Publications (3)0 Total impact
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Article: Unique Temperature Dependence and Blinking Behavior of CdTe/CdSe (Core/Shell) Type-II Quantum Dots
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ABSTRACT: Temperature dependent photoluminescence (PL) spectroscopy in a range of 5 K to room temperature (RT, 290 K) and single dot blinking behavior were investigated for CdTe/CdSe (core/shell, C/S) quantum dots (QDs). The QDs show type-II characteristics as both of the valence and conduction band levels of the CdTe core are placed higher in energy than those of the CdSe shell. The thickness of the CdSe shell was varied to control the degree of type-II character, and bare CdTe QDs were used as controls. The CdTe/CdSe (C/S) QDs have unique PL properties including (i) high susceptibility to PL thermal quenching with an exciton dissociation energy as small as 18 meV, compared with 46 meV for the CdTe QD, (ii) smaller band gap change showing only half the reduction of the control within the temperature change, and (iii) up to 27% larger PL bandwidth broadening than the control. The unique temperature-dependent properties were enhanced as the type-II character was increased by the thicker CdSe shell. Single dot levThe Journal of Physical Chemistry C. 12/2010; 115:436-442. -
Article: ZnTe/ZnSe (Core/Shell) Type-II Quantum Dots: Their Optical and Photovoltaic Properties
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ABSTRACT: Synthesis of a size series of colloidal ZnTe/ZnSe (core/shell) quantum dots (QDs) is reported. Because of the unique Type-II characters, their emission can range over an extended wavelength regime, showing photoluminescence (PL) from blue to amber. The PL lifetime measures as long as 77 ns, which clearly indicates the Type-II characteristics. ZnTe/ZnSe (Core/Shell) QDs can be further passivated by ZnS layers, rendered in water, while preserving the optical and chemical stabilities and thus proved their potentials toward "nontoxic" biological or medical applications that are free from concerns regarding heavy-metal leakage. ZnTe/ZnSe Type-II QD/polymer hybrid organic solar cells are also showcased, promising environmentally friendly photovoltaic devices. ZnTe/ZnSe Type-II QD incorporated photovoltaic devices show 11 times higher power conversion efficiency, when compared to that of the control ZnSe QD devices. This results from the Type-II characteristic broad QD absorption up to extended wavelengths and the spatially separated Type-II excitons, which can enhance the carrier extractions. We believe that ZnTe/ZnSe-based Type-II band engineering can open many new possibilities as exploiting the safe material choice. -
Article: Multilayered Semiconductor (CdS/CdSe/ZnS)-Sensitized TiO2 Mesoporous Solar Cells: All Prepared by Successive Ionic Layer Adsorption and Reaction Processes
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ABSTRACT: A model semiconductor-sensitizer layer of CdSe with under-or overlayers of CdS or ZnS by pre-or postadsorption was prepared on the surface of mesoporous TiO 2 films by a series of successive ionic layer adsorption and reaction (SILAR) processes in solutions containing corresponding cations and anions. The growth of each semiconductor layer was monitored by taking UV-visible absorption spectra and high-resolution transmission electron microscopy (TEM) images. The all SILAR-prepared multicomponent sensitizer consisting of CdS/CdSe/ZnS layers was evaluated in a poly-sulfide electrolyte solution as a redox mediator in regenerative photoelectrochemical cells. The CdS and ZnS layers with the CdSe layer sandwiched in between were found to significantly enhance photocurrents. The best photovoltaic performance was obtained from the CdS/CdSe/ZnS-sensitizer with the ZnS layer on the top, yielding an overall power conversion efficiency of 3.44% with a mask around the active film and 3.90% with no mask. The effect of the mask on short-circuit current (J sc) and overall efficiency (η) measurements was shown to be increasingly critical in semiconductor-sensitized solar cells as they exhibit high photocurrents. The polysulfide electrolyte, which acted as an effective electron transfer mediator for CdS and/or CdSe sensitizers, was not as effective for PbS-based sensitizers prepared by the same SILAR process.
