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Identifier

000460778

Title

Electrochemically active supramolecular entities in layered hybrid halide perovskites

Alternative Title

Ηλεκτροχημικά ενεργές & υπερμοριακές προσθήκες σε φυλλόμορφους υβριδικούς αλογονούχους περοβσκίτες

Author

Μακροπούλου, Ελένη-Κων/να

Thesis advisor

Στούμπος, Κωνσταντίνος

Reviewer

Αρματάς, Γεράσιμος
Σαββίδης, Πάυλος

Abstract

Halide perovskites are exceptional and unconventional semiconductors, known for their high optical absorption coefficients, extended charge carrier diffusion lengths, intense photoluminescence, and slow rates of non-radiative charge recombination [1]. Layered hybrid halide perovskites (AI2BIIX4 or AIIMIIX4, where A represents monovalent or bivalent cations, M represents bivalent p- block metals, and X represents halide anions), feature anionic sheets comprising corner- sharing metal-halide octahedra, selectively partitioned by organic cations, creating crystallographically ordered nanoscale sheets. This unique structure yields natural multiple quantum wells with stable excitonic features, exhibiting intense photoluminescence characteristics, even at room temperature. Intriguingly, a subset of these halide perovskites exhibits broadband optical emission, generating white light via the self-trapped exciton mechanism [2]. Understanding this fascinating trap-activated behavior necessitates careful material design, including the use of various organic spacersthat can potentially induce or suppress this effect. In this study, we have designed and synthesized a series of layered perovskites with electrochemically-active spacers, where the electrochemical state of the spacer influences the materials optical properties. The introduction of functional groups in the spacer cation adds to the structural complexity by engaging in weak supramolecular interactions, acting as perturbation probes to investigate the optical response concerning the electrochemical state of the spacer cation. Specifically, we have synthesized two sister A2PbBr4 compounds (A+ = 2,3 dihydroxy-phenylethylammonium ((HO)2-PEA) and 2-(3- aminoethyl)benzoic acid (HO2C-PEA)) as the redox-active and redox-inert pair of compounds, exhibiting a similar supramolecular interaction environment within the perovskite host. As evidenced by single-crystal X-ray diffraction experiments, the redox- active compound readily crystallizes in its partially oxidized semiquinone form during ambient environment synthesis, exhibiting similar photoluminescence characteristics to the redox-inert compound. These observations suggest formation and rapid quenching of the chemically reactive radical during the reaction. In order to probe this behavior, the reaction system was treated with a variety of chemical redox reagents targeting to obtain the compound in its fully reduced (catechol) and fully oxidized (quinone) form. Simultaneous investigations into the electrocatalytic reaction mechanism using cyclic voltammetry have indicated the presence of both the fully reduced form ((HO)2- PEA)2PbBr4 and the fully oxidized ((O=C)2-PEA)2PbBr4 in solution, prompting further optical and structural characterization of these metastable halide perovskite species.

Language

English

Subject

Broadband optical emission

Crystallography

Cyclic voltammetrytructural characterization

Excitonic features

Optical properties

Photoluminescence

Quantum wells

Self-trapped excitons

Semiconductor materials