Plated Nickel-Copper contacts on c-Si. From microelectronic processing to cost effective silicon solar cell production
One of the key topics for industrial implementation of fully plated NiCu contacts on Si solar cells has so far been metal adhesion to silicon. The evaluation of adhesion is not entirely consistent throughout PV research, which is discussed at first. The adhesion issue of plated NiCu contacts has then been addressed by following two different routes for adhesion promotion. Firstly an ""Interim Anneal"" route is focussing on controlled silicide formation as a bonding agent and reliably excellent adhesion greater than wafer breakage force is shown independent of surface roughness (above 2 N/mm for measurements on clamped cells and above 4 N/mm for fortified wafers). Secondly a ""Post Anneal"" route is focussing on creation of high Si surface roughness by ps laser ablation of the ARC and annealing after full metallization. Excellent adhesion above wafer breakage force is demonstrated. Comparisons to different methods of ARC patterning and resulting surface roughness are made. The presented metallization technology is feasible for standard BSF cells and next generation solar cells for both p-type and n-type emitters. Solar cell efficiencies of up to 19.4%abs for p-type BSF cells, 20.5%abs for n-type BSF cells and 22.1%abs for n-type PassDop cells are presented.