Presentation of the PyDEF post-treatment Python software to compute publishable charts for defect energy formation

First-principles calculations to identify key native point defects in Sr4Al14O25

This article reports for the first time an in-depth ab initio computational study on intrinsic point defects in Sr₄Al₁₄O₂₅ that serves as host lattice for numerous phosphors. Defect Formation Enthalpies (DFEs) and defect concentrations were computed considering the supercell approach for different oxygen atmospheres. The charge transition levels have been determined for several point defects in their thermodynamically stable state and their impact on the electronic structure of the ideal unfaulted material is discussed. Our simulations demonstrated that the formation of most of native point defects is energy intensive under oxygen-rich, -intermediate or -poor synthesis conditions, except for the oxygen vacancies under O-poor atmosphere.

In silico investigation of Cu(In,Ga)Se2-based solar cells

Photovoltaics is one of the most promising and fastest-growing renewable energy technologies. Although the price-performance ratio of solar cells has improved significantly over recent years, further systematic investigations are needed to achieve higher performance and lower cost for future solar cells. In conjunction with experiments, computer simulations are powerful tools to investigate the thermodynamics and kinetics of solar cells. Over the last few years, we have developed and employed advanced computational techniques to gain a better understanding of solar cells based on copper indium gallium selenide (Cu(In,Ga)Se2). Furthermore, we have utilized state-of-the-art data-driven science and machine learning for the development of photovoltaic materials. In this Perspective, we review our results along with a survey of the field.

DFT and hybrid-DFT calculations on the electronic properties of vanadate materials: theory meets experiments

Herein is presented a theoretical study of the electronic structure and optical properties of six vanadium oxides: Sr₂V₂O₇, Ba₂V₂O₇, Ca₂VO₄Cl, Sr₂VO₄Cl, Mg₃V₂O₈ and Zn₃V₂O₈.

Thermoelectric power factor of pure and doped ZnSb via DFT based defect calculations

The power factor of pure p-type ZnSb has been calculated via ab initio simulations assuming that the carrier concentrations are due to the doping effect of intrinsic zinc vacancies. With a vacancy concentration close to the experimental solubility limit we were able to perfectly reproduce the Power Factor measured in polycrystalline ZnSb samples. The methodology has then been successfully extended for predicting the effect of extrinsic doping elements on the thermoelectric properties of ZnSb. Germanium and tin seem to be promising p-type doping elements. In addition, we give, for the first time, an explanation of why it is difficult to synthesize polycrystalline n-type ZnSb samples. Indeed, compensative effects between intrinsic defects (zinc vacancies) and doping elements (Ga, or In) explain the existence of an optimal (and relatively high) dopant concentration necessary to convert ZnSb into an n-type semiconductor.

Optoelectronic Properties of TiS2: A Never Ended Story Tackled by Density Functional Theory and Many-Body Methods

Herein is reported a thorough computational investigation on the bulk TiS₂ material with the CdI₂ structure type and the ideal 1:2 Ti:S stoichiometry. Computations were performed using some of the most refined models, e.g., a hybrid functional together with dispersion effects (Grimme's), the GW ansatz, and the Bethe-Salpether equation for the optical properties. We showed that switching from Perdew-Berke-Enzerhof (PBE) to PBE0 leads to a gap opening. Moreover, our results demonstrate unambiguously that van der Waals interactions must be properly treated with dispersion effects in order to retrieve the experimental crystal structure and the appropriate c/ a ratio. Indeed, the calculations prove that when one uses a highly accurate computational protocol, the bulk hexagonal TiS₂ is a semiconductor with a small gap, whereas using the generalized gradient approximation (GGA) PBE functional leads to a semimetal. Furthermore, the band structure is significantly modified when dispersion parameters are taken into account. Pressure effects were also investigated, and they fully describe the previously simulated electronic transition behavior of the material, e.g., TiS₂ becomes semimetallic under strain.

Crystal Chemistry, Optical-Electronic Properties, and Electronic Structure of Cd1- xIn2+2 x/3S4 Compounds (0 ≤ x ≤ 1), Potential Buffer in CIGS-Based Thin-Film Solar Cells

CdIn₂S₄ and In₂S₃ compounds were both previously studied as buffer layers in CIGS-based thin-film solar cells, each of them exhibiting advantages and disadvantages. Thus, we naturally embarked on the study of the CdIn₂S₄-In₂S₃ system, and a series of Cd_{1- x}In_{2+2 x/3}S₄ (0 ≤ x ≤ 1) materials were prepared and characterized. Our results show that two solid solutions exist. The aliovalent substitution of cadmium(II) by indium(III) induces a structural transition at x ≈ 0.7 from cubic spinel Fd3̅ m to tetragonal spinel I4₁/ amd that is related to an ordering of cadmium vacancies. Despite this transition, the variation of optical gap is continuous and decreases from 2.34 to 2.11 eV going from CdIn₂S₄ to In₂S₃ while all compounds retain an n-type behavior. In contrast with the Al _xIn_2-xS₃ solid solution, no saturation of the gap is observed. Moreover, XPS analyses indicate a difference between surface and volume composition of the grains for Cd-poor compounds. The use of Cd_{1- x}In_{2+2 x/3}S₄ compounds could be a good alternative to CdIn₂S₄ and In₂S₃ to improve CIGS/buffer interfaces with a compromise between photovoltaic conversion efficiency and cadmium content.