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Optimizing carrier balance in CsPbBr3 nanocrystal LEDs: The role of alkyl ligands and polar electron transport layers
Authors:
Roshini Jayabalan,
Girish K. Hanumantharaju,
Theresa Hettiger,
Arup Sarkar,
Fengshuo Zu,
Aladin Ullrich,
Norbert Koch,
Denis Andrienko,
Marcus Scheele,
Wolfgang Brütting
Abstract:
The study of lead halide perovskite nanocrystal based light-emitting diodes (LEDs) has advanced significantly, with notable improvements in stability and optical properties. However, optimizing charge carrier injection and transport remains a challenge. Efficient electroluminescence requires a balanced transport of both holes and electrons within the emitting material. Here, we investigate cubic C…
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The study of lead halide perovskite nanocrystal based light-emitting diodes (LEDs) has advanced significantly, with notable improvements in stability and optical properties. However, optimizing charge carrier injection and transport remains a challenge. Efficient electroluminescence requires a balanced transport of both holes and electrons within the emitting material. Here, we investigate cubic CsPbBr\textsubscript{3} nanocrystals passivated with oleylamine and oleic acid, comparing them to ligand-exchanged nanocrystals with didodecyldimethylammonium bromide (DDABr). Nuclear magnetic resonance spectroscopy and transmission electron microscopy confirm successful ligand exchange, revealing reduced ligand coverage in DDABr-treated nanocrystals. Photoelectron spectroscopy, spectroelectrochemistry, and single-carrier devices indicate improved hole injection in DDABr-capped nanocrystals. Density functional theory calculations further reveal the influence of ligand type and coverage on energy levels, with oleic acid introducing localized states in native nanocrystals. Additionally, incorporation of a polar electron transport layer (ETL) enhances LED performance by over an order of magnitude in DDABr-capped nanocrystals, driven by improved charge balance arising from the spontaneous orientation polarization (SOP) of the ETL. These findings highlight the critical role of ligand selection, passivation degree, and charge transport control by the adjacent organic transport layers in optimizing LED efficiency.
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Submitted 30 April, 2025;
originally announced April 2025.
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Phenothiazine-Based Self-Assembled Monolayer with Thiophene Head Groups Minimizes Buried Interface Losses in Tin Perovskite Solar Cells
Authors:
Valerio Stacchini,
Madineh Rastgoo,
Mantas Marčinskas,
Chiara Frasca,
Kazuki Morita,
Lennart Frohloff,
Antonella Treglia,
Orestis Karalis,
Vytautas Getautis,
Annamaria Petrozza,
Norbert Koch,
Hannes Hempel,
Tadas Malinauskas,
Antonio Abate,
Artem Musiienko
Abstract:
Self-assembled monolayers (SAMs) have revolutionized the fabrication of lead-based perovskite solar cells, but they remain underexplored in tin perovskite systems. PEDOT is the material of choice for hole-selective layers in tin perovskite solar cells (TPSCs), but presents challenges for both performance and stability. MeO-2PACz, the only SAM reported for Sn perovskites, enables device fabrication…
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Self-assembled monolayers (SAMs) have revolutionized the fabrication of lead-based perovskite solar cells, but they remain underexplored in tin perovskite systems. PEDOT is the material of choice for hole-selective layers in tin perovskite solar cells (TPSCs), but presents challenges for both performance and stability. MeO-2PACz, the only SAM reported for Sn perovskites, enables device fabrication but consistently underperforms when compared to PEDOT. In this work, we identify that MeO-2PACz's limitations arise from excessively strong interactions with perovskite surface and poor lattice matching, leading to poor interface quality. To overcome these issues, we design, synthesize, and characterize a novel SAM-forming molecule called Th-2EPT. Th-2EPT optimizes coordination strength and improves lattice compatibility, contributing to the creation of a high-quality buried interface and dramatically suppressing non-radiative recombination. We used Density Functional Theory (DFT) to evaluate coordination strength and lattice compatibility, complemented by nanosecond-resolution optical characterization techniques to confirm significantly reduced interfacial recombination and enhanced carrier lifetimes in Th-2EPT-Perovskite films. With Th-2EPT, we demonstrated the first SAM-based tin perovskite solar cells to outperform PEDOT-based devices, delivering a record power conversion efficiency (PCE) of 8.2% with a DMSO-free solvent system.
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Submitted 27 March, 2026; v1 submitted 12 February, 2025;
originally announced February 2025.
