Toward Weak Epitaxial Growth of Silicon Phthalocyanines: How the Choice of the Optimal Templating Layer Differs from Traditional Phthalocyanines

Weak epitaxial growth typically utilizes oligomeric or polymeric phenyls or thiophenes as a templating layer to improve the deposition of metal phthalocyanines (MPc) and other disk-like molecules. In this study, we report the use of perfluorinated para -sexiphenyl ( p -6PF) as a templating layer, for the fabrication of bis(pentafluorophenoxy) silicon phthalocyanine (F 10 -SiPc)-, copper phthalocyanine (CuPc)-, and perfluorinated copper phthalocyanine (F 16 -CuPc)-based organic thin-film transistors (OTFTs). By optimizing the deposition time and substrate temperature during deposition, we were able to control the surface coverage, roughness, and growth morphology of p -6PF leading to F 10 -SiPc OTFTs with n-type mobilities (μ) of 0.14 cm 2 V –1 s –1 . In comparison, using CuPc and F 16 -CuPc with p -6PF led to mobilities of 0.009 (holes) and 0.012 cm 2 V –1 s –1 (electrons), respectively. In contrast, an unfluorinated para -sexiphenyl ( p -6P) templating layer demonstrates inferior performance as a template for F 10 -SiPc while proving to be more effective for CuPc and F 16 -CuPc. Atomic force microscopy and powder X-ray diffraction suggest that higher surface coverage of the p -6PF layer increased the grain sizes and crystallinity of F 10 -SiPc. Grazing-incidence wide-angle X-ray scattering shows improved crystallinity of F 10 -SiPc on p -6PF over p -6P and vice versa for F 16 -CuPc. Overall, these results demonstrate that p -6PF is a promising templating candidate for F 10 -SiPc-based OTFTs and that the choice of the templating layer needs to be optimized for the semiconductor.