Abstract:In this study, several naphthalene tetracarboxylic acid diimide (NTCDI) 2 derivatives substituted at the N and N' positions with long normal alkyl chains of different lengths were evaluated as soluble n-type organic thin-film transistor (TFT) materials. NTCDI derivatives with diundecyl (NTCDI-C11), didodecyl (NTCDI-C12), and ditridecyl (NTCDI-C13) exhibited acceptable solubility in chloroform, and their TFTs showed typical n-type TFT performance with relatively high field effect electron mobility (~0.2 cm 2 /Vs) after annealing at a workable temperature of 150 °C. Although NTCDI with dioctyl (NTCDI-C8) showed good solubility in chloroform, the TFT performance of this material was highly inferior to that of NTCDI-C11, NTCDI-C12, or NTCDI-C13. We could not anneal NTCDI-C8 thin films at workable temperatures in vacuo because of sublimation of the material from the substrates. In contrast, NTCDI with dipentadecyl (NTCDI-C15) and dioctadecyl (NTCDI-C18) exhibited both poor solubility for chloroform and poor TFT performance. In short, these compounds are not suitable as soluble n-type organic TFT materials.

In this study, vacuum-evaporated thin films of several naphthalene tetracarboxylic acid diimide derivatives substituted at the N and N′ positions with long normal alkyl chains of varying lengths (NTCDI-Cn) were evaluated as active materials for n-type organic thin-film transistors (TFTs). The electron mobility (μe) of the TFTs increased with increasing chain length from octyl (NTCDI-C8) to pentadecyl (NTCDI-C15); those of NTCDI-C15 and C18 TFTs were of 0.262 ± 0.016 and 0.222 ± 0.016 cm2 V−1 s−1, respectively. However, the threshold voltage of the TFTs increased with increasing chain length.

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The authors report a novel perylene derivative [N,N '-bis(3-dodecyloxy-propyl)-perylene tetracarboxylic diimide, PTCDI-C3OC12] as a soluble high-performance n-type organic semiconductor. The solubility of the PTCDI derivative was increased sufficiently to be handled using wet processes by inserting ether groups in side alkyl chains of the PTCDI derivative. The highest electron mobility obtained for a spin-coated PTCDI-C3OC12 film was 0.52 cm2/(V·s) with a very low threshold voltage of ca. 2 V. This high performance of PTCDI-C3OC12 is explained by the large grain size with an appropriate molecular packing pattern and tight intergrain connections.