October 30, 2023
Donor-acceptor (D-A) structured molecules are essential components in organic electronics. The respective molecular structure of these molecules and their synthesis are primarily determined by the intended area of application. Typically, D-A molecules promote charge separation and transport in organic photovoltaics (OPV) or organic field-effect transistors (OFET). D-A molecules showing a larger twist angle between D and A units are, e.g., extremely important for the development of high internal quantum efficiency in organic light-emitting diodes (OLEDs). A prototypical molecule of this D-A type is DCzDCN (5-(4,6-diphenyl-1,3,5-triazin-2-yl)benzene-1,3-dinitrile). In most cases, these molecules are only investigated regarding their electronic and structural interaction in bulk aggregates but not in ultra-thin films supported by a metallic substrate. Here, we present growth and electronic structure studies of DCzDCN on a Cu(100) surface. In a complementary approach, through the use of Scanning Tunneling Microscopy and Spectroscopy (STM and STS), we were able to view both the adsorption geometry and the local electronic states of the adsorbed molecules in direct comparison with the integral electronic structure of the DCzDCN/CU(100) interface using Ultraviolet and Inverse Photoemission Spectroscopy (UPS and IPS). The orientation of the molecules with the donor part towards the substrate results in a chiral resolution at the interface due to the molecular as well as the substrate symmetry and additional strong molecular electrostatic forces. Thus, the formation of various bulk-unlike homochiral structures and the appearance of hybrid interface states (HIS) modifies the molecular electronic properties of the DCzDCN/Cu(100) system significantly compared to that of a single DCzDCN molecule. This may be not only useful for optoelectronic applications but also in organic spintronics.
Similar papers 1
March 28, 2023
Organic semiconductors are a promising class of materials for numerous electronic and optoelectronic applications, including solar cells. However, these materials tend to be extremely sensitive to the local environment and surrounding molecular geometry, causing the energy levels near boundaries and interfaces essential to device function to differ from those of the bulk. Scanning Tunneling Microscopy and Spectroscopy (STM/STS) has the ability to examine both the structural a...
October 1, 2024
The growth and ordering of molecules on surfaces is an intriguing research topic as insights gained here can be of significant relevance for organic electronic devices. While often simple, rigid molecules are employed as model systems, we show results for a highly dipolar merocyanine which is studied on top of Au(100), Ag(100) and Cu(100) metal single crystals. Film thicknesses ranging from submonolayer to multilayer regimes are analyzed using UV (UPS) and X ray photoelectron...
November 8, 2016
Molecular self-assembly is a well-known technique to create highly functional nanostructures on surfaces. Self-assembly on two-dimensional materials is a developing field and has already resulted in the discovery of several rich and interesting phenomena. Here, we review this progress with an emphasis on the electronic properties of the adsorbates and the substrate in well-defined systems, as unveiled by scanning tunneling microscopy (STM). We cover three aspects of the self-...
June 10, 2024
Thin organic films and two-dimensional (2D) molecular assemblies on solid surfaces yield the potential for applications in molecular electronics, optoelectronics, catalysis, and sensing. These applications rely on the intrinsic electronic properties of the hybrid organic/inorganic interface. Here, we investigate the energy dispersion of 2D electronic states at the interface between an atomically thin self-assembled molecular film, comprised of flat, noncovalently bonded 9,10-...
April 4, 2022
The design of low-dimensional organic-inorganic interfaces for the next generation of opto-electronic applications requires an in-depth understanding of the microscopic mechanisms ruling electronic interactions in these systems. In this work, we present a first-principles study based on density-functional theory inspecting the structural, energetic, and electronic properties of five molecular donors and acceptors adsorbed on freestanding hexagonal boron nitride (hBN) and moly...
October 27, 2008
The interaction of the strong electron-acceptor tetracyanoethylene (TCNE) with the Cu(100) surface has been studied with scanning tunneling microscopy experiments and first-principles density functional theory calculations. We compare two different adsorption models with the experimental results and show that the molecular self-assembly is caused by a strong structural modification of the Cu(100) surface rather than the formation of a coordination network by diffusing Cu adat...
March 24, 2017
We present a simplified density functional theory (DFT) method to com- pute vertical electron and hole attachment energies to frontier orbitals of molecules absorbed on insulating films supported by a metal substrate. The adsorbate and the film is treated fully within DFT, whereas the metal is treated implicitly by a perfect conductor model. As illustrated for a pentacene molecule adsorbed on NaCl films sup- ported by a Cu substrate, we find that the computed energy gap betwe...
May 21, 2008
This work describes an innovative concept for the development of organized molecular systems thanks to the template effect of the pre-structured semi-conductive SmSi(111) interface. This substrate was selected because Sm deposition in the submonolayer range leads to a 8x2-reconstruction, which is a well-defined one-dimensional semi-metallic structure. Adsorption of aromatic molecules (1,4-di-(9-ethynyltriptycenyl)-benzene) on SmSi(111)-8x2 and Si(111)-7x7 interfaces has been ...
July 1, 2011
Engineering the electronic structure of organics through interface manipulation, particularly the interface dipole and the barriers to charge carrier injection, is of essential importance to improved organic devices. This requires the meticulous fabrication of desired organic structures by precisely controlling the interactions between molecules. The well-known principles of organic coordination chemistry cannot be applied without proper consideration of extra molecular hybri...
August 27, 2012
Interface dipole determines the electronic energy alignment in donor/acceptor interfaces and plays an important role in organic photovoltaics. Here we present a study combining first principles density functional theory (DFT) with ultraviolet photoemission spectroscopy (UPS) and time-of-flight secondary ion mass spectrometry (TOF-SIMS) to investigate the interface dipole, energy level alignment, and structural properties at the interface between CuPc and C60. DFT finds a siza...