www.advmat.de www.MaterialsViews.com REVIEW © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Adv. Mater. 2011, 23, 268–284 wileyonlinelibrary.com 268 Xiaowei Zhan,* Antonio Facchetti,* Stephen Barlow,* Tobin J. Marks,* Mark A. Ratner,* Michael R. Wasielewski,* and Seth R. Marder* Rylene and Related Diimides for Organic Electronics Prof. X. Zhan Beijing National Laboratory for Molecular Sciences Institute of Chemistry Chinese Academy of Sciences, Beijing 100190, China E-mail: xwzhan@iccas.ac.cn Prof. A. Facchetti, Prof. T. J. Marks, Prof. M. A. Ratner, Prof. M. R. Wasielewski Department of Chemistry Materials Research Center, and Argonne-Northwestern Solar Energy Research Center Northwestern University Evanston, Illinois 60208-3113, USA E-mail: a-facchetti@northwestern.edu; t-marks@northwestern.edu; ratner@northwestern.edu; m-wasielewski@northwestern.edu Prof. A. Facchetti Polyera Corporation Skokie, Illinois 60077, USA Dr. S. Barlow, Prof. S. R. Marder School of Chemistry and Biochemistry Center for Organic Photonics and Electronics Georgia Institute of Technology Atlanta, Georgia 30332-0400, USA E-mail: Stephen.barlow@chemistry.gatech.edu; seth.marder@chemistry.gatech.edu DOI: 10.1002/adma.201001402 1. Introduction Organic charge-transporting materials are π -conjugated mole- cular or polymeric compounds in which charge carriers migrate under the influence of an electric field. These materials can be classified as hole- or electron-transport (HT or ET) mate- rials according to whether the majority charge carriers, under a given set of conditions, arise from removal of electrons from the manifold of filled molecular orbitals or from the addition of electrons to empty orbitals, respectively. [1] Organic HT and ET materials differ from classical inorganic p- and n-type semicon- ductors in that they are generally undoped, and so that very few charge carriers are typ- ically present except under an applied field, in which case carriers can be injected from electrodes, from other proximate organic materials, or are generated via photoexci- tation. Charge transport can be described as a series of successive electron-transfer reactions between neutral and charged molecular or polymeric repeat units. In the hopping transport regime this process involves essentially localized radical cat- ions (HT) or anions (ET) and the corre- sponding neutral species, while the orbitals of a π -conjugated polymer chain can facilitate intrachain electron transfer in the superexchange or coherent tunneling regime. [2] The tendency of the holes (electrons) to migrate under the influence of a field can be described by the hole (electron) mobility, μ, of the mate- rial; this has units of velocity per unit field and is, in general, dependent on both the electric field and temperature. An addi- tional class of materials, ambipolar materials, have similar hole and electron mobilities and can act as either HT or ET mate- rials, depending on the dominant injection processes occurring under the experimental conditions of interest. In general, development of high-performance (environmen- tally stable, high-mobility) organic ET materials has lagged behind that of HT materials despite their importance for fabri- cating organic photovoltaic (OPV) cells and n-channel organic field-effect transistors (OFETs), which are particularly valuable as components of organic complementary logic circuits, which require both p- and n-channel transistors. [3,4] To achieve accept- able performance, ET materials must have: i) high electron affinity (ideally greater than ≈3 eV, but not exceeding ≈5 eV) to facilitate injection from contacting electrodes in OFETs or to facil- itate exciton separation in conjunction with typical HT materials for OPV applications; ii) good intermolecular electronic orbital overlap to facilitate high mobility; and iii) good air stability, ide- ally both as neutral and radical anion materials and, as discussed in more detail below, under device operating conditions. [1] For general reviews on ET materials, see references [1,3] and [4]. The criteria for useful ET materials described above can often be met by appending strong electron-withdrawing substituents, such as fluoro, cyano, or acyl, to π -conjugated cores such as acenes and oligothiophenes, which, in the absence of these sub- stituents, exhibit HT properties. Other classes of ET materials, such as the fullerenes, which have been widely studied for a Organic electron-transporting materials are essential for the fabrication of organic p-n junctions, photovoltaic cells, n-channel field-effect transistors, and complementary logic circuits. Rylene diimides are a robust, versatile class of polycyclic aromatic electron-transport materials with excellent thermal and oxidative stability, high electron affinities, and, in many cases, high electron mobilities; they are, therefore, promising candidates for a variety of organic electronics applications. In this review, recent developments in the area of high-electron-mobility diimides based on rylenes and related aromatic cores, particularly perylene- and naphthalene-diimide-based small molecules and polymers, for application in high-performance organic field-effect transistors and photovoltaic cells are summarized and analyzed.