Supramolecular chirality amplification in conjugated polymers/perovskite quantum dots nanoassembly for circular polarized light-responsive device

Abstract

Conjugating polymers with excellent electrical and optical properties provide flexibility, large-area processing, and cost-saving in optoelectronic device fabrication. Meanwhile, circularly polarized light (CPL)-responsive devices have attracted significant attention due to their CPL-responsibility of the controlled active layers at the molecular or nanoscale, enabling applications in quantum computing using chiral magnetic effect, chirality-based information processing, and security technologies. It can be applied by introducing molecular chiral functional groups in the side chain of conjugated polymers. However, to expand the applicability of conjugated polymers to CPL-responsive devices, the development of new conducting polymer materials that can broaden the absorption range, improve the CPL responsiveness, and induce enhanced charge mobility and conductivity is required. Compared to inorganic semiconductor materials, lower charge mobility and exciton dissociation abilities lead to decreased conversion efficiency from CPL absorption to electrical signal output. In this study, I fabricated helical self-assembled nanostructures of chiral all-conjugated block copolymers (CBPs) as organic semiconductors with expanded absorption range, enhanced CPL responsiveness, and increased crystallinity. In addition, I have developed a precisely controlled solution state self-assembly technique to employ these helical structures as nanotemplates, leading to the nano-hybrid system with perovskite quantum dots (PQDs) with excellent luminescent properties. PQDs have high charge mobility and can complement the electrical and optical properties of conductive polymers by forming p-n heterojunction. First, I synthesized chiral CBPs, P3HT-b-P*MTEGTs, with different molecular weight ratios using the Grignard metathesis polymerization method and successfully formed preferred-handed helical self-assembled nanostructures in solution by considering the solvent selectivity of each block. Through the crystallization-driven self-assembly, the molecular chirality was successfully transferred to supramolecular chirality, depending on the volume ratio of the poor solvent, and the resulting helical nanowires exhibited highly ordered arrangements. Additionally, we could fabricate hybrid helical nanowires with regularly arranged PQDs. Surprisingly, a noticeable circular dichroism signal was revealed in the absorption range of achiral PQDs, and the dissymmetric factor increased more than three times compared to the polymer helical nanowires before PQD incorporation. The hybrid nanowires with a high dissymmetric factor based on the enhanced supramolecular chirality showed highly uniform minus- (M-) or plus- (P-) helix structures with a regular pitch. To utilize this as a photodetector, I investigated the electrical signals converted from CPL absorption signals of the supramolecular helical hybrid nanostructures. The photocurrent signals measured under CPL illumination could be patterned. I focused on the unique features of randomly arranged hybrid nanostructures on the substrate. Finally, I demonstrated the applicability of patterns generated from CBP/PQD nanohybrids as a security signal or anti-counterfeiting device. The developed self-assembly nanotechnology for regularly arranged helical nanostructures of CBPs through supramolecular chirality induction elucidates the chiral transfer and amplification mechanism. I expect this research will show a significant impact on the design and synthesis of conjugated block copolymers and their application toward CPL-responsive devices requiring both excellent optical properties and semiconductor characteristics.