Microcharacterization of Interface Oxide Layer on Laser-Structured Silicon Surfaces of Plated Ni–Cu Solar Cells

Copper Outdiffusion from Copper-Plated Solar Cell Contacts during Damp Heat Exposure

“…In homojunction c-Si cells with direct contact between the metal and Si, this barrier layer is usually nickel (Ni) and is usually annealed to form an interfacial nickel silicide layer (NiSi X ). The annealed Ni layer is also understood to improve adhesion and reduce contact resistance. − A number of studies have tested for the downward diffusion of Cu (into cells) through the Ni barrier by means of accelerated testing at elevated temperatures (usually 200 °C), with detrimental degradation noted only when the Ni layer is insufficiently thick (<∼200 nm). , It is assumed that with sufficiently thick Ni barriers, the downward ingress of Cu is prevented both by the formation of NiSi X layer at the bottom of the stack and alloying at the Ni–Cu interface. ,, However, one study showed detrimental Cu precipitates underneath Ni diffusion barriers after 200 °C heat treatments and rapid cooling, suggesting that downward Cu may somehow defeat Ni barriers at moderate temperatures but that slow cooling inhibits the formation of performance-limiting extended Cu defects …”