4 research outputs found

    Density Functional Theory Study of the Reaction between d<sup>0</sup> Tungsten Alkylidyne Complexes and H<sub>2</sub>O: Addition versus Hydrolysis

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    The reactions of early-transition-metal complexes with H<sub>2</sub>O have been investigated. An understanding of these elementary steps promotes the design of precursors for the preparation of metal oxide materials or supported heterogeneous catalysts. Density functional theory (DFT) calculations have been conducted to investigate two elementary steps of the reactions between tungsten alkylidyne complexes and H<sub>2</sub>O, i.e., the addition of H<sub>2</sub>O to the WC bond and ligand hydrolysis. Four tungsten alkylidyne complexes, W­(CSiMe<sub>3</sub>)­(CH<sub>2</sub>SiMe<sub>3</sub>)<sub>3</sub> (<b>A-1</b>), W­(CSiMe<sub>3</sub>)­(CH<sub>2</sub><sup>t</sup>Bu)<sub>3</sub> (<b>B-1</b>), W­(C<sup>t</sup>Bu)­(CH<sub>2</sub><sup>t</sup>Bu)<sub>3</sub> (<b>C-1</b>), and W­(C<sup>t</sup>Bu)­(O<sup>t</sup>Bu)<sub>3</sub> (<b>D-1</b>), have been compared. The DFT studies provide an energy profile of the two competing pathways. An additional H<sub>2</sub>O molecule can serve as a proton shuttle, accelerating the H<sub>2</sub>O addition reaction. The effect of atoms at the α and β positions has also been examined. Because the lone-pair electrons of an O atom at the α position can interact with the orbital of the proton, the barrier of the ligand-hydrolysis reaction for <b>D-1</b> is dramatically reduced. Both the electronic and steric effects of the silyl group at the β position lower the barriers of both the H<sub>2</sub>O addition and ligand-hydrolysis reactions. These new mechanistic findings may lead to the further development of metal complex precursors

    Original Core–Shell Structure of Cubic CsPbBr<sub>3</sub>@Amorphous CsPbBr<sub><i>x</i></sub> Perovskite Quantum Dots with a High Blue Photoluminescence Quantum Yield of over 80%

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    All-inorganic perovskite cesium lead halide quantum dots (QDs) have been widely investigated as promising materials for optoelectronic application because of their outstanding photoluminescence (PL) properties and benefits from quantum effects. Although QDs with full-spectra visible emission have been synthesized for years, the PL quantum yield (PLQY) of pure blue-emitting QDs still stays at a low level, in contrast to their green- or red-emitting counterparts. Herein, we obtained core–shell structured cubic CsPbBr<sub>3</sub>@amorphous CsPbBr<sub><i>x</i></sub> (A-CsPbBr<sub><i>x</i></sub>) perovskite QDs via a facile hot injection method and centrifugation process. The core–shell structure QDs showed a record blue emission PLQY of 84%, which is much higher than that of blue-emitting cubic CsPbBr<sub>3</sub> QDs and CsPbBr<sub><i>x</i></sub>Cl<sub>3–<i>x</i></sub> QDs. Furthermore, a blue-emitting QDs-assisted LED with bright pure blue emission was prepared and illustrated the core–shell QDs’ promising prospect in optoelectrical application

    High-Voltage-Efficiency Inorganic Perovskite Solar Cells in a Wide Solution-Processing Window

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    Inorganic halide perovskites exhibit significant photovoltaic performance due to their structural stability and high open-circuit voltage (<i>V</i><sub>oc</sub>). Herein, a general strategy of solution engineering has been implemented to enable a wide solution-processing window for high <i>V</i><sub>oc</sub> (∼1.3 V) and power conversion efficiency (PCE, ∼12.5%). We introduce a nontoxic solvent of dimethyl sulfoxide (DMSO) and an assisted heating process in the fabrication of CsPbI<sub>2</sub>Br (CPI2) to control the improved crystallization. A wide solution-processing window including a wide range of solvent components and solute concentrations has been realized. The CPI2-based inorganic perovskite solar cells (IPSCs) exhibit a high PCE up to 12.52%. More importantly, these devices demonstrate a remarkable <i>V</i><sub>oc</sub> of 1.315 V. The performance has possessed such a region with high <i>V</i><sub>oc</sub> and PCE in all Cs-based IPSCs, unveiling wide solution-processing windows with enhanced solution processability facilitating potential industrial application especially for tandem solar cells

    Zero Thermal Expansion and Semiconducting Properties in PbTiO<sub>3</sub>–Bi(Co, Ti)O<sub>3</sub> Ferroelectric Solid Solutions

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    Zero thermal expansion (ZTE) behavior is rare but important for both fundamental studies and practical applications of functional materials. Until now, most available ZTE materials are either electrical insulating oxides or conductive metallic compounds. Very few ZTE materials exhibit the semiconductor feature. Here we report a ZTE in a semiconducting ferroelectric of 0.6PbTiO<sub>3</sub>–0.4Bi­(Co<sub>0.55</sub>Ti<sub>0.45</sub>)­O<sub>3−δ</sub>. Its unit cell volume exhibits a negligible change over a broad temperature range from room temperature to 500 °C. The ZTE is supposed to be correlated with the spontaneous volume ferroelectronstriction. Intriguingly, the present ZTE material also exhibits the semiconducting characteristic accompanied by negative temperature coefficient of resistance. The mechanism of electric conduction is attributed to the electronic hopping from one ion (Ti<sup>3+</sup>) to another (Ti<sup>4+</sup>). The semiconductor nature has also been confirmed by the noticeable visible-light absorption with the relatively lower band gap (<i>E</i><sub>g</sub>) value of 1.5 eV, while the ferroelectric property can be well-maintained with large polarization. The first-principles calculations reveal that the drastically narrowed <i>E</i><sub>g</sub> is related to the Co–Ti substitution. The present multifunctional material containing ZTE, semiconducting, and ferroelectric properties is suggested to enable new applications such as the substrate for solar conversion devices
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