Orientation-dependent work-function modification using substituted pyrene-based acceptors

O. T. Hofmann, H. Glowatzki, C. Bürker, G. M. Rangger, B. Bröker, J. Niederhausen, T. Hosokai, I. Salzmann, R. P. Blum, R. Rieger, A. Vollmer, P. Rajput, A. Gerlach, K. Müllen, F. Schreiber, E. Zojer, N. Koch, S. Duhm

Research output: Contribution to journalArticleResearchpeer-review

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.

Original languageEnglish
JournalJournal of Physical Chemistry C
Volume121
Issue number39
DOIs
Publication statusPublished - 2017

Fingerprint

Pyrene
pyrenes
Crystal orientation
Electron affinity
electron affinity
Adsorbates
Fermi level
Electronic properties
Electrodes
electrodes
Monolayers
Metals
Adsorption
Charge injection
adsorption
Semiconducting organic compounds
Molecular orientation
organic semiconductors
Photoelectron spectroscopy
electronics

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Energy(all)
  • Physical and Theoretical Chemistry
  • Surfaces, Coatings and Films

Cite this

Orientation-dependent work-function modification using substituted pyrene-based acceptors. / Hofmann, O. T.; Glowatzki, H.; Bürker, C.; Rangger, G. M.; Bröker, B.; Niederhausen, J.; Hosokai, T.; Salzmann, I.; Blum, R. P.; Rieger, R.; Vollmer, A.; Rajput, P.; Gerlach, A.; Müllen, K.; Schreiber, F.; Zojer, E.; Koch, N.; Duhm, S.

In: Journal of Physical Chemistry C, Vol. 121, No. 39, 2017.

Research output: Contribution to journalArticleResearchpeer-review

Hofmann, OT, Glowatzki, H, Bürker, C, Rangger, GM, Bröker, B, Niederhausen, J, Hosokai, T, Salzmann, I, Blum, RP, Rieger, R, Vollmer, A, Rajput, P, Gerlach, A, Müllen, K, Schreiber, F, Zojer, E, Koch, N & Duhm, S 2017, 'Orientation-dependent work-function modification using substituted pyrene-based acceptors' Journal of Physical Chemistry C, vol. 121, no. 39. https://doi.org/10.1021/acs.jpcc.7b08451
Hofmann, O. T. ; Glowatzki, H. ; Bürker, C. ; Rangger, G. M. ; Bröker, B. ; Niederhausen, J. ; Hosokai, T. ; Salzmann, I. ; Blum, R. P. ; Rieger, R. ; Vollmer, A. ; Rajput, P. ; Gerlach, A. ; Müllen, K. ; Schreiber, F. ; Zojer, E. ; Koch, N. ; Duhm, S. / Orientation-dependent work-function modification using substituted pyrene-based acceptors. In: Journal of Physical Chemistry C. 2017 ; Vol. 121, No. 39.
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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.",
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AU - Hofmann, O. T.

AU - Glowatzki, H.

AU - Bürker, C.

AU - Rangger, G. M.

AU - Bröker, B.

AU - Niederhausen, J.

AU - Hosokai, T.

AU - Salzmann, I.

AU - Blum, R. P.

AU - Rieger, R.

AU - Vollmer, A.

AU - Rajput, P.

AU - Gerlach, A.

AU - Müllen, K.

AU - Schreiber, F.

AU - Zojer, E.

AU - Koch, N.

AU - Duhm, S.

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N2 - 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.

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