Anisotropic perylenediimide/polycarbonate composites produced by a single batch solution based method Ewa Dobruchowska a,b, ⁎, Tomasz Marszalek a , Jacek Ulanski a a Department of Molecular Physics, Technical University of Lodz, Zeromskiego 116, 90-924 Lodz, Poland b Institute of Technology and Education, Koszalin University of Technology, Sniadeckich 2, 75-453 Koszalin, Poland abstract article info Article history: Received 9 April 2013 Received in revised form 4 June 2014 Accepted 5 June 2014 Available online 13 June 2014 Keywords: Perylenediimide Anisotropic crystalline layer Bi-layer composite Zone-casting Polarised UV–Vis spectroscopy Polarised photoluminescence The continuous anisotropic organic semiconductor/dielectric composites consisting of a top, unidirectionally oriented crystalline layer of perylenediimide derivative (2,9-di(pent-3-yl)-anthra[1,9-def:6,5,10-d′e′f′] diisoquinoline-1,3,8,10-tetrone) (PTCDI-C5(3)) and a bottom layer of poly(bisphenol A carbonate) (PC) support were obtained in a one batch solution process, with the use of the so called the zone-casting method. Scanning electron microscopy images have shown that the top PTCDI-C5(3) layer is made of long, parallel crystallites in the form of ribbons that exhibit birefringence when placed between a pair of crossed polarisers in the optical mi- croscope. Furthermore, the polarised UV–Vis absorbance and photoluminescence experiments revealed that the alignment of the PTCDI-C5(3) molecules is caused by π–π interactions between the conjugated perylene cores, and their stacks are parallel to the long axis of the crystallites and to the polymer surface. The high value of the calculated polarisation ratio, which equals 0.64, constitutes a confirmation of a high degree of molecular order within the semiconducting component of the zone-cast composites. © 2014 Elsevier B.V. All rights reserved. 1. Introduction The implementation of organic electronics on large areas demands multifunctional materials with clearly defined structures and properties which can be obtained in a reproducible, and requiring only a few pro- duction steps way [1,2]. Particularly, the organic field effect transistor performance depends strongly on the packing motif of organic semicon- ducting molecules in the active layer [3,4]. It is required that the mole- cules lay with “edge on” orientation in respect to the substrate, since such an alignment ensures efficient charge carrier transport along the conducting channel. This approach demands: firstly, soluble materials with a tendency for self-organisation, and secondly, effective methods of processing, yielding active layers with desired morphology. The first condition may be fulfilled by organic compounds in which molecules consist of large macrocyclic aromatic cores substituted peripherally with alkyl chains. Then, co-facially packed molecules, assembled into columnar structures, guarantee strong π-orbital overlapping and facili- tate long distance π-electron delocalisation [5–7]. Amongst the methods which allow the preparation of ordered structures, these ones that are solution based are highly valued on account of their sim- plicity and low cost [8,9]. Another advantage, in contrast to e.g. vacuum deposition techniques, is the relatively small amount of domain bound- aries in the obtained active layers. It is known that such defects present in the area between the electrodes might act as trapping centres for accumulated charge carriers and significantly reduce the device performance [10,11]. In this work, we describe optical properties of highly ordered, bi-layer and bi-functional composites, obtained in a one batch solution process, consisting of highly oriented semiconducting crystals laying on the poly- mer support which also may serve as a dielectric component [12,13]. The proposed solution eliminates one of the stages in the fabrication of fully organic field effect transistors. The preparation of composites of this kind has been made possible by using the so-called the zone-casting technique. The general idea behind the term “zone-casting” is that the solution of both components, polymer and “dopant”, is continuously de- posited through a nozzle onto a moving substrate. The driving forces of the molecular alignment are the solute concentration gradient and the temperature gradient in the meniscus region, where the molecules of the low molecular weight organic semiconductor become gradually less mobile, and when their critical concentration is reached they adapt ordered structures. There are practically unlimited possibilities of changing the system's composition: different low molecular weight dopants, polymers, solvents and also casting parameters (solution sup- ply rate, substrate velocity, solvent evaporation rate, temperature and crystallisation rate) that make the method very flexible [14]. The first application of zone-casting was realised for highly anisotropic conducting composites consisting of inner polymer matrix and organic charge transfer complexes (quasi one-dimensional organic Thin Solid Films 564 (2014) 361–366 ⁎ Corresponding author at: Institute of Technology and Education, Koszalin University of Technology, Sniadeckich 2, 75-453 Koszalin, Poland. Tel.: +48 94 348 66 51; fax: +48 94 348 66 52. E-mail address: ewa.dobruchowska@tu.koszalin.pl (E. Dobruchowska). http://dx.doi.org/10.1016/j.tsf.2014.06.013 0040-6090/© 2014 Elsevier B.V. All rights reserved. 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