Charge transfer from an adsorbed ruthenium-based photosensitizer through an ultra-thin aluminium oxide layer and into a metallic substrate

TL;DR

This study demonstrates that charge transfer from a ruthenium-based dye through an ultra-thin aluminium oxide layer to a metal substrate occurs rapidly, suggesting potential improvements for dye-sensitized solar cell efficiency.

Contribution

It provides direct evidence of ultrafast charge transfer through ultra-thin oxide layers, highlighting their suitability for enhancing dye-sensitized solar cells.

Findings

Charge transfer occurs via tunnelling through the oxide layer.

Transfer time is estimated at approximately 6 femtoseconds.

Ultra-thin oxide layers can facilitate rapid charge injection in DSSCs.

Abstract

The interaction of the dye molecule N3 (cis-bis(isothiocyanato)bis(2,2-bipyridyl-4,4'-dicarboxylato)-ruthenium(II)) with the ultra-thin oxide layer on a AlNi(110) substrate, has been studied using synchrotron radiation based photoelectron spectroscopy, resonant photoemission spectroscopy (RPES) and near edge X-ray absorption fine structure spectroscopy (NEXAFS). Calibrated X-ray absorption and valence band spectra of the monolayer and multilayer coverages reveal that charge transfer is possible from the molecule to the AlNi(110) substrate via tunnelling through the ultra-thin oxide layer and into the conduction band edge of the substrate. This charge transfer mechanism is possible from the LUMO+2&3 in the excited state but not from the LUMO, therefore enabling core-hole clock analysis, which gives an upper limit of $6.0\pm$2.5fs for the transfer time. This indicates that ultra-thin oxide layers are a viable material for use in dye-sensitized solar cells (DSSC), which may lead to reduced recombination effects and improved efficiencies of future devices.