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Surface doping of rubrene single crystals by molecular electron donors and acceptors
Authors:
Christos Gatsios,
Andreas Opitz,
Dominique Lungwitz,
Ahmed E. Mansour,
Thorsten Schultz,
Dongguen Shin,
Sebastian Hammer,
Jens Pflaum,
Yadong Zhang,
Stephen Barlow,
Seth R. Marder,
Norbert Koch
Abstract:
The surface molecular doping of organic semiconductors can play an important role in the development of organic electronic or optoelectronic devices. Single-crystal rubrene remains a leading molecular candidate for applications in electronics due to its high hole mobility. In parallel, intensive research into the fabrication of flexible organic electronics requires the careful design of functional…
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The surface molecular doping of organic semiconductors can play an important role in the development of organic electronic or optoelectronic devices. Single-crystal rubrene remains a leading molecular candidate for applications in electronics due to its high hole mobility. In parallel, intensive research into the fabrication of flexible organic electronics requires the careful design of functional interfaces to enable optimal device characteristics. To this end, the present work seeks to understand the effect of surface molecular doping on the electronic band structure of rubrene single crystals. Our angle-resolved photoemission measurements reveal that the Fermi level moves in the band gap of rubrene depending on the direction of surface electron-transfer reactions with the molecular dopants, yet the valence band dispersion remains essentially unperturbed. This indicates that surface electron-transfer doping of a molecular single crystal can effectively modify the near-surface charge density, while retaining good charge-carrier mobility.
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Submitted 11 January, 2024;
originally announced January 2024.
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Optical Transmission Enhancement of Ionic Crystals via Superionic Fluoride Transfer: Growing VUV-Transparent Radioactive Crystals
Authors:
Kjeld Beeks,
Tomas Sikorsky,
Fabian Schaden,
Martin Pressler,
Felix Schneider,
Björn N. Koch,
Thomas Pronebner,
David Werban,
Niyusha Hosseini,
Georgy Kazakov,
Jan Welch,
Johannes H. Sterba,
Florian Kraus,
Thorsten Schumm
Abstract:
The 8 eV first nuclear excited state in $^{229}$Th is a candidate for implementing an nuclear clock. Doping $^{229}$Th into ionic crystals such as CaF$_2$ is expected to suppress non-radiative decay, enabling nuclear spectroscopy and the realization of a solid-state optical clock. Yet, the inherent radioactivity of $^{229}$Th prohibits the growth of high-quality single crystals with high $^{229}$T…
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The 8 eV first nuclear excited state in $^{229}$Th is a candidate for implementing an nuclear clock. Doping $^{229}$Th into ionic crystals such as CaF$_2$ is expected to suppress non-radiative decay, enabling nuclear spectroscopy and the realization of a solid-state optical clock. Yet, the inherent radioactivity of $^{229}$Th prohibits the growth of high-quality single crystals with high $^{229}$Th concentration; radiolysis causes fluoride loss, increasing absorption at 8 eV. We overcome this roadblock by annealing $^{229}$Th doped CaF$_2$ at 1250$\unicode{x2103}$ in CF$_4$. The technique presented here allows to adjust the fluoride content without crystal melting, preserving its single-crystal structure. Superionic state annealing ensures rapid fluoride distribution, creating fully transparent and radiation-hard crystals. This approach enables control over the charge state of dopants which can be used in deep UV optics, laser crystals, scintillators, and nuclear clocks.
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Submitted 29 February, 2024; v1 submitted 21 December, 2023;
originally announced December 2023.
