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We have deposited textured ZnO:Al films over large areas using a reactive-environment hollow cathode sputtering (RE-HCS) system developed in house, and have achieved excellent carrier mobilities (up to 49.5 cm 2 /Vs at a carrier concentration of 4.42 x 10 20 /cm 3 ). Both the electrical properties and optical properties (total transmission and haze) are superior to those exhibited by commercially available SnO 2 :F. Using these textured ZnO:Al films, we have achieved an a-Si:H solar cell efficiency boost of 8% relative to commercial SnO 2 :F superstrates which resulted from improvements in all three PV parameters, namely V oc , J sc , and FF. We have also determined the dependence of cell performance on the degree of haze in the ZnO:Al films. Electrical, physical, and optical properties of ZnO:Al and SnO 2 :F, as determined by four-point probe, Hall effect, SEM, AFM, ICP, transmission (total and diffuse), and work function measurements are presented and correlated to the observed differences in a-Si solar cell performance. We have also developed a refractive index matching layer that, when inserted between the TCO and the a-Si:H layers, resulted in an increase in J sc of 3%. Finally, we present some experiments on the effect of TCO type on nc-Si:H solar cell performance. From these experiments, we confirmed that SnO 2 :F by itself is not a suitable TCO for nc-Si:H cells, but found that SnO 2 :F overcoated with TiO 2 followed by ZnO was the most effective superstrate for this type of cell.

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Tantalum is a tough, corrosion resistant metal, which would be suitable for use as bipolar plates for proton exchange membrane (PEM) fuel cells, if it was not for its high weight and price. Relatively thin tantalum coatings, however, can be deposited on other inexpensive and lighter weight metals, such as aluminum and steel, providing a passive protection layer on these easily formed substrates. We have successfully deposited, high quality α (body-centered-cubic, bcc) and β (tetragonal) phase tantalum coatings that were a few micrometers thick by dc magnetron sputtering on steel and aluminum. The growth of the thermodynamically preferred body-centered-cubic (bcc) tantalum phase was induced by a choice of deposition conditions and substrate surface treatment. The microstructure and corrosion resistance of the α-phase in an environment approximately simulating the electrochemical conditions used in a PEM fuel cell were investigated under potentiodynamic conditions. Preliminary potentiostatic measurements of a β-phase sample are also presented.