title: Multiple exciton dissociation in CdSe quantum dots by ultrafast electron transfer to adsorbed methylene blue.
abstract: Multiexciton generation in quantum dots (QDs) may provide a new approach for improving the solar-to-electric power conversion efficiency in QD-based solar cells. However, it remains unclear how to extract these excitons before the ultrafast exciton-exciton annihilation process. In this study we investigate multiexciton dissociation dynamics in CdSe QDs adsorbed with methylene blue (MB(+)) molecules by transient absorption spectroscopy. We show that excitons in QDs dissociate by ultrafast electron transfer to MB(+) with an average time constant of approximately 2 ps. The charge separated state is long-lived (>1 ns), and the charge recombination rate increases with the number of dissociated excitons. Up to three MB(+) molecules per QD can be reduced by exciton dissociation. Our result demonstrates that ultrafast interfacial charge separation can effectively compete with exciton-exciton annihilation, providing a viable approach for utilizing short-lived multiple excitons in QDs.
authors.affiliation: Department of Chemistry, Emory University, Atlanta, Georgia 30322, USA.
authors.forename: Jier
authors.initials: J
authors.lastname: Huang
authors.forename: Zhuangqun
authors.initials: Z
authors.lastname: Huang
authors.forename: Ye
authors.initials: Y
authors.lastname: Yang
authors.forename: Haiming
authors.initials: H
authors.lastname: Zhu
authors.forename: Tianquan
authors.initials: T
authors.lastname: Lian
mesh_terms: D000327:Adsorption; D019187:Cadmium Compounds / Q000737:chemistry*; D004583:Electrons; D008751:Methylene Blue / Q000737:chemistry*; D045663:Quantum Dots; D018036:Selenium Compounds / Q000737:chemistry*; D012993:Solar Energy; D013499:Surface Properties; D013816:Thermodynamics
chemical_list: D019187:Cadmium Compounds; D018036:Selenium Compounds; C058667:cadmium selenide; D008751:Methylene Blue