3 years ago

Extended Space Charge Region and Unoccupied Molecular Band Formation in Epitaxial Tetrafluorotetracyanoquinodimethane Films

Extended Space Charge Region and Unoccupied Molecular Band Formation in Epitaxial Tetrafluorotetracyanoquinodimethane Films
David Gerbert, Petra Tegeder, Friedrich Maaß
Generating well-defined molecular structures at inorganic/organic interfaces and within molecular films is fundamental for charge carrier transport and thus the performance of organic molecule-based (opto)electronic devices. Here we show by means of low-energy electron diffraction that tetrafluorotetracyanoquinodimethane (F4TCNQ) grows in an epitaxial fashion on the Au(111) surface, resulting in a unit cell which consists of one molecule. In this well-ordered crystalline films we found the formation of an extended space charge region and a dispersing unoccupied electronic molecular state using energy- and angle-resolved two-photon photoemission. The latter finding is a clear proof for band formation in the crystalline molecular structure. We suggest that the high electron affinity of F4TCNQ and a bandlike electron transport are responsible for the formation of the space charge region. Using F4TCNQ as a hole injection layer may open the opportunity to manipulate the hole injection barrier in a controlled way via variation of the F4TCNQ layer thickness.

Publisher URL: http://dx.doi.org/10.1021/acs.jpcc.7b02939

DOI: 10.1021/acs.jpcc.7b02939

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