Directed Self-assembly and Alignment of Conjugated Polymers for High Performance Plastic Electronics
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Conjugated polymers (CPs) are emerging active materials for electronic and optoelectronic devices, such as organic solar cells, thin-film transistors, light-emitting diodes, as well as optical and amperometric sensors. There has been an intensive worldwide research effort on the development of stable, organic semiconductors as potential replacements for amorphous silicon, the benchmark large area, amorphous semiconductor. However, despite ever increasing numbers of newly developed conjugated polymers, the performance of CP thin films in optoelectronic devices prepared by the current fabrication methods has been rather limited largely due to the disordered structure. Liquid crystalline polymers (LCPs) have been widely investigated for various optical, mechanical, and electrical applications due to their unique ordered nature. In general LCP design, rod-like mesogens having a large aspect ratio are connected through somewhat flexible linker units to form a main-chain or as a side chain LCP to a flexible polymer. This design allows good molecular interactions between mesogens, but prevents regularly structured crystal formation. Therefore, it is highly desired to devise a novel and universal molecular design strategy to achieve lyotropic liquid crystalline CPs that can be easily processed to form a macroscopically assembled and aligned structure. The project falls under EE 2.1 Solar Energy and EE7.1 Develop a national research program in material chemistry, material sciences and nanotechnology and will require an integrated research program with a multidisciplinary team, having partners at Qatar and United states that will span electrochemistry, material science and photophysics in order to effectively produce an efficient high performance organic electronic device. The project has a strong potential for the fundamental discovery of a novel class of lyotropic liquid-crystalline CPs with high intrinsic charge mobility, directed assembly and alignment capability, and directly writable capacity. It will also guide further research and development efforts for the full realization of their anisotropic optoelectronic properties in various organic electronic device applications. The overall aims of the project are summarized to the following three categories: (1) To develop a complete understanding of the molecular design principles that endow lyotropic liquid-crystalline properties to CPs; (2) To identify further molecular moieties that satisfy the three design requirements, functional units with a reconfigurable form factor, and cleavable side chains that can enable close interchain packing of CPs followed by directed alignment, and (3) Ultimately to explore direct writing plastic electronics by applying dip-pen lithography as a writing instrument and the lyotropic LC CPs as an ink.