Detailed analysis and contact properties of low-voltage organic thin-film transistors based on dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene (DNTT) and its didecyl and diphenyl derivatives

• Systematic comparison of low-voltage organic thin-film transistors based on pentacene, DNTT, C10-DNTT and DPh-DNTT.
• Study of morphology, effective and intrinsic mobilities, contact resistance and of the reproducibility of performance parameters.
• DPh-DNTT TFTs provide a smaller contact resistance than C10-DNTT and DNTT TFTs.
• This results in notably larger effective mobilities, especially in transistors with reduced channel lengths (L).
• For L = 1 µm, an on/off ratio of 108, a subthreshold swing of 100 mV/decade and an effective mobility of 0.68 cm2/Vs were measured.

Low-voltage organic thin-film transistors (TFTs) based on four different small-molecule semiconductors (pentacene, DNTT (dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene), C10-DNTT and DPh-DNTT) were fabricated, and a detailed comparison of the semiconductor thin-film morphology, of the current-voltage characteristics of transistors with channel lengths ranging from 100 to 1 μm, and of the contact resistances is provided. The three thienoacene derivatives DNTT, C10-DNTT and DPh-DNTT all have significantly larger charge-carrier mobilities and smaller contact resistances than pentacene. In terms of the intrinsic channel mobility (determined using the transmission line method), C10-DNTT and DPh-DNTT perform quite similarly and notably better than DNTT, suggesting that the decyl substituents in C10-DNTT and the phenyl substituents in DPh-DNTT provide a similar level of enhancement of the charge-transport characteristics over DNTT. However, the DPh-DNTT TFTs have a substantially smaller contact resistance than both the DNTT and the C10-DNTT TFTs, resulting in notably larger effective mobilities, especially in transistors with very small channel lengths. For DPh-DNTT TFTs with a channel length of 1 μm, an effective mobility of 0.68 cm2/V was determined, together with an on/off ratio of 108 and a subthreshold swing of 100 mV/decade.

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