Adhesion quality of evaporated aluminum layers on passivation layers for rear metallization of silicon solar cells

• We examine the adhesion quality of evaporated aluminum on passivation layers.
• Adhesion quality strongly varies with passivation type and evaporation process.
• SEM cross-section images are taken to gain insight into the interface region.
• A water-free surface and elevated deposition temperatures promote adhesion.
• By process optimization we achieve strong adhesion on all passivation layers.

This paper characterizes the adhesion quality of evaporated aluminum rear metallization on rear passivation layers of silicon solar cells. A peel-test is introduced for adhesion rating and the adhesion quality between various Al and passivation layers on test structures is compared and discussed. The results show that the adhesion strongly varies with passivation type and evaporation parameters. Strong adherence is attributed to the formation of a strongly bonded, extended interphase layer. We derive factors that influence adhesion quality on our sample structures and find that an intimate contact between the layers and elevated temperatures are very important parameters. Additionally, a sufficiently high adhesion quality for an evaporated rear metallization of passivated emitter and rear cells (PERC) is achieved for all investigated passivation layers.