Off-stoichiometry in I-III-VI chalcopyrite absorbers: a comparative analysis of structures and stabilities.

Chalcopyrite Cu(In,Ga)Se (CIGSe) solar absorbers are renowned for delivering high solar power conversion efficiency despite containing high concentration of lattice defects amounting to copper deficiencies of several atomic percent. The unique ability to incorporate this deficiency without triggering decomposition ( "tolerance to off-stoichiometry") is viewed by many as the key feature of CIGSe. In principle, this property could benefit any solar absorber, but remarkably little attention has been paid to it so far.

Experimental and Theoretical Study of Stable and Metastable Phases in Sputtered CuInS.

The chalcopyrite Cu(In,Ga)S has gained renewed interest in recent years due to the potential application in tandem solar cells. In this contribution, a combined theoretical and experimental approach is applied to investigate stable and metastable phases forming in CuInS (CIS) thin films. Ab initio calculations are performed to obtain formation energies, X-ray diffraction (XRD) patterns, and Raman spectra of CIS polytypes and related compounds.

Chemistry of Oxygen Ionosorption on SnO Surfaces.

Ionosorbed oxygen is the key player in reactions on metal-oxide surfaces. This is particularly evident for chemiresistive gas sensors, which operate by modulating the conductivity of active materials through the formation/removal of surface O-related acceptors. Strikingly though, the exact type of species behind the sensing response remains obscure even for the most common material systems.

Alkali Dispersion in (Ag,Cu)(In,Ga)Se Thin Film Solar Cells-Insight from Theory and Experiment.

Silver alloying of Cu(In,Ga)Se absorbers for thin film photovoltaics offers improvements in open-circuit voltage, especially when combined with optimal alkali-treatments and certain Ga concentrations. The relationship between alkali distribution in the absorber and Ag alloying is investigated here, combining experimental and theoretical studies. Atom probe tomography analysis is implemented to quantify the local composition in grain interiors and at grain boundaries.

Energy, Phonon, and Dynamic Stability Criteria of Two-Dimensional Materials.

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 to examine the realizability of hypothetical 2D materials have been established in the literature yet. Because of this, and as the calculations are always performed in an artificial simulation environment, one can unintentionally study compounds that do not exist in experiments.

Suppression of surfaces states at cubic perovskite (001) surfaces by CO adsorption.

By using first-principles approach, the interaction of CO2 with (001) surfaces of six cubic ABO3 perovskites (A = Ba, Sr and B = Ti, Zr, Hf) is studied in detail. We show that CO2 adsorption results in the formation of highly stable CO3-like complexes with similar geometries for all investigated compounds. This reaction leads to the suppression of the surfaces states, opening the band gaps of the slab systems up to the corresponding bulk energy limits.

Tailoring electronic properties of multilayer phosphorene by siliconization.

Controlling the thickness dependence of electronic properties for two-dimensional (2d) materials is among the primary goals for their large-scale applications. Herein, employing a first-principles computational approach, we predict that Si interaction with multilayer phosphorene (2d-P) can result in the formation of highly stable 2d-SiP and 2d-SiP compounds with a weak interlayer interaction. Our analysis demonstrates that these systems are semiconductors with band gap energies that can be governed by varying the thicknesses and stacking arrangements.

Band gap modulation of SrTiO upon CO adsorption.

Herein, CO chemisorption on SrTiO(001) surfaces is studied using ab initio calculations to establish new chemical sensing mechanisms. It was found that CO adsorption opens the band gap of the material. However, the mechanisms are different: the CO adsorption on the TiO-terminated surface neutralizes the surface states at the valence band (VB) maximum, whereas for the SrO-terminated surface it suppresses the conduction band (CB) minimum.

Stability and electronic properties of phosphorene oxides: from 0-dimensional to amorphous 2-dimensional structures.

Combining the screening by first-principles calculations and Born-Oppenheimer molecular dynamics simulations, we fully reconsider phosphorene oxidation and the formation of low-dimensional phosphorus oxides (PO). It is found that the previously reported 2-dimensional PO (2d-PO) structures cannot provide a full understanding of 2d-PO properties. We show that the P-O interaction can result in highly stable 0d-PO and 2d-PO structures with close energetics, but a noticeable difference in band-gap energies.

Ferroelectric KNbO3 nanofibers: synthesis, characterization and their application as a humidity nanosensor.

By virtue of its non-toxicity, high T c, and non-linear optical and ferroelectric properties, one-dimensional (1D) potassium niobate (KNbO3) may enable the development of numerous nanoscale devices. Despite the progress in 1D perovskite materials, preparing high aspect ratio KNbO3 nanostructures is still a concern. This report presents the successful synthesis of ultra-long KNbO3 nanofibers using a simple sol-gel assisted far-field electrospinning process.