23 research outputs found

    One-Pot Noninjection Synthesis of Cu-Doped Zn<sub><i>x</i></sub>Cd<sub>1‑<i>x</i></sub>S Nanocrystals with Emission Color Tunable over Entire Visible Spectrum

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    Unlike Mn doped quantum dots (d-dots), the emission color of Cu dopant in Cu d-dots is dependent on the nature, size, and composition of host nanocrystals (NCs). The tunable Cu dopant emission has been achieved via tuning the particle size of host NCs in previous reports. In this paper, for the first time we doped Cu impurity in Zn<sub><i>x</i></sub>Cd<sub>1‑<i>x</i></sub>S alloyed NCs and tuned the dopant emission in the whole visible spectrum via variation of the stoichiometric ratio of Zn/Cd precursors in the host Zn<sub><i>x</i></sub>Cd<sub>1‑<i>x</i></sub>S alloyed NCs. A facile noninjection and low cost approach for the synthesis of Cu:Zn<sub><i>x</i></sub>Cd<sub>1‑<i>x</i></sub>S d-dots was reported. The optical properties and structure of the obtained Cu:Zn<sub><i>x</i></sub>Cd<sub>1‑<i>x</i></sub>S d-dots have been characterized by UV–vis spectroscopy, photoluminescence (PL) spectroscopy, transmission electron microscopy (TEM), and X-ray diffraction (XRD). The influences of various experimental variables, including Zn/Cd ratio, reaction temperature, and Cu dopant concentration, on the optical properties of Cu dopant emission have been systematically investigated. The as-prepared Cu:Zn<sub><i>x</i></sub>Cd<sub>1‑<i>x</i></sub>S d-dots did show PL emission but with quite low quantum yield (QY) (typically below 6%). With the deposition of ZnS shell around the Cu:Zn<sub><i>x</i></sub>Cd<sub>1‑<i>x</i></sub>S core NCs, the PL QY increased substantially with a maximum value of 65%. More importantly, the high PL QY can be preserved when the initial oil-soluble d-dots were transferred into aqueous media via ligand replacement by mercaptoundeconic acid. In addition, these d-dots have thermal stability up to 250 °C

    Noninjection Facile Synthesis of Gram-Scale Highly Luminescent CdSe Multipod Nanocrystals

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    Nearly all reported approaches for synthesis of high quality CdSe nanocrystals (NCs) involved two steps of preparation of Cd or Se stock solution in advance and then mixing the two reactants via hot-injection in high temperature. In this manuscript, Gram-scale CdSe multipod NCs were facilely synthesized in a noninjection route with the use of CdO and Se powder directly as reactants in paraffin reaction medium containing small amount of oleic acid and trioctylphosphine. The influence of various experimental variables, including reaction temperature, nature and amount of surfactants, Cd-to-Se ratio, and the nature of reactants, on the morphology of the obtained CdSe NCs have been systematically investigated. After deposition of ZnS shell around the CdSe multipod NCs, the PL QY of the obtained CdSe/ZnS can be up to 85%. The reported noninjection preparation approach can satisfy the requirement of industrial production bearing the advantage of low-cost, reproducible, and scalable. Furthermore, this facile noninjection strategy provides a versatile route to large-scale preparation of other semiconductor NCs with multipod or other morphologies

    Electroplating Cuprous Sulfide Counter Electrode for High-Efficiency Long-Term Stability Quantum Dot Sensitized Solar Cells

