Ultrafast exciton quenching by energy and electron transfer in colloidal CdSe nanosheet-Pt heterostructures

Two-dimensional (2-D) semiconductor nanomaterials are receiving tremendous research interests due in part to their attractive light absorption and charge transport properties. Integration of catalytic metal nanoparticles with these 2-D semiconductors can potentially lead to new photocatalytic nanoheterostructures for efficient solar-to-fuel conversion. Here we report the synthesis and transient absorption study of colloidal quantum confined CdSe nanosheets with a Pt nanoparticle at the edge or vertex. Due to the large in-plane exciton mobility, ∼86.6 ± 0.5% of excitons generated in CdSe sheets can be transported to NS-Pt interface and quenched by energy transfer to Pt (with a half-life <150 fs). The remaining excitons (13.4 ± 0.5%) become localized due to fast hole trapping and can be dissociated by interfacial electron transfer to Pt (with a half life of ∼9.4 ± 0.7 ps). The resulting charge-separated states (with electrons in Pt and trapped holes in CdSe) are long-lived (half life of ∼75 ± 14 ns), suggesting possible applications for solar driven H₂ generation.