MOLECULAR DESIGN OF ORGANIC SEMICONDUCTORS FOR INTERFACIAL AND EMISSIVE MATERIAL APPLICATIONS

This dissertation describes the synthesis and characterization of functional optoelectronically active materials. Synthetic techniques were used to prepare polymers containing perylene diimide (PDI) or tetraphenylethylene (TPE) moieties in the polymer backbone. PDI-based structures were prepared with embedded cationic or zwitterionic moieties intended to tailor organic/inorganic interfaces in thin film photovoltaic devices. The aggregation-induced emission (AIE)-active TPE polymers were synthesized to study how AIE properties evolve in π-conjugated polymers. The syntheses discussed here focused on modulation of molecular architecture to give rise to materials with tailored optoelectronic properties. Chapter 1 provides a brief overview of the field of organic electronics and the key concepts underpinning this thesis research. Chapter 2 describes the synthesis of PDI-containing polyionenes and linear polymer zwitterions. Dual-functional PDI monomers containing tertiary amines at the imide position, and bulky bromide or phenyl groups at the aromatic core, afforded reactive and high solubility monomers. Polymers with ammonium bromide and sulfobetaine functionality in the backbone were prepared by reacting PDI monomers with the appropriate electrophiles. By controlling PDI content, macromolecular structures with tunable PDI-PDI interactions were achieved and studied spectroscopically. Chapter 3 focuses on integration of novel PDI-based materials into organic and perovskite solar cells as interfacial layers. The interfacial properties, morphology, and device enhancement were studied as a function of PDI incorporation in the polymer backbone. Trends in electronic properties and device performance were correlated to polymer structure and revealed a strong dependence on the selection of cationic vs. zwitterionic functionality. The PDI-containing polymers were found to enhance photovoltaic device performance, despite not being continuous conjugated structures, but rather having conjugated molecular segments in the polymer backbone. The effective work function modification of metal cathodes and energy level overlap with perovskite active layer permitted enhanced device performance when tertiary amine-functionalized PDI small molecules were incorporated into devices. Chapter 4 centers on the synthesis and characterization of conjugated polymers containing TPE. The optical properties of these materials were adjusted by controlling extent of vinylene groups in the polymer backbone. These vinylene-containing TPE polymers exhibited similar optical and electronic properties to poly(phenylene vinylene) (PPV) while maintaining the desirable AIE properties of TPE. Moreover, by controlling the mole percent of TPE in PPV copolymers aggregation-caused quenching (ACQ) was attenuated without perturbation of PPV’s optical properties. Finally, Chapter 5 projects an outlook of the discussed research. Emphasis is given to where research focus should be oriented to advance the technology beyond the academic space. The aim of this chapter is to highlight the impact of this work and its relationship to bringing the science closer to the general public. The experimental procedures of the materials synthesis, characterization, and device fabrication are then detailed in Chapter 6