By Achim Kraft, Member of the Plating Process Technology Team, Fraunhofer ISE; Andreas Lorenz, Fraunhofer ISE; Andrew Mondon, Fraunhofer ISE; Laura Sutor, Fraunhofer ISE; Markus Glatther, Head of the Novel Processes Department - Development and Characterization Division, Fraunhofer ISE; Sebastian Nold, Fraunhofer ISE; Jonas Bartsch, Head of the Plating Process Technology Team, Fraunhofer ISE; Stefan W. Glunz, Director of the Solar Cells - Development and Characterization Division, Fraunhofer ISE
Despite considerable progress in screen-printing processes for crystalline silicon solar cell metallization, alternatives are still of interest because of their potential cost and performance advantages. Plating processes are one alternative that can be either combined with printed seed layers or used for full front-contact deposition. Although there are advantages to both approaches, there are also challenges that must be faced. Plating nickel and copper onto printed seed layers is very simple and involves only minor process modifications. With regard to undesired pasteâ€“electrolyte interaction, noticeable progress has been made during the past few months, bringing this process closer to industrial implementation. Plating nickel directly onto silicon offers the possibility of contacting emitters even with a surfacedoping concentration as low as 8×1018cm-3, while achieving similar performance to that of an evaporated contact metallization. To obtain sufficient adhesion, an in-depth understanding of the interface processes during silicidation is necessary. Gaining this understanding has enabled high peel forces greater than 2N/mm to be realized using a standard solder-and-peel procedure at a 90-degree angle. Process simplification will make such a process highly attractive for solar cell metallization, which is all the more important, as high-efficiency concepts are appearing that require advanced metallization schemes.