Charge Transfer, Band‐Like Transport, and Magnetic Ions at F₁₆CoPc/Rubrene Interfaces

Abstract

and among all systems studied, only one was found to exhibit metallic interfacial electrical conductivity. [ 5 ] We investigate heterostructures formed by a rubrene (tetraphenyltetracene) single crystal and an F 16 CoPc (fl uorinated Co-phthalocyanine) fi lm by means of charge transport and photoelectron spectroscopy. We fi nd that the F 16 CoPc/rubrene interface has signifi cantly enhanced electrical conductance. With the exception of TTF/TCNQ, [ 5 ] the room temperature resistivity of this interface is the lowest reported so far, and temperature dependent measurements show a decrease of the resistivity upon cooling (down to ≈130 K) indicating the occurrence of band-like transport. [20][21][22][23][24][25][26][27][28][29][30] By means of Hall effect measurements, we establish that charge transport is dominated by holes in the rubrene crystal and we fi nd that the value of the hole mobility virtually coincides with that measured in a class of recently investigated organic interfaces based on F x -TCNQ (fl uorinated tetracyanoquinodimethane) and rubrene single crystals. [ 13 ] As compared to all interfaces studied in this family, on the contrary, the hole density is higher in F 16 CoPc/rubrene, which explains the low value of the F 16 CoPc/rubrene resistivity. The results of the transport measurements are corroborated by Kelvin probe microscopy experiments that enable the alignment of the chemical potential across the F 16 CoPc/rubrene interface to be determined, and confi rm that a large transfer between the two materials should be expected. Finally, we perform photoelectron spectroscopy (PES) measurements on thin fi lm F 16 CoPc/rubrene heterostructures to show that the charge transfer at the interface involves electronic orbitals centered on the magnetic Cobalt ion of the F 16 CoPc molecules. We therefore conclude that the investigated system does allow the high electrical conductivity with the presence of magnetic ions to be combined at the interface.F 16 CoPc/rubrene interface devices were formed on a polydimethylsiloxane substrate. First, a rubrene single crystal (grown by physical vapor transport) was laminated on the substrate and then a 70-nm F 16 CoPc fi lm was evaporated (under high vacuum conditions) on top of the rubrene crystal. The transport properties of rubrene single crystals (identical to those used to assemble the interfaces) were investigated via fi eldeffect transistor (FET) measurements [ 31 ] as a characterization step, and showed a room temperature mobility between 12 and 20 cm 2 V −1 s −1 in devices in which the crystal was suspended on top of a gate electrode, in agreement with previous studies. [32][33][34] In order to maintain its quality, the rubrene crystal was kept at room temperature throughout the deposition of the evaporated fi lm. As a result, the morphology of the F 16 CoPc fi lm was expected to be far from ideal, as indeed indicated by atomic force microscopy measurements showing F 16 CoPc fi lms with rather rough surfaces, consisting of small grains with irregular orientation...

Surface functionalization of WSe2 by F16CoPc

“…This signals a change in the valence of the Co center of F 16 CoPc molecules to about Co(I). This interpretation is in very good correspondence to previous studies, where a charge transfer from, e.g., metal substrates or organic materials to F 16 CoPc has been reported . Moreover, these studies have also revealed that in F 16 CoPc, the metal center receives the transferred charge, while the organic ligand remains unchanged.…”

“…The relatively low charge carrier density at our WSe 2 /F 16 CoPc interface suggests that the molecular arrangement is different from this first assumption and/or that the charge transfer per molecule is not complete due to, e.g., local hybrid formation. Interestingly, recent investigations of the interface between the organic semiconductor rubrene and F 16 CoPc demonstrated a charge density in the rubrene surface induced by charge transfer of about 1.6 × 10 −3Å−2 [15], also an order of magnitude larger than our estimation for the WSe 2 /F 16 CoPc interface. Further investigations of this interface, its structure, and potential local interactions by various techniques are necessary to rationalize all observations.…”

Charge Transfer at the Interface Between MnPc and F6TCNNQ

“…Also, charge transfer at interfaces of two molecular materials came into the focus of researchers triggered by the goal to advance the performance of organic electronic devices, or by the possibility for functionalities at such interfaces. Intriguingly, interfaces between two different organic semiconductors support charge transfer from one side to the other and resulted in electronic properties that differ substantially from those of the individual constituent materials . Even metallic behavior can occur at the interface of two initially insulating organic semiconductors .…”

“…Intriguingly, interfaces between two different organic semiconductors support charge transfer from one side to the other and resulted in electronic properties that differ substantially from those of the individual constituent materials . Even metallic behavior can occur at the interface of two initially insulating organic semiconductors . Although only a few combinations have been investigated so far, these examples indicate that organic semiconductors offer a large flexibility to control the electronic states of interfacial systems.…”

Hall Effect in Bulk‐Doped Organic Single Crystals

“…Fortunately, the Hall voltage of undoped rubrene single crystals, which possess band‐like transport properties, has been measured with the assistance of trap healing and gate bias with an FET . The interfacial doping of single crystals has recently been reported . We expected that the Hall voltage could be measured if bulk‐doped rubrene single crystals could be fabricated.…”