Effects of seed layer and substrate morphology on solar cell contacts deposited by light-induced plating
To improve two-step metallization processes for silicon solar cells, the influence of different seed layers and surface textures on the light-induced plating (LIP) deposition behaviour at different plating rates has been studied. Typical seed layers of screen- and aerosol printed silver paste have been tested on alkaline (random pyramid) and acidic texture. Silver deposition at high rate has been found to be problematic on very thin aerosol printed layers, especially for alkaline texture with high roughness. In an attempt to obtain high process speed while maintaining high conductivity, aerosol seed layers were subjected to different multi-step plating processes. Morphological features (aerosol particles, alkaline texture) were leveled by a slow pre-plating step. In a second plating step, the deposition rate was varied. The results were compared to similar experiments with untreated aerosol seed layers. Both pre-plating steps were found to effectively improve the deposi tion quality of the second plating step with high plating rate, and to improve the process robustness. On acidic texture (multicrystalline solar cells), high plating rates were found to give better qualities compared to random pyramids, even without pre-treatment. Both behaviours are attributed to differences in local field and current density between sharply and smoothly shaped plating bases.