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Center for Nonlinear Studies |
To better understand how quantum dot-quantum dot and quantum dot-surface interactions determine the overall efficiency of photovoltaic devices we have constructed an optically accessible and functional liquid junction photoelectrochemical cell. In this particular study, CdSe quantum dots are coupled to glass, single crystal TiO2, and single crystal ZnO substrates through a variety of capping ligands. This system architecture is of great interest, as the Parkinson group showed the first demonstration of multiple exciton collection with a similar architecture in 2010.[1] Correlated measurements of sensitized photocurrent and fluorescence decay time for three types of capping ligands on all three substrates show that many of these combinations have a “false” spectroscopic signature of charge transfer. That is, one would predict external current flow based on the spectroscopic measurements, yet no external current flow is detected. We also find certain capping ligand-substrate combinations promote clustering or aggregation of the quantum dots on the substrate surface as observed by atomic force microscope imaging.[2] We have previously shown that energy transfer between individual quantum dots in close physical proximity may act as an “energy sink”, possibly reducing the efficiency of quantum dots as photo-sensitizers [3]. These findings illustrate the crucial role of capping ligands on the electron transfer properties and morphology of quantum dot interfaces. In this talk, I will introduce both the relevant chemistry and photo-physics of quantum dot sensitized solar cells and discuss possible reasons for the observed false spectroscopic signature of charge transfer. REFERENCES [1] Sambur et al., Science, 2010, 330 (6000): 63-66 [2] Shepherd, Sambur, et al., J. Phys. Chem. C, 2012, 116 (39): 21069–21076 [3] Shepherd et al. J. Phys. Chem. C, 2010, 114 (35): 14831–14837
Host: Kipton Barros, T-4 and CNLS