High efficiency of two solar cells CIGS/CIS stacked mechanically

In our work, we have simulated and optimized solar cells based on the mechanically stacked system using the Analysis of Microelectronic and Photonic Structures (AMPS-1D) simulator in respect to overall performance. The structures of solar cells are based on the top cell Copper- Indium-Gallium- diselenide, CuIn1-xGaxSe2, referred to as CIGS, and the bottom cell Copper- Indium-Gallium, CIS. We have simulated each cell individually and extrapolated their optimal parameters (thickness, concentration of absorber). In the case of tandem, we calculated the efficiency of each cell optimized by separation of the solar spectrum in bands where the cell is sensible for the absorption. The current-matching limitation imposed by series connection reduces efficiency relative to independently-connected cells

Investigation Of Nanoscale Dielectric Polarization And Refractive Indices Of BaTiO3 Surfaces And Ultrathin Films

The surface and interface effects on the dielectric polarization and refractive indices of BaTiO3 single crystals and BaTiO3 ultrathin films on SrTiO3 single crystal substrates are investigated theoretically by using a microscopic model based on the orbital approximation in correlation with the dipole-dipole interaction. The spontaneous polarization of BaTiO3 single crystals is drastically reduced near the c-surface. For BaTiO3/SrTiO3 films, the spontaneous polarization is reduced in the film as its thickness decreases. However, an electronic polarization appears within the SrTiO3 substrate in the neighborhood of the interface. This polarization, which vanishes far away from the interface into the SrTiO3 bulk, is induced by the polarization of the BaTiO3 film. Furthermore, we find the refractive index either for BaTiO3 single crystals or for BaTiO3 films and SrTiO3 substrates to be strongly reduced for light polarized perpendicular to the surface.The surface and interface effects on the dielectric polarization and refractive indices of BaTiO3 single crystals and BaTiO3 ultrathin films on SrTiO3 single crystal substrates are investigated theoretically by using a microscopic model based on the orbital approximation in correlation with the dipole-dipole interaction. The spontaneous polarization of BaTiO3 single crystals is drastically reduced near the c-surface. For BaTiO3/SrTiO3 films, the spontaneous polarization is reduced in the film as its thickness decreases. However, an electronic polarization appears within the SrTiO3 substrate in the neighborhood of the interface. This polarization, which vanishes far away from the interface into the SrTiO3 bulk, is induced by the polarization of the BaTiO3 film. Furthermore, we find the refractive index either for BaTiO3 single crystals or for BaTiO3 films and SrTiO3 substrates to be strongly reduced for light polarized perpendicular to the surface

Modelling and Optimization of GaAs used in mechanically stacked solar cells

Different approaches have been made in order to reach higher efficiencies. Concepts for multilayer solar cells have been developed. This can be realised if multiple individual single junction solar cells with different, suitably chosen band gaps are connected in series in multi-junction solar cells. In our work, we have simulated and optimized solar cells based on the system mechanically stacked using computer modelling and predict their maximum performance. The structures of solar cells are based on the single junction Si, Ge and GaAs cells. We have simulated each cell individually and extracted their optimal parameters (thickness, concentration, the recombination velocity…..), also, we calculated the efficiency of each cells optimized by separation of the solar spectrum in bands where the cell is sensible for the absorption. The optimal values of physical parameters giving the best current of short-circuit and voltages of open circuit as well high conversion efficiency have obtained for the two solar materials and tandem.Different approaches have been made in order to reach higher efficiencies. Concepts for multilayer solar cells have been developed. This can be realised if multiple individual single junction solar cells with different, suitably chosen band gaps are connected in series in multi-junction solar cells. In our work, we have simulated and optimized solar cells based on the system mechanically stacked using computer modelling and predict their maximum performance. The structures of solar cells are based on the single junction Si, Ge and GaAs cells. We have simulated each cell individually and extracted their optimal parameters (thickness, concentration, the recombination velocity…..), also, we calculated the efficiency of each cells optimized by separation of the solar spectrum in bands where the cell is sensible for the absorption. The optimal values of physical parameters giving the best current of short-circuit and voltages of open circuit as well high conversion efficiency have obtained for the two solar materials and tandem

DYNAMIC DISORDER AT INTERMEDIATE TEMPERATURE AND ITS EFFECT ON THE MAGNETIC PROPERTIES OF THE ORGANIC SUPERCONDUCTOR κ-(BEDTTTF)2Cu[N(CN)2]Br

The k-(BEDT-TTF)X superconducting salts, [where BEDT-TTF is bis(ethylenedithio)-tetrathiafulvalene, abbreviated as ET, and X is a monovalent anion like Cu[N(CN) ]Br 2 , and for either Cu[N(CN) ]Cl 2 or ( )2 Cu NCN and so on], exhibit interestinmagnetic and superconducting phase transitions [1]. They are quasi-two-dimensional and the interplane coupling is very weak. The basic structural unit is a dimer consisting of two BEDTTTF molecules stacked on top of one another. This layered structure leads to highly anisotropic electronic properties. These organic superconductors have similar characteristic superconducting properties including the intrinsic Josephson Effect and the mixed-state properties. This similarity suggests the existence of the vortex phase transition in the organic layered superconductors as observed in HTSC. Because the temperature scale is much lower in organic materials, the thermal fluctuation is expected to be small compared to HTSC. Thus, the comparison between the high-Tc and organic superconductors can give important clues as to the nature of vortex phase transitions. Besides these anomalies around 50 K, unusual time dependencies in magnetic and transport properties have been reported for both deuterated and hydrogenated k-Br near 80 K. For - H - Br 8 k , the superconducting properties have been found to depend on the thermal history, in particular on how fast the sample had been cooled through 80 K. As mentioned above, the ground state of - D - Br 8 k is strongly sample-dependent: both superconducting as well as non-superconducting crystals are found. Furthermore, superconducting as well as insulating (possibly antiferromagnetic) phases in separated volume parts of the same sample have been reported. Their relative volume fraction was found to depend on the cooling rate Vc employed at around 80 K[2-3-4]: in fast cooled samples, a strong decrease of the diamagnetic signal has been observed, which has been interpreted as indicating a suppression of the superconducting in favour of the magnetic phase

