The electronic structure as well the optical response of kesterite and stannite structures Cu2ZnSnS4 Cu2ZnSnSe4 are analyzed by a relativistic full-potential linearized augmented plane wave method. energy dispersion conduction-band edge reveals larger effective electron mass two compounds (mc1≈0.18m0) compared with (mc1≈0.07m0). Whereas tensor is fairly isotropic, hole masses show strong anisotropy. fundamental band-gap estimated to be Eg≈1.5 eV for Eg≈1.0 Cu2ZnSnSe4. band gap results in...

The efficiency of $\mathrm{CuIn}{\mathrm{Se}}_{2}$ based solar cell devices could improve significantly if $\mathrm{CuGa}{\mathrm{Se}}_{2}$, a wider band gap chalcopyrite semiconductor, be added to the absorber layer. This is, however, limited by difficulty doping $n$-type $\mathrm{CuGa}{\mathrm{Se}}_{2}$ and, hence, in its alloys with ${\mathrm{CuInSe}}_{2}$. Indeed, wider-gap members semiconductor series are often more difficult dope than lower-gap same series. We find that chalcopyrites,...

We systematically investigate a novel two-dimensional nanomaterial, phosphorene, as an anode for Na-ion batteries. Using first-principles calculations, we determine the Na adsorption energy, specific capacity and diffusion barriers on monolayer phosphorene. examine main trends in electronic structure mechanical properties function of concentration. find favorable Na-phosphorene interaction with high theoretical storage capacity. that undergoes semiconductor-metal transition at Our results...

The optical band-gap energy of a nanostructured tungsten trioxide film is determined using the photoacoustic spectroscopy method under continuous light excitation. mechanism signal generation discussed. also computed by other methods. absorption coefficient as well three different crystal structures calculated first-principles Green’s function approach projector augmented wave method. theoretical study indicates that cubic structure shows good agreement with experimental data.

Single- or few-layer phosphorene is a novel two-dimensional direct-bandgap nanomaterial. Based on first-principles calculations, we present systematic study the binding energy, geometry, magnetic moment and electronic structure of 20 different adatoms adsorbed phosphorene. The cover wide range valences, including s p valence metals, 3d transition noble semiconductors, hydrogen oxygen. We find that produce rich diversity structural, properties. Our work demonstrates forms strong bonds with...

Abstract We summarize the progress made recently in understanding electronic structure of chalcopyrites. New insights into dispersion valence and conduction band allow conclusions on effective masses charge carriers their orientation dependence, which influences transport solar cell absorbers different orientation. Native point defects are responsible for doping thus bending cells. Results optoelectronic defect spectroscopy reviewed. also source a number metastabilities, strongly affect...

Cu 2 ZnSn(S,Se) 4 (CZTS(e)) solar cells suffer from low‐open‐circuit voltages that have been blamed on the existence of band gap fluctuations, with different possible origins. In this paper, we show both theoretical and experimental standpoints disorder Zn atoms is in all probability primary cause these fluctuations. First, quantification Cu–Zn CZTS thin films presented. The results indicate prevalent majority practical samples used for cells. Then, ab initio calculations arrangements...

First-principles modeling of grain boundaries (GB) in CuInSe2 semiconductors reveals that an energetic barrier exists for holes arriving from the interior (GI) to GB. Consequently, absence inside GB prevents electrons recombining. At same time, GI is purer polymaterials than single crystals, since impurities segregated GBs. This explains puzzle superiority polycrystalline solar cells over their crystalline counterpart. We identify a simple and universal mechanism barrier, arising reduced p-d...

A full-potential band structure calculation, within the local density approximation to functional theory, has been performed for polytypes 3C, 2H, 4H, and 6H of SiC. The calculated effective electron masses are found be in very good agreement with experimental values. electron-optical phonon coupling estimated polaron 3%–13% larger than corresponding bare masses. second lowest conduction minima also presented energy difference between two 4H–SiC is only 0.12 eV. 6H–SiC flat have a...

Photoelectron spectroscopy, optical characterization, and density functional calculations of ${\mathrm{ZnO}}_{1\ensuremath{-}x}{\mathrm{S}}_{x}$ reveal that the valence-band (VB) offset ${E}_{v}(x)$ increases strongly for small S content, whereas conduction-band edge ${E}_{c}(x)$ only weakly. This is explained as formation local ZnS-like bonds in ZnO host, which mainly affects VB thereby narrows energy gap: ${E}_{g}(x=0.28)\ensuremath{\approx}{E}_{g}(\mathrm{ZnO})\ensuremath{-}0.6\text{...

