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Seleno groups control the energy-level alignment between conjugated organic molecules and metals
Jens Niederhausen1, Steffen Duhm2, Georg Heimel1
1Institut für Physik, Humboldt-Universität zu Berlin, 12489 Berlin, Germany.
The Journal of Chemical Physics
|January 14, 2014
Summary
Researchers mitigated the hole injection barrier in organic electronics by utilizing seleno-functionalized organic molecules. This approach overcomes the "push-back" effect, enabling efficient charge injection for devices with low ionization energies.
Area of Science:
- Organic electronics
- Interface physics
- Materials science
Background:
- Charge injection in organic devices is hindered by interfacial energy level misalignment.
- The "push-back" effect, caused by Pauli repulsion, increases the hole injection barrier.
- Chalcogenol self-assembled monolayers (SAMs) on metals exhibit energy level alignment governed by chalcogen-metal bonds.
Purpose of the Study:
- To investigate energy-level alignment at metal-organic interfaces using seleno-functionalized conjugated organic molecules (COMs).
- To demonstrate the mitigation of the "push-back" effect for improved charge injection.
- To achieve low hole injection barriers, particularly for COMs with low ionization energies.
Main Methods:
- X-ray photoelectron spectroscopy (XPS).
- Ultraviolet photoelectron spectroscopy (UPS).
- Investigation of interfaces between tetraseleno-tetracene and Au(111), Ag(111), and Cu(111).
Main Results:
- Seleno-functionalized COMs exhibit an energy-level alignment mechanism similar to chalcogenol SAMs.
- This mechanism effectively mitigates the "push-back" effect at metal contacts.
- Exceedingly low hole injection barriers were achieved for tetraseleno-tetracene interfaces.
Conclusions:
- The interfacial energy-level alignment mechanism involving chalcogen-metal bonds is applicable to seleno-functionalized COMs.
- This finding provides a strategy to overcome injection barriers in organic electronics.
- Enables efficient charge injection for organic devices, especially those using low ionization energy materials.
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