Abstract
Energy-level alignment at organic–metal interfaces plays a crucial role for the performance of organic electronic devices. However, reliable models to predict energetics at strongly coupled interfaces are still lacking. We elucidate contact formation of 1,2,5,6,9,10-coronenehexone (COHON) to the (1 1 1)-surfaces of coinage metals by means of ultraviolet photoelectron spectroscopy, x-ray photoelectron spectroscopy, the x-ray standing wave technique, and density functional theory calculations. While for low COHON thicknesses, the work-functions of the systems vary considerably, for thicker organic films Fermi-level pinning leads to identical work functions of 5.2 eV for all COHON-covered metals irrespective of the pristine substrate work function and the interfacial interaction strength.
Highlights
M-T Chen et al Interfaces between conjugated organic molecules (COMs) and metals are of key importance in the field of organic electronics and the energy-level alignment is crucial for the performance of organic devices [1,2,3,4,5]
∆VLbond represents the shift in the electrostatic potential due to adsorption-induced charge-rearrangements ∆ρ, which are calculated as the difference of the total electron density of the combined metal/organic interface and the non-interacting densities of metal and monolayer on their own:
Special care has to be taken for the correct assignment of the vacuum level (VL) as, in case of a laterally non-uniform VL directly above the sample, the VL measured by ultraviolet photoelectron spectroscopy (UPS) is in between the limiting VL values [121]
Summary
Interfaces between conjugated organic molecules (COMs) and metals are of key importance in the field of organic electronics and the energy-level alignment is crucial for the performance of organic devices [1,2,3,4,5]. We show that the energy levels of the relatively large molecule 1,2,5,6,9,10-coronenehexone (COHON) [70] are Fermi-level pinned on the (1 1 1)-surfaces of coinage metals.
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