Role of Firing Temperature, Sheet Resistance, and Contact Area in Contact Formation on Screen-Printed Metal Contact of Silicon Solar Cell

摘要

Formation of an Ohmic contact requires a suitable firing temperature, appropriate doping profile, and contact dimensions within resolution limits of the screen-printing process. In this study, the role of the peak firing temperature in standard rapid thermal annealing (RTA) six-zone conveyor belt furnace (CBF) and two inexpensive alternate RTA systems [a custom-designed, three-zone, 5aEuro(3)-diameter quartz tube furnace (QTF) and a tabletop, 3aEuro(3)-diameter rapid thermal processing (RTP)] has been investigated. In addition, the role of sheet resistance and contact area in achieving low-resistance ohmic contacts has been examined. Electrical measurements of ohmic contacts between silver paste/n (+)-emitter layer with varying sheet resistances and aluminum paste/p-doped wafer were carried out in transmission line method configuration. Experimental measurements of the contact resistivity (rho (c)) exhibited the lowest values for CBF at 0.14 m Omega cm(2) for Ag and 100 m Omega cm(2) for Al at a peak firing temperature of 870A degrees C. For the QTF configuration, lowest measured contact resistivities were 3.1 m Omega cm(2) for Ag and 74.1 m Omega cm(2) for Al at a peak firing temperature of 925A degrees C. Finally, for the RTP configuration, lowest measured contact resistivities were 1.2 m Omega cm(2) for Ag and 68.5 m Omega cm(2) for Al at a peak firing temperature of 780A degrees C. The measured contact resistivity exhibits strong linear dependence on sheet resistance. The contact resistivity for Ag decreases with contact area, while for Al the opposite behavior is observed.