Multiple exciton dissociation in CdSe quantum dots by ultrafast electron transfer to adsorbed methylene blue.
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.
Huang
Jier
J
Department of Chemistry, Emory University, Atlanta, Georgia 30322, USA.
Huang
Zhuangqun
Z
Yang
Ye
Y
Zhu
Haiming
H
Lian
Tianquan
T
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
D019187:Cadmium Compounds; D018036:Selenium Compounds; C058667:cadmium selenide; D008751:Methylene Blue