Molecular-Level Switching of Polymer/Nanocrystal Non-Covalent Interactions and Application in Hybrid Solar Cells

Hy brid composites obtained upon blending conjugated polymers and colloidal inorganic semiconductor nanocrystals are regarded as attractive photo-active materials for optoelectronic applications. Here we demonstrate that tailoring nanocrystal surface chemistry permits to exert control on non-covalent bonding and electronic interactions between organic and inorganic components. The pendant moieties of organic ligands at the nanocrystal surface do not merely confer colloidal stability while hindering charge separation and transport, but drastically impact morphology of hybrid composites during formation from blend solutions. The relevance of our approach to photovoltaic applications is demonstrated for composites based on poly(3-hexylthiophene) and Pbs nanocrystals, considered as inadequate before the submission of this manuscript, which enable the fabrication of hybrid solar cells displaying a power conversion efficiency that reaches 3 %. Upon (quasi)steady-state and time-resolved analisys of the photo-induced processes in the nanocomposites and their organic and inorganic components, we ascertained that electron transfer occurs at the hybrid interface yielding long-lived separated charge carriers, whereas interfacial hole transfer appears slow. Here we provide a reliable alternative aiming at gaining control over macroscopic optoelectronic properties of polymer/nanocrystal composites by acting at the molecular-level via ligands' pendant moieties, thus opening new possibilities towards efficient solution-processed hybrid solar cells

Supramolecular Photoactive Systems: holding together a discrete number of molecules and shining light on them

Chemists deal with matter and its transformations. They create chemical species into an infinite variety of combinations, at least until they have imagination. Some of them hold chemical species together trying to gain control on increasing matter complexity. Supermolecules are organized entities resulting from the self-assembly of two or more chemical species held together by intermolecular forces, thus representing a further step towards complexity compared to molecules as the latter do to atoms. Novel properties peculiar of the supramolecular systems thus arise and do not result from the simple superposition of those of the component units. Self-assembly of chemical species by weak, non covalent interactions is a widespread concept to Nature's forms and functions and is attracting increasing interest in artificial systems conceived to control mechanical movements, process information, and harvest sunlight. The present PhD thesis studies some supramolecular photoactive systems that act as antennas capable of collecting incident light and transfer excitation energy or electrons from one molecular component to another

Surface Chemistry Control of Colloidal Quantum Dot Band Gap

Surface chemistry modification of as-synthesized colloidal inorganic semiconductor nanocrystals (QDs), commonly referred to as ligand exchange, is mandatory toward effective QD-based optoelectronic and photocatalytic applications. The widespread recourse to ligand exchange procedures on metal chalcogenide QDs often narrows the optical band gap, although little consensus exists on explanation of this experimental evidence. This work attempts at providing a comprehensive description of such a phenomenon by exploiting rationally designed thiol ligands at the surface of colloidal PbS QDs, as archetype of material in the strong quantum confinement regime: the thiol­(ate)-induced QD optical band gap reduction almost linearly scales with the inorganic core surface-to-volume ratio and mainly depends on the sulfur binding atom, which is here suggested to contribute occupied 3p orbitals to the valence band edge of the QDs. As opposed to QD models based on the analogy with core/shell heterostructures, the indecomposable character of ligand/core adducts (the colloidal QDs themselves) arises

Inborn prothrombotic states

Abstract non disponibil

Monitoring of hemostasis

Abstract non disponibil