Designing III-V Multijunction Solar Cells on Silicon

Single junction Si solar cells dominate photovoltaics but are close to their efficiency limits. This paper presents ideal limiting efficiencies for tandem and triple junction multijunction solar cells subject only to the constraint of the Si bandgap and therefore recommending optimum cell structures departing from the single junction ideal. The use of III-V materials is considered, using a novel growth method capable of yielding low defect density III-V layers on Si. In order to evaluate the real potential of these proposed multijunction designs, a quantitative model is presented, the strength of which is the joint modelling of external quantum efficiency and current-voltage characteristics using the same parameters. The method yields a single parameter fit in terms of the Shockley-Read-Hall lifetime. This model is validated by fitting experimental data of external quantum efficiency, dark current, and conversion efficiency of world record tandem and triple junction cells under terrestrial solar spectra without concentration. We apply this quantitative model to the design of tandem and triple junction solar cells, yielding cell designs capable of reaching efficiencies without concentration of 32% for the best tandem cell and 36% for the best triple junction cell. This demonstrates that efficiencies within a few percent of world records are realistically achievable without the use of concentrating optics, with growth methods being developed for multijunction cells combining III-V and Si materials.Comment: Preprint of the paper submitted to the journal Progress in Photovoltaics, selected by the Executive Committee of the 28th EU PVSEC 2013 for submission to Progress in Photovoltaics. 10 pages, 7 figure

Unitary Dual of GL_n at archimedean places and global Jacquet-Langlands correspondence

In [7], results about the global Jacquet-Langlands correspondence, (weak and strong) multiplicity-one theorems and the classification of automorphic representations for inner forms of the general linear group over a number field are established, under the condition that the local inner forms are split at archimedean places. In this paper, we extend the main local results of [7] to archimedean places so that this assumption can be removed. Along the way, we collect several results about the unitary dual of general linear groups over \bbR, \bbC or \bbH of independent interest

Remarkable virtual SUSY effects in W±W^{\pm} production at high energy hadron colliders

We present a complete 1-loop study of the electroweak corrections to the process $ug\to dW^+$ in MSSM and SM. The occurrence of a number of remarkable properties in the behavior of the helicity amplitudes at high energies is stressed, and the crucial role of the virtual SUSY contributions in establishing them, is emphasized. The approach to asymptopia of these amplitudes is discussed, comparing the effects of the logarithmic and constant contributions to the mass suppressed ones, which are relevant at lower energies. Applying crossing to $ug\to d W^+$, we obtain all subprocesses needed for the 1-loop electroweak corrections to $W^\pm$-production at LHC. The SUSY model dependence of such a production is then studied, and illustrations are given for the transverse $W^{\pm}$ momentum distribution, as well as the angular distribution in the subprocess center of mass.Comment: 21 pages, 12 figures, version to appear in Phys.Rev.

Spin dynamics of hole doped Y2BaNiO5

Starting from a multiband Hamiltonian containing the relevant Ni and O orbitals, we derive an effective Hamiltonian $H_{eff}$ for the low energy physics of doped Y$_{2}$BaNiO$_{5}.$ For hole doping, $H_{eff}$ describes O fermions interacting with S=1 Ni spins in a chain, and cannot be further reduced to a simple one-band model. Using numerical techniques, we obtain a dynamical spin structure factor with weight inside the Haldane gap. The nature of these low-energy excitations is identified and the emerging physical picture is consistent with most of the experimental information in Y% $_{2-x}$Ca$_{x}$BaNiO$_{5}$Comment: 4 pages, 2 figure

Logarithmic expansion of electroweak corrections to four-fermion processes in the TeV region

Starting from a theoretical representation of the electroweak component of four-fermion neutral current processes that uses as theoretical input the experimental measurements at the Z peak, we consider the asymptotic high energy behaviour in the Standard Model at one loop of those gauge-invariant combinations of self-energies, vertices and boxes that contribute all the different observables. We find that the logarithmic contribution due to the renormalization group running of the various couplings is numerically overwhelmed by single and double logarithmic terms of purely electroweak (Sudakov-type) origin, whose separate relative effects grow with energy, reaching the 10% size at about one TeV. We then propose a simple "effective" parametrization that aims at describing the various observables in the TeV region, and discuss its validity both beyond and below 1 TeV, in particular in the expected energy range of future linear electron-positron (LC) and muon-muon colliders.Comment: 23 pages and 9 figures; version submitted to Phys.Rev.D. e-mail: [email protected]

The role of the top mass in b-production at future lepton colliders

We compute the one loop contribution coming from vertex and box diagrams, where virtual top quarks are exchanged, to the asymptotic energy behaviour of $b\bar b$ pair production at future lepton colliders. We find that the effect of the top mass is an extra linear logarithmic term of Sudakov type that is not present in the case of (u,d,s,c) production. This appears to be particularly relevant in the case of the $b\bar{b}$ cross section.Comment: 9 pages and 3 figures; version submitted to Phys.ReV.D,Rapid. e-mail: [email protected]

The roughness of stylolites: Implications of 3D high resolution topography measurements

Stylolites are natural pressure-dissolution surfaces in sedimentary rocks. We present 3D high resolution measurements at laboratory scales of their complex roughness. The topography is shown to be described by a self-affine scaling invariance. At large scales, the Hurst exponent is $\zeta_1 \approx 0.5$ and very different from that at small scales where $\zeta_2 \approx 1.2$. A cross-over length scale at around \L_c =1~mm is well characterized. Measurements are consistent with a Langevin equation that describes the growth of a stylolitic interface as a competition between stabilizing long range elastic interactions at large scales or local surface tension effects at small scales and a destabilizing quenched material disorder.Comment: 4 pages, 4 figure