Many metal halides that contain cations with the ns2 electronic configuration have recently been discovered as high-performance optoelectronic materials. In particular, solar cells based on lead ...halide perovskites have shown great promise as evidenced by the rapid increase of the power conversion efficiency. In this paper, we show density functional theory calculations of electronic structure and dielectric and defect properties of CsGeI3 (a lead-free halide perovskite material). The potential of CsGeI3 as a solar cell material is assessed based on its intrinsic properties. We find anomalously large Born effective charges and a large static dielectric constant dominated by lattice polarization, which should reduce carrier scattering, trapping, and recombination by screening charged defects and impurities. Defect calculations show that CsGeI3 is a p-type semiconductor and its hole density can be modified by varying the chemical potentials of the constituent elements. Despite the reduction of long-range Coulomb attraction by strong screening, the iodine vacancy in CsGeI3 is found to be a deep electron trap due to the short-range potential, i.e., strong Ge-Ge covalent bonding, which should limit electron transport efficiency in p-type CsGeI3. This is in contrast to the shallow iodine vacancies found in several Pb and Sn halide perovskites (e.g., CH3NH3PbI3, CH3NH3SnI3, and CsSnI3). The low-hole-density CsGeI3 may be a useful solar absorber material but the presence of the low-energy deep iodine vacancy may significantly reduce the open circuit voltage of the solar cell. On the other hand, CsGeI3 may be used as an efficient hole transport material in solar cells due to its small hole effective mass, the absence of low-energy deep hole traps, and the favorable band offset with solar absorber materials such as dye molecules and CH3NH3PbI3.
CH3NH3PbI3-based solar cells have shown remarkable progress in recent years but have also suffered from structural, electrical, and chemical instabilities related to the soft lattices and the ...chemistry of these halides. One of the instabilities is ion migration, which may cause current–voltage hysteresis in CH3NH3PbI3 solar cells. Significant ion diffusion and ionic conductivity in CH3NH3PbI3 have been reported; their nature, however, remain controversial. In the literature, the use of different experimental techniques leads to the observation of different diffusing ions (either iodine or CH3NH3 ion); the calculated diffusion barriers for native defects scatter in a wide range; the calculated defect formation energies also differ qualitatively. These controversies hinder the understanding and the control of the ion migration in CH3NH3PbI3. In this paper, we show density functional theory calculations of both the diffusion barriers and the formation energies for native defects (V I +, MA i +, V MA –, and I i –) and the Au impurity in CH3NH3PbI3. V I + is found to be the dominant diffusing defect due to its low formation energy and the low diffusion barrier. I i – and MA i + also have low diffusion barriers but their formation energies are relatively high. The hopping rate of V I + is further calculated taking into account the contribution of the vibrational entropy, confirming V I + as a fast diffuser. We discuss approaches for managing defect population and migration and suggest that chemically modifying surfaces, interfaces, and grain boundaries may be effective in controlling the population of the iodine vacancy and the device polarization. We further show that the formation energy and the diffusion barrier of Au interstitial in CH3NH3PbI3 are both low. It is thus possible that Au can diffuse into CH3NH3PbI3 under bias in devices (e.g., solar cell, photodetector) with Au/CH3NH3PbI3 interfaces and modify the electronic properties of CH3NH3PbI3.
The development of noble-metal-free heterogeneous catalysts that can realize the aerobic oxidation of C-H bonds at low temperature is a profound challenge in the catalysis community. Here we report ...the synthesis of a mesoporous Mn0.5Ce0.5Ox solid solution that is highly active for the selective oxidation of hydrocarbons under mild conditions (100-120 °C). Notably, the catalytic performance achieved in the oxidation of cyclohexane to cyclohexanone/cyclohexanol (100 °C, conversion: 17.7%) is superior to those by the state-of-art commercial catalysts (140-160 °C, conversion: 3-5%). The high activity can be attributed to the formation of a Mn0.5Ce0.5Ox solid solution with an ultrahigh manganese doping concentration in the CeO2 cubic fluorite lattice, leading to maximum active surface oxygens for the activation of C-H bonds and highly reducible Mn(4+) ions for the rapid migration of oxygen vacancies from the bulk to the surface.
