During the last decades, small molecule organic semiconductors have been successfully used as active layer in organic field-effect transistors (OFETs). Despite the high mobility achieved so far with organic molecules, in order to progress in the field it is crucial to find techniques to process them from solution. The device reproducibility is one of the principal weak points of organic electronics for further commercialization. To achieve a high device-to-device reproducibility it is essential to control the morphology and polymorphism of the active layer for OFET application. In this work, the preparation of thin films is reported based on blends of the organic semiconductor dibenzotetrathiafulvalene (DB-TTF) and polystyrene by a solution shearing technique compatible with upscaling. Here, it is demonstrated that varying the deposition parameters (i.e., speed and temperature) or the solution formulation (i.e., semiconductor/binder polymer ratio) is possible to control the film morphology and semiconductor polymorphism and, hence, the different intermolecular interactions. It is demonstrated that the control of the thermodynamics and kinetics of the crystallization process is key for the device performance optimization. Further, this is the first time that DB-TTF thin films of the α-polymorph are reported.
Organic
semiconductors (OSCs) are promising materials for cost-effective
production of electronic devices because they can be processed from
solution employing high-throughput techniques. However, small-molecule
OSCs are prone to structural modifications because of the presence
of weak van der Waals intermolecular interactions. Hence, controlling
the crystallization in these materials is pivotal to achieve high
device reproducibility. In this perspective article, we focus on controlling
polymorphism and morphology in small-molecule organic semiconducting
thin films deposited by solution-shearing techniques compatible with
roll-to-roll systems. Special attention is paid to the influence that
the different experimental deposition parameters can have on thin
films. Further, the main characterization techniques for thin-film
structures are reviewed, highlighting the in situ characterization
tools that can provide crucial insights into the crystallization mechanisms.
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