Simultaneous harnessing of hot electrons and hot holes achieved via n-metal-p Janus plasmonic heteronanocrystals

Abstract

Plasmonic hybrid nanostructures have opened up avenues for developing new classes of energy conversion materials toward photocatalysis, photovoltaics, and photodetectors. At the core of these applications is how to engineer the interface between the plasmonic/non-plasmonic (typically semiconductor) components, and control the flow and extraction of energetic charge carries within the hybrid system. Despite important advancements on single carrier extraction, the construction of plasmonic nanostructures that can simultaneously harness hot electrons and hot holes has eluded the nascent field. This is because the realization of such nanostructures is extremely challenging, owing to the difficulty in controlled arrangement of disparate materials that can respectively extract hot electrons and holes into one nano-object. Here we present a new dimension for exploitation of plasmonic hot carriers through creating binary energy flow channels across the plasmonic/semiconductor interfaces. This is based on fabrication of the n-type-metal-p-type (n-M-p) heteronanocrystals that consist of plasmonic metal (Au nanorod) adjoined with both n-type (CdS) and p-type (PbS) semiconductors in a core-Janus-shell configuration. Otherwise intractable due to large lattice mismatches, the resulting n-M-p heteronanocrystals display atomically organized interfaces at M-n, M-p and p-n junctions and show suitable interfacial energy barriers. Direct imaging via spatial-resolved surface photovoltage microscopy under NIR light irradiation reveals that the CdS and PbS semiconductor domains can separately collect hot electrons and holes generated from the excitation of plasmons in Au nanorod. This results in extended lifetime of the charge-separated state, and rationalizes the superior performance of n-M-p heteronanocrystals in photocatalytic CO2 reduction even at λ > 700 nm.