Design Rules for Solar Cells with Plated Metallization
This work deals with requirements regarding the solar cell process that allow or facilitate the introduction of fabrication processes for front side metallization. By taking experience with plating on solar cells both from the literature and from practical lab work, design rules for the solar cell and the plating process have been derived. Regarding the surface texture, small features (e.g., random pyramids < 5 mm) have been found beneficial for plating processes both on printed seed layers and directly on silicon. A dense, pinhole-free anti-reflective coating suppresses so-called ghost plating as well as careful handling in production. Shunting, which is possible for laser edge isolation can be prevented by applying wet chemical edge isolation. An adjusted soldering process which brings in high energy within a short time is recommended. Infrared or inductive soldering are ideal for the connection of plated surfaces with ribbon. For plating on paste it is recommended that using plating electrolytes with pH>2 result in a good adhesion of the seed layer on the silicon surface. Further the glass content in the silver paste and the size of the glass particles have a big influence on the adhesion. A high glass content and small particles are beneficial for a following plating process. For direct plating on silicon an ablation of the ARC with a 355 nm ps-laser is the best option for adhesion.