Easily Processable Phenylene−Thiophene-Based Organic Field-Effect Transistors and Solution-Fabricated Nonvolatile Transistor Memory Elements

The synthesis of a new series of mixed phenylene-thiophene oligomers is reported; 2,5-bis(4-n-hexylphenyl)thiophene (dH-PTP, 1), 5,5'-bis(4-n-hexylphenyl)-2,2'-bithiophene (dH-PTTP, 2), 5,5' '-bis(4-n-hexylphenyl)-2,2':5',2' '-terthiophene (dH-PT(3)P, 3), 5,5' "-bis(4-n-hexylphenyl)-2,2':5',2' ':5' ',2' "-quaterthiophene (dH-PT(4)P, 4), 1,4-bis5-(4-n-hexylphenyl)-2-thienylbenzene (dH-PTPTP, 5), and 2,5-bis4(4'-n-hexylphenyl)phenylthiophene (dH-PPTPP, 6) were characterized by (1)H NMR, elemental analysis, UV-visible spectroscopy, differential scanning calorimetry, and thermogravimetric analysis. Vacuum-evaporated and solution-cast films were characterized by X-ray diffraction and scanning electron microscopy. All compounds display high p-type carrier mobilities as evaporated (up to 0.09 cm(2)/Vs) and as solution-cast (up to 0.03 cm(2)/Vs) films on both Si/SiO(2) and ITO/GR (glass resin) substrates. The straightforwardly synthesized dH-PTTP (2) displays an unprecedented combination of mobility, on/off ratio, stability, and processability. Both dH-PTTP (2) and dH-PPTPP (6) display a reversible, tunable, and stable memory effect even as solution-cast devices, with turn-on characteristics shifting from accumulation mode to zero or depletion mode after a writing voltage V(w) is applied. The charge storage is distributed over the gate dielectric structure and is concentrated near the dielectric-semiconductor interface, as evidenced by the response of "floating gate" configuration devices. Simple nonvolatile elements have been fabricated by solution-only techniques on ITO substrates using spin-coated glass resin, solution-cast oligomeric semiconductors, and painted graphite paste electrodes.