Development of Economical Improved Thick Film Solar Cell Contact. Extension Final Report, April-December 1979

摘要

In the second half of the investigation of all metal screened electrodes, the focus was on base metal pastes in addition to further work with the silver systems. Contact resistance measurements were refined. A facility allowing firing in hydrogen and other atmospheres was acquired. Several experiments were made applying screenable pastes to solar cells. Doping investigations emphasized eutectic alloys reduced to powders. Metal systems were reviewed. A previously published vapor pressure curve for silver fluoride was corrected. Base metal experiments were done with nickel and copper using lead and tin as the frit metals. Severe adhesion problems were experienced with hydrogen atmospheres in all metal systems. A two step firing schedule was devised based upon experimentation which gave evidence that the silver fluoride-silicon dioxide reaction was modified by the presence of hydrogen. It was found that nitrogen prefiring allowed the silver fluoride dissociation and oxide removal without causing catastrophic oxidation of the base metal powders. The subsequent hydrogen firing step reduced oxides tht had formed and gave the proper sintered structure. Electrodes were coherent, adherent, and solderable in both nickel lead and copper lead systems. Towards the end of the contractual period aluminum-silicon and aluminum-germanium eutectic doping additions to copper pastes were tried on 2 1/4'' diameter solar cell back contacts, both with good results (eta = 9.4% AM1 uncoated). (ERA citation 05:028602)