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Interface Modification for Energy Levels Alignment and Charge Extraction in CsPbI$_3$ Perovskite Solar Cells
Authors:
Zafar Iqbal,
Fengshuo Zu,
Artem Musiienko,
Emilio Gutierrez Partida,
Hans Kobler,
Thomas W. Gries,
Gennaro V. Sannino,
Laura Canil,
Norbert Koch,
Martin Stolterfoht,
Dieter Neher,
Michele Pavone,
Ana Belen Munoz-Garcia,
Antonio Abate,
Qiong Wang
Abstract:
In perovskite solar cells (PSCs) energy levels alignment and charge extraction at the interfaces are the essential factors directly affecting the device performance. In this work, we present a modified interface between all-inorganic CsPbI$_3$ perovskite and its hole selective contact (Spiro-OMeTAD), realized by a dipole molecule trioctylphosphine oxide (TOPO), to align the energy levels. On a pas…
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In perovskite solar cells (PSCs) energy levels alignment and charge extraction at the interfaces are the essential factors directly affecting the device performance. In this work, we present a modified interface between all-inorganic CsPbI$_3$ perovskite and its hole selective contact (Spiro-OMeTAD), realized by a dipole molecule trioctylphosphine oxide (TOPO), to align the energy levels. On a passivated perovskite film, by n-Octyl ammonium Iodide (OAI), we created an upward surface band-bending at the interface by TOPO treatment. This improved interface by the dipole molecule induces a better energy level alignment and enhances the charge extraction of holes from the perovskite layer to the hole transport material. Consequently, a Voc of 1.2 V and high-power conversion efficiency (PCE) of over 19% were achieved for inorganic CsPbI$_3$ perovskite solar cells. Further, to demonstrate the effect of the TOPO dipole molecule, we present a layer-by-layer charge extraction study by transient surface photovoltage technique (trSPV) accomplished by charge transport simulation.
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Submitted 24 July, 2023;
originally announced July 2023.
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Quantum Efficiency Enhancement of Lead-Halide Perovskite Nanocrystal LEDs by Organic Lithium Salt Treatment
Authors:
Tassilo Naujoks,
Roshini Jayabalan,
Christopher Kirsch,
Fengshuo Zu,
Mukunda Mandal,
Jan Wahl,
Martin Waibel,
Andreas Opitz,
Norbert Koch,
Denis Andrienko,
Marcus Scheele,
Wolfgang Brütting
Abstract:
Surface-defect passivation is key to achieving high photoluminescence quantum yield in lead halide perovskite nanocrystals. However, in perovskite light-emitting diodes these surface ligands also have to enable balanced charge injection into the nanocrystals to yield high efficiency and operational lifetime. In this respect, alkaline halides have been reported to passivate surface trap states and…
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Surface-defect passivation is key to achieving high photoluminescence quantum yield in lead halide perovskite nanocrystals. However, in perovskite light-emitting diodes these surface ligands also have to enable balanced charge injection into the nanocrystals to yield high efficiency and operational lifetime. In this respect, alkaline halides have been reported to passivate surface trap states and increase the overall stability of perovskite light emitters. On the one side, the incorporation of alkaline ions into the lead halide perovskite crystal structure is considered to counterbalance cation vacancies, while, on the other side, the excess halides are believed to stabilise the colloids. Here, we report an organic lithium salt, viz. LiTFSI, as a halide-free surface passivation on perovskite nanocrystals. We show that the treatment LiTFSI has multiple beneficial effects on lead halide perovskite nanocrystals and LEDs derived from them. We obtain higher photoluminescence quantum yield and longer exciton lifetime, and a radiation pattern that is more favourable for light outcoupling. The ligand-induced dipoles on the nanocrystal surface shift their energy levels toward lower hole-injection barrier. Overall, these effects add up to a four- to seven-fold boost of the external quantum efficiency in proof-of-concept LED structures, depending on the color of the used lead halide perovskite nanocrystal emitters.
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Submitted 4 March, 2022; v1 submitted 30 January, 2022;
originally announced January 2022.
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Two-dimensional plasmonic polarons in n-doped monolayer MoS2
Authors:
Fabio Caruso,
Patrick Amsalem,
Jie Ma,
Areej Aljarb,
Thorsten Schultz,
Marios Zacharias,
Vincent Tung,
Norbert Koch,
Claudia Draxl
Abstract:
We report experimental and theoretical evidence of strong electron-plasmon interaction in n-doped single-layer MoS2. Angle-resolved photoemission spectroscopy (ARPES) measurements reveal the emergence of distinctive signatures of polaronic coupling in the electron spectral function. Calculations based on many-body perturbation theory illustrate that electronic coupling to two-dimensional (2D) carr…
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We report experimental and theoretical evidence of strong electron-plasmon interaction in n-doped single-layer MoS2. Angle-resolved photoemission spectroscopy (ARPES) measurements reveal the emergence of distinctive signatures of polaronic coupling in the electron spectral function. Calculations based on many-body perturbation theory illustrate that electronic coupling to two-dimensional (2D) carrier plasmons provides an exhaustive explanation of the experimental spectral features and their energies. These results constitute compelling evidence of the formation of plasmon-induced polaronic quasiparticles, suggesting that highly-doped transition-metal dichalcogenides may provide a new platform to explore strong-coupling phenomena between electrons and plasmons in 2D.
