等。用它们制备的载流子传输层因其表面负载正电荷而不产生臭氧,所以用于制备环保型正电性有机光导体。本文重点讨论了醌类电子传输材料在单层、双层及双极性光导体中的应用研究进展。     

Electrical Scanning Probe Microscopy on Active Organic Electronic Devices

Polymer‐ and small‐molecule‐based organic electronic devices are being developed for applications including electroluminescent displays, transistors, and solar cells due to the promise of low‐cost manufacturing. It has become clear that these materials exhibit nanoscale heterogeneities in their optical and electrical properties that affect device performance, and that this nanoscale structure varies as a function of film processing and device‐fabrication conditions. Thus, there is a need for high‐resolution measurements that directly correlate both electronic and optical properties with local film structure in organic semiconductor films. In this article, we highlight the use of electrical scanning probe microscopy techniques, such as conductive atomic force microscopy (c‐AFM), electrostatic force microscopy (EFM), scanning Kelvin probe microscopy (SKPM), and similar variants to elucidate charge injection/extraction, transport, trapping, and generation/recombination in organic devices. We discuss the use of these tools to probe device structures ranging from light‐emitting diodes (LEDs) and thin‐film transistors (TFT), to light‐emitting electrochemical cells (LECs) and organic photovoltaics.     

Molecular Transport Junctions: Clearing Mists

Recent progress in the measurement and modeling of transport in molecular junctions has been very significant. Tunnel transport in the Landauer–Imry regime is now broadly understood for several systems, although a detailed understanding of the role of contact geometry is still required. We overview some clear indications from recent research and note the quite reasonable agreement between measured and calculated conductance in metal–molecule–metal junctions. The next challenge lies in obtaining a microscopic understanding of charge transport that involves reduction or oxidation of molecules.