The correlation between gate dielectric, film growth, and charge transport in organic thin film transistors: the case of vacuum-sublimed tetracene thin films† Julia W¨ unsche, a Giuseppe Tarabella, b Simone Bertolazzi, a Maimouna Bocoum, a Nicola Copped` e, b Luisa Barba, c Gianmichele Arrighetti, c Luca Lutterotti, d Salvatore Iannotta, b Fabio Cicoira e and Clara Santato * a The complex interplay of dielectric substrate properties, semiconducting film growth, crystal structure, texture, and charge carrier transport is investigated for the case of tetracene films deposited on different dielectrics (polystyrene, parylene C, polymethylmethacrylate, hexamethyldisilazane-treated SiO 2 , and untreated SiO 2 ). The tetracene hole mobility, measured in the bottom-gate organic thin film transistor (OTFT) configuration, varies over more than one order of magnitude depending upon the dielectric layer used. Atomic force microscopy and synchrotron grazing incidence X-ray diffraction measurements, analyzed with the extended Rietveld method, were used to investigate the influence of film connectivity, crystalline phase, polymorphism, and texture on charge transport. The role of the surface polarity and the processing conditions of the gate dielectric layer are also discussed. Based on our results, we propose guidelines for the selection of a gate dielectric material favorable for charge transport in tetracene films. Introduction Organic electronic devices such as organic light-emitting diodes (OLEDs), 1 photovoltaic cells, 2 thin lm transistors (OTFTs), 3 light-emitting transistors, 4,5 and biosensors 6 are undergoing an impressive progress towards large area and exible applica- tions. OLEDs have already entered the market as components of at-panel displays and light sources. However, several chal- lenges still need to be overcome to make other organic elec- tronic devices viable for a wider range of applications. Organic semiconducting thin lms constitute the basis for the large majority of organic electronic devices, such as OTFTs. The characteristics of OTFTs are affected by several factors, such as the molecular arrangement in the lm, the lm morphology, and the properties of the interfaces between the organic lm and other device materials, such as metal elec- trodes, affecting charge injection, 7,8 and gate dielectrics. 9–12 In OTFTs, where it also acts as a substrate, the gate dielectric material plays a primary role in establishing charge transport properties. Along this line, we recently demonstrated that an appropriate choice of the gate dielectric material can enhance the hole mobility in tetracene TFTs by more than one order of magnitude. 13 For lms of a given molecular organic semiconductor, several growth modes and crystal structures are observed, as a result of the weak van der Waals intermolecular forces. 14,15 As a consequence, the substrate properties radically affect the morphology, crystal structure, and texture of organic lms. 16 The gate dielectric can also inuence the charge transport properties of OTFTs via the interfacial chemistry with the semiconductor, which can control the charge carrier trap density at the semiconducting lm–dielectric interface. 10,11 Moreover, a gate dielectric with high dielectric constant can affect the charge transport in the organic semiconductor in proximity to the dielectric due to the increase in both static (statistically oriented surface dipoles) and dynamic (enhanced electron–phonon coupling) disorder. 17–19 The objective of this work is to shed light on the role of the gate dielectric material in establishing the lm morphology, crystal structure, texture and charge transport in tetracene lms. Tetracene was selected for its combined charge carrier transport and electroluminescence properties, which have been exploited in organic (light-emitting) transistors. 20–24 We studied a D´ epartement de g´ enie physique, ´ Ecole Polytechnique de Montr´ eal, CP 6079, Succursale Centre-Ville, Montr´ eal, Qu´ ebec H3C 3A7, Canada. E-mail: clara. santato@polymtl.ca; Tel: +1 514 340-4711 # 2586 b IMEM-CNR, Parco Area delle Scienze 37/A, 43100 Parma, Italy c Institute of Crystallography, CNR, Strada Statale 14, Basovizza, Km 163,5 in AREA Science Park, 34149 Basovizza, Trieste, Italy d Dipartimento di Ingegneria dei Materiali, Universit` a di Trento, Via Mesiano, 77, 38123 Trento, Italy. E-mail: luca.lutterotti@ensicaen.fr e D´ epartement de g´ enie chimique, ´ Ecole Polytechnique de Montr´ eal, CP 6079, Succursale Centre-Ville, Montr´ eal, Qu´ ebec H3C 3A7, Canada † Electronic supplementary information (ESI) available: AFM and uorescence microscopy images, XRD reconstructed pole gures, output and transfer characteristics of tetracene TFTs. See DOI: 10.1039/c2tc00337f Cite this: J. Mater. Chem. C, 2013, 1, 967 Received 4th October 2012 Accepted 18th November 2012 DOI: 10.1039/c2tc00337f www.rsc.org/MaterialsC This journal is ª The Royal Society of Chemistry 2013 J. Mater. Chem. C, 2013, 1, 967–976 | 967 Journal of Materials Chemistry C PAPER Downloaded by CNR Milano on 07 January 2013 Published on 22 November 2012 on http://pubs.rsc.org | doi:10.1039/C2TC00337F View Article Online View Journal | View Issue