The Very High Efficiency Solar Cell (VHESC) program is developing integrated optical system-PV modules for portable applications that operate at greater than 50% efficiency. We are integrating the optical design with the solar cell design, and have entered previously unoccupied design space. Our approach is driven by proven quantitative models for the solar cell design, the optical design, and the integration of these designs. Optical systems efficiency with an optical efficiency of 93% and solar cell device results under ideal dichroic splitting optics summing to 42Á7 W 2Á5% are described.

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The relationship between the electronic properties of mobility and resistivity, and electron scattering from film defects in slowly deposited cadmium sulphide polycrystalline thin films is investigated. The correlation of these properties is accomplished in a direction parallel to the substrate (``in-plane'') where the defects of interest are grain boundaries and surfaces. The Petritz (grain boundary) theory is incorporated with surface-scattering theory to formulate a simple model which predicts the effect of these defects on the electron mobility. Typical values for the grain-boundary potential and surface-scattering length are 0.07 eV and 1100 Å at a substrate temperature of 180°C for these glass-deposited films. The mobility is found to depend strongly on grain size, which was a function of substrate temperature. Hall data are presented as a function of evaporation rate, substrate temperature, film thickness, and film temperature. Finally, the grain-boundary potential is found to depend on the fabrication parameters, especially the deposition rate.

The growth and electrical properties of CuInS2 thin films are described. Two deposition schemes, single- and double-source methods, are reported. Data are presented indicating the effects of film and substrate temperature on the electrical characteristics (mobility, resistivity, and carrier concentration) of the films. Both n- and p-type films are reported, and the effects of sulfur concentrations are discussed. Some postdeposition annealing effects are also detailed.

Contact surface resistivities (product of contact resistance and area) in the 10−10 Ω cm2 range have been obtained for both silver and gold contacts to high Tc superconductors. This is a reduction by about eight orders of magnitude from the contact resistivity of indium solder connections. The contact resistivity is low enough to be considered for both on-chip and package interconnect applications. The contacts were formed by sputter depositing either silver or gold at low temperatures (<100 °C) on a clean surface of Y1 Ba2 Cu3 O7−δ (YBCO) and later annealing the contacts in oxygen. Annealing temperature characteristics show that for bulk-sintered YBCO samples there is a sharp decrease in contact resistivity after annealing silver/YBCO contacts in oxygen for 1 h at temperatures above ∼500 °C and gold/YBCO contacts for 1 h above ∼600 °C. Oxygen annealing for longer times (8 h) did not reduce the contact resistivity of silver contacts as much as annealing for 1 h. Auger microprobe analysis shows that indium/YBCO contacts contain a significant concentration of oxygen in the indium layer adjacent to the YBCO interface. Silver and gold contacts, on the other hand, contain almost no oxygen and have favorable interfacial chemistry with low oxygen affinity. Silver also acts as a ‘‘switchable’’ passivation buffer, allowing oxygen to penetrate to the YBCO interface at elevated temperatures, but protecting the YBCO surface at room temperature.