The quasiparticle (QP) band structures of both strainless and strained monolayer MoS2 are investigated using more accurate many body perturbation GW theory and maximally localized Wannier functions (MLWFs) approach. By solving the Bethe-Salpeter equation (BSE) including excitonic effects on top of the partially self-consistent GW0 (scGW0) calculation, the predicted optical gap magnitude is in a good agreement with available experimental data. With increasing strain, the exciton binding energy is nearly unchanged, while optical gap is reduced significantly. The scGW0 and BSE calculations are also performed on monolayer WS2, similar characteristics are predicted and WS2 possesses the lightest effective mass at the same strain among monolayers Mo(S,Se) and W(S,Se). Our results also show that the electron effective mass decreases as the tensile strain increases, resulting in an enhanced carrier mobility. The present calculation results suggest a viable route to tune the electronic properties of monolayer transition-metal dichalcogenides (TMDs) using strain engineering for potential applications in high performance electronic devices.

The synthesis and characterization is reported of (C NH ) SnBr , a novel organic metal halide hybrid with a zero-dimensional (0D) structure, in which individual seesaw-shaped tin (II) bromide anions (SnBr ) are co-crystallized with 1-butyl-1-methylpyrrolidinium cations (C NH ). Upon photoexcitation, the bulk crystals exhibit a highly efficient broadband deep-red emission peaked at 695 nm, with a large Stokes shift of 332 nm and a high quantum efficiency of around 46 %. The unique photophysical properties of this hybrid material are attributed to two major factors: 1) the 0D structure allowing the bulk crystals to exhibit the intrinsic properties of individual SnBr species, and 2) the seesaw structure enabling a pronounced excited state structural deformation as confirmed by density functional theory (DFT) calculations.

The electronic and optical properties of bulk and monolayer PdSe2 are investigated using first-principles calculations. Using the modified Becke-Johnson potential, we find semiconductor behavior for both bulk and monolayer PdSe2 with indirect gap values of 0.03 eV for bulk and 1.43 eV for monolayer, respectively. Our sheet optical conductivity results support this observation and show similar anisotropic feature in the 2D plane. We further study the thermoelectric properties of the 2D PdSe2 using Blotzmann transport model and find interestingly high Seebeck coefficients (>200 μV/K) for both p- and n-type up to high doping level (∼2 × 1013 cm−2) with an anisotropic character in an electrical conductivity suggesting better thermoelectric performance along y direction in the plane.

Zero-dimensional (0D) halides perovskites, in which anionic metal-halide octahedra (MX6)4− are separated by organic or inorganic countercations, have recently shown promise as excellent luminescent materials.

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–x I x (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. 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–x I x .

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 Mn4+ ions for the rapid migration of oxygen vacancies from the bulk to the surface.

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.

CsGeI3 may be used as an efficient hole transport material in solar cells although it may not be an excellent solar absorber material due to the deep electron traps induced by iodine vacancies.