Thin-Film Morphology Control in Naphthalene-Diimide-Based Semiconductors: High Mobility n-Type Semiconductor for Organic Thin-Film Transistors

Abstract

In organic thin film transistors (OTFT), the morphology and microstructure of an organic thin film has a strong impact on the charge carrier mobility and device characteristics. To have well-defined and predictable thin film morphology, it is necessary to adapt the basic structure of semiconducting molecules in a way that results in an optimum crystalline packing motif. Here we introduce a new molecular design feature for organic semiconductors that provides the optimized crystalline packing and thin film morphology that is essential for efficient charge-carrier transport. Thus, cyclohexyl end groups in naphthalene diimide assist in directing intermolecular stacking leading to a dramatic improvement in field effect mobility. Accordingly, OTFT devices prepared with vapor deposited N,N′-bis(cyclohexyl) naphthalene-1,4,5,8-bis(dicarboximide) (1) regularly exhibit field effect mobility near 6 cm2/(V s), which is one of the highest carrier mobilities reported for either n- or p-type organic semiconducting thin films.

Semiconducting Organic Molecular Materials

“…5 (13, PDIs). Among NDIs, the highest mobility in inert atmosphere was found to be 6.2 cm 2 V −1 s −1 for 12a [21], while the highest mobility under ambient condition was found to be 0.57 cm 2 V −1 s −1 for 12b [22]. OFETs based on Fig.…”

Organic π‐Conjugated Molecules for Organic Semiconductors and Photovoltaic Materials

“…Among the first n-type semiconductors reported were NDI and PDI. Among NDI derivatives, the highest mobility in inert atmosphere was found to be 6.2 cm 2 V −1 s −1 for 53 (Figure 20.10) [79], and the highest mobility under ambient conditions was found to be 0.57 cm 2 V −1 s −1 for 54 [80]. OFETs based on 55 as one PDI derivative exhibited electron mobilities of 6.0 and 3.0 cm 2 V −1 s −1 in vacuum and in air, respectively, which are the highest reported for PDI derivatives [81].…”

N,N′-Bis(2-cyclohexylethyl)naphtho[2,3-b:6,7-b′]dithiophene Diimides: Effects of Substituents

“…The higher anisotropy of 4 than those of 1 and 3 can be explained by the shorter π-π stacking distance of 4, which enhances the orbital overlap in the stacking direction, and the existence of inter-columnar Cl-Cl interactions, which may reduce the LUMO-LUMO overlap owing to the fact that the chlorine atoms marginally contribute to the LUMO of 4. From the results of crystal structure analyses, the cyclohexyl group is not suitable for realizing the 2D π-stacking structure that was observed for CH-NDI [22].…”

“…Among the many NDI derivatives examined as the active material in thin-film transistors (TFTs), N,N′-dicyclohexyl NDI (CH-NDI) is one of the most promising because it affords high electron mobility (up to 6 cm 2 ·V −1 ·s −1 ) in TFT devices [22,23]. CH-NDI has a two-dimensional (2D) π-stacking structure, often referred to as a "brick layer" structure that is similar to the molecular arrangements of 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene) and related compounds [24].…”