Toward Weak Epitaxial Growth of Silicon Phthalocyanines: How the Choice of the Optimal Templating Layer Differs from Traditional Phthalocyanines
Raluchukwu B. Ewenike, Benjamin King, Alicia M. Battaglia, J. David Quezada Borja, Zheng Lin, Joseph G. Manion, Jaclyn L. Brusso, Timothy L. Kelly, Dwight S. Seferos, Benoît H. Lessard
Abstract
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.