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, similar to 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 similar to 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 similar to 75 +/- 14 ns), suggesting possible applications for solar driven H-2 generation.