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Submitted 29 April, 2021;
originally announced April 2021.
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Temperature-dependent electronic ground state charge transfer in van der Waals heterostructures
Authors:
Soohyung Park,
Haiyuan Wang,
Thorsten Schultz,
Dongguen Shin,
Ruslan Ovsyannikov,
Marios Zacharias,
Dmitrii Maksimov,
Matthias Meissner,
Yuri Hasegawa,
Takuma Yamaguchi,
Satoshi Kera,
Areej Aljarb,
Mariam Hakami,
Lain-Jong Li,
Vincent Tung,
Patrick Amsalem,
Mariana Rossi,
Norbert Koch
Abstract:
Electronic charge rearrangement between components of a heterostructure is the fundamental principle to reach the electronic ground state. It is acknowledged that the density of states distribution of the components governs the amount of charge transfer, but a notable dependence on temperature has not yet been considered, particularly for weakly interacting systems. Here, we experimentally observe…
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Electronic charge rearrangement between components of a heterostructure is the fundamental principle to reach the electronic ground state. It is acknowledged that the density of states distribution of the components governs the amount of charge transfer, but a notable dependence on temperature has not yet been considered, particularly for weakly interacting systems. Here, we experimentally observe that the amount of ground state charge transfer in a van der Waals heterostructure formed by monolayer MoS2 sandwiched between graphite and a molecular electron acceptor layer increases by a factor of three when going from 7 K to room temperature. State-of-the-art electronic structure calculations of the full heterostructure that account for nuclear thermal fluctuations reveal intra-component electron-phonon coupling and inter-component electronic coupling as the key factors determining the amount of charge transfer. This conclusion is rationalized by a model applicable to multi-component van der Waals heterostructures.
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Submitted 14 March, 2021;
originally announced March 2021.
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Microstructure and Elastic Constants of Transition Metal Dichalcogenide Monolayers from Friction and Shear Force Microscopy
Authors:
Xiaomin Xu,
Thorsten Schultz,
Ziyu Qin,
Nikolai Severin,
Benedikt Haas,
Sumin Shen,
Jan N. Kirchhof,
Andreas Opitz,
Christoph T. Koch,
Kirill Bolotin,
Jürgen P. Rabe,
Goki Eda,
Norbert Koch
Abstract:
Optical and electrical properties of two-dimensional transition metal dichalcogenides (TMDCs) grown by chemical vapor deposition (CVD) are strongly determined by their microstructure. Consequently, the visualization of spatial structural variations is of paramount importance for future applications. Here we demonstrate how grain boundaries, crystal orientation, and strain fields can unambiguously…
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Optical and electrical properties of two-dimensional transition metal dichalcogenides (TMDCs) grown by chemical vapor deposition (CVD) are strongly determined by their microstructure. Consequently, the visualization of spatial structural variations is of paramount importance for future applications. Here we demonstrate how grain boundaries, crystal orientation, and strain fields can unambiguously be identified with combined lateral force microscopy (LFM) and transverse shear microscopy (TSM) for CVD-grown tungsten disulfide (WS2) monolayers, on length scales that are relevant for optoelectronic applications. Further, angle-dependent TSM measurements enable us to acquire the fourth-order elastic constants of monolayer WS2 experimentally. Our results facilitate high-throughput and nondestructive microstructure visualization of monolayer TMDCs, insights into their elastic properties, thus providing an accessible tool to support the development of advanced optoelectronic devices based on such two-dimensional semiconductors.
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Submitted 21 August, 2019;
originally announced August 2019.
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Theory of optically induced Förster Coupling in van der Waals coupled Heterostuctures
Authors:
Malte Selig,
Ermin Malic,
Kwang Jun Ahn,
Norbert Koch,
Andreas Knorr
Abstract:
We investigate the impact of optically induced Förster coupling in van der Waals heterostructures consisting of graphene and a monolayer transition metal dichalcogenide (TMD). In particular, we predict the corresponding dephasing rates and a fast energy transfer between the TMD layer and graphene being in the picosecond range. Exemplary we find a transition rate of thermalized excitons of about 4…
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We investigate the impact of optically induced Förster coupling in van der Waals heterostructures consisting of graphene and a monolayer transition metal dichalcogenide (TMD). In particular, we predict the corresponding dephasing rates and a fast energy transfer between the TMD layer and graphene being in the picosecond range. Exemplary we find a transition rate of thermalized excitons of about 4 ps$^{-1}$ in a MoSe$_2$-graphene stack at room temperature. This timescale is in good agreement with the recently measured exciton lifetime in this heterostructure.