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    Currently, Cu<sub>2</sub>S based on brass foil is the most commonly used counter electrode (CE) in high efficiency quantum dot sensitized solar cells (QDSCs) because of its superior catalytic activity to the polysulfide electrolyte redox couple. Regretfully, the brass substrate is limited by the shortcomings of corrosion by polysulfide electrolyte and lack of long-term stability. In order to combine the high catalytic activity of Cu<sub>2</sub>S and superior tolerance of fluorine doped tin oxide (FTO) glass to polysulfide electrolyte, Cu<sub>2</sub>S film on the FTO glass substrate (Cu<sub>2</sub>S/FTO) CE was prepared by electrodeposition of the copper film via a multipotential step technique followed by dipping into polysulfide methanol solution. The Cu<sub>2</sub>S film was proven to be composed by the interconnected nanoflakes, which ensures the highly catalytic activity to the polysulfide redox couple electrolyte in QDSCs. The CdSe quantum dot (QD) sensitized solar cells with the optimized Cu<sub>2</sub>S/FTO CE exhibit a power conversion efficiency (PCE) of 5.21%, which is very close to that with the commonly used Cu<sub>2</sub>S/brass CE (5.41%) and much higher than that of Pt CE (1.68%). Furthermore, the cell device based on the Cu<sub>2</sub>S/FTO CE shows superior stability at a working state for over 10 h without decrease in PCE, which is a serious challenge for the Cu<sub>2</sub>S/brass CE

    Inorganic Ligand Thiosulfate-Capped Quantum Dots for Efficient Quantum Dot Sensitized Solar Cells

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    The insulating nature of organic ligands containing long hydrocarbon tails brings forward serious limitations for presynthesized quantum dots (QDs) in photovoltaic applications. Replacing the initial organic hydrocarbon chain ligands with simple, cheap, and small inorganic ligands is regarded as an efficient strategy for improving the performance of the resulting photovoltaic devices. Herein, thiosulfate (S<sub>2</sub>O<sub>3</sub><sup>2–</sup>), and sulfide (S<sup>2–</sup>) were employed as ligand-exchange reagents to get access to the inorganic ligand S<sub>2</sub>O<sub>3</sub><sup>2–</sup>- and S<sup>2–</sup>-capped CdSe QDs. The obtained inorganic ligand-capped QDs, together with the initial oleylamine-capped QDs, were used as light-absorbing materials in the construction of quantum dot sensitized solar cells (QDSCs). Photovoltaic results indicate that thiosulfate-capped QDs give excellent power conversion efficiency (PCE) of 6.11% under the illumination of full one sun, which is remarkably higher than those of sulfide- (3.36%) and OAm-capped QDs (0.84%) and is comparable to the state-of-the-art value based on mercaptocarboxylic acid capped QDs. Photoluminescence (PL) decay characterization demonstrates that thiosulfate-based QDSCs have a much-faster electron injection rate from QD to TiO<sub>2</sub> substrate in comparison with those of sulfide- and OAm-based QDSCs. Electrochemical impedance spectroscopy (EIS) results indicate that higher charge-recombination resistance between potoanode and eletrolyte interfaces were observed in the thiosulfate-based cells. To the best of our knowledge, this is the first application of thiosulfate-capped QDs in the fabrication of efficient QDSCs. This will lend a new perspective to boosting the performance of QDSCs furthermore

    Controlled Sulfidation Approach for Copper Sulfide–Carbon Hybrid as an Effective Counter Electrode in Quantum-Dot-Sensitized Solar Cells

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    Because of their good conductivities and high catalytic activities, carbon materials and copper sulfides have been individually and jointly used as counter electrodes in quantum-dot-sensitized solar cells (QDSCs). However, obtaining a combination of high conversion efficiency and stability is still challenging. In this work, we present a facile method for fabricating Cu<sub>1.8</sub>S–C hybrid counter electrodes through the sulfidation of a copper–carbon composite synthesized by grinding a mixture of organic binder, commercial copper powder, and carbon material containing activated carbon and carbon black in a designed mass ratio. The assembled CdSeTe-sensitized QDSCs achieved a high PCE of 8.40%, larger than that of pure carbon (5.25%) and comparable to that of conventional Cu<sub><i>x</i></sub>S/brass-based QDSCs (8.44%). Significantly, the devices based on Cu<sub>1.8</sub>S–C showed excellent stability. The improved performance is mainly attributed to the good conductivity and stability of carbon and the high catalytic activity of Cu<sub>1.8</sub>S

    Solar Paint from TiO<sub>2</sub> Particles Supported Quantum Dots for Photoanodes in Quantum Dot–Sensitized Solar Cells

