Dr. Patrick Amsalem

Profil

Zusammenfassung

Dr. Patrick Amsalem erforscht die elektronischen Eigenschaften von Grenzflächen in Halbleitermaterialien — insbesondere wie sich Energieniveaus an Schnittstellen zwischen verschiedenen Materialien ausrichten und welche Rolle Oberflächenzustände dabei spielen. Seine Expertise liegt in der experimentellen Charakterisierung dieser Phänomene mittels Photoelektronenspektroskopie und verwandten Techniken, was direkt für die Optimierung von Solarzellen, organischen Elektronikbauteilen und anderen optoelektronischen Geräten relevant ist.

Skills

Name

Dr. Patrick Amsalem

Titel

Dr.

Fakultät

Zentralinstitut Center for the Science of Materials Berlin

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HU-FIS-Profil

Quelle ↗

Zuletzt gescrapt

28.6.2026, 01:02:30

• Die Energieniveau Anpassungen und elektronischen Eigenschaften schwach wechselwirkender Grenzflächen im Kontext organischer Halbleiter

  Quelle ↗

  Förderer: DFG Eigene Stelle (Sachbeihilfe) Zeitraum: 09/2014 - 12/2017 Projektleitung: Dr. Patrick Amsalem

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• Direct determination of monolayer MoS₂and WSe₂exciton binding energies on insulating and metallic substrates

  2018

  2D Materials · 198 Zitationen · DOI

  Understanding the excitonic nature of excited states in two-dimensional (2D) transition-metal dichalcogenides (TMDCs) is of key importance to make use of their optical and charge transport properties in optoelectronic applications. We contribute to this by the direct experimental determination of the exciton binding energy (Eb,exc) of monolayer MoS2 and WSe2 on two fundamentally different substrates, i.e. the insulator sapphire and the metal gold. By combining angle-resolved direct and inverse photoelectron spectroscopy we measure the electronic band gap (Eg), and by reflectance measurements the optical excitonic band gap (Eexc). The difference of these two energies is Eb,exc. The values of Eg and Eb,exc are 2.11 eV and 240 meV for MoS2 on sapphire, and 1.89 eV and 240 meV for WSe2 on sapphire. On Au Eb,exc is decreased to 90 meV and 140 meV for MoS2 and WSe2, respectively. The significant Eb,exc reduction is primarily due to a reduction of Eg resulting from enhanced screening by the metal, while Eexc is barely decreased for the metal support. Energy level diagrams determined at the K-point of the 2D TMDCs Brillouin zone show that MoS2 has more p-type character on Au as compared to sapphire, while WSe2 appears close to intrinsic on both. These results demonstrate that the impact of the dielectric environment of 2D TMDCs is more pronounced for individual charge carriers than for a correlated electron–hole pair, i.e. the exciton. A proper dielectric surrounding design for such 2D semiconductors can therefore be used to facilitate superior optoelectronic device function.

• High Fill Factor and Open Circuit Voltage in Organic Photovoltaic Cells with Diindenoperylene as Donor Material

  2010

  Advanced Functional Materials · 188 Zitationen · DOI

  Abstract Small‐molecule photovoltaic cells using diindenoperylene (DIP) as a new donor material in combination with the fullerene C 60 as an electron acceptor are demonstrated. In addition to the successful application in planar and bulk heterojunction devices, a comprehensive analysis including structural studies, the determination of the energy level alignment and electrical transport investigations is given, stressing the correlation between growth conditions, film morphology, and device performance. Due to pronounced crystallinity and a large surface area of DIP films grown at elevated temperature, exceptionally high fill factors of almost 75% are achieved in planar heterojunction cells. Bulk heterojunctions exhibit large‐scale phase separation forming a bicontinuous network of both molecular species, which enables efficient exciton dissociation and charge carrier transport. The high ionization potential of DIP and the favorable energy level alignment with the fullerene C 60 yield large open circuit voltages close to 1 V and comparable power conversion efficiencies of about 4% in both cell architectures.

• Impact of White Light Illumination on the Electronic and Chemical Structures of Mixed Halide and Single Crystal Perovskites

  2017

  Advanced Optical Materials · 166 Zitationen · DOI

  This study investigates the effect of white light illumination on the electronic and chemical properties of mixed halide perovskite (CH 3 NH 3 PbI 3− x Cl x ) thin films and CH 3 NH 3 PbI 3 single crystals using photoelectron and absorption spectroscopy. The pristine materials' surfaces are found to be n‐type because of surface band bending due to the presence of donor levels, likely consisting of reduced lead (Pb 0 ) that acts as surface traps. When illuminating the sample with white light (up to 1 sun), the valence features shifted to lower binding energy due to surface photovoltage, i.e., the bulk of the materials is much less n‐type. However, the surface photovoltage is only partially reversible and vanishes for prolonged illumination time. Concomitantly, a high concentration of metallic Pb 0 is found, which induces strong Fermi‐level pinning and quenching of the surface photovoltage. This is accompanied also by the formation of PbI 2 defects. Similar experiments on single crystals reveal the presence of a high concentration of reduced (metallic) Pb 0 at the sample surface after cleaving. The present findings indicate that the chemical and electronic properties of perovskite films are very sensitive to white light illumination. Accounting for these light‐induced material changes is important to fully understand its photophysical properties and for improving the lifetime of perovskite‐based devices.

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