Tuning Crystal Ordering, Electronic Structure, and Morphology in Organic Semiconductors: Tetrathiafulvalenes as a Model Case

Abstract

Tetrathiafulvalenes (TTFs) are an appealing class of organic small molecules giving rise to some of the highest performing active materials reported for organic field effect transistors (OFETs). Because they can be easily chemically modified, TTF‐derivatives are ideal candidates to perform molecule–property correlation studies and, especially, to elucidate the impact of molecular and crystal engineering on device performance. A brief introduction into the state‐of‐the‐art of the field‐effect mobility values achieved with TTF derivatives employing different fabrication techniques is provided. Following, structure–performance relationships are discussed, including polymorphism, a phenomenon which is crucial to control for ensuring device reproducibility. It is also shown that chemical modification of TTFs has a strong influence on the electronic structure of these materials, affecting their stability as well as the nature of the generated charge carriers, leading to devices with p‐channel, n‐channel, or even ambipolar behaviour. TTFs have also shown promise in other applications, such as phototransistors, sensors, or as dopants or components of organic metal charge transfer salts used as source–drain contacts. Overall, TTFs are appealing building blocks in organic electronics, not only because they can be tailored to perform fundamental studies, but also because they offer a wide spectrum of potential applications.

Role of Polymorphism and Thin-Film Morphology in Organic Semiconductors Processed by Solution Shearing

“…The charge transport in OSCs is ruled by anisotropic intermolecular interactions, and hence controlling thin-film morphology and molecular packing is essential. 14 Because organic molecules are held together by weak nondirectional van der Waals forces, they are expected to exhibit many alternative packing arrangements, with minor differences in structure and energy, leading to polymorphism. Different polymorphs can have electronic performances that differ by orders of magnitude.…”

Crystal structure of 4,4′-bis(4-bromophenyl)-1,1′,3,3′-tetrathiafulvalene

“…So far significant progress has been achieved in improving the performance of organic field-effect transistors (OFETs) using such materials as oligoacenes, oligothiophenes and polythiophenes (Mas-Torrent & Rovira, 2011;Pfattner, et al, 2016). Numerous derivatives of the sulfur heterocycle 2,2 0 -bis(1,3dithiolylidene), known as tetrathiafulvalene (TTF), have been noted as components of OFETs (Fourmigué & Batail, 2004;Bendikov et al, 2004).…”

“…A comparatively high mobility was reported for biphenylsubstituted TTF (Noda et al, 2005(Noda et al, , 2007. Correlations between mobilities and herring-bone crystal structures have been investigated (Pfattner, et al, 2016;Mas-Torrent & Rovira, 2011), including for phenyl-substituted oligothiophenes (Noda et al, 2007). Among the numerous reported halogenated tetrathiafulvalenes (Fourmigué & Batail, 2004), only a few have been crystallographically characterized.…”

High Performance Organic Field‐Effect Transistors with Solid and Aqueous Dielectric Based on a Solution Sheared Sulfur‐Bridged Annulene Derivative

“…This different polymorph of DPTTA may be associated to a surface promoted growth as it has been commonly observed in other OSCs such as in tetrathiafulvalene derivatives. [32][33][34][35]…”