Molecular Templating Growth of Silicon Phthalocyanine Based Organic Thin Film Transistors

Abstract

Molecular template growth (MTG) has recently shown to be a promising method for the fabrication of highly crystalline semiconductor films by enabling precise control over film properties such as the growth morphologies, molecular orientation, surface properties and crystallinity. The use of para-sexiphenly (p-6P) has already been shown in literature as a promising template for the fabrication of high-quality disk-like metal phthalocyanines (MPcs) while showing improved device performance when incorporated into the organic thin film transistor (OTFTs). Silicon phthalocyanines (R2-SiPc) are a class of MPc that has axial groups which make it deviate from the traditional disk like morphology, and therefore new template molecules may be required for MTG. In this thesis we explore the use of novel molecules as template layers in the development of R2-SiPc based OTFTs. We begin by implementing a fully fluorinated p-6P (p-6PF) as a template layer for the fabrication of bis (pentafluoro phenoxy) silicon phthalocyanine (F10-SiPc) OTFTs. This template layer was selected to target the fluorine-fluorine interaction between the semiconductor and the dielectric interface. First, we optimized device performance by varying the deposition conditions of the template. After which we further characterized F10-SiPc on p-6P and p-6PF where we show that p-6PF is a superior template material for the fabrication of R2-SiPc. Next, we incorporated F10-SiPc on a range of surface including bare SiO2, p-6PF, p-6P and 4 novel template layers that were synthesized to deviated from the traditional p-6P by providing a varying degree of fluorination and structural shapes. This was done to investigate the influence of the structural properties of the template layer on resulting OTFTs performance. We perform characterization of the films using grazing incident wide angle x-ray scattering and polarized Raman microscopy to quantify the molecular orientation of the F10-SiPc relative to substrate as a function of template layer. Overall, this thesis shows the need for carefully material selection paring and optimization of template deposition condition in other to yield high performance in OTFTs.