Sheared Thick-Film Electrode Materials Containing Silver Powders with Nanoscale Surface Asperities Improve Solar Cell Performance

Thick-film screen-printed fine-line metallization is one of the most important process steps in the whole production chain of photovoltaic cell manufacturing as variations in industrial solar cell performance mainly depend on electrode properties. The impact of Ag powder surface topography on viscoelastic characteristics and geometry of solar cell electrodes is studied. Numerical simulations for concentrated non-Brownian suspensions show that shear viscosity and storage modulus increase with particle roughness. Experimental rheological analysis shows improvement in thixotropy and shear storage modulus for pseudoplastic electrode materials with corrugated Ag powders. Consequently, viscoelastic recovery is enhanced for frontside electrode gridlines with rough-surface Ag powders. This results in aspect-ratio and cross-sectional symmetry enhancement for rough-surface Ag powder gridlines compared with smooth-surface Ag powder gridlines. Rough-surface Ag powder gridlines have smaller height variations, making them more suitable for high-throughput screen printing. Optical simulations show improved light redirection into the solar cell for gridlines formed from rough-surface Ag powders, leading to higher solar cell photocurrent. The improved gridline definition results in an increase in short-circuit current density, yielding average efficiency improvement of ≈0.1% absolute for monocrystalline-Si solar cells with screen-printed gridlines having rough-surface Ag powders. This results in monocrystalline-Si solar cells with 22.45% average conversion efficiency.