Jens Niederhausen

Charged and metallic molecular monolayers through surface-induced aromatic stabilization

Large π-conjugated molecules, when in contact with a metal surface, usually retain a finite electronic gap and, in this sense, stay semiconducting. In some cases, however, the metallic character of the underlying substrate is seen to extend onto the first molecular layer. Here, we develop a chemical rationale for this intriguing phenomenon. In many reported instances, we find that the conjugation length of the organic semiconductors increases significantly through the bonding of specific substituents to the metal surface and through the concomitant rehybridization of the entire backbone structure. The molecules at the interface are thus converted into different chemical species with a strongly reduced electronic gap. This mechanism of surface-induced aromatic stabilization helps molecules to overcome competing phenomena that tend to keep the metal Fermi level between their frontier orbitals. Our findings aid in the design of stable precursors for metallic molecular monolayers, and thus enable new routes for the chemical engineering of metal surfaces.

Correlation between interface energetics and open circuit voltage in organic photovoltaic cells

We have used ultraviolet and inverse photoemission spectroscopy to determine the transport gaps (Et) of C60 and diindenoperylene (DIP), and the photovoltaic gap (EPVG) of five prototypical donor/acceptor interfaces used in organic photovoltaic cells (OPVCs). The transport gap of C60 (2.5 ± 0.1) eV and DIP (2.55 ± 0.1) eV at the interface is the same as in pristine films. We find nearly the same energy loss of ca 0.5 eV for all material pairs when comparing the open circuit voltage measured for corresponding OPVCs and EPVG.

Space-charge transfer in hybrid inorganic-organic systems.

We discuss density functional theory calculations of hybrid inorganic-organic systems 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 on the ZnO(0001[over ¯]) 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 hybrid inorganic-organic systems and important for device design.

Exploring the bonding of large hydrocarbons on noble metals: Diindoperylene on Cu(111), Ag(111), and Au(111)

We present a benchmark study for the adsorption of a large

Unveiling the Hybrid n-Si/PEDOT:PSS Interface

\ensuremath{\pi}

Tuning the Electronic Structure of Graphene by Molecular Dopants: Impact of the Substrate

-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, 3.01, and 3.10 \AA{}, 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 \AA{}, is achieved using the Perdew-Burke-Ernzerhof (PBE) functional with vdW interactions that include the collective response of substrate electrons (the

Epitaxial Growth of an Organic p–n Heterojunction: C60 on Single-Crystal Pentacene

\mathrm{PBE}+{\mathrm{vdW}}^{\mathrm{surf}}

Interlayer molecular diffusion and thermodynamic equilibrium in organic heterostructures on a metal electrode

method). It is noteworthy that the calculations show that the vdW contribution to the adsorption energy increases in the order

Orientation-Dependent Work-Function Modification Using Substituted Pyrene-Based Acceptors

\text{Au}(111)l\text{Ag}(111)l\text{Cu}(111)

Monolayer Phases of a Dipolar Perylene Derivative on Au(111) and Surface Potential Build-Up in Multilayers

.