High crystalline dithienosilole-cored small molecule semiconductor for ambipolar transistor and nonvolatile memory

We characterized the electrical properties of a field-effect transistor (FET) and a nonvolatile memory device based on a solution-processable low bandgap small molecule, Si1TDPP-EE-C6. The small molecule consisted of electron-rich thiophene-dithienosilole-thiophene (Si1T) units and electron-deficient diketopyrrolopyrrole (DPP) units. The as-spun Si1TDPP-EE-C6 FET device exhibited ambipolar transport properties with a hole mobility of 7.3 × 10^-5 cm²/(V s) and an electron mobility of 1.6 × 10^-5 cm²/(V s). Thermal annealing at 110 °C led to a significant increase in carrier mobility, with hole and electron mobilities of 3.7 × 10^-3 and 5.1 × 10^-4 cm²/(Vs), respectively. This improvement is strongly correlated with the increased film crystallinity and reduced π-π intermolecular stacking distance upon thermal annealing, revealed by grazing incidence X-ray diffraction (GIXD) and atomic force microscopy (AFM) measurements. In addition, nonvolatile memory devices based on Si1TDPP-EE-C6 were successfully fabricated by incorporating Au nanoparticles (AuNPs) as charge trapping sites at the interface between the silicon oxide (SiO₂) and cross-linked poly(4-vinylphenol) (cPVP) dielectrics. The device exhibited reliable nonvolatile memory characteristics, including a wide memory window of 98 V, a high on/off-current ratio of 1 × 10³, and good electrical reliability. Overall, we demonstrate that donor-Acceptor-type small molecules are a potentially important class of materials for ambipolar FETs and nonvolatile memory applications.