Electronic, optical, and thermoelectric characteristics of (Ae)xFBiS2 (Ae=Sr, Ba, and x=1.7) layered materials useful in optical modulator devices.

The recent discovery of superconductivity behavior in the mother BiS2-layered compounds has captivated the attention of several physicists. The crystal structure of superconductors with alternate layers of BiS2 is homologous to that of cuprates and Fe-based superconductors. The full-potential linearized augmented plane-wave (FP-LAPW) technique was utilized to investigate the electronic structures and density of states in the vicinity of the Fermi energy of SrFBiS2 and BaFBiS2 compounds under the electron carriers doping. The introduction of electron doping (carries doping) reveals that the host compounds SrFBiS2 and BaFBiS2 exhibit features indicative of superconductivity. This carrier doping of SrFBiS2 and BaFBiS2 compounds (electron-doped) has a significant impact on the lowest conduction states near the Fermi level for the emergence of the superconducting aspect. The electron doping modifies and induces changes in the electronic structures with superconducting behavior in (Ae)1.7FBiS2(Ae=Sr,Ba) compounds. A Fermi surface nesting occurred under the modification of electrons (carriers) doping in the host compounds SrFBiS2 and BaFBiS2. Furthermore, the optical characteristics of the carrier-doped SrFBiS2 and BaFBiS2 compounds are simulated. Due to the anisotropic behavior, the optical properties of these materials based on BiS2 demonstrate a pronounced polarization dependency. The starting point at zero photon energy in the infrared region is elucidated by considering the Drude features in the optical conductivity spectra of SrFBiS2 and BaFBiS2 compounds, when the electron carriers doping is applied. It was clearly noticed that the spin-orbit coupling (SOC) influences the electronic band structures, density of states, Femi surface, and optical features because of the heavy Bismuth atom, which may disclose fascinating aspects. Further, we conducted simulations to assess the thermoelectric properties of these mother compounds. The two BiS2-layered compounds could be suitable for practical thermoelectric purposes and are highlighted through assessment of electrical conductivity, thermal conductivity, Seebeck coefficient, and power factor. As a result, we propose that the mechanisms of superconducting behavior in BiS2 family may pave new avenues for investigating the field of unconventional superconductivity. It may also provide new insights into the origin of high-Tc superconductivity nature.

Lowering Cost Approach for CIGS-Based Solar Cell Through Optimizing Band Gap Profile and Doping of Stacked Active Layers-SCAPS Modeling.

In this research article, we carry out investigation on compensating the efficiency loss in thin-film CIGS photovoltaic (PV) cell due to absorber coat depth reduction. We demonstrate that the efficiency loss is mainly caused by the disruption of the charge-carrier transport. We propose an architecture engineered with a stepped band gap profile for improving the efficiency of charge-carrier transport and collection. By modifying the gallium content, we tuned the band gap profile of the active layer of a reference experimental cell from which we previously collected all parameters. Using the simulator environment SCAPS-1D, we modeled a three-steps stacking profile of active layer with different gallium contents from one layer to another. Based on the results obtained, the band gap configuration herein proposed appears to be a prospective strategy for high-performance ultrathin Cu(In,Ga)Se2-based PV cell architecture engineering. By combining this approach with the optimization of the active layer doping, we enhanced the yields of the reference structure from 18.93% for a 2 µm active layer to 23.36% for only 0.5 µm thickness of active layer, that is, an enhancement of 4.4%. The fill factor increased from 73.24 to 81.73%, that is, an additional stability indicator value of 8.5%. The good values of the obtained efficiency and the improvement of the fill factor value are relevant indicators of a stable device. Active layer stacking combined with a stepped band gap profile and doping level optimization is definitely providing new perspectives in thin-film CIGS high-performance PV cell achievement.

DFT study of new organic materials based on PEDOT and 4-[2-(2-N, N-dihydroxy amino thiophene) vinyl] benzenamine.

In the present study, we theoretically determine the optoelectronic, electronic, nonlinear optical (NLO) and thermodynamic properties of new materials from the conjugated organic polymer poly (3,4-ethylenedioxythiophene) (PEDOT) doped with halogens (fluorine and chlorine), combined with the organic semiconductor 4-[2-(2-N, N-dihydroxy amino thiophene) vinyl] benzenamine (DATVB). The molecular geometry of the ground state, the optoelectronics and electronic parameters have been calculated by combining the 6-311++G (d, p) basis set with various functionals of the density functional theory (DFT). The functionals B3LYP and CAM-B3LYP have been used for NLO parameters. The energy gaps obtained for all the compounds are less than 3.0 eV. These results clearly show that PEDOT and its derivatives can be considered as good semiconductors. They can be tested for use in the manufacture of organic solar cells (OSC) and organic light-emitting diodes (OLED). The first order hyperpolarizabilities of these PEDOT hybrid compounds are much higher than those of the reference compound for NLO applications, namely para-nitroaniline (p-NA), which opens up a new field of application for PEDOT in NLO devices. The thermodynamic parameters such as the zero-point vibrational energy (ZPVE), the enthalpy (H), the heat capacity at constant volume (cv), the entropy (S) and the free energy (G) have been calculated and are reported herein.

DFT study of the influence of impurities on the structural, electronic, optoelectronic, and nonlinear optical properties of graphene nanosheet functionalized by the carboxyl group -COOH.

In this work, we propose a modified model of graphene oxide nanosheet (GON), based on the Lerf-Klinowski model, through which we attach a carboxyl group (GON-COOH) to the non-equivalent C atom of coronene-based graphene oxide with formation of sp3-like orbital bond. Beryllium, boron, nitrogen, oxygen, and fluorine atoms are integrated into the GON at identical sites in order to study their impact on the physical and chemical properties of GON. Our aim is to propose new efficient materials for applications in optoelectronics and nonlinear optics (NLO). Chemical reactivity and structural, optical, and nonlinear optical properties of GON and its derivatives GON-X (X: Be, B, N, O, and F atoms) were investigated by using the density functional theory (DFT) at the B3LYP-D3/6-31+G(d,p) level of theory. According to the results obtained, the binding energy per atom of GON compound decreases slightly with addition of atoms of the second period elements of the periodic table. The GON-F compound exhibits the smallest value of gap energy compared to other studied compounds and can then be considered a proficient candidate for photovoltaic applications. In regard to NLO properties, we found that the studied models of GON compound theoretically exhibit a larger value of the first static hyperpolarizability than urea, the reference compound for NLO properties.