Co-Assembly Of Nanostructured Hybrid Materials For Energy Applications
Self-assembly is employed in nature to build multi-dimensional hierarchical materials and represents a viable synthetic approach to construct next-generation functional materials for a large number of applications. This dissertation describes the design, synthesis and characterization of multifunctional nanostructured hybrid materials on multiple length scales by co-assembly of organic and organic/inorganic components. These materials are promising for a number of applications, and in particular for energy conversion devices. In the first part, organic-inorganic co-assembly is coupled with conventional heating (102-105 s) to generate hybrid materials for solid-state hybrid solar cells. A polyisoprene-block-polystyrene-block-polyethylene oxide (PI-b-PS-b-PEO) triblock terpolymer was employed to structure-direct alumina sol to form mesoporous block copolymer (BCP) directed alumina superstructures. In situ grazing incidence wideangle X-ray scattering and scanning electron microscopy were utilized to probe the structural evolution of methylammonium lead trihalide perovskite on mesoporous BCPdirected alumina superstructures during thermal annealing. A crystalline precursor structure not previously described was discovered to be highly crucial in enhancing perovskite film morphology and coverage, leading to better performing hybrid perovskite solar cells. Time/temperature control in thermal annealing enabled tuning the macroscopic perovskite film morphology and the crystal texture simultaneously. Extending the concept of time/temperature control in structure formation, the second part of the dissertation focuses on directed self-assembly using transient heating (10-8-10-3 s) to generate porous crystalline semiconductor and organic nanostructures. In a first example, a 308 nm pulsed XeCl excimer laser was used to induce transient melting of amorphous silicon in colloidal self-assembly-directed silica templates, which subsequently solidified into crystalline silicon nanostructures with hexagonal nonclose-packed symmetry. Subsequently, by harnessing the thermal stability enhancement of organic polymers under transient heating, direct laser writing of porous organic structures is discussed by combining block copolymer-resol co-assembly with a 10.6 [MICRO SIGN]m continuous wave CO2 laser-induced transient heating. Organic-organic hybrid thin films of PI-b-PS-b-PEO mixed with resorcinol-formaldehyde resol oligomers were heated by the CO2 laser on sub-millisecond time scales, inducing PI-b-PS-b-PEO decomposition and resol thermopolymerization, to form hierarchical porous resin polymer structures with 3D connectivity, high surface areas and exceptional chemical, mechanical and thermal properties. The porous resin structures are highly suitable for a number of potential applications, e.g., microfluidic reactors, BCP organic templating to generate crystalline silicon network nanostructures, and energy conversion and storage.
Block copolymer self-assembly; Laser Annealing; Hybrid Nanostructures
Wiesner, Ulrich B.
Disalvo, Francis J; Thompson, Michael Olgar
Materials Science and Engineering
Ph. D., Materials Science and Engineering
Doctor of Philosophy
dissertation or thesis