APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016;
Baltimore, Maryland
Session L32: Dynamic Interactions Between Nanostructures
11:15 AM–2:15 PM,
Wednesday, March 16, 2016
Room: 332
Sponsoring
Unit:
DCP
Chair: Todd Krauss, University of Rochester
Abstract ID: BAPS.2016.MAR.L32.7
Abstract: L32.00007 : Hole transfer dynamics from QDs to tethered ferrocene derivatives
1:15 PM–1:51 PM
Preview Abstract
Abstract
Author:
A. Paul Alivisatos
(Department of Chemistry, University of California, Berkeley)
Quantum dots (QDs) have shown particular promise in recent years as light
absorbers in solar energy conversion schemes. However, in solution junction
solar devices such as QD-sensitized solar cells and photocatalytic water
splitting systems, efficiencies are often limited by hole transfer from the
photoexcited QD. This process is sluggish and can lead to oxidative
photocorrosion of the QD material. In order to design highly efficient
nanocrystal systems with hole transfer rates that outcompete these
undesirable processes, a fundamental understanding of the parameters that
control these rates is imperative.\\
\\We have developed a model system to study charge transfer from
QDs to surface bound acceptors, to fundamentally understand the charge
transfer processes for QD systems, namely electronic coupling between the
donor and acceptor and the thermodynamic driving force for the hole transfer
process. Specifically, we examine hole transfer from the nearly spherical CdSe-core CdS-shell QDs with photoluminescence (PL) quantum yields over 80{\%} to ferrocene derivatives bound to the QD surface via an alkane thiol linker. In this system, we mitigate the ill-defined nonradiative charge
dynamic pathways that are intrinsic to native CdSe cores, and then
controllably engineer on the surface charge acceptors with well-defined
oxidation potentials, spatial distribution, and quantity. By Measuring the
PL lifetime decay and calibrating the number of hole acceptor ligands per QD
via quantitative `H NMR, we extracted the hole transfer rate per acceptor.
This rate per acceptor could be varied over four orders of magnitude by
changing the coupling between donor and acceptor through modulations in the
CdS shell thickness and alkane chain length of the molecule. Furthermore, owning to the large number of acceptors on the surface, we achieve systems in which \textasciitilde 99{\%} of the photoexcited holes are transferred to these well-defined mediators.\\
\\We further mapped the relationship between the thermodynamic
driving force and hole transfer rate. We systematically tune the driving
force over nearly 1 eV by varying the redox potentials of the ferrocene
ligands through functionalization of the cyclopentadiene rings. Our results
show a monotonic increase in rate as a function of the increasing driving
force with no observed inverted region. This behavior is understood by
considering the residual electron in the QD conduction band, which could
exhibit intraband excitations coupled to the hole transfer, thus creating a
many-state system that would eliminate the inverted region. The resulting
relationship between rate and energetic driving force for hole transfer can
be used to design QD-molecular systems that maximize interfacial charge
transfer rates while minimizing energetic losses associated with the driving
force.
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2016.MAR.L32.7