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    The preparation of quantum dot (QD)–sensitized photoanodes, especially the deposition of QDs on TiO<sub>2</sub> matrix, is usually a time-extensive and performance-determinant step in the construction of QD-sensitized solar cells (QDSCs). Herein, a transformative approach for immobilizing QD on the TiO<sub>2</sub> matrix was developed by simply mixing the as-prepared oil-soluble QDs with TiO<sub>2</sub> P25 particles suspension for a period as short as half a minute. The solar paint was prepared by adding the TiO<sub>2</sub>/QD composite in a binder solution under ultrasonication. The QD-sensitized photoanodes were then obtained by simply brushing the solar paint on a fluorine-doped tin oxide substrate followed by a low-temperature annealing at ambient atmosphere. Sandwich-structured complete QDSCs were assembled with the use of Cu<sub>2</sub>S/brass as counter electrode and polysulfide redox couple as an electrolyte. The photovoltaic performance of the resulting Zn–Cu–In–Se (ZCISe) QDSCs was evaluated after primary optimization of the QD/TiO<sub>2</sub> ratio as well as the thicknesses of photoanode films. In this proof of concept with a simple solar paint approach for photoanode films, an average power conversion efficiency of 4.13% (<i>J</i><sub>sc</sub> = 11.11 mA/cm<sup>2</sup>, <i>V</i><sub>oc</sub> = 0.590 V, fill factor = 0.631) was obtained under standard irradiation condition. This facile solar paint approach offers a simple and convenient approach for QD-sensitized photoanodes in the construction of QDSCs

    Color-Tunable Highly Bright Photoluminescence of Cadmium-Free Cu-Doped Zn–In–S Nanocrystals and Electroluminescence

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    A series of Cu doped Zn–In–S quantum dots (Cu:Zn–In–S d-dots) were synthesized via a one-pot noninjection synthetic approach by heating up a mixture of corresponding metal acetate salts and sulfur powder together with dodecanethiol in oleylamine media. After overcoating the ZnS shell around the Cu:Zn–In–S d-dot cores directly in the crude reaction solution, the resulting Cu:Zn–In–S/ZnS d-dots show composition-tunable photoluminescence (PL) emission over the entire visible spectral window and extending to the near-infrared spectral window (from 450 to 810 nm), with the highest PL quantum yield (QY) up to 85%. Importantly, the initial high PL QY of the obtained Cu:Zn–In–S/ZnS d-dots in organic media can be preserved when transferred into aqueous media via ligand exchange. Furthermore, electroluminescent devices with good performance (with a maximum luminance of 220 cd m<sup>–2</sup>, low turn-on voltages of 3.6 V) have been fabricated with the use of these Cd-free low toxicity yellow-emission Cu:Zn–In–S/ZnS d-dots as an active layer in these QD-based light-emitting diodes

    Highly Efficient Inverted Type-I CdS/CdSe Core/Shell Structure QD-Sensitized Solar Cells

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    Presynthesized high-quality CdS/CdSe inverted type-I core/shell structure QDs have been deposited onto TiO<sub>2</sub> electrodes after first coating with bifunctional linker molecules, mercaptopropionic acid (MPA), and the resulting quantum dot sensitized solar cells (QDSCs) exhibited record conversion efficiency of 5.32% (<i>V</i><sub>oc</sub> = 0.527 V, <i>J</i><sub>sc</sub> = 18.02 mA/cm<sup>2</sup>, FF = 0.56) under simulated AM 1.5, 100 mW cm<sup>–2</sup> illumination. CdS/CdSe QDs with different CdSe shell thicknesses and different corresponding absorption onsets were prepared <i>via</i> the well-developed organometallic high-temperature injection method. MPA-capped water-dispersible QDs were then obtained <i>via</i> ligand exchange from the initial organic ligand capped oil-dispersible QDs. The QD-sensitized TiO<sub>2</sub> electrodes were facilely prepared by pipetting the MPA-capped CdS/CdSe QD aqueous solution onto the TiO<sub>2</sub> film, followed by a covering process with a ZnS layer and a postsintering process at 300 °C. Polysulfide electrolyte and Cu<sub>2</sub>S counterelectrode were used to provide higher photocurrents and fill factors of the constructed cell devices. The characteristics of these QDSCs were studied in more detail by optical measurements, incidental photo-to-current efficiency measurements, and impedance spectroscopy. With the combination of the modified deposition technique with use of linker molecule MPA-capped water-soluble QDs and well-developed inverted type-I core/shell structure of the sensitizer together with the sintering treatment of QD-bound TiO<sub>2</sub> electrodes, the resulting CdS/CdSe-sensitized solar cells show a record photovoltaic performance with a conversion efficiency of 5.32%

