Assembly, structure, and performance of an ultra-thin film organic field-effect transistor (OFET) based on substituted oligothiophenes

作者：Haubner K; Jaehne E^*; Adler H J P; Koehler D; Loppacher C; Eng L M; Grenzer J; Herasimovich A; Scheinert S

来源：Physica Status Solidi (A) Applications and Materials Science, 2008, 205(3): 430-439.

DOI：10.1002/pssa.200723407

We report on the improved assembly and characterization of a small molecule organic field-effect transistor (OFET). Novel alpha,omega-dicyano substituted beta,beta'-dibutylquaterthiophene molecules (DCNDBQT) were synthesized and characterized by UV-Vis spectroscopy, differential scanning calorimetry, thermal gravimetric analysis and cyclic voltammetry. The ultra-thin organic film formation on TiO2 templates was effectively promoted through the specifically designed bifunctional self assembly molecules (SAM) 5-cyano-2-(butyl-4-phosphonic acid)-3-butylthiophene (CNBTPA). Excellent structural properties were found for up to 9 DCNDBQT molecule thick films prepared through UHV vacuum sublimation as investigated with UHV non-contact atomic force microscopy (nc-AFM) and X-ray diffraction. Both X-ray and nc-AFM data indicate that the DCNDBQT molecules form a well-ordered terraced structure exhibiting step heights of 1.5 nm to 2.0 nm layers. Hence, the DCNDBQTmolecules are linked to the functional SAM interface layer by H-bond inter-actions (see structure model) standing quasi perpendicular to the TiO2 template, and thus providing optimal orbital overlap neighbouring thiophene rings.
The vacuum sublimated DCNDBQT molecules form a closed packed and dense molecular layer that was used to construct and operate a nanoscopic OFET-structure. The resulting field mobilities of 10(-5) cm(2) V-1 s(-1) reflect a high current density in our ultrathin but highly ordered structure.

• 出版日期2008-3