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Submitted 1 March, 2019;
originally announced March 2019.
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Pulsed thermal deposition of binary and ternary transition metal dichalcogenide monolayers and heterostructures
Authors:
Niklas Mutz,
Tino Meisel,
Holm Kirmse,
Soohyung Park,
Nikolai Severin,
Jürgen P. Rabe,
Emil List-Kratochvil,
Norbert Koch,
Christoph Koch,
Sylke Blumstengel,
Sergey Sadofev
Abstract:
Application of transition metal dichalcogenides (TMDC) in photonic, optoelectronic or valleytronic devices requires the growth of continuous monolayers, heterostructures and alloys of different materials in a single process. We present a facile pulsed thermal deposition method which provides precise control over layer thickness and stoichiometry of two-dimensional systems. The versatility of the m…
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Application of transition metal dichalcogenides (TMDC) in photonic, optoelectronic or valleytronic devices requires the growth of continuous monolayers, heterostructures and alloys of different materials in a single process. We present a facile pulsed thermal deposition method which provides precise control over layer thickness and stoichiometry of two-dimensional systems. The versatility of the method is demonstrated on ternary monolayers of Mo$_{1-x}$W$_{x}$S$_{2}$ and on heterostructures combining metallic TaS$_{2}$ and semiconducting MoS$_{2}$ layers. The fabricated ternary monolayers cover the entire composition range of $x$ = 0...1 without phase separation. Band gap engineering and control over the spin-orbit coupling strength is demonstrated by absorption and photoluminescence spectroscopy. Vertical heterostructures are grown without intermixing. The formation of clean and atomically abrupt interfaces is evidenced by high-resolution transmission electron microscopy. Since both the metal components as well as the chalcogenides are thermally evaporated complex alloys and heterostructures can thus be prepared.
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Submitted 11 February, 2019; v1 submitted 19 November, 2018;
originally announced November 2018.
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Direct observation of state-filling at hybrid tin oxide/organic interfaces
Authors:
Ulrich Hörmann,
Stefan Zeiske,
Soohyung Park,
Thorsten Schultz,
Sebastian Kickhöfel,
Ullrich Scherf,
Sylke Blumstengel,
Norbert Koch,
Dieter Neher
Abstract:
Electroluminescence (EL) spectra from hybrid charge transfer excitons at metal oxide/organic type-II heterojunctions exhibit pronounced bias-induced spectral shifts. The reasons for this phenomenon have been discussed controversially and arguments for both electric field-induced effects as well as filling of trap states at the oxide surface have been put forward. Here, we combine the results from…
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Electroluminescence (EL) spectra from hybrid charge transfer excitons at metal oxide/organic type-II heterojunctions exhibit pronounced bias-induced spectral shifts. The reasons for this phenomenon have been discussed controversially and arguments for both electric field-induced effects as well as filling of trap states at the oxide surface have been put forward. Here, we combine the results from EL and photovoltaic measurements to eliminate the disguising effects of the series resistance. For SnOx combined with the conjugated polymer MeLPPP, we find a one-to-one correspondence between the blueshift of the EL peak and the increase of the quasi-Fermi level splitting at the hybrid heterojunction, which we unambiguously assign to state filling. Our data is resembled best by a model considering the combination an exponential density of states with a doped semiconductor.
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Submitted 20 November, 2018; v1 submitted 14 November, 2018;
originally announced November 2018.
