Modification of Charge Transfer and Energy Level Alignment at Organic/TiO₂ Interfaces

Abstract

Adsorption of titanyl phthalocyanine (TiOPc) on rutile TiO 2 (110) modified by a set of pyridine derivatives (2,2′-bipyridine, 4,4′-bipyridine, and 4-tert-butyl pyridine) has been investigated using synchrotron radiation based X-ray photoelectron spectroscopy (XPS). For the unmodified TiOPc/TiO 2 system, a strong charge transfer is observed from the first layer TiOPc into the substrate, which leads to a molecular layer at the interface with a depleted highest occupied molecular orbital (HOMO). However, precovering the TiO 2 surface with a saturated pyridine monolayer effectively reduce this process and leave the TiOPc in a less perturbed molecular state. Furthermore, the TiOPc HOMO and core levels are observed at different binding energies ranging by 0.3 eV on the three pyridine monolayers, which is ascribed to differences in surface potentials set up by the different pyridine/TiO 2 systems.

Inhomogeneous charge transfer within monolayer zinc phthalocyanine absorbed on TiO2(110)

“…The growth is of island type at room temperature. In agreement with previous studies on Pc/TiO 2 , [13][14][15][16] it is found that charge is transferred away from the molecular HOMO into the substrate. Further comparison between NEXAFS resonance shifts and PES shifts points to a considerable screening difference between molecular center and periphery.…”

“…TiO 2 is usually used as the working electrode for such devices. Previously, we have found that Pc molecules (FePc, 13,14 TiOPc, 15 and H 2 Pc (Ref. 16)) suffer from electron depletion when absorbed on TiO 2 .…”

Adsorption and Self-Assembly of Large Polycyclic Molecules on the Surfaces of TiO2 Single Crystals

“…, the direction of the TiO 2 reconstruction rows) composed from slightly tilted phthalocyanines that are presumably partially overlapping was observed. Yu et al also investigated the adsorption of TiOPc on rutile (110) and on buffer layers formed by 2,2′-bipyridine, 4,4′-bipyridine, and 4-tert-butyl pyridine using X-ray absorption spectroscopy [57]. TiOPc molecules adsorbed directly on the rutile surface were observed to strongly bind with a significant charge transfer occurring into the substrate.…”

Site-dependent charge transfer at the Pt(111)-ZnPc interface and the effect of iodine

“…Manipulation of the M Pc-substrate interaction is possible by either decorating the molecules (adding external atoms or molecules to the center or the periphery of Pcs) [43][44][45], by modifying the substrate by inserting intermediate layers [46,47], or by adding layers on top of M Pc [48][49][50][51][52]. For instance, upon adsorption of pyridine on an ordered layer of FePc on Au(111), pyridine molecules coordinate to the iron.…”