Ultrafast Charge Transfer from CdSe Quantum Dots to p-Type NiO: Hole Injection vs Hole Trapping

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Abstract

Semiconductor quantum dot (QD) to metal oxide electron injection dynamics is well documented in the scientific literature. In contrast to that, not much is known so far about hole injection time scales in such systems. The current study fills this gap. We investigate photocathodes consisting of CdSe QDs and p-type NiO to study hole injection dynamics from the valence band of the QDs to NiO. The combination of two complementary techniques, ultrafast time-resolved absorption and fluorescence spectroscopies, enabled us to distinguish between hole trapping and injection. A kinetic component on the time scale of a few hundreds of picoseconds was identified as hole injection. By changing the size of the QDs, the driving force of the hole injection was tuned and we demonstrated that the hole injection rates are well described by the Marcus theory of charge transfer. In order to enhance the overall hole injection efficiency, we have passivated the CdSe QDs by a gradient ZnS shell. The core-shell QDs show significantly slower hole injection; still, since trapping was almost eliminated, the overall hole injection efficiency was greatly enhanced.

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Subject classification (UKÄ) – MANDATORY

  • Atom and Molecular Physics and Optics
Original languageEnglish
Pages (from-to)18462-18471
JournalJournal of Physical Chemistry C
Volume118
Issue number32
StatePublished - 2014
Peer-reviewedYes

Bibliographic note

The information about affiliations in this record was updated in December 2015. The record was previously connected to the following departments: Chemical Physics (S) (011001060)