Engineering Thin Films of Silicon Phthalocyanines for Organic Thin Film Transistors

Abstract

Metal phthalocyanines (MPc) show great promise as semiconductors due to their exceptional optoelectronic properties, high thermal and photochemical stability, and ability to be easily synthesized and functionalized for specific applications. The metal/metalloid ion in the center of the MPc ring can significantly influence the electronic, optical, and magnetic properties of the compound, as well as its solubility and stability. The majority of MPc, such as copper phthalocyanine (CuPc) are used as hole-transport materials (p-type) in organic electronics. Silicon phthalocyanines (R2-SiPc) are emerging semiconductors which predominantly moves electrons and have led to high performance n-type organic thin-film transistors (OTFTs). Their low synthetic complexity paired with their versatile axial group facilitates the finetuning of their chemical properties, solution properties and processing characteristics without significantly affecting their frontier orbital levels or their absorption properties. The crystal engineering and film forming characteristics of R2-SiPc semiconductors can be tuned through appropriate axial group functionalization, therefore facilitating their integration into both OTFTs and OPVs by solution processing or vapor deposition.Our group has developed families of R2-SiPc and integrated them into OTFTs with an emphasis on thin film processing and engineering of the interfaces for improved device performance. We have established structure property relationships of the final device performance as a function of 1) R2-SiPc axial groups and peripheral groups, 2) surface chemistry and composition and 3) thin film deposition conditions. I will also be discussing our recent work using advanced film characterization such as polarized Raman microscopy and synchrotron based scanning transmission x-ray microscopy to evaluate the resulting films and optimize the OTFT performance. Figure 1