Zero-dimensional (0D) halides perovskites, in which anionic metal-halide octahedra (MX
6
)
4−
are separated by organic or inorganic countercations, have recently shown promise as excellent ...luminescent materials. However, the origin of the photoluminescence (PL) and, in particular, the different photophysical properties in hybrid organic–inorganic and all inorganic halides are still poorly understood. In this work, first-principles calculations were performed to study the excitons and intrinsic defects in 0D hybrid organic–inorganic halides (C
4
N
2
H
14
X)
4
SnX
6
(X = Br, I), which exhibit a high photoluminescence quantum efficiency (PLQE) at room temperature (RT), and also in the 0D inorganic halide Cs
4
PbBr
6
, which suffers from strong thermal quenching when
T
> 100 K. We show that the excitons in all three 0D halides are strongly bound and cannot be detrapped or dissociated at RT, which leads to immobile excitons in (C
4
N
2
H
14
X)
4
SnX
6
. However, the excitons in Cs
4
PbBr
6
can still migrate by tunneling, enabled by the resonant transfer of excitation energy (Dexter energy transfer). The exciton migration in Cs
4
PbBr
6
leads to a higher probability of trapping and nonradiative recombination at the intrinsic defects. We show that a large Stokes shift and the negligible electronic coupling between luminescent centers are important for suppressing exciton migration; thereby, enhancing the photoluminescence quantum efficiency. Our results also suggest that the frequently observed bright green emission in Cs
4
PbBr
6
is not due to the exciton or defect-induced emission in Cs
4
PbBr
6
but rather the result of exciton emission from CsPbBr
3
inclusions trapped in Cs
4
PbBr
6
.
Recently, interest in developing efficient, low-cost, nontoxic, and stable metal halide emitters that can be incorporated into solid-state lighting technologies has taken hold. Here we report ...nontoxic, stable, and highly efficient blue-light-emitting Cs3Cu2Br5–xIx (0 ≤ x ≤ 5). Room-temperature photoluminescence measurements show bright blue emission in the 456 to 443 nm range with near-unity quantum yield for Cs3Cu2I5. Here, density functional theory calculations and power-dependent PL measurements suggest that the emission results from self-trapped excitons induced by strong charge localization within the zero-dimensional cluster structure of Cs3Cu2Br5–xIx.
China’s steel sector is the largest in the world and has been a major driving force behind China’s high rate of economic growth. This sector, however, is also a major consumer of energy and, in ...particular, coal. As a result, the iron and steel sector in China is a major contributor to greenhouse gas emissions and other pollutants. In this article we examine the potential for inter-factor substitution between capital, energy and labor in the Chinese steel sector and find that capital and energy and energy and labor are substitutes. This result suggests that removal of price ceilings on energy would tend to reduce energy use and increase capital intensiveness. While the potential for substitution between energy and labor is less than that between energy and capital, the elasticity of substitution between energy and labor is high compared with previous findings for other countries. This fact suggests that there may be potential for substituting labor for energy, given China’s abundance of labor.
Five new organotin(IV) complexes, Me
2
SnL
2
(
1
),
n
–Bu
2
SnL
2
(
2
),
t
–Bu
2
SnL
2
(
3
), Ph
2
SnL
2
(
4
), and Ph
3
SnL (
5
), have been designed and synthesized by the reactions of the ...deprotonated 1-adamantanethiol ligand (L = C
10
H
15
S) with the corresponding R
2
SnCl
2
(R = Me,
n
–Bu,
t
–Bu, Ph) and Ph
3
SnCl. The complexes were characterized by elemental analysis, FT-IR, NMR spectroscopy, and X-ray crystallography. Meanwhile, optimized geometrical parameters, harmonic vibrational frequencies, and frontier molecular orbitals were calculated. The in vitro cytotoxicities of the complexes were evaluated with HeLa and HepG-2. Furthermore, the antifungal activity of the newly synthesized complexes has been evaluated, and the SEM and TEM images were prepared from
Alternaria kikuchiana Tanaka
to analyze the macroscopic action of the drug on the fungus. As a result, complex
5
has good antifungal activity and cytotoxicity.
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