The synergistic role of azeotropic solvent mixtures and atactic polystyrene on the morphology, crystallization and field
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The synergistic role of azeotropic solvent mixtures and atactic polystyrene on the morphology, crystallization and field effect mobility of thin film 6,13-bis(triisopropylsilylethynyl)-pentacene based semiconductors Isam Abdullah1 · He Lan2 · John Morrison2 · Ahmed Alharbi2 · J. Emyr Macdonald1 · Stephen G. Yeates2 Received: 4 December 2017 / Accepted: 30 March 2018 © Springer Science+Business Media, LLC, part of Springer Nature 2018
Abstract The effect of anisole/decane binary solvent mixture and the subsequent addition of low wt% aPS on 6,13-bis(triisopropylsilylethynyl)-pentacene (TIPS-pentacene) thin film morphology is investigated by optical microscopy, AFM and UV–Vis measurements. We show that, over the composition range anisole/decane of 96/4 to 85/15 wt%, the solution maintains an azeotropic composition with the boiling point of the binary mixture remaining constant at 152 °C, and the solvent composition remaining constant during evaporation and drying. It was found that addition of up to 20 wt% decane has little impact on micro-scale crystal morphology but has a significant influence on the growth mode and terrace roughness. The formation of large crystals is explained in terms of the change in solvent, increase in decane content, weakening the solute–solvent interactions and promoting efficient nucleation of the favoured H-aggregates of TIPS-pentacene. The effect of the TIPS-pentacene—aPS ratio up to 20 wt% for drop-cast thin film was similarly investigated. It is found that addition of aPS has a significant effect on both macroscopic crystal properties such as surface coverage, unity of orientation and long range order. It also changes the surface morphology and layer ordering on the nano-scale.
1 Introduction Whilst the highest charge carrier mobilities in small molecule organic semi-conductors (OSC) have been obtained from single crystal studies [1], the performance of solution grown crystalline thin films have improved dramatically over recent years [2, 3]. These improvements in organic field effect transistor (OFET) device performance have been brought about in the main by a greater understanding on the role of morphology and molecular alignment in the charge transfer efficiency of thin films [4–7]. Morphology control strategies for solution processing OSC thin films have recently been reviewed [8], with a focus on three distinct aspects: control of nucleation, crystal growth, and domain * Stephen G. Yeates [email protected] 1
School of Physics and Astronomy, Cardiff University, The Parade, Cardiff CF24 3AA, UK
Organic Materials Innovation Centre (OMIC), School of Chemistry, The University of Manchester, Manchester M13 9PL, UK
2
alignment, with particular emphasis on methods that exploit the unique characteristics of solution processing. 6,13-Bis(triisopropylsilylethynyl)-pentacene (TIPSpentacene) has become a standard high performance OSC and there is a wealth of recent studies showing how formulation [9–11] and process parameters [12–14] can give rise to organic field effe
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