Wide band gap pyromellitic diimides for photo stable n-channel thin film transistors

This study reports two novel n-channel pyromellitic diimide (PyDI) derivatives, PyDI-BOCF₃and PyDI-BSCF₃, with particularly wide energy gaps of 3.56 eV and 3.49 eV in the solid state, respectively, which induce the investigations of their charge transport properties, photostabilities and thin-film transparency of organic field-effect transistors (OFETs) in this work. Although PyDI-BOCF₃and PyDI-BSCF₃exhibit similar two-dimensional (2D) lamellar packing motifs, PyDI-BSCF₃demonstrates stronger electronic couplings than those of PyDI-BSCF₃, suggesting it may show better electrical performance in OFETs. As predicted, PyDI-BSCF₃shows an electron mobility of 0.09 cm²V⁻¹s⁻¹at a deposition temperature of 70 °C in ambient air, which is higher than the electron mobility of 0.058 cm²V⁻¹s⁻¹, obtained for PyDI-BOCF₃. In contrast, PyDI-BOCF₃exhibits better thermal stability of mobility, which was maintained at ∼0.056 cm²V⁻¹s⁻¹after increasing the deposition temperature from room temperature (RT) to 70 °C. More importantly, it is worth mentioning that the wide energy gaps of PyDI-BOCF₃and PyDI-BSCF₃lead to excellent photostability in OFETs at illumination conditions and optical transparency in the visible range even better than that of DPh-BTBT thin films on transparent glass and flexible PET substrates.