Abstract
The adsorption of molecular acceptors is a viable method for tuning the work function of metal electrodes. This, in turn, enables adjusting charge injection barriers between the electrode and organic semiconductors. Here, we demonstrate the potential of pyrene-tetraone (PyT) and its derivatives dibromopyrene-tetraone (Br-PyT) and dinitropyrene-tetraone (NO2-PyT) for modifying the electronic properties of Au(111) and Ag(111) surfaces. The systems are investigated by complementary theoretical and experimental approaches, including photoelectron spectroscopy, the X-ray standing wave technique, and density functional theory simulations. For some of the investigated interfaces the trends expected for Fermi-level pinning are observed, i.e., an increase of the metal work function along with increasing molecular electron affinity and the same work function for Au and Ag with monolayer acceptor coverage. Substantial deviations are, however, found for Br-PyT/Ag(111) and NO2-PyT/Ag(111), where in the latter case an adsorption-induced work function increase of as much as 1.6 eV is observed. This behavior is explained as arising from a face-on to edge-on reorientation of molecules in the monolayer. Our calculations show that for an edge-on orientation much larger work-function changes can be expected despite the prevalence of Fermi-level pinning. This is primarily ascribed to a change of the electron affinity of the adsorbate layer that results from a change of the molecular orientation. This work provides a comprehensive understanding of how changing the molecular electron affinity as well as the adsorbate structure impacts the electronic properties of electrodes.
Highlights
Organic electronics has received considerable attention in the past three decades, and much effort has been spent on investigating and improving devices based on conjugated organic materials (COMs)
The systems are investigated by complementary theoretical and experimental approaches, including photoelectron spectroscopy, the X-ray standing wave technique, and density functional theory simulations
For some of the investigated interfaces the trends expected for Fermi-level pinning are observed, i.e., an increase of the metal work function along with increasing molecular electron affinity and the same work function for Au and Ag with monolayer acceptor coverage
Summary
Organic electronics has received considerable attention in the past three decades, and much effort has been spent on investigating and improving devices based on conjugated organic materials (COMs). We investigated pyrene-4,5,9,10-tetraone (PyT) and two of its derivatives with electron-withdrawing functional groups, i.e., 2,7-nitro (NO2-PyT) and 2,7-bromo (Br-PyT) (chemical structures in Figure 1), which offer the additional possibility of reorientation on the surface.[20] The PyT backbone is promising because it is an ideal candidate for exploiting SIAS16,23 in order to increase its acceptor strength:[24] For the isolated (nonadsorbed) molecule, the carbonyl bonds break the conjugation of the pyrene core. Article compounds deposited on Au(111) and Ag(111) by ultraviolet and X-ray photoelectron spectroscopy (UPS, XPS) and the Xray standing wave (XSW) technique,[32,33] complemented by density functional theory (DFT) calculations
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
