Interfacial Crystallization-Driven Assembly of Conjugated Polymers/Quantum Dots into Coaxial Hybrid Nanowires: Elucidation of Conjugated Polymer Arrangements by Electron Tomography

Abstract

A simple and practical "solution-biphase method" allows the preparation of efficient charge-transporting 1D nanocrystals with coaxial p-n junctions. It involves gradual diffusion of a top layer of poor solvent (acetonitrile) into a bottom layer of poly(3-hexyl thiophene)-b-poly(2-vinyl pyridine) (P3HT-b-P2VP) conjugated polymers (CPs) and CdSe quantum dots (QDs) dissolved in chloroform. Initial interfacial crystallization-driven assembly of CPs results in the formation of seeds consisting of dimeric QDs transversely bridged by CPs. Coaxial CPs/QDs hybrid NWs are generated by 1D growth of QDs-dimeric seeds, enabling tracing of the CPs-crystallization process via the QDs. Thus, well-arranged QDs along the longitudinal axis of the NWs infer highly crystalline CPs with edge-on orientation, as confirmed by electron tomography, UV-vis spectroscopy, and grazing-incidence wide-angle X-ray scattering. This high cristallinity as well as the increased length of the resulting hybrid NWs in solution and the corresponding crystallite size in as-cast film represent a significant improvement compared to the conventional "one-pot addition method". Moreover, although randomly QDs-attached hybrids of P3HT homopolymer are produced by the solution-biphase method, branched aggregates with micrometer-long NW arms are generated from the crystal seeds containing multiple growth facets without precipitate, despite acetonitrile being a nonsolvent.