Synthesis and characterization of carbazole- and α-carboline-based thiophene derivatives as organic semiconductors for organic thin-film transistors

• Three novel organic semiconductors based on carbazole and α-carboline moieties were developed.
• Organic thin-film transistors containing the new semiconductors were fabricated and characterized.
• The semiconductor with both carbazole and α-carboline moieties exhibited good device performance.

New thiophene derivatives, end-functionalized with carbazoles (9-(5-(9H-carbazol-9-yl)thiophen-2-yl)-9H-carbazole), carbazole and α-carboline (9-(5-(9H-carbazol-9-yl)thiophen-2-yl)-9H-pyrido[2,3-b]indole), and α-carbolines (9-(5-(9H-pyrido[2,3-b]indol-9-yl)thiophen-2-yl)-9H-pyrido[2,3-b]indole) were synthesized and characterized as organic semiconductors for organic thin-film transistors (OTFTs). The best device performance was achieved via a hexamethyldisilazane dielectric surface treatment of thermally grown Si–SiO2 substrates prior to vapor-phase semiconductor deposition. Within this family, the semiconductor having an electron-donating (carbazole) and an electron-withdrawing (α-carboline) substituent exhibited the highest p-channel characteristic with a carrier mobility as high as 0.014 cm2 V−1 s−1 and a current on/off ratio of 7 × 105 for top-contact/bottom-gate OTFT devices. The device characteristics have been correlated with the film morphologies and microstructures of the corresponding compounds.

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