$\mathrm{O}\phantom{\rule{0.3em}{0ex}}1s$ absorption spectroscopy (XAS) and $\mathrm{O}\phantom{\rule{0.3em}{0ex}}K\ensuremath{\alpha}$ emission (XES) were performed to study the electronic structure of nanostructured ZnO. The band gap is determined by combined absorption-emission spectrum. Resonantly excited XES spectra showing an energy dependence in spectral shape reveal selected excitations different $\mathrm{Zn}\phantom{\rule{0.3em}{0ex}}3d$, $4s$, $4p$ states hybridization with...

Based on ab initio calculations of both the ABC- and AB-stacked graphites, interlayer potentials (i.e., graphene-graphene interaction) are obtained as a function spacing using modified Möbius inversion method, used to calculate basic physical properties graphite. Excellent consistency is observed between calculated experimental phonon dispersions graphite, showing validity potentials. More importantly, layer-related for nonideal structures (e.g., exfoliation energy, cleave stacking fault...

We report on a detailed analysis of the transport properties and superconducting critical temperatures boron-doped diamond films grown along {100} direction. The system presents metal-insulator transition (MIT) for boron concentration $({n}_{B})$ order ${n}_{c}\ensuremath{\sim}4.5\ifmmode\times\else\texttimes\fi{}{10}^{20}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$, in excellent agreement with numerical calculations. temperature dependence conductivity Hall effect can be well...

SnO2 and TiO2 polymorphs (rutile anatase) are oxides with similar crystal structures, comparable bond lengths, electronic band-gap energies, but different optical properties. In this work, we have studied the origin of these differences from band-edge structures electron-phonon coupling. The dielectric functions, effective masses were calculated by means a first-principles approach exchange-correlation described hybrid functional. phonon frequencies using finite displacement method...

Abstract Lithium‐ion batteries (LIBs) are primary energy storage devices to power consumer electronics and electric vehicles, but their capacity is dramatically decreased at ultrahigh charging/discharging rates. This mainly originates from a high Li‐ion/electron transport barrier within traditional electrode, resulting in reaction polarization issues. To address this limitation, functionally layer‐graded electrode was designed fabricated decrease the charge carrier electrode. As...

First-principles calculations have become a powerful tool to exclude the Edisonian approach in search of novel two-dimensional (2D) materials. However, no universal first-principles criteria examine realizability hypothetical 2D materials been established literature yet. Because this, and as are always performed an artificial simulation environment, one can unintentionally study compounds that do not exist experiments. Although investigations physics chemistry unrealizable provide some...

Ionosorbed oxygen is the key player in reactions on metal-oxide surfaces. This particularly evident for chemiresistive gas sensors, which operate by modulating conductivity of active materials through formation/removal surface O-related acceptors. Strikingly though, exact type species behind sensing response remains obscure even most common material systems. The paradigm ab initio modeling to date has been centered around charge-neutral species, ignoring fact that molecular adsorbates are...

Electron and hole effective masses for the polytypes 3C-, 2H-, 4H-, 6H-SiC have been calculated within framework of local density approximation including spin-orbit interaction. To establish accuracy approximations, both electrons holes in Si also calculated. It is found that agreement with well-established experimental values excellent SiC. The valence bands parametrized terms k\ensuremath{\cdot}p parameters. \textcopyright{} 1996 American Physical Society.

First-principles calculations of model grain boundaries (GBs) in CuInSe2 and CaGaSe2 show that cation-terminated GBs have a valence-band offset with respect to the interior (GI). This repels holes from GBs, thus depriving electrons there recombination at GB defects. Anion-terminated no such valence offset. CuGaSe2 has, addition, conduction-band GB/GI interface, attracting GBs. These features explain how polycrystalline chalcopyrite solar cells could outperform their crystalline counterparts.

In spite of their relatively high lattice thermal conductivity ${\ensuremath{\kappa}}_{\ensuremath{\ell}}$, the $X\mathrm{NiSn}$ ($X=\text{Ti}$, Zr, or Hf) half-Heusler compounds are good thermoelectric materials. Previous studies have shown that ${\ensuremath{\kappa}}_{\ensuremath{\ell}}$ can be reduced by sublattice alloying on $X$ site. To cast light how alloy composition affects we study this system using phonon Boltzmann-transport equation within relaxation time approximation in...