Light trapping in solar cells at the extreme coupling limit

We calculate the maximal absorption enhancement obtainable by guided mode excitation in a weakly absorbing dielectric slab over wide wavelength ranges. The slab mimics thin film silicon solar cells in the low absorption regime. We consider simultaneously wavelength-scale periodicity of the texture, small thickness of the film, modal properties of the guided waves and their confinement to the film. Also we investigate the effect of the incident angle on the absorption enhancement. Our calculations provide tighter bounds for the absorption enhancement but still significant improvement is possible. Our explanation of the absorption enhancement can help better exploitation of the guided modes in thin film devices.Comment: accepted for publication in JOSA

Accelerated ageing of surface modified flax fiber reinforced composites

The overall aim of this study is to evaluate application-oriented potential of biocomposites made of surface-modified flax fibers for use in engineering thermoplastics. The scope of the study includes analysis of the effect of a partially bio-based epoxy-coating, a silane treatment and a combined epoxy-coating / silane treatment of the flax fibers on the mechanical behavior of biocomposites after thermo-oxidative aging. The treated flax fabrics were subjected to tensile tests as well as scanning electron microscopy (SEM) to compare their mechanical behavior and fracture surface. The natural fiber reinforced biocomposites were manufactured through film-stacking of the treated fabrics and polyamide 6 (PA6) using hot-pressing. The durability of the biocomposites after climate-change tests was confirmed via tensile and bending testing. The results show beneficial mechanical behavior of treated fabrics and corresponding biocomposites, but also negative affected durability of treated composites after climate-change tests. Treatment of the fabrics with subsequent accelerated aging leads to a similar low level of tensile and bending moduli

Angular behavior of the absorption limit in thin film silicon solar cells

We investigate the angular behavior of the upper bound of absorption provided by the guided modes in thin film solar cells. We show that the 4n^2 limit can be potentially exceeded in a wide angular and wavelength range using two-dimensional periodic thin film structures. Two models are used to estimate the absorption enhancement; in the first one, we apply the periodicity condition along the thickness of the thin film structure but in the second one, we consider imperfect confinement of the wave to the device. To extract the guided modes, we use an automatized procedure which is established in this work. Through examples, we show that from the optical point of view, thin film structures have a high potential to be improved by changing their shape. Also, we discuss the nature of different optical resonances which can be potentially used to enhance light trapping in the solar cell. We investigate the two different polarization directions for one-dimensional gratings and we show that the transverse magnetic polarization can provide higher values of absorption enhancement. We also propose a way to reduce the angular dependence of the solar cell efficiency by the appropriate choice of periodic pattern. Finally, to get more practical values for the absorption enhancement, we consider the effect of parasitic loss which can significantly reduce the enhancement factor

Die Erwartungen der Industrie für 1999

Für das kommende Jahr rechnen die Konjunkturforscher mit einem nachlassenden Wirtschaftswachstum. Das reale Bruttoinlandsprodukt dürfte 1999 in der Größenordnung von 2% liegen nach 2,7% in diesem Jahr. Wie schätzt die Industrie ihre Aussichten für 1999 ein? Welche Erwartungen hat sie an die Wirtschaftspolitik der neuen Bundesregierung? --