On the origin of gap states in molecular semiconductors—a combined UPS, AFM, and X-ray diffraction study

DOI: 10.1021/acs.jpcc.1c03096

Authors: Jan Hagenlocher (University of Tübingen) , Niels Scheffczyk (University of Tübingen) , Katharina Broch (University of Tübingen) , Giuliano Duva (University of Tübingen) , Nadine Russegger (University of Tübingen) , Lisa Egenberger (University of Tübingen) , Rupak Banerjee (Indian Institute of Technology Gandhinagar) , Satoshi Kera (Institute for Molecular Science) , Frank Schreiber (University of Tübingen) , Alexander Hinderhofer (University of Tübingen)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: The Journal Of Physical Chemistry C , VOL 10

State: Published (Approved)
Published: August 2021

Abstract: Electronic states within the HOMO–LUMO gap of organic semiconductors play a key role in the energy level alignment of substrate–organic and organic–organic interfaces and therefore are a defining parameter for device functionality and efficiency. They are thought to result from structural defects influencing the specific environment of a molecule. Varying the substrate temperature for samples grown by molecular beam deposition, we are able to control their density. Using atomic force microscopy and X-ray scattering techniques, we can differentiate defects depending on their length scale and effective direction. Comparison of the respective defect density with the density of gap states, measured directly via ultra-low-background ultraviolet photoelectron spectroscopy, enables to correlate structural and electronic properties for different prototypical organic semiconductors. We investigate the impact of gap states on the energy level alignment and find a direct link between structural defects and the interface dipole.

Journal Keywords: Carbon nanomaterials; Thin films; Nanospheres; Organic compounds; Defects

Diamond Keywords: Semiconductors; Photovoltaics; Organic Light Emitting Diodes (OLEDs)

Subject Areas: Materials, Chemistry, Physics


Instruments: I07-Surface & interface diffraction

Other Facilities: SiXS at Soleil

Added On: 09/08/2021 08:32

Discipline Tags:

Surfaces Earth Sciences & Environment Sustainable Energy Systems Energy Physics Climate Change Physical Chemistry Electronics Energy Materials Chemistry Materials Science interfaces and thin films

Technical Tags:

Diffraction