Evidence for photo-induced charge separation between dye molecules adsorbed to aluminium oxide surfaces.

Ute B Cappel,Valerie Vaissier,Piers R F Barnes,Annalisa Bruno,Saif A Haque,Davide Moia

doi:10.1038/srep21276

Abstract

Excited state dynamics and photo-induced charge transfer of dye molecules have been widely studied due to their relevance for organic and dye-sensitised solar cells. Herein, we present a femtosecond transient absorption spectroscopy study of the indolene dye D131 when adsorbed to inert Al2O3 substrates for different surface concentration of the dye. Surprisingly, we find that at high surface concentrations, the first singlet excited state of the dye is converted into a new state with an efficiency of about 80%. We assign the absorption features of this state to the oxidised dye and discuss the possibility of photo-induced charge separation between neighboring dye molecules. Our study is the first to show that this process can be highly efficient without the use of donor and acceptor molecules of different chemical structures.

Highlights

Excited state dynamics and photo-induced charge transfer of dye molecules have been widely studied due to their relevance for organic and dye-sensitised solar cells
We demonstrate that a charge separation process might occur between dye molecules when they are adsorbed to an Al2O3 surface and that the charge transfer can be inhibited by controlling the packing of molecules on the surface through use of a co-adsorber that separates the dyes
In our case the appearance of the new state is dependent on the surface concentration of the dye and its appearance can be inhibited when the dye coverage becomes low

Summary

Introduction

Excited state dynamics and photo-induced charge transfer of dye molecules have been widely studied due to their relevance for organic and dye-sensitised solar cells. Our study is the first to show that this process can be highly efficient without the use of donor and acceptor molecules of different chemical structures. In this communication, we consider photo-induced inter-molecular charge transfer between dye molecules of the same chemical structure adsorbed to an inert aluminium oxide substrate. Al2O3 has been used to study the excited state dynamics of dye molecules when bound to a metal oxide surface and to calculate electron injection yields into non-inert substrates such as TiO2 by comparison of the excited state lifetimes. We demonstrate that a charge separation process might occur between dye molecules when they are adsorbed to an Al2O3 surface and that the charge transfer can be inhibited by controlling the packing of molecules on the surface through use of a co-adsorber that separates the dyes

Methods

Results

Conclusion