Colloidal semiconductor-metal nano-heterostructures have emerged as a new family of functional materials with potential applications in solar-to-fuel conversion. In these nano-heterostructures, the directly connected metal and semiconducting domains interact strongly, as evidenced by photoluminescence quenching of the semiconducting domain. However, to date, the exact quenching mechanisms and how they affect the light harvesting and charge separation properties of these heterostructures remain poorly understood. The energy level alignments of these constituent materials often allow energy, electron and hole transfer. Understanding the factors controlling the rates of these processes and thus the competition between them is necessary for the further design and optimization of these heterostructures. In an effort to understand the interaction mechanisms, we have applied ultrafast pump-probe transient absorption spectroscopy to systematically interrogate the carrier dynamics in photocatalytic Platinum-tipped CdS nanorods (NR-Pt) and CdSe@CdS dot in rods (DIR-Pt). In CdS NR-Pt, we show the ultrafast interfacial electron transfer from CdS to Pt is the dominant exciton quenching pathway for excited CdS NRs and the charge separated state is long lived due to trapping of holes in CdS NRs. To better control the location and energetic of the holes, we have investigated CdSe@CdS DIR-Pt nano-heterostructure in which ultrafast electron transfer from CdS to Pt is still the the dominant interaction mechanism. However, the slow charge recombination is induced by hole confinement in the CdSe core, which is therefore advantageous over CdS-Pt nanorods in terms of stability and optimization. In addition, we show that hole filling in the presence of sacrificial electron donor is also more efficient in CdSe@CdS DIRs than in CdS nanorods. These findings explain the experimentally-observed better hydrogen evolution performance of CdSe@CdS DIR-Pt than CdS NR-Pt and provide insights for designing more efficient nano-heterostructure-based photocatalytic systems.

Charge separation dynamics in photocatalytic semiconductor-Pt nanorod heterostructures

246th National Meeting (2013)

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