Nanoscale Confinement of Photo-Injected Electrons at Hybrid Interfaces

Abstract

A prerequisite for advancing hybrid solar light harvesting systems is a comprehensive understanding of the spatio-temporal dynamics of photo-induced interfacial charge separation.Here, we demonstrate access to this transient charge redistribution for a model hybrid system of nanoporous zinc oxide (ZnO) and ruthenium bipyridyl chromophores. The site-selective probing of the molecular electron donor and semiconductor acceptor by time-resolved X-ray photoemission provides direct insight into the depth distribution of the photo-injected electrons and their interaction with the local band structure on a nanometer length-scale. Our results show that these electrons remain localized within less than 6 nm from the interface, due to enhanced downward band-bending by the photo-injected charge carriers. This spatial confinement suggests that light-induced charge generation and transport in nanoscale ZnO photocatalytic devices proceeds predominantly within the defect-rich surface region, which may lead to enhanced surface recombination and explain their lower performance compared to titanium dioxide (TiO2)based systems.TOC GRAPHICS KEYWORDS Interfacial charge transfer; Time-resolved X-ray Photoelectron Spectroscopy; Hybrid light harvesting systems; Band bending;

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“…These usually assume depleted nanoparticles featuring upward bb, where electron transfer proceeds via particle-to-particle hopping in a random-walk fashion. The surface electronic structure of hydroxylated nanoscale ZnO discovered here might be partly responsible for the comparably low performance of this material in dye-sensitized photovoltaics. , …”

“…The surface electronic structure of hydroxylated nanoscale ZnO discovered here might be partly responsible for the comparably low performance of this material in dye-sensitized photo-electrochemical systems. 3,45 Experimental Section:…”

“…The surface electronic structure of hydroxylated nanoscale ZnO discovered here might be partly responsible for the comparably low performance of this material in dye-sensitized photovoltaics. 3,51 ■ EXPERIMENTAL SECTION Sample Preparation. ZnO nanoparticles with an average diameter of ∼15 nm have been prepared with a sol−gel method based on a zinc acetate dihydrate.…”

“…Note that the oxygen in the OH groups represents a ZnO surface atom. (e) SEM image of the ZnO nanoparticle film 45.…”

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