Thin uniform nickel seed layer formation and its impact on Ni-Cu contact adhesion for c-Si solar cell applications

Abstract

Abstract Poor contact adhesion is one of the major concerns in the low cost Ni-Cu front contact metallization for c-Si solar cells. It reduces the mechanical as well as electrical reliability of the solar cell. Thermal annealing of the Ni seed layer is generally considered as crucial step for contact adhesion and cell performance, however the deposition of Ni seed layer itself requires proper investigation. The objective of this work is to improve the contact adhesion by improving Ni seed layer characteristics. This has been achieved through detailed process optimization of electroless Ni deposition using Palladium (Pd) activation method and subsequent annealing. After optimizing the Pd activation process with respect to its nucleation and growth characteristics, a very thin (∼20 nm) conformal seed layer deposition has been obtained with excellent uniformity across textured solar cell substrate. In addition, no interfacial void formation is observed after seed layer annealing, even at 600 °C. This has resulted in significantly improved contact adhesion of 23 MPa.