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
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 Wî—¼C
bond and ligand hydrolysis. Four tungsten alkylidyne complexes, WÂ(î—¼CSiMe<sub>3</sub>)Â(CH<sub>2</sub>SiMe<sub>3</sub>)<sub>3</sub> (<b>A-1</b>), WÂ(î—¼CSiMe<sub>3</sub>)Â(CH<sub>2</sub><sup>t</sup>Bu)<sub>3</sub> (<b>B-1</b>), WÂ(î—¼C<sup>t</sup>Bu)Â(CH<sub>2</sub><sup>t</sup>Bu)<sub>3</sub> (<b>C-1</b>), and WÂ(î—¼C<sup>t</sup>Bu)Â(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%
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
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
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>–0.4BiÂ(Co<sub>0.55</sub>Ti<sub>0.45</sub>)ÂO<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