High‐Performance Air‐Stable n‐Type Organic Transistors Based on Core‐Chlorinated Naphthalene Tetracarboxylic Diimides

Abstract

Core‐chlorinated naphthalene tetracarboxylic diimides (NDIs) with fluoroalkyl chains are synthesized and employed for n‐channel organic thin‐film transistors (OTFTs). Structural analyses of the single crystals and thin films are performed and their charge‐transport behavior is investigated in terms of structure–property relationships. NDIs with two chlorine substituents are shown to exhibit a herringbone structure with a very close π‐plane distance (3.3–3.4 Å), a large π‐stack overlap (slipping angle ca. 62°), and high crystal densities (2.046–2.091 g cm−3). These features result in excellent field‐effect mobilities of up to 1.43 cm2 V−1 s−1 with minimal hysteresis and high on–off ratios (ca. 107) in air. This is similar to the highest n‐channel mobilities in air reported so far. Despite the repulsive interactions of bulky Cl substituents, tetrachlorinated NDIs adopt a slip‐stacked face‐to‐face packing with an interplanar distance of around 3.4 Å, resulting in a high mobility (up to 0.44 cm2 V−1 s−1). The air‐stability of dichlorinated NDIs is superior to that of tetrachlorinated NDIs, despite of their higher LUMO levels. This is closely related to the denser packing of the fluorocarbon chains of dichlorinated NDIs, which serves as a kinetic barrier to the diffusion of ambient oxidants. Interestingly, these NDIs show an optimal performance either on bare SiO2 or on octadecyltrimethoxysilane (OTS)‐treated SiO2, depending on the carbon number of the fluoroalkyl chains. Their synthetic simplicity and processing versatility combined with their high performance make these semiconductors highly promising for practical applications in flexible electronics.

Single-crystal field-effect transistors of new Cl2-NDI polymorph processed by sublimation in air

“…In the following, we will denote this polymorph by b-phase, whereas the formerly described phase 35 with smaller layer spacing is called a-phase. Based on these new results, we can now also re-assign the hitherto reported vacuum-processed thin-film transistors 31 to relate to the b-phase molecular packing arrangement.…”

“…3b). Because the formerly published single-crystal data for the a-phase were of low quality 31 , we grew new crystals of this polymorph by the solution evaporation method (Supplementary Table 1 and Supplementary Fig. 1b).…”

“…The synthesis of Cl 2 -NDI and the growth of a-phase crystals had been described in the earlier literature 31,35 . The b-phase single crystals were grown by sublimation at ambient pressure in air and then deposited on Si/SiO 2 substrate.…”

“…In recent years, our group as well as others reported a significant number of naphthalene diimide (NDI)-based thin film transistor studies demonstrating excellent and stable n-channel operation even in air that can be attributed to a large electron affinity and close p-stacking [30][31][32][33][34][35][36] . For NDI small molecules, the highest mobilities could be obtained for thin-film transistors of DI-DTYM2 (3.5 cm 2 V À 1 s À 1 ) 34 and for single-crystal transistors of Cl 2 -NDI (8.6 cm 2 V À 1 s À 1 ) 35 , respectively, under ambient operation.…”

Comparative study of soluble naphthalene diimide derivatives bearing long alkyl chains as n-type organic thin-film transistor materials

“…However, naphthalene tetracarboxylic acid diimide (NTCDI) is an analog of PTCDI that has a reduced -electron system compared with that of PTCDI, and has received increasing attention as a building block for soluble n-type organic semiconductors. [8,[20][21][22][23][24][25] Molecules coupled with a rigid -electron core and alkyl chains frequently exhibit thermotropic liquid crystalline mesophases. Furthermore, molecules move easier in liquid crystal phases than in solid phases because of higher fluidity.…”