Charge Transfer Dynamics at Dye-Sensitized ZnO and TiO2 Interfaces Studied by Ultrafast XUV Photoelectron Spectroscopy

Mario Borgwardt, Martin Wilke, Thorsten Kampen, Sven Mähl, Manda Xiao, Leone Spiccia, Kathrin M Lange, Igor Yu Kiyan, Emad F Aziz

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16 Citations (Scopus)

Abstract

Interfacial charge transfer from photoexcited ruthenium-based N3 dye molecules into ZnO thin films received controversial interpretations. To identify the physical origin for the delayed electron transfer in ZnO compared to TiO2, we probe directly the electronic structure at both dye-semiconductor interfaces by applying ultrafast XUV photoemission spectroscopy. In the range of pump-probe time delays between 0.5 to 1.0 ps, the transient signal of the intermediate states was compared, revealing a distinct difference in their electron binding energies of 0.4 eV. This finding strongly indicates the nature of the charge injection at the ZnO interface associated with the formation of an interfacial electron-cation complex. It further highlights that the energetic alignment between the dye donor and semiconductor acceptor states appears to be of minor importance for the injection kinetics and that the injection efficiency is dominated by the electronic coupling.

Original languageEnglish
Article number24422
Number of pages7
JournalScientific Reports
Volume6
DOIs
Publication statusPublished - 13 Apr 2016

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