Refined nickel nucleation and plated metal adhesion induced by pulsed light-induced plating on picosecond laser-ablated silicon solar cells

Abstract

This study reports the impact of pulsed Ni light-induced plating (LIP), compared to the commonly used galvanostatic Ni LIP, on the initial Ni nucleation and subsequently plated busbar adhesion of Cu-plated laser-ablated p-type passivated emitter and rear Si solar cells. Initial Ni nucleate sizes decreased from 27.8 ± 9.1 to 25.4 ± 7.9 nm when the pulse-on current density during pulsed Ni LIP was increased from 50 to 178 mA cm−2, and were smaller than the 30.4 ± 9.7 nm nucleates observed with galvanostatic plating at 25 mA cm−2 after the same charge had been delivered to the surface. The density of Ni nucleation was also increased for pulsed LIP. This increased density of smaller Ni nucleates was attributed to the higher pulse-on currents inducing a larger surface potential which favoured nucleation over Volmer Weber 3D island growth of Ni. It also led to a greater density of adhesive anchor points along busbars which contributed to more adhesive plated contacts with busbar pull forces as high as 3 N mm−1 being measured when the pulse-on current density was 100 mA cm−2. However, it is shown that higher pulse-on current densities can result in unintended parasitic reactions, such as H2 evolution, and reduced busbar adhesion.