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 (mu) 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.