Structural, magnetic, electrical and supraconducting properties of the high temperature superconductor Nd(SrBa)Cu3O6+z Effect of argon annealing

We have studied the structural and superconducting properties of two samples superconductors Nd(SrBa)Cu3O6+z. One was a conventionally annealed sample at 450°C in oxygen (0) and the other was heated in argon at 850°C followed by oxygen annealing (A0). The Tc of the sample (O) was 68 K and that of (AO) sample was 78 K. This was confirmed by our AC susceptibility, resistivity and Seebeck effect measurements. Further, there was an enhancement in the shielding and the intergranular critical current. The X-ray and neutron data showed a tetragonal structure, and that the (O) sample had a higher impurity level arising from Nd entering the Sr/Ba sites that may result in a decrease in the carrier density (p) which also was confirmed by our thermopower measurements. A combination of several factors such as changes in the Cu (1) apical oxygen distance, chain oxygen ordering, increase in p and in-phase purity for the (AO) sample may qualitatively account for the observed data.We have studied the structural and superconducting properties of two samples superconductors Nd(SrBa)Cu3O6+z. One was a conventionally annealed sample at 450°C in oxygen (0) and the other was heated in argon at 850°C followed by oxygen annealing (A0). The Tc of the sample (O) was 68 K and that of (AO) sample was 78 K. This was confirmed by our AC susceptibility, resistivity and Seebeck effect measurements. Further, there was an enhancement in the shielding and the intergranular critical current. The X-ray and neutron data showed a tetragonal structure, and that the (O) sample had a higher impurity level arising from Nd entering the Sr/Ba sites that may result in a decrease in the carrier density (p) which also was confirmed by our thermopower measurements. A combination of several factors such as changes in the Cu (1) apical oxygen distance, chain oxygen ordering, increase in p and in-phase purity for the (AO) sample may qualitatively account for the observed data

Vortex phase transition and superconducting properties of organic quasi-two-dimensional k-(BEDT-TTF) 2 Cu[N(CN) 2 ]Br

International audienceWe report investigations of the low temperature dc susceptibility and the magnetization on the layered organic superconductor κ-(BEDT-TTF)2Cu[N(CN)2]Br near 80K and the effect of disorder on the superconducting transition temperature Tc. The shielding effect (S) and the critical current density Jc were studied (with H parallel to the c axis of the crystal). Jc can be estimated by analysis of magnetic hysteresis measurement using the Bean model. For each temperature value, we observed two regimes in the critical current density Jc(H). This result implies that there exists a first-order phase transition in the vortex system in this organic superconductor. Our results show that the magnetic properties of these compounds depend strongly on the cooling rate. The structural transformation which occurs at the vicinity of 80K very strongly influences the physics of vortex lattice and the associated magnetic behavior

Correlation between band structure and magneto-transport properties in far-infrared detector modulated nanostructures superlattice

We report here carrier’s magneto-transport properties and the band structure results for II-IV semiconductors. HgTe is a zero gap semiconductor when it is sandwiched between CdTe layers to yield to a small gap HgTe/CdTe superlattice which is the key of an infrared detector. Our sample, grown by MBE, had a period d (100 layers) of 18 nm (HgTe) / 4.4 nm (CdTe). Calculations of the spectra of energy E(kz) and E(kp), respectively, in the direction of growth and in the plane of the superlattice were performed in the envelope function formalism. The angular dependence of the transverse magnetoresistance follows the two-dimensional (2D) behavior with Shubnikov-de Haas oscillations. At low temperature, the sample exhibits p type conductivity with a hole mobility of 900 cm²/V.s. A reversal the sign of the weak-field Hall coefficient occurs at 25 K with an electron mobility of 3 104 cm2/Vs. In intrinsic regime, the measured Eg ≈ 38 meV agrees with calculated Eg(Γ,300 K) = 34 meV which coincide with the Fermi level energy. The formalism used here predicts that this narrow gap sample is semi metallic, quasi-two-dimensional and far-infrared detector.We report here carrier’s magneto-transport properties and the band structure results for II-IV semiconductors. HgTe is a zero gap semiconductor when it is sandwiched between CdTe layers to yield to a small gap HgTe/CdTe superlattice which is the key of an infrared detector. Our sample, grown by MBE, had a period d (100 layers) of 18 nm (HgTe) / 4.4 nm (CdTe). Calculations of the spectra of energy E(kz) and E(kp), respectively, in the direction of growth and in the plane of the superlattice were performed in the envelope function formalism. The angular dependence of the transverse magnetoresistance follows the two-dimensional (2D) behavior with Shubnikov-de Haas oscillations. At low temperature, the sample exhibits p type conductivity with a hole mobility of 900 cm²/V.s. A reversal the sign of the weak-field Hall coefficient occurs at 25 K with an electron mobility of 3 104 cm2/Vs. In intrinsic regime, the measured Eg ≈ 38 meV agrees with calculated Eg(Γ,300 K) = 34 meV which coincide with the Fermi level energy. The formalism used here predicts that this narrow gap sample is semi metallic, quasi-two-dimensional and far-infrared detector