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Modulation of the Work Function by the Atomic Structure of Strong Organic Electron Acceptors on H-Si(111)
Authors:
Haiyuan Wang,
Sergey V. Levchenko,
Thorsten Schultz,
Norbert Koch,
Matthias Scheffler,
Mariana Rossi
Abstract:
Advances in hybrid organic/inorganic architectures for optoelectronics can be achieved by understanding how the atomic and electronic degrees of freedom cooperate or compete to yield the desired functional properties. Here we show how work-function changes are modulated by the structure of the organic components in model hybrid systems. We consider two cyano-quinodimethane derivatives (F4-TCNQ and…
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Advances in hybrid organic/inorganic architectures for optoelectronics can be achieved by understanding how the atomic and electronic degrees of freedom cooperate or compete to yield the desired functional properties. Here we show how work-function changes are modulated by the structure of the organic components in model hybrid systems. We consider two cyano-quinodimethane derivatives (F4-TCNQ and F6-TCNNQ), which are strong electron-acceptor molecules, adsorbed on H-Si(111). From systematic structure searches employing range-separated hybrid HSE06 functional including many body van der Waals contributions, we predict that despite their similar composition, these molecules adsorb with significantly different densely-packed geometries in the first layer, due to strong intermolecular interaction. F6-TCNNQ shows a much stronger intralayer interaction (primarily due to van der Waals contributions) than F4-TCNQ in multilayered structures. The densely-packed geometries induce a large interface-charge rearrangement that result in a work-function increase of 1.11 and 1.76 eV for F4-TCNQ and F6-TCNNQ, respectively. Nuclear fluctuations at room temperature produce a wide distribution of work-function values, well modeled by a normal distribution with σ=0.17 eV. We corroborate our findings with experimental evidence of pronounced island formation for F6-TCNNQ on H-Si(111) and with the agreement of trends between predicted and measured work-function changes.
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Submitted 16 January, 2019; v1 submitted 31 October, 2018;
originally announced November 2018.
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Stark Effect of Hybrid Charge Transfer States at Planar ZnO/Organic Interfaces
Authors:
Ulrich Hörmann,
Stefan Zeiske,
Fortunato Piersimoni,
Lukas Hoffmann,
Raphael Schlesinger,
Norbert Koch,
Thomas Riedl,
Denis Andrienko,
Dieter Neher
Abstract:
We investigate the bias-dependence of the hybrid charge transfer state emission at planar heterojunctions between the metal oxide acceptor ZnO and three donor molecules. The electroluminescence peak energy linearly increases with the applied bias, saturating at high fields. Variation of the organic layer thickness and deliberate change of the ZnO conductivity through controlled photo-doping allow…
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We investigate the bias-dependence of the hybrid charge transfer state emission at planar heterojunctions between the metal oxide acceptor ZnO and three donor molecules. The electroluminescence peak energy linearly increases with the applied bias, saturating at high fields. Variation of the organic layer thickness and deliberate change of the ZnO conductivity through controlled photo-doping allow us to confirm that this bias-induced spectral shifts relate to the internal electric field in the organic layer rather than the filling of states at the hybrid interface. We show that existing continuum models overestimate the hole delocalization and propose a simple electrostatic model in which the linear and quadratic Stark effects are explained by the electrostatic interaction of a strongly polarizable molecular cation with its mirror image.
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Submitted 1 August, 2018;
originally announced August 2018.
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Space Charge Transfer in Hybrid Inorganic/Organic Systems
Authors:
Yong Xu,
Oliver T. Hofmann,
Raphael Schlesinger,
Stefanie Winkler,
Johannes Frisch,
Jens Niederhausen,
Antje Vollmer,
Sylke Blumstengel,
Fritz Henneberger,
Norbert Koch,
Patrick Rinke,
Matthias Scheffler
Abstract:
We discuss density functional theory calculations of hybrid inorganic/organic systems (HIOS) that explicitly include the global effects of doping (i.e. position of the Fermi level) and the formation of a space-charge layer. For the example of tetrafluoro-tetracyanoquinodimethane (F4TCNQ) on the ZnO(000$\bar{1}$) surface we show that the adsorption energy and electron transfer depend strongly on th…
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We discuss density functional theory calculations of hybrid inorganic/organic systems (HIOS) that explicitly include the global effects of doping (i.e. position of the Fermi level) and the formation of a space-charge layer. For the example of tetrafluoro-tetracyanoquinodimethane (F4TCNQ) on the ZnO(000$\bar{1}$) surface we show that the adsorption energy and electron transfer depend strongly on the ZnO doping. The associated work function changes are large, for which the formation of space-charge layers is the main driving force. The prominent doping effects are expected to be quite general for charge-transfer interfaces in HIOS and important for device design.
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Submitted 21 June, 2013; v1 submitted 19 June, 2013;
originally announced June 2013.