    Topotactically Grown Bismuth Sulfide Network Film on Substrate as Low-Cost Counter Electrodes for Quantum Dot-Sensitized Solar Cells

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    Bi<sub>2</sub>S<sub>3</sub> films consisting of two-dimensional interconnected Bi<sub>2</sub>S<sub>3</sub> single-crystalline nanorod networks have been fabricated on a F:SnO<sub>2</sub> (FTO) glass substrate through the formation of intermediate BiOI nanosheets from layer-structured BiI<sub>3</sub> by chemical vapor deposition and subsequent hydrothermal transformation into Bi<sub>2</sub>S<sub>3</sub> networks. A continuous lattice and structure-directed topotactic transformation mechanism is supposed for the formation of Bi<sub>2</sub>S<sub>3</sub> network film. The prepared Bi<sub>2</sub>S<sub>3</sub>/FTO films were employed as counter electrode (CE) for CdSe quantum dot-sensitized solar cells for the first time and showed better photovoltaic performance than that from the convenient Pt CE. The influence of the preparation conditions for Bi<sub>2</sub>S<sub>3</sub>/FTO films on the resulting solar cell performance was systematically investigated and optimized with use of <i>J–V</i> curves, scanning electron microscopy (SEM), UV–vis absorption, and electrochemical impedance spectroscopy. To further improve the cell device efficiency, the modification of the Bi<sub>2</sub>S<sub>3</sub> network CE with metal particles was also studied

    Effects of Metal Oxyhydroxide Coatings on Photoanode in Quantum Dot Sensitized Solar Cells

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    Exploring facile modifications on photoanode to suppress charge recombination at photoanode/electrolyte interfaces is an efficient way to improve the performance of quantum dot sensitized solar cells (QDSCs). Herein, a series of metal oxyhydroxide gels have been overcoated on CdSeTe QD sensitized photoanodes via a hydrolysis and condensation process from the corresponding metal chloride (NbCl<sub>5</sub>, ZrOCl<sub>2</sub>, SnCl<sub>4</sub>, FeCl<sub>3</sub>, AlCl<sub>3</sub>, CoCl<sub>2</sub>, CuCl<sub>2</sub>, MgCl<sub>2</sub>, and ZnCl<sub>2</sub>) aqueous solutions, and their effects on the photovoltaic performance are systematically investigated. Photovoltaic measurement results indicate that the NbCl<sub>5</sub> and ZrOCl<sub>2</sub> modifications offer a remarkable enhancement in photovoltaic performance, especially in photovoltage. The SnCl<sub>4</sub> AlCl<sub>3</sub>, MgCl<sub>2</sub>, and ZnCl<sub>2</sub> treatments give a negligible influence, and the FeCl<sub>3</sub>, CuCl<sub>2</sub>, and CoCl<sub>2</sub> treatments present a negative effect on the performance. DFT calculations suggest that different metal oxyhydroxide coatings bring forward distinct densities of empty states at the surface of TiO<sub>2</sub>, which correspond to different charge recombination kinetics and therefore different photovoltaic performance. Electrochemical impedance spectroscopy (EIS) and open-circuit voltage decay (OCVD) measurements confirm further the suppressed charge recombination process after coating with the amorphous Zr or Nb oxyhydroxide layer. In all, an impressive power conversion efficiency (PCE) of 9.73% (<i>J</i><sub>sc</sub> = 21.04 mA/cm<sup>2</sup>, <i>V</i><sub>oc</sub> = 0.720 V, FF = 0.642) was obtained for CdSeTe-based QDSCs with ZrOCl<sub>2</sub> modification on photoanode
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