posted on 2018-07-09, 00:00authored byYuval Ben-Shahar, John P. Philbin, Francesco Scotognella, Lucia Ganzer, Giulio Cerullo, Eran Rabani, Uri Banin
Hybrid
semiconductor–metal nanoparticles (HNPs) manifest
unique, synergistic electronic and optical properties as a result
of combining semiconductor and metal physics via a controlled interface.
These structures can exhibit spatial charge separation across the
semiconductor–metal junction upon light absorption, enabling
their use as photocatalysts. The combination of the photocatalytic
activity of the metal domain with the ability to generate and accommodate
multiple excitons in the semiconducting domain can lead to improved
photocatalytic performance because injecting multiple charge carriers
into the active catalytic sites can increase the quantum yield. Herein,
we show a significant metal domain size dependence of the charge carrier
dynamics as well as the photocatalytic hydrogen generation efficiencies
under nonlinear excitation conditions. An understanding of this size
dependence allows one to control the charge carrier dynamics following
the absorption of light. Using a model hybrid semiconductor–metal
CdS–Au nanorod system and combining transient absorption and
hydrogen evolution kinetics, we reveal faster and more efficient charge
separation and transfer under multiexciton excitation conditions for
large metal domains compared to small ones. Theoretical modeling uncovers
a competition between the kinetics of Auger recombination and charge
separation. A crossover in the dominant process from Auger recombination
to charge separation as the metal domain size increases allows for
effective multiexciton dissociation and harvesting in large metal
domain HNPs. This was also found to lead to relative improvement of
their photocatalytic activity under nonlinear excitation conditions.