Evaluating the aluminum-alloyed p+-layer of silicon solar cells by emitter saturation current density and optical microspectroscopy measurements

Surface-passivated and surface-unpassivated aluminum-alloyed p +-layers are characterized. By varying the firing conditions and the thickness of the screen-printed aluminum paste, different sheet resistances Rsh of the p+-layer were fabricated. The emitter saturation current density J0eplotted versus Rsh follows distinctly different trends for the passivated and unpassivated samples. An aluminum paste with a boron additive achieves a much higher doping concentration and a lower sheet resistance but nevertheless follows the same J 0ecurves as the pure Al paste. The aluminum p+-layer was quantitatively analyzed with microphotoluminescence and FanoRaman measurements. The latter shows an increased defect recombination at the interface between the p+-layer and the moderately doped Si bulk. The lower ShockleyReadHall lifetime in this region can be attributed to a high defect concentration in the most highly doped layer, represents an impediment to the reduction of J 0efor Al- doped emitter regions, and needs to be optimized in future investigations.