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1.
Modulation of charge transfer exciton dynamics in organic semiconductors using different structural arrangements
Cristian Soncini, Abhishek Kumar, Federica Bondino, Elena Magnano, Matija Stupar, Barbara Ressel, Giovanni De Ninno, Antonis Papadopoulos, Efthymis Serpetzoglou, Emmanuel Stratakis, Maddalena Pedio, 2023, original scientific article

Abstract: In devices based on organic semiconductors, aggregation and inter-molecular interactions play a key role in affecting the photo-physical and dynamical carrier properties of the material, potentially becoming a limiting factor to achieving high efficiency. As a consequence, a detailed understanding of the interplay between the film molecular structure and the material properties is essential to properly design devices with optimized performance. Here we demonstrate how different molecular structural arrangements modulate the charge transfer (CT) dynamics in cobalt phthalocyanine (CoPc) thin films. By transient absorption spectroscopy and time-resolved photoemission spectroscopy, we study the influence of different CoPc structures on the dynamical electronic properties, the CoPc intra and inter- molecular de-excitation pathways up to 7 ns. We rationalize the ultrafast formation of triplet states in the CoPc through an electron exchange process between the single-occupied Co3dz2 orbital and p orbitals of the macrocycle, which obviate for an energetically unfavourable spin-flip. We found enhanced CT exciton lifetime in the case of the herringbone structure with respect to the brickwork one, possibly explainable by a more efficient CT exciton delocalization along the stacking axis.
Keywords: charge transfer, organic molecules, time resolved spectroscopies
Published in RUNG: 30.06.2023; Views: 1470; Downloads: 5
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2.
Hot-carrier and optical-phonon ultrafast dynamics in the topological insulator Bi2Te3 upon iron deposition on its surface
M Weis, K Balin, T Sobol, A Ciavardini, G Vaudel, V Juvè, B Arnaud, Barbara Ressel, M Stupar, K.C. Prince, Giovanni De Ninno, P Ruello, J Szade, 2021, original scientific article

Abstract: This paper presents a complete study of electronic structures and photoexcited carrier dynamics in topological insulators capped with iron and iron oxide. We combine static and time-resolved angle-resolved photoemission spectroscopies (ARPES, TR-ARPES) with time-resolved optical methods (transient optical reflectivity and transmission). Both single crystal and thin films of Bi2Te3 are studied. We show that monolayers of iron and iron oxide significantly affect the electronic band structure at the interface by shifting the Fermi level into the conduction band, which we explain by a band bending effect, and is confirmed by in situ XPS measurements
Keywords: time resolved spectroscopies, topological insulators, interfaces
Published in RUNG: 13.12.2021; Views: 2398; Downloads: 26
.pdf Full text (2,90 MB)

3.
Introduction to Electronic Properties and Dynamics of Organic Complexes as Self‐Assembled Monolayers
Maddalena Pedio, 2017, independent scientific component part or a chapter in a monograph

Abstract: Self‐assembled monolayers (SAMs) of organic‐conjugated transition metal complexes on surfaces is a focus of both device engineering and basic science, since it is a key factor in nearly all important aspects of device performances, including operation voltages, degradation, and efficiency. The huge amount of literature results related to the first monolayer, and reorganization and self‐assembling processes are due to the general accepted result that structural and chemical properties of the first monolayer are the key parameters for controlled thin film growth. Optical and magneto‐electronic properties are intimately connected, and the accurate determination of electronic levels, excitation, and relaxation dynamics is mandatory for the optimization of electronic, photovoltaic, and opto‐electronic devices. Quite a number of electronic states is generated by the interaction of light with complex organic molecules. Time‐resolved spectroscopies are a new investigation tool that gives the possibility of correctly addressing their origin and life time. Examples of prototypical systems are presented and discussed. We review on complementary techniques, trying to single out how different approaches are fundamental to fully characterize these complex systems.
Keywords: self‐assembled monolayer (SAM), surface structures molecular layers, nanotechnology, electronic properties, spectroscopies, time resolved
Published in RUNG: 12.06.2017; Views: 4887; Downloads: 208
.pdf Full text (5,78 MB)

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