0000000000194632
AUTHOR
Guido Roma
First principles defect energetics for simulations of silicon carbide under irradiation: Kinetic mechanisms of silicon di-interstitials
Understanding the modification of the properties of silicon carbide under irradiation from the very fundamental point of view of atomic bonds and electronic structure can become possible in the next few years, thanks to the effort made in the last two decades to understand point defects from first principles calculations, but also thanks to the coupling of these results with simulation tools designed to describe larger spatial (and temporal) scales. We discuss some of the missing tiles that would allow to advance in this direction, in particular the incomplete data on defect clusters, and we present some first principles results for small silicon aggregates. We examine the stability, migrat…
Theoretical Study on the Diffusion Mechanism of Cd in the Cu-Poor Phase of CuInSe2 Solar Cell Material
We have employed first-principles static and molecular dynamics (MD) calculations with semilocal and screened-exchange hybrid density functionals to study the diffusion of Cd in bulk CuIn5Se8, a copper-poor ordered vacancy compound of CuInSe2. The diffusion mechanism and the underlying kinetics/energetics were investigated by combining ab initio metadynamics simulations and nudged elastic band (NEB) calculations. We found that the migration of Cd occurs via a kick-out of Cu atoms, assisted by the pristine vacancies that are constitutive of this compound, and follows a double-hump energy profile. The rate-limiting step has a barrier of about 1 eV at 0 K but reduces to 0.3 eV at 850 K, pointi…
First-principles investigation of the bulk and low-index surfaces ofMoSe2
In the framework of density functional theory, the geometry, electronic structure, and magnetic properties of the bulk and low index surfaces of $\mathrm{Mo}{\mathrm{Se}}_{2}$ have been studied. We have carried out calculations with various exchange-correlation functionals to select one which is able to describe the van der Waals (vdW) interactions and gives the best geometry compared with experiments. The inclusion of the vdW forces, however, does not guarantee a reliable description for the geometry of this compound: some vdW functionals strongly overestimate the interlayer distance, similar to GGA functionals. Our investigation shows that the recently introduced optB86b-vdW functional yi…
Selenium adsorption on Mo(110): A first-principles investigation
Selenium adsorption on molybdenum surfaces is a relevant process in the production of thin-film solar cells, in particular as far as the formation of the layered compound MoSe${}_{2}$ is concerned. In this paper we investigate the energetics of Se adsorption on the (110) surface of molybdenum using first-principles calculations in the two limiting cases of low and high coverage, and we establish a comparison with the more extensively investigated case of sulfur adsorption at submonolayer coverage. The studied system provides the opportunity for testing the most crucial approximations, namely, the choice of the exchange-correlation functional and the pseudopotential generation. We find that …
Hybrid-Functional Calculations on the Incorporation of Na and K Impurities into the CuInSe 2 and CuIn 5 Se 8 Solar-Cell Materials
International audience; We have studied the energetics, atomic, and electronic structure of Na and K point defects, as well as the (Na-Na), (K-K), and (Na-K) dumbbells in CuInSe2 and CuIn5Se8 solar cell materials by hybrid functional calculations. We found that although Na and K behaves somewhat similar; there is a qualitative difference between the inclusion of Na and K impurities. Namely, Na will be mostly incorporated into CuInSe2 and CuIn5Se8 either as an interstitial defect coordinated by cations, or two Na impurities will form (Na-Na) dumbbells in the Cu sublattice. In contrast to Na, K impurities are less likely to form interstitial defects. Instead, it is more preferable to accommod…
Reducing the Schottky barrier height at the MoSe2/Mo(110) interface in thin-film solar cells: Insights from first-principles calculations
Abstract We report on first-principles calculations of the properties of the MoSe2/Mo(110) interface. Due to mismatch between the lattice parameters of the two structures, different patterns can form at the interface. We have studied the formation energy and the band alignment of six patterns for the MoSe2 (0001)/Mo(110) interface and one pattern for the MoSe2 (11 2 0)/Mo(110) interface. The MoSe2 (11 2 0)/Mo(110) interface is more stable than the MoSe 2 (0001)/Mo(110) interface and in contrast to MoSe2 (0001)/Mo(110), no Schottky barrier forms at MoSe2 (11 2 0)/Mo(110). Doping with Na modifies the band alignment at the interfaces. The Schottky barrier height decreases, provided that a Na a…
Theoretical study of Zn and Cd interstitials and substitutional interstitials in CuInSe2 via hybrid functional calculations
We have investigated the formation of Zn and Cd interstitials in the CuInSe2 solar cell material via density-functional-theory (DFT) calculations by employing the HSE06 hybrid functional. The computed formation energies for Zn interstitials were in the range of 2.09-2.68 e V, and in the range of 2.04-2.25 eV for substitutional interstitials. In constrast, the formation energies of Cd interstitials and substitutional interstitials were between 1.85-2.75 eV and 2.41-2.64 eV, respectively. Thus, these results indicate, that Cd interstitials are more likely to be formed than Zn interstitials, and that in case of Zn inclusion into CuInSe2 Zn atoms will prefer to adopt substitutional interstitial…