Atomic Force Microscopy Analysis of Aluminum Layer Properties and Correlation to Masking Functionality in Copper Plating Metallization for Solar Cells

The native AlOxgrown on a thin sputtered aluminum layer can be used as maskfor electroplating copper, e.g., for metallizing silicon heterojunction (SHJ) solarcells. Effects that influence the masking quality for selective electroplating arestudied herein. Atomic force microscopy characterization in PeakForce modehighlights the presence of some insulation defects in the native AlOxdue to localcontamination, pinholes, or tunneling currents. A focused ion beam/scanningelectron microscopy analysis is further conducted to understand some defects indetail. The AlOxinsulation can be improved by adsorbing a self-assembledmonolayer, which is mainly required along the process sequence to adjust thesurface wetting of the Al for optimal NaOHaqprinting. The mask quality andcomplete metallization sequence for solar cells are demonstrated on industrialSHJ precursors. Inkjet- and FlexTrail-printing of NaOHaqare shown to be suitableto pattern the Al layer. Promising conversion efficiency comparable to screen-printing reference is reached on large area.