Improved contact formation for large area solar cells using the alternative seed layer (ASL) process

Light induced plating (LIP) chemistry and tooling that are scalable to industrial solar cell processing are used to deposit layers of nickel (Ni), copper (Cu), and tin (Sn) on previously defined front grid patterns of large area solar cells. The Ni plated layer is in direct contact with the silicon surface enabling the formation of a nickel silicide (NiSi) contact after annealing. This Alternative Seed Layer (ASL) process involves many variables that influence the formation of the NiSi contact. This paper will investigate two different aspects of the contact formation: 1) the position of the annealing step in the process flow; i.e. after Ni plating or after Ni/Cu plating and 2) the resulting contact formation for monocrystalline silicon (mono-Si) versus polycrystalline silicon (poly-Si) substrates. A decrease in the series resistance (R_series) measurement and increase in efficiency after annealing has been demonstrated for both mono- Si and poly-Si cells with Ni only and Ni/Cu annealing.