Engineering the Template Layer for Silicon Phthalocyanine-Based Organic Thin Film Transistors

Multi-phenyl and multi-thiophene rod-like molecules are typically used for weak epitaxial growth (WEG) of highly ordered organic semiconductor films enabling controllable microstructure properties and improved device performance. However, very few templating molecules have been reported, making it challenging to establish structure-property relationships. As semiconductors are integrated into organic thin film transistors (OTFTs), the impact of templating layers on semiconductor microstructure and device performance must be established. Herein, four aromatic molecules with similar structure to para-sexiphenyl (p-6P) are synthesized and incorporated as the template layer in bis (pentafluoro phenoxy) silicon phthalocyanine (F10-SiPc) OTFTs. The use of fluorinated p-6P (p-6PF) yields devices with the highest electron field-effect mobility of 0.14 cm2 V-1 s-1 while a partially fluorinated p-6P (p-6PF4) results in improved threshold voltage. X-ray diffraction (XRD) demonstrates varying F10-SiPc crystallinity with choice of templating layer with the most crystalline films resulting from the use of p-6PF. By grazing incidence wide angle X-ray scattering (GIWAXS) and polarized Raman microscopy, all templating layers yield films with F10-SiPc molecules predominantly aligned face-on to the substrate. However, rod-like p-6P derivatives increased the face-on orientation of F10-SiPc. This study highlights the importance of template layer selection and deposition optimization in WEG-based OTFTs. As emerging semiconductors are integrated into organic thin film transistors (OTFTs), the use of templating layers improves device performance. Herein, four novel aromatic molecules are synthesized and incorporated as the template layer in bottom-gate top-contact OTFTs leading to changes in semiconductor molecular orientation and morphology and the resulting device performance. image