The Photovoltaic Cavity Converter (PVCC) under development is a novel approach to convert highly concentrated solar radiation into electricity via a photon entrapment process and subsequent spectral stripping. Equipped with a multi-bandgap, single junction cell system PVCC circumvents most of the present limitations of the four (or more)-junction cell systems with vertical architecture. Our previous studies have shown that the PVCC concept has the potential to reach a collective conversion efficiency of 50% in the near term. Based on our past experiences regarding the cavity geometry and the light injection method we have developed a second generation design for the PVCC that overcomes the limitations of the first generation prototype.
Recent improvements in 'surface engineering' have helped to increase one-sun silicon solar cell efficiencies to more than 24% for float-zone grown single-crystal silicon. Texturing of the cell surface, to enhance the light coupling into cell, constitutes a significant part of this dramatic progress. Most single-crystal silicon substrates with a (100) surface orientation can be textured with relative ease using a selective or anisotropic chemical etching method. Other silicon materials, like ribbon-grown, (111) dendritic web and polycrystalline substrates do not lend themselves to chemical material removal without elaborate micro- lithographic masking method. This paper investigates the feasibility of using excimer micromachining as an alternative method of texturing silicon solar cells in general. Experiments are conducted with (111) float-zone and dendritic web-grown substrates. Using a 'diamond' patterned mask and a Kr2 excimer laser, contiguous arrays of V- shaped micro-grooves are formed on each substrate. The resulting surface texture is examined by surface profilometry and the results are correlated to the original surface micro characteristics of the samples. Sample carrier lifetimes and solar reflectances are measured prior to- and after the laser processing. The results verify the technical feasibility of excimer micro machining of (111) float zone and dendritic web single crystal substrates.
In this paper we present the preliminary analytical and experimental results of a novel low temperature
metal impregnation method to increase the critical currents in thick film and bulk HTSC materials.
The method described results in a structurally more controllable and effective microcomposite than the
ones obtained with metal- and metal-oxide precursors. The physical procedure involves the infiltration of
the interstices of the porous, fully treated superconductor with low-melting point, low T superconductor
under high pressure. Deep penetration of the metal into the granular superconducting matrix creates large
surface areas of strong Proximity Effect. Improved intergrain coupling increases the DC Josephson current
and therefore J, the critical current.
Prior to the experimental work a theoretical study was conducted. Indium was chosen as the impregnation
material. Computations showed.that the infiltrated system should have at least a four orders higher critical
current (4.47 x 104 A/cm2) as compared to the same array with vacuum barriers of 20A thickness between
the grains (0.31 A/cm2). On the experimental side, high T, porous, 1-2-3 samples impregnated with
gallium exhibited very low contact resistance (2. 1 x 10-6 cm2) at 85°K, a value about two orders of
magnitude better than the 1-2-3 systems containing intergranular silver. Further experiments with indium
impregnated samples are planned. This new low temperature method allows the manufacture of highly
flexible wires and films when used with suitable substrates.
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