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Exploring the Bonding of Large Hydrocarbons on Noble Metals: Diindoperylene on Cu(111), Ag(111), and Au(111)
Authors:
C. Bürker,
N. Ferri,
A. Tkatchenko,
A. Gerlach,
J. Niederhausen,
T. Hosokai,
S. Duhm,
J. Zegenhagen,
N. Koch,
F. Schreiber
Abstract:
We present a benchmark study for the adsorption of a large pi-conjugated organic molecule on different noble metal surfaces, which is based on X-ray standing wave (XSW) measurements and density functional theory calculations with van der Waals (vdW) interactions. The bonding distances of diindenoperylene on Cu(111), Ag(111), and Au(111) surfaces (2.51 A, 3.01 A, and 3.10 A, respectively) determine…
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We present a benchmark study for the adsorption of a large pi-conjugated organic molecule on different noble metal surfaces, which is based on X-ray standing wave (XSW) measurements and density functional theory calculations with van der Waals (vdW) interactions. The bonding distances of diindenoperylene on Cu(111), Ag(111), and Au(111) surfaces (2.51 A, 3.01 A, and 3.10 A, respectively) determined with the normal incidence XSW technique are compared with calculations. Excellent agreement with the experimental data, i.e. deviations less than 0.1 A, is achieved using the Perdew-Burke-Ernzerhof functional with vdW interactions that include the collective response of substrate electrons (PBE+vdW^{surf} method). Noteworthy, the calculations show that the vdW contribution to the adsorption energy increases in the order Au(111) < Ag(111) < Cu(111).
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Submitted 25 April, 2013; v1 submitted 12 April, 2013;
originally announced April 2013.
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On the interpretation of valence band photoemission spectra at organic-metal interfaces
Authors:
L. Giovanelli,
F. C. Bocquet,
P. Amsalem,
H. -L. Lee,
M. Abel,
S. Clair,
M. Koudia,
T. Faury,
L. Petaccia,
D. Topwal,
E. Salomon,
T. Angot,
A. A. Cafolla,
N. Koch,
L. Porte,
A. Goldoni,
J. -M. Themlin
Abstract:
Adsorption of organic molecules on well-oriented single crystal coinage metal surfaces fundamentally affects the energy distribution curve of ultra-violet photoelectron spectroscopy spectra. New features not present in the spectrum of the pristine metal can be assigned as "interface states" having some degree of molecule-substrate hybridization. Here it is shown that interface states having molecu…
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Adsorption of organic molecules on well-oriented single crystal coinage metal surfaces fundamentally affects the energy distribution curve of ultra-violet photoelectron spectroscopy spectra. New features not present in the spectrum of the pristine metal can be assigned as "interface states" having some degree of molecule-substrate hybridization. Here it is shown that interface states having molecular orbital character can easily be identified at low binding energy as isolated features above the featureless substrate sp-plateau. On the other hand much care must be taken in assigning adsorbate-induced features when these lie within the d-band spectral region of the substrate. In fact, features often interpreted as characteristic of the molecule-substrate interaction may actually arise from substrate photoelectrons scattered by the adsorbates. This phenomenon is illustrated through a series of examples of noble-metal single-crystal surfaces covered by monolayers of large pi-conjugated organic molecules.
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Submitted 18 September, 2012;
originally announced September 2012.
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Substrate dependent bonding distances of PTCDA - A comparative XSW study on Cu(111) and Ag(111)
Authors:
A. Gerlach,
S. Sellner,
F. Schreiber,
N. Koch,
J. Zegenhagen
Abstract:
We study the adsorption geometry of 3,4,9,10-perylene-tetracarboxylic-dianhydride (PTCDA) on Ag(111) and Cu(111) using X-ray standing waves. The element-specific analysis shows that the carbon core of the molecule adsorbs in a planar configuration, whereas the oxygen atoms experience a non-trivial and substrate dependent distortion. On copper (silver) the carbon rings resides 2.66 A (2.86 A) abo…
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We study the adsorption geometry of 3,4,9,10-perylene-tetracarboxylic-dianhydride (PTCDA) on Ag(111) and Cu(111) using X-ray standing waves. The element-specific analysis shows that the carbon core of the molecule adsorbs in a planar configuration, whereas the oxygen atoms experience a non-trivial and substrate dependent distortion. On copper (silver) the carbon rings resides 2.66 A (2.86 A) above the substrate. In contrast to the conformation on Ag(111), where the carboxylic oxygen atoms are bent towards the surface, we find that on Cu(111) all oxygen atoms are above the carbon plane at 2.73 A and 2.89 A, respectively.
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Submitted 3 November, 2006;
originally announced November 2006.